The V-179, V-230 and V-213 types of VVER plants are equipped with a six-loop VVER-440 reactor. In each loop, there are main isolating valves (MIV) on the cold and hot legs, one main circulation pump (MCP) per loop and horizontal steam generators (SG). The pressurizer, with safety valves, is connected to the primary loop. The two generations of the VVER-440 type of reactors have very similar layouts in their primary systems. Typical oper­ating parameters are Thot=297°C, Tcold=266°C, p=12.3 MPa. However, the design bases of the VVER-440/230 and the VVER-440/213 are essentially different, which manifests in the design of safety systems and confinement (IAEA, 1992; 1996a).

There are 16 nuclear power plant units of type VVER-440/213, namely, four in Hungary, four in the Czech Republic, four in Slovakia, two in Russia and two in Ukraine. The owners of these plants are preparing for the LTO of these units.

The design bases for the VVER-440/213 safety systems are similar to those used in Western PWRs, including the postulating of a double-end guillotine break of the main circulation line in the reactor coolant sys­tem. The safety systems exhibit triple redundancy and the reactors have bubbler condenser-type, pressure suppression containments capable of withstanding the imposed loads and maintaining containment func­tionality, even following large break LOCA events. The design of the VVER-440/213 plants considered internal and external hazards to some extent. Protection against single failures in the auxiliary and safety sys­tems has generally been provided in the design. The safety concerns with VVER-440/213 plants are discussed in the IAEA report (1996a). The VVER-440/213 has essentially inherent safety characteristics, for example robustness of the design, low heat flux in the core, large water inventory in the primary system and a large containment volume, which compen­sates to a large extent for other deficiencies in the containment concept. At all of the plants, most of the safety deficiencies have been addressed by retro-fitting and plant modifications. Due to the robustness of the design, it was feasible to upgrade the safety of the original VVER-440/213 design to a level comparable with the PWR plants of the same age. The latest constructed units of VVER-440/213, such as Mochovce NPP Units 1 and 2, had several improvements and modifications made during the design and construction phase.

There are specific modifications of the VVER-440 design: the Finnish nuclear power plant at Loviisa, represents a combination of the VVER-440/230 basic design and nuclear island equipment with a Westinghouse-type, reduced pressure, ice-condenser containment and sev­eral other western-designed and manufactured systems, like the complete

instrumentation and control (I&C) systems. These units have a very suc­cessful operational history and excellent safety features. A comprehensive lifetime management programme was launched in the very early stages of operation, and has allowed LTO of the Loviisa units. The Armenian reac­tor also represents a modification of VVER-440 with an enhanced seismic capacity. The shut down Units 3 and 4 at Kozloduy NPP, Bulgaria represent an intermediate type between 230 and 213 series.

I t should be noted that, the VVER-440s have certain inherent safety characteristics that are superior to most modern PWR plants, for example robust design, large water inventory in the primary system relative to the reactor power and large volume of the confinement.