Mühleberg Nuclear Power Plant
Encyclopedia
The Mühleberg Nuclear Power Plant (in German Kernkraftwerk Mühleberg, abbreviated to KKM) is located in the Mühleberg
municipality in the (Canton of Berne
, Switzerland
) north of the village of Mühleberg and near the hydroelectric plant. It is operated by the BKW FMB Energie AG
.
, the then Bernische Kraftwerke AG
decided to build a second nuclear power plant in the canton of Berne. Mühleberg
was identified as possible location and the Swiss Federal Office of Energy (SFOE) approved this choice on . Two years later, on , a first partial construction permit was issued, followed on by the final one.
The reactor entered criticality in March 1971 but due to a fire in a turbine housing the plant had to be shut down for repairs. It eventually started commercial operation on .
KKM is at the moment the only Swiss nuclear power plant that does not have an unlimited operating license. Due to the problems noticed during the commissioning and to some ongoing tests on the emergency cooling systems performed in the United States
, until 1980 it received a series of six month license extensions, then increased to one year. They were followed by a 5 year, a 7 year, and a 10 year license extension. These extensions were justified by technical improvements the operator was instructed to perform. The operating license was extended again in 1998 and was due to expire on , however, an unlimited license was granted on December 21, 2009.
The plant had requested a limitation removal in 1990 and again in 1996, but they were both rejected by the Swiss Federal Council
for political and technical reasons. A third request pending since 2005 at the SFOE was accepted on December 21, 2009.
Acceptance of the power plant by the local population has varied. When KKM was built there was little opposition to nuclear energy, but the situation rapidly changed after the Chernobyl disaster
. In 1992 a public referendum in the canton of Berne rejected granting an unlimited operating license to the power plant, with 51% voting against. In 2003, 68% of the population rejected the initiative named Strom ohne Atom, that proposed that the plant should be shut down in 2005 to be replaced by non-nuclear power generation. A similar proposal at cantonal level had already been rejected in 2000 by 64% of voters. In 2006 the Bernese government put forward a medium-term energy strategy including the renunciation to nuclear power. Swiss parliament, however, noted this and withheld their approval, delegating any decision on an eventual shutdown to the federal authorities. The same organ in 2007 urged the Bernese government to work towards granting an unlimited operating license.
No decision has been made about a definitive shutdown date.
on that they had submitted to federal authorities a framework permit application to build two new nuclear reactors, one of which would be located in Mühleberg. Although precise technical specifications were not defined, the reactor of choice should be of 3rd generation
light water type with a net electric power between 1200 and 1600 MW. Cooling should be ensured by an hybrid tower
. Following the Fukushima Daiichi nuclear disaster
the permit application was suspended indefinitely.
(BWR) of type 4 provided by General Electric Technical Services Company (GETSCO), a then subsidiary of General Electric
specialized in nuclear power plants. All the 240 assemblies contain uranium oxide rods. The pressurized vessel has a diameter of 4.04 m and is 19 m high, has a wall thickness of 10.2 cm and operates at 288 °C and 72 bar.
The thermal power of 1097 MW is converted into 355 MW of net electrical power by two Brown Boveri steam turbine generators connected to the 220 kV and 50 kV grids. The power output was increased in 1990 from the original 320 MW.
The system is cooled with water pumped from the Aar. This in average increases the river temperature by 1.3 °C. To prevent damage to the fish population, the power plant's activity must be reduced when the river temperature exceeds 18 °C.
The reactor is hosted in a five floor concrete-steel building. The walls have a thickness of 60 cm. In its lowest, partially underground part is located the 1.7-1.8 m thick steel and concrete pressure suppression drywell. The structure is able to withstand an earthquake. In case of a plane crash, however, the building could be damaged. The reactor would nevertheless remain intact due to the five 30–50 cm thick insoles and the massive drywell.
The reactor is fed with water through two loops, each provided with its own pump. A third pump serves as reserve.
The emergency cooling of the nucleus is entrusted to three independent systems. A doubly redundant low pressure core spray with a 2·100% heat removal capacity is activated in case of leaks any size in the coolant system. Small leaks may be compensated by the redundant high pressure reactor core isolation cooling system (RCIC) or the redundant alternate low pressure system (ALPS).
By loss of cooling agent in the drywell, the excessive steam will spread into a torus-shaped pressure-suppression pool, where it will condense decreasing the pressure. The 4000 m3 big torus is filled with 2000 m3 water and is in turn cooled by a redundant torus cooling system and a redundant shutdown and torus cooling system with a total of 4·100% residual heat removal capacity. In the extreme case of a meltdown a further system is entrusted with the integrity of the primary containment by spraying and flooding the drywell.
Emergency power is provided through two connections with the nearby Mühleberg Hydroelectric Power Plant and three diesel generators.
In 1989 the SUSAN (Selbstständiges, unabhängiges System zur Abfuhr der Nachzerfallswärme) emergency building started operation.
Bunkerized and partially underground, its function is to ensure an emergency shutdown of the reactor even in case of extreme external agents like plane crashes or simultaneous downfall of the dams upstream the plant with resulting submergence of the structures. Amongst others it contains the RCIC, the ALPS, the TCS, some systems for pressure reduction and two of the three emergency diesel generators.
Due to the 2006 moratorium on the recycling of spent fuel, the entire stock of exhausted rods is now transferred to the ZZL for storage.
In 1986, due to the presence of similar cracks, many components of the cooling water circulation loop had to be exchanged. A substitution of the pressure vessel is however not considered necessary by the Swiss Federal Nuclear Safety Inspectorate (ENSI) that confirms that the power plant is able to operate in security at least until 2012, when the license will expire. Further technical improvements are nevertheless needed for an extension until 2032, as desired by the operator.
As of February 2009 no operative nuclear event (INES
level 2 or above) ever occurred. Since 1995 only one anomaly took place.
Mühleberg
Mühleberg is a municipality in the Bern-Mittelland administrative district in the canton of Bern in Switzerland.-Geography:Mühleberg has an area of . Of this area, 53.6% is used for agricultural purposes, while 32.9% is forested...
municipality in the (Canton of Berne
Canton of Berne
The Canton of Bern is the second largest of the 26 Swiss cantons by both surface area and population. Located in west-central Switzerland, it borders the Canton of Jura and the Canton of Solothurn to the north. To the west lie the Canton of Neuchâtel, the Canton of Fribourg and Vaud. To the south...
, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
) north of the village of Mühleberg and near the hydroelectric plant. It is operated by the BKW FMB Energie AG
BKW FMB Energie AG
The BKW FMB Energie AG is a power production and distribution utility with headquarter in Berne, Switzerland. Through some subsidiaries or partner companies it also provides gas and heat...
.
Mühleberg 1
In parallel with the planning of Beznau 1Beznau Nuclear Power Plant
The Beznau Nuclear Power Plant is located in the municipality Döttingen on an artificial island in the Aar river...
, the then Bernische Kraftwerke AG
BKW FMB Energie AG
The BKW FMB Energie AG is a power production and distribution utility with headquarter in Berne, Switzerland. Through some subsidiaries or partner companies it also provides gas and heat...
decided to build a second nuclear power plant in the canton of Berne. Mühleberg
Mühleberg
Mühleberg is a municipality in the Bern-Mittelland administrative district in the canton of Bern in Switzerland.-Geography:Mühleberg has an area of . Of this area, 53.6% is used for agricultural purposes, while 32.9% is forested...
was identified as possible location and the Swiss Federal Office of Energy (SFOE) approved this choice on . Two years later, on , a first partial construction permit was issued, followed on by the final one.
The reactor entered criticality in March 1971 but due to a fire in a turbine housing the plant had to be shut down for repairs. It eventually started commercial operation on .
KKM is at the moment the only Swiss nuclear power plant that does not have an unlimited operating license. Due to the problems noticed during the commissioning and to some ongoing tests on the emergency cooling systems performed in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, until 1980 it received a series of six month license extensions, then increased to one year. They were followed by a 5 year, a 7 year, and a 10 year license extension. These extensions were justified by technical improvements the operator was instructed to perform. The operating license was extended again in 1998 and was due to expire on , however, an unlimited license was granted on December 21, 2009.
The plant had requested a limitation removal in 1990 and again in 1996, but they were both rejected by the Swiss Federal Council
Swiss Federal Council
The Federal Council is the seven-member executive council which constitutes the federal government of Switzerland and serves as the Swiss collective head of state....
for political and technical reasons. A third request pending since 2005 at the SFOE was accepted on December 21, 2009.
Acceptance of the power plant by the local population has varied. When KKM was built there was little opposition to nuclear energy, but the situation rapidly changed after the Chernobyl disaster
Chernobyl disaster
The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...
. In 1992 a public referendum in the canton of Berne rejected granting an unlimited operating license to the power plant, with 51% voting against. In 2003, 68% of the population rejected the initiative named Strom ohne Atom, that proposed that the plant should be shut down in 2005 to be replaced by non-nuclear power generation. A similar proposal at cantonal level had already been rejected in 2000 by 64% of voters. In 2006 the Bernese government put forward a medium-term energy strategy including the renunciation to nuclear power. Swiss parliament, however, noted this and withheld their approval, delegating any decision on an eventual shutdown to the federal authorities. The same organ in 2007 urged the Bernese government to work towards granting an unlimited operating license.
No decision has been made about a definitive shutdown date.
Mühleberg 2
The operators Axpo and BKW announced through their subsidiary company Resun AGResun AG
Resun AG is a company located in Aarau . Its purpose is to manage the construction of two new nuclear reactors...
on that they had submitted to federal authorities a framework permit application to build two new nuclear reactors, one of which would be located in Mühleberg. Although precise technical specifications were not defined, the reactor of choice should be of 3rd generation
Generation III reactor
A generation III reactor is a development of any of the generation II nuclear reactor designs incorporating evolutionary improvements in design developed during the lifetime of the generation II reactor designs...
light water type with a net electric power between 1200 and 1600 MW. Cooling should be ensured by an hybrid tower
Cooling tower
Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...
. Following the Fukushima Daiichi nuclear disaster
Fukushima Daiichi nuclear disaster
The is a series of equipment failures, nuclear meltdowns, and releases of radioactive materials at the Fukushima I Nuclear Power Plant, following the Tōhoku earthquake and tsunami on 11 March 2011. The plant comprises six separate boiling water reactors originally designed by General Electric ,...
the permit application was suspended indefinitely.
Reactor and generators
The KKM consists of a single boiling water reactorBoiling water reactor
The boiling water reactor is a type of light water nuclear reactor used for the generation of electrical power. It is the second most common type of electricity-generating nuclear reactor after the pressurized water reactor , also a type of light water nuclear reactor...
(BWR) of type 4 provided by General Electric Technical Services Company (GETSCO), a then subsidiary of General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
specialized in nuclear power plants. All the 240 assemblies contain uranium oxide rods. The pressurized vessel has a diameter of 4.04 m and is 19 m high, has a wall thickness of 10.2 cm and operates at 288 °C and 72 bar.
The thermal power of 1097 MW is converted into 355 MW of net electrical power by two Brown Boveri steam turbine generators connected to the 220 kV and 50 kV grids. The power output was increased in 1990 from the original 320 MW.
The system is cooled with water pumped from the Aar. This in average increases the river temperature by 1.3 °C. To prevent damage to the fish population, the power plant's activity must be reduced when the river temperature exceeds 18 °C.
| Unit | Type | Net electrical capacity | Gross electrical capacity | Construction start | Critical state | Connected to electricity grid | Commercial operation | Shutdown |
|---|---|---|---|---|---|---|---|---|
| Mühleberg | BWR Boiling water reactor The boiling water reactor is a type of light water nuclear reactor used for the generation of electrical power. It is the second most common type of electricity-generating nuclear reactor after the pressurized water reactor , also a type of light water nuclear reactor... |
355 MW | 372 MW | Mar. 1967 | Mar. 1971 | Jul. 1971 | Nov. 1972 | - |
Safety measures
As all Swiss nuclear power plants, the KKM is subjected to a periodic complete safety assessment. The most recent one took place in 2007.The reactor is hosted in a five floor concrete-steel building. The walls have a thickness of 60 cm. In its lowest, partially underground part is located the 1.7-1.8 m thick steel and concrete pressure suppression drywell. The structure is able to withstand an earthquake. In case of a plane crash, however, the building could be damaged. The reactor would nevertheless remain intact due to the five 30–50 cm thick insoles and the massive drywell.
The reactor is fed with water through two loops, each provided with its own pump. A third pump serves as reserve.
The emergency cooling of the nucleus is entrusted to three independent systems. A doubly redundant low pressure core spray with a 2·100% heat removal capacity is activated in case of leaks any size in the coolant system. Small leaks may be compensated by the redundant high pressure reactor core isolation cooling system (RCIC) or the redundant alternate low pressure system (ALPS).
By loss of cooling agent in the drywell, the excessive steam will spread into a torus-shaped pressure-suppression pool, where it will condense decreasing the pressure. The 4000 m3 big torus is filled with 2000 m3 water and is in turn cooled by a redundant torus cooling system and a redundant shutdown and torus cooling system with a total of 4·100% residual heat removal capacity. In the extreme case of a meltdown a further system is entrusted with the integrity of the primary containment by spraying and flooding the drywell.
Emergency power is provided through two connections with the nearby Mühleberg Hydroelectric Power Plant and three diesel generators.
In 1989 the SUSAN (Selbstständiges, unabhängiges System zur Abfuhr der Nachzerfallswärme) emergency building started operation.
Bunkerized and partially underground, its function is to ensure an emergency shutdown of the reactor even in case of extreme external agents like plane crashes or simultaneous downfall of the dams upstream the plant with resulting submergence of the structures. Amongst others it contains the RCIC, the ALPS, the TCS, some systems for pressure reduction and two of the three emergency diesel generators.
Waste management
The KKM yearly produces around 35–38 m3 of radioactive waste. They are compressed in situ and transferred to the Central Interim Storage Facility (ZZL) for conditioning. After this procedure they are returned to the interim storage facility of the Mühleberg plant. KKM estimates its storage capabilities to last at least until 2022.Due to the 2006 moratorium on the recycling of spent fuel, the entire stock of exhausted rods is now transferred to the ZZL for storage.
Cracks in the pressure vessel
Major concerns on the security of the reactor arise from the formation since the 1990s of some cracks in the shell of the primary containment. This is due to steel corrosion by the coolant. Notwithstanding the countermeasures (reinforcements of the shell, chemical additives in the coolant), the cracks are increasing in length year after year. The longest one are one third of the limit allowed by the security specifications and it is expected that by 2012 they should still be less than half this value. The situation is continuously monitored and other chemical measures for its stabilization are being tested.In 1986, due to the presence of similar cracks, many components of the cooling water circulation loop had to be exchanged. A substitution of the pressure vessel is however not considered necessary by the Swiss Federal Nuclear Safety Inspectorate (ENSI) that confirms that the power plant is able to operate in security at least until 2012, when the license will expire. Further technical improvements are nevertheless needed for an extension until 2032, as desired by the operator.
Nuclear events
| Year | INES level | Total | |||||||
|---|---|---|---|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ||
| 2008 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| 2007 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| 2006 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 |
| 2005 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| 2004 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| 2003 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 4 |
| 2002 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 |
| 2001 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| 2000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 1999 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 |
| 1998 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| 1997 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 |
| 1996 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 |
| 1995 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| Total | 22 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 23 |
As of February 2009 no operative nuclear event (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....
level 2 or above) ever occurred. Since 1995 only one anomaly took place.
1998
- During a routine check of the reactor protection system in June 1998, a technician opened a steam relief valve in error. The steam that escaped condensed within the torus and heated the water it contained. After 14 minutes the raised temperature within the torus triggered an emergency shutdown of the reactor. The opening of the incorrect valve and the delay before the control room staff reacted appropriately led the event to be classified as INESInternational Nuclear Event ScaleThe 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....
level 1 (Swiss scale level B).
Significant events before 1995
- In September 1986 a faulty filter in the reconditioning unit for low and middle-active waste leaked a small quantity of radioactive aerosol. As result the surrounding area now shows an anthropogenic average dose rate of 0.0051 mSv/y (status 2007). For comparison the corresponding Swiss legal limit for population exposure is 0.3 mSv/y and the natural dose in the Mühleberg region achieves 1 mSv/y
- In July 1971, during systems tests prior to full commercial operation, some turbine oil ignited. The fire caused heavy damage to the turbine's housing, including cables connected to safety systems. Sufficient safety system connections remained to allow the reactor to be shut down. The nuclear part of the plant was not affected, but the power generation systems needed extensive repairs. The incident caused the start of commercial operation to be significantly delayed.
See also
- Nuclear power in SwitzerlandNuclear power in SwitzerlandSwitzerland has four nuclear power plants, with five reactors in operation as of 2008. These plants produced 26.3 TWh in 2007...
- BKW FMB Energie AGBKW FMB Energie AGThe BKW FMB Energie AG is a power production and distribution utility with headquarter in Berne, Switzerland. Through some subsidiaries or partner companies it also provides gas and heat...
- Resun AGResun AGResun AG is a company located in Aarau . Its purpose is to manage the construction of two new nuclear reactors...