The IAEA Conference on The Safety of Nuclear Power: Strategy for the Future, held in Vienna, September 1991, addressed the safety of operating nuclear power plants built to earlier standards.
Participants in the conference, which was directed to decision makers on nuclear safety and energy policy, expressed the desire to achieve international consensus on this issue. Subsequently, at the IAEA General Conference, Member States endorsed the recommendations in a resolution urging the IAEA to develop a common basis on which an acceptable level of safety for all operating plants built to earlier standards could be judged.
Since that time, the relevant IAEA programme has focused on the development of guidance to assist Member States in the safety reassessment of operating plants. In addition, INSAG developed a report, entitled A Common Basis for Judging the Safety of Nuclear Power Plants Built to Earlier Standards, INSAG-8 (1995), supplemented by practical guidance issued by the IAEA.
The IAEA Safety Guide 50-SG-O12, Periodic Safety Review of Operational Nuclear Power Plants (1994), provides guidance on the conduct of periodic safety reviews (PSR) of operational nuclear power plants. This Safety Guide describes the review strategy, the safety factors to be reviewed, the roles and responsibilities of the parties involved and the review procedure. It aims at providing a comprehensive reassessment of an operational plant, including whether the plant is safe as judged by current standards and practices and whether appropriate means are in place to maintain plant safety. In the meantime, the IAEA Safety Guide 50-SG-O12 has been revised and is now available as the IAEA Safety Standards Series No. NS-G-2.10, Periodic Safety Review of Nuclear Power Plants (2003).
The IAEA Safety Series Report No. 12, Evaluation of the Safety of Operating Nuclear Power Plants Built to Earlier Standards - A Common Basis for Judgement was issued in 1998 to provide details for the safety assessment and judgement process. It provides practical advice on the main judgements to be made in any review process of plant safety.
These IAEA publications are based on the knowledge, experience and national programmes in Member States, to reassess safety of operating plants. The IAEA Extrabudgetary Programme on the Safety of WWER and RBMK NPPs has also contributed to the safety reassessment of plants built to earlier standards and the associated safety improvement programmes in the central and eastern European countries, and the countries of the former Soviet Union operating or constructing plants of these types.
A complementary approach to disseminating the knowledge and experience of Member States is to provide the lessons learned directly. The occurrence and recurrence of events, deviations from current international practice in design and operation, and results of PSA studies allow valuable insights into weaknesses in plant safety and into corrective measures to resolve them.
Experience feedback, including learning from incidents and incorporating systems, procedures and design changes is an important prerequisite for incident-free and safe operation of NPPs. The IAEA is issuing several publications in this area and this report on generic safety issues is an important complementary effort in this direction.
There is a generally accepted approach to characterizing the safety concerns in nuclear power plants, which need to be resolved, as ‘safety issues’. When such safety issues are applicable to a generation of plants of a particular design or to a family of plants of a similar design, they are termed “generic safety issues”. Examples of generic safety issues are those related to reactor vessel embrittlement, reliability of insertion of control rods or strainer clogging.
The approach of using generic safety issues for identifying and resolving safety concerns has been practiced in many Member States since the 1970s. These generic safety issues are used as a reference to facilitate the development of plant specific safety improvement programmes and to serve as a basis for reviewing their implementation.
In 1998, the IAEA completed IAEA-TECDOC-1044 Generic Safety Issues for Nuclear Power Plants with Light Water Reactors and Measures Taken for their Resolution and established the associated LWRGSIDB database (Computer Manual Series No. 13). This TECDOC and database basically contain a list of generic safety issues, on the basis of broad international experience, could be used by the Member States as a reference in reassessing their operating plants. The applicability of these issues to each plant under review would, however, have to be checked on a case-by-case basis. It must also be pointed out that such a list of generic safety issues cannot ensure that all the possible safety concerns would be identified, since these would also be influenced by plant specific situations.
1.2. OBJECTIVE
In 1999, the CANDU senior regulators identified the need to have an analogous document addressing generic safety issues pertaining to PHWRs. They agreed to start compiling this TECDOC and to update it regularly. The first draft compilation was produced in 2000. This TECDOC is expected to assist Member States in the reassessment of operating plants by providing a list of generic safety issues identified in PHWR nuclear power plants together with measures proposed, in progress or taken to resolve these issues. Not all the issues presented here are applicable to all Member States or to all reactors within individual Member States. Operators, scientific/technical support organizations and regulators are encouraged to check the applicability of these generic safety issues for operating plants and their safety re-evaluation on a case by case basis.
The use of these generic safety issues for each specific plant under review cannot ensure that all the possible safety concerns would be identified, since these would also be influenced by plant specific situations.
The TECDOC covers issues thought to be of significance to Member States, based on a consensus process. Those issues, which have been generally resolved by Member States or concluded to be of low safety significance, were not included.
This publication is a record of the successful recognition of the safety lessons embedded in plant operation, analysis and regulation.
1.3 SCOPE
The generic safety issues for PHWRs compiled in Section 4 of this report reflect the broad experience of Member States, in resolving safety concerns and in maintaining improvements to current practice.
As can be seen from the actions taken in Member States with respect to the appropriate technical solutions, most issues have been successfully addressed.
Some of the generic safety issues identified in this report for PHWRs are common to other reactor types as well, and these are identified.
The Section 4 compilation also includes those safety issues, which are currently considered pending, i.e. where the root causes and the measures to be taken are being investigated. For pending issues, interim judgements have been made by Member States with respect to continued safe plant operation.
With respect to such pending issues, this report reflects the status of knowledge and experience so far in dealing with them.
In the context of both these categories of issues, the measures taken for a particular issue are not a complete record of actions taken by all Member States but are intended as representative responses by individual Member States which could be useful to other Member States which are still in the process of evaluating the applicability and significance of the issues for their plants.
This TECDOC reflects material received to date from Member States through the CANDU senior regulators. However, additional material from Member States on new issues or on measures taken in response to the issues described will be incorporated, as appropriate, in future revisions. It should also be emphasized that the absence of a response from a Member State does not indicate that no action on the issue has been taken.
1.4 STRUCTURE
Section 2 provides an introduction to the use of the generic safety issues for PHWRs compiled in this TECDOC. In particular, there are more details on the structure of the issues as presented and the associated rationale.
Section 3 presents generic observations on safety aspects identified from the issues in Section 4, grouped according to the source of the issues.
Section 4 is the main body of the report and contains about 86 generic safety issues related to design and operation, grouped according to areas.
2. USE OF THE REPORT