Annealing of the reactor pressure vessel of the first unit in Loviisa Nuclear Power Station

The RPV (Reactor Pressure Vessel) of the first unit in Loviisa NPS (Nuclear Power Station) will be annealed in the re-fuelling outage in summer 1996. This is the first annealing of a RPV of a WWER-440 plant of type B-213. Since no archive material was available for the research and surveillance program, a tailored weld seam which very well corresponds to the real core weld in the RPV was manufactured. The weld was completed in the same factory (Izorsky) with the same method and procedure as the original weld. In addition, a typical cladding of a WWER-440 RPV was manufactures for the cladding studies. Further the HAZ zone was studied by simulating the heat treatment of the real HAZ of the RPV-weld. In this paper the research work for licensing of the annealing as well as the new surveillance program to follow the re-embrittlement of the RPV after annealing are described. 2 refs, 2 tabs