Page last updated at 13:39 GMT, Thursday, 10 January 2008

UK nuclear power: The contenders

A new generation of nuclear power stations in the UK has been given the formal go-ahead by the government.

UK nuclear power plant worker

Ministers have invited energy companies to submit plans to build new nuclear plants, which will replace the ageing fleet that currently provides about 18% of the UK's electricity.

In July 2007, the government announced that four designs had successfully met the criteria to continue on to the first stage of the assessment process:

"GENERATION III+" TECHNOLOGY

The UK's current fleet of Magnox and Advanced Gas Cooled Reactors (AGRs) are Generation I and Generation II designs, the vast majority of which are fast approaching the end of their 40-year operating lives.

The new power plants that could replace them are Generation III+ reactors - a term used to describe the latest designs.

Generation IV reactors are not likely to be commercially available for at least another 20 years, but manufacturers are developing a number of designs.

The characteristics of Generation III+ designs include:

    Modular construction - components are built elsewhere and shipped to the reactor site Evolutionary design - years of experience operating reactors has allowed engineers to simplify designs and cut construction and generation costs, while improving safety measures Passive safety features - in the event of a "severe accident", safety systems use natural forces such as gravity, circulation and evaporation, rather than "active" systems such as pumps, motors and valves Waste - industry experts say the new more efficient reactors, over their design lives, will generate only 10% of the waste the UK's entire nuclear sector has produced to date Cost - manufacturers say the final figure depends on a number of factors, such as location, number of reactors, and the planning and licensing process, but each plant is estimated to cost between £400-970m

AREVA EPR
Diagram of Areva EPR nuclear power plant
1. Reactor core
2. Control rod drive mechanism
3. Pressuriser
4. Steam generator
5. Generator turbine
6. Cooling water
7. Containment shell

Reactor type: Pressurised Water Reactor (PWR)
Generation capacity: 1,600 MW
Design life: 60 years
Construction time: approximately 42 months
Manufacturer: Europe-based Areva/Framatome ANP
Currently licensed in UK? No

The EPR (European Pressurised Reactor) is the latest design from Areva, and the 1,600 MW reactor is described as "the highest unit power to date".

The manufacturers say the reactor offers significantly reduced power generation costs because it requires less fuel and is designed to be operational for 92% of its 60-year life.

Finland is currently building the first EPR reactor at Olkiluoto, which is expected to start producing electricity by 2011. France started work on the second reactor of this kind in 2007.

WESTINGHOUSE AP1000
Diagram of AP-1000 nuclear power plant
1. Reactor core
2. Steam generators
3. Pressuriser
4. Passive cooling water tank
5. Steel containment shell
6. Turbines

Reactor type: PWR
Generation capacity: 1,117 MW
Design life: 60 years
Construction time: 36 months
Manufacturer: US-based Westinghouse
Currently licensed in UK? No

Westinghouse says the AP1000's passive safety systems have simplified its design. Compared with reactors that produce the same amount of power, it uses 50% fewer valves, 35% fewer pumps, 70% less cabling and can be contained in a building almost half the size.

This has a knock-on effect regarding the time it takes to construct the reactor. Westinghouse says: "Construction forecasts, verified by independent reviewers, indicate that an AP1000 could be built in three years or less."

The AP1000 is currently the only generation III+ design to be licensed by the US Nuclear Regulatory Commission, and Westinghouse has been awarded a contract to build a number of the power plants in China.

CANDU ACR1000
Diagram of ACR-1000 nuclear power plant
1. Reactor core
2. Horizontal fuel channels
3. Steam generators
4. Heat transfer pumps
5. Emergency injection system
6. Steel containment wall
7. Turbine generators

Reactor type: Pressurised Heavy Water Reactor (PHWR)
Generation capacity: 1,200 MW
Design life: 60 years
Construction time: 42 months "from first concrete to fuel loading"
Manufacturer: Canada-based Atomic Energy of Canada Ltd
Currently licensed in UK? No

The Candu ACR1000 is a light-water-cooled, heavy-water-moderated tube reactor and is the latest design in a line of reactors that stretches back to the 1940s.

Its horizontal fuel channels allow the reactor to be refuelled with slightly enriched uranium while it is still generating heat to power the steam generators, reducing the amount of time the plant is "offline" and not supplying electricity to the grid.

The first ACR1000 is expected to be built in Canada, and producing electricity by 2014.

GE ESBWR
Diagram of GE ESBWR nuclear reactor
1. Reactor core
2. Passive cooling system
3. Gravity-driven cooling system
4. Suppression pool
5. Containment vessel
6. Control rods
7. Turbines

Reactor type: Boiling Water Reactor (BWR)
Generation capacity: 1,560 MW
Design life: 60 years
Construction time: 36 months "from first concrete to first core load"
Manufacturer: US-based General Electric/Hitachi
Currently licensed in UK? No

The GE ESBWR (Economic Simplified Boiling Water Reactor) has 25% fewer pumps, valves and motors than the preceding reactor design, according to General Electric.

GE says that the reactor building is able to withstand earthquakes, hurricanes and tornados. Although the possibility of a large aircraft colliding with the structure is not part of the formal design specification, the manufacturers say the outer shell is robust enough to withstand such an event.

The ESBWR is currently going through the US Design Certification process, and the manufacturers are hopeful that the design will be in commercial operation by about 2015.



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