Abstract

In 2020, the CFD analyses have been performed on a whole reactor vessel model. The action of accumulators during the PTS transient was considered. Using these data, an attempt to the efficient use of sub-modelling is carried out in order to obtain a strong reduction in the computational costs compared to a full 3D analysis. The analyses were given a probabilistic view by using the Master Curve approach for determining the material(s) fracture toughness.

In parallel with these activities, a literature review work was carried out at NRG. The single temperature dependence of the Master Curve was incorporated into characterizations of fracture toughness for all RPV steels of interest such as SA 508 Grade 3 and Grade 4N for both forging and weld material. The literature review helps to prove that the Master Curve approach models the temperature dependence of fracture toughness for a generic pressure vessel before and after irradiation. This is because all of these steels have a BCC matrix phase lattice structure. Based on ASTM E1921, the types of microstructure falling under a BBC matrix, such as bainite, tempered bainite, tempered martensite, ferrite and pearlite, could also be evaluated using the Master Curve model. Furthermore, it is found that the chemical composition is one of parameter to look for as driving force in embrittlement RPV due to irradiation. For the very high nickel steels examined (SA508 Grade 4N), when not combined with copper and moderate manganese, irradiation is not a serious embrittling agent.

This paper describes the work performed at NRG in the years 2017–2020 in investigting the Pressurized Thermal Shock (PTS) phenomenon, summarizes the achievements and gives a general judgement of the lessons learned. Moreover, this paper aims to illustrate the scope of planned research on PTS and its role in the new NRG research program PIONIER 2021–2024. An overview of NRG’s effort to align itself with the international community is given. Particular attention is given to the probabilistic problematic related to PTS. In order to better understand this problematic and improve the current state of knowledge NRG will create a PFM tool. The tool aims to use the best practices from existing PFM software to try to answer to questions requiring attention (e.g. thermal-hydraulic uncertainty). The experience accumulated during the previous activities will be included in the tool.

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