Collision Probabilities Method Extention for Simplified 3-D Geometries

Abstract

To solve the neutron transport equation at general 2-D geometries the cell-level code CONDOR v. 2.7.01 (E.A. Villarino 2002) uses a method which couples spatial elements using neutron currents, which had been previously calculated by the Collision Probabilities method. Such methodology, usually known as Heterogeneous Response Method (HRM) has been shown as a powerful method to solve complex geometries with high reduction of the computational resources, where the most relevant effort was carried out in past decades to obtain a well-optimized and stable ray-tracing method to perform the CP calculations on each spatial element (E. A. Villarino, R. Stamm´ler, A. Ferri & J. Casal 1992). Nevertheless, the current development of Fuel Assemblies, in-core and ex-core devices (mainly for Research Reactors) with high axial heterogeneity is demanding a 3-D extension of current methods available. Unfortunately, develop a general 3-D HRM method, leads to the development of a complete new ray-tracing scheme and implies a big implementation and validation effort. Furthermore, most calculations at cell level do not need high complex 3-D geometries. The present work, developed in the framework of the Upgrade of INVAP´s proprietary calculation line developed with the contribution of the Argentine National Agency of Technological and Scientific Promotion (Agencia Nacional de Promoción Científica y Tecnológica -ANPCyT), through the funds of the Argentine Technological Funds (Fondo Tecnológico Argentino, FONTAR), presents the basics of an alternative solution for the 3-D problem extension, that considers only an axial extension of the HRM method, in order to be included in CONDOR code in the near future. Furthermore, this method is intended to allow the modeling of most of cases of interest at cell-level Accordingly, the theoretical basis for the HRM extension to simplified 3-D geometries is presented, where the coupling with already optimized 2-D ray-tracing is presented and several proposals for implementation are presented.