Basic aspects of WWER-1000 materials selection

A comparison is made of technical and economic parameters of WWER-1000 and PWR 1000 MW reactors. Differences in the diameters of pressure vessels and in the vessel neck design are given by the transport conditions. Other differences in design affect the in core measurement outlets which in PWR reactors run through bushings in the reactor bottom while in WWER reactors they are effected through the vessel lid. The latter design is safer but increases the load on the lid. Periodical in-service inspections of PWR's are carried out from the inside of WWER's from the outside. The two reactors also differ in the number of parts which are welded to make the pressure vessel. The integral structure of the pressure vessels of large PWR reactors is made up of three parts welded together by two peripheral welds outside of the reactor core. The vessel parts are forged of ingots weighinig up to 500 tons each. Pressure vessels of WWER-1000 reactors consist of seven parts welded together with 6 welds of which 2 are placed in the reactor core. The biggest ingots weigh 205 tons. A similar comparison of the technical and economic characteristics is made for WWER-440 and WWER-1000 reactors. The internals of both reactor types are made of Cr18Ni10Ti steel but for the WWER-1000 the yield point at 350 degC is increased. Welding materials for the internals are the same for both reactors. The stepper motor contains austenitic as well as corrosive materials with permanent magnetic characteristics. In view of its increased capacity the WWER-1000 also has a higher total weight (798 t as compared with 536 tons for the WWER-440), howewer, the specific weight per 1 kW of output is less (0.8 kg/kW as compared with 1.2 kg/kW). (E.S.)