Recent Progress in Helium-Cooled Ceramic Breeder (HCCB) Blanket Module R&D and Design Analysis

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. He purge gas pipe Be (Be12Ti) pebbles Ceramic breeder pebbles RAFS FWwith He coolant channels Cooling plate He coolant manifolds for FW/Breeding zones HCCB Blanket Module Design • Helium (~8 MPa) coolant operating (350C-500C) • Low pressure (0.1-0.2 MPa) helium/%H2 purge gas to extract tritium HCCB TBM module (710  389  510 mm)

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 Li2TiO3 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. 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: keff = f(T, e, j) Analysis method: neutronics and coupled thermo-fluid and thermo-mechanics analysis

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

6. This CAD model was translated to a MCNP model input using MCAM (developed at ASIPP) for Neutronics analysis He Be Fe structure Li2TiO3

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/m2 DEMO 2- 3 MW/m2 Be pebble bed strain profiles at 1 cm away from the back of the FW. Top: first iteration; bottom: second iteration.

8. Keff increases as temperature and strain increase 1stIteration 2ndIteration 3rdIteration Impact on Design The effective thermal conductivity (near the FW region) increases from 2.25 to 5.8 W/m2K during the first iteration and decreases to 5.4 W/m2k 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. Be zone temperature

9. 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. linear velocity-displacement transducer (LVDT) Error < 0.1 μm High temperature creep study for Li2TiO3 pebbles Li2TiO3 f = 1.8 - 2 mm All pebbles was checked at SEM to evaluate surface irregularities, cracks and shape before the tests

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. Creep Failure Map (JAERI Li2TiO3 pebbles) Force distribution at contact under an applied loading of 2.0 MPa Preliminary finding 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.

12. Experiments provided time dependent deformation data for pebble creep deformation rate derivation (in progress) Creep deformation rate is needed for the pebble bed thermo-mechanics analysis 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: 800C, 8N load Deformation along the axial direction

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

14. Tritium concentration profiles in various parts Purge gas in 4 3 2 1 x10-5 in Li2TiO3 bed Purge gas out in He coolant in Structure • Experiments are being conducted to validate numerical calculations: • blanket relevant pressure regime • with purge gas flow

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 The total amount of gas which has permeated after time t is T = 723K, P0=13Pa, 6.65Pa, 1.3Pa D is the diffusion coefficient, Ks is its Sieverts’ constant. P = DKs is the permeability of the material

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