The Development of a Nodal Method for the Analysis of PWR Cores with Advanced Fuels

Abstract

This thesis outlines the development of a nodal method with the purpose of addressing difficulties encountered in the modelling of advanced fuels. The standard calculational route used when modelling a Uranium (U) fuelled Pressurised Water Reactor (PWR) is not accurate enough to analyse a PWR containing U and Plutonium (Pu). This is because the assumptions made when developing the standard route are not necessarily representative of situations involving advanced fuels. To address some of these poor assumptions a nodal method has been developed which can solve the SPN equations in multiple energy groups. The SPN equations are an asymptotic approximation of the full neutron transport equation, and as such will include more physical effects than the neutron diffusion equation. The theory behind the development of this nodal method is outlined in this thesis along with an extensive set of benchmark tests for verification of the method. It is found that through a similarity transformation of the determining equations, existing nodal diffusion solvers can obtain solutions to the SPN equations without any approximations. Previously EDF Energy have developed an embedded methodology to address the shortcomings of the standard calculational route. This procedure solves the diffusion equation in greater detail on local sub-meshes in order to correct the standard 2 group nuclear data, and reduces the pin power errors by ≈ 50% by capturing spectral effects on the interface between two significantly different fuel types. In this thesis the incorporation of the SPN nodal method into the embedded methodology is described. A small light water reactor benchmark is solved to test the accuracy of the embedded methodology combined with the SPN nodal method. It is concluded that similar accuracy to diffusion is attained with the SPN equations. This is because the homogenisation procedure produces an error larger than the improvements due to the use of the SPN equations. To address the limitations discovered in this thesis future work is proposed based on the author’s experience of research in the area.