Experimental investigation of safety against unstable fracture of the pressure components of nuclear reactors

A study was made to determine if the Japanese standard that specifies a minimum usable temperature 500C to the high temperature side at below the yield point even when the yield stress is very slightly exceeded is reasonable in specifying the allowable plastic region for certain types of nuclear reactor containment vessel incidents. This study was conducted in the form of large scale brittle fracture propagation termination tests on weld joints made on A516 Gr. 70 steel plate for nuclear containment vessels, and the results were combined with the results on tests made on base material last year. It was judged that the demands of the present specifications were excessive. It also seems that there is need for more logic being incorporated into the present safety standards that are based on CAT curves of fracture analysis diagrams (FAD) that rely on NDT temperatures from drop weight tests