Technical Working Group on Life Management of
Nuclear Power Plants (TWG-LMNPP)

The history of the TWG began in 1968 when the working group on engineering aspects of reactor pressure vessel irradiation embrittlement was established in the IAEA. However after some time it was decided that the scope of activities of that group should not be narrowed to just the problem of RPV irradiation embrittlement. In 1975 the group reconsidered the topics of its involvement. From that time the group was called "International Working Group on Reliability of Reactor Pressure Components" (IWG-RRPC). In the same year the first terms of reference of the IWG-RRPC were introduced and 1975 had become the official date for the establishment of the IWG.

In 1990 the IWG-RRPC was renamed further to the "International Working Group on Life Management of Nuclear Power Plants" (IWG-LMNPP) and operated till 2001 under this title. In 2001 the IAEA decided to change some of features of the group and therefore the name of the group. Since then the group is called Technical Working Group on Life Management of NPPs. (TWG - LMNPP).

In accordance with the Terms of Reference the main objectives of the TWG-LMNPP remain as follows:

  • To assist the International Atomic Energy Agency is providing its Member States with information, comments and in advising on policies and strategies of plant ageing and life management. Plant ageing management stands for all the engineering, operations and maintenance actions to control within acceptance limits ageing degradation and wear of key components of the plants. Plant life management integrates the previous ageing management and economical aspects in order to:

  • Optimise the operation, maintenance and service of plant key components

  • Maintain the level of safety and performance as well as a return of investment as high as possible during the total service life of the plant

  • To facilitate the exchange of information and experience in the field of understanding and monitoring of ageing mechanisms affecting main NPP systems and components.

  • To provide guidance on general issues which limit NPP lifetime, practical assistance in identification of NPP lifetime limiting features, mitigation measures, assessment of economic cost/benefit of life management for optimisation of the lifetime and decommissioning process.

The TWG-LMNPP should provide the Secretariat of the IAEA with advice and recommendations on the Agency's activities and forward programmes in this area by means of Technical meetings, training courses, co-ordinated research projects, workshops, establishing, operating and maintaining databases etc., when they have particular relevance to reliable plant life operation and management, and, specifically, on the priority, scope and content of publications in the form of guides and manuals and meetings to be organised and sponsored by the Agency. The scope of the TWG activities include the following aspects:

  • Design Materials

  • Fabrication

  • Monitoring, testing, inspection and data bases of their results

  • Degradation mechanisms, their significance and mitigation

  • Assessment and means of plant life management

  • Strategic, economic and administrative aspects of NPP life management including it's decommissioning.

The list of the activities giving the scope of the working group is not fully comprehensive. There are some other items which are important for NPP life management. These items may currently be part of the scope of activities of other groups in the IAEA. The TWG-LMNPP co-ordinates its activities in the field of interest with both groups inside the IAEA and other international organisations.


Topical priorities have been set up and are subjects to reconsideration during TWG regular meetings based upon recommendations from Member States and Project Performance Appraisal System (PPAS) acting within the Agency. The latest list was approved in February 2001 and given below in the sequence of order of priority:

  1. RPV Integrity

    • radiation damage

    • fracture mechanics

    • optimisation of surveillance programmes

    • annealing and other mitigation methods

    • material databases

    • surveillance databases

    • PTS analysis

    • inspection procedures validation/qualification

    • monitoring processes of material degradation and plant operation

    • pressure tubes integrity.

  2. Steam Generator Life Management

    • corrosion and water chemistry

    • wear/mechanical problems (internals)

    • inspection procedures validation/qualification

    • monitoring

    • replacement/repair.

  3. Primary Circuit Operation and Integrity

    • corrosion/erosion and water chemistry

    • fatigue

    • material ageing and its monitoring

    • monitoring of loads and water chemistry

    • inspection procedures validation/qualification

    • LBB concepts and leak monitoring

    • repairs

  4. Reactor Internals Operation and Integrity

    • corrosion, IASCC

    • wear

    • NDE and inspection qualification

    • irradiation ageing

    • replacement and repair.

  5. Secondary Circuit

    • erosion/corrosion

    • water chemistry (optimisation and monitoring).

  6. Containment/civil structures

    • ageing

    • monitoring/NDE

  7. Cables

    • ageing

    • detection/monitoring/testing

  8. Other items of importance

    • valves

    • pumps

  9. Economic aspects of life management programmes in relation to plant management safety, maintenance and decommissioning.

There are also some important items considered by the group but not ranked in the priority list as they are of general importance for all components. Among them:

  • guidelines and recommended practices

  • international aspects of codes and standards

  • international databases

  • quality assurance

  • regulation requirements and licensing procedures

  • maintenance man-dose management

  • component cleaning.


The membership of the TWG-LMNPP includes 27 countries and 2 international organisations. They are as shown in the table below:













  • IRAN















  • EC


Contact: Mr. K. Kang for more details.

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