Amid signs of a revival in orders for nuclear power reactors, the sale of Westinghouse's former nuclear division to Toshiba last month might stand out as a landmark but not necessarily because the industry seems ready to take off.

In fact, nuclear experts around the world, both skeptics and supporters of the technology, are surprised by the high price. Toshiba agreed to pay $5.4 billion for a collection of nuclear power manufacturing facilities, of which Westinghouse was the centerpiece, that had been assembled by British Nuclear Fuels. The sale closed at three times the price markets expected just six months ago.

There is much talk of a rebirth of the nuclear construction industry, but analysts say that most of it is just that. In the United States, the secretary of energy recently referred to 16 new reactors on the drawing boards, but not one has been ordered, and industry experts do not expect to see any orders until late 2007 at the earliest. "I think we all were surprised by the price," said Michael Morris, president and chief executive of American Electric Power, the largest power generator in the United States. With his company serving five million customers in 11 states, Morris favors more nuclear power.

Peter Bradford, a former member of the U.S. Nuclear Regulatory Commission, and later head of the state public service commissions of both New York and Maine, said: "It's hard to imagine people putting a $5 billion bet on new reactors as matters stand now, with uncertainty around climate change policy and impossibility of getting financing for them in private markets."

China has announced its intention of quadrupling its nuclear output in the next 20 years, which suggests about 30 more reactors, but only two are under construction. China has also stated that it wants to develop its own reactor. In Europe, politicians in Italy, Britain and Poland have been examining the merits of new nuclear plants. But the only nuclear plant being built in Europe outside the former Soviet bloc is a Finnish reactor that was the focus of 12 years of debate before construction began last year. Much of the optimism on nuclear construction is based on the expectation that two recent trends will continue.

The first is the rising cost of competing fuels, as well as increasing government controls on carbon emissions. The second is the inability of methods for reducing such emissions from other energy sources, like coal, to become widespread. Nuclear power plants are more expensive to build than natural gas or coal plants, and take several years longer to construct. But once they are built, they generate energy steadily and cheaply and emit negligible amounts of greenhouse gases. "Climate change gets people to think nuclear is going to pay off, in five years or 20," said Richard Sedano, a former member of the Vermont Public Service Commission and now director of the Regulatory Assistance Project, which advises regulators on electric policy.

In European countries where rules about carbon emissions are already firmly established, some critics of nuclear power have started to question whether building new reactors is a cost-effective way of reducing these emissions. More nuclear power generation "doesn't make sense economically and environmentally," said Norman Baker, deputy environment minister for Britain's Liberal Democrat Party. Spending a pound on improving energy efficiency cuts carbon emissions seven times as much as spending the same pound on new nuclear construction, Baker said. "If you're interested in climate change, you should demand clean coal and renewable resources." European energy markets have changed significantly since the 1970s, the last time large numbers of nuclear plants were built.

Many power companies have been privatized, and the energy market has been opened up to competition in many countries. Any new construction would need to be financed by a private company, which in turn would need to guarantee to investors that the reactor would eventually make a profit. It is not a sure bet, energy analysts say. It is "too early to speak about a nuclear renaissance," according to a recent report on the European market by Standard & Poor's, the rating agency. Peter Kernan, an S&P analyst who helped write the report, said, "The market environment is now significantly riskier than it was when the original nuclear plants were built." Predicting sale prices for energy is nearly impossible.

"Operators would need to be convinced there is a sound and robust business case" for building a plant before they start devoting capital to it, Kernan said. He said there is no evidence yet to suggest that. Marc Herlach, a lawyer at Sutherland, Asbill & Brennan who represented British Nuclear Fuels in the Toshiba deal and who specializes in energy asset sales, defended the price, saying it made sense because of the rising cost of other fuels and concerns over greenhouse gases. "This is a different environment," he said.

In the United States, the Nuclear Regulatory Commission recently approved the design of a new Westinghouse reactor, the AP-1000. The letters stand for "advanced passive," because the reactor would have fewer moving parts in its safety systems. No one has bought it yet. Toshiba licenses technology from General Electric, which sells reactors that boil water in the reactor vessel and then run the water through a turbine to convert energy to mechanical energy, and then to electricity. In contrast, the Westinghouse design heats water in the reactor but under high pressure, so it does not boil; that water is then run through a heat exchanger to make steam that goes through the turbine.

With the sale, Toshiba becomes the only vendor to sell both boiling-water and pressurized-water designs. But in the short term, the least glamorous parts of Westinghouse's business may prove the most valuable for Toshiba: the company's extensive repair and maintenance services.