Session: CS-17-03 Environmental Fatigue Issues (Joint with M&F)-3: INCEFA SCALE & International Studies

Paper Number: 154606

154606 - Challenges and Solutions for Experimental Eaf 

Abstract: 

Meeting the stringent requirements of strain-controlled testing standard ASTM E606 for environmentally-assisted fatigue, EAF in simulated reactor coolant is challenging. Lack of solution for sufficiently accurate and reliable measurement of strain within the smooth gauge section of a LCF specimen in hot water environment is a potential game stopper. A common way to circumvent this problem has been to apply remote control of strain through robust displacement sensors attached on the specimen shoulders. However, when studying EAF with austenitic stainless steels, precision of applied strain is unavoidably compromised, due to unpredictable changes in correlation between cyclic strains and displacements.

Another widely used approach has been to contain the hot water within a center bore of a hollow specimen. This allows direct measurement of axial strain measurement within the specimen gauge in gaseous environment, but design and manufacture of the specimens requires special attention to maintain comparability with the applied design reference curves. The test failure criteria have evolved from fracture to various percentages of load drop or leak in the hollow specimen. Current focus towards “total life” design approaches will emphasize importance of transferability and failure criteria in experimental EAF research.

GE Global Research Center and VTT have solved the challenge of applying direct strain control based on strain measuring devices gently mounted on solid polished specimens. This has opened us a closer insight to the differences between cyclic responses in air and PWR coolant environment, which can be attributed to relative rates of strain (moving dislocations) and diffusion of absorbed hydrogen. Furthermore, the obtained strain – life data suggest that excessive conservatism was embedded in the environmental penalty factors (F_en per NUREG/CR-6909) determined through stroke-controlled testing. However, VTT’s pneumatic load train provided limited capacity for fast straining and insufficient control for transient simulation with variable amplitudes and rates.

This paper discusses in quantitative terms the common challenges in experimental EAF and lessons learned in design and commissioning of a third generation EAF facility. Our mission is to encourage colleagues in adoption of direct strain control for ASTM E606 compliant EAF testing, filling of knowledge gaps for plant application and research towards mechanism informed parametric modelling of environmental effects in fatigue of primary circuit components.

Presenting Author: Tommi Seppanen VTT Technical Research Centre of Finland Ltd.

Presenting Author Biography: To be added later

Authors:

Tommi Seppanen VTT Technical Research Centre of Finland Ltd.
Esko Arilahti VTT Technical Research Centre of Finland Ltd.
Jouni Alhainen VTT Technical Research Centre of Finland Ltd.
Juho Juvalainen VTT Technical Research Centre of Finland Ltd.
Pekka Moilanen VTT Technical Research Centre of Finland Ltd.
Jussi Solin VTT Technical Research Centre of Finland Ltd.