Customization of ENUN 24P Cask for Transport of High Burnup Spent Fuel in China

The ENUN 24P dual-purpose metal cask has been adapted from the ENUN cask series concept developed by Ensa, to fulfil specific spent fuel transport requirements across People’s Republic of China. Among those, it is designed to allow the transportation of spent nuclear fuel from Ling Ao and Daya Bay Nuclear Power Plants (NPPs) located in southeast China, to Lanzhou storage facility (long distance until almost 4000 km) crossing China in different regions and climate conditions through road & rail transportation.During the development of this project, Ensa’s skilled staff from the Design & Engineering, Project Management and Field Services departments has faced several technical challenges in order to customize an existing solution licensed in Spain (the ENUN 32P), for the particular specifications and requirements of the Chinese scenario. Within those technical solutions provided, the following are highlighted and described along this paper:-- The structural design of the impact limiters was slightly modified to considerably reduce its maximum diameter, because of constrained limits of the transport route while maintaining the same cask center of gravity maximum acceleration. Through detailed scoping analyses, Ensa was able to assure the original G load limit suffered by the cask to comply with the requirements stated by the principal international standards (IAEA SSR-6 [1], 10 CFR 71 [2] and ADR 2015 [3]) for the hypothetical accident conditions.-- An innovative trunnion design concept was implemented to fit in the cask with the reduced impact limiters and assure enough energy absorbing material to void contact between the trunnions and the rigid target (i.e. the transport road) during postulated hypothetical impact accidents. This new trunnions design concept implied the development of a new lifting yoke and transportation skid, customized for the loading and transport operations of the cask.-- Since the burnup credit methodology was not already allowed to use by the Chinese nuclear regulator at the time of ENUN 24P design, the configuration of the basket implied several design modifications to assure the subcriticality of the high burnup fuel with very low cooling time.Ensa has performed deep evaluations of all the safety functions of the customized ENUN 24P cask to assure full compliance with the international transportation regulations, for high radioactive spent fuel (IAEA SSR-6 [1], 10 CFR 71 [2] and ADR 2015 [3])). Ensa is currently in the last step of the processes for licensing the cask in Spain and in People’s Republic of China for transportation. In addition, the manufacturing work flow at Ensa workshop has been carefully planned and fixed to be able to supply the first unit of the ENUN 24P customized cask within a very constrained time schedule, and comply with the customer agenda for the transportation of high burnup spent fuel across China in the beginning of 2017.