INcreasing Safety in NPPs by Covering gaps in Environmental Fatigue Assessment

Project Information

INCEFA - PLUS

Grant agreement ID: 662320

DOI

10.3030/662320

Project closed

EC signature date 8 June 2015

Start date 1 July 2015

End date 31 October 2020

Funded under

• Euratom

Total cost

€ 6 140 668,75

EU contribution

€ 2 550 128,00

Coordinated by

AMENTUM CLEAN ENERGY LIMITED.
United Kingdom

Periodic Reporting for period 4 - INCEFA - PLUS (INcreasing Safety in NPPs by Covering gaps in Environmental Fatigue Assessment)

Reporting period: 2020-01-01 to 2020-10-31

Summary of the context and overall objectives of the project

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

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

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 completed in the framework of the “Comité Européen de Normalisation” (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 from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the Fourth Period, activities and results at the project end can be summarised as:
o Maintaining progress on the project through regular plenary meetings.
o Continuation of ad hoc teleconference and face-to-face meetings to maintain momentum in several critical areas:
Data upload to MatDB
Expert Panel reviews and support to partners
Development of a draft collaborative agreement between the project and USNRC, EPRI and NRA
Analysis of data.
o Successfully negotiating an extended duration of the project from 60 to 64 months due to the Covid19 pandemic.
o Completing approximately 250 tests.
o Completing reviews of data by the INCEFA-PLUS appointed Expert Panel.
o Focussing data analysis on three main themes:
The effects of different test parameters.
• Strain range and surface roughness effects dominate.
• Mean stress does not affect environmental fatigue sensitivity.
Impact of specimen diameter and lab-to-lab scatter.
• Project conclusions were insensitive to specimen diameter, and to the combination of solid and hollow specimen types.
• A factor 1.5 on life was quantified for lab-to-lab variation.
Impact on existing EAF procedures.
• Results are consistent with what has been previously reported in the literature, and underpin already existing fatigue procedures that have been recently developed to incorporate a margin corresponding to a factor 3 on fatigue life.
o Continuing to pursue finalising an International Fatigue Database Agreement between the consortium, USNRC, EPRI and NRA; good progress has been made but there remain some commercial challenges.
o Promoting the project and its objectives to the international community at relevant conferences.
o Organising the second dissemination workshop as a virtual event. Fifty-nine attendees were signed up; significant positive engagement was a feature.
The high degree of interest in and support for the project from Japan and the USA, as well as from European industry stakeholders within and beyond the project helps increase confidence in acceptance of the methodologies endorsed by the project.
With regard to exploitation, the agreed common data formats achieved through the FATEDA-CEN workshop are potentially the basis of a future European standard. The data generated by the project is of high value supporting existing improved environmental fatigue assessment methodologies. The US and Japanese interests in the data are a testament to this. Subject to being able to finalise a data sharing agreement, the project partners, and hence the underpinned methodology, will benefit from this interest due to the ability to include data obtained outside of the project, made accessible to the partners in return for access to the project’s data. There has also been an expression of interest within Europe to link INCEFA-PLUS development of assessment guidelines with activities being pursued by TC-54 with respect to EN-13445-3 fatigue rules. An unanticipated area for possible future exploitation, is the testing protocol developed by the project; this is a valuable reference document for the project and could be the basis of a future ISO standard for environmental fatigue testing.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The agreement of a testing protocol that is being adhered to by 16 partners from across Europe is a major development. This testing protocol is being added to as the project advances and by the end of the testing phase of the project is 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).

The analysis of the high quality fatigue data has, for the material studied by the project, significantly underpinned already developed advanced European and US capabilities for fatigue assessment, resulting in improved reliability of fatigue endurance predictions.

The CEN FATEDA workshop developed common data formats for fatigue endurance data which have already led within the INCEFA-PLUS project to improved abilities to combine data from a number of different organizations.

INCEFA-PLUS organogram