fusion technology institute department of engineering physics, university of wisconsin-madison ins 1...

1Fusion Technology InstituteDepartment of Engineering Physics, University of Wisconsin-Madison INS

Solid Wall Recirculating Blanket: Geometry,

Materials Compatibility, Structural Evaluation,

Fabrication and Fluid Circuits

I.N. Sviatoslavsky*, M. Sawan*, E.A. Mogahed*, S. Majumdar, R. Mattas, S. Malang, P.J. Fogarty, M. Friend, C. Wong

*University of Wisconsin, Madison, WI 53706

APEX Quarterly MeetingGrand Canyon, AZApril 7-10, 2003


Layout and Geometry of Recirculating Blanket

• Geometric layout of the reactor torus is patterned after ARIES-AT with changes in minor and major radii, neutron wall loading and surface heating.

• The structure is nano-composited ferritic steel and the coolant is low viscosity FLIBE (Li2BeF4) formulation.

• Outboard blanket (OB) is 30 cm deep, followed by a secondary blanket 40 cm thick, then a shield, 10 cm thick and finally, a vacuum vessel 30 cm thick. The primary OB blanket is banana shaped, 30 cm wide at the mid-plane tapering to 23 cm at the upper and lower extremities. The overall height is 8 m.

• The inboard blanket (IB) is straight and uniform in cross section. There is no secondary IB blanket. It is 30 cm thick, and is followed by a shield 40 cm thick and then, a vacuum vessel 30 cm deep. The overall height is ~7.7 m.


Geometry of the OB Blanket Module/Sector

• Each OB blanket module has 5 FW U bend channels traversing the blanket from top to bottom. Each FW channel has a smaller tube running along its length. This tube will contain molten Pb as a neutron multiplier.

• The rear side of the primary OB blanket module is a near square box, with rectangular channels attached to the side and back walls.

• The Flibe coolant enters the module on the bottom, travels up through the FW channels and at the top splits into two streams:

1. One stream (~2/3 of the mass flow) returns down through the side and back channels of the square box.

2. The second stream (~1/3 of the mass flow) returns through the large central channel in the square box.

• Nine modules stacked toroidally constitute a sector. A sector is a unit that can be removed unilaterally for reactor maintenance. There are 16 sectors in the reactor.


Midplane cross section of an outboard module.

Midplane cutaway of outboard module showing the channels progressing

toward the lower extremity.


Geometry of the IB Blanket Module/Sector

• The IB blanket modules are identical to the OB in regards to the coolant flow. However, instead of banana shaped, they are straight and of uniform cross section top to bottom. There are also Pb tubes of neutron multiplier on the IB side.

• Five IB modules stacked toroidally make up a sector. Both IB and OB sectors are mounted on a common skid for retracting it from the torus, passing between the outboard legs of the TF coils.


A CAD rendering of a cutaway of an OB sector consisting of, in this order: FW, primary blanket, secondary blanket,

shield and vacuum vessel. Outboard blanket sector, showing nine modules joined together to a common coolant header.

FW channels

Primarymodule

Secondarymodule

Shield Vacuumvessel


Inboard Blanket plusPrimary O.B. Blanket

Inboard BlanketInboard Blanket plus

Primary and SecondaryO.B. Blanket


Inboard / Outboard Blanketswith Shield Module

Inboard / Outboard Blankets,Shield Module, and Vacuum Vessel


Structural Material

• A relatively new structural material has been investigated in recent years as potentially attractive for fusion energy. Ferrritic/martensitic steels have always been considered attractive for fusion, but the operating temperature for them was limited to 550-600oC.

• Nano-composited ferritic steels contain a high density of small particles of Y2O3 or TiO2 dispersed in the ferritic matrix. One such material developed by ORNL is 12 YWT and sometimes called oxide dispersion strengthened (ODS).

• 12 YWT has superior high temperature characteristics. An upper temperature limit of 800oC and compatibility with Flibe up to 700oC.


0

200

400

600

800

1000

1200

1400

0 100 200 300 400 500 600 700 800 900 1000

Comparison of the Ultimate Tensile Strengths of Several Conventional ODS and Nanocomposited Ferritic Steels

12Y- 1

12- YWT

17- Y3

12- YW

Ultimate Tensile Strength (MPa)

Temperature (°C)

Larson-Miller parameter plot of the uniaxial thermal creep behavior of 12YWT as compared to two other ODS ferritic

steels and one ferritic-martensitic steel 9Cr-WMoVNb


B

B

B

B

B

B

B

B

J

J

J

JJ

JJ J

0

50

100

150

200

250

300

350

500 550 600 650 700 750 800 850 900Tempaerature (C)

B 12YWT

J MA957 B

B

B

B

B

B

B

B

J

J

J

JJ

J J J0

50

100

150

200

250

500 550 600 650 700 750 800 850 900Temperature (C)

B St 12YWT

J St MA957

Calculated creep rupture stress for MA957 and 12YWT for 2 year lifetime

Calculated allowable time dependent stress intensity for MA957 and 12YWT

based upon 2/3 of the creep rupture stress


Materials Compatibility

• The main compatibility issue for the recirculating blanket was

“ferritic steel with Pb.”

There is a lot of data available from ORNL, INEEL and from Russia. This issue has been settled from Russian experiments which show that static tests with strict O2 control show acceptable corrosion results at 700oC. Furthermore, a thin plating of W on the inside of tubes can be deposited, if this becomes necessary.

• ORNL has set the compatibility of ferritic steel with Flibe at 700oC. Information from S. Zinkle.


Stress Analysis (S. Majumdar-ANL)

• Heat conduction and elastic stress analyses were carried out by using the finite element program ABAQUS. Unit-poloidal-thickness slices at the bottom, mid-plane and top of the module were analyzed. No heat conduction was assumed in the poloidal direction. The stress analysis was conducted with the generalized plane strain assumption.

• The primary stress limits for the membrane (Pm and PL) and bending (Pb) are as follows:

⊇

Pm ≤Sm at thickness- averaged temperature St at thickness- averaged temperature and design life

€

PL + Pb ≤KSm

€

PL +PbK t

≤St

where K is the bending shape factor (=1.5) and Kt = (K+1)/2.

and

e


Peak first wall temperature at the mid-plane of the recirculating blanket.


Primary membrane plus bending stressdistribution at the bottom of the recirculating blanket.


Thermal Stress and Cyclic Ratcheting

Primary plus secondary stress limit for cyclic ratcheting is the Test A2 of the

ITER Structural Design Criteria (ISDC) which is as follows:

X + Y 1

where

Sy is the average temperature of the section during the secondary stress cycle, i.e.

during plasma-on and plasma-off conditions, and Q is the secondary stress

intensity range during the cycle.

€

X =PL + Pb / K t

Sy

€

Y =ΔQSy

,


Thermal stress intensity at the mid-plane of the blanket.


•Both X and Y are satisfied.


Fabrication

• A major disadvantage of ODS steel is joining. The only method that has produced acceptable joints is diffusion bonding or hipping. Conventional joining such as TiG or MiG, or plasma produces inferior welds and cannot be used for joints where structural integrity is paramount.

• Fabrication of the FW and blanket assembly utilizes preliminary conventional welding to achieve closure for sealing and then is followed by diffusion bonding.

• Two methods have been proposed for the assembly of the FW channels.


Method 1

U shaped channel 1.5 mm thick

Pb channel

Side wall reinforcement

Front FW sheet 1.5 mm thick

Exploded view of FW channel assembly

FW channel assembly diffusion bonded together

Rear plate with Pb tubes attached

Rear plate with Pb tubes attached

Exploded view of FW channel assembly

Side wall reinforcement


Method 2

An exploded view of the components prior to bonding

Assembled FW channels after diffusion bonding


External module box, 1.5 mm thick

Side return channels

Rear return channels

Main central return channelMain central return channel

Assembly of the rear blanket box with return channels indicated.


Complete assembly of outboard blanket module. The units are coupled and diffusion bonded together to form a single module.


Fluid Circuits

A chart showing fluid routing in the recirculating blanket.

1008 MW FW

208.8 MW

702.7 MW

side/back

central

409.9 MW FW

73.9 MW

249.5 MW

side/back

central

Outboard

In board

4544 kg/s

625 °C

625 °C

681 °C

102 MWSecondary

Blanket

681 °C

616 °C

6395 kg/s

19859 kg/s

Mixer

He

480°C

660 °C

HX

500 °C

500°C

Outboard

to turbine

1614 kg/s

4544 kg/s

237 kg/s

681 °C

500 °C

6158 kg/s

14118 kg/s

5741 kg/s

19859 kg/s

586 °C

4544 kg/s

681 °C

586 °C

237 kg/s

6395 kg/s

681 °C

616 °C

9574 kg/s

1614 kg/s

1614 kg/s

6158 kg/s

4127 kg/s

586 °C

4127 kg/s

9574 kg/s

1920 MW

733 MW

102 MW

586 °C


Fluid Circuits (contd.)

• Each module has three Flibe connections

1. Supply line

2. Return line from side and back channels

3. Return line from the rear main central channel

• These connections are made through a triplex tube, that is, three concentric tubes with a common axis

1. The outermost tube is the cool fluid supply2. The next is the return from the rear side and back channels3. The innermost tube is the hot return from the rear main central channel

• There are three good reasons for using a triplex tube:

1. Saves on heat losses

2. Reduces tritium diffusion out of the tubes to the environment

3. Only one tube (outermost) needs to be severed. The other connections are slip joints and can tolerate minor leakage.


Module (left), connection (middle), sector (right)

One OB blanketsector

One OB module

Triplexconnection

Nine modulesconnected toone header


Conclusions

• Utilizing ODS ferritic steel 12YWT with Flibe as a coolant and Pb as neutron

multipler appears to make a good combination for an advanced high

temperature blanket which can operate at a high efficiency with a He gas

Brayton cycle

• Even though the recirculating blanket is somewhat complicated, its forward

looking aims, that of maximizing nuclear parameters to achieve a high

conversion efficiency, are well worth striving for.

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