[en] The Thermal Oxide Reprocessing Plant (THORP) at the Sellafield nuclear licensed site carried out its final commercial shear of spent nuclear fuel in November 2018, since when the facility has undergone rundown prior to cessation of operations. The Magnox Reprocessing Facility (MRF) is also due to cease operating, around the end of 2020. Following the cessation of spent fuel reprocessing, the facilities and supporting infrastructure will transition into Post Operational Clean Out (POCO), which will become an increasingly significant portion of Sellafield Limited's (SL) activities. POCO is defined as the set of activities undertaken directly after a nuclear facility comes to the end of its operational life, in order to place the plant in a suitable state for the subsequent decommissioning steps. The decommissioning strategy at SL is for deferred dismantling of these facilities, which will be subject to a period of Surveillance and Maintenance (S and M) following completion of POCO. This paper outlines the development and implementation of a regulatory strategy for POCO activities at the Sellafield site by the Office for Nuclear Regulation (ONR), the independent nuclear safety, transport and security regulator in the United Kingdom. The paper also describes how this regulatory strategy is applied to nuclear installations undergoing transition into POCO and subsequent decommissioning. ONR works jointly with the Environment Agency, as the environmental regulators in England, to ensure that matters relevant to them have been duly considered. In developing a regulatory strategy, ONR has taken a site-wide approach, moving away from regulation on a facility-by-facility basis, to promote consistency, as well as maximising efficiency and effectiveness. The aim of this integrated approach was to prevent complications during future decommissioning and dismantling that have been experienced previously at similar facilities in France. The strategy recognised that once reprocessing operations are concluded, the hazard present will be reduced significantly, which provides the opportunity for ONR to consider how best to deliver a proportionate approach to regulatory interventions. Once POCO has been completed and the facility has transitioned into a period of S and M, the scale and frequency of ONR's interventions will reduce, commensurate with the safety case covering the remaining hazard and activities associated with maintaining the facility prior to final decommissioning. This approach allows ONR to consider risks holistically, considering the full life cycle of the facility and by taking due account of the interdependencies between facilities across the site. The strategy also aligns with existing regulation of high hazard and risk reduction activities, which remain ONR's top priority. As SL progresses with POCO activities in THORP and across the rest of the site, ONR will review its regulatory strategy to ensure that the intended safety benefits are realised. (authors)

[en] Short communication. 1 ref

[en] Full text: The humanised CDR-grafted anti-Lewis Y monoclonal antibody (hu3S193) was developed for targeting Lewis Y expressing epithelial tumours such as cancer of the breast. We are exploring the potential use of smaller molecular size versions of this intact antibody. The faster blood clearance of diabody and F(ab')₂ molecules may be advantageous in achieving optimal and rapid tumour uptake for diagnostic and potentially therapeutic applications. The development of the scFv-S residue linker construct (diabody) is a collaborative venture with CSIRO. This protein is expressed in the bacterial secretion vector pPOW3 and soluble product isolated, without refolding processes. The F(ab')₂ fragment was obtained by pepsin digest of parental hu3S193. To facilitate evaluations, the radiometal indium-111 was used to label CHX-A-DTPA chelated F(ab')₂ and diabody. The immunoreactivity of the radiolabelled constructs was 58.6% and 41.3%, while the K, was 5.33x10⁶μM and 1.68x10⁶μM for the F(ab')₂ and diabody respectively. Radioconjugates were injected into BALB/c nude mice bearing Lewis Y-positive MCF-7 tumours, and biodistribution properties and gamma camera imaging were performed at various time points post injection. Prominent kidney uptake was observed with both constructs. The uptake of radiolabelled F(ab')₂ in xenografts was maximal at four hour p.i. 14.5±1.0%ID/g, while the diabody peaked at one hour p.i. - 4.7±0.6%ID/g. Diabody and F(ab')₂ tumour:blood ratios at four hours were 5:1 and 2:1, respectively and increased to 40:1 and 70:1, respectively at 48 hours. Further investigations with small molecular weight antibody constructs are being pursued. Copyright (2000) The Australian and New Zealand Society of Nuclear Medicine Inc