9.8.8.1. Introduction

The objective of the DEFORM‑5 [9.8‑1] model is to provide a predictive capability to quantify 1) margin to cladding failure, and 2) cladding failure timing and location in stainless steel‑clad metallic fuel pins. It performs this function by using the current understanding of metallic fuel operating behavior and failure mechanisms in the form of mathematical formulations to model the relevant physical phenomena. (For a review of observed metallic fuel irradiation performance, see Ref. 9.8‑2). In the DEFORM‑5 model, calculated cladding mechanical response to transient thermal and pressure loading conditions is compared to expected failure characteristics and criteria to yield quantified measures of margin to failure, failure time, and failure location. DEFORM‑5 applicability is focused on irradiated metallic fuel, in which the fuel has swollen into contact with the cladding.