Environmentally Assisted Fatigue (EAF) has been focus of various research activities and has been addressed in nuclear Codes and Standards like German safety standard KTA 3201.2 [1], 3211.2 [2] or ASME CC N-792 [3] for example.

Based on experimental investigation under laboratory conditions a numerical correction factor Fen was proposed in NUREG CR-6909 [4] in 2007 after precursors in the Japanese JSME code [6]. In 2012 the EPRI Technical Report “Guidelines for Addressing Environmental Effects in Fatigue Usage Calculations” [7] introduced some practical guidelines for the application of the EAF to real plant components based on the set of formulas from 2007. Since this report the set of formulas have been adapted several times (e.g. in ANL-LWRS 47-2011 [8]) while the current revision of NUREG/CR-6909 in 2014 [9] describes the current state of the art.

At E.ON Kernkraft GmbH a goal-oriented and engineering based research program called NuMEA (Numerical Methods to take Environmentally Assisted Fatigue into Account) has been established, focusing on recommendations of the EPRI guideline in the context of application to real plant components and available temperature measurement data.

First main focus of the R&D activity is to calculate the EPRI sample for verifying developed procedures and taking different procedures for determining the sign to be assigned to the relevant stress intensity into account. The documentation of the procedures applied within the EPRI guideline is not comprehensive enough for real-plant evaluation application. Thus, additional definitions and procedures have been developed to ensure practical application of the procedures being developed. Additionally, updated formulas being recently introduced in the context of the NUREG/CR-6909 Rev. 1 [9] have been implemented.

Second topic of the activities is to develop a procedure to take hold-time effects into account numerically based on existing experimental data. Motivated by the fact that the introduction of a potentially beneficial effect of hold times is foreseen in the framework of piping design of the German KTA safety standards, the existing engineering approach (PVP2014-2819 [10]) is appended to fatigue calculation of NPP components.

This paper presents the results and the highlights of the E.ON R&D project NuMEA.

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