The objectives of the Heavy-Section Steel Irradiation Program Fifth Irradiation Series were to determine the effects of neutron irradiation on the transition temperature shift and the shape of the KIc curve described in Sect. XI of the ASME Boiler and Pressure Vessel Code. Two submerged-arc welds with copper contents of 0.23 and 0.31% were commercially fabricated in 215-mm-thick plates. Charpy V-notch (CVN) impact, tension, dropweight, and compact specimens up to 203.2 mm thick [1T, 2T, 4T, 6T, and 8T C(T)] were tested to provide a large database for unirradiated material. Similar specimens with compacts up to 4T were irradiated at about 288°C to a mean fluence of about 1.5 × 1019 neutrons/cm2 (> 1 MeV) in the Oak Ridge research reactor. Both linear-elastic and elastic-plastic fracture mechanics methods were used to analyze all cleavage fracture results and local cleavage instabilities (pop-ins). Evaluation of the results showed that the cleavage fracture toughness values determined at initial pop-ins fall within the same scatter band as the values from failed specimens; thus, they were included in the database for analysis (all data are designated KJC).
The CVN results were analyzed by hyperbolic tangent and exponential curve-fitting models to obtain the temperature shifts at the 41-J level. The temperature intervals associated with one standard deviation on energy were similar to that given for welds in Regulatory Guide 1.99 (Rev. 2). A Weibull-based analysis validated the shift results from the tan/i fits and showed that neutron fluence variations among the specimens were not significant to the observations. Using an exponential model, three-parameter nonlinear regression analyses of the KJc data showed that the intercept value of the ASME equation could be used. Equations of the same form were fit as mean curves and showed that the temperature shifts for KJc (at 100 MPa ∙ √m) exceeded the CVN 41-J shifts for both welds. The same observation applies to the shifts of curves fit as lower boundaries to the data. Analyses of curve shape changes gave somewhat mixed results from the various mean curve fits, but curves constructed to lower bound all the data do indicate a substantial slope decrease, especially for the higher copper weld. The results were used to compare various procedures for shifting the ASME KIc curve to establish a suitable bounding curve for irradiated material.