Development of a 500 litre drum for the encapsulation of steam-generating heavy-water reactor sludge at Winfrith

Abstract

Winfrith Technology Centre was once a leading UKAEA development site for nuclear technology. UKAEA's task now is to decommission the nuclear reactors and other facilities and restore the site for alternative use. On the site is the prototype steam-generating heavy-water reactor (SGHWR) that produced 100 MW(e) of electricity during its 22 year operational life. During this period the reactor produced large quantities of radioactive sludge and there are also the remains of ion exchange resins from various clean-up operations including the circuit decontamination campaigns at each annual shutdown. These sludges were directed to and stored in four external tanks and over the years there has been a steady build-up of sludge in these facilities, until 1990 when the reactor shut down permanently. Plans were made for the sludge in these tanks to be retrieved, encapsulated in drums and stored on site until a permanent national repository became available. Due to changes in circumstances following the relatively sudden closure of the SGHWR in 1990 and additional requirements from the operators of the Drigg low-level waste site, the original encapsulation plans of UKAEA had to be set aside. Following further considerations, RWE NUKEM, working in partnership with UKAEA, is now contracted to retrieve, condition and encapsulate the sludge in a new plant currently being constructed, and to export the drums to an existing refurbished on-site store. The Winfrith treated radwaste store (TRS) was constructed to store 500 I drums of intermediate-level waste in a matrix stacked nine high. This paper describes the drum development work undertaken prior to the introduction of RWE NUKEM and completion of the revised design of drum for use within the TRS. It also briefly describes the process for which the drum is being utilised in the newly designed sludge treatment plant. The drum design has had a number of iterations from a concept that was first drafted in 1989 to the present design that has undergone extensive finite-element modelling to support its introduction. Although the drum has a fairly standard body, the flange and lid have been modified to suit a revision to the original concept of attaching the lid by welding. This paper tracks the development of the lid bolting arrangements and the impact on the revised design of parts of the new encapsulation facility. The means of satisfying the requirements for the introduction of the new drum as an IP2 package are also described.