Reliability analysis for the auxiliary cooling system of the experimental VHTR

The auxiliary cooling system is the system for removing residual heat in the normal operation of the multi-purpose, high temperature gas-cooled experimental reactor, and also one of the engineered safety features used at the time of emergency under the pressurized operational condition of the primary system. Accordingly, the securing of the reliability of the auxiliary cooling system at the time of normal and abnormal conditions is one of the important factors for the operation of this experimental reactor. In this paper, the analysis of the reliability of the auxiliary cooling system is reported. For the analysis, a part of the method of reliability analysis was used, of which the works of systematization have been forwarded in Kawasaki Heavy Industries, Ltd., for the purpose of applying to the design. The auxiliary cooling system comprises two independent systems with 100 % capacity each, and each system is composed of a helium circulator, an auxiliary cooler, pipings and valves. The cooling water system for the auxiliary cooler exists outside the containment vessel. The evaluation of the reliability, the fault tree used as the basis of calculation, the treatment of the failure of start-up, the calculation and the failure data, and the results of calculation are described. The probability of the total loss of function is 2.2 x 106/ year. (Kako, I.)