CSNI Workshop

Structural reliability evaluation and mechanical probabilistic approaches for examining NPP components

Lyon, France
25-27 September 2006

Hosted by Électricité de France with support from the USNRC (USA), EPRI (USA), SKI (Sweden) and GRS (Germany)

Initiated originally to discuss and disseminate the results of the NEA probabilistic structural integrity of a pressurised water reactor pressure vessel benchmark (PROSIR), the workshop was broadened to cover probabilistic approaches to mechanical components in nuclear power plants. The workshop assessed the current practices and the state of the art with respect to these approaches. Information obtained as a result of this assessment will be utilised to develop a consensus on these approaches and identify issues or gaps in the present knowledge for the purpose of formulating and prioritising needs in this area.

Regulators, researchers and industry representatives need to exchange information and views on the current regulation and technical issues associated with RI-ISI and NDT qualification by discussing and contrasting the different approaches taken for the further optimisation of in-service inspections in nuclear power plants. The workshop also covered R&D activities performed by international and regional task groups.

Workshop background

Pressurised thermal shock continues to be an important issue for long-term operation. In the past, FALSIRE, and ICAS benchmarks (OCDE/NEA projects) assessed deterministic approaches and first highlighted probabilistic issues. Probabilistic approaches are more and more widely used. The CSNI and its Integrity of Components and Structures working group (IAGE WG) considered there was a need to clearly understand how calculations were performed in the different NEA member countries. Furthermore, recommendations on improvements or on common basis that could be adopted were found to be very valuable. Consequently, in June 2001 the CSNI initiated a benchmark on the probabilistic approach to examining the reactor pressure vessel.

The main objectives of the benchmark on "Probabilistic Approaches of RPV" (PROSIR) were to:

confirm performance of probabilistic approaches for RPV structural integrity;
compare and improve probabilistic fracture mechanic tools;
identify the major parameters and uncertainties that play a role in these approaches (e.g. flaw-type and distribution, toughness models and uncertainties, crack arrest, warm pre-stressing);
issue some recommendations on best practices.

The benchmark consisted of four phases over a period of 4 years:

Phase 1: Fitting of the methodology used by different participants through deterministic cases;
Phase 2: Probabilistic cases;
Phase 3: Sensitivity studies;
Phase 4: Reporting workshop.

Several organisations (or teams) from nine OECD/NEA member countries and the European Commission (USA , Sweden, Czech Republic, Germany, Spain, Japan, Korea, EC and France) accepted the invitation to participate in the benchmark.

Building up on this benchmark, this workshop aims to gather participating organisations but also others (utilities, researchers, academics) who could contribute to the discussion and share their experience and techniques on probabilistic approaches of mechanical components in nuclear power plants.

The CSNI Working Group on the Integrity on Components and Structures and in particular its sub-group on the metallic components has produced several studies over the last few years. Recent relevant references are given below.