On method of evaluating ratchet due to vessel heat near liquid surface

In the structural design of FBRs, it is an important subject to prevent the phenomenon that structures cause progressive plastic deformation due to the repetition of thermal stress. This phenomenon is called ratchet phenomenon. In addition to the ratchet phenomenon which has been considered in the design standard used so far, on the ratchet phenomenon due to the move of liquid sodium surface, the equation for its evaluation was proposed anew, ans was verified by the analysis and the experiment, therefore, its outline is reported. In the case of the moving free liquid surface of high temperature sodium in the reactor vessels of FBRs, there is the possibility of causing the progressive plastic deformation like the expansion or contraction of reactor vessels due to only the repetition of thermal stress even under the condition without primary stress. This phenomenon must be estimated accurately and prevented. As for the move of temperature distribution and stress distribution, three cases of stationary cycling, hot front cycling and cold front cycling were considered. Ratchet mecahnism and the method of evaluating ratchet, and the experimental verification are described. (K.I.)