Modeling Pellet to Cladding Interaction and Related Mechanisms in Irradiated Fuel Elements

SCK•CEN Mentor

Rozzia Davide, drozzia@sckcen.be, +32 (0)14 33 80 36

Expert group

LBE Components and Experiments

SCK•CEN Co-mentor

Boer Brian , bboer@sckcen.be , +32 (0)14 33 31 69

Introduction

During the normal operation of nuclear reactors, the fuel–cladding gap may close, as a result of the different thermal expansion, creep and swelling of both the fuel and the cladding (pellet cladding interaction - PCI). In this equilibrium state, a significant increase of local power (like a transient power ramp in the order of 100 kW/m-h), induces tensile circumferential stresses in the cladding. In presence of corrosive fission products (e.g., iodine), and beyond specific material dependent stress threshold, cracks typical of stress corrosion appear and grow-up (stress corrosion cracking - SCC). The cracks may spread out from the cladding internal surface, causing the fuel failure.  Among the operational and design limits developed to prevent this fuel failure mechanism, a recent review of the “Fuel Safety Criteria” evidenced that the limit on uniform cladding transient strain normally adopted as basic safety criterion for the avoidance of mechanical fracture of the cladding during transients due to pellet-cladding interaction is not fully reliable, especially for high burn-up fuels.

Objective

Development and validation of numerical tools that account for this phenomenon is thus of primary importance to reactor operation. In this connection, OECD NEA sets up the “public domain database on nuclear fuel performance experiments – International Fuel Performance Experiments (IFPE) database”, with the aim of providing a comprehensive and well-qualified database on MOX-UO2 fuel with Zircaloy cladding for model development and code validation. The present activity aims to assess the capabilities of Fuel Performance Code (TRANSURANUS) in predicting PCI/SCC and related mechanisms by developing suitable input decks based on a selected database relevant to PCI/SCC from the IFPE.

The minimum diploma level of the candidate needs to be

Academic bachelor

The candidate needs to have a background in

Other , Physics , Nuclear fuel technology