Strengthening basic nuclear safety
Agency activities in nuclear safety concentrated on supporting intergovernmental efforts to strengthen nuclear safety worldwide. The focus was on preparing for the implementation of the Convention on Nuclear Safety, fostering the exchange of information on safety issues, developing common safety standards, providing a variety of expert services and supporting co-ordinated research work in Member States.
The Convention on Nuclear Safety entered into force on 24 October 1996. In June, a third informal meeting of representatives of signatories and other interested States completed draft rules of procedure, financial rules for meetings of the Contracting Parties, and draft guidelines regarding the form and structure of national reports and on the review process under the Convention for consideration at the Preparatory Meeting of Contracting Parties in 1997. By the end of 1996, 65 countries had signed the convention and 32 countries had deposited instruments of ratification, acceptance or approval.
With the assistance of experts from regulatory, operating and engineering organizations, a report was prepared supplementing information issued earlier (in INSAG-4) by describing practices that have proved to be of value in establishing and maintaining a sound safety culture. It expands on the development and improvement of safety culture as a dynamic, progressive process, detailing three stages of development: safety based on rules and regulations; good safety performance becoming an organizational goal; and steady improvement of safety performance. Practices are divided into general practices pertaining to certain values needed for continuous evolution of improved safety performance, and specific practices covering a wide range of activities including analysis of events, the regulatory approach, employee participation and safety performance measures. Recommendations emphasize the importance of consistent commitment to improving safety, the learning process and the role of the regulatory body.
Safety is a topical issue in the development of fusion reactors. Recent developments in fusion safety were reviewed and discussed at a meeting in Naka, Japan. The topics addressed were safety activities within national and international fusion programmes, including selected experimental studies, safety analysis and assessment methods, and considerations relating to magnet and seismic safety, recycling of activated materials and disposal of radioactive waste. Although fusion safety studies have been under way for over two decades, continuing research efforts are required on the optimization of protection as fusion technology develops. Exploration of specific aspects, such as the generation of radioactive dust in fusion reactors, are gaining importance.
In order to advise on the revision of all of the Agency's nuclear safety standards, the Nuclear Safety Standards Advisory Committee (NUSSAC) held its first two meetings in 1996. In the revision process, documents dealing with operational safety will receive the highest priority. A plan for the revision of documents dealing with design and siting was agreed upon. As quality assurance and governmental organization were considered important for nuclear, radiation and waste safety, and not just for nuclear installations, the Agency's Advisory Commission on Safety Standards (ACSS) initiated work on the revision of the existing Code on governmental organization to broaden its scope and cover all areas of safety.
As a result of the fourth series of peer discussions of senior regulators from 23 Member States on regulatory practices, a report was prepared on measures needed to assess the safety of existing nuclear power plants and the effectiveness of regulations and regulatory actions. The discussions addressed the merits of both the 'prescriptive' and the 'performance based' regulatory approaches. A combination of the two was found to be desirable, with a trend towards the performance based approach, which focuses on results obtained through the operating organization's activities to demonstrate compliance with regulations. The peer discussions also yielded a number of good safety practices.
Assistance through a technical co-operation model project to the nuclear regulatory authority of Slovakia (SNRA) in the areas of emergency preparedness, radioactive waste control, quality assurance, site inspection, periodic safety assessment and training had a substantial impact on the ability of SNRA to become an independent regulatory body. The experience acquired was used in providing assistance to the nuclear regulatory bodies of the Czech Republic and Hungary, and in drafting programmes of assistance to the regulatory bodies of Armenia and Ukraine.
Upon request, the Agency has been providing assistance and a wide range of services aimed at establishing and enhancing nuclear safety in Member States. Reviews revealed that all organizations involved in nuclear safety have become increasingly aware of the need to consider and implement corrective measures to meet general safety objectives, and to take account of current trends towards plant life extension and decommissioning. To improve the implementation of nuclear safety assistance programmes and services, a new strategy for providing assistance to Member States was developed, incorporating greater integration of safety related activities. Following an initial approach from a Member State for nuclear safety assistance, a review of the actual situation in the Member State will be carried out against a pre-defined and accepted international 'reference situation'. The comparison will be in the form of an overview to identify general areas where the Agency could provide the maximum benefit to Member States such as establishing and strengthening regulatory bodies, training personnel, providing safety review missions and endorsing assessment capabilities.
Engineering safety activities continued to focus on ageing, fire and seismic safety, and on the safety of plants built to earlier standards. A CRP on the management of ageing of concrete containment buildings concluded with the preparation of a report presenting information on potential degradation mechanisms, areas susceptible to degradation and methods for detecting and mitigating the effect of ageing. This information provides a technical basis for implementing plant specific ageing management programmes. Instrumentation and control and power cables are critical nuclear power plant components from both the safety and plant life perspectives. Work under phase I of a CRP on the management of ageing of in-containment instrumentation and control cables was completed, resulting in recommendations for ongoing qualification and condition monitoring methods in nuclear power plants. Phase II of this CRP, focusing on the development and validation of the most promising condition monitoring techniques, was started.
A safety report on the assessment of the overall fire safety arrangements of nuclear power plants was issued and two reports, one on fire safety during the operation of nuclear power plants and the other on the preparation of fire hazard analyses for such plants, were completed. A fire safety mission visited the Temelin nuclear power plant in the Czech Republic.
Within the scope of a CRP on benchmark studies for the seismic analysis and testing of WWER type nuclear power plants, a second full scale dynamic test was conducted for the reactor building of Unit 5 of the Kozloduy nuclear power plant (WWER-1000). Experts are involved in the prediction of test results using state-of-the-art analytical methods and simplified procedures. A detailed comparison of their findings will be completed in 1997. Assessments of the seismic input for many WWER plants have been completed and certain upgrades have already been implemented in these plants. Delays were experienced in the work schedule for structural upgrades, which require substantial effort and financial resources. As a result, expert missions to review these upgrades were also facing delays. Nevertheless, a total of nine reviews were conducted for WWER or other types of plants in relation to siting and external hazards under the Agency's Engineering Safety Review Services.
The final report of a regional project on evaluation of the safety aspects of WWER-440 model 213 nuclear power plants was published. The project, initiated in 1991 at the request of the Atomic Energy Commission of the former Czechoslovakia, was designed to co-ordinate assistance in studying selected aspects of the safety of WWER-440/213 plants. It integrated the results of national activities carried out in the Czech Republic, Hungary, Slovakia and Ukraine. The report includes a comprehensive description of assessments. General conclusions in the report centre on the safety of plants based on the WWER-440 model 213, particularly of the Bohunice V2 reference plant. Detailed responses to the comments of an international peer review relating to design and beyond design basis accident analysis and management are also included in the report.
MELSIM, a severe accident simulation training system comprising a workstation with a personal computer and networking developed by the Agency for the Czech Dukovany and Chinese Qinshan nuclear power plants, was demonstrated during the General Conference. The simulation is based on the US Nuclear Regulatory Commission's severe accident analysis computer code MELCOR.
Operational Safety Review Team (OSART) missions, which are comprehensive on-site operational safety reviews, continued to be conducted at the request of Member States. Follow-up visits, routinely conducted 12 to 18 months after an OSART mission, indicated a high rate of completion or satisfactory progress on recommendations and suggestions made by the OSART mission. The OSMIR database includes the results of 32 OSART missions and 15 follow-up visits conducted during the last five years; by the end of 1996, 93 copies of OSMIR had been disseminated to the nuclear industry.
Peer reviews of self-assessments continued. In 1996, Assessment of Safety Significant Events Teams (ASSETs) performed four such peer reviews, conducted seven training seminars to familiarize plant staff with ASSET guidance for plant self-assessment of operational safety performance, and organized a regional training course on operational safety assessment techniques in Madrid, Spain.
In order to assist countries in making the best and most effective use of the Incident Reporting System (IRS), a joint IAEA-OECD/NEA Advisory Committee (IRRS-AC) was constituted. At its first meeting in March in Vienna, this Committee made recommendations on the operation, maintenance and improvement of the IRS.
A report summarizing national practices on the use of unusual events in operational experience feedback was issued to supplement earlier information. The full text and image database, known as AIRS (Advanced Incident Reporting System), containing approximately 2500 national reports, underwent trial use by participating Member States of the IRS. Several topical studies were performed in the framework of IRS activities: events connected with vendor/contractor activities, events during low power and shutdown modes and single human failures resulting in significant degradation of safety equipment.
The second mission of a new module of safety services, peer review of the national operational experience feedback processes, was organized in November in Ukraine. Important events and generic problems reported to the IRS were summarized in the IRS Highlights 1995-1996. National presentations at two IRS meetings in 1996 (the Joint Meeting to Exchange Information on Recent Events in Nuclear Power Plants and the Annual Meeting of the IRS National Co-ordinators) revealed that recent events at nuclear power plants occurred as a result of problems with batteries, valves, fuel and control rods, pressure tubes and signal systems, and that foreign material intrusion and corrosion phenomena continue to be a source of concern.
Over 270 research reactors are currently operating around the world. To promote the exchange of experience on the safety of these reactors, preparations were made to launch an Incident Reporting System for Research Reactors (IRSARR), including the development of a computerized data storage system with an associated user's guide, and the compilation of initial data selected from reported incidents. Safety related advisory missions visited research reactors in five Member States (Colombia, Egypt, the Syrian Arab Republic, Thailand and Zaire). A special meeting of research reactor managers and regulators from nine Member States holding project facility agreements with the Agency convened in Vienna to discuss their experience with such missions and to suggest improvements. The need to share information on the major findings of all individual missions was expressed. Information on good practices identified and recommendations made for the further improvement of research reactor safety could be shared through a comprehensive electronic database.
International Peer Review Service (IPERS) missions visited two nuclear power plants in 1996: Temelin in the Czech Republic and Atucha I in Argentina. In addition, a pre-review for the probabilistic safety assessment (PSA) of Ulchin Units 3 and 4 in the Republic of Korea was carried out.
One of the IPERS missions included a review of the Level 2 PSA, which considers accident progression within the plant and assesses the characteristics of potential releases of radioactive material to the environment during severe accidents. It was found that specific features of the particular containment design can significantly influence the course of events during severe accidents. The review showed that the information and results from a Level 2 PSA are increasingly used for studying severe accident management measures and features that are intended to terminate or mitigate severe accidents.
A CRP on methodologies for the optimization of surveillance testing and maintenance of safety related equipment at nuclear power plants was launched. The overall objectives are to develop strategies and exchange experience with regard to: the improvement and optimization of the maintenance and test programmes for safety related systems and equipment; techniques for safety specific optimization of maintenance and surveillance testing; definition of acceptance criteria; and regulatory acceptance of the optimization process. Another activity was the completion of a report on regulatory oversights of safety related maintenance activities at nuclear power plants.
Member States operating WWER and RBMK reactors requested a review of the completeness of proposed safety improvements for these reactors. It was found that the programmes of safety modifications developed by countries operating such plants are generally structured in response to deficiencies identified through Agency activities. Guidance was also provided for the resolution of the generic safety issues that were identified. The technical findings were compiled in a database which includes all identified safety issues. In addition, the plant specific status of the implementation of safety upgrades has been linked to the database on assistance projects established by the G24 Nuclear Safety Assistance Co-ordination secretariat in Brussels.
Guidelines were developed for accident analysis on the basis of the conservative approach normally used for licensing new plants. Studies were carried out on the use of best estimate methods to determine success criteria in PSAs and develop emergency operating actions. The goal is to ensure that plant specific accident analysis will be performed for each installation, including safety related hardware and software modifications.
The integrity of WWER reactor pressure vessels (RPVs), particularly in WWER-440/230 plants, remains a matter of concern. In addition to uncertainties in the vessel material properties, and delays in implementation of related necessary plant modifications, deficiencies were found in the pressurized thermal shock analysis (PTS) for RPV integrity assessment. Consequently, the demonstration of RPV integrity may not be conservative and the emergency operating procedures may not be adequate to guide the operator in the case of a PTS event. Guidelines on PTS analysis for WWER reactors were therefore developed and a CRP to provide a basis for judgement on the reliability of material properties data was established.
The International Nuclear Event Scale (INES) facilitates the communication and understanding of nuclear and other radiation incidents to the public. In 1996, 59 countries provided information on 66 events. Three incidents were classified as serious incidents (Level 3): one involved a spread of contamination in a nuclear power plant and two concerned radiation exposure over the dose limit in non-reactor installations. Ten Level 2 incidents were reported, the majority of which involved some degradation of provisions for defence in depth. Work was undertaken on simplifying the INES procedure for rating the severity of defence in depth degradations, developing a computerized INES rating procedure and gaining a better understanding of the use of INES at the national level.