Demonstration of the Structural Performance of Ensa’s ENUN 52B in a Range of Impact Scenarios in Storage and Transportation

The ENsa UNiversal ENUN 52B is a dual purpose metal cask developed by Ensa for dry storage and transportation of up to 52 BWR spent fuel assemblies, to meet the site-specific interim storage requirements of Sta. Ma de Garoña NPP (Spain) and future transport from the plant to the Spanish centralized interim storage facility (ATC). The ENUN 52B cask design meets the principal storage and transportation regulations for high radioactive material from the Spanish Government and the Spanish nuclear authority (CSN). In addition, the ENUN 52B has been also designed to comply with safety standards from the IAEA, regulations from the US Code of Federal Regulations and recommendations from the US Nuclear Regulatory Commission. The cask consists of a single carbon steel shell with structural, containment and gamma shielding capabilities. The closure system is constituted by two bolted lids separated by a pressurized helium gap for pressure and continuous leaks monitoring. The spent fuel assemblies are accommodated in the basket, which is assembled through an interlock cell structure made of stainless steel and MMC plates. Structural performance of the ENUN 52B cask in the tipover accident scenario of storage, 0.381m drops accident scenario of storage, 1m drop onto a punch accident scenario of transport, as well as penetration impacts in normal condition of storage and transport, have been simulated by state-of-the-art explicit transient finite element methods and evaluated against the requirements of the ASME Boiler and Pressure Vessel Code [1], [2]. For the analyses of the accident impact scenarios, the finite element models consisted of the complete package modelled in detail and in three dimensions, to take into account the complex interaction between the components and the non-linearity’s in the cask geometry, the material behaviour and overall cask behaviour. This paper presents the analysis methodology, modelling technique and evaluation methodology in the analyses of the impact events for the demonstration of the performance of the ENUN 52B in the application for competent authority approval as a dual purpose cask. As an example, analysis results, package response and evaluation results of the base down drop accident specified under the storage regulation are also described in this paper.