Establishment of Integrity Evaluation Method for Reserved Shutdown System of High-Temperature Engineering Test Reactor (HTTR)

A high-temperature engineering test reactor (HTTR) has a reactivity control system which is accompanied with a reserved shutdown system (RSS). The RSS consists of B4C/C pellets, a guide tube, an electric plug, a motor which contains a brake and reducer, and so on. In accidents when the control rods cannot be inserted, the electric plug is pulled out by the motor and the B4C/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 in the following: (1) The oil which separated from the grease of the motor reducer flowed down from the gap of the oil seal, (2) the separated oil penetrated into the brake, (3) the penetrated oil mixed with the abrasive powder released from the brake disk, and finally, (4) the adhesive mixture blocked the rotation of the motor. A new evaluation method was proposed to detect signs of the motor sticking. Through the overhaul inspection of all RSS drive mechanisms of an HTTR, it was revealed that the proposed method was effective to evaluate the integrity of the RSS drive mechanism.