Practical Experience with Remediation of a Former Active Handling Building Site in the United Kingdom - 9058

Since the year 2000, Nuvia has been contracted to carry out the decommissioning of a former Active Handling Building A59 on the United Kingdom Atomic Energy Authority (UKAEA) site at Winfrith in Dorset. This is in support of UKAEA's mission, which is to carry out environmental restoration of its nuclear sites and to put them to alternative uses wherever possible. Latterly, a new body, the Nuclear Decommissioning Authority (NDA), has become responsible for managing the UK decommissioning legacy and since 2004 UKAEA has been contracted to the NDA to deliver decommissioning work at Winfrith and other UK sites. The earlier operations concentrated mainly upon the clearance and decontamination of two heavily shielded suites of caves, originally used to carry out remote examination of irradiated nuclear fuel elements, together with a range of within-building support facilities. In 2006 the main containment building structure was demolished as well as the two suites of caves, leaving the base slab for final removal. The demolition contract with UKAEA required removal of the base slab and recovery for disposal of a quantity of encast, internally contaminated items such as secondary active drain pipes, active ventilation ducting and more than 100 steel mortuary tubes set up to 6.6m deep into the slab. The scope of the work also required the underlying soil to be carefully monitored for the presence of radioactive contamination and, if detected, its remediation to an end state suitable for un-restricted use without planning or nuclear regulatory controls. These latter operations form the basis of this paper, which reviews some of the significant tasks undertaken during the process and also sets out the development of a robust waste monitoring strategy for the recovered concrete debris ahead of its disposal. This has enabled more than four thousand tons of debris to be classified as SOLA (Substance of Low Activity), allowing disposal to landfill. This will include details of the development of a system, including a bag monitoring procedure, used to support the classification of some concrete debris as SOLA material. Currently, the base slab has been completely demolished and all encast items recovered for disposal, including the deep mortuary tubes. This was only achievable by the installation of a dewatering system which enabled safe excavation. These latter operations were challenging owing to the significant depth of some of the items to be removed and the unconsolidated sediments underlying the site. The paper will discuss the main issues involved with the remediation of features within the concrete slab and the underlying soils. These will include comments on the ground conditions, soil structures, groundwater levels and problems associated with provision of waste storage areas and their various impacts upon project progress. Several challenging areas of the slab such as the original decontamination bay and pressurised suit area sump have been removed and the paper will describe how the underlying soils were monitored using a Groundhog TM based system ahead of final remediation and waste sentencing.