Consequence of the coincidence of irradiation embrittlement; surface cracking and pressurized thermal shock (PTS) in RPVs of LWRs

One important project within the German Research Programme Integrity of Components focuses on the consequences of a small break LOCA with respect to the Pressurized Water Reactor (PWR) pressure vessel integrity. To answer the question of possible failure model resulting from overcooling transients, a lower bound approach had to be developed as a preventive tool to demonstrate the safety margin for extremely long range operation, and a necessary step to a better understanding of the effect of superimposed mechanical, thermal and residual strsses. Therefore, a conservatively severe pattern of thermal transients was evaluated and correlated to an embrittled component-like thick walled hollow cylindrical specimen. The validation of theoretical fracture mechanics analyses for the RPV and the model by means of large scale experiments will be performed under realistic conditions of temperature (absolute and differential) pressure, crack pattern, and material embrittlement