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The Beznau Nuclear Power Plant (in German Kernkraftwerk Beznau, abbreviated KKB) is located in the municipality Döttingenmarker (Canton of Aargaumarker, Switzerlandmarker) on an artificial island in the Aarmarker river. It is operated by the Nordostschweizerische Kraftwerke AG (NOK).


Beznau 1 and 2

Beznau 1 is the first commercial nuclear power reactor in Switzerland.

Putting an end to the traditional predilection of the Swiss power utilities for hydroelectric power, in the beginning of the 1960s the NOK started to take into account the construction of a nuclear power plant. On the Swiss Federal Office of Energy (SFOE) recognized the artificial island in Beznau as potential location for a reactor. The corresponding construction permit was issued on and, after only four years, on commissioning was authorized. On Beznau 1 started commercial operation.

In the meantime the procedure for the construction of the identical reactor Beznau 2 had begun. The location and a first construction permit were approved on , followed on by the final one. The commissioning started on and the reactor finally entered the commercial operation phase on .

Beznau 1 obtained an unlimited operating license already on . On the contrary Beznau 2 received temporary licenses until , when the Swiss Federal Council removed the limitation.

The power plant was built in the 1960s, when little opposition to nuclear projects was present. Over the years Beznau has been the scene of some antinuclear manifestations, but such opposition never widespread among the majority of the local population. The cantonal citizens systematically rejected all votes on early shutdown of existing plants and on building suspension of new ones. Finally, in 2007 the cantonal parliament entrusted the government to act in order to promote the building of a new reactor.

As of 2008 no date for a definitive shutdown of the KKB has been set. This should nevertheless lie in the 2020s, when the two reactors will become 50-60 years old.

Beznau 3

In view of the substitution of the plant, the Resun AG submitted to the federal authorities on a framework permit application for a third reactor.. Although the technical specifications will be defined in a second time, the reactor of choice should be of 3rd generation light water type with a net electric power between 1200 and 1600 MW. The cooling should be ensured by an hybrid tower.

Technical specifications

Reactors and generators

The KKB is composed of two identical pressurized water reactors units (Beznau 1 and 2) delivered by Westinghouse Electric.

Both reactors are certified for the use of MOX fuel. As for October 2008 (37th operational cycle) Beznau 1 hosted 16 bars out of 121 contain MOX, while for Beznau 2 this ratio increased to 24 of 121 (35th cycle).

Characterized by a thermal power of 1130 MW, each unit produces 365 MW net electricity through two Brown Boveri steam generators. Over the years the net electric power produced has been increased twice: it was 350 MW until and 357 MW until . The energy is delivered to the 220 kV grid.

The plant is cooled using the water of the Aarmarker river and through the district heating system REFUNA, that provides eleven surrounding municipalities with 150 GW·h/y.

Unit Type Net electrical power Gross electrical power Construction start Critical state Connected to electricity grid Commercial operation Shutdown
Beznau 1 PWR 365 MW 380 MW Sep. 1965 Jun. 1969 Jul. 1969 Dec. 1969 -
Beznau 2 PWR 365 MW 380 MW Jan. 1968 Oct. 1971 Oct. 1971 Mar. 1972 -

Safety measures

Since the commissioning of the two reactors numerous upgrades have been carried out to improve safety. In the 1990s the steam generators and the control technology of the reactor protecting system have been replaced. The control rooms were consequently adapted and new turbine controls installed. Furthermore each reactor block has been equipped with an emergency building (NANO, NAchrüstung NOtstandsystem). These contain additional safety systems for the reactor emergency shutdown and for the feeding of the steam generators, a 50 kV emergency power line, and a diesel generator. They are heavily protected from external hazards and, if needed, are able to cool and shut down the power plant without human intervention.

The at least 1.5 m thick concrete-steel housings protect the critical systems from external agents like earthquakes or plane crashes. Each unit of the KKB has a large dry type containment in steel.

The core emergency cooling is performed by a redundant high-pressure safety injection system with a total of three strands (one in the NANO). The two steam generators are provided with water by two main feeding pumps. If they fail, feeding is taken over by one of the security systems: a double-stranded auxiliary feedwater system with 200% after-heat removal capacity or one of the two emergency feedwater systems, one if which is part of the NANO. Finally, in case of problems with the cooling, two containment spray systems are entrusted with the removal of excessive heat and pressure by condensation of the resulting steam.

The power plant is connected thorough five strands to the external power grid. Two of them are mainly used to deliver the power plant output to the 220 kV grid. They are nevertheless equipped with an emergency diesel generator each. Two other strands provide emergency power and are connected to the nearby hydroelectric power plant and the 50 kV grid. Further two diesel generators expressly equipped to be able to work in case of flood are also available. The NANO is connected through the fifth strand to the 50 kV grid and contains a fifth generator. The plant main UPS system can provide electricity for at least 2 h of normal operation.

Waste Management

The KKB possesses since 1993 a separate interim radioactive waste storage facility (ZWIBEZ). It is composed by an hall for low level operational waste and a second one for the dry storage of spent fuel. The waste needing conditioning is stored in the central interim storage facility (ZZL). These two deposits should ensure the storage of the plant's waste until at least 2020.

Nuclear events

Year INES level Total
0 1 2 3 4 5 6 7
2008 4 0 0 0 0 0 0 0 4
2007 7 1 0 0 0 0 0 0 8
2006 2 0 0 0 0 0 0 0 2
2005 2 0 0 0 0 0 0 0 2
2004 2 0 0 0 0 0 0 0 2
2003 4 0 0 0 0 0 0 0 4
2002 2 0 0 0 0 0 0 0 2
2001 5 0 0 0 0 0 0 0 5
2000 4 0 0 0 0 0 0 0 4
1999 5 0 0 0 0 0 0 0 5
1998 2 0 0 0 0 0 0 0 2
1997 6 1 0 0 0 0 0 0 7
1996 3 1 0 0 0 0 0 0 4
1995 3 0 0 0 0 0 0 0 3
Total 51 3 0 0 0 0 0 0 54

As of February 2009 no event with INES level 2 or above ever occurred. Since 1995 three anomalies took place, but none of them involved radioactive material release.

Level 1 events


  • In August, during the yearly revision of Beznau 2, the 50 kV emergency power line was deactivated. Consequently the diesel generator of Beznau 1 was switched on at low regime as prescribed by the security regulations. After the reconnection of the 50 kV line, the generator run at higher load because of technical reasons, but it eventually failed due to a defective relay. It was therefore to assume that while the 50 kV line was not active the generator would not have been able to run at full loading. Since also the unit 2 generator was not available due to the planned revision, the emergency power could be provided only by the hydroelectric plant or some reserve generators that are activated in case of flood. The decrease in redundancy comported a deviation from the normal operation parameters and was therefore classified as a level 1 event (swiss scale level B).


  • In the course of a periodic inspection carried out by the operating personnel, a manually operated valve, which should have been open, was found to be closed. As result of the false position, one of three emergency cooling systems of Beznau 1 was not ready for immediate use over a period of two weeks. This breach of the technical specifications led to the incident being assessed as level 1 (swiss scale level B).


  • After the revision outage, at 1 to 2% of reactor power, the new protection system for Beznau 1 and its internal power supply was to be started up with a test program. During synchronization with the new protection equipment, one of the two turbo groups inadvertently increased the load, and this caused a rise in reactor power to 12.6%. Since only the auxiliary feedwater pumps are in operation during low power, the amount of water supplied was insufficient to feed the steam generator, leading to an automatic reactor scram. The inadvertent demand on the turbo group was caused by an unforeseen reaction of the automatic turbine controller. Besides, the reactor already went critical at 251 °C instead of at the prescribed minimum temperature of 276 °C. The deviation from the operation specifications led to a level 1 assessment (swiss scale level B).

Significant events before 1995

  • In July 1992, during a revision of Beznau 1, two technicians working in the reactor sump died by suffocation. This was caused by an excessive atmospheric concentration of the argon used for welding. This tragic accident was not due to the nuclear nature of the plant and therefore didn't receive an INES assessment.


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