Modernization of moisture separator-reheaters of NPP with VVER-440 and VVER-1000 reactors

Abstract

Moisture separator-reheaters (MSR) are designed to separate the moisture from steam and its subsequent overheating. The design moisture of the steam after drying in the MSR separator should not be more than 1%, however, in operation it exceeds this level, which affects the efficiency and reliability of the turbine. In connection with the expiry of the design lifetime, the SPP-220M and the SPP-1000 devices require replacement or modernization. The structures of SPP-220М and SPP-1000 are unified with SPP-500-1, and all these devices have common advantages and disadvantages. It is noted that the leading foreign companies that supply the MSR to NPPs are also working to improve their devices. The experience of the German company Balcke Durr, which took part jointly with JSC «NPO CKTI» in the modernization of SPP-500-1 at nuclear power plants in Russia, as well as independently in the project of modernization of the MSR at the Loviisa NPP in Finland, is presented. The results of the development of JSC «NPO CKTI» on the modernization of an SPP-220M for the power unit with a VVER-440 and an SPP-1000 reactor for the power unit with a VVER-1000 reactor are presented. The projects are executed on the basis of JSC «NPO CKTI»’s own experience and taking into account the experience of joint development with the Balcke Durr firm. The projects are designed taking into account the following conditions: new devices are installed on existing foundations; devices are fi t into the old dimensions; the location of connecting flanges allows to keep the existing pipelines. The design basis for the project included a computational experiment based on an MSR model developed by the authors, as well as thermal hydraulics calculations. Numerical simulation allowed to optimize the design of separation units. Thermohydraulic calculations made it possible to optimize the superheater design. Based on the calculation results, it is shown that the modernization of the apparatus will allow to dry the wet steam at 0.6%, to lower the hydraulic resistance along the wet steam path by 26% for the SPP-220M and 36% for the SPP-1000, and to reduce the weight of the apparatus by 12%. Recommendations are proposed for the modernization of existing and the creation of promising structures for MSR.