Conceptual Design development for Chornobyl NPP construction with capacity 2000 mwt has been entrusted to the Ural branch of “Teploelectroproject” institute. Conceptual design approved by USSR Energy Ministry 29.09.67, has been developed in three options: - with application of RBMK-1000 reactor; - with gas- graphite reactor RK-1000 application; - with PWR-1000 reactor application. According to the detailed design technical and economic parameters of the first option were the lowest, but a status of developments and an equipment deliveries possibility were most expedient.

Application of RBMK-1000 reactors was determined by joint Decision of USSR Energy Ministry and USSR Machine-Building Ministry dated 19.06.69 and approved by USSR Council of Ministers, dated 14.12.70. According to the Decree of USSR Energy Ministry dated 30.03.70 the further designing of the Chornobyl NPP was entrusted to institute "Hydroproject ". Project Development for reactor block of ChNPP first-stage, including working design, was executed by Institute of Energy Technologies (VNDPIET) USSR Machine-Building Ministry as the Subcontractor. Unit with RBMK -1000 reactor with power capacity 1000 mwt - a heterogeneous channel reactor on thermal neutrons in which graphite is used as moderator and water - as the coolant has been accepted as basic for Chornobyl NPP.

Chornobyl NPP was the third plant with RBMK -1000 type reactors after Leningrad and Kursk NPPs, commissioned in 1973 and 1976.
Fundamental feature of a channel reactors design was absence of the special durable containment, peculiar to PWR type reactors, constructed in USSR and widely used in other countries. Serial manufacturing of unique high-strength big dimensional containments was restrained at that time by necessary capacities absence. In these conditions channel reactors construction assured fast development of nuclear engineering as for their construction reactor containments were not required. Such energy installations, moreover, gave possibility to achieve high capacity of one unit - 1000, and then - 1500 mwt. Last circumstance is important as the maximal capacity of PWR type reactors was determined, first of all, by the dimensions of containment, capable to withstand high pressure and, at the same time, allowing its rail transportation. Prepared to realization in that period designs of PWR reactors have been limited by power units capacities - 440 mwt, and only by 1980 power of such units was increased up to 1000 mwt.

Besides on RBMK reactors it is possible to reload nuclear fuel ('in running order'), that allows to increase its capacity factor. Reactor core of RBMK-1000 represents a cylindrical graphite stack with a diameter 11,8 m and height 7 m penetrated by 1661 vertical channel with diameter 80 mm of zirconium alloy. Inside channels there are reactor control organs and fuel assembly (FA) containing 18 rod fuel elements (FE) of uranium dioxide in an encasement of zirconium alloy. Water incoming from below in a reactor passes in channels with FA and it is heated up to boiling. Generated steam after separation comes directly on the turbine, and then in the condenser, after that with pumps using the condensate comes back into reactor. Such scheme is called single-circuit and is typical for reactors with the boiling heat-transfer. Feature of channel reactors is that the water supply and steam-and-water mixture removal is carried out for each channel separately. In RBMK-1000 reactor these channels are grouped in two contours independent from each other, each of them covers half of reactor.