Working Group on Integrity and Ageing of Components and Structures (WGIAGE)
The main mission of the Working Group on Integrity and Ageing of Components and Structures (WGIAGE) is to advance the current understanding of those aspects relevant to ensuring the integrity of structures, systems and components under design and beyond design loads, to provide guidance in choosing optimal ways of dealing with challenges to the integrity of operating as well as new nuclear power plants, and to make use of an integrated approach to design, safety and plant life management.
The working group shall report to CSNI and assist the committee with its work. With prior approval of CSNI, the working group shall collaborate with or respond to requests from the CSNI Programme Review Group, working groups and other NEA committees or other international organizations.
OECD member country representatives are joined at the group's meetings by representatives from the IAEA, the European Commission and JRC Petten.
The working group has a general mandate to reflect on the logical basis for the maintenance of the integrity of nuclear power plant components, systems and structures, and to propose general principles on the optimal ways of dealing with challenges to integrity – in particular those from ageing. Specifically, the mandate will be the following:
The working group shall constitute a forum to exchange views, information and experience on generic technical aspects of integrity and ageing of components and structures. It will review, as necessary, national and international programmes concentrating on research, operational aspects and regulation.
The working group shall stimulate, in relevant technical areas, new research and recommend and lead possible international co-operative projects.
The working group shall: a) develop technical positions on specific integrity issues of operating and new nuclear power plants and research reactors covering the entire life cycle and; b) identify areas where further work is needed.
The working group shall discuss the potential impact of ageing and other challenges to integrity on the safety, regulation, and operability of operating and new nuclear power plants and research reactors.
Programme of work
The WGIAGE consists of a main group three subgroups dealing with: a) integrity and ageing of metal structures and components; b) integrity and ageing of concrete structures and; c) seismic engineering. All subgroups deal with the structural integrity issues in a broad sense, and although disciplines are similar (e.g. structural mechanics and materials behaviour), the expertise needed to address group-specific issues is different. The main group serves as an entry point for CSNI. CSNI technical goals related to ageing, which are not covered by the sub-group work, will be managed by the time-limited task groups coordinated by the main group.
The principal mechanisms currently used by the working group to accomplish its objectives are: a) the conduct of meetings (including annual group meetings and specialist expert meetings and workshops) to share information and plan/coordinate/manage activities; b) the collaborative writing of consensus documents (e.g. state-of-the-art reports, technical reports and technical opinion papers) and; c) highlights related to the integrity and ageing of components and structures via technical notes.
The main group's recent activities include:
identifying current experience and areas for further improvement on plant ageing management at the member countries;
identifying technical areas of mutual interest related to age-related degradation of materials in safety-related systems, structures and components (SSCs) during long-term operation of nuclear power plants.
Integrity of metal components and structures
The integrity of metal components and structures sub-group's recent activities include:
identifying and assessing the recent results on the topic of fatigue, especially taking environmental effects into account;
developing a benchmark on the probabilistic structural integrity of a PWR reactor pressure vessel;
identifying technical areas of mutual interest related to: a) the structural integrity evaluation of piping systems using deterministic and/or probabilistic methods and; b) the demonstration that flaws in piping systems will exhibit leaks prior to failure;
identifying the different approaches that are followed in different countries in the performance or non-performance of hydro-proof tests and the rationale that lies behind each approach;
comparing structure mechanical analysis methods for integrity assessment of metallic components of selected pressurized and boiling water reactors under severe accident loading.
Ageing of concrete structures
The integrity and ageing of concrete structures sub-group's recent activities include:
improving robustness assessment of structures impacted by a large missile at medium velocity;
providing general recommendations for ageing management of concrete nuclear facilities subject to concrete degradation with a focus on alkali-silica (aggregate) reaction (ASR);
investigating the comparative advantages and disadvantages of various post-tensioning techniques in reactor containments;
reviewing existing methods for non-destructive evaluation of NPPs thick-walled concrete structures.
Seismic behaviour of components and structures
The seismic behaviour of components and structures sub-group's recent activities include:
quantifying the existing margins in seismic analysis of safety class components for high seismic loads associated with existing design practices within a benchmark activity;
compiling a catalogue of seismic events recorded by NPPs around the world in co-operation with the IAEA;
improving the accuracy of the design basis ground motion by investigating the latest information about the earthquake recording techniques;
reviewing current practices in member countries on the definition of seismic input from far and near field sources and its control point;