Fourth Annual Two-Day Conference on Probabilistic Safety Assessment in the Nuclear Industry

Abstract

Royal Lancaster Hotel, London, 29-30 November 1995 The purpose of the conference, organised by IBC Technical Services, was to raise issues concerning the use of probabilistic safety assessment (PSA) as a tool for optimising the safety of existing and planned nuclear reactors. A summary of presentations is given below. An overview of IAEA guidance on the safety assessment of new nuclear installations and those built to earlier safety standards, with particular reference to the use of PSAs, was provided by Friedrich Niehaus (IAEA, Austria). In addition, guidance on the development of safety principles for the design of future nuclear power plants was described. A view of PSA from a regulator's perspective, specifically that of HM NII, was given by Geoff Grint (Health and Safety Executive). The role of PSA as one part of a plant safety case was outlined and the completeness to which PSA is expected to account for contributions to risk was described. In addition, the usefulness of PSA in support of plant modifications, assessment of maintenance procedures, and for the monitoring of risk over time was described. The use of PSA based computer programs for use in accident consequence assessment was described by Dr J A Jones (NRPB). These programs model atmospheric dispersion and deposition of radioactive material and calculated doses to the exposed population according to the distribution of radioactivity. A methodology for the identification and assignment of functions to man and machine was described by Alastair Fewins (NNC Ltd). Two practical examples of the application of the methodology were given. A structured approach used in the peer review of safety documentation in support of the Naval Nuclear Propulsion Programme (NNPP) for the Ministry of Defence was described by Colin Welsh (Rolls Royce and Associates Ltd). Key issues concerning the use of PSAs for operating Nuclear Power Plants (NPPs) were outlined by Dr Bert Eendebak (N.V. KEMA, The Netherlands). Special attention was given to the use of PSAs for the assessment of NPPs of a standardised type and for the review and selection of proposed modifications for NPPs. Examples were given for two existing NPPs in The Netherlands. The problems and benefits of formal fire hazard assessment combined with Probabilistic Risk Assessment (PRA) techniques were reviewed by Paul Scott (Ove Arup and Partners). In addition the problems of improving fire safety with a limited safety budget were considered. Practical findings in relation to ageing nuclear power plants were detailed and a simple screening methodology to be used prior to a detailed Fire Hazard Analysis was proposed. A number of `non-nuclear' organisations are in the process of adopting human reliability and human factors analyses in their safety assessments. A procedure for addressing human factors issues through human reliability analysis was given by Bill Gall (DNV Technica) and the link between human factors and safety management was illustrated. A PSA study was commissioned under the CEC's PHARE programme to assess the level of safety of the reactors at Bohunice V-1, the benefits of modifications which were already committed, and to recommend possible areas for improvement. The scope of the PSA model and the key results obtained were described by Mike Lewis (Electrowatt Engineering Services (UK) Ltd). BNFL's experience in preparing and implementing effective PSAs for existing nuclear chemical plants at Sellafield was outlined by Alec Bounds (British Nuclear Fuels plc.). The methodologies by which fault identification is achieved and by which fault frequencies and consequences are determined were also described. Examples were given, by Ian Kempsell (BNFL Engineering Group), of the use of PSAs by BNFL in the planning of decommissioning operations. In the case of an ILW silo, optimum solutions were derived for seismic enhancement and control of a potential hazard for fire. In the case of a second waste silo, the lowest risk crane replacement option was selected. An overview of NNC's involvement in PSAs and PSA related work on reactors in Eastern Europe and the former Soviet Union was provided by John Walker (NNC Ltd). The purposes of these PSAs include quantification of the safety levels achieved by the plants and the establishment of reliability targets for replacement equipment where there is a need for modification. The use of PSA codes for the assessment of the environmental consequences of possible accidents at the Paks Nuclear Power Plant (Hungary) was described by Laszlo Koblinger (KFKI Atomic Energy Research Institute, Hungary). M Gooding