Approaching Dynamic PSA Within CANDU 6 NPPs

The plant dynamics and the interactions of plant systems and operator with the random evolution of parameters led to the development of dynamic reliability methodologies. The present paper approaches a dynamic PSA methodology by making use of the thermal–hydraulic model of CANDU 6 reactor, implemented in RELAP5 Mod.3.3, and of IDDA code. IDDA (Integrated Dynamic Decision Analysis) is a software code that with the help of enhanced dynamic event tree methodology provides results in terms of system unavailability. The coupling of the two above mentioned codes allows a full representation of the plant operational states, as well as of all the possible occurrence patterns that complete the spectrum of possible probability-consequence conditions. The plant transient considered for the CANDU 6 thermal–hydraulic model is the total Loss of Feed Water (LOFW) supply to the secondary side of steam generators. That is followed by depletion of water inventory and subsequent cool down via Emergency Water System (EWS). The present dynamic PSA approach reveals those situations where the correct intervention of protective equipment could bring to unexpected events. This allows taking the most appropriate decisions for the given plant configuration.