Application of Non-Linear Iterative Nodal Expansion Method for CANDU Analysis (Part 1: Derivation of the Steady-State Nodal Diffusion Formulation)

Abstract

The steady-state nodal diffusion formulation of the non-linear iterative nodal expansion method (NEM) is derived independently and is illustrated in detail in this paper. A simple two-dimensional two-group diffusion code with the capability of both finite-difference method (FDM) and NEM techniques is also developed. The preliminary numerical tests show that the formulation derived in the paper is correct, and the NEM always shows superior accuracy over the FDM for a given mesh design, even for CANDU® analysis. The coarse-mesh (about 20-cm mesh spacing for a pressurized-water reactor (PWR) and 30-cm mesh spacing for a CANDU reactor) NEM results are as accurate as the fine-mesh (about a 1- to 1.5-cm mesh spacing for PWR, and a 5-cm mesh spacing for a CANDU reactor) FDM results for both PWR and CANDU analysis.