The radioactive core in a reactor at the crippled Fukushima nuclear power
plant appears to have melted through the bottom of its containment
vessel and on to a concrete floor below, experts say, raising fears of a
major release of radiation at the site.

Richard Lahey, who has
worked on the plant at Fukushima, told the Guardian officials seemed to
have “lost the race” to save the reactor, but added that there was no
danger of a Chernobyl-style catastrophe.

His warning came as Nick
Clegg, the deputy prime minister, signalled that Britain could take a
step back from nuclear power in the wake of the disaster.

Speaking
on a trip to Mexico, Clegg said the resulting uncertainty for the
nuclear industry could make it more likely the industry would need a
public subsidy, which the coalition would be unable to provide.

“We
have always said there are two conditions for the future of nuclear
power [the next generation of power stations] have to be safe and can
not let the taxpayer be ripped off,” he said.

Eight new nuclear plants are due for construction in the UK.

Meanwhile
the Health Protection Agency said that traces of radioactivity believed
to come from the Fukushima disaster had been detected across the UK by
emergency monitoring stations in Oxfordshire and Glasgow.

The
agency that “the minutest” levels of radioactive iodine had been
detected at its air monitoring stations over the last nine days, but
they posed no risk to health.

At Fukushima, workers have been
pumping water into three reactors in a desperate bid to keep the fuel
rods from melting down. But Lahey, who was head of safety research for
boiling-water reactors at General Electric when the company installed
the units at the plant, said his analysis of radiation levels suggested
these attempts had failed at reactor two.

He said at least part of
the molten core, which includes melted fuel rods and zirconium alloy
cladding, seemed to have sunk through the steel “lower head” of the
pressure vessel and on to the concrete floor below.

“The
indications we have, from the reactor to radiation readings and the
materials they are seeing, suggest that the core has melted through the
bottom of the pressure vessel in unit two, and at least some of it is
down on the floor of the drywell,” Lahey said. “I hope I am wrong, but
that is certainly what the evidence is pointing towards.”

The
major concern when molten fuel breaches a containment vessel is that it
will react with the concrete floor of the drywell, releasing radioactive
gases into the surrounding area. At Fukushima, the drywell has been
flooded with seawater, which will cool any molten fuel that escapes from
the reactor and reduce the amount of radioactive gas released.

Lahey said: “It won’t come out as one big glob; it’ll come out like lava, and that is good because it’s easier to cool.”

The
drywell is surrounded by a secondary steel-and-concrete structure
designed to keep radioactive material from escaping into the
environment. But an earlier hydrogen explosion at the reactor may have
damaged this.

“The reason we are concerned is that they are
detecting water outside the containment area that is highly radioactive
and it can only have come from the reactor core,” Lahey added. “It’s not
going to be anything like Chernobyl, where it went up with a big fire
and steam explosion, but it’s not going to be good news for the
environment.”

The radiation level at a pool of water in the
turbine room of reactor two was measured recently at 1,000 millisieverts
per hour. At that level, workers could remain in the area for just 15
minutes, under current exposure guidelines.

A less serious core
meltdown happened at the Three Mile Island nuclear plant in Pennsylvania
in 1979. During that incident, engineers managed to cool the molten
fuel before it penetrated the steel pressure vessel. The task is a race
against time, because as the fuel melts it forms a blob that becomes
increasingly difficult to cool.

In the light of the Fukushima
crisis, Lahey said all countries with nuclear power stations should have
“Swat teams” of nuclear reactor safety experts on standby to give swift
advice to the authorities in times of emergency, with international
groups co-ordinated by the International Atomic Energy Authority.

The
warning came as the Japanese authorities were being urged to give
clearer advice to the public about the safety of food and drinking water
contaminated with radioactive substances from Fukushima.

Robert
Peter Gale, a US medical researcher who was brought in by Soviet
authorities after the Chernobyl disaster, in 1986, has met Japanese
cabinet ministers to discuss establishing an independent committee
charged with taking radiation data from the site and translating it into
clear public health advice.

“What is fundamentally disturbing the
public is reports of drinking water one day being above some limit, and
then a day or two later it’s suddenly safe to drink. People don’t know
if the first instance was alarmist or whether the second one was
untrue,” said Gale.

“My recommendation is they should consider
establishing a small commission to independently convert the data into
comprehensible units of risk for the public so people know what they are
dealing with and can take sensible decisions,” he added.

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