An Experimental And Zone Simulation Study On Vertical Cable Tray Combustion

As a clean and effective energy, nuclear power is increasingly becoming the main part of global new energy. In 2011, National Development and Reform Commission proclaimed 《Long-term development planning (2011-2020)》, and stressed that nuclear power development is based on the principle of "Safety First". In the process of nuclear disasters, the nuclear fire is one of the most frequent and risk accidents. According to the investigation results, more than 47.3% of all the nuclear fire accidents are related to electric cables. Nuclear power is a type of clean and effective new energy, increasingly growing into an important part of new energy around the world, and the security of nuclear power plant is also a controversial issue. The fire accident is a major threat to nuclear power plant safety based on the investigation data.Numerical simulation on fire has been a significant approach for the research in the fire engineering field with the development of computer simulating softwares CFAST, a zone fire simulating soft, calculates faster and has wider application area compared to other numerical softwares, and what’s more, it can directly get the evolution of user-defined fire parameters over time. So it has much more possibilities to be used in practical application. It’s necessary to investigate the feasibility of CFAST’s application in simulating vertical cables fire. In 2002, the NFPA-805 proclaimed by USA Fire Protection Association proposed to apply the performance-fire-protection standard to fire control of light-water reactor nuclear power plant, and indicates that the fire model of fire protection design should be verified.This paper is mainly about the effect of cable space and closed room on the fire process of vertical cables, validation of double zone model feasibility for simulating vertical cables fire dynamics engineering, and additionally research on optimizing plan design of fire source for zone model simulation.A series of tests with different cable spacing on vertical fire were carried out in closed and open room respectively to study on the effect of cable space and closed room on the fire process of vertical cables. Firstly, by the comparison of mass loss rate (MLR) of (vertical cable tray)VCT with various cable spacing in enclosed and open space, it is found that the spacing between cables has significant influence on the MLR and a critical zone exists in the closed room function to vertical fire process. The criteria of the zone is decided by the heating effect of fire flame on cables and the heat feedback to cables from gas layer. Based on the vertical temperature distribution in closed room, dimensionless temperature gradient analysis leads to a temperature transition region in the cable combustion process in closed room, and therefore, the vertical cable fire development is in accordance with the basic consumption of zone simulation.The tests of vertical cable combustion in closed room validates the feasibility of double zone model in the application in the simulation of vertical cable fire dynamics engineering. The testing results indicate that CFAST cannot catch the trend of temperature changes of vertical combustion, but it can properly predict the time of temperature reaching the peak when the fire source of vertical combustion is fixed. However, when the fire source is set to move upward with code revision, CFAST can accurately catch the temperature evolution trend. So it suggests setting fire source to move upward for the simulation prediction of vertical cable combustion development.This work can provide a principle for nuclear fire risk assessment and help people better understand cable combustion character in closed room. Meantime, this paper corrects the disadvantage of inaccurately simulation of vertical cable fire and enhances the simulation accuracy of double zone model in calculating vertical fire by revising the double zone model code of CFAST. The outcome proposes the best design plan for the fire source for research on zone simulation of vertical cable combustion.