Chernobyl Nuclear Power Plant
The Chernobyl Nuclear Power Plant is a nuclear power plant undergoing decommissioning. ChNPP is located near the abandoned city of Pripyat in northern Ukraine, northwest of the city of Chernobyl, from the Belarus–Ukraine border, and about north of Kyiv. The plant was cooled by an engineered pond, fed by the Pripyat River about northwest from its juncture with the Dnieper River. On 26 April 1986, during a safety test, unit 4 reactor exploded, exposing the core and releasing radiation. This marked the beginning of the Chernobyl disaster.
Originally named the Chernobyl Nuclear Power Plant of V. I. Lenin after the founding leader of the Soviet Union, the plant was commissioned in phases with the four reactors entering commercial operation between 1978 and 1984. In 1986, in what became known as the Chernobyl disaster, reactor No. 4 suffered a catastrophic explosion and meltdown; as a result of this, the power plant is now within a large restricted area known as the Chernobyl exclusion zone. Both the zone and the power plant are administered by the State Agency of Ukraine on Exclusion Zone Management. The three other reactors remained operational post-accident maintaining a capacity factor between 60 and 70%. In total, units 1 and 3 had supplied 98 terawatt-hours of electricity each, with unit 2 slightly less at 75 TWh. In 1991, unit 2 was placed into a permanent shutdown state by the plant's operator due to complications resulting from a turbine fire. This was followed by Unit 1 in 1996 and Unit 3 in 2000. Their closures were largely attributed to foreign pressures. In 2013, the plant's operator announced that units 1–3 were fully defueled, and in 2015 entered the decommissioning phase, during which equipment contaminated during the operational period of the power station will be removed. This process is expected to take until 2065 according to the plant's operator. Although the reactors have all ceased generation, Chernobyl maintains a large workforce as the ongoing decommissioning process requires constant management.
From 24 February to 31 March 2022, Russian troops occupied the plant as part of their invasion of Ukraine.
Construction
In 1966, plans to construct Chernobyl Nuclear Power Plant were first conceived, during the development of nuclear production of energy in the Soviet Union. Construction of the Chernobyl Nuclear Power Plant began in 1972. The plant was meant to have 12 units, made up of six construction phases, and if completed would have been the largest nuclear power plant in the world. The plant would eventually consist of four RBMK-1000 reactors, each capable of producing 1,000 megawatts of electric power, and the four together produced about 10% of Ukraine's electricity. Like other sites which housed multiple RBMK reactors such as Kursk, the construction of the plant was also accompanied by the construction of a nearby city to house workers and their families. In the case of the ChNPP, the new city was Pripyat. During construction, a mobile crane was deployed and was used to lift pre-fabricated builds weighing up to 640 tons. It was the only crane of such design in the country, and was also used to install the nuclear reactor. Over 20 specialized organizations involved with the construction were working simultaneously, specializing in electric wiring, heat insulation, hydraulic engineers, chemical protection, etc. The work would be coordinated and directed by the headquarters, which was managed by site manager Vasilii Trofimovich Kizima. Most welders formerly served in the tank forces, which gave them endurance training prior to becoming construction workers at Chernobyl. Concrete pouring was done as high as 50 meters above ground level, and the Komsomol-and-youth brigade of Viacheslav Volkov completed carcassing the reactor shaft by 1974.Operations
Construction of the station concluded in the late 1970s, with reactor No. 1 being commissioned in 1977. It was the third Soviet RBMK nuclear power plant, after the Leningrad and Kursk power plants, and the first plant on Ukrainian soil. The completion of the first reactor in 1977 was followed by reactor No. 2 in 1978, No. 3 in 1981, and No. 4 in 1983. Two more blocks, numbered five and six, of more or less the same reactor design, were planned at a site roughly a kilometre from the contiguous buildings of the four older blocks. This is similar to the layout of units 5 and 6 at Kursk and shows the similarity in design between the RBMK sites. Reactor No. 5 was around 70% complete at the time of Reactor 4's explosion and was scheduled to come online approximately seven months later, in November 1986. In the aftermath of the disaster, construction on No. 5 and 6 was suspended, and eventually cancelled on April 20, 1989, days before the third anniversary of the 1986 explosion. At one point six other reactors were planned on the other side of the river, bringing the total to twelve.Reactors No. 3 and 4 were second-generation units, whereas No. 1 and 2 were first-generation units, like those in operation at the Kursk power plant. Second-generation RBMK designs were fitted with a more secure containment structure, visible in photos of the facility.
Units
Design
Electrical systems
The power plant is connected to the 330 kV and 750 kV electrical grid. The block has two electrical generators connected to the 750 kV grid by a single generator transformer. The generators are connected to their common transformer by two switches in series. Between them, the unit transformers are connected to supply power to the power plant's own systems; each generator can therefore be connected to the unit transformer to power the plant, or to the unit transformer and the generator transformer to also feed power to the grid.The 330 kV line was normally not used, and served as an external power supply, connected to a station's transformer – meaning to the power plant's electrical systems. The plant was powered by its own generators, or at any event got power from the 750 kV national grid through the main grid backup feed in the transformer, or from the 330 kV level feed in grid transformer 2, or from the other power plant blocks via two reserve busbars. In case of total external power loss, the essential systems could be powered by diesel generators. Each unit's transformer is therefore connected to two 6 kV main power line switchboards, A and B, powering principal essential systems and connected to even another transformer at 4 kV, which is backed up twice.
The 7A, 7B, and 8B boards are also connected to the three essential power lines, each also having its own diesel generator. In case of a coolant circuit failure with simultaneous loss of external power, the essential power can be supplied by spinning down turbogenerators for about 45 to 50 seconds, during which time the diesel generators should start. The generators were started automatically within 15 seconds at loss of off-site power.
Turbo generators
Electrical energy was generated by a pair of 2x500 MW hydrogen-cooled turbo generators per unit. These are located in the -long machine hall, adjacent to the reactor building. The turbines—the venerable five-cylinder K-500-65/3000 steam turbine were supplied by the Kharkiv turbine plant; the electrical generators are the TBB-500. The turbine and the generator rotors are mounted on the same shaft; the combined weight of the rotors is almost and their speed was 3,000 revolutions per minute.The turbo generator is long and its total weight is. The coolant flow for each turbine is 82,880 t/h. The generator produced 20 kV 50 Hz AC power. The generator's stator was cooled by water while its rotor was cooled by hydrogen. The hydrogen for the generators was manufactured on-site by electrolysis. The design and reliability of the turbines earned them the State Prize of Ukraine for 1979.
The Kharkiv turbine plant later developed a new version of the turbine, K-500-65/3000-2, in an attempt to reduce use of valuable metal. The Chernobyl plant was equipped with both types of turbines; block 4 had the newer ones. The newer turbines, however, turned out to be more sensitive to their operating parameters, and their bearings had frequent problems with vibrations.
Reactor fleet
The construction of two partially completed reactors, No. 5 and 6, were suspended immediately after the accident at reactor No. 4, and eventually cancelled in 1989. Reactors No. 1 and 3 continued to operate after the disaster. Reactor No. 2 was permanently shut down in 1991 after a fire broke out due to a faulty switch in a turbine. Reactors No. 1 and 3 were to be eventually closed due to a 1995 agreement Ukraine made with the European Union.Ukraine agreed to close the remaining units in exchange for EU assistance in modernizing the shelter over reactor No. 4 and improving the energy sector of the country, including the completion of two new nuclear reactors, Khmelnytskyi 2 and Rivne 4. Reactor No. 1 was shut down in 1996 with No. 3 following in 2000.
Computer systems
SKALA was the process computer for the RBMK nuclear reactor at the Chernobyl nuclear power plant prior to October 1995. Dating to the 1960s, it used magnetic-core memory, magnetic tape data storage, and punched tape for loading software.SKALA monitored and recorded reactor conditions and control board inputs. It was wired to accept 7200 analog signals and 6500 digital signals. The system continuously monitored the plant and displayed this information to operators. Additionally, a program called PRIZMA processed plant conditions and made recommendations to guide plant operators. This program took 5 to 10 minutes to run, and could not directly control the reactor.