DEVELOPMENT OF DECOMMISSIONING TECHNIQUES ON A MAJOR NUCLEAR FACILITY AT UKAEA WINFRITH

Building A59 at Winfrith contains two heavily shielded suites of caves originally used to carry out remote examination of irradiated nuclear fuel elements from the UK based nuclear power stations and other experimental reactors. These heavily contaminated facilities were declared redundant around 1996 and after competitive tender a full decommissioning contract was awarded to RWE NUKEM by the site owners and nuclear site licence holders, UKAEA, commencing in July 2000. Decommissioning operations have steadily advanced to such an extent that both suites of caves have been fully cleared of equipment, benching and services and substantially decontaminated so that the next stage of major structural dismantling could be undertaken. This paper briefly summarises the major tasks achieved during the decommissioning over the past year and describes how the process used to clean the heavily contaminated, encast ventilation ducts used to provide in-cave depression was developed and deployed. This was particularly important since the ducts contained the last major source of intermediate level waste that had to be removed from the structure. The essential challenge was to achieve this objective in a cost-effective manner without incurring exposure of staff to high levels of radiation and contamination. The achievement of the duct cleaning provided the opportunity to initiate the removal of large and heavy internal shield walls and doors in the facility by a novel method involving the use of a heavy lift stack truck. Details will be given of the nature and magnitude of the problems that had to be overcome and the lessons learnt during the process which led to the removal of 12 heavy structures weighing 16-33Te by this technique. The means of further decontamination and disposal of these items using a variety of equipment items, largely as free release materials, will also be described. Recovery, and disposal of the zinc bromide used in the shielding windows of both facilities will also be described, including useful data on the methods for disposal of both lightly and heavily tritium-contaminated solutions. The report will fully explain how the achievement of cost-effective and safe solutions to all these problems has been greatly assisted by the employment of a non-adversarial team-working approach between client and contractor throughout the programme. The fact that the whole