The influence of LWR coolant environment to the lifetime of materials has been discussed recent years. Nowadays the consideration of environmentally assisted fatigue is under consideration in Codes and Standards like ASME and the German KTA Rules (e.g. Standard No. 3201.2 and Standard No. 3201.4) by means of so called attention thresholds. Basic calculation procedures in terms of quantifying the influence of LWR coolant environment by the Fen correction factor were proposed by Higuchi and others and are given in NUREG/CR-6909. This paper deals with the application of the proposed assessment procedures of ANL and the application to plant conditions. Therefore conservative assessment procedures are introduced without assuming the knowledge of detailed stress and strain calculations or temperature transients. Additionally, detailed assessment procedures based on Finite-Element calculations, respecting in-service temperature measurements including thermal reference transients and complex operational loading conditions are carried out. Fatigue evaluation of a PWR primary circuit component is used in order to evaluate the influence of plant like conditions numerically. Conclusions regarding the practical application are drawn by means of comparing the ANL approach considering laboratory conditions, conservative assessment procedures for the determination of cumulative fatigue usage factors of plant components and detailed assessment procedures. Plant like loading conditions, complex component geometries, loading scenarios and reference temperature transients shall be taken into account. Practical issues like the determination of the mean temperature or the strain rate have to be considered adequately.

In PVP2011-57942 we reported improved endurance in fatigue tests with intermediate annealing to roughly simulate steady state operation between fatigue transients in NPP components. Quantification of this effect is in focus of our continued research on fatigue performance of niobium stabilized stainless steel (1.4550, X6CrNiNb1810mod). Similar effect is expected in nuclear power plants during normal operation — e.g. in a PWR surge line or in pressurizer spray lines. Holds affect cyclic stress strain response. Stress amplitude, tensile mean stress and apparent elastic modulus are increased immediately after a hold, while decreased by cycles in between. Axial shortening is measured during hot holds at zero stress. This all suggest cyclic accumulation of lattice defects and recovery during holds. Recovery may occur through thermally activated dislocation migration together with diffusion, grouping and annihilation of lattice defects. More than one thermally activated processes control the rates of contraction during hold periods at elevated temperatures. Hold hardening delays crack formation by preventing plastic strain localization, in components also on macroscopic level. A mechanism informed model is sought for transferring laboratory data to real plant components in terms of improving accuracy of numerical fatigue usage assessment. Anticipated mechanisms behind gradual changes in material responses are discussed in relation to quantitative effects of holds.

Distribution system operators in rural areas of Germany are frequently facing imminent equipment overloading caused by the feed-in of local renewable Distributed Generation (DG). A grid operator's last resort to maintain system stability and avoid protection tripping is to temporarily curtail local feed-in until hosting capacity in the network has caught up with the demand. Due to technological limitations in today's networks the volume of curtailed energy can be greater than what would strictly be necessary. This paper presents a case study of a 110 kV overhead line in Avacon´s network and demonstrates the limitations of today's approach to DG curtailments, especially the relative coarse granularity of control steps. The authors develop a novel control algorithm for emergency curtailments that takes advantage of technological improvements and describes the architecture for a successful deployment at the example of Avacon´s network and SCADA. The authors compare the amount of curtailed energy under today´s best practice with the theoretical optimum and the novel approach.

Consideration of environmentally assisted fatigue (EAF) is in discussion internationally. In German KTA Rules the effect is taken into account by means of so called attention thresholds. While the laboratory phenomena themselves are being accepted widely, numerical calculation procedures are revised continuously and transition from laboratory to real plant components is not clarified yet. Since NUREG/CR-6909, formulas for calculating the Fen factors have been modified several times. For example in ANL-LWRS47-2011 a new set of formulas was published and slightly revised by ANL in 2012. Various calculation procedures like the strain-integrated method and simplified approach have been published while each approach yields to different results. Beyond this, additional topics like weld factors or plasticity correction factors have to be taken into account. Calculation procedures depending on the level of detail and in the description of loads are yielding to significant variations in the results. Respecting these topics in context of different levels of detail in computational simulations, numerical cumulative usage factor (CUF) evaluation results are likely to differ, depending on the assumptions made. On the basis of a practical example, methods and approaches will be discussed and recommendations in terms of avoiding over-conservatism and misinterpretation will be presented.

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.