KS 150
Encyclopedia
KS 150 is a heavy water
Gas Cooled Reactor
(HWGCR) nuclear reactor
design. A single example, A-1, was constructed at the Bohunice Nuclear Power Plant in Jaslovské Bohunice
, Czechoslovakia
. The power plant suffered a series of accidents, the worst being an accident on February 22, 1977 rated INES
-4. Since 1979 the plant has been undergoing decommissioning.
(western Slovakia
) started in 1958 and took an unexpected 16 years. A-1 was commissioned on October 24, 1972.
The KS 150 reactor was designed in the Soviet Union and built entirely in Czechoslovakia, by Škoda Works
. This type of reactor had never been deployed before. One advantage of the design was its ability to use unenriched uranium
mined
in Czechoslovakia, similar to a CANDU reactor
.
Because of its experimental design the power plant suffered from accidents resulting in over 30 unplanned shutdowns. On January 5, 1976 two workers were killed due to a leak of carbon dioxide
, which was used as a coolant. A 'technical' (mechanical?) failure occurred during refuelling and a fresh fuel assembly was shot off the reactor into the reactor's hall.
The most serious accident from 1977 (see below) was rated INES
-4. The damage could have been repaired with a large investment but on May 17, 1979 the government, dissatisfied with high costs, low performance and accidents, decided to decommission the plant. Plans to build the second reactor block A-2 were canceled.
The accidents were kept secret, although wild stories circulated among the public.
A1 Nuclear Power Plant was in operation for 19,261 hours altogether, it generated 1,464 GWh and supplied 916 GWh to the network. Maximum output achieved was 127 MW.
Decommissioning, decontamination and dismantling of the plant still continues and is expected to be completed in 2033.
Seventy metal uranium
wires, each clad in a compound of magnesium
and beryllium
, are bundled together to form a fuel rod.
The reactor's pressure vessel is of 15 cm carbon steel in a cylindrical shape with diameter 5.1 m and height 20 m. Within the pressure vessel (in the active zone) is a cylindrical vessel of aluminium- magnesium-silicon alloy for the heavy water moderator.
Fuel channels are vertical, each containing a single fuel rod cooled with circulating carbon dioxide
. The core is in a pressurized vessel to allow refuelling during operation. The heavy water moderator is cooled in a separate circuit.
Carbon Dioxide gas used as a primary coolant is streamed around the fuel rods. After being heated by the rods it is piped to six steam generator
s. The resulting steam powers three turbogenerators.
The accident was rated as level 4 on International Nuclear Event Scale
(in comparison, the Three Mile Island accident
was rated level 5).
25% of the fuel elements in a heavy water
moderated carbon dioxide
cooled 100 MW(e) power reactor were damaged due to operator error. The operators failed to remove silica gel
packs from a new fuel element. The silica gel was used to keep the unused fuel dry during storage and transport. The silica gel packs blocked the flow of the coolant resulting in overheating of the fuel and the pressure channel holding it. As a result of overheating the heavy water leaked into the part of the reactor (the gas circuit) where the fuel elements are accommodated, the fuel cladding was subject to corrosion and a considerable amount of radioactivity leaked into the primary cooling circuit (CO2 gas). Through leaks in the steam boilers (similar basic design to a MAGNOX
or AGR
plant) some parts of the secondary circuit became contaminated.
Heavy water
Heavy water is water highly enriched in the hydrogen isotope deuterium; e.g., heavy water used in CANDU reactors is 99.75% enriched by hydrogen atom-fraction...
Gas Cooled Reactor
Gas Cooled Reactor
A gas-cooled reactor is a nuclear reactor that uses graphite as a neutron moderator and carbon dioxide as coolant...
(HWGCR) nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
design. A single example, A-1, was constructed at the Bohunice Nuclear Power Plant in Jaslovské Bohunice
Jaslovské Bohunice
Jaslovské Bohunice is a small village in Slovakia in the Trnava District. It is best known for the nearby Bohunice Nuclear Power Plants complex....
, Czechoslovakia
Czechoslovakia
Czechoslovakia or Czecho-Slovakia was a sovereign state in Central Europe which existed from October 1918, when it declared its independence from the Austro-Hungarian Empire, until 1992...
. The power plant suffered a series of accidents, the worst being an accident on February 22, 1977 rated INES
International Nuclear Event Scale
The International Nuclear and Radiological Event Scale was introduced in 1990 by the International Atomic Energy Agency in order to enable prompt communication of safety significance information in case of nuclear accidents....
-4. Since 1979 the plant has been undergoing decommissioning.
History
The decision to build a nuclear power plant in Czechoslovakia was made in 1956. Construction of A-1 in Jaslovské BohuniceJaslovské Bohunice
Jaslovské Bohunice is a small village in Slovakia in the Trnava District. It is best known for the nearby Bohunice Nuclear Power Plants complex....
(western Slovakia
Slovakia
The Slovak Republic is a landlocked state in Central Europe. It has a population of over five million and an area of about . Slovakia is bordered by the Czech Republic and Austria to the west, Poland to the north, Ukraine to the east and Hungary to the south...
) started in 1958 and took an unexpected 16 years. A-1 was commissioned on October 24, 1972.
The KS 150 reactor was designed in the Soviet Union and built entirely in Czechoslovakia, by Škoda Works
Škoda Works
Škoda Works was the largest industrial enterprise in Austro-Hungary and later in Czechoslovakia, one of its successor states. It was also one of the largest industrial conglomerates in Europe in the 20th century...
. This type of reactor had never been deployed before. One advantage of the design was its ability to use unenriched uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
mined
Uranium mining
Uranium mining is the process of extraction of uranium ore from the ground. The worldwide production of uranium in 2009 amounted to 50,572 tonnes, of which 27% was mined in Kazakhstan. Kazakhstan, Canada, and Australia are the top three producers and together account for 63% of world uranium...
in Czechoslovakia, similar to a CANDU reactor
CANDU reactor
The CANDU reactor is a Canadian-invented, pressurized heavy water reactor. The acronym refers to its deuterium-oxide moderator and its use of uranium fuel...
.
Because of its experimental design the power plant suffered from accidents resulting in over 30 unplanned shutdowns. On January 5, 1976 two workers were killed due to a leak of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, which was used as a coolant. A 'technical' (mechanical?) failure occurred during refuelling and a fresh fuel assembly was shot off the reactor into the reactor's hall.
The most serious accident from 1977 (see below) was rated INES
International Nuclear Event Scale
The International Nuclear and Radiological Event Scale was introduced in 1990 by the International Atomic Energy Agency in order to enable prompt communication of safety significance information in case of nuclear accidents....
-4. The damage could have been repaired with a large investment but on May 17, 1979 the government, dissatisfied with high costs, low performance and accidents, decided to decommission the plant. Plans to build the second reactor block A-2 were canceled.
The accidents were kept secret, although wild stories circulated among the public.
A1 Nuclear Power Plant was in operation for 19,261 hours altogether, it generated 1,464 GWh and supplied 916 GWh to the network. Maximum output achieved was 127 MW.
Decommissioning, decontamination and dismantling of the plant still continues and is expected to be completed in 2033.
Technical Details
KS 150 is a heavy water moderated, gas cooled reactor (HWGCR) able to refuel during operation.Seventy metal uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
wires, each clad in a compound of magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
and beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...
, are bundled together to form a fuel rod.
The reactor's pressure vessel is of 15 cm carbon steel in a cylindrical shape with diameter 5.1 m and height 20 m. Within the pressure vessel (in the active zone) is a cylindrical vessel of aluminium- magnesium-silicon alloy for the heavy water moderator.
Fuel channels are vertical, each containing a single fuel rod cooled with circulating carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. The core is in a pressurized vessel to allow refuelling during operation. The heavy water moderator is cooled in a separate circuit.
Carbon Dioxide gas used as a primary coolant is streamed around the fuel rods. After being heated by the rods it is piped to six steam generator
Steam generator (nuclear power)
Steam generators are heat exchangers used to convert water into steam from heat produced in a nuclear reactor core. They are used in pressurized water reactors between the primary and secondary coolant loops....
s. The resulting steam powers three turbogenerators.
- Fuel: unenriched metal uranium, 23.1 tonnes in the reactor.
- Core: diameter 3.56 m, height 4 m.
- Coolant gas on exit from reactor: pressure 5.4 MPaMPA-Academic degrees:* Master of Professional Accountancy* Master of Public Administration* Master of Public Affairs* Master of Physician's Assistant-Chemicals:* Medroxyprogesterone acetate, also known by the brand name Depo-Provera* Morpholide of pelargonic acid...
(~54 atm), temperature 426°C. - Conversion efficiency: 18.5%.
- Moderating heavy water: temperature 65°C (Max/exit 90°C)
- Capacity: 143 MWe.
1977 Accident
On February 22, 1977, during a fuel change, a combination of human mistakes and design problems caused the worst nuclear accident in Czechoslovakian history. Some fuel rods were being replaced while the reactor was active in a standard procedure. In this instance however humidity absorbers covering the rods were not removed, causing local overheating of the fuel (since transmission of heat to the coolant gas was reduced). The active zone was damaged, heavy water got in contact with the coolant and both primary and secondary circuits were contaminated.The accident was rated as level 4 on International Nuclear Event Scale
International Nuclear Event Scale
The International Nuclear and Radiological Event Scale was introduced in 1990 by the International Atomic Energy Agency in order to enable prompt communication of safety significance information in case of nuclear accidents....
(in comparison, the Three Mile Island accident
Three Mile Island accident
The Three Mile Island accident was a core meltdown in Unit 2 of the Three Mile Island Nuclear Generating Station in Dauphin County, Pennsylvania near Harrisburg, United States in 1979....
was rated level 5).
25% of the fuel elements in a heavy water
Heavy water
Heavy water is water highly enriched in the hydrogen isotope deuterium; e.g., heavy water used in CANDU reactors is 99.75% enriched by hydrogen atom-fraction...
moderated carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
cooled 100 MW(e) power reactor were damaged due to operator error. The operators failed to remove silica gel
Silica gel
Silica gel is a granular, vitreous, porous form of silica made synthetically from sodium silicate. Despite its name, silica gel is a solid. It is a naturally occurring mineral that is purified and processed into either granular or beaded form...
packs from a new fuel element. The silica gel was used to keep the unused fuel dry during storage and transport. The silica gel packs blocked the flow of the coolant resulting in overheating of the fuel and the pressure channel holding it. As a result of overheating the heavy water leaked into the part of the reactor (the gas circuit) where the fuel elements are accommodated, the fuel cladding was subject to corrosion and a considerable amount of radioactivity leaked into the primary cooling circuit (CO2 gas). Through leaks in the steam boilers (similar basic design to a MAGNOX
Magnox
Magnox is a now obsolete type of nuclear power reactor which was designed and is still in use in the United Kingdom, and was exported to other countries, both as a power plant, and, when operated accordingly, as a producer of plutonium for nuclear weapons...
or AGR
Advanced gas-cooled reactor
An advanced gas-cooled reactor is a type of nuclear reactor. These are the second generation of British gas-cooled reactors, using graphite as the neutron moderator and carbon dioxide as coolant...
plant) some parts of the secondary circuit became contaminated.