Safety of the Dry Spent Nuclear Fuel Storage. Thermal Regimes

Safe thermal conditions of the spent fuel assemblies storage represent a key issue of the storage facility safety. The numerical estimation of the thermal state of fuel assemblies was carried out using the methodology of the conjugate heat transfer problems solving. Due to slow changes of decay heat of fuel assemblies during the storage, the modelling of thermal processes inside storage equipment is generally accepted to carry out in the quasi-static formulation. The study was conducted for ventilated storage container with hermetic storage cask filled by helium- containing 24 WWER-1000 fuel assemblies. Detailed structure of the storage cask was modelled taking into account conductive, convective and radiation heat transfer. The temperature field of the concrete container, guided tubes and temperature and velocity fields of the cooling helium inside the cask and cooling air outside the cask were calculated. The hottest assemblies and the maximum temperatures in each assembly were detected. The calculations have been performed for normal equipment operation at average summer temperatures of the place where the storage facility is located. The developed computational model was verified by comparison of calculated and measured temperatures of cooling air outside the storage cask.(author)