Nuclear reactor safety systems availability upgrading analysis

The analysis evaluate the consequences of the removal of the autoclosure interlock (ACI) on the Residual Heat Removal System (RHRS) suction/isolation valves at the nuclear power plant. The deletion of the RHRS ACI is in part based on a probabilistic safety analysis (PSA) which justifies the removal based on a criterion of increased availability and reliability. Three different areas are to be examined in PSA: the likelihood of an interfacing system LOCA, RHRS unavailability, and low temperature overpressurization control. The paper emphasises particularly the RHRS unavailability and the likelihood of an interfacing system LOCA evaluation utilising the current control circuitry configuration and then with the proposed modification to the control circuitry. (author)