The Graph Theoretic Approach for Nodal Cross Section Parameterization

TL;DR

This paper introduces a novel graph theoretic approach (GTA) for parameterizing cross sections in nodal diffusion nuclear reactor models, enabling more flexible and rigorous evaluation methods compared to traditional trial-and-error techniques.

Contribution

The paper develops a new graph theoretic framework that generalizes cross section models into a non-orthogonal, extensible space and formulates derivatives using graph calculus.

Findings

GTA models match traditional models in PWR case studies

GTA provides a flexible framework for cross section evaluation

Proof-of-principle demonstrates potential for improved reactor modeling

Abstract

Presently, models for the parameterization of cross sections for nodal diffusion nuclear reactor calculations at different conditions using histories and branches are developed from reactor physics expertise and by trial and error. In this paper we describe the development and application of a novel graph theoretic approach (GTA) to develop the expressions for evaluating the cross sections in a nodal diffusion code. The GTA generalizes existing nodal cross section models into a ``non-orthogonal'' and extensible dimensional parameter space. Furthermore, it utilizes a rigorous calculus on graphs to formulate partial derivatives. The GTA cross section models can be generated in a number of ways. In our current work we explore a step-wise regression and a complete Taylor series expansion of the parameterized cross sections to develop expressions to evaluate them. To establish proof-of-principle of the GTA, we compare numerical results of GTA generated cross section evaluations with traditional models for canonical PWR case matrices and the AP1000 lattice designs.