Experimental Program to Monitor the Irradiation Induced Embrittlement of the French Reactor Pressure Vessel Steels

Abstract

By monitoring the irradiation-induced embrittlement of materials, the Pressure Vessel Surveillance Program (PVSP) contributes to the RPV integrity and lifetime assessments. This program is implemented on each PWR Unit in France; it is mainly based on Charpy tests, which are widely used in the nuclear industry to characterize the mechanical properties of the materials. Moreover, toughness tests are also carried out to check the conservatism of the PVSP methodology. This paper first describes the procedure followed for the Pressure Vessel Surveillance Program. It presents the irradiation capsules: the samples materials (low alloy Mn, Ni, Mo vessel steel including base metals, heat affected zones, welds and a reference material) and the mechanical tests performed. Then it draws up a synthesis of the analysis of about 180 capsules removed from the reactors at fluence levels up to 7.1019 n/cm2 (E > 1 MeV). This database gathers the results of more than 10,000 Charpy tests and 250 toughness tests. The experimental results confirm the conservatism of the Code-based methodology applied to the toughness assessment.

Warm PreStress effect on highly irradiated reactor pressure vessel steel

“…a large increase of the fracture toughness with temperature associated with a change of fracture mechanism. Neutron irradiation induces an increase of the transition temperature related to microstructural changes [1] which can be addressed either by Charpy V-notch impact tests as in surveillance programs [2] either directly based on isothermal quasi-static toughness tests. Fracture toughness lower bound curve and its shift with irradiation are then used to ensure the structural integrity of the RPV in nominal and hypothetical accidental situations.…”