Session: HT-02-01 Structures under Extreme Loading Conditions (Joint Topic)

Paper Number: 61794

Start Time: Thursday, July 15, 2021, 09:00 AM

61794 - Pressurized Thermal Shock Analysis With Sub-Modeling 

In 2020, the PTS effort has shown a further intensification of the collaboration between computational fluid dynamic (CFD) and fracture mechanics. The CFD analyses carried out in the past years have been extend to include the whole reactor vessel and the action of accumulators during the transient. Using these data, an attempt to the efficient use of sub-modelling I carried out in order to determine a strong reduction in the computational costs. The analyses were given a probabilistic meaning by using the Master Curve approach for determining the material(s) fracture toughness.

Next to these activities an intensive literature review work was carried out based on the work carried out by Versteylen in 2019. 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 accurately the temperature dependence of fracture toughness for all pressure vessels before and after irradiation. This is because all of these steels have a BCC matrix phase lattice structure. Based on ASTM E1921, the various type of microstructure falling under a BBC matrix, such as bainite, tempered bainite, tempered martensite, and 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 further reviews the efforts produced at NRG in the years 2017-2020 in order to better understand the Pressurized Thermal Shock (PTS) phenomenon, summarizes the achievements and gives an general judgement of the leassons learned. Moreover, this paper aims to illustrate the scope of the future research on  PTS and its role in the new NRG’s research program PIONIER 2021-2024. An overview of NRG’s efforts 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 situation NRG will create a PFM tool. The tool aims on the one side to take the best from existing PFM software and on the other side to try and answer to certain points of attention (e.g. thermal-hydraulic uncertainties). The experience accumulated during the previous activities will be included in the tool.  

Presenting Author: Lorenzo Stefanini NRG

Authors:

Lorenzo Stefanini NRG
Casper Versteylen NRG
Fajar Pangukir NRG
Heleen Uitslag-Doolaard NRG
F. H. E. (Ciska) De Haan - De Wilde NRG