The BNFL Vitrified Residue Transport and Storage Flask

Abstract

A highly active liquor residue arises from the reprocessing of spent nuclear fuel. Arisings from the Sellafield reprocessing operations will be vitrified into a solid form within special stainless steel containers to enable long term safe storage. BNFL are committed to the return of these residues to their overseas customers. This has necessitated the provision of a customised transport flask design to safely transport the vitrified residues safely back to their countries of origin. Residues from a number of fuel reprocessing waste streams will be vitrified at Sellafield, both from Magnox fuel arisings and oxide fuel arisings. BNFL operating plans require that the feed to the vitrification process is in general a mixture of the various waste streams. However, customers have required that any flask design should accommodate residues containing varying mixtures of the streams ranging from a Magnox dominated mix with high gamma activity to an oxide dominated mix with high neutron activity. This requirement, together with the constant full length source strength of vitrified residue, has imposed unusual and severe constraints for the flask shielding design. A flask design has been evolved capable of transporting 21 vitrified packages whilst satisfying the stringent shielding requirements within the overall UK weight and size limitations. This has necessitated the fine optimisation between shielding requirements, heat transfer requirements and overall size and weight limitations. Liaison between the UK and France has resulted in the harmonising of certain key handling dimensions and features between the UK and French flask designs.