IRRADIATION CREEP AND VOID SWELLING OF AUSTENITIC STAINLESS-STEELS ATLOW DISPLACEMENT RATES IN LIGHT-WATER ENERGY-SYSTEMS

The majority of the high fluence data on he void swelling and irradiat ion creep of austenitic steels was generated at relatively high displa cement rates characteristic of fast reactors. The application of these data to other reactor systems which operate at lower displacement rat es requires that some estimate be made of the dependence of swelling a nd irradiation creep on displacement rate. Austenitic components in ty pical light water reactors (LWRs) experience displacement rates that a re an order of magnitude or more lower than that found is fast reactor s. Since irradiation creep has a component that is proportional to swe lling, it is anticipated that irradiation creep ir ill exhibit a sensi tivity to displacement rate that is a direct expression of the depende nce of swelling on displacement rate. Until recently, however, the non -swelling-related component of creep was also thought to exhibit its o wn dependence on displacement rate, increasing at lower fluxes. This p erception originally arose from the work of Lewthwaite and Mosedale on irradiation creep of cold-worked steels in the Dounreay Fast Reactor at temperatures in die 270-350 degrees C range. It now appears that th is interpretation is incorrect and, in fact, the steady-state value of ale non-swelling component of irradiation creep is relatively insensi tive to displacement rate. The earlier perceived flux dependence appea rs to have arises from a failure to properly separate the transient an d steady-state regimes of irradiation creep. As evidence begins to acc umulate on void swelling of stainless steels at LWR-relevant displacem ent rates, voids are being observed at lower-than-expected temperature s and often at very low dpa levels, implying that the 'temperature shi ft' phenomenon may indeed be operating to increase swelling. It is dem onstrated in this paper that if swelling exceeds similar to 10% at PWR -relevant temperatures, stainless steels become very brittle. (C) 1997 Elsevier Science B.V.