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.
Some welds made with Linde 80 flux and containing a high copper impurity level have exhibited postirradiation Charpy upper-shelf energy levels below 68 J (50 ft · lb). The J-R curve behavior of seven such low upper-shelf welds has been characterized in the ductile upper-shelf regime in both the preirradiation and the postirradiation conditions with fluences of ~1 × 1019 neutrons (n)/cm2 (E > 1 MeV). With the single specimen compliance (SSC) technique, these J-R curves were determined from compact toughness (CT) specimens ranging from 12.7 to 101.6-mm thick, over a temperature range of 75°C to 288°C. For these reactor vessel steels exhibiting low upper-shelf energy levels, the J-R curves were shown to follow a power-law relationship for small crack extensions, that is, less than 2 mm. In some cases, a possible size dependence of the J-R curve has been seen, but the results are inconclusive on this point. Correlations between J-R curve parameters (JIc and average value of tearing modulus, Tavg) and Cv upper-shelf energy have been suggested at 200°C. These findings could enhance the significance of Cv reactor surveillance data with respect to structural integrity. However, JIc and Tavg have demonstrated an inverse relationship with temperature that is not reflected by the Cv upper-shelf trend. Therefore, correlations between Cv energy and J-R curve must be adjusted to account for temperature.
The Light Water Reactor-Pressure Vessel Surveillance Dosimetry Improvement Program of the Nuclear Regulatory Commission (NRC) has irradiated, in a pressure vessel wall/thermal shield mock up facility, mechanical test specimens of the ASTM A302-B correlation monitor reference plate and the A533-B Plate 03 from the Heavy Section Steel Technology Program. This report presents Charpy-V, compact tension, and tension test results from simultaneous irradiations in simulated surveillance capsule and through-vessel-wall locations. The investigation is part of a broad NRC effort developing key neutron physics-dosimetry-metallurgy correlations for use in making highly accurate projections of radiation-induced embrittlement to reactor vessels. Irradiation in the surveillance capsule location was found to reproduce reasonably well the irradiation effect to the vessel inner surface and quarter thickness positions. The toughness gradient observed between in-wall locations after irradiation was small for both materials; the difference between transition temperatures for wall surface versus mid-thickness locations was 31°C or less, independent of the test method used. The adjustment of the ASME lower bound, that is, dynamic, KIR toughness curve by the radiation-induced elevation of the Charpy-V 41-J or the compact specimen 100 MPa√m temperature was conservative when compared against static toughness data. The elevation of the Charpy-V (Cv) curve (41-J index) by irradiation frequently did not provide a conservative estimate of the temperature elevation defined by fracture toughness tests (100 MPa√m index); on the other hand, correction of the fracture toughness data for the lack of test specimen constraint (βIc correction) did result in a transition temperature elevation less than the 41-J elevation, in most cases.
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