Stochastic Modelling as a Tool for Quality Assessment and Quality Improvement Illustrated by Means of Nuclear Fuel Assemblies

Summary The design of fuel rods is essential for a safe and economic operation of nuclear power plants. Recent considerations have led to the idea of an increase of the average fuel rod burn-up, which would lead to a better efficiency and smaller environmental exposure by reducing the number of fuel assemblies to be disposed of. However, any further increase of the burn-up means an additional stress for the fuel rods, in particular for the cladding tube material, and necessitates a new verification of fuel rod integrity. This is not so easy with the traditional approach and, thus, requires a more realistic description of the processes in the reactor core, enabling more reliable and more accurate predictions of the performance of the fuel rods. The predictions are the foundation of a good fuel rod design and constitute the proof of its integrity. Instead of the commonly used deterministic models, in this paper a stochastic model is proposed, which would provide new possibilities for showing the fuel rod integrity. The proposed stochastic model removes the wellknown weaknesses of the traditional approach and applies directly all existing knowledge and uncovers any remaining ignorance in order to realistically model the existing uncertainty.