Safety Issues and the IAEA Nuclear Safety Programme

A. Carnino, L. Lederman, K. Talbot

1. Introduction

The future utilization of nuclear power development and applications as a reliable source of energy production depends primarily on the ability of nuclear power plant (NPP) operators and regulators to demonstrate excellence in safety and economic competitiveness. Safety and economics in an increasingly deregulated electricity market are the principal yardsticks used by decision makers and by the public when considering the acceptability of nuclear power.

Against this background, the vision and the role of the International Atomic Energy Agency (IAEA) is the globalization of nuclear safety. Therefore, the objective of the IAEA Nuclear Safety Programme is to assist Member States in achieving and maintaining a high level of safety of nuclear installations operating worldwide through the international harmonization and implementation of non-binding Safety Standards and the provision of technical advice and services.

International harmonization of safety is also being achieved as demonstrated by the entry into force in 1996 of the Convention on Nuclear Safety (CNS). The Convention established a powerful mechanism to achieve and maintain a high level of safety worldwide through the enhancement of national measures and international co-operation.

The following secsions describe the scope of IAEA activities and how they are being implemented to respond to current safety issues.

2. Nuclear Safety Programme

The Agency’s Nuclear Safety (NS) programme has been structured and its activities prioritized based on recommendations from programme reviews by Member States and insights from major international conferences. The NS Programme for 2000-2001 stems from: (1) Programme Performance Assessment System (PPAS) which has been established to evaluate, periodically, systematically and as objectively as possible the performance of the Agency’s activities. PPAS peer reviews on Nuclear, Radiation and Waste Safety have been conducted in 1997 and 1999; (2) findings and conclusions of the International Conference on Topical Issues in Nuclear, Radiation and Radioactive Waste Safety, Vienna, 1998 and (3) insights from International Conference on the Strengthening of Nuclear Safety in Eastern Europe, Vienna 1999.

To implement the programme, the IAEA organizes international meetings to promote information exchange, develops non-binding safety standards and other technical documents, and provides a wide range of safety services, training courses and workshops.

2.1. Programme Structure

The programme is structured in five major areas:

Further information is available at the IAEA Nuclear Safety web site NUSAFE at http://www-ns.iaea.org/nusafe/

2.2. Safety Standards of the IAEA

Under Article III.A.6 of its Statute, the Agency is authorized ‘to establish or adopt, in consultation and, where appropriate, in collaboration with the competent organs of the United Nations and with the specialized agencies concerned, standards of safety for protection of health and minimization of danger to life and property". Since soon after the Agency's inception the Secretariat has been involved in developing and establishing such standards.

In 1996, the Secretariat revised the process of preparation and review of Safety Standards. To this end, it created a set of advisory bodies with harmonized terms of reference to assist it in preparing and reviewing all documents. The five Committees are: the Advisory Commission for Safety Standards (ACSS), the Nuclear Safety Standards Advisory Committee (NUSSAC), the Radiation Safety Standards Advisory Committee (RASSAC), the Waste Safety Standards Advisory Committee (WASSAC) and the Transport Safety Standards Advisory Committee (TRANSSAC). The Agency assigned to each of these Committees a Scientific Secretary from its staff, who co-ordinates the work of the Committee with the relevant Agency policies and programmes, and appoints a Technical Officer also from the IAEA Secretariat for the preparation of each document.

The Safety Standards Series documents fall into three categories:

In addition, the Agency publishes Safety Reports which provide examples and descriptions of methods which can be applied in implementing both Safety Requirements and Safety Guides. They are documents for fostering information exchange.

IAEA Safety Standards are being published in five categories, namely:

The above documents describing requirements and guides are developed by international experts drawn from utilities and regulators throughout the world. They are reviewed and approved by all Member States operating nuclear facilities as well as an expert standing committee charged with ensuring the high quality of such documents. They can therefore be said to contain the global consensus of requirements for safe operation of nuclear power plants. Under a programme of upgrading to the latest international best practises these standard documents are all being revised and reissued by the end of 2001.

http://www-ns.iaea.org/publications provides an overview of the set of safety requirements and guides documents in preparation.

The development of the IAEA’s safety standards has concentrated mainly on particular types of facility: the nuclear safety standards primarily address nuclear power plants and research reactors; the waste safety standards address facilities involved in the various stages of waste management (including decommissioning), but particularly repositories; and the radiation safety standards are either independent of the type of facility (e.g. radiation protection measures) or focused mainly on facilities outside the ‘nuclear industry’. It had already been recognized that some types of facility are not specifically addressed by the existing IAEA safety standards, and a programme of work was proposed to identify new standards that might be necessary for other installations of the fuel cycle. The Tokaimura accident at a fuel processing facility in Japan highlighted this issue, particularly in relation to criticality safety at non-reactor facilities.

As a first step for defining the work required the IAEA has compiled in 1999 safety issues for fuel cycle facilities in Member States. The report is available from the IAEA Secretariat.

2.3. Safety Review Services of the IAEA

The IAEA has been providing safety review services to nuclear power plants (NPPs) and research reactors since the early 1980s. A central element of these services are peer review missions conducted by international experts who provide independent advice based on IAEA standards and best international practices. These missions are consistent with the IAEA’s statutory responsibilities for establishing and seeing to the application of safety standards at the request of IAEA Member States.

In the last years, the scope of safety services have been expanded and new services have been established in response to specific needs of Member States. The following are the safety review services offered by the Agency.

International Regulatory Review Team (IRRT)

Inaugurated in 1989, the IRRT programme provides advice and assistance to Member States to strengthen and enhance the effectiveness of their nuclear safety regulatory body whilst recognizing the ultimate responsibility of each Member States for regulating nuclear safety.

Operational Safety Review Teams (OSART)

The purpose of the OSART programme, established in 1982, is to assist Member States in enhancing the operational safety of nuclear power plants and to promote the continuous development of operational safety within all Member States by the dissemination of information on good practices.

Engineering Safety Review Services (ESRS)

The ESRS, initiated in 1989, provides advice on selected engineering safety aspects of NPPs in construction or in operation. Areas of work include: siting, design, fire safety, and the impact of ageing in NPP safety. Specific services are:

Design Safety Review Services (DSRS)
Seismic Safety Review Service (SSRS)
Fire Safety Review Service (FSRS)
Ageing Management Advisory Team (AMAT)
Software Safety Review Service (SWSRS)

International Probabilistic Safety Assessments Review Team (IPSART)

IPSART (formerly IPERS) was established in 1988 to make international expertise available for reviewing probabilistic safety assessments (PSAs) and their applications.

Peer Review of Operational Safety Performance Experience (PROSPER)

An IAEA operational safety service (derived from the former ASSET service) to peer-review self-assessments by NPPs of their operational safety performance and its trends based on operating experience.

Review of Accident Management Programmes (RAMP)

An IAEA service to assist the Member States in preparation, development and implementation of accident management programmes of their NPPs.

Safety Culture Enhancement Programme (SCEP)

A service intended to give support to senior utility managers on the enhancement of the management of safety and safety culture. It provides training to increase the understanding of safety culture issues, to perform a self-assessment and develop improvement initiatives.

Integrated Safety Assessment of Research Reactors (INSARR)

INSARR missions are an IAEA safety service offered, to assist Member States in ensuring and enhancing the safety of operating research reactors. Reviews are also conducted in accordance with provisions of agreements between the IAEA and some Member States.

International Nuclear Event Scale Information Service (INES)

INES is a scale to put incidents and accidents in nuclear power plants and other nuclear installations into perspective, explaining in simple terms their significance and relative importance to the public. The INES range is from level 1 (anomaly) through level 7 (major accident). Deviations of no safety significance are level 0.

Incident reporting and analysis (IRS)

The Incident Reporting System (IRS) is a mechanism to facilitate the exchange of information with regulators on events of safety significance at nuclear power plants and the lessons learned. The system is operated jointly by the IAEA and the OECD Nuclear Energy Agency.

2.4. IAEA Assistance through Technical Co-operation projects and Extra-Budgetary Programmes

The Agency, pursuant to its Statute, helps Member States to comply with its safety standards through, inter alia, technical co-operation (TC) programmes. In doing so, it attaches high priority to the establishment and strengthening of nuclear, radiation and waste safety infrastructures in Member States.

Under its TC programmes, the Agency provides safety related technical assistance in the form of experts' services, equipment and training. The current safety related TC programme includes more than 130 national, regional and interregional projects of which about 35% are devoted to nuclear safety and 65% to radiation and waste safety. In addition, in 1998 about 60 national, regional and interregional workshops and training courses have been organized. The projects cover a very wide range of nuclear, radiation and waste safety issues, from the establishment of basic technical, legislative and regulatory infrastructure for the use of radiation and radioactive materials in medicine, research and/or industry to assistance in further strengthening the much more complex and sophisticated safety infrastructure needed for the development and operation of nuclear reactors.

To ensure that the IAEA assistance focus on the priority safety matters for each country a systematic approach has been established.

The systematic approach involves development , jointly by the Agency and the Member State, of a Country Nuclear Safety Profile (CNSP), describing the actual nuclear safety situation in the Member State; comparison of the actual situation in the Member State (as described in the CNSP) with a predefined 'reference situation' based on the Agency's Safety Requirements. This review, carried out jointly by the Agency and the Member State, aims to identify the areas where the actual situation falls short of the reference situation, and therefore where Agency assistance could most effectively be applied; and the formulation of an agreed Country Nuclear Safety Action Plan (CNSAP), based on the review findings, the Member State's priorities and the Agency's ability to provide suitable and effective assistance to the Member State.

Three complementary regional TC projects for Europe in particular are providing continuing assistance in important areas of safety of NPPs in Eastern Europe and countries of the former Soviet Union, through seminars, workshops, safety review missions and expert advice. This is a follow up of an Extrabudgetary Programme on WWER and RBMK safety implemented by the IAEA from 1990 to 1998 [1]. These projects cover:

The work plans agreed for implementation in 2000 under these projects have specifically considered the results of the International Conference on Strengthening of Nuclear Safety in Eastern Europe. This conference held in Vienna in June 99 was organized by the IAEA in co-operation with the European Commission and the OECD/Nuclear Energy Agency. It assessed the past decade of nuclear safety efforts in countries operating WWER and RBMK NPPs and remaining safety issues which require further work. A significant input was the results of the IAEA’s Extrabudgetary Programme on the Safety of WWER and RBMKs. A main achievement of this Programme was the preparation of the Safety Issues Books, which provide a clear picture of the design and operational safety issues and their safety importance. Based on these results, international consensus was reached on the safety issues related to WWER and RBMKs and the priority measures required [1]. The conference conclusions are available at the IAEA web site and a comprehensive report (over 1000 pages) including all background papers has been published [2].

Since 1998 the IAEA is also implementing an extrabudgetary programme on the safety of nuclear installations in South East Asia, Pacific and Far East countries. The objective of the programme is to strengthen nuclear safety and to enhance the technical capabilities of regulatory authorities and supporting technical organizations starting with the application to research reactors. Participating countries are China, Indonesia, Malaysia, Philippines, Thailand and Vietnam.

Focus is on providing assistance for strengthening national regulatory frameworks and technical and management capabilities including: nuclear legislation, regulations, safety assessment, licensing, inspection and enforcement Other areas of assistance include emergency planning and preparedness; promotion of safety culture concepts and preparation of information to decision makers and to the public to build up understanding and confidence in nuclear safety.

The programme is also a mechanism for establishing a regional forum to exchange information to harmonize the implementation of nuclear safety concepts among countries in the region.

An Advisory Group meets annually and provides advice to the IAEA on programme implementation.

3. Current Safety Issues

The current safety issues and the relevant IAEA activities are presented next in four major areas, namely: safety from the regulatory point of view, safety in operation, safety in engineering and safety achievement and verification. In addition, other safety topics related to the Y2K concerns, the safety of research reactors and the current problem of maintaining nuclear knowledge will also be discussed.

3.1. Safety from the regulatory point of view

3.1.1 Issues

One of the fundamental safety principles is the establishment of legislative and regulatory framework for the regulation of nuclear installations and the effective independence of regulatory body from the organization charged with the promotion or utilization of nuclear energy. This topic was specifically discussed during the First Review Meeting of the Contracting Parties of the Convention of Nuclear Safety (CNS) in 1999. It was found that "The legislative framework is well established in most countries and that generally, the regulatory bodies of Contracting Parties appeared to act in a clearly independent way in a "de facto" sense, relying on a well established management policy of the regulatory body. It was noted that in several cases, it would be desirable, and in some cases even necessary, to improve the "de jure" independence of the regulatory body as a complement to its "de facto" status, inter alia to facilitate future evolution of the regulatory body".

Contracting Parties reported on their national regulatory strategies. The advantages and limitations of regulations of a detailed prescriptive nature as compared to less prescriptive, goal oriented approaches and the complementary use of risk informed assessments were discussed. No preferable approach was identified.

Of utmost importance is a stable and a strong regulatory system. This requires an efficient, independent and technically competent regulatory body and a well established safety approach which ensures harmonization in the safety decision making process. The licensing process needs to be transparent and objective. Predictability and stability of judgement are important aspects to limit the total duration of the process to no more than some five years. The interface between the regulatory body and its licensees should also provide the means for the required quick responses from both sides. The regulatory body should ensure that all aspects of nuclear safety, technical and managerial, are being properly addressed at the utility level. Periodic international peer reviews are an appropriate instrument to provide an independent assessment and a comparative perspective to similar work going on world-wide.

Regulatory inspection and enforcement is an essential tool for monitoring the safety level at installations. In line with non-prescriptive regulatory approaches, inspections tend to depart from pure compliance to performance and/or process checking. Such an orientation certainly reinforces the prime responsibility of the operating organization in safety.

Harmonization of regulatory decisions concerning licensability of the new reactors would also be desirable for increasing public confidence and understanding of nuclear safety.

Our emphasis is now on efficiency and efficacy of the regulatory bodies. Quality assurance in relation to the activities performed by the regulatory body is essential for a disciplined approach. Therefore, regulatory bodies need to implement internal quality assurance systems to provide adequate confidence that specified requirements are met. This includes tasks related to audits checks, examinations and other practices with daily work activities.

3.1.2. IAEA activities

Agency’s relevant activities to assist regulatory bodies concentrate in 2 areas. The development of safety standards with requirements for legal and governmental infrastructure for nuclear, radiation, radioactive waste and transport safety and several safety guides on specific areas such as: organization and staffing of the regulatory body, documentation produced and required to regulate nuclear facilities, review and assessment by the regulatory body and inspection and enforcement. The second area of assistance is the provision of peer review services to advice on strengthening the technical capabilities and the effectiveness of regulatory bodies, whilst recognising the ultimate responsibility of each Member State to regulate nuclear safety of its installations.

Specific areas addressed by the IRRT service (see section 2.3) includes the review of the completeness of national regulations and its consistency with IAEA standards, the organization, means and responsibilities of the regulatory body, the license process, safety assessment and inspection and enforcement.

In 1998-99 IRRT missions of different scopes have been conducted in Romania, Slovakia, Ukraine, Switzerland and Slovenia and in the frame of the above mentioned extra budgetary programme in Indonesia, Malaysia and Vietnam.

This service is being increasingly requested and several missions are already scheduled for implementation in 2000 and 2001-2002.

3.2 Safety in Operation

3.2.1 Issues

In order to determine the major challenges facing NPP operational safety over the next few years the Agency has held several meetings of senior utility and regulatory representatives from the majority of member states operating NPPs. Technical committee meetings held in Canada in 1998 and Vienna in 1999 and an IAEA Working Group paper on Shortcomings in Safety Management delivered to the IAEA International Conference on Topical Issues in Vienna in August 1998 [3] have revealed the following issues.

The main challenges to the safe development of the nuclear industry over the next 5 years will be driven by the need to balance safety and competitiveness during times of; financial stress, deregulation and increased market competition, country financial restructuring, early plant closures from political and other pressures, equipment obsolescence, a diminishing nuclear work force and knowledge pool and the cost of eventual decommissioning. The effectiveness of management from the most senior executive and government decision maker to the front line supervisor in developing and sustaining good operational safety practises and a good safety culture is considered to be the overriding factor with economics playing an important role and technical issues to a lesser degree. The effectiveness of the regulator to detect early signs of management shortfalls and in taking decisive action is also considered a key factor.

The development and maintenance of a good safety culture is seen as a way of sustaining good performance during such changing times but which can be easily depleted by financial, political and other management distractions. The first requirement is for a continuing demonstrated commitment from the top management at both corporate and plant level. Management must establish the necessary work environment for a good safety culture to develop with openness, good communication, monitoring performance learning lessons from events and deviations both technical and human performance are crucial factors. A continual questioning attitude and striving for improvements to operational safety are paramount and are evident in high performance organisations who wish to stay in front of the competition. Peer reviews are useful for this purpose.

Ensuring nuclear competence is maintained in all sectors and at all levels of the industry including nuclear stations, vendors, contractors, regulatory bodies, universities, research centres, from the board rooms and government decision makers to the front line mechanics and operators is also considered essential for the long term health of the industry.

Developing ways to safely manage ageing plant in an economic and competitive manner and the continuation, particularly in the eastern European countries, of plant safety hardware - improvement and modernisation - as well as improving operational safety monitoring and analytical techniques are also considered important for a sustainable nuclear future.

3.2.2 IAEA activities

Once in operation the responsibility for maintaining the safety of the plant and for the protection of the public from harmful effects of radiation rests with the plant operator. The general requirements necessary to perform this function are described in the Agency document called "Requirements, The Safety of Nuclear Power Plants: Operation.". Other documents which give more detail are called "Safety Guides" and are produced for each operational area as listed in Table 1.

Having developed these standard requirements, utilities and regulators require assistance in their applications and help with achieving performance at a level equivalent to best international practise with a particular emphasis on the future.

The relevant Agency activities to assist in the quest for excellence in the management of operational safety and safety culture are the Operational Safety Services, which utilise guidelines developed from the safety standards and expert peers selected from high performance plants, utilities and regulators.

OSART (see 2.3) assist plants in upgrading a broad range of operational activities including all aspects of management and with a module (under development) designed to get a measure of the status of the organisational safety culture in various areas. The process utilises an international group of peers who evaluate the plant functional area performance indicating where improvement is necessary. The regulator is kept informed of progress and findings and on approval of the Member State, the final report is de-restricted and available to the nuclear industry and governments. Follow-up visits to the OSARTs are conducted 18 months after the mission to review progress in implementing improvements. On average at the follow-up visit, greater than 90% of the recommendations and suggestions from the original OSART are either resolved or making satisfactory progress towards a timely resolution. During these reviews, good practices are also identified and made available to the rest of the industry. The good practices and issues from de-restricted reports are contained in a CD ROM entitled OSMIR (OSART Mission Results), which is available to the industry. To date 106 OSART review missions and 50 follow-up missions have been conducted in 31 countries.

Pre-OSART (OSART) Missions (to plants under construction/commissioning, i.e. in pre-operational phase): These missions, which are conducted close to the time of initial start-up, normally review the same areas as a regular OSART mission plus some of the following areas: Commissioning; Project Management; Civil Engineering and Construction; Mechanical Equipment Installation; Electrical and Instrument and Control Equipment Installation; Quality Assurance in Construction and Commissioning; Preparation for Start-up and Operation. As mentioned earlier the ability to learn from experience and correct problems before they become serious is an essential attribute of good operational safety. In the mid 1980’s the ASSET was developed to assist Member States in enhancing safety performance through the analysis of NPP events. A unique methodology to get to the root cause of events was developed. Through approximately 150 missions, ASSET has had a significant influence in helping, especially the eastern European nations, develop a practical learning from event experience process. Many plants have however, now developed operating experience programmes that encompass major and minor events and deviations, use more than one analysis technique, focus more strongly on human factors and have developed more sophisticated corrective action processes. The Agency has therefore developed a new service derived from ASSET called PROSPER (see 2.3) with the intent of assisting a plant with its total operating experience process and which is presently under trial operation.

Based on a document issued by the Agency on Safety Culture [4] and a 1999 document on the Management of Operational Safety in NPPs [5] which links the concept of Safety Culture and the Management of an organisation necessary to achieve a good safety culture, a complete range of services are now offered in a SCEP (see 2.3). Services range from an initial seminar to assist with self assessment of a plant. Safety Culture status, through help in identifying problems and developing correction actions to external assessment of the Management of Safety and Safety Culture. The latter can be performed either via an augmented OSART, which includes a safety culture module or by stand alone mission Safety Culture Assessment Team (SCAT), in which a 4-5 person expert team analyses and gives advice for improvement from the Corporate management, including the Board of Directors, to the front line.

The essential influence by corporate and executive management of utilities, regulators and government decision makers in achieving improvements in safety performance of nuclear plants has been recognised by the Agency as a critical factor in the future of the business as it faces many financial and political challenges. The Agency is now developing guidelines to assist this level of management in developing strategies for safe successful nuclear business performance and is developing corporate level indicators to assist. A workshop format is being prepared to avail government decision makers and members of corporate management and Boards of Directors with knowledge of what should and should not be done when managing a nuclear business from that level to ensure safety is not compromised or degraded.

In summary the Agency provides and is developing a full scope of standards and services to utilities and regulators in Member States to assist in improvements to all aspects of operational safety from corporate management to the front line.

3.3 Safety in Engineering

3.3.1 Issues

Key factors have to be met for a strong and robust design in terms of safety. The prime goal is the prevention of accidents. The design needs to include the appropriate application of the defence in depth principle so that there are several levels of protection and multiple barriers to prevent releases of radioactive materials, and to ensure that failures or combinations of failures that might lead to significant radiological consequences are of very low probability.

Site selection for NPPs designed, constructed and put into operation in the past four decades have been subject to varying levels of safety analysis. The evolution of safety criteria during this period and associated new requirements enacted by nuclear and non-nuclear regulatory bodies (e.g. environmental impact assessment) led to extensive work world wide on the re-evaluation of existing sites.

To demonstrate the systematic implementation of defence in-depth, a comprehensive safety assessment and independent verification are necessary to confirm that the design of the installation will fulfil the safety objectives and requirements. New designs have built in better prevention of accidents including severe accidents, more robust defence-in depth, increased prevention of human errors, reduction of exposure to radiation of site personnel and reduced releases of radioactive materials to the environment. International reviews play an important role in this area.

The operating experience of existing installations is essential for developing the new evolutionary reactors. This means including from the design stage a number of improvements leading to less demands to be put on the operators and easing the operational procedures. A well designed and tested containment should decrease the frequency of large radioactive releases to negligible levels. This needs to be fully demonstrated both based on deterministic and best estimate probabilistic analysis as well as through defence in-depth. On site and off site protection to workers and to the population in general should be clearly elaborated through the design features and in the frame of emergency plans and environmental impact assessments.

3.3.2 IAEA assistance

The relevant Agency activities are the development of safety requirements on Siting and Design and the provision of engineering safety services. Various safety guides under development should provide guidance in the interpretation and implementation of these requirements.

Site safety and external hazard analysis involve a broad range of disciplines including geology, seismology, hydrology, meteorology, vulcanology and tectonics and other matters such as local population distribution and man-induced events (e.g. air plane crashes).

In the context of site re-evaluation, the seismic safety considerations are often a central topic of review. These reviews focus on two major aspects: the adequacy of the design basis safety input and the seismic capacity of plant structures, equipment and distribution systems. Upgrading measures are often identified during these reviews.

The state of the art on Seismic Qualification of Existing Nuclear Facilities was reviewed at a post conference seminar organized in conjunction with SMIRT 13 in Japan in 1998 [6]. The review highlighted the large amount of recent work carried out by the IAEA and Member States particularly for NPPs operating in Eastern Europe. IAEA assistance and peer review services have been very intense and some 100 review missions have been conducted in 25 countries.

The Safety Requirements on Design take account of the developments in safety by, for example, including the consideration of severe accidents in the design process. Other topics that have been given more detailed attention include management of safety, design management, plant ageing and wearing out effects, computer based safety systems, external and internal hazards, human factors, feedback of operational experience, and safety assessment and verification. These requirements are applicable to safety functions and the associated structures, systems and components, as well as to procedures important to safety in nuclear power plants. They are primarily for land based stationary nuclear power plants with water cooled reactors designed for electricity generation or for other heat production applications (such as district heating or desalination). It is recognized that in the case of other reactor types, including innovative developments in future systems, some of the requirements may not be applicable, or may need some judgement in their interpretation.

There is a general consensus that severe accidents must be explicitly considered in the design of future plants to ensure that the impact on individuals and the environment beyond the site fence is limited to an acceptably low level. Limiting the need for off-site countermeasures is an objective in many countries when considering the design of future NPPs.

The evaluation of the amount of fission products that can leak from the containment in the case of severe accident sequences is an essential input for the design of the containment and of its associated systems. Therefore, the IAEA developed and published [7] a simplified approach to estimating reference source terms for LWR designs.

Regarding new evolutionary and innovative reactor designs the IAEA is respectively assisting China to review of the safety aspects of Tianwan NPP, an AES-91 with WWER 1000 model 428 design in construction.

The AES-91 has been designed on the basis of the WWER 1000/320 plants in operation and OPB-88 and other current Russian standards. Its distinct safety features include a double wall containment with an inner pre-stressed concrete cylindrical shell and steel liner, an outer reinforced concrete building and a core catcher in the reactor cavity. Initial reviews carried out assisted by the IAEA indicate that the safety concerns previously identified for the WWER 1000/320 [8] have been generally addressed in the new design.

The IAEA is reviewing the design safety standards developed by Republic of Korea for the next generation reactors to be designed in that country.

The IAEA is also assisting in review of design aspects, external events and environmental impact of a Pebble Bed Modular Reactor (PBMR) a High Temperature Gas-Cooled Reactor (HTGR) design currently being developed in South Africa. This is leading to the development of a new approach of safety demonstration based on the defence in-depth concept.

The PBMR design aims at achieving a high degree of safety through reliance on inherent safety features. Such features include ceramic-coated fuel particles that can retain fission products under both normal and accident conditions, stabilizing neutron physics characteristics, and the ability to dissipate decay heat by natural heat transport mechanisms, preventing excessive temperatures from being reached. Such design features should allow the technical demonstration of a very high level of public protection with significantly reduced active safety systems and emergency planning requirements.

Design review services and reviews of plant modifications have been performed for various types of NPPs including older generation WWER and RBMKs. Main insights of these reviews are included in reference [1].

3.4 Safety Achievement and Verification

3.4.1 Issues

In order to face the challenge of mastering operating and maintenance costs in a competitive environment, longer fuel cycles and life management are most appealing but safety must remain the overriding priority. Modern I&C to support human factors requirements is also essential for existing installations.

As a nuclear power plant ages, the safety margins provided by the design need to be carefully monitored and the related degradation of system structures and components must be effectively managed. This process requires the establishment of a systematic ageing management programme to ensure that the required safety functions are available throughout the service life of the plant including its extended life

Safety achievement and verification requires routine reviews of plant operation (including hardware and procedural modifications, operating experience, plant management and personnel competence) and special reviews following major events of safety significance.

Some countries have introduced systematic safety reassessment, termed periodic safety review (PSR) to ensure the high level of safety required throughout plant lifetime.

An essential element to ensure a high level of safety throughout plant lifetime is the complete compilation and review of plant specific safety information which needs to be contained in plant specific safety analysis reports (SARs). SARs need to represent the actual plant configuration and modifications, therefore a process of periodic updating and review is necessary. In some countries, this work is realized in the frame of the periodic safety reviews.

Probabilistic and deterministic methods for safety analysis are normally used in a complementary way in safety reassessments to confirm the adequacy and efficiency of provisions within the defence in depth concept. In this context of particular importance is the completeness and the technical quality of these analysis.

Requirements for SARs for operating countries vary from country to country, and in some countries the norms for older plants did not contain the full scope safety analysis expected today.

The status of SARs for WWER and RBMK NPPs was specifically addressed in the conclusions of the International Conference on Strengthening Nuclear Safety in Eastern Europe. Considering the importance of SARs, the IAEA selected the completeness of plant specific SARs as a criterion for assessing the completeness, adequacy and maturity of assistance programmes. The contents of SARs presented at the conference showed a wide variation with respect to scope, quality and depth. Therefore, continued international assistance in this area was considered appropriate.

3.4.2 IAEA activities

Activities in the area of ageing management have been considerably strengthened in the past years. In 1999, a Safety Report [9] was published on the Implementation and Review of a NPP Ageing Management Programme. It deals with the organizational and managerial aspects of NPP ageing management, including assessments of the programme effectiveness.

Five comprehensive technical documents have also been published on Assessment and Management of Ageing of Major NPP Components Important to Safety. These reports address: steam generators, concrete containment buildings, CANDU pressure tubes, PWR pressure vessels and PWR vessel internals. Additional five documents are in preparation for CANDU reactor assembly, PWR primary piping, metal components of BWR containment and BWR vessel internals. The focus of the programme is now shifting from providing guidance to the actual applications. Therefore, a specific service, is being offered by the Agency to advice and peer review plant specific Ageing Management Programmes.

In the area of probabilistic safety assessment (PSA), the Agency maintains a comprehensive programme, which supports the development of technical capabilities for PSA work in Member States. It includes PSA applications, living PSA, a framework for quality assurance for a PSA programme and regulatory review of PSAs. A comprehensive overview of IAEA’s PSA activities was published in 1999 [10].

An underlying concern addressed by the IAEA activities is the technical quality of PSAs and their appropriateness for use in various applications. Therefore, in addition to the development of technical documentation, the IAEA provides, upon request, PSA peer review services (IPSART - see 2.3). The basic objective being to assess the adequacy of the treatment of technological and methodological issues, and whether specific conclusions and applications are adequately supported by the PSA technical analysis.

In 2000, work on regulatory review of PSAs will proceed with focus on level 2 PSA. In addition, PSA peer review services are being expanded to review PSA applications.

The concern about the technical quality of PSAs was also raised in 1996 by the IAEA in relation to WWERs and RBMKs at the International Conference on Strengthening Nuclear Safety in Eastern Europe. It was concluded that the IAEA could provide one useful forum for systematic information exchanges among Eastern European countries on the consistency of deterministic and probabilistic results.

In 1999, a meeting to exchange information among PSA practitioners modelling and data for WWER 1000 PSA was organized by the IAEA.

The lack of consistency, completeness or quality of analysis is also a safety issue for the deterministic accident analysis. Therefore, the IAEA has recently completed the preparation of a Safety Report on Accident Analysis for NPPs [11].

The objective of the report is to establish a set of practical suggestions, based on the best practice world-wide for performing deterministic safety analysis. These cover: classification of initiating events and acceptance criteria; methodology for the analysis; types of accident analysis; computer codes; user effects on the analysis; input data preparation; presentation and evaluation of results; quality assurance; and specific guidance for individual reactor types.

The report covers both design basis and beyond design basis accidents, although the former is covered in more detail. Focus is on thermohydraulic aspects of safety analysis; neutronic, structural and radiological aspects are also covered to some extent. Best estimate as well as conservative accident analysis are included.

According to the generally established defence in depth concept in nuclear safety, consideration in the plant operation is also given to highly improbable severe plant conditions that were not explicitly addressed in the original design of currently operating NPPs.

Accident management is one of key components of effective defence in depth. It means in particular, that accident management provisions should take place in any case, even if all provisions within the design basis are adequate.

Various components of the prevention and mitigation of severe accidents have been partially reflected in "traditional" documents used in operation of NPPs, such as Safety Analysis Reports, PSA studies (all levels and level 2 in particular), Emergency Operating procedures and Emergency Plans. It is, however, considered that importance of the issue requires integration of all available relevant plant specific information into a comprehensive set of consistent documents, the Accident Management Programme (AMP). Exchange of experiences and best practices can considerably facilitate and contribute to the quality of the work document to be developed for individual plants.

Considering the above, the IAEA developed a comprehensive report [12] on the Implementation of Accident Management Programmes in NPPs. The report covers basic principles of the accident management programme, including specification of its objectives, a short description of severe accident progression; possible strategies for the accident management, and characterization of the plant equipment performance under severe accident conditions. The detailed actions and project steps of the proposed AMP are divided into three phases: preparation, development and implementation. Additional information is provided sometimes also referring to programmes already in place, and practical examples of how various components contributing to an AMP can be performed, including actual applications.

In the past the nuclear industry has often looked upon safety and production as conflicting objectives. However, the operating experience developed over the past thirty years has led the industry to understand that this is not so. In fact, plants with excellent safety records also tend to be good performers. Therefore, a complete set of parameters to monitor NPP performance should include both safety and economic performance indicators. Nonetheless, the objective of this report is to identify a set of indicators to monitor performance in areas that directly affect the operational safety of the plant. Thus, purely economic indicators have not been included.

It should be recognized that while indicators provide valuable information in the effective management of plant performance, they are but one of a larger set of tools - including PSA, regulatory inspection, quality assurance and self-assessment - that can be used by nuclear plant operators to assess operational safety performance. The integration of information compiled through the application of all such evaluation tools will yield the best results.

The IAEA activities on safety performance indicators focused on elaboration of a framework for the establishment of an operational safety performance indicator programme. The development of this framework was based on NPP operational safety performance and the identification of operational safety attributes. For each operational safety attribute, overall indicators, were established to provide an overall evaluation of relevant aspects of safety performance,. Associated with each overall indicator there is a level of strategic indicators to bridge from overall to specific indicators. Finally each strategic indicator was supported by a set of specific indicators, which represent quantifiable measures of performance. The programme development was enhanced by pilot plant studies, conducted over a 15 month period from January 1998 to March 1999. The result of all this work is compiled in the reference [13].

Similar to the work realized for WWER and RBMK NPPs generic safety issues have been also compiled and published by the IAEA [14] for Light Water Reactors (LWRs). Current safety issues have been identified in the areas of design and operation. For each one of the issues the safety concern and its safety significant are discussed and the corrective measures taken in various countries are presented. All together 85 safety issues related to design and 37 related to operation are discussed. Work is under way to prepare an equivalent compilation for Heavy Water Reactors.

Fire hazard has been identified as a major contributor to a plant’s operational safety risk; the international nuclear power community (regulators, operators, designers) has been studying and developing tools for defending against this hazard. Considerable advances have been achieved in the past two decades in design and regulatory requirements for fire safety, fire protection technology and related analytical techniques. Likewise, substantial efforts have been undertaken world-wide to implement these advances in the interest of improving fire safety both at new nuclear power plants and at those in operation.

The IAEA endeavours to provide assistance to Member States in improving fire safety in nuclear power plants. In order to achieve this general objective, the IAEA developed guidelines and good practices, to promote advanced fire safety assessment techniques, to exchange state of the art information between practitioners, and to provide engineering safety advisory services and training in the implementation of internationally accepted practices.

A systematic assessment of fire events using the root cause analysis methodology was published in 1999 [15]. This methodology is recognized as an important element of fire safety assessment. Experience shows that even incidents involving minor fire events, when analysed with this method, invariably yield a number of insights into causal factors which other methodologies might miss. If adequate and proper attention is given to these insights, most of which relate to procedures and policies, then the incidence of fire events may be significantly reduced.

Fire Safety Review Services, as indicated in section 2.3, are also offered by the Agency to assist Member States to evaluate the adequacy of fire safety provision of nuclear facilities and to implement safety improvement measures required.

3.5 Other Safety Topics

Y2K

A major safety concern during 1999 was the safety of NPPs and research reactors regarding the millennium bug (Y2K). The IAEA in response to a specific resolution passed at the 1998 General Conference implemented an active assistance programme. A guidance document [16] was prepared early in 1999 and the document was broadly adopted in many countries. Three workshops have been organized to provide training and to exchange experience among Member States on specific elements of the Y2K programmes and contingency planning. In addition some 20 assistance missions have been conducted by the IAEA to NPPs in 9 countries.

The diligent work of NPP operators and regulators and the international assistance provided, ensured a transition to the new millennium safe and on-line.

Research Reactors

There are 259 research reactors declared as operational in 59 countries. Nearly fifty percent of these reactors are more than 30 years old. In addition there are 238 in extended shutdown and 106 in decommissioning. During the past few years the safety of research reactors is receiving increased attention world wide. Safety concerns stem from the old age of some reactors, poor operational conditions and regulatory supervision and the extended shutdown mode in which a large number of reactors remain.

The IAEA has been strengthening its assistance in the area of research reactors safety. A Safety Requirements document has been published including design and operational aspects and four additional safety codes are in preparation. The IAEA experience with traditional operational safety services for NPPs such as the OSARTs is being harmonized for utilization in INSARR missions. An Incident Reporting System for of research reactors has also been established to facilitate the exchange of experience among Member States operating of research reactors.

Further assistance is focusing on strengthening regulatory bodies, operators retraining, self assessment, ageing management, safety culture and decommissioning.

Competence in Nuclear Safety

There are serious concerns regarding the ability of NPP regulators, operators and of the nuclear industry in general to maintain the technical competence required for the safety of nuclear installations. This is generally attributed to the slowdown of nuclear power programmes in may countries, decreasing nuclear research, unattractive market for new professionals and an ageing workforce.

A proactive approach to address this situation is needed. International organizations and bilateral programmes can play an important assistance role but ultimately governments must ensure that necessary commitments and resources are in place. The underlying condition is the maintenance at the national level of a university degree in engineering or science related to nuclear technology and the associated research.

The IAEA has been offering annually a wide range of training courses both at regional and inter-regional levels covering various topics in the area of nuclear safety Under development is also Integrated Training Strategy oriented towards nuclear safety education.

In 1999, the Agency conducted the first nine week Basic Professional Training Course on Nuclear Safety. The course took place in Saclay, France in co-operation with the INSTN (CEA). A comprehensive text (about 1000 pages) was prepared by the lectures and distributed to the participants. Specific areas of concentration of other training courses on nuclear safety include: Regulatory Control in NPPs, Operational Safety and Management of NPPs, Probabilistic Safety Assessment, Managing Safety aspects of NPP ageing and Safety of Research Reactors. Standard reference texts are being prepared for some of these courses.

The IAEA will participate in an international effort co-ordinated by the OECD/NEA to develop a proactive international approach for assuring nuclear safety competence in the 21st century.

4. Conclusions

The principles of nuclear safety are now quite well known and implemented world-wide. International harmonization of safety is also being achieved as demonstrated by the entry into force in 1996 of the Convention on Nuclear Safety. The Convention established a powerful mechanism to achieve and maintain a high level of safety world-wide through the enhancement of national measures and international co-operation.

To go beyond the present nuclear safety levels, management of safety and safety culture will be the means for achieving progress. Management of safety at the installations as well as its control and monitoring by the safety authorities become a key to the future of nuclear energy.

At utilities and nuclear installations operators, the first requirement for safety management is a commitment from the top management at both corporate and nuclear power plant (NPP) level. The second requirement is to develop the necessary work environment for developing a good safety culture through openness, communication, listening to staff problems and noticing on time the warnings indicating possible degradation of safety. The third requirement is a commitment to develop and maintain a good safety culture. The last requirement on operating organizations is to stay "humble": do not take for granted that the good level of safety will stay for ever, especially in the field of safety culture, keep a questioning attitude. Peer reviews are useful for this purpose.

Peer reviews from external organizations or international ones represent also a good way for operators and for regulatory authorities to exchange experience and to further enhance the monitoring of safety in operating organizations.

Despite its modest cost the Agency’s Nuclear Safety Programme is noticeably impacting on the safety improvements of nuclear installations world-wide. Member States are consistently supporting the Programme and expressing satisfaction with the results achieved to date.

A valuable indicator of the usefulness of the IAEA activities is the result of follow up missions from various safety services. Records show a very large percentage of acceptance and implementation of IAEA recommendations. In the area of operational services, for example, OSART follow up missions normally carried out 18 months after the original mission show that about 90% of the IAEA recommendation generally implemented.

Reference to IAEA reviews and implementation of its recommendation has been included in the national reports of various countries in the frame of the Convention on Nuclear Safety. These references increase the confidence of other Contracting Parties that nuclear safety is being given the high level of attention required. It also demonstrates a transparent approach which will ultimately increase the public trust on the safe use of nuclear power.

Reference should also be made to the recognition by the international scientific community of the invaluable contribution of the IAEA activities to the improvement of the safety of NPPs in Eastern Europe. The IAEA has provided a unique forum where consensus was established on the safety improvements required and their priorities.

In this context the Conference on the Safety of NPPs in Eastern Europe "agreed that there is no question that considerable progress on nuclear safety has been made in Eastern Europe".

It is therefore essential that technical and political discussions regarding the safety of these NPPs take full consideration of the immense effort which has taken place both at national and international levels over the past decade. Any other course of action which is not soundly based on technical findings will severely damage the safety of NPPs world-wide.

The Agency will continue to play its role by providing updated safety standards, safety review services and technical assistance in safety standards implementation to its Member States in order to maintain a world-wide high level of safety in nuclear installations.

http://www-ns.iaea.org/publications

References

  1. Final Report of the Programme on the Safety of WWER and RBMK Nuclear Power Plants, IAEA-EBP-WWER-14, May 1999, Vienna, Austria.
  2. International Conference on the Strengthening of Nuclear Safety in Eastern Europe (Keynote Papers), IAEA-CN-75, June 1999, Vienna, Austria.
  3. International Conference on Topical Issues in Nuclear, Radiation and Radioactive Waste Safety; IAEA-CN-73; August/September 1998, Vienna, Austria.
  4. Safety Culture, Safety Series No. 75, INSAG-4, 1991, IAEA, Vienna, Austria.
  5. Management of Operational Safety of Nuclear Power Plants, INSAG-13, 1999, IAEA, Vienna, Austria.
  6. Seismic Qualification of Existing Nuclear Power Plants, SMIRT-13 Post Conference Seminar No. 16, Nuclear Engineering and Design, Volume 182 (1998) No. 1, May 2, 1998, Northern Holland.
  7. A Simplified Approach to Estimating Reference Source Terms for LWR Designs, IAEA-TECDOC-1127, December 1999, Vienna, Austria.
  8. Safety Issues and their Ranking for WWER-1000 Model 320 Nuclear Power Plants, IAEA-EBP-WWER-05, March 1996, Vienna, Austria.
  9. Implementation and Review of a Nuclear Power Plant Ageing Management Programme, Safety Reports Series No. 15 (STI/PUB/1072), 1999, IAEA, Vienna, Austria.
  10. IAEA Activities on Probabilistic Safety Assessment, Ana Gomez-Cobo, Volume II, International Topical Meeting on PSA, Washington, D.C., August 22-26, 1999.
  11. Accident Analysis for Nuclear Power Plants, Safety Report Series (in publication), IAEA, Vienna, Austria.
  12. Implementation of Accident Management Programmes in Nuclear Power Plants, IAEA, Safety Report Series (in publication), IAEA, Vienna, Austria.
  13. Indicators to Monitor Nuclear Power Plant Operational Safety Performance, Ana Gomez-Cobo, ICONE-8042-8th International Conference on Nuclear Engineering, April 2-6, 2000, Baltimore, MD, USA.
  14. Generic Safety Issues for Nuclear Power Plants with Light Water Reactors and Measures taken for their Resolution, IAEA-TECDOC-1044, September 1998, Vienna, Austria.
  15. Root Cause Analysis for Fire Events at Nuclear Power Plants, IAEA-TECDOC-1112, September 1999, Vienna, Austria.
  16. Achieving Year 2000 Readiness Basic Processes, IAEA-TECDOC-1072, March 1999, Vienna. Austria.
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