Thin slit streaming experiment for ITER by using D-T neutron source

There are very thin and long slits at boundaries between vacuum vessel and port plugs in ITER. The slits are 0.5–2 cm in width and their length amount about 200 cm in depth. Therefore, it is a key issue to evaluate neutron-shielding effects of assembly with such thin and long slits. In order to verify them, our group has started to conduct the D-T neutronics experiment with an experimental iron assembly at the Fusion Neutronics Source (FNS) in Japan Atomic Energy Agency (JAEA) under the ITER/ITA Task 73–10. Fission rates among a slit in the assembly were measured with U-238 and U-235 micro-fission chambers. From our experiment, the following facts were found: (1) the C/E value of U-238 fission rate is within 0.9–1.1 at the most measured points and (2) the C/Es of the U-235 fission rate were almost closed to the unity within 0.9–1.2. However, they tended to decrease for the depth slightly.