Methodology for spent fuel dry cask thermal-hydraulics analysis for long term storage

Abstract

One of the largest challenges facing the nuclear industry is with the management of nuclear spent fuel. As the available space in the nuclear spent pools is shrinking, nuclear power plants have needed a temporal solution to storage the nuclear spent fuel before a more definitive or a country centralized solution is coming. This necessity has been met by using nuclear dry casks. This technology has been used for a long time but with the increase in burnout in the fuel and in the casks lifetime due to lack of progress in constructing central storage facilities has meant that more knowledge is needed regarding the behavior of the fuel during this part of its cycle.In this sense, one of the key parameters is the Peak Cladding Temperature (PCT), which should not surpass 400 °C (USNRC, 2003). At that temperature, the hydrides dissolved in the clad can change their orientation and could cause embrittlement in the clads that could lead to rod failure. In order to ensure that this temperature limit is not surpass, simulations are needed to verify it. These simulations can be done with Finite Elements (FE) codes such as Ansys Mechanical and with sub-channel codes such as COBRA SFS, but the most common way to simulate the dry cask thermal behavior is through Computational Fluid Dynamics (CFD) codes like Ansys Fluent, STAR-CCM+, CFX or OpenFoam, among others.V