A PROGRAMME FOR THE STUDY OF FATIGUE OF FUSION REACTOR STRUCTURAL MATERIALS

Abstract

Fatigue of fusion reactor first wall structural materials is considered as an important life limiting factor. The first wall is subjected to an intense irradiation of neutrons which cause atomic displacements and a relatively high production of helium. This production of helium is higher as compared with fast fission reactors because of the strong increase of the cross section of (n,a) reactions for energies higher than 5 MeV. Since at present no fusion neutron source with sufficient intensity exists, the effects of this environment have to be investigated by simulation, for example in fission reactors. The difficulty however is to reach the correct He/dpa ratio. For nickel containing materials such as AISI 316 SS, sufficient He production can be obtained by irradiation in a mixed spectrum reactor, due to the high cross section of the Ni (nth,a) reaction. Since AISI 316 is the prime candidate first wall structural material for Intor, a collaborative programme between the US, Japan and the CEG on the study of its fatigue properties has been established. Part of this programme is planned at the S.C.K./C E.N. in Mol. The aims of the programme, which are presented in this contribution, are: 1. Study of the influence of different He to dpa ratios. For this purpose post-irradiation fatigue test will be performed on specimens irradiated in the Belgian BR2 reactor and in HFIR. 2. Comparison of post and in-pile fatigue. Similar specimens will be tested in-pile and after irradiation. For this purpose a miniature fatigue testing module is being designed which will allow in-pile fatigue loading of a small hourglass specimen. Two to four of such modules will be placed in one irradiation rig. Possible factors, which might contribute to a different in-pile and post irradiation behaviour are discussed.