NTL 11 Spent Fuel Flask – Meeting the Challenge of Regulatory and Technological Change

By June 2005, when shipments of spent fuel for reprocessing from Germany are concluded, the NTL11 flask type will have been responsible for transporting a total of 1500 tonnes of heavy metal in the form of spent fuel. Excluding domestic transports in France and the UK, this represents 25% of the total European spent fuel transported for reprocessing since the flasks came into service in 1977. Approximately 40% of the total for the flask type will have been transported to BNFL’s Sellafield facility, the remainder to Cogema at La Hague. The NTL11 flask can justifiably be described as being the workhorse of BNFL’s European spent fuel transport business. The NTL11 flask started life under the ownership of Nuclear Transport Limited, an associate company of BNFL, and in recent years the original fleet of five flasks has been absorbed into the BNFL inventory. A recent build programme has seen a further four flasks added to the fleet, an expedient measure to cope with the additional transport requirements imposed by the need to meet the June 2005 deadline for the removal of contracted fuels from Germany. While there have been certain evolutionary changes affecting the package design, there have also been more significant changes in the Design Safety Case. These have sometimes been necessary to meet regulatory changes, or the challenges posed by the regulators. In other cases advantage has been taken of improvements in analytical techniques to demonstrate increased margins of operational safety. Where possible those margins have also been increased by other means, such as taking advantage of commercial trends to reduce package thermal loads. The NTL11 flask was designed around the reactor and fuel characteristics prevailing in the 1970's. Over the lifetime of the flask the responsible engineering teams have faced and met the successive challenges to develop the capability of the Package to face the changing requirements of the industry and the Transport Regulations. Both Package design and Safety Case have been revised such that it has continued to service the needs of the industry more than a quarter of a century after first use.