Determination of the lifetime of an austenitic big-sized plate under creep-fatigue stress. Comparative evaluations of design calculation and experiment

In components of power plant construction operational transients induce stresses varying in duration, leading to local materials damage in consequence of creep-fatigue. These stresses are results of operational changes as well as of start up and shut down processes. The design of such components is in this connection confronted with problems which cannot be responded with procedures based upon the existing rules. Such creep-fatigue occured in the wall of the reactor tank of the FBR type reactor SNR 300. In consequence of performance changes, there occurs a change in the temperature distribution in sodium. From this results a temperature gradient changeable in time over the wall, effecting a corresponding secondary stress. Connected with primary loads from the own weight of the coolant or of the incorporated structures, there results a creep-fatigue stress condition of the reactor tank wall with - a primary stress (tension) constant in time, - a secondary stress (bend) variable in time. The calculated design of the reactor tank wall was effected on the basis of simplified inelastic considerations and parallel to planning in order to estimate the creep-fatigue of the material. The design was examined with the help of a similar-to-service model test. (orig./MM)