Feasibility Study of Modelling a CANDU Fuel Element Using a Multiphysics Object-Oriented Simulation Environment

Abstract

The thermal and mechanical behaviour of nuclear fuel is a complex and highly coupled problem. The ability to predict this behaviour under normal operating and accident conditions is of utmost importance. Using Idaho National Laboratory's Multiphysics Object-Oriented Simulation Environment (MOOSE) a HORizontal nuclear fuel Simulation Environment (HORSE) is developed. MOOSE is a computational framework that uses a Jacobian-Free Newton-Krylov (JFNK) method to solve all differential equations in the simulation at once, making it more efficient than current operator splitting methods. HORSE takes a bottom-up approach to modeling a CANDU® fuel element. In phase one a smeared pellet model is developed that simulates the heat generation in the fuel and the transfer of the heat through the sheath to the coolant. This model is used to ensure that the gap heat transfer and mechanical contact between the pellet and sheath is behaving as expected. In phase two, a discrete pellet model is developed that takes into account the mechanical contact between pellets and bambooing of the sheath. The objective of this work is develop a thermo-mechanical model of a CANDU® fuel element that contains as much of the pellet and sheath phenomena as possible, including fuel swelling and densification, fission gas production and release, thermal and irradiation creep, while also providing the ability to easily change the fuel from stoichiometric UO₂ to hyperstochiometric UO₂ and thoria-based fuels. Preliminary results from phase one will be presented.