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WHEN President George Bush outlined a new energy policy in his State of the Union address this year, he emphasised the need to develop hydrogen power 鈥� a keystone of the environmentalists鈥� dream of a future powered by renewable energy.

But the resulting bill looked quite different. The bulk of the money, some $15 billion, was earmarked to pay not for that green vision but to subsidise a new generation of nuclear power plants. The provisions go far beyond anything given to other energy sources (see 鈥淲hat鈥檚 expected to be in the energy bill鈥�), and are so extreme even some long-time advocates of nuclear power oppose them.

After a long debate, the US Senate scrapped the bill at the eleventh hour last week. But it is expected to be revived by Congress in September. The final version will be written by a House and Senate conference committee, whose chairman has vowed to reinsert the nuclear provisions, which include loan guarantees of up to 50 per cent for the construction of new nuclear plants, and guaranteed purchase of power from those plants at a premium price. They also extend the law that exempts US nuclear plants from liability for accidents above a fixed amount, which by some estimates could leave the taxpayer liable for up to $500 billion, in the case of a serious accident.

Estimating the cost of the subsidies is difficult, because it depends on the number and type of new plants built and on their performance, but a recent analysis by the Congressional Budget Office puts it at up to $14 or $16 billion. That would provide for six or seven large new plants, with a total output of up to 8400 megawatts 鈥� enough to meet around 1 per cent of the country鈥檚 electricity needs. That is a drop in the bucket compared with the 103 existing nuclear plants in the US, which provide some 20 per cent of the nation鈥檚 electricity. But it is seen as a first step towards building the thousands of plants necessary to significantly reduce the world鈥檚 greenhouse gas emissions.

The final bill is also expected to earmark $1.1 billion for a demonstration nuclear plant, to be built in Idaho, that would make hydrogen by using the energy generated to split water. This is significant because hydrogen-powered fuel cells, though at an early stage of development, are our only viable alternative to the petrol engine. So linking nuclear power to hydrogen production could eventually allow reactors to provide fuel for cars. As well as producing electricity, nuclear power could then replace oil, making this, in the long term, one of the most ambitious nuclear programmes ever.

But it will be a tough sell. Unlike conservation or renewable energy technology, nuclear power does not have many people clamouring for more. Memories of Chernobyl and Three Mile Island, and now the spectre of a terrorist attack on a nuclear plant, have ensured that the general public is as wary of nuclear power as ever.

Even some supporters of nuclear power feel the provisions go too far. 鈥淐ommercial power plants should be developed on a level playing field without government subsidising one industry over others,鈥� says John Sununu, a Republican senator from New Hampshire and long-time nuclear advocate. Yet the provisions鈥� supporters remain evangelical about the promise of nuclear power. 鈥淭he time has come to give a rebirth to this energy source,鈥� says Pete Domenici, a Republican senator and the bill鈥檚 sponsor. 鈥淎merica is back in the nuclear power business.鈥� Domenici will chair the committee that writes the final bill next month.

He and other advocates say nuclear power will help reduce the country鈥檚 dependence on foreign oil and give America the lead in energy technology. They also argue it solves the problems of greenhouse gas and airborne pollution caused by fossil fuels, and offers the best hope of averting global warming. Renewable sources don鈥檛 have a chance of meeting enough of our energy needs quickly enough, they say.

A new generation of nuclear plants 鈥渨ill have a vital role in displacing carbon dioxide, and a significant role in improving air quality鈥�, says Neil Todreas, a nuclear engineering expert at the Massachusetts Institute of Technology. His vision goes further than the provisions expected to be included in the final bill. To reduce global CO₂ emissions significantly, he and his colleagues have just calculated that 1000 to 1500 gigawatts of nuclear generating capacity 鈥� three to five times the current capacity worldwide 鈥� would need to be built by 2050.

Todreas concedes that such a future would require far more than the present known reserves of uranium, but he is confident that enough of the element will be found. He points out that whenever the price of any mineral resource doubles, its supply increases 10-fold as a result of more exploration.

Advocates also promise that future reactors will be safer and more economical to run than before. These include a variety of so-called 鈥渇ourth generation鈥� concepts that are on the drawing boards of nuclear engineers and at the handful of companies that have built plants in the past.

Reactors work by turning the heat generated by fissionable fuel into steam, which then drives a turbine. Most conventional reactors use water as a coolant, but the new designs have reactors cooled by gas, lead, molten salt, sodium or supercritical water. One of the key benefits envisioned for these plants is the possibility of using different forms of fuel, such as different isotopic mixes of uranium, or even thorium or other fuel. This could minimise the quantity and toxicity of the waste that needs to be disposed of and protected from terrorists.

It is these designs that seem to have inspired the Bush administration鈥檚 enthusiasm for nuclear power. But they could expose a new set of problems. Critics say, for example, that the high operating temperatures of most of these plants could make them vulnerable to unexpected materials failures. More fundamentally, the designs are mostly still on paper. Developing them to commercial viability would take about 20 years鈥� work, with no guarantee of success.

For now, the subsidies are likely to go to more modest designs. One contender is the 鈥減ebble-bed鈥� reactor, for which uranium is made into graphite-coated spheres rather than the rods used in conventional reactors. Fresh fuel pellets are added to the top of a cylindrical reactor, while used pellets are removed from the bottom, so the plant never has to shut down for refuelling.

The coolant in this system is the inert gas helium, so during normal operation there is nothing reactive or corrosive within the vessel; by contrast, water-cooled reactors risk hydrogen explosions and oxygen reactions should the water molecules split. Also, the pebble-bed system is designed with 鈥減assive鈥� safety features, so no human intervention is required in the event of an accident, at least initially. The fuel pebbles are designed so that even if the coolant is lost, heat dissipates out of the reactor faster than it is generated. This should, in theory, make it impossible for the nuclear reaction to lead to a Chernobyl-type explosion.

In economic terms, perhaps the biggest innovation is that the reactor would be assembled almost entirely from factory-built modules and transported to the site in standard containers rather than being built from scratch on site. This could cut the cost of construction and allow plants to be built in stages, rather than all at once.

Unlike the fourth-generation designs, pebble-bed reactors are not an untested idea. Some small test reactors have been built 鈥� one in China that produced 10 megawatts, and a 40-megawatt plant in Germany. South Africa decided this year to go ahead with construction of a full-scale pebble-bed reactor of about 1200 megawatts.

But it seems most likely that the US funding will go towards newer versions of existing, standard water-cooled reactor types, which incorporate the passive safety features and standardised designs. Such plants have been built in Japan and are under construction in South Korea. The designs have already been approved by the US Nuclear Regulatory Commission, and so perhaps offer the best chance of fulfilling Domenici鈥檚 aim of seeing new reactors up and running by 2010.

Not surprisingly, there is deep scepticism about this vision from environmental groups and other advocates of sustainable energy. Apart from the reactors鈥� safety, critics say any expansion of nuclear power raises questions about the disposal of spent fuel. Fuel from existing plants still faces an uncertain future, despite last year鈥檚 approval by Congress of a nuclear waste repository at Yucca Mountain in Nevada.

The consumer group Public Citizen has initiated a lawsuit against the repository plan, as has the state of Nevada. The site sits above an aquifer that provides drinking water for local farms and communities, which they say is a violation of Environmental Protection Agency guidelines. Public Citizen鈥檚 Lisa Gue says that even if the site gets full approval, it will not be able to hold all the spent fuel expected from existing plants by the time their licences expire, let alone from any new plants.

Critics also argue that any plan to increase reliance on nuclear power inevitably risks nuclear proliferation, by encouraging the development of technology that can just as easily be used to make nuclear weapons as nuclear power. The provisions expected to be added to the bill also go a step further, reversing a ban of nearly 30 years on reprocessing of spent fuel and the commercial use of plutonium, by directing $865 million into a reprocessing plant. Reprocessing separates unused fuel from radioactive waste, but in doing so creates pure plutonium, a key ingredient in nuclear weapons. President Jimmy Carter banned reprocessing in 1977, fearing the resulting plutonium could end up in the wrong hands. 鈥淭his is the same kind of thing we are criticising North Korea for,鈥� says Navin Nayak of the US Public Interest Research Group. 鈥淚t makes the plutonium much more accessible and more vulnerable to threats of terrorist activity.鈥�

Crisis of confidence

But despite the pleas of anti-nuclear campaigners, the ultimate success or failure of the plan may depend more on economic concerns. The reasons no new nuclear plant has been ordered in 30 years are purely financial. Nuclear-generated electricity still costs twice as much as electricity produced from coal and gas, even without including indirect costs such as waste disposal, and there is no guarantee new designs will make it any cheaper. Meanwhile confidence in the reliability of nuclear reactors is at an all-time low. Plants are being forced to shut down for months at a time, and sometimes for good, as cracks and corrosion in the ageing reactors affect critical parts (see 鈥淎re ageing US reactors safe?鈥�). Such unanticipated problems are the kind that can be expected in any new technology, and a new generation of plants would start that cycle again.

If the nuclear provisions originally in the Senate bill are enacted in September, even in a watered-down form, it will give nuclear power a huge boost. But it remains to be seen whether even that will be enough to revive the nuclear power industry. Andrew Kadak, another nuclear engineer at MIT, who formerly managed a nuclear power plant, points out that today鈥檚 oversupply of generating capacity in the US means there is little incentive to build new power plants of any kind.

However, the balance could tip towards nuclear power if economic growth increases the demand for power, or if prices rise as fossil fuels become more scarce. 鈥淚f the economy starts turning around, utilities will look into the nuclear option,鈥� says Kadak.