Chernobyl Nuclear Power Plant

Template:Infobox NPP The Chernobyl Nuclear Power Plant (Ukrainian: Державне спецiалiзоване пiдприємство "Чорнобильська АЕС", Russian: Чернобыльская АЭС) is a decommissioned nuclear power station near the city of Prypiat, Ukraine, 18 km northwest of the city of Chernobyl, 16 km from the Ukraine-Belarus border, and about 110 km north of Kiev. It was the site of the Chernobyl disaster in 1986, but due to high power demand, continued to operate until December 2000. Workers remain at the site because the remaining three reactors at the Chernobyl plant, although no longer in operation, still contain nuclear fuel which needs to be monitored.

The nuclear power plant site is to be cleared by 2065. On January 3, 2010 a Ukrainian law stipulating a "program" toward this objective came into effect.

Construction

Location

The V.I. Lenin Nuclear Power Station (Russian: Чернобыльская АЭС им. В.И.Ленина) as it was known during the Soviet times, consisted of four reactors of type RBMK-1000, each capable of producing 1000 megawatts of electric power (3.2 GW of thermal power), and the four together produced about 10% of Ukraine's electricity at the time of the accident. The Chernobyl station is 18 km (11 mi) northwest of the city of Chernobyl, 16 km (10 mi) from the border of Ukraine and Belarus and about 100 km (62 mi) north of Kiev. Construction of the plant and the nearby city of Pripyat to house workers and their families began in 1970, with reactor No. 1 commissioned in 1977. It was the third nuclear power station in the Soviet Union of the RBMK-type (after Leningrad and Kursk), and the first ever nuclear power plant on Ukrainian soil. The completion of the first reactor in 1977 was followed by reactor No. 2 (1978), No. 3 (1981), and No. 4 (1983). Two more reactors, nos. 5 and 6, capable of producing 1000 MW each, were under construction at the time of the accident. Reactor No. 5 was almost complete at the time of the accident and was scheduled to start operating in late 1986. However, it has since been abandoned; construction cranes still stand next to it to this day.

Units 3 and 4 were second generation units, where as units 1 and 2 were first generation units (like those in operation at Kursk Nuclear Power plant). Second generation RBMK designs were fitted with a more secure accident localization system, as can be seen in pictures. It is fortunate as can be, that the accident happened in a second generation unit, if it had happened in a first generation unit it could have been even more devastating. Today, many countries that were in the former USSR have been paid money from the EU to shut down such first generation units, as they pose a threat to the environment. All units at the complex were of the RBMK-type, a Soviet nuclear reactor that was used only in USSR and never exported. These reactors were primarily designed for making plutonium for nuclear weapons, with electric power as a byproduct.

Reactor

Main article: RBMK

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 is normally not used, and serves as an external power supply, connected by a station transformer to the power plant's electrical systems. The plant can be powered by its own generators, or get power from the 750 kV grid through the generator transformer, or from the 330 kV grid via the station transformer, or from the other power plant block via two reserve busbars. In case of total external power loss, the essential systems can be powered by diesel generators. Each unit transformer is connected to two 6 kV main power boards, A and B (e.g. 7A, 7B, 8A, 8B for generators 7 and 8), powering principal non-essential drivers and connected to transformers for the 4 kV main power and the 4 kV reserve busbar. The 7A, 7B, and 8B boards are also connected to the three essential power lines (namely for the coolant pumps), 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 the spinning down turbogenerators for about 45–50 seconds, during which time the diesel generators should start up. The generators are started automatically within 15 seconds at loss of off-site power.

Turbogenerators

The electrical energy is generated by a pair of 500 MW hydrogen-cooled turbogenerators. These are located in the 600-meter-long machine hall, adjacent to the reactor building. The turbines, the venerable five-cylinder K-500-65/3000, are 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 200 t and their nominal rotational speed is 3000 rpm. The turbogenerator is 39 m long and its total weight is 1200 t. The coolant flow for each turbine is 82,880 t/h. The generator produces 20 kV 50 Hz AC power. The generator's stator is cooled by water while its rotor is cooled by hydrogen. The hydrogen for the generators is 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 (now Turboatom) 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.

Accidents

1982

In 1982, a partial core meltdown occurred in reactor No. 1 at the Chernobyl plant. The extent of the accident was not made public until years later. The reactor was repaired and put back into operation within months.

1986

Reactor #4 with its enclosing sarcophagus.

Main articles: Chernobyl disaster and Chernobyl disaster effects

On Saturday, April 26, 1986, a disaster occurred at reactor No. 4, which has been widely regarded as the worst accident in the history of nuclear power. As a result, reactor No. 4 was completely destroyed and has since been enclosed in a concrete and lead sarcophagus to prevent further escape of radiation. The population of the nearby areas were evacuated. Large areas of Europe were affected by the accident, but increased radiation exposure outside of Ukraine, Belarus and Russia "are comparable to an annual dose from natural background radiation and are, therefore, of little radiological significance" according to the United Nations Scientific Committee on the Effects of Atomic Radiation.

1991 fire

The Chernobyl Nuclear Plant utilized one large, open turbine hall for all four reactors without any separating walls. Each reactor had two turbines. On October 11, 1991, a fire broke out in the turbine hall of Reactor 2. The fire began in Reactor 2's Turbine 4 (ТГ-4 in Russian) due to a hydrogen leak, causing damage to the turbine and the turbine hall roof. The adjacent reactor hall and reactor were unaffected.

After the 1991 fire, there was discussion about replacing the damaged Turbine 4 in Reactor 2 with Turbine 7 from Reactor 4 (the reactor damaged in 1986), because Turbine 7 had not been damaged in the 1986 explosion, was subsequently unused, and was in working order. This would provide a low-cost alternative to full replacement of the turbine.

Ukraine's 1991 independence from the Soviet Union generated further discussion on the Chernobyl topic, because the Rada, Ukraine's new parliament, was composed largely of young reformers. Discussions about the future of nuclear energy in Ukraine helped move the government toward the political decision to cancel the operation of Reactor 2.

Decommissioning

From 1991, Western nations pushed Ukraine to shut down the Chernobyl plant. After the fire at reactor 2, it was decided that the plant would be taken out of service in two stages, with one of the two remaining reactors being shut down by the year 1996 and another by the year 2000. It was decided that reactor 1 would be shut down first for two reasons: the first being that it is the older of the two; the other being that so much labour and money was invested into making reactor 3 operational four years prior to the fire, that to shut it down so soon would be uneconomical.

Unit 3 was the last reactor to be operated at the Chernobyl plant. To meet the year 2000 deadline, the reactor was shut down on 15 December 2000 during the official ceremony of the power plant shut-down with Ukrainian President Leonid Kuchma present in the control room during the event. At about 1:17 PM local time, the reactor team pressed AZ5, Rapid Emergency Defence; within seconds the power readout meter was reading zero. The shutdown went as planned.

Even after the last reactor shutdown, people continue to work at the Chernobyl plant until reactor units 1, 2, and 3 are totally decommissioned, which is expected to take years. The first stage of decommissioning is the removal of the highly radioactive spent nuclear fuel, which is placed in deep water cooling ponds. However, storage facilities for this are not suitable for long term containment, and those on site do not have the capacity for all the spent fuel from units 1, 2 and 3. A second facility is planned for construction that will use dry storage technology suitable for long term storage and have the required capacity.

Removal of uncontaminated equipment has begun at unit 1 and this work could be complete by 2020–2022.

The remains of reactor unit 4 will remain radioactive for some time. The isotope responsible for the majority of the external gamma radiation dose at the site is Caesium-137 which has a half-life of about 30 years. It is likely that with no further decontamination work the gamma ray dosage at the site will return to background levels in about three hundred years. However, as most of the alpha emitters are longer lived, the soil and many surfaces in and around the plant are likely to be contaminated with transuranic metals such as plutonium and americium, which have much longer half-lives. It is planned that the reactor buildings will be disassembled as soon as it is radiologically safe to do so.

Sarcophagus replacement

Main article: New Safe Confinement

On 17 September 2007 it was announced that a new steel containment structure named the New Safe Confinement (NSC) would be built to replace the aging and hastily built sarcophagus that currently protects reactor unit 4. The project, financed by an international fund managed by the European Bank for Reconstruction and Development (EBRD), will be designed and built by the French-led consortium Novarka, which includes the companies Bouygues and Vinci. Novarka will build a giant arch-shaped structure out of steel, 190 m wide and 200 m long to cover the old crumbling concrete dome that is currently in use.

It is expected to take a year to design the new building and another two years to build it. The steel casing project is expected to cost $1.4 billion (£700 million, €1 billion). A separate deal has also been made with the American firm Holtec to build a storage facility within the exclusion zone for nuclear waste produced by Chernobyl.

Tours to Chernobyl

The Ministry of Atomic Power of Ukraine now lets tourists go on special tours of the area.

Exlusive tour to Chernobyl Zone >>

See also

• List of nuclear reactors
• Nuclear power

Other Chernobyl articles

• Chernobyl compared to other radioactivity releases
• Chernobyl disaster
• Chernobyl disaster effects
• Chernobyl Heart
• Cultural impact of the Chernobyl disaster
• List of Chernobyl-related articles
• List of Chernobyl-related charities
• Zone of alienation

Other accidents

• List of civilian nuclear accidents
• List of military nuclear accidents
• Three Mile Island accident

Nuclear safety

• International Nuclear Event Scale
• Loss of coolant accident
• Nuclear meltdown
• Radioactive contamination

Other

• Radiotrophic fungus

External links

• Chernobyl Nuclear Power Plant - official website Template:En icon
• Chernobyl Nuclear Power Plant at Google Maps
• Construction of the Chernobyl Nuclear Power Plant - video Template:Ru icon
• Shut down of reactor no. 3 in December 2000 - video Template:Ru icon
• Slide show of a visit to the Chernobyl reactor in April 2006 by a German TV team joint by Research Center Juelich
• Steel Sarcophagus Announcement.
• «Zone — virtual walk with comments» Template:Ru icon by Nataliya Monastirnaya