Methodical extension of existing PSA taking into account special requirements from overarching impacts. Use of dynamic simulation methods for the analysis of emergency measures in case of aggravating boundary conditions due to overlapping impacts. Final report on work package AP 2

In the recent past, advanced methods for dynamic PSA have been developed by GRS: These methods are now available for applications. Dynamic PSA methods are used to model and analyse time-dependent interactions between the plant process, human actions and stochastic influences in a more detailed and comprehensive manner. This is not possible with the conventional PSA methodology. Such interactions may arise in event sequences induced by hazards, where emergency measures are carried out by plant personnel even under aggravated conditions. In this project, the advanced methods for dynamic PSA developed by GRS have been applied to investigate the effectiveness of emergency measures under such aggravated conditions, where the influence of dependencies and uncertainties from stochastic parameters on human actions is considered in the time sequence. The scenario analysed is a fire event, during which an internal flooding from a leakage of the fire water supply in the reactor annulus is assumed. The scenario starts with a fire in a cable duct of the reactor annulus. During the firefighting activities, a break of the fire water supply pipe in the reactor annulus is postulated, interrupting the water supply needed for extinguishing the fire successfully. The aggravating condition for the extinguishing process is given through the delay of the fire fighting activities due to the time needed to stop the leakage. The analyses performed have demonstrated how a human procedure can be modelled and analysed in detail applying dynamic PSA methods, where various uncertain influencing factors and dependencies have been taken into account. In addition, it has been shown that the probabilistic results derived from a dynamic PSA can be used to quantify the impact of stochastic influencing factors on times when relevant actions are carried out. This information can be used to identify influencing factors – even those that occur with only a very low probability – for which the execution times of such actions are significantly delayed. Time delays of necessary actions may present an impact important to safety if the actions are not carried out during the required time period with the result that the emergency measure is not successful. In that way the probabilistic results of a dynamic PSA of emergency operating procedures can be used as a basis for developing measures to avoid such time delays and therefore can contribute to improve plant safety.