An introduction to a multidimensional reactor simulation environment with the capability of advanced modelling of nuclear fuel under accident conditions

In this paper, a Simulation Environment (SE) is introduced which has the capability of performing comprehensive and accurate analysis of different types of nuclear reactors and behaviour of their fuel under various steady-state and accident conditions. The SE currently consists of three main novel cods, a CFD-based, multidimensional code which works in transient and steady states for both single and two-phase flows and two separate neutronic codes. First code solves the point kinetics equations with multi-group delayed neutron precursors using four different methods. The second code solves multidimensional multi-group diffusion equations in transient and steady states and isotropic or anisotropic forms. Using the finite volume method for spatial discretization has provided considerable flexibility regarding geometry and boundary conditions, so that the most sophisticated details of fuels geometry such as spacer grids could be modelled accurately. The most important innovations incorporated into this SE are ''simultaneous solution'' approach which is a novel method for coupling the neutronic and thermohydraulic analyses based on the use of the point-implicit solver, ^multi-region porous media'' model which is an improvement over the original model by modifying the method of resistance coefficients evaluation and the approach by which this model is applied to the core of nuclear reactor and an introduction to the ''improved SIDK'', a temporal discretization method for accident analysis which has been obtained by combing the key feature of the original method that is decoupling of the prompt and delayed neutron equations with the separated solution approach of the point-implicit solver. The advantages provided by the mentioned innovations are partially indicated by presenting some practical examples and to demonstrate the accident modelling capabilities of this novel SE some relevant results associated with the case studies on TRR are presented and discussed which includes analyses of two DBAs i.e. RIA and LOCA. (author)