Consideration of Uncertainties in Analyzing Nuclear Power Facilities’ Fire Hazard

Abstract

Paying increased attention to the safety of nuclear power facilities is a key element for their further development. An approach to analyzing their fire safety with due regard to the uncertainty factors associated with the parameters of applied models and with the fire breakout and development conditions is presented. The two-zone fire modeling code that takes into account the specific features of transportable (floating) nuclear power plants is used, and its basic characteristics are given. An original approach to a dynamic probabilistic safety assessment is applied, which is based on a global optimum search algorithm. This algorithm is used in this study for taking into account the uncertainties associated with combustion models, possible human actions, and change in the equipment’s operation modes. The proposed method incorporates a genetic algorithm for searching the global optimum, the main purpose of which is to find the most hazardous fire development scenarios in accordance with adaptive variation of parameters within their uncertainty boundaries. Application of the method is demonstrated for two versions of fire breakout in the process rooms of a transportable power unit equipped with a nuclear power installation. The basic parameters of the two-zone fire model and dynamic probabilistic safety assessment are given. The results of computations for the dynamic probabilistic safety assessment demonstrate the complex nature of interaction among different processes. The data from analyzing the influence of the main parameters are given, a comparison with the standard calculation version and with the use of uncertainty analysis is carried out, and the conditional probability of the worst scenario is estimated. Owing to the consideration of uncertainties and the search for the most dangerous scenarios, it became possible to establish the fire development scenarios that can lead to essentially more severe consequences than those determined in using the standard parameters of two-zone fire models.