Sensitivity study of break opening characteristics for large LOCA using CATHENA

A study was performed using a CATHENA based generic model of a CANDU6 reactor to demonstrate the sensitivity of system response to single and two-stage break opening characteristics following a Reactor Inlet Header Large Break LOCA. Figures of merit for the analysis were the power pulse amplitude and the 5 second integrated normalized power. The analysis demonstrates in a qualitative manner a threshold time for 'instantaneous' break opening, and a threshold initial break size above which shutdown system trip times remain unchanged. The analysis also attempts to establish the relative impacts of initial and second stage opening times on figures of merit. (author)