VVER-Type Reactors of Russian Design

Abstract

This chapter contains detailed description of the design and technical layout of Russian VVER-type reactors. Both the VVER-440 and the VVER-1000 reactor types are described. VVER reactors are a special design of Pressurized Water Reactors with some particular design features listed in the introduction. The most important of them are:

• A hexagonal geometry of the fuel assemblies (FA) with arrangement of the fuel rods in a triangular grid

• Zirconium-niobium alloy as fuel rod claddings material

• Possibility to transport all large-sized equipment by railway to enable a complete manufacturing process under factory conditions (resulting in a limitation of the outer diameter of the reactor pressure vessel)

• An original design of horizontal type steam generators with a tube sheet in the form of two cylindrical heads

VVER reactors are the most frequently built reactor type in the world. Presently, there are 23 units of VVER-440 and 28 units of VVER-1000 worldwide in operation (see tables in Sects. 2.3 and 3.3). In the introduction, a historical overview on the design of VVER-440 and VVER-1000 reactors is given. First units with predecessors of VVER-440 type reactors were erected at the Novovoronesh NPP site in 1972 and 1973. The second step in the development of VVER-440 type reactors was the V-230 design, where the number of mechanical control rods was reduced from 73 to 37 due to introduction of boron as a moderator. In the period from 1973 to 1982, all 14 units were constructed with the V-230 design. The third step in VVER-440 development was V-213 reactor design referred to as the second generation of the standard VVER-440 reactors; their design basis included a double-ended instantaneous guillotine break of the maximum diameter primary pipeline. The development of VVER-1000 reactors was started by OKB Gidropress in 1966. The first reactor with an electrical power of 1,000 MW was commissioned at Novovoronezh NPP Unit 5 in 1980. In the design, the traditional engineering solutions of VVER were used with the appropriate modernization from the experience obtained in the design, manufacture, and operation of the VVER prototypes. The design concept was oriented to an increase in economic efficiency of the nuclear power plant (NPP) construction and operation, ensuring safety in accordance with the regulatory documents that were valid at the time. An instantaneous double-ended guillotine break of the main coolant pipeline was considered as the maximum design basis accident. The reactor plant was placed into a containment of prestressed concrete. Further on, the design modifications ended up in elaboration of V-302 Project implemented at the South-Ukraine NPP Unit 1 and V-338 Project implemented at the South-Ukraine NPP Unit 2 and the Kalinin NPP Units 1 and 2. Elaboration of these projects classified as small series designs and their realization was under way from 1976 to 1987. All the power units of VVER-1000 NPPs, beginning with 1985, were constructed to a standard design that contains the V-320 reactor plant, capable of being sited in seismic areas with earthquakes up to magnitude 9 (SSE), the reactor of small series; D nom 850 circulation loops without gate valves; wet reloading of internals; PGV-1000 horizontal steam generators; and GTsN-195M reactor coolant pumps (large series). The main feature of the enhanced standard VVER-1000 reactor is the application of jacket-free fuel assemblies (their quantity increased from 151 pcs. to 163 pcs. and the reduction of control rods from 109 to 61 [ up to 49 at the South-Ukraine NPP Unit 1]) and the application of ShEM drives in reactor trip system. The large series designs have been realized since 1978 up to now. Twenty-eight Generation II power units with VVER-1000 have been constructed and are in operation at NPPs. The accidents at TMI-2 and Chernobyl-4 NPPs have shown that it is necessary to take into consideration the beyond design basis accidents (BDBA) during their design and operation. In 1988 a new V-1000 design was launched (V-392 Project), which focused on safety improvements in response to new requirements of regulatory documents in order to prevent occurrence of BDBAs and to mitigate their consequences in the case that they happened. The idea was implemented in the RP design of V-392 Project incorporated into NPP-92 design. The main RP equipment of the V-392 design, including the reactor, was implemented in a set of RP V-428 at “Tianwan” NPP. The information on this NPP design was incorporated into the chapter on VVER-1000 reactors. The modifications to V-392 RP design can be found in the design of RP V-412, which are being implemented now at “Kudankulam” NPP. Designs of Units with RP V-392, V-428, and V–412 are referred to Generation III reactors.In both VVER-440 and VVER-1000 sections of the chapter, first, the main design parameters of these reactors are given. Second, the buildings and structures are described that house the reactor plant and auxiliary systems. As a special feature of VVER-440, two power units of this reactor type are incorporated into one main building of the NPP.. Further, a tower, being a part of the reactor building with V-213 reactor plant, houses the vacuum-bubbler passive system to reduce pressure in the containment. Quite comprehensive sections are devoted to the primary circuit systems and equipment. The reactor coolant system, reactor, main circulation pumps, pressurizer, steam generators, and chemical and volume control systems are described. While the VVER-440 reactors dispose of six primary circuit loops, the VVER-1000 has four loops. Special attention is paid to the core and fuel design. Special features of the VVER-440 core design are the fuel assemblies with housings and control assemblies, which consist of two parts: an absorber part and a fuel follower. When the absorber part is withdrawn from the reactor core, the fuel follower is inserted into the core. In VVER-440, profiled fuel assemblies with Gd₂O₃ burnable absorber are used to decrease the power peaking factor in the core.. The control elements for VVER-1000 reactors are of the cluster type, similar to western PWR designs. Typically, 18 absorber rods are placed in a control assembly. In subsequent sections, the secondary circuit components (Main Steam Line System, Main Feedwater System, Turbine, Generator, and Moisture Separator Reheater) are described. The power units with VVER-440 are equipped with two turbines and generators of 220 MW electrical power and the power units with VVER-1000 have one 1,000-MW-turbine driving one generator. Further I&C as well as electrical systems are briefly described. The instrumentation and control systems of some of the VVER-440 units have been recently updated. The refurbishments were mainly aimed at the introduction of advanced features for data processing, transmission, and archiving. In Sects. 2.2 and 3.2, the safety philosophy and safety systems ofVVER-440 and VVER-1000 are described. The applied concept of safety assurance for power units of Generations II and III is outlined. For the Generation III VVER designs, significant improvements were implemented in accordance with the up-to-date international requirements for NPP safety assurance. The data on the VVER reactors under construction, operation, and decommissioning are presented in Sects. 2.3 and 3.3.