The reactor vessels of the nuclear production reactors at the Savannah River Site (SRS) were constructed in the 1950's from Type 304 stainless steel plates welded with Type 308 stainless steel filler using a multipass metal-inert-gas process. A mechanical properties database for irradiated material has been developed for the vessel with materials from archival primary coolant system piping irradiated at low temperatures (75 to 150°C) in the State University of New York at Buffalo reactor (UBR) and the High Flux Isotope Reactor (HFIR) to doses of 0.065 to 2.1 dpa. Fracture toughness, tensile, and Charpy-V impact properties of the weldment components (base, weld, and weld heat-affected-zone (HAZ)) have been measured at temperatures of 25°C and 125°C in the L-C and C-L orientations for materials in both the irradiated and unirradiated conditions for companion specimens. Fracture toughness and tensile properties of specimens cut from an SRS reactor vessel sidewall with doses of 0.1 and 0.5 dpa were also measured at temperatures of 25 and 125°C. The irradiated materials exhibit hardening with loss of work hardenability and a reduction in toughness relative to the unirradiated materials with a slight sensitivity to exposure. Irradiation increased the yield strength between 22% to 187% with a concomitant tensile strength increase between-9% to 29%. The irradiation-induced decrease in the elastic-plastic fracture toughness (JD at 1 mm crack extension) is between 26% to 64%; the range of JICvalues are 72.8 to 366 kJ/m2 for the irradiated materials. Similarly, Charpy V-notch results show a 38% to 59% decrease in impact absorbed energies. The C-L orientation shows significantly lower absorbed energies and fracture toughness parameters than the L-C orientation for both the base and HAZ components in both the unirradiated and irradiated conditions.

Data on the influence of low dose 400-550°C irradiation on the mechanical properties of structural steels (Types 304, 316, 316L, 316H and 316L(N) and associated weld metals) at temperatures from 20°C to 750°C, have been compiled from published literature and the results of British, Dutch, French and German laboratories. Properties evaluated include tensile, impact, creep, fatigue, and creep-fatigue. The preliminary results, which cover the dose range from 0 to 5 displacements per atom (and/or up to 9 appm helium) are presented as comparisons between irradiated and unirradiated control data, covering a range of strength and cyclic properties. The results show that low dose irradiation can have a significant influence on the properties, i.e.:• increases in tensile proof strength,• reductions in tensile ductility,• decreases in impact energy,• reductions in creep-rupture strength and ductility, and • reductions in creep-fatigue endurance.

Recent welding tests using either neutron irradiated or tritium charged material have shown that there was a good chance of success when there was no repeated heat cycle during welding, e.g., stringer bead welding, single pass laser welding, etc. However, the replacement/repair of the actual load carrying components often requires thick plate welding which can only be realized with multi-layer welding. In the present study, 20-mm-thick grooved plate of type 304 stainless steel was irradiated and then butt-welded by multi-layer welding. The weld heat input used was 1.0 and 2.0 MJ/m, which required 28 and 14 passes to fill up the groove. The samples were irradiated to 2.5x1021 ~ 1.8x1023 n/m2 (E>1MeV), which resulted in 0.1~1.6 appm of helium being produced. A conventional gas tungsten arc welding procedure was employed. The welded joints were subjected to the tensile test, side bend test, root bend test and cross-sectional metallography. The samples containing as much as 0.14 appm of helium passed all the tests; the mechanical properties fulfilled the standard requirement for the unirradiated base metal. At 0.6 appmHe and 1.0 MJ/m heat input, the welded joint showed sufficient strength, however, tiny intergranular cracking was observed in the HAZ where repetitive thermal cycles operated.