Severe Accident Analysis of a Steam Generator Tube Rupture Accident Using MAAP-CANDU to Support Level 2 PSA for the Point Lepreau Station Refurbishment Project

Abstract

A Level 2 Probabilistic Safety Assessment was performed for the Point Lepreau Generating Station. The MAAP-CANDU code was used to simulate the progression of postulated severe core damage accidents and fission product releases.

This paper discusses the analysis results for the reference case of the Steam Generator Tube Rupture accident scenario, one of eight cases simulated for this initiating accident. The reference case assumed most safety-related plant systems were not available: the steam generator feedwater; the emergency water supply; the moderator, shield and shutdown cooling systems; and all stages of the emergency core cooling.

The simulation predicted that severe core damage began at 3.7 h, containment failed at 6.4 h, the moderator boiled off by 8.2 h, and the calandria vessel failed at 42 h. A total release of 5.3% of the initial inventory of radioactive isotopes of Cs, Rb and I was predicted by the end of the simulation (139 h). Almost the entire initial noble gas inventory in the core was transported with the containment atmosphere to the environment, primarily after the containment failure. No hydrogen/carbon monoxide burning was predicted in the containment.