12th aec air cleaning conference

i

,: 12th AEC AIR CLEANING CONFERENCE

SIZE CHARACTERISTICS OF PLUTONIUM AEROSOLS

Harry J . Ettinger, John C. Elder and Manuel Gonzales Los Alamos Scientific Laboratory

Health Division Los Alamos, Mew Mexico

N O T I C E This report was prepared as an account of work sponsored by the United Stater 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 asumes 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.

This document L PUBLICLY RELEAsABm

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of 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. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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12th AEC AIR CLEANING CONFERENCE

SIZE CHARACTERISTICS OF PLUTONIUM AEROSOLS

Harry J. Ettinger, John C. Elder and Manuel Gonzales Los Alamos Scientific Laboratory*

Health Division -. Los Alamos, New Mexico

Abstract

A program is in progress to measure size characteristics and activity concentrations (source term) of plutonium aerosols generated by typical operations handling significant quantities of plutonium. This will provide a basis for generating similar aerosols in the laboratory to study the effectiveness of multiple stages of HEPA filtr - tion. Initial data shows Pu concentrations ranging up to 16.5 x 10 dpm/m3, with the following aerodynamic size characteristics :

8

aerodynamic activity median diameter (aamd) = .52 to 5.5 pm

geometric standard deviation (a ) = 1.5 to 6.60

I. Introduction g

Increased concern regarding the potential release of radioactive particulates to the atmosphere has resulted in new stringent air cleaning requirements for facilities handling plutonium. These in- clude proposals to require decontamination factors of l o 9 to This can be attained by use of multiple High Efficiency Particulate Aerosol (HEPA) fi ters, which singly can provide decontamination fac-

While extensive test data is available to sub- stantiate this level of performance for individual HEPA filters, and filtration theory predicts multiple filter installations will provide the overall protection required, quantitative substantive data is not available. There is also concern that filter performance against lab- o r a t o r y test aerosols, such as DOP, is not fully representative of performance against plutonium aerosols. Because of this interest in realism, a field sampling program was designed to measure size characteristics and activity concentrations (source term) of plutonium aero- s o l s generated by typical operations at several AEC facilities handling significant quantities of plutonium. Definition of these aero- s o l s would provide a basis f o r generating similar aerosols in t ~ e laboratory to study the effectiveness of multiple stages of HEPA f i l - tration.

Initially three plants, represent'ng diffeq nt production and research operations, utilizing both 23'Pu and 235Pu, were selected to provide air sampling data to characterize plutonium source terms under a variety of operating conditions. Wide variations of activity con- centration and size characteristics were expected due to: (1) dif- ferences in the amount cf material handled, and mechanical and chemical operations at each slte; and (2) aerosols incident on the main

t o r s of 103 to 10 i .

"Work performed under the auspices of the U. S. Atomic Energy Com- mission.

~ ~ ~


exhaus t f i l t e r s may undergo p r e v i o u s s t a g e s of f i l t r a t i o n a t t h e glovebox. T h e r e f o r e , sampling data would be r e p r e s e n t e d as r anges of v a l u e s to d e s c r i b e a e r o s o l c o n c e n t r a t i o n and s i z e c h a r a c t e r i s t i c s . Due t o t h e n a t u r e o f some o p e r a t i o n s performed i n t h e s e p l a n t s , sampling l o c a t i o n s and o p e r a t i o n a l p r o c e s s e s a r e i d e n t i f i e d only i n t h e s e g e n e r a l terms :

1. r e s e a r c h and development ( r and d )

2 . r ecove ry (chemica l o p e r a t i o n s )

3. p roduc t ion (mechanical o p e r a t i o n s )

The f o l l o w i n g d i s c u s s i o n w i l l p r i m a r i l y b e d i r e c t e d a t t h e s i z e c h a r a c t e r i s t i c s of plutonium a e r o s o l s , w i t h on ly b r i e f mention of a c t i v i t y l e v e l s . Data p r e s e n t e d i s p r e l i m i n a r y , and was summarized on ly f o r p r e s e n t a t i o n a t t h e Round T a b l e Discuss ion a t t h i s A i r C leaning Conference.

11. Sampling Procedures

The 8-s tage Andersen impactor‘’) was s e l e c t e d t o be t h e pr imary sampler for particle size analysis. This dev ice is simple, easy t o o p e r a t e i n t h e f i e l d , p r o v i d e s s i z e s e p a r a t i o n ove r a f a i r l y wide r ange of p a r t i c l e d i ame te r s on t h e basis o f t h e i n e r t i a p r o p e r t i e s

The impactor backup membrane f i l t e r and t h e e i g h t impact ion p l a t e s are a l p h a counted for a n a l y s i s . N e t count r a t e i s p r o p o r t i o n a l to t h e mass of p a r t i c l e s d e p o s i t e d on each p l a t e i f two assumptions are made: (1) a b s o r p t i o n of a l p h a p a r t i c l e s i n t h e p a r t i c l e ( s e l f - a b s o r p t i o n ) i s n e g l i g i b l e , and 2 ) s p e c i f i c a c t i v i t y (dpm/gm) i s con a l p h a p a r t i c l e has a r ange o f a t least 1 0 ym i n Pu02 compared to a p h y s i c a l diameter of 3 to 4 v m c o l l e c t e d on t h e f i r s t s t a g e of t h e impactor . The re fo re , a n a l p h a p a r t i c l e emi t ted anywhere w i t h i n a 4 ym Pu02 p a r t i c l e should emerge from t h e p a r t i c l e wi th s u f f i c i e n t energy to be counted. Spectroscopy samples suppor t t h i s h y p o t h e s i s f o r t h e p a r t i c l e s i z e range of i n t e r e s t i n t h i s s t d y . However, one of t h e t h r e e f a c i l i t i e s d i s c h a r g e s a mixture of 231Pu and 239Pu i n h i g h l y v a r i a b l e r a t i o s . The re fo re , data o b t a i n e d to d a t e have on ly been d e f i n e d i n te rms of aerodynamic a c t i v i t y median diameter (aamd) and geometr ic s t a n d a r d d e v i a t i o n ( G ) r a t h e r t h a n mass median d i a - me te r . The aamd probably r e l a t e s m g s t c l o s e l y to t h e performance of an a i r c l e a n e r a g a i n s t t h e s e a e r o s o l s .

of t h e a e r o s o l , and i t s c a l i b r a t i o n i s w e l l documented. t 2 , 3 )

. A 5 MeV mnt

Previous e v a l u a t i o n of t h e Andersen i m c t o r has i n d i c a t e d a p o t e n t i a l e r r o r due to p a r t i c l e rebound.(5,gy I f t h e p a r t i c l e does not adhere t o t h e f i r s t p l a t e it c o n t a c t s , b u t d e p o s i t s on t h e nex t s t a g e , or rebounds from a l l succeeding s t a g e s to be c o l l e c t e d b y t h e backup f i l t e r , t h e i n d i c a t e d a e r o s o l s i z e c h a r a c t e r i s t i c s a r e i n error. Use of a “ s t i c k y ” impact ion s u r f a c e would i n t e r f e r e w i t h a lpha coun t ing procedures and was not a c c e p t a b l e . An a l t e r n a t e t e c h - n ique i s t h e a p p l i c a -’ n of membrane f i l t e r media to t h e s u r f a c e o f t h e impactor p l a t e s . 1’’ I n t e s t s now under way, a d j a c e n t impactor sampling s t reams have been i n s t a l l e d a t one sampling s i t e , and samples ob ta ined cove r ing t h e p l a t e s of one impactor w i t h v i n y l m e t r i c e l


membrane f i l t e r s (MF) l e a v i n g t h e p l a t e s o f t h e o t h e r impactor bare . By a l t e r n a t i n g t h e MF c o a t i n g on each impactor each d a y , data i n d i c a - t i n g rebound (or no rebound) can be developed d e s p i t e p o s s i b l e s l i g h t d i f f e r e n c e s between t h e two sampling streams. Alpha spec t roscopy has provided i n f o r m a t i o n on t h e p o t e n t i a l e r r o r a s s o c i a t e d w i t h a b s o r p t i o n o f t h e a l p h a p a r t i c l e s b y t h e f i l t e r media a p p l i e d t o impactor p l a t e s as a n an t i - rebound a g e n t . P re l imina ry a n a l y s i s of t h e v i n y l m e t r i c e l media showed ve ry l i t t l e a b s o r p t i o n and i n d i c a t e i t s s u i t a b i l i t y as an impactor an t i - rebound a g e n t .

Sampling l o c a t i o n s a t each p l a n t were s e l e c t e d to monitor t h e more contaminated a i r s t reams i n each p l a n t , and sampling systems were des igned t o p rov ide i s o k i n e t i c sampling c o n d i t i o n s . Samples are c o l - l e c t e d f o r v a r y i n g l e n g t h s o f t i m e , depending on t h e a c t i v i t y i n t h e d u c t . For convenience of h a n d l i n , coun t ing , and sh ipp ing , a c t i v i t y p e r sample i s l i m i t e d t o about 105 dpm, t h e r e f o r e , t h e t i m e r e q u i r e d t o c o l l e c t a sample of t h i s o r d e r of magnitude v a r i e s g r e a t l y f o r each sampling l o c a t i o n . Sampling p e r i o d s are s e l e c t e d a t t imes when normal a c t i v i t i e s i n t h e b u i l d i n g are underway; %.e . , no t a t lunch t i m e or break t i m e or n e a r q u i t t i n g t ime .

A gas f low p r o p o r t i o n a l c o u n t e r i s used t o count a lpha a c t i v i t y on each s a m p l e . T h i s coun te r i s approximate ly 33% e f f i c i e n t f o r b a r e samples and 22% e f f i c i e n t f o r s t a n d a r d s o u r c e s covered w i t h a . O O O 2 5 " m y l a r f i l m . The m y l a r f i l m i s used t o cover each impactor p l a t e and f i l t e r t o minimize contaminat ion problems. N e t count r a t e i s deter- mined f o r each sample and u t i l i z e d as p r e v i o u s l y d i s c u s s e d i n d e t e r - mining cumula t ive p e r c e n t smaller t h a n a s t a t e d aerodynamic p a r t i c l e

e t e r s ( E C D ) 7 a re submi t ted f o r computer a n a l s as a data s e t of 8 y8f and p l o t t e d on a l o g v a l u e s t o be f i t b minimum chi -squares method p r o b a b i l i t y g r i d . ($1 median d i ame te r (aamd) and geometr ic s t a n d a r d d e v i a t i o n ( a ) f o r t h e a e r o s o l , and t h e d e v i a t i o n of each data p o i n t from t h e besg f i t l i n e . The l a t t e r v a l u e can be u t i l i z e d i n a t e s t to confirm or r e j e c t t h e assumption o f log normality of t h e distribution. A range of aamd and ( a ) d e s c r i b e s v a r i a t i o n s i n t h e s i z e c h a r a c t e r i s t i c s of t y p i c a l Pu aeFoso1s.

o n t ra tes and t h e cor responding e f f e c t i v e c u t o f f diam- size* Net F 'I'

T h i s a n a l y s i s d e f i n e s aerodynamic a c t i v i t y

To p rov ide a frame of r e f e r e n c e , T a b l e 1 summarizes t h e opera- tional c h a r a c t e r i s t i c s a s s o c i z t e d w i t h each sampling site. Table 2 i n d i c a t e s t h e v a r i a t i o n s i n t o t a l a c t i v i t y a t each sampling s i t e . Concen t r a t ion data was ob ta ined u s i n g b o t h Andersen impactors and a d j a c e n t membrane f i l t e r s . Major v a r i a t i o n s between week-day and week-end samples are apparent f o r s i t e A . Even g r e a t e r v a r i a t i o n s between s i t e A and s i t e s B and C a re , a l s o i n d i c a t e d .

111. Aerosol S i z e C h a r a c t e r i s t i c s

S i z e c h a r a c t e r i s t i c s o f t h e Pu a e r o s o l s d e f i n e d by t h e Andersen impactors are summarized i n Table 3 , which a l s o i n d i c a t e s t h e s i g n i f - i c a n c e o f t h e rebound problem. Ar i thmet ic mean v a l u e s o f aerodynamic a c t i v i t y median d iameter (aamd) and geometr ic s t anda rd d e v i a t i o n ( 0 ) are l i s t e d a l o n g w i t h t h e i r ex t remes . V a r i a t i o n s a r e a p p a r e n t , whigh i s not t o o s u r p r i s i n g c o n s i d e r i n g t h e l a r g e number of d i f f e r e n t


aerosol -producing o p e r a t i o n s conducted i n t h e s e p l a n t s .

Somewhat s u r p r i s i n g was t h e s i z e d i s t r i b u t i o n of t h e Pu a e r o s o l a t Loca t ion B . S i z e c h a r a c t e r i s t i c s of t h e a e r o s o l measured h e r e a r e d i s t i n c t i v e due to t h e h igh pe rcen tage of ve ry small p a r t i c l e s i n t h e d i s t r i b u t i o n . I n t h e 14 impactor measurements made t o d a t e , t h e cum- u l a t i v e perce'nt smaller t h a n 0.43 u m ( f i n a l impactor s t a g e E C D ) has averaged 60%; t h a t i s , 60% of t o t a l a c t i v i t y measured i n t h e impactor sampler passed through t h e impactor and was c o l l e c t e d on t h e backup membrane f i l t e r . A d i s t r i b u t i o n of t h i s t y p e i s n o t r e a d i l y charac- t e r i z e d by t h e Andersen impactor , and t h e s e r e s u l t s have no t been cons ide red i n t h i s p r e s e n t a t i o n .

F i g u r e s 1 th rough 6 are inc luded as l o g p r o b a b i l i t y r ep resen - t a t i o n s of t y p i c a l plutonium s i z e d i s t r i b u t i o n s , a n d t h e ex t remes . F igu re 1 r e p r e s e n t s a sample which c l o s e l y approximates t h e mean a e r o s o l a t Loca t ion A (aamd = 1 . 7 0 urn and CI = 2.33). F i g u r e s 2 and 3 r e p r e s e n t two extremes of og f o r t h i s sarnplffng l o c a t i o n . F i g u r e s 4 t h rough 6 show t y p i c a l s i z e d i s t r i b u t i o n s f o r l o c a t i o n s C , D and E . I n each f i g u r e a bes t f i t l i n e d e f i n e d by t h e ch i - squa res method(8) i s provided . Examination of t h e data i n Table 3 r e v e a l s no s i g n i f i c a n t p a r t i c l e rebound. Had t h e uncoated p l a t e s d i s p l a y e d a c o n s i s t e n t l y lower aamd and h ighe r d t h a n coa ted p l a t e s , o r larger amounts o f a c t i v i t y on t h e backup F i l t e r , a rebound problem would be sugges t ed . P r e l i m i n a r y r e s u l t s of rebound t e s t s conducted wi th t w i n i m p a c t o r s has a l s o i n d i c a t e d no rebound problem.

S p e c t r o copy of s v e r a 1 samples has shown t h e p resence a t Loca- t i o R A of 238Pu and 235Pu i n s imilar quant i t * es which compl i ca t e s measurement of s i z e c h a r a c t e r i s t i c s . c o n t r i b u t i n g to t h e t o t a l a l p h a a c t i v i t y on each impactor p l a t e prob- a b l y o r i g i n a t e a t d i f f e r e n t u n r e l a t e d o p e r a t i o n s r e s u l t i n g i n two d i s t i n c t s i z e d i s t r i b u t i o n s as i n d i c a t e d i n F i g . 7 . Samples t o i n v e s t i g a t e t h e makeup o f composite d i s t r i b u t i o n s u s i n g a l p h a spec- t r o s c o p y have been o b t a i n e d , and a r e undergoing a n a l y s i s . Impactor samples w i l l p rov ide 23QPu t o 239Pu r a t i o s for each s t a g e , r e l a t i n g i s o t o p e c o n c e n t r a t i o n to aerodynamic s i z e .

The 23hPu and 239Pu p a r t i c l e s

V I . Acknowledment

The c o o p e r a t i o n , gu idance , and a s s l s t a n c e o f many people and groups at Rocky P l a t s Div, Dovr Chemical Co. ; Mound L a b o r a t o r i e s , Monsanto Research; Los Alamos S c i e n t i f i c Labora tory i s g r a t e f u l l y acknowledged.


~ . . .- . . . .. . . .

1.

2.

3.

4.

5.

6.

7.

8.

9.

References

Andersen, A. A., A Sampler for Respiratory Health Hazard Assess- ment, AIHA Journal, - 27: 160 (1966).

Flesch, J. P., Norris, C. H., Nugent, A. E., Jr., Calibrating Particulate Air Samplers With Monodisperse Aerosols : Application to The Anderser! Cascade Impactor, AIHA Journal, - 28: 507 (1967).

May, K. R., Calibration of a Modified Andersen Bacterial Aerosol Sampler, Applied Microbiology, _. 12: 37 (1964).

Andersen, E. C., LASL Group H-4, private communication.

Hu, J. N. H., An Improved Impactor For Aerosol Studies--Modified Andersen Sampler, Environmental Sciences and Technology, in press.

Knuth, R., Health Protection Engineering Division USAEC, NYOO. private communication. May (1972).

Mercer, T. T., On The Calibration of Cascade Impactors, Annals of Occupational Hygiene, - 6: 1 (1963).

Sokal, R. R., and Rohlf, F. J., Biometry, (W. H. Freeman and Company, 1969), Chap. 16.

Whipple, G. C., "The Element of Chance In Sanitation", Journal of The Franklin Institute, - 182: 37, 205 (1916).


, . , . . . .... , . - I ~.___._._....._-.__I.__~. . . “. ~ ., ”. . . .. . ~ . . .. ..... ~. .. . . . . . . .. ,~. ,.

Locat ion

A

Table 1

Sampling Locat ions

P lu tonium I so tope

238 & 239

239

239

238

238

Maj o r Operat i o n

r & d

r ecove ry

production

r & d

p roduc t ion & recovery

Q

A

N

. .-

12th AE

C A

IR C

LEA

NIN

G C

ON

FER

EN

CE

-

[I

)[

I)

[I

)[

I)

[I

)[

I)

h

dh

hh

h

Table 3

Andersen Impactor

Size Characteristics of Pu Aerosol

DescriptAon Location

Weekdays, no coating A

Weekends, no coating A

'All Samples, DM-800 coating A

All Samples, AA coating A

Weekdays, AA coating B

Weekdays, no coating C

Weekdays, AA coating C

,Weekdays, DM-800 coating D

'Weekdays, DM-800 coating E

All samples (excluding B ) ,

# obs.

63

12

5

10

14

6

11

9

11

127

aamd (urn>

n;e an

1.70

1.92

2.10

1.86 %

2.83

2.37

3.20

1.87 --

max

3-30

3.32

2.50

2.70

-

3.53

3.25

5.51

2.99

5.51

min - . 5 2

1.03

1.25

.92

1.96

1.61

1.80

57

0.52

I

0

iliean max - 2.33 4.94

2.37 3.20

2.09 2.61

2.38 3.37

3.03 6.40

2.98 6.6

3.11 4.36

2.21 2.63

-- 6.60

min

1.53

-

2.03

1.74

1.83

1.98

2.06

2.13

1.58

1.53

:860% smaller than last impaction stage; not amenable to analysis using Andersen impactor.

1 DM-800-Gelmen vinyl metricel membrane filters (.8 pm pore size)

, AA-Millipore Filters ( . 8 pm pore size) i

c

. .

F igure 1: . Size Character ist ics of Pu Aerosol--

g* Representative of Mean aamd and c

LOCATION A

Qs = 3.33

Pu PARTICLE S I Z I N G BY IMPACTOR AT LOCATION A

I 2 5 IO 20 30405060’8080 90 96 98 99 99.9 CUMULATIVE PERCENT LESS THAN STATED DIAMIETER

I

Figure 2: Size Character ist ics of P u Aerosol-- !

Representative of Dis t r ibut ion With High c LOCATION A

: g*

,

Pu PARTICLE S I Z I N G BY IMPACTOR AT LOCATION A - I I I 1 1 1 1 I 1 0 0 - , I I I 1 1 I -' - - - - - - - - - - D -

n - aamd =1.6pm - E c g = I.?

8 a w I- - w - - z - a - Q 0 2 - Q 2 >

Y

10.0 - - - - - - - -

- - - - - -

- - - - - - - - - - - -

i 1 I 1 1 1 1 1 I I I I t I , i 0.1 ' I 2 5 IO 20 30 4050607080 90 95 98 99 99.9

Figure 3: S ize Character ist ics of Pu Aerosol-- Representative of Dist r ibut ion with Low CT

LOCATION A go

- ' Pu PARTICLE SIZING BY IMPACTOR AT LOCATION C

/ /

I I t 1 I l l l S I 0, I I I 1 1 B I 2 5 10 20 304050507080 90 95 98-99 99.9

CUMULATIVE PERCENT LESS THAN STATE0 DIAMETER

Figure 4: Size Characterist ics of P u Aerosol -- Typical Distr ibut ion - Location C

n

E * a Y

W

- - - - - - - - -

tT w a

0.1 1 I I I 1 r l l I i 1 1 1 1 f

CUMULATIVE PERCENT LESS THAN STATED DIAMETER I 2 5 IO 20304050m7oao 90 95 9899 99.9

- -

Figure 5: Characteristics of Pu Aerosol -- Typical Distr ibut ion - Location D

. . Pu PARTICLE SIZING BY IMPACTOR AT LOCATION E

100 I 1 I I I I I I I I I I I I I $ - - - - - -

n c

E U % L 10.0

Crg = 2.1

L - - - - - - -

1.0 - - - - - - - - -

0.1' I I I I l l t l l I I I i t 1 1 I 2 5 IO 20 30 405060 7080 90 95 98 99 99.9

CUMULATIVE PERCENT LESS THAN STATED DIAMETER I - -_ " _ c L . - - -- L . "

L

I Figure 6: Size Characterist ics of Pu Aerosol -- !

TYP i

cai Dis t r ibut ion - Location E i

i i

Pu PARTICLE SIZING BY IMPACTOR A 7 LOCAVlON A I 1 1 I IO0

1 1 t 1 1 1 1 t t I 1 I 1 0.1 f

I 2 5 IO 20 3040506070 80 90 95 98 99 99.9 CUMULATIVE PERCENT LESS THAN STATED DIAhlrnER

Figure 7: Size Characteristics of P u Aerosol-- Represmtat ive of Composite Distribution.

12th aec air cleaning conference

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