A Nuclear Britain

20 September 2007 (Last Updated July 28th, 2020 13:39)

Move over climate change, Britain has nuclear power on the agenda. And as Mitch Beedie finds out, it has high hopes for the future of the nation with its growth blueprint.

A Nuclear Britain

Under the surface, the bubbles have already started to boil as Britain prepares to hand down its findings from public consultation on the future growth of its nuclear industry. Greenpeace and the World Wildlife Fund have stepped out of discussion after labelling the process a 'rubberstamping exercise designed to push through the prime minister's pre-ordained policy on nuclear energy'.

Nuclear power was originally introduced in the UK with a promise of electricity 'too cheap to meter' but at the time was criticised for actually being more to do with developing a weapons capability.

And now, the British Government is again being vocal in its support of nuclear's involvement in the UK's energy production for the future, despite showing support for renewables and other forms of energy.

Although Britain now has 19 nuclear reactors generating about one-fifth of its electricity, all but one are scheduled for retirement by 2023. The present balance is actually 22% from nuclear (including 4% imported from France), 37% from gas and 34% from coal.

Securing the supply

The issue lies in the figures – closing nuclear plants will reduce the nuclear percentage to below 7% and will seriously hinder the government's plans to reduce CO2 emissions. On top of this, the UK's relentlessly upwards energy consumption means that the nation certainly needs to increase supply. Consumption is about 6MWh per person and rising. To keep up, some 25GW to 30GW of new capacity is planned over the next two decades.

The government has clearly spelt out nuclear power's advantages. Nuclear does not produce carbon dioxide, so it makes a minimal contribution to the greenhouse effect. It produces large amounts of electricity reliably from small amounts of fuel, and at around the same cost as coal.

The government believes that nuclear economics remain robust for generating costs up to £43/MWh for a central gas price of 37p/therm and a carbon price of €36/t CO2. And, although uranium is not itself a renewable resource, breeder reactors can produce more than they consume.

"Britain currently has 19 nuclear reactors generating about one-fifth of its electricity."

There are, however, disadvantages that the UK government has not spelled out. Irrespective of the merits, it seems again to be showing how not to make major policy decisions. It only released full details of costs after the public campaign to consult the UK population, and the decision seems to have already been quietly taken. That is before even knowing the full costs, including how to clean up the legacy of the last two nuclear generations.

First generation Magnox reactors

In 1953, the government approved construction of the first reactors at Calder Hall, commissioned by the UKAEA (United Kingdom Atomic Energy Authority). Calder Hall was the world's first commercial nuclear power station, although its major purpose initially was to produce weapons-grade plutonium.

The first eight Magnox (magnesium non-oxidising) reactors used a magnesium alloy to clad the fuel rods. The fuel itself was natural (unenriched) uranium, with a graphite moderator and carbon dioxide cooling. Later Magnox units were progressively scaled up.

Thermal efficiencies were initially very low, starting from 22% and increasing to 28%. Originally licensed for 30 years, the life was extended up to 50 years for some. Economic reasons will, however, see all closed by 2011.

Second generation AGRs

Advanced gas-cooled reactors (AGR) were in 1964 adopted as the UK's second generation reactors, based on a prototype at Windscale, Cumbria.

"Nuclear does not produce carbon dioxide, so it makes a minimal contribution to the greenhouse effect."

14 AGRs were built at seven sites from 1976 and 1989. Like the first generation, they are graphite moderated and CO2 cooled but these use enriched oxide fuel. Thermal efficiencies were much higher – around 40% – because coolant temperatures were well over 600°C (double that of most reactors).

There was little standardisation, however, and there were significant operating problems. In 2006, for example, British Energy temporarily closed four AGRs because of boiler degradation in the non-nuclear part of the plants.

Two fast neutron (breeder) reactors were built at Dounreay, including a 254MW prototype reactor. A large Westinghouse pressurised water reactor (PWR) – more complex than most PWRs – was brought on line in 1995. This was meant to be the first of four reactors, but in 1995 public sector support for new nuclear plants was withdrawn.

Change in direction

Until the 1980s, the UK government aimed to increase the nuclear share. Privatisation and deregulation in 1989 kept nuclear generation in the public sector but in 1996 all nuclear stations apart from the Magnox ones were transferred to the private sector.

The construction of many gas-fired power plants during the 'dash for gas' running up to 2001 caused considerable energy overcapacity in the UK. Wholesale prices declined so far as to be below production costs for British Energy. Between 2003 and 2005, BE was extensively restructured and the government ended up with a 39% share, which it is looking to reduce to about 30%.

Sowing the seeds for new plants

A 2006 review of UK energy policy placed nuclear firmly back on the national agenda, recommending that new plants be financed and built by the private sector. The UK is adopting a two-stage licensing process similar to that of the USA. A generic design authorisation for the new third-generation reactors will be followed by site-specific licences.

"A 2006 review of UK energy policy placed nuclear firmly back on the national agenda."

Several companies are involved in the pre-licensing applications (generic design assessment – GDA): Westinghouse for its AP1000 reactor, Areva NP (with EdF, British Energy, E.On, Iberdrola, RWE npower and Suez) for its EPR, GE-Hitachi (with Iberdrola, RWE npower and BE) for its ESBWR and Atomic Energy of Canada Ltd for its ACR-1000. Each GDA will take three years.

British Energy controls many of the likely sites for new plants.

Modular and standardised designs have helped to simplify this new generation of nuclear equipment, shorten construction schedules, reduce operating costs and improve safety levels.

All but one are light water reactors (LWRs), which use ordinary (light) water as moderator and coolant. The Westinghouse and Areva designs are pressurised water reactors (PWRs), which pressurise the water to prevent it from boiling. The GE-Hitachi design is a boiling water reactor (BWR), which allows the water to boil. AECL uses a pressurised heavy water reactor (HWR), using heavy water as coolant and moderator.

Westinghouse AP1000 PWR

Westinghouse's AP1000 PWR produces almost 1,200MW and was developed from the AP600. It has two Delta−125 steam generators, each connected to the reactor pressure vessel by a single hot leg and two cold legs. Four pumps circulate the coolant. A pressuriser is connected to one of the cold leg pipes to maintain sub-cooling in the reactor coolant system (RCS).

The nuclear island footprint and core diameter are the same as for the AP600. It has a taller reactor vessel, larger steam generators, a larger pressuriser and slightly taller, canned reactor coolant pumps with higher reactor coolant flows. The AP1000 can operate with a full core loading of MOX fuel.

Areva 1,600MW EPR

Areva's 1,600MW EPR (European pressurised reactor) is also a PWR and is now being built at Olkiluoto 3 in Finland. It has a double-wall reactor containment building, an inner pre-stressed concrete housing internally covered with a metallic liner and an outer reinforced concrete shell, both 1.3m thick. This houses the reactor vessel, steam generators, pressuriser and reactor coolant pumps.

"Modular and standardised nuclear reactor designs have helped to simplify a new generation of nuclear equipment."

The EPR has a slightly higher thermal output than previous PWRs, with economiser sections for the steam generators and an advanced steam turbine design.

GE-Hitachi 1,550MW ESBWR

The 1550 MWe ESBWR (economic simplified boiling water reactor) from GE-Hitachi has a standardised, modular LWR design. It uses natural circulation, eliminating forced-circulation recirculation pumps and associated motors, piping, valves, heat exchangers, controls and electrical support systems.

The larger in-vessel water inventory and large-capacity pools for make-up inventory means that the water level always covers the core. A 110% steam bypass, with the ability to work in island mode, increases the plant's operating flexibility. It also speeds return to service and improves the forced outage rate after a turbine trip, load rejection, or grid failure.

For a complete grid collapse the ESBWR isolates from the grid, reduces core thermal power and cuts turbine output to supply only house loads.

CANDU ACR-1000

The advanced CANDU reactor ACR-1000 from Atomic Energy of Canada Ltd is an evolutionary, 1,200MW pressure tube reactor. The ACR-1000 retains many features of the CANDU plant design, such as a modular, horizontal fuel channel core, a low-temperature heavy-water moderator, water-filled vault, two independent diverse shutdown systems, on-power fuelling and a reactor building accessible for on-power maintenance.

ACR-1000 enhancements include a compact core design with higher output, light water coolant (reducing heavy water inventory by two-thirds), fuel bundles that use low-enriched uranium (LEU) fuel to achieve higher burn-up and negative void reactivity.

No help required

Reactors are only one part of the total fuel cycle, however. Apart from the uranium itself, which is imported, the UK has from the start been self-sufficient in conversion, enrichment, fuel fabrication and – in theory at least – reprocessing and waste treatment.

"Construction costs are not the only commitments made for nuclear plants."

There is a 6,000tpa conversion plant at Springfields. Enrichment is performed by Urenco (Capenhurst), which is part owned by the British government, although it plans to sell its 33% share.

Fuel fabrication of Magnox, AGR and PWR fuel is done at Springfields, and other PWR fuel is bought on the open market. MOX fuel is also made for export at Sellafield.

British Nuclear Group (BNG) also reprocesses at Sellafield. The magnesium alloy cladding of Magnox is chemically very reactive so fuel cannot be stored indefinitely and must be reprocessed. The 850tpa THORP plant at Sellafield takes oxide fuel, predominantly for international customers. Only about half of the proposed 2,160t of AGR fuel has been reprocessed, though. In 2005, a pipe failure spilled 83,000l inside a hot cell and stopped processing, with BNG being fined £500,000.

Until 1982, some low and intermediate-level wastes were disposed of in deep ocean sites but this was stopped in 1993 following an international ban. Sellafield used to discharge large amounts of radioactive effluents into the sea, but a £750m investment by British Nuclear Fuels Ltd (BNFL) in new treatment plants in the 1980s reduced this to about 1% of previous levels.

In its technical overview of the UK nuclear industry, the World Nuclear Association estimates that around 100t of reactor-grade plutonium and 60,000t of reprocessed and depleted uranium waste will have built up by 2012. In the UK, plutonium waste is separated and stored indefinitely, since recycling has not been seen as economic.

There are three types of uranium waste: 25,000t of UF6 depleted uranium tails from enrichment, 30,000t of Magnox depleted uranium from reprocessing and 5,000t of normal reprocessed uranium from oxide fuels. The wastes will either be buried in geological formations, stored long term, or (if it ever becomes economic) used as fuel.

"The UK's relentlessly upwards energy consumption means that the nation certainly needs to increase supply."

Solid low-level wastes are now disposed of in a 120ha repository at Drigg in Cumbria, near Sellafield.

Some high-level wastes have been vitrified there and will be stored for 50 years in stainless steel canisters in silos, to allow cooling before disposal.

In 2006, the Committee on Radioactive Waste Management (CoRWM) recommended early closure of the repository and abandoning reprocessing of used fuel.

They suggested deep (200m to 1,000m deep) geological disposal of high and intermediate-level wastes, with 'robust interim storage'. It did however also point to social and ethical concerns with burial, which largely remain unaddressed.

The government hopes to agree future repositories with relevant communities, however, with incentives to volunteer. Even once found, commissioning repositories could take decades.

Nuclear planning flawed

In February 2007 a High Court judgement found that the government's public review had been flawed, with key economic details only being announced once the review was over. A new consultation has been promised, and the final decision has been delayed until the end of 2007. Not all information has yet been made public, though, and the AGRs may again be life-extended which could reduce the UK's overall energy gap.

Construction costs are not the only commitments made for nuclear plants. The UK's legacy of high and intermediate-level nuclear waste is estimated at 475,000m³. These include a complex mix of civil and military waste that is difficult to condition for permanent disposal.

"The UK is adopting a two-stage nuclear licensing process similar to that of the USA."

The government at the end of 2001 announced it would take over most public sector civil nuclear liabilities, which are now estimated at over £70bn.

On top of this are the other historical costs – billions have been pumped into nuclear that, had they instead funded energy efficiency measures and renewable resources, could have eliminated any 'energy crisis' that we now face.

Successive UK governments have spent years pretending that the UK's carbon emissions are structurally reducing, when it was only actually burning more natural gas. Now that this cannot be ignored any more, the way forward seems to be 'more of the same'.