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PROGRESS REPORT

SNAP lOA

NUCLEAR AUXILIARY POWER UNIT DEVELOPMENT

APRIL-JUNE 1961

(Title Unclassified)

yiBTMCTED 4)ATA This docun •stricted data as defined in

the '"'^Pl'"' tn.ffp. un-

*^ts material cqBJj0K~?i9ffi|Bttf<m effecting tbf ftttJonal «»rm^fB^hc Uni^^j^teitffl wfthln the iDe«nIn« of y»«SI)^0Bsge inv^^^jilt- 18 U SiC, S«CB. 793 ftnal^^J 'ie tra»aral8 Mk or reTelatlo!> of -wbtch IB aa^nisoner to *.u ymnSfSSbtliZed P^fUB it prohibited by law." V*

ATOMICS INTEI^ATIONAL A DIVISION OF NORTH AMERICAN AVIATION, INC.

'ii'^^^Li^'siu->

nSTRtSUTmN OF TH!S DOCUMENT IS UHL

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NAA-SR-6693 SPECIAL DISTRIBUTION

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sponsored by the United States Government Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights

autC

Exempt from CCRP Re-re\iew Requirei|ients (per 7/22/82 Duff/Caudle memorandum) /M ^ /»^

PROGRESS REPORT

SNAP lOA

NUCLEAR AUXILIARY POWER UNIT DEVELOPMENT

APRIL-JUNE 1961

(Title Unclassified)

4

^^ rv. r. TTiison ^Projec;-Engineer, SNAP lOA

"This mtt aftUc»nai d foa affectfnr tSi

States wJtliln tha Srw», Title 1». U.SC,

^ l e n or TeT»Iatl«B |orlied perion

Z^l^/K^ H. Dieckamp Space Systems Director

BESaagEfcBftTA \H*%\ i n liaiiJiiiillul ui llie lin any manner to an un

authorized person is prbKlbited.

WiSUll

i ATOMICS INTEI^^TIONAL A DIVISION OF NORTH AMERICAN AVIATION, INC. P.O. B C t f ^ ^ O ^ . CANOGA PARK, CALIFORNIA

CONTRACT: AT(l l - l ) -GEN-8 ISSUED: NOVEMBER 15, 1961

i C y i J O S ^ CANOGA PARK, CALIFORNI

..•II IHHtJiigR

wsTRtsuTON Of THB m m m IS miMfnii % J ^

DISTRIBUTION

Category: SPECIAL

Advanced Resea rch Pro jec t Agency Aerospace Technical Intell igence Center AiResearch Manufacturing Co. of Arizona Air F o r c e Ball is t ic Miss i le Division Air F o r c e Special Weapons Center Air Univers i ty L ib ra ry Argonne National Labora tory Army Ball is t ic Miss i le Agency Atomic Energy Commission, California Patent Group Atomic Energy Commission, Washington Battelle Memoria l Insti tute Brookhaven National Labora tory Bureau of Naval Weapons Bureau of Ships Bureau of Yards and Docks Chicago Operat ions Office Chicago Patent Group Chief of Naval Operat ions Direc tor of Defense Resea rch and Engineering (OABCW) Je t Propuls ion Labora tory Lawrence Radiation Labora to ry Lockheed Aircraf t C o r p . , California Division Lockheed MSC, Palo Alto Los Alamos Scientific Labora tory NASA, Ames NASA, Goddard NASA, Langley NASA, Lewis NASA, Marsha l l NASA, Washington NASA, Western Operat ions Office Naval Ordnance Labora tory Naval Radiological Defense Labora to ry Naval R e s e a r c h Labora to ry New York Operat ions Office Nuclear Development Corp . of Amer i ca Oak Ridge National Labora to ry Office of the Chief of Ordnance, DOFL Office of Naval Resea rch Office of Technical Information Extension, USAEC, Oak Ridge, Tenn, Pro jec t RAND Ronae Air Development Center School of Aviation Medicine The Mart in Co. Wright Air Development Division AI L ib ra ry (CPAO - 2 copies)

Copy No.

1-2 3 4-5 6-10

11-16 17 18 19 20 21-25 26 27 28-29 30-31 32 33-34 35 36 37 38-39 40 41 42-44 45 46 47 48 49-51-53-58 59 60 61-62 63 64-65 66 67 68-69 70-99

100 101 102 103 104-106 107-150

• 50 •52 •57

NAA-SR-6693 2 ^ ^ mtffc:::;

CONTENTS

P a g e

I . P r o g r a m O b j e c t i v e s 7

t II . P r o g r a m S u m m a r y 9

^ III . F l i g h t S y s t e m 10

< IV. S y s t e m T e s t s 14

A. S l O A - P S M - 1 ( M e c h a n i c a l E n v i r o n m e n t a l T e s t APU) . . . . 14

1. Ob jec t i ve 14

2. Schedu le 14

3 . C u r r e n t S ta tus 14

B . S l O A - P S M - 2 (Analog S i m u l a t o r ) 16

1. Ob jec t i ve 16

2. Schedu le 16


C. S l O A - P S M - 3 ( P e r f o r m a n c e T e s t APU) 16

1. Ob jec t i ve 16

2. Schedu le 16

I 3. C u r r e n t S ta tus 16

D. F S M - 1 ( N o n - n u c l e a r Qua l i f i c a t i on T e s t APU) 17

1. Ob jec t i ve 17

2. Schedu le 17


E . F S M - 2 ( In t eg ra t i on Mockup) 17

1. Ob jec t i ve 17

2. Schedu le 18

3. C u r r e n t S t a tu s 18

F . F S - 1 ( N u c l e a r Qua l i f i c a t i on T e s t APU) 18

1. O b j e c t i v e 18

2. Schedu le 18


" V . D e v e l o p m e n t P r o g r a m 19

^ A . P u m p 19

B . E x p a n s i o n C o m p e n s a t o r 27

7*"''"~~~"— N A A - S R - 6 6 9 3

CONTENTS

Page

C Thermoe lec t r i c Converter 27

1. Design Studies 27

2. Mate r ia l s Development 31

3. P r o c e s s Development 34

4. P r o c e s s Engineering 38

5. Testing 39

6. Quality Control 52

VI. Operational Analysis 53

A. Design Point 53

B. Dynamic Behavior 62

C. Instrumentat ion 66

D. NaK Freez ing P r i o r to Reactor Operation 67

TABLES

I. Weight Status - Flight System 13

II. SNAP Development and Qualification Systems 15

III. Coefficient of The rma l Expansion of Lead Tel lur ide 33

IV. Compress ive P r o p e r t i e s of n-Type Lead Tel lur ide 33

V. Effect of Heat Trea tment on Res is tance of PbTe 34

VI. Contact Res is tance of Elements from Reference P r o c e s s . . . . 36

VII. Contact Res is tance of General Ins t rument Elements 37

NAA-SR-6693

FIGURES ""

Wk Page

1. F l i g h t S y s t e m - E l e v a t i o n (L141-07002) 11

2. T h e r m o e l e c t r i c P u m p P r e s s u r e vs AT for C o n s t a n t F l o w

( P r i m a r y Data ) ' 21

3 . T h e r m o e l e c t r i c P u m p P r e s s u r e v s F l o w for C o n s t a n t AT . . . . 22

4 . T h e r m o e l e c t r i c P u m p P r e s s u r e v s F l o w for AT = 5 0 0 ° F . . . . 23

5. T h e r m o e l e c t r i c P u m p 102-D (7580-1814B (®) 24

6. L o s s in Ef fec t ive T e m p e r a t u r e D r o p A c r o s s T / E a s a F u n c t i o n

of C h a n n e l Width 26

7. C o n c e p t u a l D e s i g n - E x p a n s i o n C o m p e n s a t i o n 28

8. 4 . 2 - W a t t Modu le - V a c u u m D e s i g n SNAP 1 OA T / E G e n e r a t o r . . . 30

9. T a b u l a r Modu le Conf igu ra t i on 32

10. Hot P r e s s i n g A p p a r a t u s (7580-1819G) 35

11 . R e s i s t a n c e P r o f i l e A p p a r a t u s (7580-5510) 40

12. R o o m T e m p e r a t u r e Seebeck A p p a r a t u s 41

13. E l e m e n t P e r f o r m a n c e T e s t A p p a r a t u s (7580-5505) 42

14. W e s t i n g h o u s e T h e r m o e l e c t r i c Modu le A v e r a g e P e r f o r m a n c e . . . 44

i 15 . Li fe T e s t D a t a N o r m a l i z e d to AT = 3 6 0 ° F - Two W e s t i n g h o u s e

SNAP lOA C o u p l e s 45

16. W e s t i n g h o u s e T h e r m o e l e c t r i c Modu le - A v e r a g e Da ta 47

17. E n c a p s u l a t e d W e s t i n g h o u s e C o u p l e s - N o r m a l i z e d Da ta 49

18a. p - T y p e T h e r m o e l e c t r i c E l e m e n t 50

18b. n - T y p e T h e r m o e l e c t r i c E l e m e n t 51

19- E n e r g y D i s s i p a t e d p e r sq ft v s R a d i a t o r B a s e T e m p e r a t u r e . . . 54

20. R a d i a t o r A r e a vs R a d i a t o r B a s e T e m p e r a t u r e 55

2 1 . M i n i m u m R e q u i r e d R a d i a t o r A r e a v s C a r n o t Ef f i c i ency 57 22 . D e g r a d a t i o n R a t e p e r Y e a r v s M a x i m u m C o n v e r t e r Hot S t r a p

T e m p e r a t u r e 59 23 . T h e r m o e l e c t r i c G e n e r a t o r E x p e r i e n c e 60 24. M i n i m u m R a d i a t i n g A r e a v s A v e r a g e C o n v e r t e r Hot S t r a p

T e m p e r a t u r e (for year -er iH~power output of 500 w) 61 >

25 . SNAP lOA R e a c t o r P o w e r T r a n s i e n t ( from 50< S u b c r i t i c a l to S e n s i b l e H e a t G e n e r a t i o n ) 64

•* 26. SNAP lOA R e a c t o r S t a r t u p T r a n s i e n t (During P e r i o d of S e n s i b l e Hea t G e n e r a t i o n ) 65

N A A - S R - 6 6 9 3 - 5

lOi mil utti iMfc^tnir'" '" " ' '

FIGURES

Page

27. Unprotected SNAP lOA System in 2000 Nautical Mile Orbit Perpendicu la r to Line of Ea r th and Sun 68

28. Flow Required to Prevent Freez ing of NaK Before Equil ibr ium T e m p e r a t u r e s a r e Reached in Space 70

THE TWO PREVIOUS PROGRESS REPORTS ISSUED ARE:

NAA-SR-6023 October-November I960 Issued: March 1, 1961

NAA-SR-6294 December 1960-March 1961 Issued: June 15, 1961

NAA-SR-6693 6

•

I. PROGRAM OBJECTIVES

The objective of the SNAP lOA p r o g r a m is to develop a nuclear power

sys tem for space application. This development effort will lead to flight tes ts

under the SNAPSHOT p r o g r a m in conjunction with the Air F o r c e . The sys tem

is being developed to the following specifications:

a) An e lec t r i ca l output of at leas t 500 w at 28 v should be provided over

the sys tem lifetime of 1 yea r .

b) Maximum sys tem weight should be 875 lb, including the special com

ponents and diagnostic ins t rumentat ion n e c e s s a r y to complete the

SNAPSHOT object ives . The operat ional SNAP lOA sys tem design

objective is 775 lb . The shield in this system will be designed to

provide protect ion for the electronic payloads in the flight vehicle

in the p resen t configuration, which provides 17-1/2 ft separat ion

between r eac to r and payload.

c) The SNAP lOA sys tem shall utilize the SNAP 2 reac tor with minimum

modificat ions.

d) The sys tem will be essent ia l ly static in its operat ion. Power con

vers ion will be accomplished by a the rmoe lec t r i c genera tor coupled

to the r eac to r heat source by means of an e lect romagnet ica l ly pumped

liquid meta l hea t - t r ans fe r loop.

e) The sys tem shall be designed to el iminate the need for active control

following orbi ta l s ta r tup .

f) The sys tem will be qualified to withstand the environment encountered

in vehicle ascent and space envi ronments .

g) The unit must be designed to facilitate safe ground handling and launch

ing and must be developed to contribute a minimal radiological hazard

at launch to the launch faci l i t ies , personnel , and surrounding inhabit

an t s .

h) The power conversion subsys tem shall be of a design to accommodate

future growth.

i) The shield shall be so designed that over a period exceeding one year

the total integrated dose at the dose plane, 17-1/2 ft from the bottom of 12 7

the r eac to r , shall not exceed 10 nvt and 10 r .

NAA-SR-6693

The SNAPSHOT p r o g r a m is a joint AEC-USAF effort to f l ight- test SNAP

uni ts . SNAPSHOT flights a r e intended to es tabl ish the capabil i t ies of nuclear

auxi l iary power, overcoming both technical and psychological b a r r i e r s , so that

its future use in space sys tems can be p rogrammed with confidence (see

WDLPR-345). A set of flight t es t s for the SNAP lOA sys tem forms a par t of

this effort. These flight t es t s a r e cur ren t ly scheduled for the Spring of 1963

based on cu r ren t launch site availabili ty information. A detailed schedule is

now being establ ished for the completion of the flight tes t systena as well as for

cer ta in other in te r im sys tems n e c e s s a r y for vehicle integrat ion work. The

f i rs t SNAP lOA flight sys tem is scheduled for del ivery in January 1963.

NAA-SR-6693 8

— PrmijEi:—————"

I I . PROGRAM SUMMARY

During the repor t period the major development act ivi t ies have centered

on the the rmoe lec t r i c power conversion sys tem. Techniques have been es tab

lished for measur ing room and elevated t empe ra tu r e the rmoe lec t r i c p rope r t i e s ,

and la rge scale test ing devices have been fabricated and successfully put into

operat ion. P r i m a r y development act ivi t ies have been concentrated on the

requi red encapsulant and the contacting of lead te l lur ide to var ious shoe m a t e

r i a l s . P r e l i m i n a r y r e su l t s from this p r o g r a m indicate that a ce ramic enamel

fired onto the surface of the lead te l lur ide will provide suitable protect ion against

sublimation at SNAP 1 0A operating conditions.

Lead te l lur ide contacting has produced suitably low re s i s t ance contacts on

the n-type lead te l lur ide e lements but adequate p- type e lements have not yet

been produced. La rge scale work has s ta r ted on fabrication brazing and a s s e m

bly techniques, with p re l imina ry r e su l t s indicating successful insulator and

radia tor brazing can be obtained. During the repor t period, backup t h e r m o

elect r ic conver ter work was initiated on a swaged concentr ic tube-type module.

No significant t es t r e su l t s a r e as yet available on this p r o g r a m .

The f irst prototype sys tem flight type ha rdware design and p rocurement

was init iated for inclusion on the PSM-1 sys tem s t ruc tu ra l tes t vehicle. F a b r i

cation and vendor capability exists to supply all of the PSM-1 components, a l

though there may be some short schedule de lays .

During this per iod a contract was awarded by the Air F o r c e to the Lockheed

Miss i les and Space Company to provide vehicles for SNAP lOA flight sy s t ems .

A major effort, and a continuing one, is that of coordinating the var ious in te r

face considerat ions between the SNAP lOA system and the launch vehicle. In

support of this activity the SNAP lOA flight sys tem design and analytical effort

has been augmented to expedite final decisions requi red for the flight sys tem.

NAA-SR-6693 9

111. FLIGHT SYSTEM

The SNAP lOA sys tem cons is t s of a SNAP 2 r e a c t o r as a heat source , an

a r r a y o£ in tegra l the rmoe lec t r i c c o n v e r t e r - r a d i a t o r units mounted on smal l

tubes , and a liquid me ta l pump which t r ans f e r s hotNaK from the reac to r to these

tubes . E lec t r i c energy is produced by the the rmoe lec t r i c p roces s whxch occurs

when a t empera tu re difference is maintained between opposite faces of selected

m a t e r i a l s . A lightweight shield composed of l i thium hydride is placed between

the r eac to r and the payload to reduce the radiat ion dose .

The configuration is shown in F igure 1. It consis ts of a t runcated conical

shaped s t ruc tu re that supports the r eac to r and shield at its smal l end and a t -

.aches to the vehicle a . i ts la rge end. The reac to r separa t ion from the payload

is dictated by minimum overa l l weight r equ i r emen t s . The radia tor and con

ve r t e r a ssembly a r e placed in the shadow of the shield, dec reasmg neutron

sca t te r to minimise the shielding weight. The overal l height of the package >s

a function of the rad ia tor a r e a requ i red to diss ipate the heat to space.

The vacuum conver te r sys t em cons is t s of a conver te r a s sembly with the

NaK inlet manifold a. the top of the radia tor and the NaK outlet manifold at the

bottom. Fo r ty conver te r tubes run ver t i ca l ly the length of the rad ia to r . The

conver te r e lement is at tached to the conver te r tube a. i ts inner end and to an

individual rad ia to r at i ts outer end. The rad ia tors a r e s i . e d and spaced at the

outer surface of the APU to produce uniform power f rom each conver ter e lement .

An a l te rna te SNAP lOA system employing a different conver ter is under

considerat ion. It differs from the vacuum conver ter sys tem in that it employs

two NaK loops, a one-piece radia tor , and a separa te ly packaged conver te r

assembly which mainta ins a t empe ra tu r e difference a c r o s s the the rmoe lec t r rc

ma te r i a l due to heat t r ans fe r between the two loops. The p r i m a r y loop t r a n s -ui + tv,^ -^^A^atnT This svs tem is r e f e r r e d fers heat from the conver te r a ssembly to the rad ia to r , i n i s y

to as the "two-loop" or "void- f ree" sys tem.

In the p resen t configuration, the void-free conver ter cons is t s of 16 conver ter

tube a s s e m b l i e s . They a r e a r ranged within a separa te jacket for containing the

condary coolant. The individually jacketed conver ter modules a r e a r ranged

ound the inside of the radia tor assembly . F u r t h e r work is being directed

toward this la t te r design and conver ter approach.

seconc

arc

NAA-SR-6693 10

UNCLASSIFIED

-BEACTOR VESSEL SUPPORT 5TA-AI 22S.O VE RADIATOR

END-OF-LIFE 5CCAM ACTUATOR

DRUM RELEASE ACTUATOR

CONTROL DRUM

CONTROL MOTOB

RE-ENTBY FUSIBLE BAND

TELEMETRY SCRAM ACTUATOR

"1 A

LOWER SUPPORT RING

J7 STftt

Figu re 1. Fl ight System - Elevation

UNCLASSIFIED

NAA-SR-6693 11

millerc

Text Box

BLANK

- SEsm The cu r ren t weight specification for the SNAPSHOT fl ight- test s e r i e s is

875 lb including 50 lb al located for special diagnostic instrumentat ion and a

50-lb contingency. The p resen t weight objective for operat ional SNAP lOA s y s

t ems is 775 lb . The al located weight breakdown for individual sys t em compo

nents for the SNAPSHOT flights is given in Table I. Weights have not been

demonst ra ted on any component. The present cen te r -of -grav i ty stations for

each component, referenced to a zero datum station at the base of the APU,

a r e a lso given.

TABLE I

WEIGHT STATUS - FLIGHT SYSTEM

Reactor Core

Reactor Vesse l and Grid P la tes

Reactor Contro ls , Reflector , and Structure

Rad ia to r -Conver te r , Including Conver ter Tubes

Piping

St ruc ture , Including Meteoroid Protec t ion

Startup Controls and Ins t rumentation, Wiring, and Insulation

Expansion Compensator

Pumps

Shield and Casing

Destruct Charge

Diagnostic Ins t rumentat ion

Contingency

TOTAL

Curren t Design Status Weight

(w/NaK) (lb)

130

26

137

182

16

77

20

14

25

223

10

50

0

910

Curren t SNAPSHOT

Specification Weight

(lb)

125

23

110

142

17

70

20

10

25

223

10

50

50

875

Center-of-Gravity Station

(in. )*

108.4

101.8

109.3

36.9

53.2

44.8

62

3.7

120.1

85.6

108.4

62

- -

*Center -of -gravi ty station for ent i re APU = 78 in.

NAA-SR-6693

SECRET

IV. SYSTEM TESTS

An important aspect of the SNAP lOA P r o g r a m is a s e r i e s of developmental

and qualification sys tems t e s t s to be conducted on prototype flight sys t ems . These

t e s t s a r e designed to explore the s t ruc tura l , t he rma l , and other environmental

behavior cha rac t e r i s t i c s of these power sys tems p r io r to actual flight tes t .

The cu r ren t sys tems tes t experience is summar ized in Table II. No tes t

experience is available to date; however this table will be used as a format to

r eco rd tes t data in the future. A m o r e detailed s ta tement of t es t objectives,

schedules, and cu r ren t status follows.

A. SlOA-PSM-1 (Mechanical Environmental Tes t APU)

1. Objective

The PSM-1 APU (Auxiliary Power Unit) will undergo p rog rammed shock

vibrat ion and acce lera t ion input forces to evaluate the s t ruc tu ra l design of the

assembled APU and to de te rmine the capability of the subsequent APU's to with

stand the t ranspor ta t ion and launch environnnent. Modifications to improve the

design and to reduce sys tem weight will be made as the tes t information becomes

avai lable .

2. Schedule

Assembly of the PSM-1 APU is scheduled for connpletion on September 15,

1961. The mechanical environmental testing will begin immediate ly following

the final assembly and is scheduled for completion June 30, 1962.

3. Cur ren t Status

The mechanical environmental t es t equipment that is requi red to pe r fo rm

the shock, vibration, and simulated acce lera t ion (static loading) tes t has been

received and is being installed and checked out in the labora tory building

(Building 027, SNAP complex a rea , Santa Susana, California). The t r ansduce r s

and recording ins t rumentat ions have been received.

The PSM-1 APU tes t p r o g r a m has been wri t ten and is being reviewed to

ref lect t es t object ives.

Mass mockup and prototype components have been designed for the initial

t e s t s and a r e being fabricated for the APU assembly .

NAA-SR-6693 14

rr^SIGRFF—-

c/>

j re«d^£i»04

TABLE II

SNAP DEVELOPMENT AND QUALIFICATION SYSTEMS

> >

T e s t S y s t e m

S l O A - P S M - 1

S l O A - P S M - 2

S l O A - P S M - 3

S l O A - F S M - 1

S l O A - F S M - 2

S l O A - F S - 1

P u r p o s e

S t r u c t u r e D e v e l o p m e n t

E l e c t r i c a l S imula t ion of T E C o n v e r t e r

T h e r m a l and E n v i r o n m e n t a l D e v e l o p m e n t

N o n - N u c l e a r Qual i f ica t ion

Vehic le I n t e g r a t i o n and S t r u c t u r a l Qual i f ica t ion

N u c l e a r Qual i f ica t ion

T e s t S t a r t Date

Scheduled

Oct . 1, 1961

D e c . 1. 1961

May 1, 1962

Oct . 1, 1962

A c t u a l

T e s t E x p e r i e n c e - To ta l T i m e

At Des ign Condi t ions

0

0

0

0

Down Due to S y s t e m F a i l u r e s

0

0

0

0

Down Due to Equ ipmen t o r S y s t e m

Modif icat ion

0

0

0

0

Other

0

0

0

0

R e m a r k s

To be d e l i v e r e d to LMSC M a r c h 1, 1962

To be d e l i v e r e d to LMSC July 15, 1962

The tools and equipment requi red to assemble and check out the APU

a re being reviewed,

B. SlOA-PSM-2 (Analog Simulator)

1. Objective

The PSM-2 analog s imulator will be e lec t r ica l ly connected to the proto

type orbi ta l payload package to de termine the compatibili ty of the SNAP lOA

APU to the e l ec t r i ca l r equ i rements of the payload.

2. Schedule

The analog s imulator will be designed, fabricated, and checked out

for del ivery and integrat ion evaluation between July 1, 1961 and March 1,

1962.

3. Cur ren t Status

The analog s imulator r equ i rements have been es tabl ished. Specifications

for a power supply s imulator that will have the cha rac t e r i s t i c s of the orbi ta l

sys tem a re being p repa red . Vendors have been contacted to de termine fabr ica

tion capability and del ivery schedules .

C. SlOA-PSM-3 (Performance Test APU)

1. Objective

The PSM-3 APU will be subjected to non-nuclear t h e r m a l environmental

conditions that a r e imposed on the sys tem while in orbi t . The APU will be in

stalled in a la rge vacuum ves se l and operated at the designed coolant flow and

sys tem t empera tu re to evaluate sys tem performance and degradation c h a r a c t e r

i s t i c s ,

2. Schedule

Assembly of the PSM-3 APU will be completed November 15, 1961. The

performance test ing will begin on December 1, 1961 and will continue until

September 1, 1962,

3. Cur ren t Status

The design of the PSM-3 assembly has been completed. (This design is

the same as for PSM-1 with the exception that an e l ec t r i ca l hea ter has been

NAA-SR-6693 16 :sMmt

i|iii I 1 H li li li "" '

' -^SEEitt:::;::^ substituted for the r eac to r core ves se l , and t e m p e r a t u r e , p r e s s u r e , and flow t r a n s d u c e r s a r e requ i red . ) Fabr ica t ion of s t ruc tu ra l components has begun.

The engineering and design of the vacuum sys tem inst rumentat ion and

control sys tem, and the APU e lec t r i ca l load bank a r e near ing completion. The

vacuum v e s s e l is being fabricated and the bids for the vacuum pumping sys tem

a re being reviewed.

Tools and equipment requi red to a s semble and check out the APU a r e

being reviewed and p rocured .

The detailed tes t p r o g r a m to be c a r r i e d out on the PSM-3 APU assembly

is being p r epa red .

D. FSM-1 (Non-Nuclear Qualification Test APU)

1. Objective

The FSM-1 APU will undergo mechanical environmental t e s t s con

sisting of shock and vibrat ion loading and the rmal environmental t e s t s p e r

formed at design conditions operating in a hard vacuum. These t e s t s will

demons t ra te or qualify the APU to fulfill the non-nuclear objectives of the

SNAP lOA concept.

2. Schedule

Assembly of FSM-1 will be completed on Apr i l 1, 1962. Mechanical

environmental qualification t e s t s will begin on May 1, 1962. The sys tem ope r

ation test ing at design t empera tu re in a hard vacuum will follow the mechanical

test ing and will be completed on May 1, 1963.

3. Cur ren t Status

Work has not been ini t iated.

E . FSM-2 (Integration Mockup)

1. Objective

Launch vehicle integrat ion and capability of the APU s t ruc tu ra l and

sys tem design to withstand dynamic input forces from hot static firing of the

booster engines will be demons t ra ted .

mmiff NAA-SR-6693

17

2. Schedule

The design of the FSM-2 APU will be completed before January 1, 1962

and will be s imi la r to the design of F S M - 1 . Assembly of the APU will be com

pleted by May 1, 1962. Acceptance test ing p r io r to del ivery to the vehicle inte

gration and hot stat ic firing tes t site will be completed before July 1, 1962.

Delivery to the tes t site and integrat ion tes t s will s t a r t on July 15, 1962.

3. Cur ren t Status

Work has not been init iated.

F . FS-1 (Nuclear Qualification Test APU)

1. Objective

After completion of the mechanical environmental acceptance t e s t s , the

FS-1 APU will be operated at design reac to r power and sys tem t empe ra tu r e s in

a hard vacuum to demons t ra te and qualify the flight sys tem.

2. Schedule

Design of the FS-1 will be completed before June 15, 1962. The APU

will be assembled and instal led for tes t before September 1, 1962. Operation

and qualification test ing will begin on October 1, 1962 and will be completed be

fore December 1, 1963.

3. Cur ren t Status

General analyt ical and design work on the flight sys tem has been init iated.

No significant mi les tones have been reached.

NAA-SR-6693 18

V. DEVELOPMENT PROGRAM

The development p r o g r a m this repor t period has been concentrated p r imar i ly

in the a r ea of the rmoe lec t r i c power conversion techniques. Much smal le r efforts

a r e being expended on the other NaK loop components , i . e . , the EM pump and

volume compensator unit. During this period no significant development effort

has been expended on other port ions of the SNAP lOA sys tem being funded under

this p r o g r a m . (Reactor development and other basic work is being adminis tered

under the SNAP 2 p r o g r a m being conducted for the AEC by Atomics International.)

A. PUMP

The objective of the SNAP lOA Pump P r o g r a m is to develop a the rmoelec t r i c

pump sys tem utilizing PbTe as the the rmoe lec t r i c e lements to develop 1 psi of

NaK-78 flowing at 12 gpm at 1000 °F . The development to date has succeeded in

establishing design techniques which predict pump performance within 5%. This

has been demonst ra ted by the successful operat ion of a Chromel-Constantan

the rmoe lec t r i c pump.

The p r o g r a m has been divided into four major technical a r e a s :

1) Magneto-hydrodynamic (MHD) analysis .

2) E lec t r i ca l and magnetic c i rcui t optimization.

3) Heat t r ans fe r ana lys i s .

4) Fabr ica t ion and m a t e r i a l development.

Tes ts have been performed on three dc conduction pumps which demonst ra te

that p r e s s u r e drop inc reases not only with increas ing velocity but also with in

c reas ing magnetic field. These p r e s s u r e l o s s e s , additional to those explained by

hydraulic theory, a r e categor ized as magnetohydrodynamic (MHD) l o s s e s . A

cor re la t ion of the MHD losses has been obtained from the operating pump data.

The re su l t s indicate that the l o s ses a r e actually eddy cu r ren t losses occurr ing

at the inlet and exit regions of the throat where the magnetic flux gradient is at

a maximuna. Such losses can general ly be expressed by the equation

P = 0,27 B^VWalO""^

NAA-SR-6693

19

where B is the magnetic field in gausses , V is the velocity in c m / s e c , W is

the channel width (normal to the magnetic field direct ion) , and cr is the liquid

e lec t r i ca l conductivity.

The e lec t r i ca l and magnetic c i rcui t optimization effort has been centered on

obtaining a f i rm pump design equation. To substantiate the p resen t design phi

losophy, a Chromel-Constantan in tegra l source pump has been designed and

tes ted .

This pump was designed to pump 6 gpm of NaK-78 at 1000°F with a head of

1 psi and SOO^F impre s sed a c r o s s the t h e r m o e l e c t r i c s . F igure 2 is a plot of the

tes t r esu l t s obtained. Per formance at the 5 0 0 ° F - A T point was extrapolated f rom

the 6-gpm curve . This value of A T was not achieved during the tes t due to heat

rejection l imitat ions of the tes t loop. F igure 2 also plots developed p r e s s u r e vs^

A T for other values of constant flow r a t e . This data was used to obtain the more

convenient per formance curves of p r e s s u r e vs flow as shown in Figure 3,

F igure 4 compares the exper imenta l and calculated pump performance at

A T = 500°F. The uppermost curve, A, was obtained from the equation

_ BWE B^VW^ ^ R ~ " R

Curve B was obtained by subtract ing the MHD losses previously descr ibed .

Hydraulic losses through the channel were calculated and the final analytic p e r

formance curve is r epresen ted by C. The close compar ison of the calculated

and exper imenta l per formance curves indicate that the p resen t design equations

a r e effective and account for ~95% of the major l o s s e s .

F igure 5 is a photograph of the (102-D) pump tes ted . The hot NaK to be

pumped is contained in the center channel (A) and provides the hot junction for

the the rmoe lec t r i c m a t e r i a l (B) sandwiched between the channel and the copper

buswork (C). Two channels (D) through which cold NaK is c i rculated a r e brazed

to the sides of the unit and provide the cold junctions for the the rmoelec t r i c e l e

men t s . The d iscs (E) a r e t e rmina l s of the immers ion thermocouples penetrat ing

the channels to m e a s u r e the liquid meta l t empe ra tu r e s at al l en t rances and exi t s .

The bare leads (F) a r e thermocouples located at the hot and cold junctions of the

the rmoe lec t r i c s t r ips to m e a s u r e the A T .

NAA-SR-6693

Figure 2. The rmoe lec t r i c Pump P r e s s u r e vs AT for Constant Flow (P r imary Data)

UNCLASSIFI NAA-SR-6693

21

UNCLASSIFIED

1.4

1.3

1.2

I.I

1.0

.-. 0.9

0.8

10 Q.

l l J

cc

(O 0.7 lU (T Q.

0.6

0.5

0.4

0.3

0.2

0.1

r ~~~~~

r^ L ^

- ^ . . ^ ^^^Snr. X.^^00op

^ ^ <

^

< . . , ^ ^

^ ^

^ ^

^

^ ^ ^ ^

- 1

^ - - ^

" ^

0 1 2 3 4 5 6

FLOW RATE (gpm)

Figure 3. The rmoe lec t r i c Pump P r e s s u r e vs Flow for Constant AT

NAA-SR-6693 22

UNCLASSIFIED

UNCLASSIFIED

1.4 =•

1.3

1.2

^ • ^

M a. "^ UJ (£ 3 (0 to UJ Q: Q.

I.I

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

= ^

^ ^ ^^^^**^*^

^yr. -r ^

,

C4/r,„ ::-^^^:^o

^ " ' " ^ ^ ^^^^^"*'"***'- ^ 2 ^ ^ - ^

: ^ ^ ^

\ ^

1 2 3 4 5

FLOW RATE (gpm)

Figure 4. The rmoe lec t r i c Pump P r e s s u r e vs Flow for A T = 500°F

UNCLASSIFIED

NAA-SR-6693 23

> >

C"3

era

C/3

f'sni

Figure 5. Thermoelec t r ic Pump 102-D

The unit is 2,5 in, long, weighs approximately 12 lb, and m e a s u r e s 8 m,

wide and 5 in, high. The pump is p resen t ly operating at a 1000 "F hot junction

t empera tu re to m e a s u r e degradat ion as a function of life.

The heat t r ans fe r analys is effort has concentrated on optimizing the channel

shape and the heat reject ion assembly ( radiator) . By going to smal le r channel

s i zes , it is apparent that the t empera tu re drop a c r o s s the boundary layer would

be lessened; however , the p r e s s u r e drop i n c r e a s e s . Analysis was performed

which demons t ra t e s the optimum channel size along with the associa ted t r a d e

offs. F igure 6 p re sen t s the r e su l t s of this analys is as applied to a PbTe pump

operating at a maximum 300"F a c r o s s the the rmoe lec t r i c , where all l o s se s a r e

presented in degrees Fahrenhe i t . As noted, there is not much to gain in AT

a c r o s s the the rmoe lec t r i c by going to smal le r channel s i ze s , as the p r e s s u r e

drop is the controll ing c r i t e r ion .

Fo r heat reject ion a rad ia tor with a surface a r e a of less than 1 ft would be

sufficient.

Major emphas is in the a r e a of fabrication and m a t e r i a l development has

been on the p rob lem of bonding the PbTe to the pump wall , and of containing the

PbTe to prevent sublimation at operating t empe ra tu r e s in the vacuum environ

ment . Two approaches a r e being pursued, and p re l imina ry resu l t s indicate

feasibil i ty.

One method of pump fabrication encapsulates the PbTe within s ta in less

s teel utilizing one side of the rec tangular pump throat as a pa r t of the encapsu

lant. Initial fabrication has at tempted to isos ta t ica l ly bond the the rmoelec t r i c

to the s ta in less s tee l container at 1600°F and 10,000 ps i . P r e l im ina ry m e t a l -

lographic examination indicated incomplete bonding and some melting of the

PbTe . The melting is a t t r ibuted to p r io r weld operat ions and not to the bonding

p r o c e s s . These p re l imina ry resu l t s indicate a need for compacting powdered

PbTe to higher densi t ies p r io r to bonding and for higher bonding t e m p e r a t u r e s .

An a l ternat ive fabrication approach is to rol l bond the PbTe within a thin

(0.010-in.) i ron c a s e . The ro l l bonding technique employs powdered PbTe and

is conducted at room t empera tu re followed by the s inter ing operation on the unit.

This fabrication technique has achieved successful bonds. The PbTe compact

encased in i ron is then brazed to the pump wall . A disadvantage of this fabr ica

tion p roces s is that the i ron encapsulant will sa tura te and effectively reduce the

flux a c r o s s the pump throat by about 5%.

„ NAA-SR-6693

yilLiSSilEI

CHANNEL WIDTH D (in,) Figure 6, Loss in Effective Tempera tu re Drop Across T / E as a Function

of Channel Width

NAA-SR-6693

UNCLASSIFIED

B. EXPANSION COMPENSATOR

The operat ion of the NaK p roces s sys tem requ i res that no voids exist at any

t ime after ini t ial NaK loading. Since NaK loading is accomplished on the ground

at essent ia l ly ambient t empera tu re , expansion compensation is requi red in the sys

t em to accommodate the t h e r m a l expansion of the NaK at operating t e m p e r a t u r e .

The p resen t method of expansion compensation employs a bellows backed up by

static gas p r e s s u r e , A conceptual design of this device is shown in F igure 7. A 3

unit of this type has been fabricated which provides 135 in. of expansion. The

unit has to date been put through 220 t he rma l cycles from minimum to maximum

volume and has been subjected to environmental qualification testing for v ib ra

tion and shock r e s i s t ance ; no fa i lures have occur red .

C. THERMOELECTRIC CONVERTER

The the rmoe lec t r i c development p r o g r a m has been di rected toward the

solution of ce r ta in bas ic p roblems associa ted with the fabrication of a conver ter

using lead te l lur ide as the the rmoe lec t r i c m a t e r i a l . These problems include

development of contacting and encapsulation p r o c e s s e s as well as an invest iga

tion of the bas ic p roper t i e s of lead te l lu r ide . The ma te r i a l s p roper t i e s m e a s

ured to date include the coefficient of t h e r m a l expansion, the compress ive

p rope r t i e s , sublimation p r e s s u r e , and cer ta in of the diffusion p r o p e r t i e s . A

reference p r o c e s s has been selected for the contacting and encapsulation of lead

te l lur ide . The problems of the assembly of the the rmoe lec t r i c e lements into

modules a r e being studied.

1. Design Studies

Design studies have been conducted to develop methods of assembl ing

individually contacted and encapsulated lead te l lur ide e lements into both a

sys tem utilizing the vacuum conver ter concept, and one utilizing the void-free

conver ter concept.

a. Vacuum Conver ter

The p r i m a r y objective of the vacuum conver ter design study has been

to de te rmine methods of minimizing (1) the s t r e s s levels in the lead te l lur ide

e lements due to the shock and vibrat ion forces during the launch phase and (2)

the t he rma l s t r e s s due to the difference in expansion between the lead tel lur ide

and the heat source tube at operat ing tenapera tures .

NAA-SR-6693 27

CSJ CO 00 ^

I

gesmme

F i g u r e 7. Conceptual Design - Expansion Compensation

%iamisif^

T h r e e d i f f e ren t m e a n s e x i s t for m i n i m i z i n g the t h e r m a l s t r e s s e s :

1) A f lex ib le h e a t s o u r c e t u b e .

2) A f l ex ib le a t t a c h m e n t to the t h e r m o e l e c t r i c e l e m e n t .

3) A f lex ib le r a d i a t o r .

An eva lua t i on of the nae thods u s ing t h e s e m e a n s i n d i c a t e d tha t t he

t h i r d would r e q u i r e t h e l e a s t d e v e l o p m e n t and r e s u l t e d in the d e s i g n shown in

F i g u r e 8 be ing c h o s e n a s the b a s i c r e f e r e n c e d e s i g n .

In t h i s d e s i g n e a c h t h e r m o e l e c t r i c e l e m e n t h a s i t s own r a d i a t o r and

t h u s i s f r e e to g r o w a x i a l l y and r a d i a l l y wi thout c a u s i n g s h e a r s t r e s s e s in the

e l e m e n t . A l l e l e m e n t s a r e t h e r n a a l l y in p a r a l l e l and e l e c t r i c a l l y in s e r i e s . The

h e a t f r o m the f l a t t ened s t a i n l e s s s t e e l NaK tube i s conduc ted t h r o u g h the e l e c t r i

c a l i n s u l a t o r and the t h e r m o e l e c t r i c e l e m e n t , and r e j e c t e d a t the r a d i a t o r . The

e l e m e n t s a r e c o n n e c t e d e l e c t r i c a l l y in s e r i e s by the u s e of f lex ib le c o p p e r s t r a p s

a t the ho t j u n c t i o n ; the a l u m i n u m r a d i a t o r j o i n t e d by f l ex ib le s t r a p s f o r m s the

c o n d u c t o r a t the co ld j u n c t i o n . The u s e of the r a d i a t o r a s an e l e c t r i c a l c o n d u c t o r

e l ina ina t e s the n e e d for an i n s u l a t o r a t the co ld j u n c t i o n and thus a c h i e v e s the

m a x i m u m a v a i l a b l e c o l d - j u n c t i o n t e m p e r a t u r e .

The l e a d t e l l u r i d e e l e m e n t s w i l l be r e q u i r e d to w i t h s t a n d the s h o c k

and v i b r a t i o n f o r c e s of the l aunch p h a s e whi le c a r r y i n g the load due to the r a d i

a t o r . To v e r i f y t ha t the l ead t e l l u r i d e h a s suff ic ient s t r e n g t h to w i t h s t a n d t h i s

load , a g r o u p of 16 e l e m e n t s wi th w e i g h t s s i m u l a t i n g the r a d i a t o r w e r s u b j e c t e d

to the qua l i f i c a t i on s h o c k and v i b r a t i o n s p e c t r u m . No f a i l u r e s o c c u r r e d un t i l the

shock and v i b r a t i o n l e v e l s w e r e i n c r e a s e d by a f a c t o r of t h r e e above the q u a l i f i c a

t ion t e s t . H o w e v e r , to i n c r e a s e r e l i a b i l i t y , m e t h o d s of ho ld ing the e l e m e n t u n d e r

c o m p r e s s i o n a r e be ing i n v e s t i g a t e d .

b . V o i d - F r e e C o n v e r t e r

A c o n v e r t e r u t i l i z ing c l o s e l y p a c k e d e l e m e n t s in a v o i d - f r e e c o n f i g u r a

t ion i s be ing i n v e s t i g a t e d a s an a l t e r n a t e a p p r o a c h to the v a c u u m d e s i g n . T h i s

c o n v e r t e r w i l l u s e a t w o - l o o p s y s t e m u t i l i z ing NaK for h e a t t r a n s f e r f r o m the

r e a c t o r to the hot j u n c t i o n s and f r o m the co ld j u n c t i o n to the s p a c e r a d i a t o r .

A s p e c i f i c a t i o n b a s e d on t h i s c o n c e p t h a s b e e n w r i t t e n and the

W e s t i n g h o u s e E l e c t r i c C o r p . h a s b e e n a w a r d e d a c o n t r a c t to d e v e l o p a c o n v e r t e r

N A A - S R - 6 6 9 3

fflflFT " ^

oo

> >

oj en o JO

I

BRAZE

2 67 in.

N-SEMICONDUCTOR

era

o o C/3

Figure 8, 4.2-Watt Module - Vacuum Design SNAP lOA T / E Generator

module s imi la r to that shown in F igure 10, The cyl indrical geometry resu l t s in

the mechanical p roper t i e s required to meet the shock and vibration conditions of

the launch environment . In addition, the design completely contains the lead

tel lur ide under compress ion and therefore offers the possibil i ty of operation at

elevated t empera tu re with negligible degradat ion,

2, Mate r ia l s Development

Exper iments utilizing the Knudsen effusion method for determining vapor

p r e s s u r e of high puri ty lead te l lur ide have been completed. The p r e s s u r e can

be calculated f rom the following equation:

1 / ^. \ 12.200 . „ „ . log p (atm) = T(°K)

-5 At 900 °F the vapor p r e s s u r e is 3.5 x 10 m m Hg. This p r e s s u r e gives r ea son able agreement with measu red ra t e s of weight l o s s .

Diffusion of lead, te l lur ium, and the dopants in the l ead te l lu r ide as a resu l t

of t he rma l gradients and diffusion of ma te r i a l s used as contacts and encapsulants

is being studied. Analytical study techniques have been developed for the p rec i se

determinat ion of lead and te l lu r ium to within ± 0,2 wt % and of the doping const i tu

ents to within 5% of the nominal va lues .

The coefficient of t he rma l expansion has been m e a s u r e d in the range 21

(room t empera tu re ) to 536' 'C. The resu l t s of these measu remen t s a r e given in

Table III.

The compress ive p rope r t i e s of 3M (pressed and sintered) PbTe and Trancoa

(extruded) n-type PbTe at room t empera tu re a r e tabulated in Table IV.

Heat t r ea tmen t of both n - a n d p- type lead te l lur ide has been shown to resu l t

in an inc rease in the e l ec t r i ca l r e s i s t iv i ty . Determinat ions have been made on

both bare e lements and e lements with i ron contacts . The resu l t s a r e s u m m a

rized in Table V.

Thermal cycling was found to inc rease the cap- to-cap r e s i s t ance of p-type

lead te l lur ide substantial ly and the n-type slightly.

NAA-SR-6693

PbTe -I-I

6 -A IS I 347 SS

5 > I

o

r r r ^ ss ^ ^ ^ B ^ ^ Fe

A-AISI 347 SS

H-AISIMg-222

ALTERNATE MATERIALS A-AISI TYPE 321 STAINLESS STEEL B-AISI Mg 222 C-LOW CARBON STEEL AI SI 1008 D-PbTe (NO ALTERNATE) E-LOW CARBON STEEL AlSl 1008 F-AI SI Mg 222 G-AISI TYPE 321 STAINLESS STEEL H-SYNTHAMICA 202

Figure 9. Tabular Module Configuration

TABLE III

COEFFICIENT OF THERMAL EXPANSION OF LEAD TELLURIDE

T e m p e r a t u r e Range

(°C)

21-38

21-93

21-149

21-204

21-260

21-316

21-371

21-427

21-482

21-536

p - T y p e Ex t ruded

Specimen 1 (Room T e m p . Dens i ty

= 8.05 g m / c m ^ )

25.01

23.64

22.88

22.13

21.42

20.98

20.89

20.77

20.72

20.83

Coefficient of T h e r m a l Expans ion x 10 °C"

n - T y p e Ex t ruded

Specimen 1 (Room T e m p . Densi ty

= 8.17 g m / c m 3 )

21.24

21.94

21.49

20.86

20.22

20.00

20.05

20.16

20.18

20.29

Specimen 2 (Room T e m p . Densi ty

= 8.07 g m / c m 3 )

20.70

22.35

22.21

22.80

21.78

21.12

21.18

21.17

21.09

21.13

Specimen 3 (Room T e m p . Dens i ty

= 8.20 g m / c m 3 )

27.82

21.18

20.63

20.80

20.91

21.04

21.08

21.16

20.97

TABLE IV

COMPRESSIVE PROPERTIES OF n -TYPE LEAD TELLURIDE

Specimen No.

5-51

5-52

5-53

19-4

19-5

19-9

Manufacturer

3M

3M

3M

Trancoa

Trancoa

Trancoa

US-psi

11,500

11,700

11,000

13,600

16,750

13,600

YS-psi

5,900

6,000

5,000

7,500

11,400

7.800

E-ps i

417,000

338,000

417,000

714,000

1,000,000

793,000

Total Strain at Maximum

St ress (%) 9.6

10.9

10.9

4,7

4 ,5

5.0

Density (gm/cm^)

7.63

7.62

7.57

8.06

8.16

8.08

•„ . . -—--^„: . " NAA-SR-6693

TABLE V

EFFECT OF HEAT TREATMENT ON RESISTANCE OF PbTe

Pel le t Number and Type

9-13 Iron Contacts (n-type)




8-40 Iron Contacts (p-type)



S P - l - " n " Casting (1-in. long)

S P - 2 - " p " Casting (1-in. long)

Res is tance /xD,

Initial

186

180

181

190

821

710

600 *

800

600*

Fina l

252

247

243

242

1796

1221

805

968* *

1077

Test Tempera tu re

(°F)

1000

1200

1000

1200

1200

1200

1000

1200

1200

Time at Tempera tu re

(hr)

50

68.5

100

100

50

100

100

100

100

*End-to-end re s i s t ance (no Fe shoes)

3. P r o c e s s Development

A re fe rence p r o c e s s specification for the application of iron contacts to

lead te l lur ide has been adopted and severa l hundred e lements p repared by this

p r o c e s s . A mild s tee l contact is p repa red by punching a disk from 1015 sheet

stock and se r r a t i ng the surface with a dovetail pa t te rn . This disk is abras ive ly

cleaned and vapor coated with a thin film of lead te l lu r ide . The lead te l lur ide

pellet is abras ive ly cleaned and assembled in a graphite die with the coated d i sks .

The die is heated to 1600''F and a p r e s s u r e of 5000 psi is applied to form the

contact . It is held under these conditions for 30 min after which it is cooled to

1200"F and removed from the p r e s s . The equipment used in this p r o c e s s is

shown in F igure 10.

An evaluation of the e lements contacted by this p r o c e s s has shown a con

sistently low contact r e s i s t ance for the n - e l e m e n t s . The p-e lements have shown

a higher r e s i s t ance but the average of the two contacts is within the specified

l imi t s . The average value of the contact r e s i s t ance is shown in Table VI.

NAA-SR-6693

UNCLASSIFIED

Figure 10. Hot P re s s ing Apparatus

UNCLASSIFIED NAA-SR-6693

35

-ttttit

TABLE VI

CONTACT RESISTANCE OF ELEMENTS FROM REFERENCE PROCESS

Element Type

n

P

Contact Res is tance

2.1 m i c r o - o h m - i n .

10.3 m i c r o - o h m - i n .

The cu r ren t specification cal ls for an average contact r e s i s t ance of 7.7 m i c r o -

ohm-inch , The cap - to -cap r e s i s t ance of the e lements i nc r ea se s during this

operat ion. This inc rease in r e s i s t ance is of the o rde r of a factor of two in the

n -e lements and a factor of four or more in the p - e l e m e n t s . Subsequent t e s t s

have shown that this inc rease in r e s i s t ance is annealed out in the heating of the

n -e lements to the operat ing tennperature , but in the p -e lement has been shown

to be associa ted with cracking of the m a t e r i a l . The full extent of this mechan

i s m has yet to be invest igated.

Al ternate p r o c e s s e s have been investigated for the application of contacts .

A par t icu lar ly a t t rac t ive method uses the cold compacting of iron and lead

tel lur ide powders to form a contacted e lement . The respect ive powders a r e

p r e s s e d at 5000 psi to form compacts and a r e subsequently hot p r e s s e d at the

same t ime , p r e s s u r e , and t empera tu re conditions that a r e used in the reference

p r o c e s s . This p r o c e s s appears to yield e lements of more uniform quality that

a r e apparently free of c r a c k s , A var ia t ion of this p rocess makes use of a t r a n

sition zone consist ing of a mixture of equal pa r t s of i ron powder and lead te l lur ide

powder. This m a t e r i a l is placed between the cap and the pellet to compensate

for the high coefficient of expansion of lead te l lur ide and the re la t ively low

coefficient of expansion of i ron. Another p rocess which improves the match in

expansions is one in which 304 s ta in less s tee l disks a r e used as the contacts

in place of the i ron . Initial t es t s of this p rocess have shown a tendency toward

very high contact r e s i s t ances because of the p resence of a chrome oxide insu

lating layer on the s tee l . Both of the a l te rna te p roce s se s a r e receiving further

study.

General Instrument, under subcontract to Atomics International, i spursu ing

a pa ra l l e l p r o g r a m in this a r e a . Their reference p r o c e s s , r e f e r r e d to as the

NAA-SR-6693

di rec t fusion p r o c e s s , is meta l lurgica l ly s imi lar to the AI p r o c e s s . Bonds a r e

promoted between iron and lead te l lur ide through the application of heat and p r e s

su re . Their p roces s differs from the AI p rocess in that it uses somewhat higher

t empe ra tu r e s and lower p r e s s u r e s . The iron cap is made of thinner sheet stock

and uses a cupped edge ra the r than a s e r r a t ed surface to promote mechanical

bonding. An exact compar ison of contact r e s i s t ances has not been possible be

cause the lip on the contact m a t e r i a l prevents the making of e lec t r i ca l m e a s u r e

ments at the t rue contact in ter face . The measu remen t s made at the edge of the

pellet appear to be higher than the AI p rocess e l ements . Table VII p resen t s the

resu l t s of cu r ren t Genera l Ins t rument contacting p r o c e s s e s .

TABLE VII

CONTACT RESISTANCE OF GENERAL INSTRUMENT ELEMENTS (Based on 50% yield)

P r o c e s s

Direct Fusion

NiP Braze

n-Type

12,6 m i c r o - o h m - i n .

9.2 m i c r o - o h m - i n .

p-Type

28.7 m i c r o - o h m - i n .

20.3 m i c r o - o h m - i n .

Genera l Ins t rument has an a l te rna te p rocess which makes use of a nickel phos

phide b raze m a t e r i a l to form a bond between iron and lead te l lu r ide . Elements

contacted by both of the GI p r o c e s s e s a r e now being evaluated.

A number of approaches to the encapsulation problem have been investigated.

During the repor t period a v i t reous enamel has been selected as the reference

coating at AI. The enanael used was a modification of one manufactured by the

F e r r o Corporat ion under the name of AL-2 , The modification consis ts of adding

one par t l i thium ti tanate powder to four pa r t s of the AL-2 enamel . This mixture

is applied to the pel le ts by a water base sl ip and cured by firing at 1100°F in an

argon a tmosphe re . Weight loss measu remen t s of pel lets with this coating have

shown very smal l lo s ses after t e s t s of 500 hr in vacuum at 900°F. The specif i

cation cal ls for less than 5% weight loss per 10,000 hr under these conditions,

and this r equ i rement has been bet tered by more than a factor of 10. An a l te rna te

coating m a t e r i a l is being invest igated. This m a t e r i a l cons is ts of eutectic mixture

of the fluorides of l i thium, calc ium, and magnes ium. Additions to this bath a re

n e c e s s a r y to promote wetting of the pellet . The coating is applied by dipping the

NAA-SR-6693

element in the bath which is held at 750°C. The weight loss of the pellet has

been well within the specified l imi t s . Other v i t reous enamels a r e being inves t i

gated under this p r o g r a m .

General Ins t rument has successfully demonst ra ted the use of a close-fitting

Isomica sleeve to prevent sublimation. Tes ts to date have been performed using

e lements in which the sleeve is fitted over a contacted element , and a s lu r ry of

mica flakes is used as a cement to form a seal between the sleeve and the i ron

contact . It is proposed that future e lements be encapsulated p r io r to contacting

and that the lip on the contact encompass the sleeve to provide a mechanical sea l .

The Isomica sleeve has been tes ted up to 1100°F in vacuum under i so the rma l con

ditions with very smal l weight l o s s .

The p resen t naodule assembly, as shown in F igure 8, r equ i re s the develop-

nnent of b raze cycles suitable for joining 321 s ta in less s tee l to metal l ized beryl l ia ,

beryl l ia to copper , copper to i ron, and i ron to a luminum. The differential ex

pansion between beryl l ia and the s ta in less s teel r e su l t s in excess ive s t r e s s in the

beryl l ia with consequent c racking. Several b raze cycles have been investigated

in connection with this problem but have not shown significant improvements .

Higher expansion ce r amic ma te r i a l s and lower expansion adjoining meta l com

ponents a r e being investigated in an at tempt to c o r r e c t the situation. B r a z e s for

bonding the a luminum radia tor to the i ron contact a r e being invest igated.

4. P r o c e s s Engineering

A p r o g r a m to e s t a b l i s h f i r m m a t e r i a l s and p r o c e s s specifications has been

init iated. The establishnaent of a specification for the p rocurement of a constant

quality of lead te l lur ide is a ma t t e r of p r ime impor tance , as uncontrolled var ia t ions

in the quality of the feed m a t e r i a l will prevent the development of a rel iable end

product . Comments on this specification have been received from some vendors

and other vendors a r e developing further data to substantiate thei r posi t ions .

Analytical studies of the re fe rence design concentrated on s t r e s s due to

bonds between d i s s imi l a r ma te r i a l s and the effect of fabrication to le rances on

thermocouple perfornnance. An exact solution for the s t r e s s e s between lead

te l lur ide and the i ron contacts could not be der ived, but semi-quant i ta t ive ca lcu

lations indicate that the s t r e s s e s caused by mismatch in coefficients of expansion

a r e in the range of s eve ra l thousand ps i . This s t r e s s is probably sufficient to

cause c racks of the lead te l lu r ide .

NAA-SR-6693 38 mm

5. Test ing

A number of devices have been developed for test ing the rmoe lec t r i c

e lements both in the a s - r e c e i v e d conditions and after var ious stages in thei r

p repara t ion . Apparatus developed to date pernaits m e a s u r e m e n t of the e lec t r ica l

r e s i s t ance profile of an element and the Seebeck coefficient in the vicinity of

room t e m p e r a t u r e . These ins t ruments a r e shown in F igu re s 11 and 12. Similar

appara tus to pe rmi t these m e a s u r e m e n t s to be made in the vicinity of the oper

ating t empe ra tu r e is under development. Other equipment is being developed

to make per formance t e s t s on completed e lements . This equipnaent will provide

a vacuum environment and hot and cold junction t e m p e r a t u r e s of 900''F and 600°F

respect ive ly . Data on open c i rcui t voltage, matched load voltage, cur ren t out

put, in ternal r e s i s t ance , and power output will be obtained. At the p resen t t ime,

a s ix-s tage prototype life t es t fixture has been completed and additional sys tems

a r e being planned. The prototype equipment i s shown in F igure 13. The element

testing p r o g r a m is being used in d i rec t support of the p r o c e s s development p r o

g r a m . E lec t r i ca l m e a s u r e m e n t s a r e the p r i m a r y t e s t s being used for the evalua

tion of the developmental p r o c e s s .

Tes t r e su l t s obtained to date during this r epo r t per iod include the

following:

a. Westinghouse Couples Tes t s No. 1-8-900A, No. 2-2-900V, and

No. 3-8-900V

As descr ibed below, these t e s t s used unencapsulated couples ob

tained from Westinghouse in December I960. They were placed on tes t to

complete the evaluation of the m a t e r i a l s used in the Westinghouse SNAP 10

genera tor , and to de te rmine the effect of vacuum environment and lower

t e m p e r a t u r e s on the per formance of the couples . Tes t No. 4-2E-850V is an

additional t es t to de te rmine the effect of encapsulation on the per formance

of the couple. Based on a p re l imina ry analys is of the data, it appears that

the GeBiTe the rmoe lec t r i c m a t e r i a l cannot be used unencapsulated to mee t

the 10,000-hr lifetime objective when operated in vacuum or iner t gas at

9 0 0 ^ hot junction. Tes t No. 4-2E-850V tends to indicate that the use of

encapsulated GeBiTe at 850°F is feasible. Theore t ica l calculat ions show

that the SNAP lOA per fo rmance objectives can be met by the use of a couple

consisting of PbTe and BeBiTe at 850°F.

NAA-SR-6693 • " " ' T : 7 : _ . 39

»*:>•

>

vD

Figure 11. Resis tance Profile Apparatus

CO

CO oo

> > I

I

o

ers

Figure IZ. Room Tempera ture Seebeck Apparatus o o

C 3

I

> >

I

C-3

CO

as-

Figure 13. Element Per formance Test Apparatus

1) Tes t No. 1-8-900A (Figure 14)

Subject: Westinghouse 8-couple module No. Z F - 3

Mater ia l : (Ge, Bi) Te (p), PbTe (n)

Atmosphere : Hermet ica l ly sealed in argon

Insulation: E lec t r i ca l , mica (probably phlogophite mica ) . Thermal , none.

Operating T e m p e r a t u r e s : 950°F hot case surface 560°F cold case surface

880-900°F es t imated hot ma te r i a l t empe ra tu r e

630-650' 'F es t imated cold m a t e r i a l t empe ra tu r e

Heater fai lure at end of the 4th week caused shutdown. The im

proved per formance following the shutdown may be due to improved heat t ransfe r

after re la t ive motion of t he rma l contact surfaces , since the open c i rcui t voltage

inc reased .

3000-hr data as % of 1000-hr data

Po\ver

Open Circui t EMF

Load Voltage

Cur ren t

Internal Res i s tance*

55%

89%

73%

76%

135%

The degradation of open c i rcui t EMF alone would account for power

reduction to 79%, or 42% of the total l o s s . In other words , the loss is divided

about 58/42 between increas ing in ternal r e s i s t ance and decreas ing EMF.

2) Tes t No. 2-2-900V (Figure 15)

Subject: Two Westinghouse couples from d isassembled SNAP lOA conver ter


Atmosphere : Vacuum, 5 mic ron

Insulation: E lec t r i ca l , mica . The rma l , none.

T e m p e r a t u r e s : Hot contact - 900**F Cold contact - 640"F

• Calculated from (V„„ - V, ) I. All other data a r e m e a s u r e d values .

NAA-SR-6693

> I

00

C 3 j c 1

Ri

35

30

25

20

1.75 P

WATTS 1.50

1.25

VO.C 0.450 VOLTS

0.425

0.250

VOLTS °-225

0.200

0.175

INTERNAL RESISTANCE

— o — a -

I SHUTDOWN a RESTART

I—13—

CASE TEMPERATURES 950-560"'F OPERATION IN ARGON AT 15 psia

POWER OUT

l — O —

I- o -o 1

LOAD VOLTAGE

l - T T - CURRENT

WEEKS _L -L

500 1000 J

1500 2000 2500

HOURS

F i g u r e 14. W e s t i n g h o u s e T h e r m o e l e c t r i c Module A v e r a g e P e r f o r m a n c e

3000

VL VOLTS

AMPS

—69 ilUtNTIAL -AVERAGE MATERIAL TEMP 9 0 0 - 6 4 0 * F PRESSURE 5 MICRON ABSOLUTE

14 16 18 20 22 24 29 31

MARCH I I I I

6 8 10 12 14 16 18

APRIL I I I r

100 200 300 400 500 600 700 770

Figure 15a.

DATE

HOURS

m a

9 0

8.5

8.0

7.5

7.0

14 16 18 20 22 24 29 31 2 4 6 8 10 12 14 16 18 I

100

Figure 15b.

F igure 15. Life Test Data Normalized to A T = 360°F - Two Westinghouse SNAP lOA Couples

O O

m G

?o

NTEF

_ ^

?NAL RESISTANCE 1 1 1 O G

r^-rrfr^ ic"

^ ^ — c

o

O ^

)

o c

r ^ r ^ ,-J3

o

= i l R ^ ^ = : NAA-SR-6693

45

mm Shutdown at about 250 hr due to hea te r fa i lure . T e m p e r a t u r e cycle

caused no significant change in pe r fo rmance .

770-hr data as % of init ial data (from average curve shown)

Power 83%

Open Circui t EMF 95%

Load Voltage 89%

Cur ren t 94%

Internal Res i s tance 120%

The power loss in this t es t was assoc ia ted with a decreas ing open

c i rcui t voltage and an increas ing in ternal r e s i s t ance with re la t ive effects of

about 10/7 . In other words , 59% of the loss is due to decreas ing EMF, 41% to

increas ing r e s i s t a n c e .

3) Tes t No. 3-8-900V (Figure 16)

Subject: Westinghouse 8-couple t e s t module identical to that of Tes t 1-8-900A, except that pa r t of the container had been removed to break the he rmet ic seal and instal l ins t rumentat ion.

Mater ia l : (Ge, Bi) Te (p), PbTe (n) _5

Atmosphere : Vacuum 5 x 1 0 m m Hg

Insulation: E lec t r i ca l , mica . Thermal , none.

T e m p e r a t u r e s : Hot contact - 900°F Cold contact - 620°F

900-hr data as % of f i r s t week 's average

Power 84%

Open Circui t EMF 97%

Load Voltage 91%

Cur ren t 91%

Internal Res i s tance* 110%

Degradation again is due to both a d e c r e a s e in EMF and an inc rease

in in ternal r e s i s t ance , the EMF drop accounting for 37% of the total l o s s .

The degradation noted in this t e s t is not significantly different than

that of Tes t 1-8-900A for the per iod from 1000 to 1900 h r .

^Internal Res is tance calculated from voltage and cu r r en t data .

NAA-SR-6693

WATTS

VOLTS

AMPS

fix 10"'

1 2 3 4 5

PERIOD OF AVERAGE (WEEKS) Figure 16. Westinghouse Thermoe lec t r i c Module — Average Data

iimnNiiiiiiii

NAA-SR-6693 47

(MKWimiil.JII-IL.

4) Tes t No. 4-2E-850V (Figure 17)

Subject: Two Westinghouse couples from the d i sassembled conver ter , s imi lar to those of Tes t 2-2-900V except encapsulated by AI with a v i t reous enamel .


Atmosphere : Vacuum, 5 mic rons

Insulation: E lec t r i ca l , boron n i t r ide . The rma l , none.

T e m p e r a t u r e s : Hot contact: 850°F Cold contact: 490°F

No significant change in per formance has occur red during the

570 hr of operation to da te . If anything, the output has inc reased very slightly

during the t e s t .

b . Atomics International - Contacted and Encapsulated E lements

F igu re s 18a and 18b show the per formance of an n- and p - P b T e e le

ment contacted to i ron by a hot p r e s s technique and encapsulated with a v i t reous

enamel . The p resen t per formance of the n-e lement exceeds the r equ i remen t s

of the SNAP lOA conver te r . The p -e lemen t will r equ i r e considerable improve

ment .

1) Tes t No. 5 (Figures 18a and 18b)

Subject: Two Al-manufactured pel le ts using 3-M PbTe basic m a t e r i a l

Mater ia l : PbTe p and n, ho t -p re s sed to i ron contacts , encapsulated w^ith a vi t reous enamel

Atmosphere : Vacuum, 1 x 10" mm Hg (p) 1 X 10-5 inm Hg (n)

T e m p e r a t u r e s : Hot contact - 900°F Cold contact - 600°F

These e lements a r e being operated separa te ly , with a copper

c i rcui t connecting hot and cold end of each.

c. General Ins t rument Elements

General Ins t rument has tes ted PbTe e lements encapsulated in Isomica

s leeves in a vacuum under i so the rma l conditions at lOOO'F for per iods in excess

of 500 hr with negligible weight l o s s . Metal lurgical examination of the units

indicates no react ion between the PbTe and the I somica . E lements contacted to

i ron by a fusion p r o c e s s and encapsulated with Isomica a r e p resen t ly on t e s t a t

AI and GI.

NAA-SR-6693 48

WATTS

1.0

0.9

0.8

0.7

0.16

0.14

VOLTS 0.12

0.10

0.08

100 -

AMPS 9.0 -

8.0

LOAD POWER

AT=360"F

T H = 8 5 0 » F

OPEN CIRCUIT EMF

"GTO-

LOAD VOLTAGE

CURRENT _CL

J L

-o-

o—o m Q M ^ o-o o o -o -Q-^

-Q-Q Q-GHD_A

J I L 4 6 8 10 12 14 16 IB 20 22 24

DAYS OPERATION Figure 17. Encapsulated Westinghouse Couples —

Normal ized Data

moiriEHTiiiL NAA-SR-6693

49

1 4.4 O

X 4.0

3.8

MIL

LIW

ATT

S

00

80

00

CO ^ 5

In 44

i 4 3 _ l =! 42

41 28

{5 27

0 26

3 25 5 24

23

en 5-5 1 5.0

< 4.5

4.0 1

— (

—

- A

' Q ^

3 1

> — <

a

z

0 1-3 X

Ji

)

c

/

C 1

(

(

^

INTERNAL RESISTANCE^^

1 1 1 1

POWER OUTPUT

OPEN CI

L

C

DAD VC

JRRENl

RCUIT

LTAGE

r ,

^

y

1 r

y

L

^

/

i

A

-

b

]

) j

i

)

4th 5th Q\h 7th Qfh 9th iQth ||th 12 th 13th 14th 15th igth

JUNE 1961 Figure 18a. p-Type The rmoe lec t r i c Element

NAA-SR-6693 50 'COIinDEtiML

> >

I

vO UJ

5 660

O 650

' O 6 4 0

X 630

CO

b 33 O > 32 _) =! 31 S

CO 410

^ 4 0 0

^ 390 _J

d 380

370

CO

5 -^ '6 = 15

26

K! 25

1 24

23

»

" ^

(

~ Z

- c

<

5i

) — c

i

>

< )

5 ^ o 1

> 5 '

c

G 1

)

o 1

1 A

1

o 1

\ J 5

- c

e

O

1 A

) — C

> '

<

[

1 INTERN,

(

o ' 6 1

1 A

r

r

1 ' \L RESISTANCE /

1 1 1 DPEN CIRCUIT VOLTAGE

1

" " ^

30WER OUTPUT -1 A O N; •

1 ' LOAD VOLTAGE

A A 1 i

0

D 3

AY

(

O

9 10 1

OF JUNE, 196!

k J

•r

o

^

:URRENT

n o ®

- e j — i

1 -

3

^

? o 1 1 1 1 LESS THAN 10% VARIATION [ 1 INDICATED TO DATE

1 12 13 14 15 16

Figure 18b. n-Type Thermoelec t r ic Element

6. Quality Control

The l a rge number of e lements to be used in each conver ter and the

cr i t ica l dependence on the p rope r t i e s of lead te l lur ide r equ i r e that an exacting

quality control p r o g r a m be establ ished. A data collection and reduction sys tem

has been establ ished to control the fabrication p r o g r a m . Stat is t ical control of

both the incoming m a t e r i a l and the steps in the fabrication p r o c e s s have been

establ ished.

A distr ibution control p r o g r a m for al l raw m a t e r i a l s received from

vendors has been implemented. Certain percen tages a r e routed through e lec

t r i ca l and the rmoe lec t r i c m e a s u r e m e n t s , density m e a s u r e m e n t s , shock and

vibrat ion test ing, and chemical and meta l lu rg ica l analys is p r io r to r e l e a s e for

subsequent use in the development p r o g r a m .

NAA-SR-6693

VI. OPERATIONAL ANALYSIS

A. DESIGN POINT

Based on the requi red sys tem p a r a m e t e r s and the res t r i c t ions of vehicle

compatibili ty and technical l imitat ions imposed by the r eac to r and power con

vers ion sys tem, an optimum design point can be selected for the sys tem. The

express ion relat ing the design p a r a m e t e r s to e l ec t r i ca l power i s :

(0.292) 77 77 77 ea-AlT^ - T^^ 'F 'o 'c I B o/

P = , ^ " '-^ — . . . ( 1 ) € 1 - 71 -n

'o 'c

where

P = e l ec t r i ca l power (watts) 71T-, = rad ia tor effectiveness rj = device efficiency

71 = Carnot efficiency ' c e = radia tor emiss iv i ty

-9 2 4 cr = Stefan-Boltzman constant (1.71 x 10 Btu/ft - s e c - ' i l )

2 A = radiat ing a r ea (ft )

T = rad ia tor base t empera tu re (°R) B

T = t empera tu re of space = 460 °R

0.292 = conversion factor

A high rad ia tor effectiveness is requi red because the sys tem is r e s t r i c t ed

to a confined a r e a . This involves accepting a weight penalty since a low radia tor

weight could be obtained by designing to a lower fin effectiveness.

A high emiss iv i ty is achieved by applying a suitable coating to the radia tor

surface . F igure 19 shows energy dissipat ion per square foot vs radiating t e m p e r

a ture for th ree values of 7^^ x e . The SNAP lOA design point is indicated. F i g -r

ure 20 shows radia tor a r e a vs_ radiat ing t empera tu re for seve ra l power dissipating

requ i rements assuming SNAP lOA design values for € and T}^.

NAA-SR-6693 53

SSIFlEi

1400

1200

1000

(0

t 900 o

8 UJ

<

8

It! O UJ

a

600

700

600

500

S 400 ui z UJ

300 ^ /

/

L«

^

i f

i7p« =0.900-...^/

-7 € =0.807^ /

P c =0.700

^ Tn / / /

/ /

/ /

-/- DESK

/

3N POINT

VA /

1

500 6 0 0 700 800

RADIATOR BASE TEMPERATURE (*F) Figure 19. Energy Dissipated per sq ft vs Radiator

Base Tempera tu re

900

NAA-SR-6693 54

UNCLASSIFlEi

UNCLISSIFIEO

\

— n

\ \ ^

\

. V \

V \

\ n \ N \DESIGN \ \ POINT \

\

\

\ \

\

\

17 € =0.807

1

\

\

\

\ \

\

\

\

\

\

\

\

\

\

\

\

\

\

POWER D KILOWATT

90

So

40

^ 3 0

SSiPATED-S

500 600 700 800 900 RADIATOR BASE TEMPERATURE (*F)

Figure 20 . Radiator Area vs Radiator Base Tempera tu re

i

NAA-SR-6693 55

The total radiat ing a r ea requi red for the SNAP lOA power conversion sys tem 2 2

is 62 ft . In addition, the the rmoe lec t r i c pump will requi re about 2 ft of r a d i

a to r . The rad ia to r s will be fabricated of a luminum.

Each the rmoe lec t r i c couple is attached to an individual rad ia tor , thus 1420

radia tor segments form the ent i re the rmoe lec t r i c conver te r . The segment a r e a s

range from 8 to 14 in. and the radia tor thickness va r i e s f rom 20 to 100 mi l .

Cur ren t is conducted between the thermoelements by a conduction s t r ap which

also se rves as the conver ter hot s t r ap . An emiss iv i ty of 0.85, which is the

p resen t s t a t e -o f - t he -a r t for an emiss ive coating, is used in the calcula t ions .

Since the a r e a available for radiat ion is l imited and the conver te r hot s t r a p

t empera tu re is also constrained by l imitation on the PbTe , the re is an optimum

tempera tu re drop from the conver ter hot - to-cold junction. This AT divided by

the conver te r hot s t r a p t empera tu re is the Carnot efficiency.

T - T

'c 1^ • • • P >

where

TTT = conver te r hot s t r ap t empera tu re (°R) rl

T = conver ter cold s t r ap t empera tu re (°R)

Equation 2 is r e a r r anged into the form T^ = T ^ ( l - 77 ) and with an expected

lera ture drop of 10°F from the col

Equation 1 is then put in the forna:

t empera tu re drop of 10°F from the cold junction to the rad ia tor , T.^ = T - 10.

^ 1 . . . (3)

' ^ C { [ T H ( 1 - ^ C ) - ^ 0 ] - T o }

where

^1 = (1 - " o '^c) P . /°-292 7/^77^6^

Fixing T ^ at a t empe ra tu r e of 850°F and solving radia tor a rea (A) for

severa l values of Tj , the minimum radiating a r e a is shown to occur at a Carnot

efficiency of about 20% (Figure 21). Fo r a device efficiency of 0.105, a rea l i s t i c

value for initial pow^er operation based on p resen t s t a t e -o f - the -a r t the rmoe lec t r i c

conver ter technology, 7J x 7 gives an overal l sys tem efficiency of 2.1% at the

beginning of operat ional life.

NAA-SR-6693

ittlrlSIFlEi

! < UJ Q: <

*

\

\

\

0 TH = 850* F

^ ^

/

/

/

/

0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.22 Q23 0.24 0.25

CARNOT EFFICIENCY M 0

Figure 21. Minimum Required Radiator Area vs Carnot Efficiency

NAA-SR-6693 57

ilCLASSIFii

JCWttrl~-. ~'

Degradation of the t he rmoe lec t r i c s , which is caused mainly by the subl ima

tion and res i s t ance inc rease of the lead tel lur ide in the space a tmosphere , in

c r e a s e s the init ial power requi rement by an amount equal to:

^i = r r ^ •••('*)

where

P = init ial e l ec t r i ca l power (watts)

P , = e lec t r i ca l power (watts)

A D = ra te of degradat ion in output power per year

F igure 22 indicates the degradation ra te per year upon which the design is

based. The presen t design objective is to achieve the lowest possible degradation

r a t e . A pes s imis t i c assumption is that all the the rmoe lec t r i c element p e r

formance degrades at the ra te of that element which is at the highest t e m p e r a t u r e .

F igure 23 indicates what has been achieved to date on the rmoelec t r i c develop

ment and test ing p r o g r a m s .

Solving Equation 4 for radiating a r e a at s eve ra l average conver ter hot s t r ap

t e m p e r a t u r e s , using the degradation ra t e s shown in F igure 23, indicates the

optimum operating t e m p e r a t u r e . F igure 24 shows minimum radiat ing a r ea

plotted vs average conver ter hot s t r a p t empera tu re for r eac to r A T ' S of 50, 100,

and 200"F for a requi red power output at yea r -end of 500 w e lec t r i ca l .

A reac to r AT of 100°F was chosen for the SNAP lOA sys tem because l a rge r

A T ' S resu l t in ex t reme radiating a r e a penalt ies with smal l weight saving while

conversely sma l l e r r eac to r A T ' S resu l t in ex t reme weight penal t ies with c o r r e

spondingly smal l savings in radia tor a r e a .

An additional a r ea requ i rement comes about because of the uncertainty in

maintaining a constant r eac to r t empera tu re during the sys tem operating life.

Calculations indicate that prepoisoning of the reac tor will be sufficiently accura te

so that a t empera tu re change of no more than 30"F will occur during the yea r .

Deviating 30 °F from the average conver ter hot s t r ap t empera tu re of 850 "F r e -2 2

quires 2 ft of radiating surface in addition to the 60 ft shown at the design point in F igure 24.

NAA-SR-6693 58

ISECH:

cotinrwTui-" I .UU

" \j.\\J

a:

^

1 gO.Oi o

0.001

-

:

-

-

-

- /

>

/

/

/ /

750 800 850 900 950 MAXIMUM CONVERTER HOT STRAP TEMPERATURE (*F)

1000

Figure 22. Degradation Rate per Year vs Maximum Conver ter Hot Strap Tempera tu re

COilOINIiilL " =

NAA-SR-6693 59

COiMlML

100,000

- \

D-

10,000

- s

w

UJ o < IT P 1000 UJ

o o I-UJ

z

100

PbTe-PbTe (MARTIN) TRANSIT DESIGN

\ (PRESSURE CONTACTS) S

\ \

\ \

\ \

\ \

\

SNAP lOA DESIGN RANGE PbTe (WESTINGHOUSE-WAPD-

DANKO-SWAG ED ENCAPSULATED)

V PbTe-GeTe (AI) \ \ I WATT MODULES \

\ (NO ENCAPSULATION) \ \

•PbTe-PbTe—KD N •(MARTIN) SNAP3 \ (NO ENCAPSULATION^

i: n

PRESSURE CONTACTS) X^lV^p 1S CON*

•Sh

, SNAP 10 CONVERSION \ (WESTINGHOUSE)(NO

^ ENCAPSULATION)

\ \

\ \

\ \ S

\ \

PbTe-GeTe TAP 100—t l WESTINGHOUSE AF (ENCAPSULATED)

900 1000 1100

HOT JUNCTION TEMPERATURE ("F)

1200

Figure 23 . Thermoe lec t r i c Generator Experience

NAA-SR-6693 60

yNyLnMdiritiJ

^ 90 CVJ

RA

DIA

TIN

G

AR

EA

o

z 2

60

R A

^

^ . , = 200 • F /

VW ^ ^ ..^^

\

[

V -

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= IOO*Fy/

1 ,

/

/ / / /

7 >^^j^j— AiR=!)uy

ESI6N POINT 1 ^ ^ * * — " ^ X

750 800 850 900 950

AVERAGE CONVERTER HOT STRAP TEMPERATURE CF)

Figure 24. Minimum Radiating Area vs Average Conver ter Hot Strap T e m p e r a t u r e (for yea r -end power

output of 500 w)

N A A - S R - 6 6 9 3 61

UICLASSIFIEI

B. DYNAMIC BEHAVIOR

Presen t safety requ i rements dictate that the r eac to r not be made c r i t i ca l

until the es tabl ishment and confirmation of a sat isfactory orbi t . P r e l im ina ry

studies have been completed on the sys tem dynamics during the init ial s ta r tup

phase; these studies indicate the s ta r tup t rans ien t can be adequately controlled

without neutron inst rumentat ion or other fas t - t ime constant-feedback control

loops.

Startup will involve essent ia l ly four dist inct operat ional phases :

1) Startup is initiated by a t e lemete red ground command signal to activate

and s ta r t the in terna l p r o g r a m m e r assoc ia ted with the power sys tem

package.

2) The in ternal p r o g r a m m e r takes over the sequential operat ion of events

during the s ta r tup cycle, based on a previously determined and p r e se t

timing cycle .

3) When the reac to r reaches approximately i ts power rat ing, a simple

on-off control ler is switched into the control loop to maintain r eac to r

outlet t empera tu re at a p r e s e t value.

4) At a p rede te rmined t ime the control ler is deactivated and long- t e rm

stabili ty is set by the inherent cha rac t e r i s t i c s of the reac tor and

power conversion sys tem.

This method of s ta r tup is based on simplici ty of hardware requirenaents and

maximum rel iabi l i ty .

At vehicle launch, the reac tor is subcr i t ica l with safety and control reflector

d rums out (in their leas t react ive position). The NaK is at about 60 to 100°F and

an auxil iary flow of approximately 10% ex is t s , having been initiated on the launch

pad. Following launch and upon confirmation of a p roper orbit , the following a c

tions occur :

1) A ground command signal act ivates the APU progranamer .

2) The p r o g r a m m e r actuates the safety d rums and they a r e snapped in, -8

bringing the reac to r to a 50^ subcr i t ica l power level of at leas t 10 w.

3) About 5 min la ter the p r o g r a m m e r actuates the stepping drive to the

control d rum and react ivi ty is inser ted at about 1^/min. Reactor

NAA-SR-6693

p o w e r s t a r t s to i n c r e a s e ( see F i g u r e 25) and c r i t i c a l i t y i s a t t a i n e d

a p p r o x i m a t e l y 50 m i n a f t e r i n i t i a t i on of the c o n t r o l d r u m d r i v e a t a 7 - 6

p o w e r l e v e l b e t w e e n 10 and 10 w .

4) S ix ty - f ive m i n a f t e r c o n t r o l d r u m a c t i v a t i o n the p r o g r a m m e r a c t u a t e s

t h e e j e c t i o n d e v i c e for t h e t h e r m a l s h i e l d .

5) R e a c t o r p o w e r e n t e r s the s e n s i b l e h e a t r a n g e ( see F i g u r e 26), peak ing

a t abou t 40 kw, a t wh ich t i m e the t e m p e r a t u r e coe f f i c i en t s p r o m p t l y

(in l e s s t han 10 min) r e d u c e the p o w e r to t h e o r d e r of 2.5 kw^. R e a c t o r

ou t l e t t e m p e r a t u r e r a p i d l y r i s e s to about 2 5 0 ° F c a u s i n g flow to p e a k

a t about 60% of r a t e d flow. As the t h e r m o e l e c t r i c p u m p supply

a t t a i n s q u a s i t h e r m a l e q u i l i b r i u m , flow r a p i d l y r e d u c e s to about 30%

of r a t e d and t h e n i n c r e a s e s to an i n t e r m e d i a t e p e a k of 45%. T h e flow

i n c r e a s e p r o d u c e s a second p e a k in r e a c t o r p o w e r . The c o n t r o l d r u m

c o n t i n u e s to s t e p a t l<^/min.

6) A p p r o x i m a t e l y 100 m i n a f t e r a c t u a t i o n of the c o n t r o l d r u m , the

p r o g r a m m e r cu t s off t he a u x i l i a r y pow^er to the p u m p . The

I j i / m i n d r u m r a t e c o n t i n u e s and r e a c t o r flow, ou t le t t e m p e r a t u r e ,

and p o w e r i n c r e a s e .

7) O n e - h \ i n d r e d - a n d - s i x t y m i n a f t e r c o n t r o l d r u m a c t u a t i o n , r a t e d out le t

t e m p e r a t u r e i s a t t a i n e d and the f eedback c o n t r o l l e r a u t o m a t i c a l l y t a k e s

o v e r . T h e c o n t r o l l e r r e s p o n d s to t e m p e r a t u r e only, a s the s low r o d

r a t e s e m p l o y e d e l i m i n a t e any r e q u i r e m e n t for d r u m p o s i t i o n o r n e u t r o n

flux f eedback c o n t r o l .

8) With in 10 m i n a f t e r t h e c o n t r o l l e r h a s t a k e n ove r , p o w e r t e m p e r a t u r e

and flow a t t a i n e q u i l i b r i u m c o n d i t i o n s a t the p r e s e t v a l u e s .

9) C o n t r o l l e r o p e r a t i o n c o n t i n u e s unt i l the v a r i a t i o n in r e a c t i v i t y due to

n o n - s t a b i l i z e d r e a c t o r p a r a m e t e r s r e a c h e s a p r e s e t v a l u e , at which

t i m e the c o n t r o l l e r i s d e - e n e r g i z e d and the s y s t e m b e c o m e s e n t i r e l y

p a s s i v e and i s c o n t r o l l e d only t h r o u g h the i n h e r e n t t e m p e r a t u r e

c o e f f i c i e n t s .

T h e t y p i c a l o p e r a t i n g p r o f i l e i s shown in F i g u r e 25 for the r e g i o n be low

s e n s i b l e h e a t g e n e r a t i o n and in F i g u r e 26 for t h e r e g i o n in wh ich s e n s i b l e h e a t

N A A - S R - 6 6 9 3

WliLlldMlrltlJ

CONTROL DRUM RATE OF 10/min. INITIATED THERMAL SHIELD EJECTOR

UJ $ O Q.

IT O \-O < UJ

0 10 20 30 40 50 60 70

TIME AFTER INSERTION OF SAFETY DRUMS (min.)

Figure 25. SNAP lOA Reactor Power Trans ien t (from 50^ Subcri t ical to Sensible Heat Generation

NAA-SR-6693 64 ilCLISSIFlEi

IttASSIFI

o _l u. Q UJ I -< Q:

l i . o

o

cr o I -o <

a:

100

9 0

8 0

70

60

50

401-

3 0

20

iO\

1000

r- 9 0 0

UJ 8 0 0 (T

< 7 0 0 UJ Q.

UJ 6 0 0 -

UJ 5 0 0 -

O 4 0 0

Q:

H 3 0 0 O < UJ a: 200

100

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X <

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UJ

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X - C (OU. »o

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K X \ T' ^

t A /

1

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/ J k /

i V

'i H

J /

_z

F

T

\ ^

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70 80 90 100 110 120 130 140 150 160

TIME AFTER INSERTION OF SAFETY DRUMS (min)

50

45

4 0

3 5

3 0

2 5

170 180

UJ

o Q.

o o

2 0 < UJ

15 °^

10

F i g u r e 2 6 . S N A P lOA R e a c t o r S t a r t u p T r a n s i e n t ( D u r i n g P e r i o d of S e n s i b l e H e a t G e n e r a t i o n )

UlCiASSIFIi

N A A - S R - 6 6 9 3

65

- f trnnrf —~ —

is generated. Fu r the r studies a r e being conducted on the sys tem as well as the

inherent react ivi ty per turbat ion associa ted with the reac to r to es tabl ish f i rm

control sys tem per formance specifications.

C. INSTRUMENTATION

During the r epor t period contacts were establ ished with the vehicle contrac tor

to in tegra te the var ious ins t rumentat ions associa ted with the power systena in the

Agena vehicle . This integrat ion phase is expected to be a continuing effort and

will r esu l t in modification to the ins t rumentat ion descr ibed h e r e .

Te lemet ry t ransnaiss ion of APU data is requ i red to pernnit evaluation of

performance , degradation effects, and malfunctions; a command sys tem is also

requi red to init iate var ious safety m e a s u r e s and routine operational ac t ions .

Rea l - t ime data t r ansmis s ion and commands a r e requ i red during the ascent phase

and the one-year orbi tal phase of the flight t e s t s ; data s torage is requi red during

the f i rs t ninety days of the orbital phase .

The ascent phase covers the per iod from launch through burnout of the

second stage. During this per iod r e a l - t i m e t r ansmis s ion of about 80 data points,

50 sampled once per minute, and 30 sampled once per second, will be requi red .

In addition, about five on-off signals will be t r ansmi t t ed . P r o c e s s e s monitored

will include absolute t e m p e r a t u r e s , differential t e m p e r a t u r e s , posi t ions, s t ra in ,

vibration, and command s ignals . Command signals include r eac to r des t ruc t

and ref lector ejection signals to init iate actions to preclude the possibi l i ty of

nuclear excurs ions in the event of an abort . Since the command sys tem is a

vital link in the APU safety system, command capabili ty will be continuously

provided during c r i t i ca l phases of the ascent . To ensure rel iabi l i ty of the com

mand sys tem it i s anticipated that duplicate command r e c e i v e r s will be requi red .

During the orbi tal phase, from second-s tage burnout through the year of

operating life, about 150 data points will be moni tored. P r o c e s s e s monitored

during this per iod will include absolute t e m p e r a t u r e s , differential t e m p e r a t u r e s ,

posi t ions, radiat ion levels , voltages, c u r r e n t s , command signals, and p r o

g r a m m e r s ignals . All data will be t r ansmi t t ed in r e a l t ime, upon command,

during the one-year operating life and will also be s tored on a tape in the Agena

during the f i rs t 90 days . The tape is to be continuously available to the APU,

as it provides the only means of diagnosing fa i lures ; it mus t be capable of storing

NAA-SR-6693 66

mcm^^mmmmmmmm

da ta du r ing the i n t e r v a l s b e t w e e n r e a d o u t s t a t i o n s . In the event of SNAP s y s t e m

f a i l u r e , t he t a p e r e c o r d e r wi l l r e c o r d for 2 - 1 / 2 h r and then s top ; t hus f a i l u r e

da t a for the p e r i o d f r o m 2 - 1 / 2 h r b e f o r e to 2 - 1 / 2 h r a f t e r the f a i l u r e wi l l be

a v a i l a b l e for d i a g n o s i s . The t a p e s y s t e m wi l l a l s o be r e a d out upon c o m m a n d

du r ing r o u t i n e o p e r a t i o n of t h e A P U . To avoid l o s s of s ign i f i can t da ta t h a t m i g h t

o c c u r d u r i n g the r e a d o u t p e r i o d , a l l da ta wi l l be s i m u l t a n e o u s l y t r a n s m i t t e d in

r e a l t i m e .

The t e l e m e t e r i n g s y s t e m in t h e Agena \vill p r o v i d e dc a m p l i f i c a t i o n of d a t a

s i g n a l s , a t i m e b a s e , a u t o m a t i c c a l i b r a t i o n , and r e f e r e n c e j unc t ion c o m p e n s a

t ion for a b s o l u t e t e m p e r a t u r e s i g n a l s , and wi l l con t a in the n e c e s s a r y m u l t i p l e x i n g

and t r a n s m i s s i o n e q u i p m e n t . T h i s e q u i p m e n t i s be ing d e s i g n e d and p r o v i d e d by

the v e h i c l e c o n t r a c t o r . Sufficient s igna l cond i t ion ing e q u i p m e n t wi l l be p r o v i d e d

w^ithin the APU to c o n v e r t a l l t r a n s d u c e r s i g n a l s to one of t h r e e dc v o l t a g e r a n g e s ;

0-10 m v , 0 -50 m v , and 0-5 v .

D. NaK F R E E Z I N G PRIOR TO R E A C T O R O P E R A T I O N

The APU wi l l be l a u n c h e d wi th the r e a c t o r shut down (i. e . , no n u c l e a r h e a t

g e n e r a t i o n ) and wi th the h e a t t r a n s f e r s y s t e m a t a n o m i n a l 5 0 ° F . Fo l lowing

e jec t ion of the a e r o d y n a m i c n o s e cone the APU wi l l r e j e c t h e a t to the s p a c e

e n v i r o n m e n t , which i s below^ the 470°R NaK f r e e z i n g t e m p e r a t u r e for a l l o r b i t s

and a p p r o a c h e s 0°R for a s h a d e - s u n o r b i t . T h u s , t he APU wi th a r a d i a t o r s o l a r -

a b s o r p t i v i t y - t o - t h e r m a l - e m i s s i v i t y r a t i o of about 1/4 and a h e a t t r a n s f e r s y s t e m

h e a t c a p a c i t y of only 40 B t u / ° F wi l l r e j e c t h e a t to s p a c e and d e c r e a s e in

t e m p e r a t u r e un t i l the r e a c t o r i s s t a r t e d s o m e 5 to 1 5 h r a f t e r l a u n c h .

In v iew of the above , an a n a l y s i s w a s p e r f o r m e d to a s c e r t a i n the t i m e to

f r e e z e in a 2,000 n a u t i c a l m i l e o r b i t p e r p e n d i c u l a r to the l ine of e a r t h and sun .

T h e r e s u l t s of t h i s a n a l y s i s a r e p r e s e n t e d in F i g u r e 27 w h e r e t i m e to f r e e z e i s

p lo t t ed a g a i n s t i n i t i a l ( launch cond i t ions ) s y s t e m t e m p e r a t u r e for two c a s e s -

s t agnan t NaK and c i r c u l a t i n g NaK. Without NaK c i r c u l a t i o n and wi th an i n i t i a l

t e m p e r a t u r e of 5 0 ° F , the s y s t e m would f r e e z e in l e s s than 10 m i n . With NaK

c i r c u l a t i n g , to p e r m i t u t i l i z a t i o n of t h e e n t i r e h e a t - t r a n s f e r s y s t e m hea t c apac i t y ,

the s y s t e m would f r e e z e in l e s s t han 50 m i n . E v e n with the i n i t i a l t e m p e r a t u r e

a t an u n r e a l i s t i c 8 0 0 ° F and wi th NaK c i r c u l a t i o n , t he s y s t e m would f r e e z e in

l e s s than 1.5 h r . T h u s , e l eva t ing s y s t e m in i t i a l t e m p e r a t u r e d o e s not offer

N A A - S R - 6 6 9 3

100

80

^ > > 1

O CO 00 jjd

o o sO UJ

c E

^ o z UJ N UJ UJ Q: u.

o l -UJ

60

40

20

/

/y

^ - ^

^ , r ' ) (

NaK CIRCULA

STAGNANT N

•)

TION

/

QK

IS**"**

100 200 300 400 500 600 700 800

cr*3

CO OO

INITIAL SYSTEM TEMPERATURE (•'F)

Figure 27. Unprotected SNAP lOA System in 2000 Nautical Mile Orbit Perpendicular to Line of Ea r th and Sun

CZ3

s ign i f i can t c o m p e n s a t i o n , and s i n c e t i m e to h e a t - g e n e r a t i o n by the r e a c t o r i s in

e x c e s s of 5 h r , a m e a n s of i n t r o d u c i n g hea t to the s y s t e m or d e c r e a s i n g the r a t e

of h e a t l o s s f r o m the s y s t e m i s n e c e s s a r y to p r e v e n t NaK f r e e z i n g .

One such m e a n s i s a t h e r m a l s h i e l d . T h e f e a s i b i l i t y of m a i n t a i n i n g the h e a t

t r a n s f e r s y s t e m above the NaK f r e e z i n g t e m p e r a t u r e wi th a t h e r m a l sh ie ld h a s

b e e n i n v e s t i g a t e d . A s c h e m e c o n s i d e r e d invo lves enve lop ing the r a d i a t o r a r e a

wi th a m a t e r i a l p o s s e s s i n g a m i n i m u m s o l a r - a b s o r p t i v i t y - t o - t h e r m a l - e m i s s i v i t y

r a t i o of t h r e e (po l i shed gold exh ib i t s a r a t i o of a p p r o x i m a t e l y 8) , Such a sh ie ld ,

in conjunc t ion wi th NaK c i r c u l a t i o n , can be d e s i g n e d to m a i n t a i n NaK t e m p e r a

t u r e we l l a b o v e the f r e e z i n g po in t . The r e q u i r e d NaK c i r c u l a t i o n r a t e vs in i t i a l

s y s t e m t e m p e r a t u r e i s shown in F i g u r e 28; for an i n i t i a l t e m p e r a t u r e of 5 0 ° F ,

2% of r a t e d flow i s r e q u i r e d . It i s expec t ed tha t t he flow wi l l be p r o d u c e d by

m e a n s of a u x i l i a r y p o w e r supp l i ed to the NaK p u m p .

N A A - S R - 6 6 9 3

o

> I

CO

I

N O

2 E

SB*

crs>

t o OO

3 U-u. O 3

a UJ cr 3 O UJ

O

\

\ \

\

EMISSIVITY OF INSULATING SURFACE =0.1

X

10

Figure 28

20 30 40 50 60 70 80 90

INITIAL SYSTEM TEMPERATURE (*F)

Flow Required to Preven t F reez ing of NaK Before Equil ibr ium Tempera tu re s a r e Reached in Space

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