Establishment of integrity evaluation method for Reserved Shutdown System of High-Temperature engineering Test Reactor (HTTR)

Hamamoto, Shimpei  ; Kawamoto, Taiki; Kondo, Makoto; Sawahata, Hiroaki ; Takada, Shoji; Shinozaki, Masayuki

High Temperature engineering Test Reactor (HTTR) has the reactivity control system which is accompanied with the Reserved Shutdown System (RSS). The RSS consists of BC/C pellets, guide tube, electric plug, motor which contains brake and reducer, and so on. In accidents when the control rods cannot be inserted, an electric plug is pulled out by motor and the BC/C pellets fall into the core by gravity. It was revealed that the motor in the RSS drive mechanism did not work as the result of pre-start up checks as described followings: (1) The oil which was separated from a grease of motor reducer flowed down from gap of oil seal, (2) the separated oil penetrated into the brake, (3) the penetrated oil was mixed with abrasion powder released from brake disk, finally, (4) the adhesive mixture blocked the rotation of the motor. A new evaluation method was proposed to detect a sign of the motor sticking. Through the overhaul inspection of all RSS drive mechanisms of HTTR, it was revealed that the proposed method was effective to evaluate the integrity of the RSS drive mechanism.