Investigation on cause of outage of Wide Range Monitor (WRM) in High Temperature engineering Test Reactor (HTTR); Post Irradiation Examination (PIE) toward investigation of the cause

Shinohara, Masanori ; Motegi, Toshihiro; Saito, Kenji ; Takada, Shoji; Ishimi, Akihiro ; Katsuyama, Kozo 

An event, in which one of WRMs were disabled to detect the neutron flux in the reactor core, occurred during the period of reactor shut down of HTTR in March, 2010. The actual life time of WRM was unexpectedly shorter than the past developed life time. Investigation of the cause of the outage of WRM toward the recovery of the life time up to the past developed life is one of the issues to develop the technology basis of HTGR. Then, two experimental investigations were carried out to reveal the cause of the outage by specifying the damaged part causing the event in the WRM. The one is a post irradiation examination using the X-ray computed tomography scanner in Fuels Monitoring Facility (FMF) to specify the damaged part in the WRM. The other is an experiment using a mock-up simulating the WRM fabricated by the fabricator. This report summarized the results of the PIE and the experimental investigation using the mock-up to reveal the cause of outage of WRM.