Beznau is the oldest operating nuclear power plant in Europe. Image courtesy of Axpo Holding AG.
The power plant has been operational since 1969. Image courtesy of Axpo Holding AG.
The Beznau NPP is owned and operated by Axpo. Image courtesy of Axpo Holding AG.
The Beznau NPP produces approximately 6,000GWh of electricity a year. Image courtesy of Axpo Holding AG.

The Beznau nuclear power plant (NPP) in Döttingen, Aargau, Switzerland, is Europe’s oldest operating NPP. It is also one of the three nuclear power facilities in the world that completed 50 years of commercial operations in 2019.

Owned and operated by Swiss public utility Axpo Holdings, the first 365MW pressurised water reactor (PWR) unit of the Beznau NPP entered commercial service in December 1969, while a second unit of similar capacity was commissioned in March 1972.

The world’s other two 50-year old nuclear power plants still in operations are the Tarapur NPP in India and the Nine Mile Point nuclear power station in the US that started commercial operations in October 1969 and December 1969, respectively.

Location and site details

The 750MW Beznau NPP is situated on an artificial island in the Aare River, approximately 3.5km away from Döttingen.

The two-reactor facility lies 40km to the north-west of Zurich, near the German border.

Beznau nuclear power plant details

Beznau is the oldest of the four operating nuclear power stations that accounted for more than one-third of Switzerland’s total electricity production in 2018.

The two Westinghouse reactor units of 1,130MWt thermal capacity each are capable of generating 6,000GWh of electricity a year, which is approximately double the amount of total electricity consumed by the Zurich city. The plant also supplies hot water to the Refuna district heating system in the lower Aare River valley.

The first unit of the plant resumed operations in March 2018 after a three-year shutdown, to carry out safety upgrades in the reactor pressure vessel.

Both the units of the Beznau nuclear energy generation site produced 5,541GWh of electricity in 2018.

Beznau nuclear power plant make-up

The Beznau nuclear power station consists of two Westinghouse-design two-loop PWR units in two separate containment buildings.

Each cylindrical, double-walled containment building is 66.5m-high and has 38m diameter. The outer containment wall is made of 90cm-think concrete with 0.6cm-thick steel liner, while the inner steel containment shell is 3cm-thick.

The reactor core of each unit comprises 121 fuel assemblies of U-235 fuel rods that are placed inside a 10.7m-high and 3.3m-diameter reactor pressure vessel with up to 17cm-thick steel wall.

Each containment building houses two main coolant pumps and two steam generators. The generated steam is routed to an adjacent turbine building that houses two 3,000rpm steam turbines and generators.

The electricity is generated at a voltage of 15.5kV, which is stepped-up to 220kV by a transformer for transmission into the grid.

Cooling system for the Beznau NPP

The nuclear power plant requires 40m³ of water per second from the Aare River in full-load operation and is designed to operate with open-circuit cooling system without requiring any cooling tower.

Cooling water pumps are also not required for the plant as it utilises the water flowing through the headrace channel of the Beznau hydroelectric plant.

Retrofits and upgrades at Beznau nuclear power plant

Axpo  spent approximately £1.9bn (42.5bn) on retrofits, upgrades, and maintenance of Beznau nuclear power facility as of 2018.

The steam generators of the units were replaced in 1993 and 1999, respectively.

The reactor protection and control system of both the units was modernised with Areva’s 4-channel TELEPERM XS system in 2001.

The turbine control and protection system was upgraded with ABB’s Advant digital system in 2004.

The reactor pressure vessel heads of both the units were replaced in 2015. An earthquake and flood-proof new emergency power supply system with four diesel engines, as well as an upgraded plant information system were also installed in the same year.


Siemens, in consortium with Sulzer, was engaged for the replacement of steam generators of the plant, while Framatome manufactured and fabricated the new steam generators.

VSL, an arm of French conglomerate Bouygues, was sub-contracted for the installation of steam generators.

Westinghouse was awarded a contract worth €130m ($172m) to build two new emergency power buildings with two diesel engines each, in 2010. The diesel engines were supplied by MTU Friedrichshafen, a subsidiary of Rolls-Royce Power Systems.

Westinghouse secured another contract worth €25.6m ($35m) to replace  the  reactor vessel (RV) heads in September 2011. It had also received a contract for the delivery of RV heads in 2009.

The company installed the new plant information system NEXIS (New EXtended Information System) in 2015, under a contract awarded in 2011.

L3 MAPPS was contracted to update the full scope simulator at the Beznau NPP for the new emergency power system as well as the new plant information system in May 2012.