Revised criticality emergency arrangements at UKAEA Dounreay

The UKAEA's Dounreay site in the North of Scotland has been in operation for over 40 years pioneering R and D in the fast reactor fuel cycle. With this programme completed the UKAEA is now undertaking a programme of work to restore the environment of the site for future generations. As the Nuclear Site Licensee, UKAEA is required to prepare and demonstrate the adequacy of the Site Emergency Arrangements. The storage and handling of fissile material on the site could give rise to a criticality if operations are inadequately controlled. As a part of our ongoing continuous improvement programme, a complete review of the plan for such an incident was instigated to ensure that it meets with best practice as we embark on our decommissioning programme. This led to a new set of arrangements based on the concept of STARBURST, which in essence requires a rapid evacuation of staff from any possible source of a criticality event. The evacuation and egress through a security fence adds an additional challenge and as does the existence of several possible sources of the initiating event. The actual routes taken were optimised to reduce dose uptake and a software package was utilised to undertake crowd modelling to ensure that the exists in the fence were appropriately placed and sized. Two buildings were carefully selected and adapted to act as Criticality Evacuation Centres having been assessed for their ability to provide adequate shelter and shielding for several hundred staff. Portable lead shield was designed and manufactured to allow for the immediate assessment of criticality lockets. The methodology of how best to process staff through the Criticality Evacuation Centres was keenly debated and tried. It proved most effective to monitor and assess staff who were close to the 'incident' building with confirmatory reassurance monitoring for other staff being undertaken when resource could be released. The need to prioritise and rank potentially exposed staff is recognised and was simplified using a nonogram. The STARBURST arrangements were successfully demonstrated to the Nuclear Installations Inspectorate in April 1999. These revised arrangements are now in line with the best practice in the industry and well suited for our future requirements. (author)