This is only the latest in a series of accidents, fires and leaks which have undermined public confidence in the safety of nuclear power.

According to the Japanese Science and Technology Agency, tests on two of those closest to the leak suggest they were subjected to radiation "equivalent to exposure to an atomic bomb".

The statement will provide an unpleasant echo for the Japanese public, which is still greatly influenced by the dropping of atomic bombs on Hiroshima and Nagasaki in World War Two.

The town of Tokaimura was also the site of Japan's previous worst nuclear accident, in 1997. At another facility close to the uranium processing plant, 35 workers were contaminated by radiation after a fire was not extinguished properly and caused an explosion.

In another serious accident in July, radiation levels 11,500 times the safety limit leaked out of a pipe in a plant in Tsuruga, 320 km (200 miles) west of Tokyo.

But like it or not, the nuclear industry is extremely important to delivering Japan's vast energy requirement.

Since the oil crisis of 1973, successive governments have made concerted efforts to become self-sufficient - and opted for nuclear energy to achieve this goal.

The country has few natural resources and relies on its 51 commercial nuclear power plants for about one-third of its electricity.

Growth plans

By the year 2010, Japan wants to raise that production level to 42% of its energy needs.

Pursing a goal of self-sufficiency, the Japanese nuclear industry originally wanted to use plutonium in fast-breeder reactors, which could generate more plutonium.

Japan is now the only nation still developing fast-breeder nuclear reactors since France decided in 1997 to close its Superphoenix reactor following a series of problems.

But the high costs, as well as an accident at the fast-breeder reactor Monju in 1995, forced the industry to seek an alternative in MOX fuel, a combination of uranium and plutonium recycled from spent nuclear fuel.

This task is done at recycling plants in France and the UK, and shipped back to Japan.

Just days ago, Tsuneo Futami, director of the Tokaimura plant, said: "Considering Japan's scarce resources, it is very important to have MOX fuel."