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(se abrirá en una nueva ventana) .