Оценка точности моделирования на основе двухзонного подхода для анализа пожарной безопасности объектов ядерной энергетики

Abstract

The possibility of using a two-zone model for simulating fires at nuclear power facilities in particular, at transportable nuclear power plants (TNPP), such as a floating nuclear power unit (FNPU), is considered. For taking into account the uncertainty of parameters used in carrying out numerous calculations, and also when a fire breakout occurs, the specifics of a TNPP involves the need to perform fast assessment and produce correct recommendations to prevent the occurrence of hazardous effects. For this purpose, an express procedure is needed. The main characteristics of TNPPs are pointed out, namely, that they are accommodated in compact compartments, in which lack of ventilation is possible; that the plant components can be arranged at different height elevations, and that heat conduction between different compartments may play an essential role. The fire modeling approaches existing around the world are analyzed, and a conclusion is drawn that the use of two-zone modeling can provide the required compromise between accuracy and speed of calculations. For practical purposes, it is proposed to adapt the existing experience with two-zone modeling based of developing the PABMT code (fires, safety analysis, and maritime transport). To estimate the code accuracy, the two-zone modeling results are compared with the results of experiments and calculations carried out using a computational fluid dynamics (CFD) code. Cases close in characteristics to the TNPP conditions are considered: fire breakouts in a room, in a cylindrical compartment, and in the FNPU process compartments. For the accuracy estimation purposes, the following parameters were used: the hot gas upper layer temperature, pressure, and oxygen concentration. The obtained results show that the estimation of relative difference for the PABMT code is in good agreement with other studies, and that the code can be used as a basis for making express assessments of fire conditions at a TNPP.