PERFORMANCE CHARACTERISTICS AND CAPABILITY OF THE M4/12 MOX PACKAGE

International Nuclear Services has completed the transport packages for the execution of Sellafield Ltd’s European MOX business. Two M4/12 packages are now ready for service. The specification of the package performance had to take into account many factors. The seemingly endless permutations of the plutonium isotopic provided a challenging target to ensure a specification which would not be found wanting. The special security requirements of the road transport system impose constraints on package weight, geometry and heat load. Customer preferences influence payload, and fuel quality criteria dictate many aspects of internal design and impose overall limits on the internal temperatures, which in turn limit the thermal rating of the package. Ensuring the package capability is not restrictive for a considerable period into the future has required a degree of predictive reasoning more extensive than applied to packages for uranium fuels. Not only must developments in reprocessing and fuel manufacturing be anticipated, but also changes in core management at the customer power stations. Add to this that in the early stages of design no contracts were in place, and subsequently the preferences of the customer to have the flexibility to switch MOX fuel supply between different reactors - the opportunities to get things wrong were legion. Reactor core management requirements, by pushing fuel burnup higher, result inevitably in changes to the plutonium isotopic resulting in a MOX fuel that imposes increasingly greater constraints on the shielding and thermal performance of the MOX transport package. Future developments in MOX technology could involve ‘multiplepass’ cycles, where MOX fuel is reprocessed and the separated plutonium incorporated in further MOX fuel. While not considered a commercial probability at this point in time, it provides an interesting theoretical discussion with respect to the capability of the M4/12.