Non-destructive evaluation and correlation with the mechanical properties to obtain embrittlement degradation of RPV materials within the NOMAD project

The objective of NOMAD is to develop a tool that is capable to non-destructively evaluate the degree of neutron induced embrittlement of the RPV. The final NDE system (outside the NOMAD scope) should be capable of inspecting the degradation of the microstructure through the cladding. Therefore, a combination of several techniques based on micro-magnetic, electrical and ultrasonic methods was investigated. They were first calibrated on a set of existing (CHIVAS-x) and newly irradiated (NOMAD_3) Charpy samples from a variety of RPV materials irradiated in different conditions. In addition, large blocks with and without cladding of one RPV material were irradiated in the BR2 reactor to a large range of neutron fluences in the NOMAD_1 and _2 campaign. They were measured by the most promising NDT techniques to mimic the actual field conditions. To be independent of the irradiation conditions, the damage parameter metrics is defined as the ductile-to-brittle transition temperature (DBTT) which is characteristic of the material microstructure. This paper gives an overview of the status of the NOMAD project with focus on the evaluation and correlation between the mechanical properties and non-destructive parameters. NDE results from 6 NDE set-ups enabling the measurement of 28 parameters were compared to the DBTT results measured using Charpy impact tests. A selection of all results are presented and discussed together with some recommendations for future investigations.