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

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When hydrogen contents of the pressure vessel steel have been analysed on account of the fracture of the cladding, the normal use and cold shutdown are usually considered. Hydrogen is normally not assumed to be absorbed through the steel cladding except where the cladding is penetrated. According to Rossini (1967), in a certain case of an unclad pressure vessel (irradiation damage was not taken into account), Westinghouse calculated the equilibrium hydrogen content to be 0.32 ppm under normal use, with content increasing during the shutdown and stabilising at about 2 ppm after a number of months. The pressure test may thus be the most dangerous situation for the hydrogen embrittlement of the reactor pressure vessel steel because after shutdown at high temperatures, a fast diffusion quickly stabilises the hydrogen content. The stress fields at the tips of the cracks and inclusions function as hydrogen traps and the hydrogen content at those sites is locally higher than the average hydrogen content. Brinkman and Beeston (1970) observed that a rise in the irradiation dose increases the residual hydrogen content of steel even if the irradiation takes place in an inert helium atmosphere. The hydrogen contents on Table 1 are higher than what the n,p reactions are calculated to generate (below 0.1 ppm even at high doses). The anneals (48 h) at temperatures between 100-325°C did not lead to a decrease in the hydrogen content but only at temperatures considerably higher than 300°C was hydrogen released from the hydrogen traps in steel. Brinkman and Beeston (1970) reasoned that this hydrogen could not be diffused at test temperatures and was closely bound to traps so that it did not cause a delayed fracture and did not affect the mechanical properties of the steel.