1. 1 Recent Progress in Helium-Cooled Ceramic Breeder (HCCB) Blanket Module R&D and Design Analysis Ying, Alice With contributions from M. Narula, H. Zhang, D. Papp FNST Meeting August 12-14, 2008 UCLA

2. 2 HCCB Blanket Module Design RAFS FW with He coolant channels He purge gas pipe Be (Be 12 Ti) pebbles Ceramic breeder pebbles Cooling plate He coolant manifolds for FW/Breeding zones  Helium (~8 MPa) coolant operating (350  C-500  C)  Low pressure (0.1-0.2 MPa) helium/%H 2 purge gas to extract tritium HCCB TBM module (710  389  510 mm)

3. 3 Summary Efforts are being carried out in the following areas: –Utilizing the strain dependent thermo physical characteristics of Be pebble beds for tritium performance optimization –Investigate the creep failure of Li 2 TiO 3 pebbles at high temperatures (as a part of thesis research for a master degree) –Perform tritium permeation analysis for purge gas flow design (as a part of thesis research for a master degree)

4. 4 Strain dependent thermo physical property on tritium performance optimization The amount of the allowable beryllium in a breeding zone is limited by a maximum operating temperature of 600C The effective thermal conductivity of a Be pebble bed depends on: k eff = f(T, ,  ) Analysis method: neutronics and coupled thermo-fluid and thermo-mechanics analysis

5. 5 The trend of analysis is to incorporate a CAD model with various physics simulation codes Be pebble bed zones Breeder zone and associated coolant panels FW coolant CAD model Major parts of a 1/5th model of the HCCB module CAD model

6. 6 Fe structure He Be Li 2 TiO 3 This CAD model was translated to a MCNP model input using MCAM (developed at ASIPP) for Neutronics analysis

7. 7 Overall temperature distributions in a Neutronics module are in the lower end of the allowable temperature windows A look-alike test blanket module due to a lower neutron wall load of ITER as compared to that of a typical DEMO value ITER 0.78 MW/m 2 DEMO 2- 3 MW/m 2 Be pebble bed strain profiles at 1 cm away from the back of the FW. Top: first iteration; bottom: second iteration.

8. 8 Impact on Design 1 st Iteration 2 nd Iteration 3 rd Iteration K eff increases as temperature and strain increase Be zone temperature The effective thermal conductivity (near the FW region) increases from 2.25 to 5.8 W/m 2 K during the first iteration and decreases to 5.4 W/m 2 k at the second iteration; while the maximum temperature decrease of 43C at the first iteration and 1C at the second iteration. This amount of temperature difference attributes to an additional 20% of Be added into the front zone region, where neutron multiplication can be enhanced.

9. 9 High temperature creep study for Li 2 TiO 3 pebbles PropertiesLi 2 TiO 3 Density (g/cm 3 )3.189 Porosity %16 E young (GPa)200.6 Coeff. Poisson ν 0.27 Tensile strength (MPa) 139 Compressive Strength (MPa) 1113 Conductivity (W/mK) at 298 K 3.28 Li 2 TiO 3  = 1.8 - 2 mm All pebbles was checked at SEM to evaluate surface irregularities, cracks and shape before the tests linear velocity-displacement transducer (LVDT) Error < 0.1 μm Deadweights to provide a compressive load Pebble under test The tests were performed at: Temperature: 700, 800, 950 °C ; Load: 8, 16, 24, 30 N.

10. 10 SEM Images of deformed pebbles Pebble after 4h deformation at 800C, under 16N load (left) Pebble, cracked after 15hrs deformation at 800C under 20N load (right)

11. 11 Creep Failure Map (JAERI Li 2 TiO 3 pebbles) Force distribution at contact under an applied loading of 2.0 MPa The forces exerted on the pebbles during the operation should be less than 15 N; or the pressure applied to the pebble bed from containing structural less than ~ 5 MPa. Preliminary finding

12. 12 Experiments provided time dependent deformation data for pebble creep deformation rate derivation (in progress) Deformation along the axial direction 800C, 8N load An FEM model was developed to predict the behavior of pebbles at high temperature under compressive loads. The material behavior was assumed to follow the general power-law rule: Creep deformation rate is needed for the pebble bed thermo-mechanics analysis

13. 13 Tritium permeation analysis for purge gas flow design Purge gas velocity profiles breeder structure coolant Purge gas in Neutronics (nuclear heating & tritium production rate) Fluid flow (velocity profile) Heat transfer (temperature) Tritium transport (permeation) Purge gas out

14. 14 Tritium concentration profiles in various parts Purge gas in in Li 2 TiO 3 bed in He coolantin Structure Purge gas out 4321 x10 -5 Experiments are being conducted to validate numerical calculations: - blanket relevant pressure regime - with purge gas flow

15. 15 Some experimental results concerning pressure dependence on permeation T = 673K, P0=13Pa, 6.65Pa, 1.3Pa Compare with Calculation, P0=665Pa, T=623K, it is a good match with the Experimental result T = 723K, P0=13Pa, 6.65Pa, 1.3Pa The total amount of gas which has permeated after time t is D is the diffusion coefficient, K s is its Sieverts’ constant. P = DK s is the permeability of the material

16. 16 Experimental set-up underway to study the effect of velocity profile on tritium permeation