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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - INCEFA - PLUS (INcreasing Safety in NPPs by Covering gaps in Environmental Fatigue Assessment)

Teaser

Summary

OBJECTIVES
US NRC and ASME guidance for Environmentally-Assisted Fatigue (EAF) assessment can result in calculated high fatigue usage factors that are frequently inconsistent with Nuclear Power Plant (NPP) experience. So the overall aim of the project is to develop new or modified guidelines for assessment of EAF damage susceptibility for NPP components. The project has the following specific objectives:

A) Identify the most significant differences between conditions producing EAF damage in NPPs and laboratory tests.
B) Test to improve understanding of the sensitivity to these differences of fatigue life in Pressurised Water Reactor (PWR) primary environment.
C) Develop a new or modified procedure for assessing fatigue degradation in reactor coolant under plant conditions to avoid excessive conservatism inherent in current US NRC guidelines and draft ASME Code Cases.

DESCRIPTION OF WORK
The project is divided in two main parts. The first is focused on the characterization of a limited selection of typical austenitic stainless steel alloys employed in NPPs, testing for the effects of mean stress/strain, hold time periods and material surface finish on fatigue endurance. Sensitivities to these three parameters will be mainly tested in Light Water Reactor (LWR) environments. Tests in air for all types of specimen are restricted to only those necessary to cross reference the LWR results with the data already available for fatigue endurance in air and forming the majority of data used to underpin existing guidance (NUREG/CR-6909). The three experimental parameters were selected as common priorities by the proposed collaborators based on an in-kind project through which a description of the current state-of-the-art for this technical area was developed. The second part of this project involves the development of a modified or new procedure for estimating the fatigue degradation of the materials based on the experimental results of the first part of the project. This methodology is supposed to take better account of the effects of mean stress/strain, hold time and surface finish. This will enable better management of nuclear components, making possible the Long Term Operation (LTO) of NPPs under safer conditions. The project also includes a specific Work Package for the dissemination of the different results derived from the above described activities.

MAIN DELIVERABLES
The main deliverable of the project is a new or modified fatigue analysis procedure. It will incorporate the new data generated within the project:
1) New parameters that have effects on the fatigue degradation,
2) New and more representative fatigue curves (S-N),
3) New or tentative modification to the expressions for environmental factor assessment,
4) Guideline for fatigue assessment of components of NPP
Besides a new/revised fatigue analysis procedure the project will also establish a new fatigue data format standard. For that purpose the workshop FATEDA has been started in the framework of the â€œComitÃ© EuropÃ©en de Normalisationâ€ (European Committee for Standardisation, CEN). More information on FATEDA can be found under https://www.cen.eu/work/areas/ICT/eBusiness/Pages/WS-FATEDA.aspx .

Work performed

This report summarizes progress on the INCEFA-PLUS project from month 1 to month 18. During this period major developments in each WP have comprised:
â€¢ WP1- Project management
o The Advisory Board has been formed and terms of reference agreed.
o The inaugural meeting of the General Assembly took place immediately after the Mo12 meetings. The GA has been very helpful in developing a solution to Areva project resourcing challenges.
o The Consortium Agreement remains outstanding due to delays responding to partner queries. However, a new, hopefully final, version is now being signed by partners.
o Since the Kick-off meeting in the UK, there have been three further project and ExComm meetings, held at 6 month intervals, plus a number of issue specific web teleconferences. The venue for the 6 monthly meetings has been agreed to rotate round the consortium.
â€¢ WP2 - Test programme
o The testing protocol and Phase 1 test conditions are now fully agreed by the Consortium, this is a major achievement since it is necessary to ensure commonality of testing between labs.
o Delays in issuing of specimens have resulted in delays to commencement of Phase 1 testing and supporting material characterisation. There have also been delays in laboratory readiness for some partners.
o However, Phase 1 testing is now underway and is expected to gather pace during the first half of 2017 as more laboratories become ready and more specimens (especially ground ones) are issued.
o Although Phase 2 testing will now also have to be delayed the project outcome remains secure since many WP3 activities can occur before WP2 ends.
o A major focus for the Mo19 meetings was agreement of measures to minimize any further delays.
â€¢ WP3 - Development of a fatigue analysis procedure
o The FATEDA CEN workshop was launched and has met all its deadlines. Standard fatigue data formats are now agreed, consistent with ISO-12106, and a working XML interface is now available for these formats.
o As a precursor to beginning development of methodologies within INCEFA-PLUS, EDF performed a thorough review of existing methodologies (US, European, French, German and Japanese) for the project. The review listed the advantages and limitations of each approach and is now a key reference document for the project as it makes decisions on possible methodologies to emerge from INCEFA-PLUS.
o A full day web meeting has developed ideas for data analysis that have now been endorsed and further developed by the full project. The need for digitizing existing public data for combining with INCEFA+ data is agreed, as is the desire to produce advances in fatigue assessment consistent with NUREG/CR-6909.
â€¢ WP4 - Development of INCEFA-PLUS website, training seminars and workshops
o Significant web traffic has continued demonstrating interest in the public INCEFA-PLUS web presence and the INCEFA-PLUS ResearchGate profile.
o The project was presented at several international events and conferences (e.g. PVP2016, 18ICMFM, NUGENIA Forum), and also to the World Nuclear Association CORDEL project. At one of the conferences the presentation was included in a session co-organized by the INCEFA-PLUS project.

It is noteworthy that the project has not limited itself to production of deliverable reports, but has been pro-active creating additional documents supporting meeting of the overall objectives. Examples include, the testing protocol and the review of existing methodologies. The availability of these documents is being advertised to the wider community.

The next project gatherings will be at VTT in Finland in June 2017 and will comprise the final FATEDA meeting, ExComm, Project and General Assembly meetings.

Final results

The agreement of a testing protocol that is being adhered to by 16 partners from across Europe is a major development. This testing protocol will be added to as the project advances and by the end of the testing phase of the project will be a major reference that could form the basis of a future ISO standard for fatigue testing in high temperature water environments (there is currently no such standard).