Development of a software tool for the analysis and verification of emergency operating procedures through the integrated simulation of plant and operators actions

Probabilistic safety assessment (PSA) includes operator actions as elements in the set of the considered protection performances during accident sequences. Nevertheless, its impact throughout a sequence is not usually analyzed dynamically. In this sense, it is convenient to make a more detailed analysis about its importance in the dynamics of the sequences, allowing for sensitivity studies with respect to human reliability and response times. For this reason, new developments in simulation software must be able to incorporate operator actions in conventional thermalhydraulic simulations. In this paper, we present one of these new tools, the TRETA/TIZONA–COPMA III coupled codes, which can be used for evaluating the impact in the final plant state of the execution by operators of procedures and the evaluation of the available times for the manual actions of the operators. This software tool consists of a closed-loop plant/operator simulator: a thermalhydraulic code for simulating the plant transient (TRETA for PWR NPPs and TIZONA for BWR NPPs) and the procedures processor (COPMA III) to simulate the operator actions requested by the procedures, both coupled by a data communication system which allows the information exchange (SWBus). The first pilot cases have been performed in order to analyze sequences initiated by secondary side breaks leading to loss of heat sink sequences in a PWR plant. These tests have been carried out using the real plant EOPs for COPMA-III and a PWR plant model for TRETA code. The results of these simulations are presented in this paper.