nuclear power plant beznau - axpo switzerland · pdf fileaxpo – electricity for...

Nuclear Power Plant Beznau Reliable, environmentally compatible electricity production

Axpo – electricity for Switzerland

Nuclear Power Plant Beznau is part of the pool of power giants operated by Axpo, the Swiss energy utility with strong local roots and a presence in Europe. Axpo is 100 percent owned by the cantons of Northeastern Switzerland, and together with partners supplies elec-tricity to about 3 million people in Switzerland. Axpo is active along the entire value chain, from electricity gener-ation to transmission grids, trading, sales and services.

Axpo has an environmentally compatible pool of power plants with largely CO2-free electricity production. Nuclear power plants, river-based hydroelectric plants and biomass power plants cover the base load of the electricity supply. High-pressure pumped storage power plants with their reservoirs are used to compensate fluctuations and peaks in demand. This pool of power plants is perfectly aligned with the requirements of safe and cost-efficient electricity production.

Schaffhausen

Frauenfeld

St. GallenAppenzell

Vaduz

Basel

Delémont

Solothurn

Neuchâtel

Liestal Zurich

Zug

Lausanne

SionBellinzonaGeneva

Chur

GlarusLucerne

Sarnen Altdorf

Schwyz

StansBerne

Fribourg

AarauHerisau

• Axpo/Kantonswerke • CKW

Electricity for about 3 million people in Switzerland. Axpo/Cantonal power plants Centralschweizerische Kraftwerke (CKW)

View of Beznau Island with the nuclear power plant in the background.

Nuclear Power Plant Beznau

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Electricity production around the clock

Together with the run-of-river hydroelectric plants, Nuclear Power Plant Beznau is thus one of Switzerland’s most environmentally compatible power plants.

Vital base load capacityApart from a few weeks each year during which refueling, maintenance and annual inspections take place, the nu-clear power plant produces electricity around the clock. Nuclear power and river-based hydroelectric plants cover the base load of the electricity supply. When the system goes offline each summer for maintenance, the electricity demand can be met by the hydroelectric plants.

Over 500 people work at the nuclear power plants. The plants are monitored by a team of specialized operating staff working in a three-shift pattern. In the control room, the settings, values and changes relating to all compon-ents are indicated and displayed. The slightest deviations from the defined set points are announced immediately, both acoustically and visually, so that the correct pre-cautions can be taken.

Nuclear Power Plant Beznau comprises two largely iden-tical plants, Unit 1 and Unit 2, each with an output of 365 megawatts (MW). Both plants are designed for 8000 full-load hours or approximately 355 days a year. Together they generate approximately 6000 gigawatt-hours (GWh) a year. This corresponds to around twice the electricity consumption of the city of Zurich.

First nuclear power plant with environmental product declarationNuclear Power Plant Beznau is the first power plant in Switzerland for which an EPD®, Environmental Product Declaration, has been drawn up in accordance with ISO 14025. The key feature of the environmental product declaration is a life cycle assessment. It enables the quantification and estimation of emissions into the envi-ronment and also of the utilization of resources along the entire process chain of electricity production. As further environmental information, a survey was made of bio- diversity in the area around the nuclear power plant, radi-ation exposure of the staff and the electromagnetic fields.

Containment building of Nuclear Power Plant Beznau.


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Nuclear power plants are basically steam power plants. The heat necessary for evaporation of the water is not, however, the result of a combustion process but is obtained in a nuclear reactor. The steam is routed to a turbine that drives a generator. In the process, the rotor of the generator turns on the same shaft as the turbine, at 3000 revolutions per minute. At this high speed, its magnetic field generates an electrical voltage in the windings of the fixed stator. As a result, the kinetic energy is converted into electrical energy in exactly the same way as in a bicycle dynamo. The generator voltage is 15.5 kilovolts (kV). It is increased to 220 kV by a trans-former and thus rendered transportable. The electricity is ultimately delivered to the high-voltage grid via a switching station.

Electricity from kinetic energy

Transformers in operation.


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Machine hall with turbines and generator.

View inside the nuclear power plant

The two round containment buildings dominate the image of Nuclear Power Plant Beznau. The primary sys-tems, in which steam is generated from nuclear power, are situated in these double-walled buildings with a height of 67.5 m and a diameter of 38 m. They are sur-rounded by a gas-tight welded steel containment (3). It is 30 mm thick. The steel containment is completely enclosed by a concrete containment (1), which is 90 cm thick, with an intermediate space of 1.5 m. The concrete containment has on the inside a gas-tight steel liner (2), which is 6 mm thick. The air from the cavity is suckedinto the interior of the steel liner where a vacuum is created. This prevents air – and radioactivity – from acci-dentally escaping to the outside. Accommodated in the machine hall are the secondary systems and the turbine generator assemblies, which first convert the heat generated into mechanical energy and then into elec-trical energy. The heat for the Refuna district heating supply is also taken off here.

1 Concrete containment

2 Steel liner

3 Steel containment

4 Reactor pressure vessel

5 Control rod drive

6 Steam generator

7 Reactor main coolant pump

8 High-pressure turbine

9 Moisture separator reheate

10 Low-pressure turbines

11 Generator

12 Transformer

13 Condenser

14 Feedwater tank

127 °C

155 bar, 300 °C

55 bar, 270 °C

2 bar, 247 °C

0,04 bar, 30 °C

15,5 kV

120 °C

230 kV

Kreislaufschema


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127 °C

155 bar, 300 °C

55 bar, 270 °C

2 bar, 247 °C

0,04 bar, 30 °C

15,5 kV

120 °C

230 kV

Kreislaufschema

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Containment building

Spent-fuel storage pool

Fuelstore

Machine hall

Control room

1 Control rod drive

2 Reactor pressure vessel

3 Pressurizer

4 Control rods

5 Fuel assemblies

6 Reactor main coolant pump

7 Steam generator

8 High-pressure feedwater heater

9 Feedwater tank

10 Feedwater pump

11 Low-pressure feed heater

12 Condensate pump

13 Condenser

14 High-pressure turbine

15 Low-pressure turbines

16 Generator

17 Transformer

18 Moisture separator reheater

19 Refuna steam cogeneration

20 Refuna heat exchanger

View into the open reactor pressure vessel.

The energy cycle


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127°C

155 bar, 300°C

55 bar, 270°C

2 bar, 247°C

0.04 bar, 30°C

15.5 kV

120°C

230 kV

Kreislaufschema

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2

3

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Containment building

Concrete containmentSteel linerSteel containment shell Machine hall

Refuna district heating

Cooling water return

Cooling water extraction

Steam generation

The two units at Nuclear Power Plant Beznau are equipped with pressurized water reactors, i.e. they have two separ-ate water circulation systems. The pressurizer system ensures such a high pressure in the primary loop that the water in the core cannot boil, despite a temperature of 312°C. In the steam generators, the water in the primary loop releases the absorbed heat to the secondary loop. The steam produced by the low pressure drives turbines connected to steam generators. In the condenser, the steam is converted back into water – ready for another cycle of steam generation.

1 Flywheel

2 Pump motor

3 Pump impeller

4 Control rod drive

5 Pressure vessel lid

6 Control rod

7 Fuel assembly

8 Core support plate

9 Main steam outlet

10 Steam dryer

11 Manhole cover

12 Moisture separator

13 Main steam to turbines

14 Feedwater to steam generator

15 Feedwater inlet

16 U-tube bundle

17 Tube plate

18 Water chamber


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Steam generator

Pressurizer

Reactor pressure vessel

Reactor main coolant pump

Cooling by water from the River Aare

The steam must be cooled down in the condensers to convert it back into water after passing through the turbines. In full-load operation this means taking 40 m3

of cooling water per second from the River Aare. As the drop between the headrace channel and the lower course of the Aare is 6 m, the cooling water does not need to be conveyed through the condensers using pumps, as is usual in other nuclear power plants. In Beznau it runs naturally from the headrace channel of the hydroelectric power plant to the Aare riverbed further down. This was one of the reasons why the site on Beznau Island was chosen at the time.

Jan. Feb. March Apr. May June July Aug. Sept. Oct. Nov. Dec.

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18°

16°

14°

12°

10°

8°

6°

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2°

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Temperaturerhöhung durch KKBnach Durchmischung mit dem Aarewasser

MonatsmaximumMonatsminimum


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Temperature increase due to NPP Beznau after mixing with the water of the River Aare

Monthly maximumMonthly minimum

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1 Unit 1

2 Unit 2

3 Cooling water inlets in the headrace channel

4 Cooling water outlets in the natural riverbed of the Aare

5 Hydroelectric power plant

6 Weir power plant

7 Substation (connection to electricity transmission network)

Following pages: In the control room, electricity production is monitored

continuously.

Safety first and foremost


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• Theentireprimaryloopisencasedinsidethesteel containment made of 30 mm thick steel plates that are welded gas-tight.• Thevacuuminthespacebetweenthesteelcontain- ment and the concrete containment prevents radioactive gases from escaping.• Asteellinersealsofftheinsideoftheconcretecon- tainment.

Shielding of the radioactive radiationThe 3 m thick biological shield and the shielding concrete effectively prevent the escape of radioactive radiation. The concrete containment has a wall thickness of 90 cm.

Operational safetyMaximum attention is paid to operational safety – not just during normal operation but also in the event of any extraordinary events, such as unforeseeable defects in plant components. For this reason, the most important plant components, such as controllers and alarm re-leasers, are present in duplicate or in multiple form. If one fails, there is always a second or a third available that can perform the same function.

For Axpo, safety takes top priority. Nuclear Power Plant Beznau is protected against earthquakes, floods, and airplane crashes. Critical systems and sections of build-ings function independently, have multiple redundancies built in and are spatially separated. In addition, Nuclear Power Plant Beznau invests in safety technology and replacement on an ongoing basis.

Six barriersRadioactive products are created during nuclear fission. These highly radioactive materials may not escape into the environment. Several barriers ensure that this cannot happen:• Thefissionproductsarevirtuallyunabletoleavethe microstructure of the hard sintered fuel pellets.• Thegas-tightweldedcladdingtubesofthefuelas- semblies prevent fission products from escaping into the cooling water.• Thefuelassembliesareenclosedinthereactorpres- sure vessel and water circulates around them. This remains in the enclosed primary loop.

Double-walled containment building67.5 m high, 38 m outer diameter

Steel containment (3 cm)

Shielding concrete

Concrete containment (90 cm)

Biological shield

Fuel assemblies

Reactor pressure vessel

Cladding tube

Fuel pellets

Intermediate space with vacuum

Steel liner (0.6 cm)

Uranium as a fuel

How long will uranium reserves last?Uranium is the raw material that fuels today’s nuclear power plants. It is a metal found nearly everywhere in terrestrial volcanic rocks and in substantial quantities in the oceans. The globally known uranium reserves, which can be mined economically for a price of 130 US dollars per kilo, are sufficient for the next 100 years at current usage levels. Actual uranium reserves are sub-stantially higher. A rise in market prices would make it worthwhile to develop new deposits or use new means of extraction. The available alternatives include extracting uranium from phosphates or seawater, two approaches that have already been proved. Under these conditions, reserves should last for many centuries or even millennia. Recycling of nuclear fuel by means of reprocessing and increasingly enhanced utilization of the fuel in reactor operation are reducing the consumption of fresh uranium and thus significantly extending the ranges referred to. Even a rise in price could be absorbed since uranium costs amount to only 5 to 10 percent of the cost of gener-ating electricity in a nuclear power plant.

Higher energy contentOne metric tonne of ore yields on average approximately 1 to 5 kilos of natural uranium. The uranium’s high energy content – one metric tonne of uranium can generate the same amount of energy as 10,000 metric tonnes of crude oil – even makes it profitable to develop deposits with a relatively low uranium content. Natural uranium consists mainly of a mixture of two atoms that differ merely in their physical properties. Only uranium 235, which is present in natural uranium in a concentration of 0.7 percent, is fissile in light water reactors. The remain-der consists of nonfissile uranium 238. To be able to oper- ate nuclear reactors, the proportion of fissile uranium 235 must be increased from 0.7 percent to 3 to 5 percent, i.e. it must be enriched.

Once extracted, the ore is crushed. The uranium is leached from the ore using acid and subsequently pro-cessed into uranium concentrate (U3O8). This is also referred to as “yellow cake” because of its yellowish color. The next processing step is conversion of the uranium concentrate into gaseous uranium hexafluoride (UF6).


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Two fuel pellets of uranium dioxide (UO2) will supply electricity for a four-person household for one year.

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From enrichment to fuel assemblyGas centrifuges are used primarily for the next refining step – enrichment. After enrichment, the uranium hexa-fluoride is converted into powdered uranium dioxide (UO2), pressed into pellets and sintered at 1700°C, i.e. transformed into ceramic material. To manufacture fuel rods, the pellets are loaded into zirconium tubes. The fuel rods are welded gas-tight, grouped into assemblies of different sizes depending on the type of power plant and, after a rigorous outgoing inspection by a plant rep-resentative, delivered to the power plant. There they can be used to produce energy without further processing.

Careful waste handling

At Nuclear Power Plant Beznau waste is produced with varying levels of radioactivity. 99 percent of the radioactivity remains in the irradiated fuel assemblies which are stored in the water-cooled spent-fuel storage pool for at least six months. They are then removed to storage con-tainers and taken to the interim storage facility of Nuclear Power Plant Beznau (Zwibez). Here low-level waste is

stored before being carted away to a geological reposi-tory. Solid radioactive nuclear waste is transported to the central interim storage facility in Würenlingen (Zwilag) where it is incinerated or melted down. This process reduces the volume and improves final disposability through vitrification.

View onto the low-level waste in the NPP Beznau interim storage facility.Control panel of the NPP Beznau interim storage facility for low-level waste.


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Wastewater

From operation, laboratory, showers, laundry etc.

Ion-exchange resins

From chemical water purification

Combustible material

Preservatives, cleaning materials etc.

Fusible objects

Pumps, valves, pipes, insulating materials etc.

Spent-fuel assemblies

Cleaning with chemical precipitation, centri-fuging, microfiltration

Solidified with synthetic polymer, placed into canisters

Incineration in the incineration and melting plant in Zwilag

Melting down in the incineration and melting plant in Zwilag

At least six months’ stor-age in the water-filled spent-fuel storage pool

Residue (sludge) solidified with concrete, placed into canisters

Ash solidified with glass in molds, placed into canisters

Melt solidified in molds, placed into canisters

Transport to the Zwibez for interim storage

Each year the operation of NPP Beznau produces approximately one hundred 200-liter canisters of solidified low-level residues amounting to a volume of around 20 m3. They are carted away to geological repositories in NPP Beznau or put into interim storage in Zwilag.

Highly radioactive residues are vitrified and placed in special flasks – around 1.5 m3 per year from NPP Beznau

The Regionale Fernwärme Unteres Aaretal (Refuna) sup-plies 11 municipalities in the region and around 15,000 residents with heat from the Nuclear Power Plant Beznau. The connected load in 2010/11 was approximately 81 MW. This means that 12,000 tonnes of fuel oil can be saved annually. In winter 1983/84 the Paul Scherrer Institute (PSI) was connected to the environmentally compatible heating system. The first private customers followed a year later. Today, the length of the main network is 31 km and that of the local network 103 km.

Heat is extracted between the high- and low-pressure section of the turbine where steam with a temperature of 127°C is extracted and routed to a heat exchanger. There, the heat contained in the steam is transferred to the district heating network, whose water heats up in the process to 120°C. As each of the two power plants has such a heat extraction system, district heating is available at all times, including during the annual inspection. The power station’s electrical output decreases by up to 7.5 MW during heat extraction.

District heating for the region


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Refuna pipe bridge over the Aare Canal.

The main lines are 31 km long and the local lines are 103 km long.

Das Refuna Fernwärme-Leitungsnetz

Hot feed Standby heating plantsCooled-down return Booster pump stations

Klingnau

DöttingenKleindöttingen

Leuggern

Aare

Aare

Endingen

Würenlingen

Siggenthal station

ABB Turgi

Stilli

Riniken

Rüfenach

Villigen

Paul Scherrer Institute (PSI)

Nuclear Power Plant Beznau Main pumping station

Das Refunda Fernwärme-Leistungsnetz

Limm

at

Axporama

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Besuchen Sie uns und erleben Sie Energie mit allen Sinnen!

Axporama_Imagebroschuere_100715.indd 8 15.07.10 18:08

Visitor CenterAxpo | AxporamaSchlossweg 16 | CH-5315 BöttsteinT +41 56 250 00 31 | F +41 56 250 00 [email protected]/erleben

Axporama opening timesMonday to Friday 9 a.m. – 5 p.m.Saturday, Sunday, holidays 11 a.m. – 5 p.m.

Unrestricted viewing for individuals and families. Free entry. Guided tours for booked groups are also possible outside the opening hours. Please contact the center in good time.

Plant tour of Nuclear Power Plant BeznauVisitor groups may tour NPP Beznau with an experienced guide. Please contact the Axporama visitor center if you are interested. Your application should be made at least two weeks prior to the desired date.

Axporama Visitor Center


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Axporama

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Besuchen Sie uns und erleben Sie Energie mit allen Sinnen!

Axporama_Imagebroschuere_100715.indd 8 15.07.10 18:08

The Axporama visitor center is situated close to NPP Beznau. The exhibition offers an ex-citing insight into the world of energy and provides extensive information about the energy mix of Axpo.

Axpo | Nuclear Power Plant BeznauBeznau | CH-5312 DöttingenT +41 56 266 71 11 | F +41 56 266 77 01www.axpo.com

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nuclear power plant beznau - axpo switzerland · pdf fileaxpo – electricity for...

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