ODonnell Consulting

Methods for Evaluating Cyclic Life of Components in Reactor Water

“Methods for Evaluating the Cyclic Life of Nuclear Components Including Reactor Water Environmental Effects” W. J. O’Donnell, J. S. Porowski, N. Irvine, B. Tomkins, D. Jones, and T. O’Donnell, Presented at ASME Pressure Vessel and Piping Conference, New Orleans, Louisiana, June 21-21, 1992, PVP Vol. 238, ASME 1992.

Keywords: fatigue design; power plant components; environmental effects; corrosion fatigue; safe life

Current ASME fatigue design curves for nuclear power plant components are based entirely on data obtained in air, and largely at room temperature. The 30 year old fatigue curves include environmental effects only as a portion of the factors of 2 and 20 to obtain the design curve for polished specimens. More recent data have shown that reactor water environmental effects are greater than was assumed when current Code design curves were developed. It is therefore desirable to include reactor water environmental effects in component cyclic life assessments.

Corrosion fatigue S-N data must be interpreted in terms of the water chemistry (pure water vs. BWR and PWR conditions), cyclic strain rate, mean stress effects, flow conditions, temperature, the composition of the materials, etc. The sulfur content, and particularly and the morphology or area fraction of sulfide inclusions, has been found to be important in ferritic steels in LWR environments. It is not feasible to conduct S-N corrosion-fatigue tests at the slow cyclic rates representative of reactor operating conditions, and at the mean stress levels, and environmental conditions of interest in reactor component structural materials in order to quantify all of these effects on safe life.

A method of including these effects in improved cyclic life evaluations is proposed wherein crack initiation and propagation are evaluated and integrated to quantify the safe life. This approach makes use of available da/dN data in order to correct S-N fatigue life assessments for reactor operating conditions including environmental effects.