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

- 20 -

The effect of hydrogen on the impact toughness of the A533B and A542 steels in the Charpy-V test is presented in Figure 11. In both cases, hydrogen reduced the upper plateau values; slightly more for the higher strength A542 steel than for the A533B steel. The effect of hydrogen content on the upper plateau values of the irradiated specimens should also be known. This type of measurements should be performed at different strain rates. Summing up the Japanese studies, it should be noted that their premise was taken directly from the prior American studies and it was assumed that a hydrogen content of 1-2 ppm is a very conservative estimate for the pressure vessel steel. Although hydrogen (at 2.3 ppm) did not have a major effect on the hardness and tensile test results, the tests did provide indications of a possible embrittlement in the impact tests and in the delayed fracture tests. Koutsky and Splichal (1983) measured the hydrogen content of stainless cladding that has been irradiated and exposed to PWR conditions for a long time and came up with a hydrogen level of 3-4 ppm. Because this represents the equilibrium content of the boundary of the cladding and the pressure vessel steel, they reasoned that hydrogen embrittlement can potentially damage the steel of pressure vessels. For that reason, the Czech studies have used much higher hydrogen contents than the previous studies (Havel et al., 1980; Tvrdy et al., 1981, 1984; Koutsky and Splichal, 1984, 1985, 1986; Koutsky et al., 1985). The Czech studies primarily used CrMoV, CrNiMoV and 10MnNi2Mo pressure vessel steel. Figure 12 presents the threshold stress intensity values of the 15CrMoV and 20Cr2.5MoV steel when specimens were continuously hydrogen charged during the test in a 1 M HC1 + 0.1 M N 2 H 4 solution with a cathodic current density of 200 A/m 2 . 3.3 CZECHOSLOVAKIAN STUDIES