Windscale Pile 1: A New Approach

One of the most technically challenging reactor decommissioning projects in the UK, if not the world, is being tackled in a new way managed by a team lead by the United Kingdom Atomic Energy Authority. Windscale Pile 1, a graphite moderated, air cooled, horizontal, natural uranium fuelled reactor was damaged by fire in October 1957. De-fuelling, initial clean-up and isolation operations were carried out in the 1960’s. During the 1980’s and 90’s a successful Phase1 decommissioning campaign resulted in the plant being cleared of all accessible fuel and graphite debris and it being sealed and isolated from associated facilities and put on a monitoring and surveillance regime while plans for dismantling were being developed. For years intrusive inspection of the fire damaged region has been precluded on safety grounds. Consequently early plans for dismantling were constructed using pessimistic assumptions and worst case predictions. This in turn lead to technical, financial and regulatory hurdles which were found to be too high to overcome. The new approach utilises the best from several areas: • The design process incorporates principles of the US DoE safety analysis process to address safety, and adds further key stages of design concept and detail to generate concurrent development of a technical solution and a safety case. • A staged and gated Project Management Process provides for stakeholder involvement and consensus at key stages. • Targeted knowledge acquisition is used to minimise uncertainty. • A stepwise approach to intrusive surveys is employed to systematically increase confidence. The result is a process which yields the optimum solution in terms of safety, environmental impact, technical feasibility, political acceptability and affordability. The change from previous approaches is that the project starts from the hazards and associated hazard management strategies, through engineering concept, to design manufacture and testing of the resulting solution rather than starting with the engineer’s “good idea” and then trying to make it work, safely and at an affordable price. Progress has been made in making the intrusive survey work a reality. This is a significant step in building a realistic picture of the physical and radiological state of the core and in building confidence in the process.