Hydrogen embrittlement of the pressure vessel structural materials in a WWER-440 nuclear power plant

The materials used in a nuclear reactor pressure vessel wall are susceptible to hydrogen embrittlement (HE) related phenomena which can produce in-service catastrophic fracture of this structural component. Consequently, the assessment of the structural integrity of this component against the deleterious damage caused by a hydrogenating source is key from the safety point of view. In this paper, the effects of tempering time applied to pressure vessel structural materials in a WWER-440 nuclear power plant on the hydrogen accumulation are analyzed. Thus, HE is studied at the prospective damage place, i.e., the interface between the layers composing the cylindrical vessel: (i) stainless steel acting as a cladding material and (ii) low carbon steel acting as a base material. The hydrogen radial distributions were obtained by finite element numerical simulation of the hydrogen diffusion assisted by the stress and strain. Results show that the duration of the tempering treatments applied to both steels clearly affects the hydrogen concentration accumulated in a WWER-440 nuclear reactor during its operation time.