page_title: VVER
section_title: Design
hierarchical_section_title: VVER / Design
caption_attribution_description: English: Reactor Hall of Mochovce NPP unit 1 and 2
context_page_description: The water-water energetic reactor, or VVER is a series of pressurized water reactor designs originally developed in the Soviet Union, and now Russia, by OKB Gidropress. The idea of a reactor was proposed at the Kurchatov Institute by Savely Moiseevich Feinberg. VVER were originally developed before the 1970s, and have been continually updated. As a result, the name VVER is associated with a wide variety of reactor designs spanning from generation I reactors to modern generation III+ reactor designs.
  Power output ranges from 70 to 1300 MWe, with designs of up to 1700 MWe in development. The first prototype VVER-210 was built at the Novovoronezh Nuclear Power Plant.
  VVER power stations have been mostly installed in Russia and the former Soviet Union, but also in China, Finland, Germany, Hungary, Slovakia, Bulgaria, India, and Iran. Countries that are planning to introduce VVER reactors include Bangladesh, Egypt, Jordan, and Turkey.
context_section_description: The Russian abbreviation VVER stands for 'water-water energy reactor' (i.e. water-cooled water-moderated energy reactor). The design is a type of pressurised water reactor (PWR). 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 pressurizers providing a large reactor coolant inventory
  Reactor fuel rods are fully immersed in water kept at 15 MPa pressure so that it does not boil at the 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.
caption: VVER-440 reactor hall at Mochovce Nuclear Power Plant
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