Doel 3 & Tihange 2 - Some Peer-reviewed Scientific Papers & Reports

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heat-treated 12X2MFA steel welds. In addition, they noted that when the steel was kept in the normal PWR primary circuit water, the hydrogen content of the steel rose to 1.29-1.33 cm 3 H/100 g Fe, but the maximum hydrogen content may be 5.25 cm 3 H/100 g Fe locally.

3 HYDROGEN EMBRITTLEMENT

3.1 AMERICAN STUDIES

Because the irradiation strengthens the pressure vessel steel, it has often been suspected that the irradiation and the hydrogen synergistically embrittle the steel together. In early studies (Broomfield, 1965;. Rossin et al., 1966; Brinkman and Beeston, 1970), where the hydrogen charging was performed after irradiation, hydrogen embrittlement was not more likely in the irradiated material than it was in unirradiated steel. Figure 1 shows the joint action of irradiation and hydrogen for l%Cr-0.5%Mo steel in the elongation to fracture which decreases slightly under the influence of hydrogen even if the hydrogen does not affect the tensile strength (Figure 2). Figures 1b and 2b show that the hydrogen significantly reduces both the local elongation and the actual fracture stress. Rossin et al. (1966) studied the low-strength A212B steel at room temperature with hydrogen contents of 1 and 7 ppm and irradiation levels of 2.6-3.3 x 10 19 n/cm 2 (E > 1 MeV). Figure 3 shows how the notch tensile strength (NTS) on this steel depends on the irradiation dose. The hydrogen content of 1 ppm caused a drop of only a few percentage points in both the tensile and the notch tensile strength and there was no difference between irradiated and unirradiated material. At a hydrogen content of 7 ppm, both the notch tensile strength and the tensile strength were reduced by about 14%. The elongation to fracture of the notched specimen dropped to half on an unirradiated specimen and to zero on an irradiated specimen, as shown in Figure 3b. The same is true for the reduction of area at fracture.