Test blocks of a manganese-nickel-molybdenum (Mn-Ni-Mo) low-alloy steel, machined from a nozzle cut-out of a 230-mm-thick forging shell, were provided by France in 1978 to be investigated in the second phase of an IAEA-coordinated research program on the behavior of advanced pressure vessel steels under neutron irradiation.

The results obtained by different laboratories exhibit a great deal of scatter in Charpy-V transition temperatures, both in the initial condition and after neutron irradiation. Therefore, the shifts in Charpy-V transition curves induced by neutron irradiation at similar fluences of about 3 × 10²³ n ∙ m^-2 (E ⩾ 1 MeV) cover a wide temperature range from 0 up to 110°C.

A more detailed investigation of these results was undertaken, and additional Charpy tests were conducted to clarify the considerable uncertainty about the sensitivity of this forging to radiation embrittlement. The differences in results were found to be due to the various orientations and locations of the Charpy-V specimens extracted by the different laboratories, in some cases to insufficient test data in the transition region of the Charpy curve, and to the detrimental effect on Charpy-V properties of segregated zones (ghost lines) found in specific locations of large forgings.