Boat sampling and inservice inspections of the reactor pressure vessel weld No. 4 at Kozloduy NPP, Unit 1

The paper deals with reactor pressure vessel (RPV) boat sampling performed at Kozloduy Nuclear Power Plant, Unit 1, from August to November 1996. Kozl oduy NPP, Unit 1 has no reactor vessel material surveillance program. Chang es in the material fracture toughness resulting from the fast neutron irrad iation which cannot be monitored without removal of the vessel material. Th erefore, the main objective of the project was to cut samples from the RPV wall in order to obtain samples of the RPV material for further structural analyses. The most critical area, i.e. weld No. 4 was determined as a locat ion for boat sampling. Replication technique was applied in order to obtain precise determination of the weld geometry necessary for positioning of th e cutting tool prior to boat sampling, and determination of divot depth lef t after boat sampling and grinding of sample sites, Boat sampling was perfo rmed by electrical discharge machining (EDM). Grinding of sample sites was implemented to minimize stress concentration effects on sample sites, to el iminate surface irregularities resulting from EDM process, and to eliminate recast layer on the surface of the EDM cut. Ultrasonic, liquid penetrant, magnetic particles, and visual examinations were performed after grinding t o establish baseline data in the boat sampling area. The project preparatio n activities, apart from EDM process, and the site organization lead was en trusted to INETEC. The activities were funded by the PHARE program of the E uropean Commission. (C) 1999 Published by Elsevier Science S.A. All rights reserved.