Comparison of Predicted Transition Temperature Shifts Between Static Fracture Toughness and Charpy-V Impact Properties Due to Irradiation for an A508 Pressure Vessel Steel

Abstract

Nuclear pressure vessel steels are subjected to irradiation embrittlement which is monitored using Charpy tests. Reference index temperatures, such as the temperature for which the mean Charpy rupture energy is equal to 56 J (T56J), are used as embrittlement indicators. The safety integrity evaluation is performed assuming that the shift of RTNDT due to irradiation is equal to the shift of T56J. In this work a material model integrating a description of viscoplasticity, ductile damage and brittle fracture is used to simulate both the Charpy test and the fracture toughness test (CT geometry). The model is adjusted on an unirradiated material. It is then applied to irradiated materials assuming that irradiation affects hardening. It is shown that irradiation probably also affects brittle failure. The shift of RTNDT and the predicted shift of T100MPam are then compared for a given level of irradiation.

Local approach to fracture based prediction of the ΔT56J and shifts due to irradiation for an A508 pressure vessel steel

“…The ability of the model to predict fracture toughness for the unirradiated material using the ! A ¦ relation obtained from Charpy data was shown in a previous study [13] and is reported on fig. 7a.…”

“…This strategy allows to transfer the results of the Charpy tests to larger structures and further to study the effect of different damage mechanisms as irradiation or ageing on the DBT temperature. For example in the case of unirradiated materials, the evolution of the elastoplastic fracture toughness can be predicted based on Charpy impact data [9,13]. The aim of this study is to predict and to compare the irradiation involved shifts of index temperatures obtained from Charpy and fracture toughness tests using a micro-mechanical description of the involved damage processes.…”