Effective Thermal Conductivity and Edge Conductance Model for a Spent-Fuel Assembly

Abstract

In a typical transportation or storage cask, each spent-fuel assembly resides in a square enclosure that is backfilled with a nonoxidizing gas. For design purposes, it is desirable to have a simple yet accurate method to predict the maximum fuel rod temperature in a spent-fuel assembly in these casks. An effective thermal conductivity (k[sub eff]) and an edge thermal conductance (h[sub edge]) model are developed for the interior and edge regions of a spent-fuel assembly residing in an enclosure. The model includes conductive and radiative modes of heat transfer. Predictions using the proposed k[sub eff]/h[sub edge] model are compared with five sets of experimental data for validation. The model is compared with predictions generated by the engine maintenance, assembly, and disassembly (E-MAD) and Wooten-Epstein correlations, which represent the state of the art in this field. The model is applied to a typical pressurized water reactor and a typical boiling water reactor spent-fuel assembly, and a set of both nonlinear and linear formulations of the model are derived. The proposed model is based on rigorous models of the governing heat transfer mechanisms and can be applied to a large range of assembly and enclosure types, enclosure temperatures, and assembly decay heat more » values. The proposed model is more accurate than comparable lumped correlations and is more amenable for simple, repetitive design applications than other detailed numerical models. « less