1. JAERI nuclear analyses for IFMIF T. Umetsu, M. Yamauchi and M. Sugimoto Presented by Takeo NISHITANI Japan Atomic Energy Agency (JAEA) IAEA Technical Meeting on „Nuclear Data for the International Fusion Materials Irradiation Facility (IFMIF)“, Forschungszentrum Karlsruhe (FZK), Institut für Reaktorsicherheit, Germany, October 4-6, 2005

2. Neutronics analysis for the concrete wall PURPOSE: replacing heavy concrete (baseline design) at the front wall to stainless steel + normal concrete or water cooling layer for surveying optimal combination METHOD: MCNPX2.4.0 + LA150 + energy- & angular-dependent d-Li(thick) source term

3. Effectiveness of heavy concrete as a radiation shielding of Test Cell wall Heavy concrete (n) – baseline SS316 (20cm) + heavy concrete (n) Normal concrete (n) SS 316 (20cm) + normal concrete (n) Fe (20cm) + heavy concrete (n) Heavy concrete (  ) – baseline SS316 (20cm) + heavy concrete (  ) Normal concrete (  ) Fe (20cm) + heavy concrete (  ) SS316 (20cm) + normal concrete (  ) Fe (20cm) + normal concrete (  ) (cm) (  Sv/h) Neutron dose for normal concrete ~ 10 (@2m) to 100 (@4m) times higher

4. Effect of water cooling channel at surface layer (cm) (  Sv/h) No liner (heavy concrete only) (n) Water(5%) in liner (n) Water(10%) in liner (n) No water in liner (n) Liner 20cm (SS316 10cm + SS316/water 10cm, water content:0, 5,10%) No liner (heavy concrete only) (  ) Water(5%) in liner (  ) Water(10%) in liner (  ) No water in liner (  ) Marginal effect of dose decrease at deep positions

5. Summary When replacing heavy concrete at the front wall to normal concrete, neutron doses become ~ 10 (at 2m depth) to 100 (4m depth) times higher. Introducing steel layer at the surface partly remedies this situation. Replacing steel layer to water channel results in marginal reduction of estimated doses. Future directions: Selection of materials combination at surface layer to control the nuclear heating and dose due to residual activities at maintenance.

6. Estimation of Radioactivity in the IFMIF Liquid Lithium Loop due to the Erosion and Corrosion of Target Back-wall Surrounding structural materials are extremely activated. Activated compositions of the target back-wall suffer erosion and corrosion, and move into liquid lithium. They are transported by lithium flow and accumulate in the loop. Radioactive nuclides in the lithium loop of IFMIF produced by erosion and corrosion effects of the target back wall were estimated by a design code ACT-4 developed in JAERI.

7. Method of Analysis The IFMIF neutron spectrum in the back-wall was calculated by McDeLicious code. The activation build-up in the back wall during the operation and the decay after shutdown were calculated by the ACT-4 code. Original activation cross sections for ACT4 were combined with cross sections in the IEAF-2001 library from 13.72 MeV to 56 MeV for 7 nuclides.

8. Decay curves of radioactivities produced in IFMIF Li target back wall of SS316 Stainless steel The total amount of radioactivity in the back-wall made of SS 316 was calculated to be 2  10 18 Bq/m 3 one month after the shutdown

9. Dose rate distributions around the IFMIF Li loop for several cooling times. The 100% amount of the corrosion products was supposed to uniformly accumulate on the inner surface of lithium loop (100% plate-out) of which total inner surface area is 572 m 2. Hands-on limit

10. Dose rate decay curves around the IFMIF Li loop as a function of cooling time. Dose rate (µSv/h) Time after operation stop (days) According to the results, hands-on maintenance cannot be accepted until the end of one year cooling in the case of 100% plate-out. However, if the deposit of the corrosion products is 10% (10% plate-out), hands-on maintenance becomes possible (the cold trap efficiency is required to be more than 90 %). Hands-on limit

11. Summary ■ The total amount of radioactivity in the back-wall made of stainless steel type 316 was calculated to be 2  10 18 Bq/m 3 (several tens Ci/cc) one month after the shutdown (Erosion/Corrosion rate : 1 mm/y). ■ The concentration of the activity in lithium is not large compared with the amount of the deuteron-lithium reaction remnant 7 Be. ■ However, the data such as the accumulation on piping and removal efficiencies in cold trap are not sufficient at present. ■ The radiation dose rate around the lithium pipe turned out large owing to the corrosion products produced by one-year IFMIF operation, when 100 % plate-out was supposed. Therefore, the cold trap is required to be highly efficient so that more than 90 % corrosion products can be removed.