Numerical simulation of a shock absorber used for protecting of casks for spent nuclear fuel

Abstract

The preparation and implementation of nuclear facilities decommissioning is a complex of different activities strongly related to safety. After shut down of both reactor units in 2004 and 2005, it was designed of a new spent nuclear fuel (SNF) storage facility to the storage function envisages a separate place for handling of casks with SNF. The SNF handling operation itself induces some challenges for safety. One of such risks could be the dropping of Cask with SNF during its lifting operation. A special shock absorber was designed to avoid failure of fuel assemblies in case of hypothetical dropping of this Cask. This shock absorber consists of 14 fir wood layers and reinforced concrete slabs on the top. It is very important evaluate the interaction of these layers during dynamic impact. The dynamic impact characteristics of the cask under free-drop conditions should be investigated via the proposed numerical simulation method and to evaluate the reliability of the shock absorber during dynamic loading.The paper presents a dynamic analysis of the ability of shock absorbers to perform their safety functions considering the drop on them of different types of SNF casks. Numerical simulation was performed using Ansys computer code and the results were compared with analytical calculation results. The interaction and friction between wood layers was investigated via the proposed numerical simulation method. The results show that the fall of the container from a height of 3.2 m can be increased to 5 m, or the shock absorber performs its function when the weight of the SNF cask varies from 117 to 150 ton. The weight of the metallic and reinforced concrete casks used in Lithuania is between the estimated weight limits. That’s allows us to conclude that designed shock absorbers fulfil the assigned stopping function of the falling SNF casks.