The Voda Voda Energo Reactor (VVER), or WWER, (from Russian: Водо-водяной энергетический реактор; transliterates as Vodo-Vodyanoi Energetichesky Reaktor; Water-Water Power Reactor) is a series of pressurised water reactor designs originally developed in the Soviet Union, and now Russia, by OKB Gidropress. Power output ranges from 300 MWe to 1700 MWe with the latest Russian development of the design. VVER power stations are used by Armenia, Bulgaria, China, Czech Republic, Finland, Hungary, India, Iran, Slovakia, Ukraine, and the Russian Federation.
The earliest VVERs were built before 1970. The VVER-440 Model V230 was the most common design, delivering 440 MW of electrical power. The V230 employs six primary coolant loops each with a horizontal steam generator. A modified version of VVER-440, Model V213, was a product of the first nuclear safety standards adopted by Soviet designers. This model includes added emergency core cooling and auxiliary feedwater systems as well as upgraded accident localization systems.
The larger VVER-1000 was developed after 1975 and is a four-loop system housed in a containment-type structure with a spray steam suppression system. VVER reactor designs have been elaborated to incorporate automatic control, passive safety and containment systems associated with Western third generation nuclear reactors.
The VVER-1200 is the version currently offered for construction, being an evolution of the VVER-1000 with increased power output to about 1200 MWe (gross) and providing additional passive safety features.
The Russian abbreviation VVER stands for 'water-water energy reactor' (i.e. water-cooled water-moderated energy reactor). This describes the pressurised water reactor (PWR) design. The main distinguishing features of the VVER compared to other PWRs are:
- Horizontal steam generators
- Hexagonal fuel assemblies
- No bottom penetrations in the pressure vessel
- High-capacity pressurisers providing a large reactor coolant inventory
Reactor fuel rods are fully immersed in water kept at 15 MPa of pressure so that it does not boil at normal (220 to over 300 °C) operating temperatures. Water in the reactor serves both as a coolant and a moderator which is an important safety feature. Should coolant circulation fail the neutron moderation effect of the water diminishes, reducing reaction intensity and compensating for loss of cooling, a condition known as negative void coefficient. Later versions of the reactors are encased in massive steel pressure shells. Fuel is low enriched (ca. 2.4–4.4% 235U) uranium dioxide (UO2) or equivalent pressed into pellets and assembled into fuel rods.
Reactivity is controlled by control rods that can be inserted into the reactor from above. These rods are made from a neutron absorbing material and depending on depth of insertion hinder the chain reaction. If there is an emergency, a reactor shutdown can be performed by full insertion of the control rods into the core.
Primary cooling circuit
As stated above, water in the primary circuit is kept under constant pressure to avoid boiling. Since the water transfers all the heat from the core and is irradiated, integrity of this circuit is most crucial. In the circuit four subsystems can be distinguished:
- Reactor: Water flows through fuel rod assemblies and is heated by the nuclear chain reaction.
- Volume compensator (Pressurizer): To keep the water under constant but controlled pressure, the volume compensator regulates pressure employing self-regulation of saturated steam-water interface and by means of electrical heating and relief valves.
- Steam Generator: In the steam generator, heat from primary coolant water is used to boil water in the secondary circuit.
- Pump: The pump ensures proper circulation of the water through the circuit.
To ensure safety primary components are redundant.
Secondary circuit and electrical output
The secondary circuit also consists of different subsystems:
- Steam Generator: Secondary water is boiled taking heat from the primary circuit. Before entering the turbine remaining water is separated from the steam so that the steam is dry.
- Turbine: The expanding steam drives a turbine, which connects to an electrical generator. The turbine is split into high and low pressure sections. To prevent condensation (Water droplets at high speed damage the turbine blades) steam is reheated between these sections. Reactors of the VVER-1000 type deliver 1 GW of electrical power.
- Condenser: The steam is cooled and allowed to condense, shedding waste heat into a cooling circuit.
- Deaerator: Removes gases from the coolant.
- Pump: The circulation pumps are each driven by their own small steam turbine.
To increase efficiency of the process, steam from the turbine is taken to reheat coolant before the deaerator and the steam generator. Water in this circuit is not supposed to be radioactive.
The cooling circuit is an open circuit diverting water from an outside reservoir such as a lake or river. Evaporative cooling towers, cooling basins or ponds exhaust waste heat from the generation circuit, releasing it into the environment. In addition to generating electricity most VVERs have a capability to supply heat for residential and industrial use. Operational examples of such systems are the plants at Jaslovské Bohunice and Dukovany. 
A typical design feature of nuclear reactors is layered safety barriers preventing escape of radioactive material. VVER reactors have four layers:
- Fuel pellets: Radioactive elements are retained within the crystal structure of the fuel pellets.
- Fuel rods: The zircaloy tubes provide a further barrier resistant to heat and high pressure.
- Reactor Shell: A massive steel shell encases the whole fuel assembly hermetically.
- Reactor Building: A concrete containment building that encases the whole first circuit is strong enough to resist the pressure surge a breach in the first circuit would cause.
Currently operating Russian VVERs are inherently safer designs than the RBMK reactors of Chernobyl disaster. They do not have the vulnerability that the RBMK reactors had of a risk of a power surge transient or criticality accident. The Soviet Union opted to construct graphite-moderated RBMK series nuclear reactors without containment structures on grounds of cost as well as the relative ease of re-fueling RBMK reactors. Fuel elements in a RBMK reactor can be replaced while still operational, allowing continued operation and plutonium extraction compared to the VVER which needs to be shut down. Many levels of protection and containment have both been proposed and constructed for RBMK and VVER type reactors.
Operational life of VVER 1000
When first built the VVER design was intended to be operational for 35 years. A mid-life major overhaul including a complete replacement of critical parts such as fuel and control rod channels was thought necessary after that. Since RBMK reactors specified a major replacement programme at 35 years designers originally decided this needed to happen in the VVER type as well, although they are of more robust design than the RBMK type. Most of Russia's VVER plants are now reaching and passing the 35 year mark. More recent design studies have allowed for an extension of lifetime up to 50 years with replacement of equipment. New VVERs will be nameplated with the extended lifetime.
In 2010 the oldest VVER-1000, at Novovoronezh, was shut down for modernization to extend its operating life for an additional 30 years; the first to undergo such an operating life extension. The works include the modernization of management, protection and emergency systems, and improvement of security and radiation safety systems.
The VVER-1200 (or NPP-2006 or AES-2006) is an evolution of the VVER-1000 being offered for domestic and export use. Specifications include a $1,200 per kW electric capital cost, 54 month planned construction time, and expected 60 year lifetime at 90% capacity factor. The VVER 1200 will produce 1,200 MWe of power. Safety features include a containment building and missile shield. It has full emergency systems that include an emergency core cooling system, emergency backup diesel power supply, advanced refueling machine, computerized reactor control systems, backup feedwater supply and reactor SCRAM system. The nuclear reactor and associated systems are in a single building with another building for the turbogenerators. The main building comprises the reactor, refueling machine and diesel backup power supply, steam generators and reactor control systems.
If a VVER-1200 experiences a loss of coolant accident or loss of power accident the turbogenerators 'coast down' for 30 seconds, during which time a shutdown can be initiated using residual power in the system. Further emergency power is available from a backup set of diesel generators kept on standby to maintain cooling flow to the reactor. The reactor design has been refined to optimize fuel efficiency.
The first two units are being built at Leningrad Nuclear Power Plant II and Novovoronezh Nuclear Power Plant II. More reactors with a VVER-1200/491 like the Leningrad-II-design are planned (Kaliningrad and Nizhny Novgorod NPP) and under construction. The VVER-1200/392M under construction at the Novovoronezh NPP-II is selected for the Seversk, Zentral and South-Urals NPP. A standard version was developed as VVER-1200/513 and based on the VVER-TOI (VVER-1300/510) design.
Passive heat removal system
A passive heat removal system had been added to the existing active systems in the AES-92 version of the VVER-1000 used for the Kudankulam Nuclear Power Plant in India. This has been retained for the newer VVER-1200 and future designs. The system is based on a cooling system and water tanks built on top of the containment dome. The passive systems all safety functions for 24 hours, and core safety for 72 hours.
A number of designs for future versions of the VVER have been made:
- MIR-1200 (Modernised International Reactor) - designed in conjunction with Czech company ŠKODA JS to satisfy European requirements
- VVER-1500 - VVER-1000 with dimensions increased to produce 1500 MWe gross power output, but design shelved in favour of the evolutionary VVER-1200
- VVER-TOI is aimed at development of typical optimized informative-advanced project of a new generation III+ Power Unit based on VVER technology, which meets a number of target-oriented parameters using modern information and management technologies.
|Akkuyu||Turkey||(4 × VVER-1200/513) (AES-2006 with TOI-Standard)||Under construction.|
|Balakovo||Russia||4 × VVER-1000/320
(2 × VVER-1000/320)
|Unit 5 and 6 construction suspended.|
|Belene||Bulgaria||(2 × VVER-1000/466B)||Planned.|
|Bohunice||Slovakia||2 × VVER-440/230
2 × VVER-440/213
|Split in two plants, V-1 and V-2 with two reactors each. VVER-440/230 units decommissioned in 2007.|
|Bushehr||Iran||1 × VVER-1000/446
(3 × VVER-1000/446)
|A version of the V-320 adapted to the Bushehr site. Unit 2 and 3 planned, unit 4 cancelled.|
|Dukovany||Czech Republic||4 × VVER 440/213||Now upgraded to 502 MW in 2009-2012.|
|Greifswald||Germany||4 × VVER-440/230
1 × VVER-440/213
(3 × VVER-440/213)
|Decommissioned. Unit 6 finished, but never operated. Unit 7 and 8 construction suspended.|
|Kalinin||Russia||2 × VVER-1000/338
1 × VVER-1000/320
(1 × VVER-1000/320)
|Unit 4 under construction, operational 2011.|
|Hanhikivi||Finland||1 × VVER-1200/491||Planned, operational 2024.|
|Khmelnitskiy||Ukraine||2 × VVER-1000/320
(2 × VVER-1000/392B)
|Unit 3 and 4 under construction.|
|Kola||Russia||2 × VVER-440/230
2 × VVER-440/213
|Koodankulam||India||(2 × VVER-1000/412) (AES-92)||Under construction, operational 2012/2013 with four additional units planned.|
|Kozloduy||Bulgaria||4 × VVER-440/230
2 × VVER-1000
|VVER-440/230 units decommissioned 2004-2007.|
|Leningrad II||Russia||2 × VVER-1200/491
(2 × VVER-1200/491)
|The units are the prototypes of the VVER-1200/491 (AES-2006) and under construction.|
|Loviisa||Finland||2 × VVER-440/213||Western control systems, Totally different containment structures. Later modified for a 496 MW output.|
|Metsamor||Armenia||2 × VVER-440/230||One reactor was shut down in 1989.|
|Mochovce||Slovakia||2 × VVER-440/213
(2 × VVER-440/213)
|Units 3 and 4 construction suspended due to lack of funds, planned to be operational in 2012.|
|Novovoronezh||Russia||1 x VVER-210 (V-1)
1 x VVER-365 (V-3M)
2 × VVER-440/179
1 × VVER-1000/187
|All units are prototypes. Unit 1 and 2 shutdown. Unit 3 modernised in 2002.|
|Novovoronezh II||Russia||(2 × VVER-1200/392M) (AES-2006)||The units are the prototypes of the VVER-1200/392M (AES-2006) and under construction.|
|Paks||Hungary||4 × VVER-440/213||Two VVER-1200 units planned|
|Rheinsberg||Germany||1 × VVER-70 (V-2)||Unit decommissioned|
|Rivne||Ukraine||2 × VVER-440/213
2 × VVER-1000/320
(2 × VVER-1000/320)
|Unit 5 and 6 planning suspended.|
|South Ukraine||Ukraine||1 × VVER-1000/302
1 × VVER-1000/338
1 × VVER-1000/320
(1 × VVER-1000/320)
|unit 4 construction suspended.|
|Stendal||Germany||(4 × VVER-1000/320)||All 4 units construction cancelled after Germany reunification.|
|Temelin||Czech Republic||2 × VVER-1000/320
(2 × VVER-1000/320)
|Unit 3 and 4 construction suspended. Now unit 3 and 4 in planning again (operated in 2025).|
|Tianwan||China||2 × VVER-1000/428 (AES-91)
(6 × VVER-1000/428M)
|Unit 3 to 8 firmly planned.|
|Volgodonsk||Russia||2 × VVER-1000/320
(2 × VVER-1000/320)
|Unit 3 and 4 is under construction and planned to be operational in 2013 and 2014.|
|Zaporizhzhia||Ukraine||6 × VVER-1000/320||Largest nuclear power plant in Europe.|
- See the Wikipedia pages for each facility for sources.
Russia recently installed two nuclear reactors in China at the Tianwan Nuclear Power Plant, and an extension consisting of a further two reactors was just approved. This is the first time the two countries have co-operated on a nuclear power project. The reactors are the VVER 1000 type, which Russia has improved incrementally while retaining the basic design. These VVER 1000 reactors are housed in a confinement shell capable of being hit by an aircraft weighing 20 tonnes and suffering no expected damage. Other important safety features include an emergency core cooling system and core confinement system. Russia delivered initial fuel loads for the Tianwan reactors. China planned to begin indigenous fuel fabrication for the Tianwan plant in 2010, using technology transferred from Russian nuclear fuel producer TVEL.
The Tianwan Nuclear Power Plant uses many third party parts. While the reactor and turbo-generators are of Russian design, the control room was designed and built by an international consortium. In this way the plant was brought to meet widely recognised safety standards; safety systems were already mostly in place but the previous monitoring of these systems did not meet international safety standards. The new VVER 1000 plant built in China has 94% of its systems automated, meaning the plant can control itself under most situations. Refueling procedures require little human intervention. Five operators are still needed in the control room. The IAEA has referred to the station as the "safest nuclear power plant in the world".
In May 2010 Russia secured an agreement with the Turkish government to build a power plant with four VVER-1200 reactors at Akkuyu, Turkey. However, due to the accident experienced in Fukushima, anti-nuclear environmentalist groups heavily protested the proposed reactor at Akkuyu.
On 11 October 2011 an agreement was signed to build Belarus’ first nuclear power plant at Astravyets, using two NPP-2006 reactors with active and passive safety systems. The first unit is planned to be completed by 2017.
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- AES-2006 (VVER-1200), Rosatom.
- VVER Reactor at Virtual Nuclear Tourist.