1. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 1 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 Meeting Grand Canyon, AZ April 7-10, 2003

2. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 2 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 (Li 2 BeF 4 ) 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.

3. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 3 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.

4. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 4 Midplane cross section of an outboard module. Midplane cutaway of outboard module showing the channels progressing toward the lower extremity.

5. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 5 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.

6. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 6 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 Primary module Secondary module ShieldVacuum vessel

7. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 7 Inboard Blanket plus Primary O.B. Blanket Inboard Blanket Inboard Blanket plus Primary and Secondary O.B. Blanket

8. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 8 Inboard / Outboard Blankets with Shield Module Inboard / Outboard Blankets, Shield Module, and Vacuum Vessel

9. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 9 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 550-600 o C. Nano-composited ferritic steels contain a high density of small particles of Y 2 O 3 or TiO 2 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 800 o C and compatibility with Flibe up to 700 o C.

10. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 10 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

11. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 11 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

12. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 12 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 O 2 control show acceptable corrosion results at 700 o C. 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 700 o C. Information from S. Zinkle.

13. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 13 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 (P m and P L ) and bending (P b ) are as follows: where K is the bending shape factor (=1.5) and K t = (K+1)/2. and e

14. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 14 Peak first wall temperature at the mid-plane of the recirculating blanket.

15. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 15 Primary membrane plus bending stress distribution at the bottom of the recirculating blanket.

16. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 16 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 S y 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.,

17. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 17 Thermal stress intensity at the mid-plane of the blanket.

18. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 18 Both X and Y are satisfied.

19. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 19 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.

20. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 20 Method 1 Exploded view of FW channel assembly FW channel assembly diffusion bonded together Rear plate with Pb tubes attached Exploded view of FW channel assembly Side wall reinforcement

21. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 21 Method 2 An exploded view of the components prior to bonding Assembled FW channels after diffusion bonding

22. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 22 Assembly of the rear blanket box with return channels indicated.

23. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 23 Complete assembly of outboard blanket module. The units are coupled and diffusion bonded together to form a single module.

24. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 24 Fluid Circuits A chart showing fluid routing in the recirculating blanket.

25. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 25 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 supply 2.The next is the return from the rear side and back channels 3.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.

26. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 26 Module (left), connection (middle), sector (right) One OB blanket sector One OB module Triplex connection Nine modules connected to one header

27. Fusion Technology Institute Department of Engineering Physics, University of Wisconsin-Madison INS 27 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.