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

6. Hydrogen concentration in PWR wall

factor for the development of the hydrogen flakes in the RPV wall, as elaborately explained in Chapter 2. The chemical composition of the different parts of the RPV have been analyzed at two different times. First, a ladle analysis was performed during the pouring of the molten steel in the ingot. This analysis is performed by the producer of the steel, KRUPP. The second chemical analysis is performed on the forged components by RDM. In this so called product analysis, two samples are taken from the bottom end of the forged product and analyzed. [1] Electrabel has listed the H concentrations found in the different components of the RPV. The targeted maximum concentration set by RDM is 1.5 ppm. It can be seen in Table 6.1, that the H content in each of the components is at or below this limit. [1] It is however not clear which of the two chemical analyses these concentrations result from. Table 6.1: H concentration in the different RPV components after their production. [1]

Component of RPV H (ppm) Transition flange head 1.170 Transition flange RPV 1.450 Nozzle shell 1.000 Core upper shell 1.400 Core lower shell 1.500 Transition ring 1.500

Of course, one can say this chemical analysis has been performed more than 30 years ago and therefore the hydrogen will have diffused out of the steel over time. However, as mentioned in section 3.3, studies have found that hydrogen can be trapped for at least 13 years in certain types of traps. [40] It is generally accepted that the hydrogen cracks are formed immediately after the production of the components. Therefore, a big part of the hydrogen in the steel will be present as molecular H 2 in the cracks. As hydrogen is retained for at least 13 years in those cracks, there is no reason to assume that this would not be the case after a little more than twice this time. Therefore, one will also have to account for this hydrogen in the steel. 6.3 In-service hydrogen generation The three sources of hydrogen during service of the reactor will also contribute to the concentration of hydrogen in the RPV wall. First the contribution from the dissolved hydrogen in the primary water and the radiolysis of the primary water will be calculated. Afterwards, a similar calculation will be performed for the hydrogen generated by corrosion of the RPV wall. 60