Master Curve Testing on Reconstituted Surveillance Charpy Specimens

Abstract

The original WWER-440 surveillance had 6 sets of specimens and each set had 12 Charpy, 12 COD (crack opening displacement) and 6 tensile specimens made from base material, weldment and HAZ (heat affected zone). The Charpy size precrack TPB (three point bend) COD specimens were located at the end of the chains, where the flux is rapidly decreasing. During the period of 1970–90, when the WWER-440-V213 units were designed, built and started to operate, the Charpy impact transition curve measurement was the accepted method to evaluate the radiation embrittlement. The technology and the standards to use small size fracture mechanical specimens in surveillance capsules were not developed at the time period when most of the second generation reactors — including the WWER-440 V 213 type — were designed, therefore the fracture toughness specimens were considered less interesting for the utilities and the safety authorities. Fracture toughness curves were elaborated in the laboratories on large size unirradiated specimens and radiation embrittlement adjustments were made according to the Charpy shift. However, during the past 30 years fracture mechanics has rapidly developed, and the testing moved to the direction of using small and mini sized specimens. The development of the Master Curve evaluation method [4,5] allowed the use of small specimens for fracture toughness testing in surveillance programs, and the results obtained on irradiated specimens may be used directly in the lifetime evaluation. The purpose of this work was to develop a specimen production technology and testing procedure to measure these data using the remnants of irradiated surveillance Charpy specimens, and the comparison of the data calculated from CMOD and LLD on irradiated CrMoV type RPV material and weldment.