CSNI validation matrix for the assessment of thermal-hydraulic codes for BWR LOCA and Transients

As Italian representative inside the thermal-hydraulic task group of Organization for Economic Cooperation and Development (OECD) / Nuclear Energy Agency (NEA) / Committee on the Safety of Nuclear Installations (CSNI), the current author contributed to a preliminary activity which ended up in an OECD publication. The framework of the activity is assessment and validation of system thermal-hydraulic codes. Preliminary steps were taken to fix the requirements for the validation. Importance was given to the experimental data and to the scaling processes. The document evolved in about five years to the form a pillar document in the area of nuclear thermalhydraulics. Coauthors were top level researches and specialists working in the area of nuclear thermal-hydraulics at the time. The present report is the second one and together with the first report (issued in 1984) shows the maturing of the ideas for ensuring a suitable qualification level for the system thermal-hydraulic codes

Effectiveness of Core Exit Thermocouple (CET) Indication in Accident Management of Light Water Reactors

The working group on Analysis and Management of Accidents (WGAMA) of the Committee on the Safety of Nuclear Installations (CSNI) of OECD-NEA had a task on the effectiveness of CET indication in accident management (AM) of light water reactors (LWR). The task collected and reviewed the design basis of CET application for AM procedures through a survey of the CET use in the NEA member countries, and reviewed pertinent experimental results from such test facilities as LOFT, ROSA/LSTF, PKL and PSB-VVER focusing on the time delay in CET from core temperature rise. Scaling issues were discussed considering extrapolation of experimental results to LWR. This paper summarizes major outcomes of the task and indicates possible future work.JRC.F.5-Nuclear Reactor Safety Assessmen

Core Exit Temperature Effectiveness in Accident Management of Nuclear Power Reactor

Core exit temperature (CET) measurements play an important role in the sequence of actions under accidental conditions in pressurized water reactors (PWR). Given the difficulties in placing measurements in the core region, CET readings are used as criterion for the initiation of accident management (AM) procedures because they can indicate a core heat up scenario. However, the CET responses have some limitation in detecting inadequate core cooling and core uncovery simply because the measurement is not placed inside the core. Therefore, it is of main importance in the field of nuclear safety for PWR power plants to assess the capabilities of system codes for simulating the relation between the CET and the peak cladding temperature (PCT)

Deterministic Safety Analysis for Nuclear Power Plants. IAEA Specific Safety Guide

The IAEA’s Statute authorizes the Agency to establish safety standards to protect health and minimize danger to life and property — standards which the IAEA must use in its own operations, and which a State can apply by means of its regulatory provisions for nuclear and radiation safety. A comprehensive body of safety standards under regular review, together with the IAEA’s assistance in their application, has become a key element in a global safety regime. In the mid-1990s, a major overhaul of the IAEA’s safety standards programme was initiated, with a revised oversight committee structure and a systematic approach to updating the entire corpus of standards. The new standards that have resulted are of a high calibre and reflect best practices in Member States. With the assistance of the Commission on Safety Standards, the IAEA is working to promote the global acceptance and use of its safety standards. Safety standards are only effective, however, if they are properly applied in practice. The IAEA’s safety services — which range in scope from engineering safety, operational safety, and radiation, transport and waste safety to regulatory matters and safety culture in organizations — assist Member States in applying the standards and appraise their effectiveness. These safety services enable valuable insights to be shared and I continue to urge all Member States to make use of them. Regulating nuclear and radiation safety is a national responsibility, and many Member States have decided to adopt the IAEA’s safety standards for use in their national regulations. For the contracting parties to the various international safety conventions, IAEA standards provide a consistent, reliable means of ensuring the effective fulfilment of obligations under the conventions. The standards are also applied by designers, manufacturers and operators around the world to enhance nuclear and radiation safety in power generation, medicine, industry, agriculture, research and education. The IAEA takes seriously the enduring challenge for users and regulators everywhere: that of ensuring a high level of safety in the use of nuclear materials and radiation sources around the world. Their continuing utilization for the benefit of humankind must be managed in a safe manner, and the IAEA safety standards are designed to facilitate the achievement of that goal

Neutronics/Thermal-hydraulics Coupling in LWR Technology – CRISSUE-S WP3: Achievements and Recommendations Report

Controlled fission power has been utilised for electricity production worldwide in nuclear power plants (NPPs) based on light water reactor (LWR) technology for several decades. It has proven its efficiency and safety during these years and has manifested itself as a reliable and durable energy source. The foundation pillar in the peaceful utilisation of fission nuclear power has always been the strong emphasis on safety. Safety has been accomplished by continuously pursuing in-depth reviews and re-evaluation of safety-related issues incorporating findings from ongoing nuclear safety research activities worldwide. Specific requirements have been deployed at the design and in the permissible operation conditions of the NPPs in order to always ensure adequate margins against critical system conditions, thus preventing the occurrence of accidents. It is realised that as new findings and analysis capabilities become available safety will be increased, and it is further possible that the safety margins presently employed will eventually be relieved (decreased) without compromising the actual safety. Prevention and mitigation measures, however, must be properly balanced with cost-reduction needs. A thorough knowledge of fundamental issues – in the present case the interaction between neutronics and thermal-hydraulics – allows pursuing the goal of ensuring safety at reasonable costs. Consistent with this goal, the CRISSUE-S project was created with the aim of re-evaluating fundamental technical issues for LWR technology. Specifically, the project seeks to address the interactions between neutron kinetics and thermal-hydraulics that affect neutron moderation and influence the accident performance of the NPPs. This is undertaken in the light of the advanced computational tools that are readily available to the scientific community today. The CRISSUE-S activity deals with the control of fission power and the use of high burn-up fuel; these topics are part of the EC Work Programme as well as that of other international organisations such as the OECD/NEA and the IAEA. The problems of evaluating reactivity-induced accident (RIA) consequences and eventually deciding the possibility of NPP prolongation must be addressed and resolved. RIAs constitute one of the most important of the “less-resolved” safety issues, and treating this problem may have significantly positive financial, social and environmental impacts. Public acceptance of nuclear technology implies that problems such as these be satisfactorily resolved. Cross-disciplinary interaction (regulators, industry, utilities and research bodies) and co-operation within CRISSUE-S provides results which can directly and immediately be beneficial to EU industry. Concerning co-operation at an international level, the participation of the EU, former Eastern European countries, the USA, and observers from Japan testify to the wide interest these problems engender. Competencies in broad areas such as thermal-hydraulics, neutronics and fuel, overall system design and reactor surveillance are needed to address the problems that are posed here. Excellent expertise is available in specific areas, while limited knowledge exists in the interface zones of those areas, e.g. in the coupling between thermal-hydraulics and neutronics. In general terms, the activities carried out and described here aim at exploiting available expertise and findings and gathering together expert scientists from various areas relevant to the issues addressed. Added value for the CRISSUE-S activity consists of proposing and making available a list of transients to be analysed by coupled neutron kinetics/thermal-hydraulic techniques and of defining “acceptability” (or required precision) thresholds for the results of the analyses. The list of transients is specific to the different NPP types such as PWR, BWR and VVER. The acceptability thresholds for calculation precision are general in nature and are applicable to all LWRs. The creation of a database including the main results from coupled 3-D neutron kinetics/thermal-hydraulic calculations and their analysis should also be noted. The CRISSUE-S project is organised into three work packages (WPs). The first WP includes activities related to obtaining and documenting relevant data. The second WP is responsible for the state-of-the-art report (SOAR), while the third WP concerns the evaluation of the findings from the SOAR and includes outcomes of the entire project formulated as recommendations, mainly to the nuclear power industry and to regulatory authorities. The present report is the result of the third WP and summarises the results, selects the most important findings and indicates the industry position on related subjects. It emphasises achievements, highlights the most important conclusions reached in the second WP and briefly refers to the first WP. A comprehensive report such as the present one, composed of contributions from the different CRISSUE-S participating organisations, unavoidably implies non-homogeneous treatment of the various topics, although an effort was made to provide consistency between the various sections. However, it is realised that the adopted level of detail is not commensurate with the safety relevance or the technological importance of the issues discussed. The report has been written to accomplish the objectives established in the contract between the EU and its partners. Expected beneficiaries include institutions and organisations involved with nuclear technology (e.g. utilities, regulators, research, fuel industry). In addition, specific expected beneficiaries are junior- or senior-level researchers and technologists working in the considered field of research and development and application of coupled neutron kinetics/thermal-hydraulics. Six plenary CRISSUE-S meetings took place over the course of the project implementation period. The meetings were held at: University of Pisa, Pisa, Italy, 25-26 February 2002 (kick-off meeting). OECD/NEA, Issy-les-Moulineaux, Paris, France, 5-6 September 2002. Technical University of Catalonia (UPC), Barcelona, Spain, 23-24 January 2003. SKI, Stockholm, Sweden, 26-27 June 2003. European Commission, Luxembourg, 12 November 2003 (status information meeting). University of Pisa, Pisa, Italy, 11-12 December 2003 (final meeting). An Internet site has been established at the University of Pisa and has been kept alive during the project lifetime (2001-2003). The address is www.ing.unipi.it/crissue_s. The site also contains the discussion records of the six meetings. The importance of the CRISSUE-S project has been expressed by the OECD/NEA Nuclear Science Committee. This interest has also been emphasised by the OECD/NEA Committee on the Safety of Nuclear Installations, as the project discusses many of their activities. It was agreed that the CRISSUE-S reports be published by the OECD/NEA as its contribution to the project. This report was produced by the members of the CRISSUE-S project for use within their organisations. The present version is being made widely available for the greater benefit of organisations and experts working in the nuclear power area. Several of the graphics in the report are in colour; interested readers can request a colour version of the report on CD-ROM from the NEA