Plugging the energy gap

Back on the Government's agenda with a vengeance is its energy policy. Speaking at a CBI (Confederation of British Industry) meeting at the end of November, Prime Minister Tony Blair, announcing a review of the Government's energy policy, said, 'Around the world you can sense a feverish rethinking. Energy prices have risen, energy supply is under threat, and climate change is producing a sense of urgency'. 'The future', he said, 'is clean energy and nations will look to diversify away from energy dependence on one source'.  

The publication of the review, which is expected in the summer, will recommend whether or not the Government facilitates the development of a new generation of nuclear power stations. By 2020 the UK is likely to have witnessed the decommissioning of coal and nuclear plants that together generate over 30 per cent of the country's current electricity supply. With the UK's own gas and oil reserves dwindling, the nation this year transferred from being self-sufficient in gas supply to being a gas importer. Without secure alternatives we could find ourselves at the mercy of volatile global markets. What choices do we have?  

Electricity generation 

Electricity is generated by turning a giant coil of wire in a magnetic field. To turn the coil requires a turbine, which is most commonly driven by hot, high pressure steam. The steam can be heated by: 

• burning fossil fuels, ie coal (as in coal-fired power stations):C + O₂  CO₂ 
  or methane, ie natural gas (as in gas-fired power stations): CH₄ + 2O₂  CO₂ + 2H₂O 
  The hot gases from these chemical reactions can also drive the turbines directly, or in the most efficient 'combined cycle' plants, both methods are used, with steam generated with the waste heat from the turbine. Around 40 per cent of the UK's electricity is derived from fossil fuels, but they do produce green house gases, in particular CO₂; 
• a nuclear reaction (as in nuclear power stations) - here the fuel is pellets of uranium dioxide sealed in hundreds of metal rods. When nuclei of uranium atoms (²³⁵U) are hit by neutrons and absorb one they split (fission) to form the more stable isotope (²³⁶U), releasing very large amounts of heat and more neutrons. Under controlled conditions, these neutrons can interact with more uranium atoms, splitting more nuclei and thus forming a chain reaction that releases very large amounts of heat. (One kilogram of natural uranium has a volume of ca 50 cm³ and produces 40 000 kW h, which is equivalent to the electricity produced by 16 tonnes of coal.) 

The nuclear option 

Unlike fossil fuels, the nuclear option emits no CO₂, which is why it is often referred to as a 'clean' energy provider. However, extracting the uranium, building plants and decommissioning them are all energy intensive, and CO₂ is inevitably a byproduct. And nuclear power has its own ghosts - notably the spent radioactive waste from the reactors coupled with many people's fear of a catastrophic explosion, nuclear terrorism and potential links to incidents of cancer.  

The used fuel rods represent 'high-level' waste, and contain uranium, plutonium and other highly radioactive isotopes made during fission, which have half-lives of the order of tens of thousands of years. This waste requires cooling in large water tanks - to dissipate the heat as well as protect workers from radiation - followed by encasement in concrete or glass and storage in inert, steel containers for at least 10 years. This can reduce the radioactivity levels by 100 times, when it is considered fit to handle and ship to a site for secure storage for thousands of years. Areas currently being evaluated for long-term storage of this waste are space, under the sea bed and in large stable geological formations on land such as underground repositories. In the UK there is ca 1200 m³ of high-level waste, which will rise to ca 3000 m³ in 2020, all of which is currently contained at Sellafield in Cumbria. 

Renewables 

As evidence gathers to link CO₂ emissions to global warming and climate change, and the nuclear power industry fights to convince the public that it is a proven, reliable and further advanced technology and its waste is in control, renewable energy sources are gaining support. Generally these fall into one of three categories: 

• wind, wave and hydroelectric power can be used to drive turbines. Hydropower - in which flowing water, from a dam for example, is used to spin the turbine - accounts for 0.1 per cent of UK electricity generation; 
• solar energy which exploits the photo-electric effect in a semiconductor diode to generate electricity; 
• biomass - eg fast burning crops such as willow. This emits CO₂, but only the CO₂ which was captured from the atmosphere by the plants. 

Apart from the energy used in their construction, these technologies do not add to CO₂ emissions in normal operation and leave no legacy of toxic waste. According to a report, written by John Loughhead (executive director, UK Energy Research Centre), renewables, if developed and supported by Government financial incentives, could supply up to 40 per cent of current energy demand by 2050. The report represents the views of 150 chemists, physicists, engineers and economists who met at the Geological Society in London in October to discuss the energy supply challenges facing the UK.  

Opponents of nuclear energy in the UK put forward renewable forms of energy as the answer to providing all the energy the country needs and reduce carbon emissions at the same time. But what growth there has been in renewables, mainly wind power, over the past few years, has not cut carbon emissions in the UK, it is merely replacing nuclear plants as they are decommissioned.  

Moreover, energy consumption in the UK, like other western industrial nations, is high and people expect to have power at the flick of a switch. The average daily use of electricity in the UK (industry and domestic) in the summer is 10 GW (GW is a gigawatt, a billion watts (10⁹ W)). This figure shoots up to 40 GW at peak times, the equivalent to having 400 million 100 W light bulbs switched on. In winter, the average daily use of electricity is 20 GW, going up to 50 GW at peak times. So an extra 15-20 GW generating capacity is required in the winter together with the ability to switch from 10 GW to 20 GW within an hour. This requirement is not currently possible with renewable energy sources. Wind, wave and sun power fluctuate and cannot provide energy necessarily when it is required and much is wasted. The challenge will be for chemists to work out a way of storing excess energy so that it can be released when needed.  

According to the Loughhead report, fossil fuels will remain the most important source of energy for the next 50 years, despite a growing role for renewables. Future energy demand, it states, must be met by a diverse range of clean energy sources; nuclear fission energy will inevitably play a key role in this mix. Clean systems, including carbon capture and storage, should be pursued urgently, the report concludes. 

But perhaps we should all use less electricity and save energy. This would save money, maybe the planet and could avoid the need to make some of these difficult choices altogether. 

Kathryn Roberts