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Irradiation assisted stress corrosion cracking (IASCC) is one of the critical concerns when stainless steel components have been in service in light water reactors (LWRs) for a long period. In the IASCC research field, mainly out-of-pile SCC tests for irradiated materials have been performed since there are many difficulties involved with neutron irradiation SCC tests. Hence as a part of the key techniques for in-pile SCC tests, we have embarked on the development of a test technique to obtain information concerning the effects of applied stress level, water chemistry, irradiation conditions, etc. Fig. 11-1 shows a general view of newly developed testing units for in-pile IASCC tests in the core of the Japan Material Testing Reactor (JMTR). The loading level is controlled by the pressure difference between the internal helium gas of the bellows and the external water. When a uniaxial constant load (UCL) specimen ruptures, the bellows contracts rapidly, and the electrical resistance between contact points in the bellows is reduced. This resistance change is monitored and indicates a rupture. For IASCC growth tests, an electrical potential drop by crack growth is monitored using the direct current potential drop (DCPD) method. Figs. 11-2 (a) and (b) show the outer views of UCL and compact tension (CT) specimens. Intergranular stress corrosion cracking (IGSCC) was observed after an in-pile SCC test on a UCL specimen of thermally sensitized Type 304 Stainless Steel. By these mock-up tests, the key techniques for in-pile SCC tests were confirmed. The results from in-pile IASCC experiments are expected to be especially significant for IASCC studies on reactor materials in ageing LWRs. |
