Japan nuclear fallout hits U.S. rescuers: 17 contaminated after second blast

Seventeen US helicopter crewmen helping in the Japanese rescue efforts were contaminated with radiation today as fears grew of a nuclear meltdown.

They were treated on the aircraft carrier Ronald Reagan as a second explosion rocked a crippled power plant and caused radioactive fallout. Smoke poured from Fukushima Daiichi's No 3 reactor, two days after a blast at its No 1 reactor, 150 miles north of Tokyo.

The death toll from Friday's earthquake and tsunami was expected to go well above a 10,000 estimate after 2,000 bodies were found washed up on beaches. More than 450,000 people have been evacuated from devastated towns and cities along the north-east coast, including 180,000 from an exclusion zone around the power plants.

Officials at Fukushima Daiichi said cooling water at its No 3 reactor had completely evaporated which exposed the white-hot fuel rods. This increases the risk of the rods melting the steel core and releasing radiation down into the earth.

Nuclear expert Malcolm Grimston said: "It is serious, the challenge is to get cooling water into the centre. It's clear there is quite a lot of damage to the fuel itself, and it's quite likely the fuel has started melting."

Dramatic footage captured today's blast which injured 11 workers and triggered the release of more than six months of radiation in a single hour.

The explosion, which was felt and triggered the release of more than six months of radiation in a single hour. The explosion, which was felt 25 miles away, exposed up to 160 people to high doses of radiation.

People evacuated from the area were being checked by men in white protective suits using Geiger counters. Twenty-two are receiving treatment for radiation poisoning.

As officials tried to play down health risks, America moved USS Ronald Reagan away from the stricken Fukushima plant after detecting radiation in smoke that drifted 100 miles offshore.

A total of 17 naval officers were contaminated as they flew through the radioactive steam cloud during disaster relief missions to the devastated city of Sendai.

The radioactivity was detected when the crew members returned to the carrier aboard three helicopters. They experienced almost a month's radiation in just one hour and destroyed their clothes when they returned to the ship. The helicopters were also decontaminated.

Paul Harris, a Briton who teaches in Sendai, told his sister that Japanese authorities warned the public to wear wet cloths on their faces if they leave their homes in a bid to avoid contamination.

Engineers at Fukushima Daiichi tried frantically to cool white-hot radioactive fuel rods with sea water but hydrogen in the released steam mixed with oxygen in the atmosphere to set off today's second explosion.

Radiation measured at Fukushima today rose over the legal limit of 500 micro sieverts per hour. Two readings of 650 and 751 micro sieverts per hour were recorded in two locations. People are usually exposed to 1,000 micro sieverts in an entire year.

Japan's chief cabinet secretary Yukio Edano said the reactor core encasing nuclear rods remained intact, easing fears of the risk to the environment and public.

Chief scientific advisor to the UK Government Sir John Beddington said: "There is a reasonable chance that the Japanese will be able to keep the water pumping through. The reasonable worst case scenario is a meltdown, where we would see an explosion taking material up to 500 metres into the air, it would last for hours rather than weeks and months, and we would then expect a big decline in radioactive fallout."

What has happened to the Fukushima Daiichi nuclear reactors?

There are three at Fukushima. This morning, a building above the No 3 reactor exploded. It follows a similar blast at the No 1 reactor on Saturday. The second has suffered cooling malfunctions, exposing fuel rods, and experts say another explosion is possible.

What about Japan's other reactors?

Two others have suffered problems. The International Atomic Energy Agency declared a state of emergency at the Onagawa site, 93 miles north of Fukushima, after a fire led to excessive radiation being recorded. Also, the cooling system pump has failed at the Tokai facility but the back-up is said to be working.

What caused the explosions?

In overheated reactors, extra hydrogen is produced in the water surrounding the reactor. This then combines with steam to cause an explosion. Experts say that although outside cladding has been damaged, all three reactor cores at Fukushima 1 and 3 are intact, reducing fears of a massive radiation leak.

The reactors were switched off when the explosion occurred, so why is there a problem?

Nuclear reactors remain hot even when switched off because of residual radioactivity in fuel rods. Water must be pumped in to cover these rods and cool them. The electricity supply to the pumps failed after the quake, then the back-up generators were swamped by the tsunami. If a cooling system is not restored, it could lead to a meltdown - when the core melts and radiation escapes.

How much radiation is there so far?

The government said radiation levels were below legal limits after today's explosion. However, levels equivalent to six months of background radiation had been detected at the plant.