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Reactor pressure vessel (RPV) surveillance capsules contain Charpy-V notch ductility Cv specimens, but many do not contain fracture toughness specimens; accordingly, the radiation-induced shift (increase) in the brittle-to-ductile transition region ΔT is based upon the ΔT determined from Cv tests. Since the American Society of Mechanical Engineers (ASME) KIc and KIR reference fracture toughness curves are shifted by the ΔT from Cv, assurance that this ΔT does not underestimate ΔT associated with the actual irradiated fracture toughness is required to provide confidence that safety margins do not fall below assumed levels.
To assess this behavior, comparisons of ΔTs defined by elastic-plastic fracture toughness and Cv tests have been made using data from RPV base and weld metals in which irradiations were made under test reactor conditions. Using “as-measured” fracture toughness values KJc, average comparisons between ΔT(Cv) and ΔT(KJc) reveal that, on average, ΔT(Cv) tends to underestimate ΔT(KJc) for plates by 22°C and to overestimate ΔT(KJc) for welds by 5°C on average.
When the fracture toughness data are adjusted to account for specimen size using a “βIc correction,” the trends are the same as for KJc, with the underestimate for plates an average of 10°C and the overestimate for welds 11°C on average.
Comparison of ΔTs at various index levels implies that the Cv curve for irradiated material tends to be shallower than that for unirradiated material. However, the shape of the KJc curve for irradiated and unirradiated material is the same, but the Kβc curve for irradiated material is steeper than that for unirradiated material.
nuclear pressure vessel steels, transition temperature shift, upper shelf energy, J, integral, fracture toughness, correlations, Charpy-V notch, embrittlement, cleavage, statistical analysis, upper shelf change, materials irradiation, radiation, irradiation effects, elastic-plastic fracture toughness
Mechanical engineer, Materials Engineering Associates, Inc., Lanham, MD