The VVER, or WWER, (from ; transliterates as Vodo-Vodyanoi Energetichesky Reactor; 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 440 MWe to 1200 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.