In-situ irradiation test of mica substrate bolometer at the JMTR reactor for the ITER diagnostics

Irradiation tests of a mica substrate bolometer were carried out at the Japan Materials Testing Reactor up to the fast neutron fluence of 0.1 dpa. A performance of the bolometer was investigated during the irradiation. Significant increase of the meander resistance from 275 to 446 Ω was observed in the fast neutron fluence of 0.06 dpa. In the post-irradiation examination (PIE), it was confirmed that the gold meander contained 46% mercury which was produced by the nuclear transmutation reaction of ¹⁹⁷Au(n,γ) ¹⁹⁸Au→¹⁹⁸Hg+β^-. The bolometer sensitivity was measured by the change of the meander resistance for the input power. The sensitivity decreased slightly at constant reactor power. There was not significant change in the bolometer response time. During the cool down phase of the first cycle all connections went open circuit. Some recovered on start-up of the second cycle, however, all connections went open circuit again near the end of the second cycle. They were not recovered any more at the third cycle. Breaks of the gold meander were observed in the PIE. The use of gold meanders might be problematic in ITER.