Development of irradiation capsules with adjusting neutron spectrum

In JMTR, irradiation tests of structural materials simulating fast reactor conditions were studied. The ratio of helium production to displacement damage (dpa) was used as an index of the irradiation effect, and the method was adopted to simulate the value in a fast reactor. It was thought to be possible to simulate fast reactor irradiation in JMTR, a light water reactor, by placing a component inside the capsule that shields thermal neutrons. As a result of the study, cadmium was found to be an appropriate material for shielding thermal neutrons. Therefore, the effect of the capsule containing cadmium on the reactor was evaluated, and it was confirmed that there were no safety issues. The results of tests on the loss of cadmium in the primary cooling water of the reactor confirmed that there was no corrosion effect on the reactor structural materials due to cadmium leakage. Although there were some problems in the molding of the cadmium, these problems could be solved by improving the casting method. By shield capsules, irradiation tests of stainless steel under less thermal neutron spectra were carried out. According to the analysis, we confirmed that thermal neutron shielding by cadmium enabled to simulate of the He/dpa ratio of the fast reactor.