Modifications to the Shutdown Systems to Augment Reactor 27 Trip Coverage to Cater to a Single Pump Trip in a CANDU 600 Reactor

Abstract

The original design of the CANDU 600 reactor did not provide automatic trip coverage on shutdown system number 2 (SDS2) for the loss of electrical power to a single primary heat transport system pump. As a first step to improving the design, the overall plant response to a single pump trip was studied by performing a pump trip test from full power at the Point Lepreau Generating station. This was subsequently followed by an extensive design assist analysis using the computer code SOPHT. Based on this analysis, changes will be made to the high ROH pressure trips on both shutdown systems. Modifications to the SDS1 low flow trip and to the SDS2 low core differential pressure trips will also be made. These changes will improve trip coverage on both shutdown systems, and also provide an economic benefit of avoiding an unnecessary reactor shutdown if the plant responds as expected to a single PHTS pump trip. As the shutdown system design of the CANDU 600 reactor incorporates channelized Programable Digital Comparators, these changes involve software programming only. Hence no hardware modifications nor costly plant shutdowns are required to implement these changes.