Analysis Of Hydrogen Combustion Outside PCS Internal Heat Exchanger And Its Influence

In severe accidents,the zirconium water reaction produces a large amount of hydrogen and inevitably releases a large amount of heat.PCS internal heat exchanger is a nuclear safety class equipment and an important component of PCS system,which could export heat from the containment.Vapor condenses near PCS internal heat exchangers when heat is removed in response to severe incidents.This process leads to an increase in the concentration of hydrogen and air,which increases the possibility of hydrogen combustion near the internal heat exchanger of PCS.Therefore,the commercial fluid calculation software ANSYS was used to conduct hydrogen combustion outside PCS internal heat exchanger and its influence analysis.Hydrogen combustion model outside PCS internal heat exchanger and its validation.The hydrogen combustion model must be verified by experiment data before used.Liu Yinhe’s cylindrical experiment in Xi’an Jiaotong University is choosed to verify the numerical model of hydrogen combustion.The Fluent module in ANSYS was used to simulate the flame propagation velocity and peak combustion pressure under the initial conditions of 10%initial hydrogen concentration,0.1 MPa initial pressure and 323 K and 423 K initial temperature,respectively.The calculated results are in good agreement with experimental data.Therefore,the hydrogen combustion model outside PCS internal heat exchanger selected in this paper could effectively simulate the combustion of hydrogen outside PCS internal heat exchanger.Analysis of hydrogen combustion and thermal characteristics of PCS internal heat exchanger.The influence of vessel diameter,ignition position,position of heat exchange tube,initial hydrogen concentration,initial temperature,initial pressure,convective heat transfer coefficient in heat exchanger tube and tube bundle on thermal characteristics of the heat exchanger was studied by using Fluent module in ANSYS.The container diameter is 1 m,1.5m,1.5 m;Ignition position selected 0.2 m,0.3 m,0.4 m;The distance between heat exchange tube and center of the container is 0 m,0.2 m and 0.4 m;The initial hydrogen concentration is8%,10%and 12%;The initial temperatures is 363 K,413 K and 463 K;The initial pressure is0.35 MPa,0.45 MPa and 0.55 MPa.The range of convective coefficient in heat exchange tubes is 200～2000 W(m~2 K).The tube bundle consists of three heat exchange tubes.It is found that the most important factors affecting the thermal characteristics of the heat exchanger are the initial hydrogen concentration and the convective coefficient in the heat exchange tube.Stress analysis of PCS internal heat exchanger under hydrogen combustion condition.The Static Structural module of ANSYS is used to simulate the stress of the heat exchanger under external hydrogen combustion condition.Primary membrane stress、local membrane stress and local membrane stress plus bending stress are obtained after stress linearization on the path including upper and lower head shell along wall thickness direction and the maximum stress point along the heat exchanger tube wall thickness direction.Then,compare them with ASME sectionⅢdivision 1 subsection NC and Appendices level C criteria.It is found that the stress level of the evaluation path meets the requirement of the evaluation standard under the condition analyzed in this paper.