EVALUATION OF VARIABILITY IN MATERIAL PROPERTIES AND CHEMICAL COMPOSITION FOR MIDLAND REACTOR WELD WF-70

摘要

The Heavy-Section Steel Irradiation (HSSI) Program at Oak Ridge National Laboratory (ORNL) includes a task, the Tenth Irradiation Series, to investigate the effects of radiation on the fracture toughness of the low upper-shelf submerged-arc welds in the reactor pressure vessel (RPV) of the canceled Midland Unit 1 nuclear plant. The welds carry the Babcock and Wilcox Co. (B&W) designation WF-70, a weld which exists in many commercial pressurized-water reactors. Various sections of both the beltline weld and the nozzle course weld were studied. A major part of the study involved the determination of variations in chemical composition and reference temperature (RT_(NDT)) throughout the as-received welds. The RT_(NDT)s, all controlled by the Charpy behavior, varied from -20 to 37°C (-4 to 99℉) while the upper-shelf energies varied from 77 to 108 J (57 to 80 ft-lb). Even though all the welds carry the WF-70 designation, the bulk copper contents range from 0.21 to 0.34 wt % in the beltline weld and from 0.37 to 0.46 wt % in the nozzle course weld. The variation (2σ) of 41-J temperatures for 25 data sets of the Midland weld was 17°C and is comparable to that for the high upper-shelf HSSI weld 72W and that from 13 data sets for HSST Plate 01. Statistical analyses of the Charpy and chemical composition results are discussed. Although the NDT temperatures and CVN transition temperature ranges were similar for the two welds, the fracture toughness results indicated that the nozzle course weld had a 27°C (49℉) higher transition temperature than the beltline weld. Some postirradiation data are available and are presented in this paper, but the major part of the irradiation effects study will be reported subsequently.