VVER
The VVER (From (Russian: Водо-водяной энергетический реактор, translitterates as Vodo-Vodyanoi Energetichesky Reactor, translates as Water-Water Energetic Reactor, WWER. Water-water stands for coolant and moderator.) is a series of pressurised water reactors that were developed and used by the former Soviet Union, its satellites, Finland and the present-day Russian Federation. The VVER was a more expensive reactor design, and the former Soviet Union opted for the graphite-moderated RBMK series nuclear reactors on the grounds of cost as well as the ease of re-fueling the RBMK while the reactor was still operational compared to the VVER which needed to be shut down to be re-fueled and is of a much safer design.
The earliest VVERs were developed before 1970. The most common design, the VVER-440 Model V230, employs six primary coolant loops, each with a horizontal steam generator. The modified version of the VVER-440, Model V213, was a product of the first uniform safety requirements drawn up by the Soviet designers. This model includes added emergency core cooling and auxiliary feedwater systems as well as upgraded accident localization systems. The larger VVER-1000 design, which was developed after 1975, is a four-loop system housed in a containment-type structure with spray type steam suppression system.
The VVER series nuclear reactors were also scaled down in size and was used by the Soviet Navy's nuclear submarine fleet as well as by surface warships.
The Russian abbreviation VVER stands for water-cooled, water-moderated energy reactor. This means, that the reactor is of the pressurized water reactor (PWR) design. The fuel is low enriched (ca. 2.4–4.4% 235U) uranium dioxide (UO2) pressed into pellets and assembled into fuel rods. These fuel rods are fully immersed into water that is kept under pressure (15 MPa) so that it cannot boil. This water serves both as coolant and moderator, which guarantees intrinsic safety under normal circumstances: Should the circulation fail, the moderating effect diminishes, thus reducing the intensity of the reaction to compensate the loss of cooling (negative void coefficient). The whole reactor is encased in a massive steel pressure-shell.
The intensity of the nuclear reaction 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 the depth of insertion hinder the chain reaction. In the case of emergency, an emergency switch-off can be performed by full insertion of the control rods into the core.
Usable life of: VVER 1000
When built in the former USSR, the VVER design was thought to have a 35 year life time. A mid-life major overhaul including the complete replacement of critical parts was specified. Since the design of the older RBMK design specified the replacement of fuel and control rod channels etc., designers originally decided this needed to happen in VVER plants even though they are of a more robust design than the RBMK type. Most of Russia's VVER plants are now reaching and passing the 35 year mark. The world's nuclear industry was shocked when Russian nuclear authorities announced that rather than shutting down current reactors they would give a life extension to the plants and uprate them by 5%, including also RBMK units similar to the RBMK 1000 plant involved in the Chernobyl Accident.
Primary cooling circuit
As stated above, the water in this circuit is kept under constant pressure to avoid boiling. Since this water removes all the heat from the core and is irradiated, the integrity of this circuit is most crucial. In this circuit four distinct stations can be distinguished:
- Reactor: The water flows through the fuel rod assemblies, removing the heat supplied by the nuclear chain reaction
- Pressurizer: To keep the water under constant but not over-high pressure, the pressurizer regulates the pressure by means of electrical heating and relief valves.
- Steam Generator: In the (horizontal) steam generator, the heat from the primary water is used to boil water from the secondary circuit.
- Pump: The pump ensures the proper circulation of the water through the circuit.
To ensure safety, the components are redundant.
Secondary circuit and electrical output
The secondary circuit consists also of different stations:
- Steam Generator: Secondary water is boiled, removing heat from the primary circuit. Before exiting, the remaining water is removed from the steam, so that the steam is dry.
- Turbine: The expanding steam drives the turbine, which is connected to the electrical generator. The turbine is split into a high- and a low-pressure part. To prevent condensation (Water droplets at high speed damage the turbine blades) the steam is reheated between the sections. Reactors of VVER-1000 type deliver 1GW of electrical power.
- Condenser: The steam is cooled down and is allowed to condense by delivering its heat to a cooling circuit
- Deaerator: Removes gases from the coolant
- Pump: The circulation pumps are driven by small steam turbines of their own
To increase the efficiency of the process, steam from the turbine is taken to reheat the coolant before the deaerator and the steam generator. Water in this circuit is not supposed to be radioactive.
Cooling circuit
This is an open circuit, the water is usually taken from an outside reservoir like a lake or river. In order not to heat the reservoir too much, thus polluting the environment, cooling basins (or cooling towers) allow the water to cool down before reentering the reservoir.
Safety barriers
A typical design feature of nuclear reactors are layered safety barriers preventing escape of radioactive material. The 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 resistive to heat and high pressure.
- Reactor Shell: A massive steel shell encases the whole fuel assembly hermetically.
- Reactor Building: The 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.
Unlike some other modern designs, the VVER does not include a containment building sufficiently strong to shield the reactor from outside incidents such as airplane crashes.
VVER-1200
The VVER-1200, an evolutionary design of the VVER-1000, is being offered for export. Specifications include a $1200/kW-electric capital cost, a 54 month planned construction time, and an expected 50 year life at a 90% capacity factor. The VVER 1200 will produce 1200MWe of power and has a contanment builing and missile shield. It will have full emergency system's that include; Emergency Core Cooling System, Emergency Backup Diesel Power Supply, Advanced Refueling Machice, Full Reactor Control Systems via Computer Systems, Backup Feedwater Supply and Full Reactor SCRAM System. The nuclear reactor and its main systems will be hosted in one single building and there will be another building for the turbogenerators. The main builing will comprise of; Reactor, Refueling Machine and Diesel Backup Power Suppy, Steam Generators, Reactor Control Systems.
The VVER 1200 can experience a Loss Of Coolant Accident and Loss Of Power Accident due to turbogenerators that 'coast down' after shutdown and backup power supply, set of diesel generators that restore cooling to the reactor, within about 30 seconds. The reactor is also designed with a high fuel burn-up, which means that the nuclear fuel lasts longer.
Power plants
| Power plant | Country | Reactors | Notes |
|---|---|---|---|
| Balakovo | Russia | 4 × VVER-1000/V320 (2 × VVER-1000/V320) |
Unit 5 under construction. Construction of unit 6 was halted 1993 |
| Belene | Bulgaria | (2 × VVER-1000/V446B) | Under construction, operational 2013/2014 |
| Bohunice | Slovakia | 2 × VVER-440/V230 2 × VVER-440/V213 |
Split in two plants, V-1 and V-2 with two reactors each. VVER-440/V230 units decommissioned in 2007 |
| Bushehr | Iran | 2 × VVER-1000/V446 | |
| Dukovany | Czech Republic | 4 × VVER 440/V213 | |
| Kalinin | Russia | 2 × VVER-1000/V338 1 × VVER-1000/V320 (1 × VVER-1000/V320) |
Unit 4 under construction, operational 2011 |
| Khemelnitski | Ukraine | 1 × VVER-1000 | |
| Kola | Russia | 2 × VVER-440/V230 2 × VVER-440/213 |
|
| Koodankulam | India | (2 × VVER-1000/V412) | Under construction, operational 2007/2009 with four additional units planned |
| Kozloduy | Bulgaria | 4 × VVER-440/V230 2 × VVER-1000 |
VVER-440/V230 units decommissioned 2003-2006 |
| Loviisa | Finland | 2 × VVER-440/V213 | Western control systems, Totally different containment structures. Later modified for a 488 MW output |
| Metsamor | Armenia | 2 × VVER-440/V230 | One reactor was shut down in 1989 |
| Mochovce | Slovakia | 2 × VVER-440/V213 (2 × VVER-440/V213) |
Units 3 and 4 under construction, operational 2012 |
| Novovoronezh | Russia | 2 × VVER-440/V179 1 × VVER-1000/V187 |
All units are prototypes |
| Paks | Hungary | 4 × VVER-440/V213 | |
| Rivne | Ukraine | 2 × VVER-440/V213 1 × VVER-1000 (1 × VVER-1000) |
Unit 4 under construction |
| South Ukraine | Ukraine | 3 × VVER-1000 | |
| Temelin | Czech Republic | 2 × VVER-1000/V320 | |
| Tianwan | China | 2 × VVER-1000/V428 | |
| Volgodonsk | Russia | 1 × VVER-1000/V320 (1 × VVER-1000/V320) |
Unit 2 under construction, operational 2009 |
| Zaporizhzhia | Ukraine | 6 × VVER-1000 | Largest nuclear power plant in Europe |
- See the Wikipedia pages for each facility for sources.
Russia has recently finished installing two nuclear reactors in China. This is the first time this has happened between China or Russia. The reactors are of the VVER 1000 type which Russia has built upon from other early versions, using the basic PWR design. These VVER 1000 reactors are housed in a confinement shell, which is cabable of getting hit from an aircraft weighing 20 tonnes, with no expected damage. Russia will deliver the first load of nuclear fuel for the VVER 1000 reactors, and then China should be able to use their own nuclear fuel plants to make the enriched nuclear fuel. China claims it is the "safest nuclear power plant".
The newer version, VVER 1000, uses many third party parts to form the reactor. While the main reactor and turbogenerators are of Russian design, the control room is designed and built by another company. This happened so that the new VVER 1000 plants meet most international safety standards. These include; Emergency Core Cooling System, Confinement System. These systems were mostly in place, but the monitoring of these systems did not meet ANY international safety standards. The new VVER 1000 plant built in China (see above), has 94% of its systems automated, meaning the plant can control itself under most situations. Even the refueling process requires little human intervention, Even though; 5 people are still needed in the control rooom.
References