"We say 'No' to nuclear... to construction of plants which would be outdated by the time they are built... the plants which are not secure and create waste problems," said Marcello Saponaro, the head of Greens in the northern region of Lombardy.

Italy should join international research into the fourth generation of nuclear power generation which is considered much safer than existing plants but would take decades to become operational, Saponaro told Reuters.

Economic Development Minister Claudio Scajola said earlier this month Italy should start building nuclear plants in five years to ease dependence on energy imports. Italy relies on oil and gas imports to cover more than 80 percent of energy needs.

Fulvio Conti, chief executive of Italy's biggest utility Enel, which owned all Italian nuclear stations before the ban, has said the return to nuclear would cut by 20-30 percent Italians' power bills, among the highest in Europe.

But Italian environmentalists disagree saying such estimates do not take into account huge costs of nuclear waste management.

Italy's Greenpeace, WWF and environmentalists group Legambiente said boosting renewable energy generation and energy efficiency were much more immediate, simple and less expensive ways "to stop energy fever" than a nuclear energy relaunch.

"It is not true that nuclear energy is cheap," they said in a joint statement.

"A nuclear kilowatt hour seems to have low cost only where the state takes care of nuclear waste and plant decommissioning. Such costs have discouraged private investors in the past decades," the statement said.

According to some industry estimates, renewables account for about 15-17 percent of Italy's energy mix and most of that comes from hydroelectric power. Wind and solar power make up a small fraction of the total, way behind Germany and Spain.

FIERCE OPPOSITION

Even supporters of Italy's return to nuclear power say it would be extremely difficult to swing public opinion in favour of the atom and find sites for new plants and waste storage.

"It is impossible to find sites in Italy where every square centimetre is populated," Saponaro said.

Giovanni Pavesi, mayor of the small town of Viadana in Lombardy which in early 1980s resisted the government attempts to build a nuclear power station there, said his town was ready to protest if it was picked up as a suitable site again.

Under Italian law, local authorities have a final say in approval of any big industrial project and have blocked construction of a high-speed railway in the north of the country and of a regasification terminal in the south.

Nuclear renaissance backers have recently voiced suggestions to review the Italian consitution to give Rome the power to decide on major industrial projects. But environmentalists said any such move would run into a fierce opposition.

"If they try (to pass such a decision) they would immediately find people -- workers, farmers, entrepreneurs and housewives marching on to Rome," Saponaro said.

"Italy is a democratic state, not a dictatorship. No one can impose a decision on people... no one can go above your head and build a nuclear station," he said.