The dynamic aspects of loading conditions for reactor internals, piping and the like, are thought to play important roles in the initiation of failures due, for example, to stress corrosion cracking (SCC) and fatigue. Some reports show that a strain rate on the order of 10−7 s−1 most affects susceptibility to SCC in the BWR reactor water environment. Environmental fatigue, which exhibits a shorter fatigue life in reactor water than that in air, is considered to have a remarkable correlation with strain rate and its affect on fatigue life. Despite its significant affect on SCC and fatigue, the actual strain rate of components is not known and practical evaluation methods have not been developed; consequently, such failure modes as SCC and fatigue are not evaluated in design. For this paper, strain rates induced by dynamic loading during such operations as plant start-up were calculated at typical points, such as reactor internals, piping and so on. The finite element method was applied to calculate the strain history of each point, and the strain rate was evaluated. The strain rate evaluation results clearly demonstrated that thermal transients provide greater peak strain rate values than pressure transients. Strain rates on the order of 10−7 s−1 were obtained for most points of major components during such thermal transients as plant start-ups. The major factors determining the strain rate magnitude were discussed, based on the calculation results. It was shown that the rate of temperature rise was the most important parameter, because it exhibited much larger sensitivity than the other parameters on the strain rate and could be controlled by plant operation procedures. In addition, a simple strain rate evaluation method based on Green’s function was developed for a specific point with a given design condition.

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