Development of a New Materials Surveillance Technology for Fast Reactors

Abstract This paper describes current the efforts within the Japan Atomic Energy Agency to develop a new materials surveillance technology for sodium-cooled fast reactors that aims at raising the confidence levels in operating reactors’ structural integrity to the ones which could otherwise be achieved only by a vast amount of long-term material test data that needs decades to accumulate. The technology would allow for monitoring ongoing materials degradation processes in an actual reactor, namely fatigue and creep-fatigue, by inserting a newly developed specimen for this purpose into the reactor and establishing procedures to observe and evaluate the specimen to get desired information such as the extent of degradation and residual life. To establish the test procedure, a passive creep-fatigue test model was developed in the framework of the “Civil Nuclear Energy Research and Development Working Group (CNWG)”, a collaboration agreement between the US and Japan, and a demonstration test was performed under cyclic thermal loads using an electric furnace. Temperature conditions had been determined based on finite element analyses. As a result, the test specimen failed by several hundred thermal cycles. Macroscopic inspection of the specimen after the test showed the test had been performed successfully without buckling. Fracture surface observations suggested that the failure caused probably by fatigue or creep-fatigue. Further discussed in this paper includes some improvements on the specimen that are deemed necessary in actual implementation such as paths to downsizing the specimen.