The 2002 Drigg post-closure safety case: implementation of a multiple factor safety case

British Nuclear Fuels plc (BNFL) owns and operates the Drigg disposal site, which is the UK's principal facility for the disposal of low level radioactive waste (LLW). Disposals are carried out under the terms of an authorization granted by the UK Environment Agency (the Agency). The Agency periodically reviews the authorization to take account of new information and any revisions to regulatory requirements. In September 2002 new Operational Environmental and Post-Closure Safety Cases (OESC and PCSC respectively) were submitted to the Agency to support the next authorization review. The OESC assesses radiological safety aspects up until closure of the site, including a post-operational management phase, whilst the PCSC considers the longer-term radiological safety. The Drigg disposal facility has been operational since 1959. For the first 3 decades of operations, disposals were solely by tumble tipping wastes into excavated trenches. This was phased out in favour of vault disposal and disposals to the trenches were completed in 1995. The first vault (Vault 8) commenced operations in 1988 and construction of future vaults is planned up to the estimated end of disposal operations in about 50 years time. This paper describes the main components of the 2002 Drigg PCSC and how they relate to each other. Central to the safety case is a systematic comprehensive post-closure radiological safety assessment (PCRSA). However, the importance of the more qualitative aspects of the safety case, including a demonstration of optimisation, is also highlighted. In addition, other confidence-building activities which are key to developing and presenting the safety case are discussed. (author)