More than fifty countries have signed the Convention on Nuclear Safety since it was opened for signature in September 1994. The Convention applies to land based civil nuclear power plants and obliges Contracting Parties to establish and maintain proper legislative and regulatory frameworks to govern safety. Through the Convention, States commit themselves to the application of fundamental safety principles for nuclear installations and agree to participate in periodic peer review meetings to submit national reports on the implementation of their obligations.
This year has confirmed the general interest of Member States in the Agency's nuclear safety review services, with continuing requests in particular for OSART and ASSET missions. Follow-up missions are also considered useful as confirming implementation of solutions to safety problems previously identified. The number of site and seismic review missions has increased; these missions are linked in many cases to safety re-evaluations of plants built to earlier standards. Since fire hazards and fire protection have proved to be of concern for existing nuclear power plants, fire safety missions are now being performed at the request of Member States.
The Agency has continued its programme on the safety of nuclear power plants built to earlier standards. Consensus has been reached on all safety issues on WWER and RBMK type reactors in close co- ordination with the G-24 Nuclear Safety Assistance Co-ordination Secretariat. For WWER-440/230 reactors, reviews of the safety upgradings and progress achieved have begun.
Fifty-four countries are now participating in the International Nuclear Event Scale (INES) information system, which was jointly developed by the Agency and the OECD/NEA. National officers of participating countries met in 1994 to review the systems operation, noting that the system is proving effective in facilitating common understanding and the prompt communication of events.
Work under a joint IAEA-UNDP initiative to strengthen nuclear and radiation safety infrastructures in countries of the former USSR continued in three stages: collection of more detailed information through further fact-finding missions; preparation of country specific programmes; and preparation of assistance packages. Using the information from the fact finding missions, country specific programmes have been prepared for eight countries and are awaiting suitable donors.
A CRP on accident methodology validation could not be implemented owing to budgetary constraints.
Principles, criteria and standards for nuclear safety
A meeting of senior regulators was held during the regular session of the General Conference. The meeting included regulators from over forty countries with nuclear power programmes and covered the following topics: utilization of INES, the future direction of Agency safety services and the control of large radiation sources.
New 'Terms of Reference' were discussed to ensure proper understanding and interpretation by all members of the reconstituted Nuclear Safety Standards Advisory Group (NUSSAG),which met for the first time in 1994 with nine new members. It was noted that the Terms of Reference continued to give emphasis to NUSS and other Agency standards and included a requirement to give advice to the Agency on nuclear safety issues and programmes relevant to the regulatory process. It was concluded that NUSSAG should serve as a source of expert advice on regulatory matters, giving priority to providing guidance on the development, coverage and efficient implementation of NUSS.
The following NUSSAG taskgroups were formed:
With the intention of strengthening the Agency's contribution to ensuring radiation protection and nuclear safety, a database on regulatory organizations and practices in Member States (ROPDB) is being established by the Agency in co-operation with the OECD/NEA. This database lists the organizations that govern nuclear programmes, and describes the practices that ensure radiation protection and nuclear safety. Some 48 items have been classified and summarized, in five categories, i.e. general, the licensing process, regulatory inspection and enforcement, emergency preparedness and international co-operation.
The Agency, in fulfilment of its commitments to a joint initiative with UNDP to strengthen radiation and nuclear safety infrastructures in countries of the former USSR, has continued to collect detailed information through fact-finding missions and the preparation of country assistance programmes. Fact- finding missions were undertaken to Moldova, in April, and to Belarus, in May, making a total of eight missions to the countries of the former USSR. Visits to other countries are in the planning stage. On the basis of these missions, country assistance programmes were prepared for Belarus, Estonia, Kazakhstan, Kyrgyzstan, Latvia, Lithuania, Moldova and Uzbekistan.
Enhancing the performance of regulatory bodies and training in nuclear safety
The Agency organized an International Regulatory Review Team (IRRT) mission to China to carry out a review of the National Nuclear Safety Administration (NNSA). The objective of the mission was to obtain a clear understanding of the actual status of the NNSA and its effectiveness in meeting its duties. It was concluded that the initial challenges of organization and structuring the development of a consistent set of codes and regulations and the carrying out of licensing and commissioning activities for the Qinshan and Guangdong nuclear power plants had been met by NNSA.
Within the framework of a technical co-operation project aimed at strengthening regulatory bodies, the first co-ordination and programming meeting was held in April in Kiev, Ukraine, to assess the status and identify the needs and priorities for assistance through workshops, training courses, expert missions, fellowships and scientific visits. A regulatory assistance programme was established covering expert services for the development of national nuclear safety legislation, regulatory requirements for operational safety, commissioning and decommissioning, conduct of the licensing process and regulatory staff training.
Engineering aspects of site safety: Seismic and other external events
The final Research Co-ordination meeting of a CRP on seismic data for the siting and site revalidation of nuclear facilities was held in Tunis. A significant result was the establishment of a databank on this subject at ENEA, in Italy.
The second Research Co-ordination meeting of a CRP on a benchmark study for the seismic analysis and testing of WWER type nuclear power plants was held at the Kozloduy power plant in Bulgaria in June. As part of this CRP, full scale dynamic testing of the Paks nuclear power plant in Hungary was carried out. In addition, measurements were taken at more than 100 locations around the plant. These results will be used for benchmarking the analytical results from this CRP.
Safety aspects of ageing of nuclear power plants
Drafts of 11 safety practices reports on the assessment and management of the ageing of major nuclear power plant components were prepared by experts and reviewed in September at a Technical Committee meeting. These reports, dealing with major PAR, BAR and CANED components, are now being revised.
Activities in the area of fire safety were focused on the assessment of the implementation and effectiveness of fire prevention, detection and mitigation techniques and on guidelines on fire protection inspection. A Safety Practices document on the assessment of the implementation and effectiveness of the overall fire safety arrangements of nuclear power plants was finalized. A Safety Guide on fire safety during the operation of nuclear power plants was submitted to Member States for comments. Another Safety Practices document on the evaluation of fire hazard analysis for nuclear power plants has been submitted for publication.
Two fire safety missions were conducted in 1994: one to the Borssele nuclear power plant, Netherlands, and the other to the Medzamor plant in Armenia.
Application of insights from PSA to operational safety
With a growing number of regulatory bodies in the world requesting plant specific probabilistic safety assessments (PSAs) for every operating reactor, the regulatory use of PSA increased in many Member States. A Technical Committee meeting was held in December to discuss this topic. The evaluation of a questionnaire sent to Member States showed differences in the actual use of PSA. It was found that most of the countries were using PSA in support of more traditional safety assessment techniques to balance safety related decisions. Only a small number of more experienced countries were using PSA in connection with basic licensing. It was recommended that more concise guidance be developed, in particular for application to older reactors.
An IAEA-TECDOC, to be published as a result of a Technical Committee meeting on the identification of generic and plant specific safety issues based on PSA results, describes the experience and practices in this field, including the support given by PSA techniques. It was demonstrated that additional and important plant specific and generic safety issues can be identified on the basis of a systematic comparative evaluation and interpretation of PSA information and results from past PSAs.
The services of consultants were used to begin preparation of a guide on the use of PSA to optimize operational limits and conditions. This PSA application is attracting much interest worldwide and the methodology is mature enough to warrant the preparation of international guidance.
A comprehensive users manual for PSAPACK,a software package developed by the Agency, was finalized. This package contains the necessary tools to perform a level 1 PSA and, in addition, a module to apply the information and results of the completed PSA for operational safety management.
Complementing the users manual is a programmers manual that contains a detailed description of the software modules and their interfaces. This manual is used for adaptation and further development of the package by users.
Information on unusual events in nuclear power plants
Development began of a compendium of actions to be taken in response to events reported to the Agency's Incident Reporting System (IRS). In order to assist national organizations involved in IRS activity, special guidelines were developed to identify the causes of events reported to the IRS and for better reporting of human dominated occurrences in nuclear power plant events. To improve the ability of nuclear safety experts to draw conclusions from the collection of IRS national reports, the full text and an image database known as AIRS (Advanced Incident Reporting System) were developed. It is planned that this database will be available for trial use in the first half of 1995.
A document on national practices in operational safety experience feedback was prepared and will be issued as a supplementary document to Safety Series No. 93, Systems for Reporting Unusual Events in Nuclear Power Plants.
Systematic analysis of operational experience
A new initiative in IRS activities was the holding of a meeting to review and prepare an in-depth study of a single event at the international level, in this case the primary system coolant leak event at the Kola-2 nuclear power plant on 3 March 1994.
Safety performance indicators for nuclear power plants
The decreasing tendency in the reporting rate to the IRS was discussed at the annual meeting of IRS co- ordinators. The co-ordinators agreed that this was a serious threat to the objectives of the IRS. The need was stressed for personal commitment on the part of co-ordinators to meet the objectives of the system.
At a Technical Committee meeting held in November, the use of safety indicators for regulatory bodies was discussed and it was agreed that safety indicators could be efficiently used to monitor the safety level at nuclear power plants. Different levels of safety indicators were considered, including high level (top management) and low level (supervisory) indicators.
Operational Safety Review Team(OSART) services
During 1994, there were six OSART missions, including two safety review missions and seven follow-up visits. From 1983, when the first OSART mission was conducted, to the end of 1994, 77 missions to 62 power plant sites in 28 Member States had been completed and 30 follow-up visits had been carried out.
A fundamental review of the OSART programme was carried out using the services of consultants, including consideration of its place in the Agency's services with respect to the Convention on Nuclear Safety and means to ensure that the programme effectively meets the current needs of nuclear power plants and regulatory authorities.
A new database compiling OSART mission results was presented at a review meeting. The availability of the database on diskette and as a hard copy will improve the dissemination of OSART results within the nuclear community by facilitating access to and use of the results.
Assessment of Safety Significant Events Team (ASSET) services
In 1994, six ASSET review missions were carried out at nuclear power plants in Bulgaria (Kozloduy), Romania(Cernavoda), Russian Federation (Kalinin), South Africa (Koeberg)and Ukraine (Chernobyl and Zaporozhe). One follow-up mission was performed at the Balakovo nuclear power plant in the Russian Federation, while 17 training missions were undertaken in 12 countries.
The mission to the South Ukraine nuclear power plant, requested in October 1994, had to be postponed to January 1995 owing to a cholera epidemic in the region.
The cycle of ASSET missions to WWER-1000 nuclear power plants will be completed in 1995 with visits to the South Ukraine and Rovno plants. Theservices of consultants were used to compile the results of ASSET missions to the WWER-1000 plants already visited: Khmelnitsky, Kalinin, Balakovo, Zaporozhe and Kozloduy.
The ASSET Users Manual, derived from ASSET Guidelines: Revised 1991 Edition(IAEA- TECDOC-632), incorporates the latest refinements in ASSET analysis procedures. This manual is intended as a practical tool for: plant managers carrying out their own analysis of plant safety performance and producing the standard ASSET report for peer review missions; and members of ASSET teams performing analysis missions and drafting the standard ASSET report.
The ASSET option peer review was recommended for adoption at the June meeting of ASSET users. ASSET peer review missions do not require root cause analysis of plant safety performance deviations to be carried out by external experts, as needed for other options in the ASSET service. The plant management requests plant staff to carry out their own analysis according to the procedures of the ASSET Users Manual and produce the standard ASSET report, which is submitted to an international ASSET mission for peer review.
Engineering Safety Review Services (ESRS)
The review of the seismic of existing nuclear power plants continued to be the main focus of activities. The tectonic stability, seismic input and plant structures, components and distribution systems for the Kozloduy, Paks, Medzamor, Bohunice and Mochovce nuclear power plants continued to be reviewed. Interim results from seismic assessments and upgrading programmes were evaluated by the review teams.
A site review for the Temelin nuclear power plant in the Czech Republic continued, and a review of various siting issues was finalized.
Accident prevention and mitigation
Two CRPs related to accident management were completed, with the final reports prepared. A Technical Committee meeting on accident management procedures and guidance was held; a report on this was finalized and distributed and should be the basis of a publication in the IAEA-TECDOC series.
Development of safety standards for research reactors
Two drafts of Safety Guides on the commissioning of research reactors and on operational limits and conditions for research reactors were completed and submitted to Member States for comments. The first document provides guidance on the safety aspects of the commissioning process for new research reactors, as well as the recommissioning process after major reactor modifications, or the commissioning of new experiments having major safety significance. The second document provides guidance on the selection of operating conditions, which include safety system settings, limiting conditions on equipment and operational characteristics of the reactor, and surveillance and administrative requirements.
Implementation of safety standards for research reactors
Three Integrated Safety Assessment of Research Reactor (INSARR) missions visited Indonesia, Jamaica and Mexico in 1994. In Indonesia, the Triga Mark II (1 MW) research reactor at Bandung and Triga Mark II (100 kW) at Yogyakarta were visited. The mission made several recommendations regarding the updating of safety documentation. In Jamaica, the team reviewed a 20 kW Slowpoke research reactor and in Mexico a 1 MW Triga Mark III reactor and two subcritical assemblies. Recommendations were made to enhance the overall operational safety of these research reactors.
Conduct and review of PSAs
During 1994, there were five International Peer Review Services (IPERS) PSA review missions and one pre-review mission. The reviews considered PSAs for nuclear power plants in Bulgaria, Hungary, the Republic of Korea, Romania, Slovakia and Slovenia. They were conducted by international reviewers from regulatory bodies, operating organizations, consulting companies and nuclear power plant manufacturers. A focus of a major part of the reviews was on PSAs recently developed for WWER type nuclear power plants, including the first one for a WWER-1000. One of the reviews considered the IPE (individual plant examination) type PSA for the Yonggwang 3 and 4 nuclear power plants in the Republic of Korea.
The IPERS reviews are conducted according to procedures given in the document Procedures for Conducting Peer Reviews of Probabilistic Safety Assessment: Guidelines for the IPERS Programme(IAEA-TECDOC-543), which was issued in 1990. A revision of this document was finalized to include experience gained from completed missions, level 2 and level 3 PSA techniques and progress made in PSA methodology and techniques.
One topic attracting great interest is shutdown PSA. The final draft of a shutdown PSA methodology guide was approved at a Technical Committee meeting held in Arnhem, Netherlands,in November. The document will be published in the Agency's Safety Series. Also discussed at this meeting was the current status of the development of shutdown PSA worldwide. A status report was prepared and will be published in 1995.
A Technical Committee meeting on advances in reliability analysis for PSA contributed to the preparation of a status report on the state-of-the-art of PSA methods and applications. A comprehensive review was also carried out of the status of PSA activity in eastern Europe. The review indicated that a major effort is currently under way to prepare PSAs for nuclear power plants in this region.
Safety impact of human actions
In September, an Assessment of Safety Culture in Organizations Team (ASCOT) review took place in parallel with the ASSET mission to the Koeberg nuclear power plant in South Africa. In general, a strong effort to promote and enhance safety culture was found at this plant. An indication of this was the commendably open interface with the regulatory body, and the Koeberg plant management's commitment to achieve and maintain high standards of safety.
A Technical Committee meeting on experience with strengthening safety culture in nuclear power plants was organized in June. The purpose of the meeting was to exchange experience in the area of safety culture and to encourage agreement on a common position on specific topics. The papers presented at the meeting covered a wide range of topics, including experience with assessing and monitoring safety culture, as well as practical techniques for changing and improving the safety culture of organizations. A report, which will be published as an IAEA-TECDOC, addresses the following topics: the regulatory interface and its effect on safety culture; implementing good safety culture in the nuclear industry; and the contractor’s safety culture.
Computer based techniques for the man-machine interface
A CRP on the development of safety related expert systems was completed. The various topics in the CRP concerned hazard identification, emergency operating procedures, modelling nuclear power plant behaviour during transients, verification and validation, as well as diagnosis, human factors and PSA. The results of the CRP indicate that expert systems can be used for safety related applications. However, before implementation in nuclear installations, user acceptance and regulatory concerns must be dealt with.
Reliability of hardware
The Agency's Component Reliability Database continued to be an important source of data for PSA and safety analysis. The database will be expanded in the future to include common cause failure data. A technical document containing component failure data collected at 15 research reactors in 10 countries was prepared. This document is expected to become a major source of data for research reactor safety studies worldwide.
Safety aspects, principles and criteria for future nuclear power plants
In response to comments from the International Nuclear Safety Advisory Group (INSAG), the draft of a document on the development of safety principles for the design of future nuclear power plants was revised at an Advisory Group meeting and by consultants. This document was prepared in response to General Conference Resolutions GC(XXXV)/RES/553 and GC(XXXVI)/RES/582. The document presents two complementary technical objectives for future nuclear power plants, the first applying to all plants and the second intended primarily for future nuclear power plants. The first technical safety objective addresses the prevention and mitigation of accidents, both within and beyond the traditional deterministic design basis, with its critical focus on the objective of protecting public health and safety. The second complementary design objective has as its focus the minimization of off-site effects. Explicitly considered are certain severe accidents in the design of the plant -- ‘severe accidents addressed in the design’.
A survey was carried out using the services of consultants on the safety aspects of designs for future LWRs (innovative reactors). The term innovative is used in accordance with the definition developed by the Agency referring to reactors with radical changes in safety systems for which prototype demonstrations are feasible. Among the innovative designs considered are: PIUS (Sweden), VPBER-600 (Russian Federation) and ISIS (Italy). There were detailed analyses of safety features, plant response to important sequences, PSA aspects, research and development activities and regulatory aspects.
Assistance to Member States in the review of plants built to earlier standards
The Agency provided assistance to Pakistan in the safety assessment and upgrading of the Karachi Nuclear Power Plant (KANUPP). As part of this assistance, a Steering Committee meeting was convened to review KANUPP's programme of safety improvements and to provide advice concerning the completeness of their programme and the priority given to programme activities.
The Agency also convened a technical exchange meeting between Canadian and Indian experts to review degradation mechanisms for Zircaloy-2 pressure tubes, as are currently installed in the Rajasthan Atomic Power Station and other Indian reactors.
Assessment of the safety of individual nuclear power plants
WWER-440/230 programme: A report was prepared on safety improvements to WWER-440/230 nuclear power plants containing the results of follow-up missions to the Bohunice, Kola, Kozloduy and Novovoronezh nuclear power plants and the findings of the Agency review of major safety upgrading for the Bohunice plant. On the basis of earlier identified safety issues, the report describes the plant specific situation, including remedial actions taken by the plant authorities, and remaining safety concerns. Conclusions on the progress achieved and the actions remaining to solve the issues at the various plants are presented. Areas of operational experience and PSA studies are also summarizad in the report.
A follow-up mission was conducted to the Kola nuclear power plant to assess the safety improvements made against the list of safety measures given in IAEA-TECDOC-640, Ranking of Safety Issues for WWER-440 Model 230 Nuclear Power Plants. It was found that in the design area, only about one third of the issues specified had been either partially or fully implemented, though the remaining issues are expected to be addressed in the future. It was recommended that compensatory measures be implemented as soon as possible and close attention be paid to the integrity of the reactor pressure vessel.
A mission was organized to the Kozloduy plant to update information on the status of upgrading measures. Relevant information was included in the database.
The applicability of the leak before break (LBB) concept was reviewed at the Bohunice and Kozloduy nuclear power plants. Guidance for the application of this concept specifying the conditions to be fulfilled and the programme needed to implement the LBB concept was prepared.
RBMK programme: In March, the Agency organized a mission to the Chernobyl nuclear power plant to review the scope and status of safety modifications implemented and proposed and the safety aspects related to plant operation. The review found numerous safety deficiencies in the two units of the plant which remain operational, in particular in Unit 1, which is a first generation RBMK design.
A safety review mission to the Ignalina nuclear power plant in Lithuania was conducted to assess the utility of earlier findings and the recommendations of the Agency's RBMK programme for this particular power plant. The review covered the following areas: core monitoring and control; pressure boundary integrity; accident mitigation; safety and support systems; and instrumentation and control. Recommendations were made regarding the safety standards applied to the design and operation of the power plant, the exchange of information with other plants and the need to establish adequate control in order to ensure orderly and timely implementation of modifications.
A topical meeting on multiple pressure tube rupture in channel type reactors was convened to exchange experience on approaches adopted in Member States operating this type of reactor, and review analysis methodology, criteria and the results obtained. The review was carried out in two areas: pressure tube integrity and the potential for failure propagation; and multiple pressure tube rupture scenarios. Recommendations made for further work in this area covered the analysis of accident scenarios which could lead to multiple pressure tube rupture, validation of the computer code used and obtaining a better understanding of some of the physical phenomena involved.
WWER-1000 programme: The first safety review mission to a WWER-1000 plant was conducted in May at the Zaporozhe nuclear power plant. The purpose of the mission was to review plant specific design and operational safety issues. The results of the review provided major insights for further work. The services of consultants were used to consolidate the Agency's findings and recommendations and to identify a list of safety issues for WWER-1000 reactors.
An intercomparison exercise was carried out between the Russian safety standard (OPB-88) and the Agency's NUSS codes. The results of this comparison were used as input for documents on safety issues for WWER-1000 and WWER-440/213 nuclear power plants.
A core control and protection strategy is of particular interest for the WWER-1000 type reactor. A review of the design of core control and protection systems was carried out focusing on core design, including burnable absorber and control rod designs, core power distribution and control strategy and instrumentation systems.
WWER-440/213 programme: At the request of the Slovak safety authorities, the Agency organized a review in May of the safety upgrading measures proposed for the Mochovce nuclear power plant. It was concluded that the improvements suggested correctly addressed the issues and most of the proposed measures were endorsed.
An analysis was made of the safety issues for WWER-440/213 reactors, compiling the results of reports and various studies. The issues were ranked according to their safety significance based on degradation of defence-in-depth and safety function performance.
The bubbler-condenser is a key element in the safety of WWER-440/213 nuclear power plants. In recognition of this, preparation was started of guidelines on the evaluation of the bubbler-condenser metallic structure. An in-depth study of its strength was undertaken to determine possible weak points and the safety improvement measures required.
Database on technical information: The results of the WWER and RBMK programmes are incorporated in a computerized database which contains different sets of recommendations addressing the safety issues and information on plant status. A questionnaire was prepared to update information on plant status for WWER-440/230 type reactors.
A workshop was organized in Vienna on the use of Agency databases on safety issues to provide training and to discuss data collection procedures. Recommendations were made to prepare a user friendly format for interrogation, which was later implemented for the database on safety issues of WWER-440/230 nuclear power plants.
In co-operation with the G-24 Nuclear Safety Assistance Co-ordination Secretariat, the Agency participated in the preparation of a procedure to check the accuracy of data in the G-24 Project Data Bank. The procedure was used on a trial basis for Agency entries in the Project Data Bank.
International Nuclear Event Scale reporting system
Portugal joined the INES information system in July, making a total of 54 countries who are committed to the prompt communication of those nuclear events significant for safety (level 2 and above), or those significant for the public interest (level 1 and below). In 1994, 63 events were reported to the system. Eight events at level 2 occurred at nuclear power plants. Three events reported at levels 2 or 3 occurred at nuclear facilities other than power plants.
The third meeting of the INES Advisory Committee took place in March. At the meeting, additional guidance was drafted for the INES User's Manual. This guidance will be published as an addendum to the manual. The use of this guidance is expected to eliminate the overrating or underrating of events in nuclear power plants and other nuclear facilities.
In order to facilitate prompt and consistent INES rating by the INES co-ordinator at the plant level, a computerized analysis procedure, INESAR, was developed for the assessment of the consequences for safety (actual and potential) of nuclear events.
At a meeting of Senior Regulators, held during the regular session of the General Conference in September, the use of INES by regulatory bodies was discussed. While it was generally agreed that INES constitutes a valuable service for the prompt reporting of incidents to the media and the public, it was stressed that the strength of INES lies in its promptness, which also defines its limitations. Efforts should be made to use INES only for its intended purpose, namely prompt reporting of incidents to the media and the general public. In addition, no technical conclusions should be drawn on the basis of statistical analyses of INES reports. The matters raised at the Senior Regulators meeting were discussed by the INES National Officers at their annual meeting in October. The National Officers also reviewed experience and feedback on the use of INES.