Out of 435 nuclear power plants in operation, as of 2014 225 have been operating for more than 30 years and 63 for more than 40 years. In view of this, many countries give a high priority to continuing the operation of plants beyond the time frame originally anticipated (for example, 30 or 40 years).
Long term operation (LTO) of a nuclear power plant may be defined as operation beyond an established time frame set by, for example, licence term, design, standards, licence or regulations, which has been justified by safety assessment, with consideration given to life limiting processes and features of systems, structures and components (SSCs). Proper and safe LTO is based on experience and practice in areas such as ageing management programmes (AMPs), other plant programmes relevant for LTO, time-limited ageing analyses (TLAAs) and plant licence renewal. Other activities, including periodic safety review, current licensing basis and plant modifications, are also relevant to LTO. Effective AMPs are key elements in the safe and reliable operation of nuclear plants during the time frame originally planned for operation and for the period of LTO.
The IAEA Safety Aspects of Long Term Operation (SALTO) peer review service was introduced in 2005. Components of the SALTO peer review service have already been provided to 16 Member States operating 166 nuclear power plants.
Safety Report No. 57 "Safe Long Term Operation of Nuclear Power Plants", published in 2008, addresses mainly the following LTO-related topics:
- Principles of and approach to LTO
- Preconditions for LTO
- Scoping and screening of SSCs
- Ageing management review (AMR)
- Review of AMPs
- Revalidation of TLAAs.
This Safety Report is also used as the basis of the IAEA SALTO peer review service.
Safety Guide NS-G-2.12 "Ageing Management for Nuclear Power Plants" was published in 2009. This Safety Guide deals with the establishment, implementation and improvement of AMPs for SSCs important to safety in nuclear power plants. It mainly focuses on managing the physical ageing of SSCs important to safety, but also provides recommendations on safety aspects of managing obsolescence and on the application of AM for LTO.
The requirements for the design and operation of nuclear power plants are established in the Specific Safety Requirements publications SSR 2/1 on Safety of Nuclear Power Plants: Design published in 2012 and SSR 2/2 on Safety of Nuclear Power Plants: Commissioning and Operation published in 2011. SSR 2/2 contains also Requirement 16: Programme for long term operation, which is the IAEA highest level basis for recommended activities for safe LTO.
The most recent document in the area of LTO is a Safety Report No. DD1085 "Ageing Management for Nuclear Power Plants: International Generic Ageing Lessons Learned" (also called "IGALL Safety Report") which was published in 2014. The objective of this report is to provide a technical basis and practical guidance on managing ageing of SSCs that are important to the safety of nuclear power plants. IGALL contains, for SSCs important to safety:
- A generic sample of AMR tables
- A collection of proven AMPs
- A collection of typical TLAAs.
This information is publicly available and can be found as "IGALL database" on the IAEA web pages. The current IGALL database consists of more than 2000 line items in the AMR table, 76 AMPs and 27 TLAAs.
International peer review
International peer review is a useful tool for member states to exchange experiences, learn from each other and apply good practices in dealing with LTO of NPPs. The peer review service is also an important mechanism through which the IAEA supports member states in enhancing the safety of NPPs.
The SALTO peer review was performed as a pilot for the Hungarian regulatory authority and Paks nuclear plant in Hungary, starting in 2005. It consisted of series of limited-scope SALTO missions, a Pre-SALTO mission, SALTO mission and SALTO follow-up mission. Further limited-scope SALTO missions for Karachi NPP in Pakistan and South Ukraine NPP in the Ukraine and SALTO mission for Kori NPP in South Korea were performed in 2007. Based on this experience, a first edition of SALTO Guidelines was published in 2008.
Following SALTO missions were performed using these guidelines:
- Dukovany, Czech Republic – Pre-SALTO
- Borssele, the Netherlands – Pre-SALTO
- Kori 1, Republic of Korea – SALTO Follow-up
- Koeberg, South Africa – Limited-scope SALTO
- Dukovany – SALTO Follow-up
- Borssele – SALTO + SALTO Follow-up
- Wolsong 1 – SALTO
- Tihange 1, Belgium – Pre-SALTO.
A large amount of experience was collected and SALTO peer review service was changed and improved significantly. Experience gained out of these missions and repeated requests of NPPs to add a new review area of "Human resources, competency and knowledge management for LTO" led to revision of SALTO Guidelines in 2013. The scope, time schedule, terminology, reporting and procedures for SALTO peer review services were also standardized in this document. Another target was to bring SALTO methodology and terminology closer to OSART missions. New SALTO guidelines were published in January 2014 and were used already in a draft version in 2013 for the following missions:
- Armenia 2 – Pre-SALTO
- Angra 1, Brazil – Pre-SALTO
- Borssele – SALTO Follow-up
- Ringhals 1 and 2, Sweden – Pre-SALTO
- Wolsong 1 – SALTO Follow-up)
- Dukovany – SALTO.
Numerous expert missions based on SALTO methodology were also performed for NPPs and regulators in Armenia, Brazil, Bulgaria, China, Hungary, Mexico, Pakistan and the Ukraine.
SALTO workshops were introduced in 2012 as a preparatory phase for SALTO missions. In 2013, the IAEA provided eight SALTO workshops/seminars to six Member States (Bulgaria, Canada, China, Japan, Mexico and Sweden). Growing importance of LTO activities and these workshops/seminars resulted in an increased understanding of the SALTO peer review service and in an increased number of SALTO mission requests.
Objectives
The key objectives of the peer review are to provide:
- An objective assessment of the status of the preparedness for LTO with respect to international nuclear safety standards, for the host organization (operating organizations and technical support organizations)
- Recommendations and suggestions for improvement in areas where performance falls short of international best practices, for the host organization
- An opportunity for key staff at the host organization to discuss their practices with experts who have experience with related practices in the same field
- Information regarding good practices identified in the course of the review, for member states
- Opportunities for reviewers and observers from Member States and the IAEA staff to broaden their experience and knowledge of their own field.
The SALTO peer review addresses the following areas:
- A. Organization and functions, current licensing basis (CLB), configuration/modification management
- B. Scoping and screening of systems, structures, and components, and plant programmes relevant to LTO
- C. Ageing management reviews for mechanical, electrical and I&C components and civil structures
- D. Review of ageing management programmes for mechanical, electrical and I&C components and civil structures
- E. Revalidation of time-limited ageing analyses for mechanical, electrical and I&C components and civil structures
- F. Human resources, competence and knowledge management for LTO.
The scope of the SALTO peer review does not include: Assessment or review of the plant design; Assessment of the environmental impact of LTO;
Economic assessment and long term investment strategies.
Review process
Pre-SALTO missions should be conducted well in advance of entering the LTO period. This mission should review the completeness of the plant intended activities for preparation for safe LTO and the compliance of those activities with the IAEA standards and recommendations. The SALTO mission reviews the status of the LTO activities close to their completion or when completed, and prior to entering the LTO period. To check the progress in implementing recommendations and suggestions to resolve issues, a follow-up SALTO mission is conducted. The length of SALTO missions is normally from seven to ten working days.
The SALTO peer review is conducted by a team of international experts with experience applicable to the areas of review. The typical team composition includes a majority of external experts (experienced experts from utilities, regulatory authorities or support organizations) and IAEA staff members (including the team leader and the deputy team leader, if applicable).
The SALTO peer review team uses four steps to acquire the information needed to develop their recommendations and suggestions:
- Review of written material and databases;
- Discussion and interviews;
- Direct observation of performance, status and activities;
- Discussion of evaluations and tentative conclusions within the team and with counterparts.
The SALTO mission report details issues with recommendations and suggestions. The report is submitted through official channels to the Member State and is usually publicly available unless agreed otherwise.
The IAEA is encouraging Member States to invite SALTO peer review missions. This peer review for reviewing AM and other activities relevant to LTO can be carried out at any time during the lifetime of a plant but is strongly recommended prior to entering LTO period.
Issues from 21 missions are summarized, by review area, in three tables to left. The most important issues for safe LTO of plants identified by SALTO missions relate to unclear definition of LTO plant policy, poorly established configuration or modification management, lack of access to design basis, incomplete scoping and screening of SSCs for LTO, poor interaction of plant programmes with AM, AMPs not addressing all generic attributes of effective AMP, insufficient environmental qualification programme including revalidation of qualified lifetime, inconsistency of databases, inappropriate AMP of reactor containment and insufficient human resources for LTO activities.
About the author
Robert Krivanek, International Atomic Energy Agency (IAEA), Project manager for LTO, Operational Safety Section, Department of Nuclear Safety and Security, Vienna International Centre, P.O. Box 100, 1400 Vienna, Austria
