Advanced Model of Radiative Heat Transfer in a Rod Geometry

Abstract

Radiative heat transfer is very important in different fields of mechanical engineering and related technologies including heat transfer in furnaces, aerospace, nuclear reactors, different high-temperature assemblies. In particular, in the course of a hypothetical severe accident at pressurized water reactor (PWR) the temperatures inside the reactor vessel reach high values at which taking into account of radiative heat exchange between the structures of reactor (including core and other reactor vessel elements) gets important. Existing models of radiative heat exchange use many limitations and approximations like approximate estimation of view factors and beam lengths. The module MRAD was used in this paper to model the radiative heat exchange in rod-like geometry typical of PWR. Radiative heat exchange is computed using dividing on zones (zonal method) as in existing radiation models implemented to severe accident numerical codes such as ICARE, SCDAP/RELAP, MELCOR but improved in following aspects: • new approach to evaluation of view factors and mean beam length; • detailed evaluation of gas absorptivity and emissivity; • account of effective radiative thermal conductivity for the large core; • account of geometry modification in the course of severe accident. Special attention is paid to deriving of exact analytical values of view factors and mean beam lengths (which are a good tool in radiative heat transfer concerning gas media) for a number of “standard” geometries. Generalized Hottel’s method of strings is used for rods of finite lengths. Monte-Carlo method is used for validation of new model in application to “standard” geometries. The developed model is successfully applied for modeling of PARAMETER-SF1 and QUENCH-06 tests, which use the triangular and square rod assembly respectively.