Embrittlement behaviour of different international low activation alloys after neutron irradiation

The embrittlement behaviour of ferritic/martensitic steels, after irradiation in the Petten High Flux Reactor (HFR), was investigated by Charpy-V tests with subsize specimens. The main objective, apart from studying the effects of particularly low doses, was to compare the irradiation response of low activation alloys from various countries with different levels of Cr, minor alloying elements and impurities. Specimens were irradiated at temperatures ranging between 250 degrees C and 450 degrees C to dose levels between 0.2 and 2.4 dpa. The evaluation clearly showed a tendency to a much reduced embrittlement problem for the advanced reduced-activation alloys; it could not, however, be attributed to lower Cr-contents. Instead, the role of helium, already suspected in our earlier work, could be correlated with the characteristic burn-up of different boron levels in the steels. This correlation translates for a fusion reactor environment into a non-saturating deterioration of alloys even without any boron, due to helium-yielding high energy neutron reactions with the base elements. Though the effect seems to be less detrimental for the more homogeneous distribution of the helium in the matrix. (C) 1998 Elsevier Science B.V. All rights reserved.