||Corrosive salt from seawater may be adding to problems at the Fukushima Daiichi nuclear plant,
damaged two weeks ago by the megaquake and tsunami in Japan.
The flood swept away backup power units meant to keep cooling water flowing through the reactors in
an emergency, forcing the plant's operators to use seawater to cool its reactors and ponds storing
Concerns are now arising about the effect of salt deposits in reactors and cooling systems as the
water is boiled away by intense heat from the fuel.
As much as 26 tonnes of salt may have accumulated in reactor unit 1, and twice that amount in the
larger units 2 and 3, according to estimates in The New York Times by Richard Lahey, who was General
Electric's chief of safety research for boiling water reactors when the company installed them at
Lahey told the newspaper that an international group of nuclear experts is informally urging
Japanese emergency workers to try to flood the vessels with fresh water as soon as possible to flush
the salt deposits back out to sea.
The worry, says Lahey, is that the salt will form coatings on the fuel rods, making them heat up
even faster by insulting them from the cooling effects of water.
Andrew Sherry of the Dalton Nuclear Institute at the University of Manchester, UK, told New
Scientist that two additional problems might arise.
One is that salt deposits may be clogging up pipes, pumps and valves in the cooling systems,
preventing them from functioning properly once power is restored.
"It's going to restrict flow, there's no doubt about that," says Sherry. "Whether it leads to
problems restarting the pumps and opening valves, I don't know."
The second is that chloride in the salt may be creating holes in the outer zirconium oxide layer of
the fuel rods' zirconium alloy cladding. This "corrosion pitting" could potentially eat right down
to the radioactive fuel, forming holes and cracks that would allow volatile radioactive elements to
This could add to damage from other sources, mainly the explosions of hydrogen gas released from
reactions of zirconium oxide with steam, that has led to release of vapours containing radioactive
iodine-131 and caesium-137.
In the past two days, levels of both isotopes have been increasing in soil, seawater, food and
drinking water in the region. Yesterday the levels of iodine-131 reached double the safe level in
Tokyo tap water, 220 kilometres to the south, prompting the authorities there to advise against
using the water in formula milk for babies. The ban was lifted today, after levels fell, but concern
Levels in milk and vegetables produced near the nuclear plant have also been rising to the point
where residents of Fukushima province were warned yesterday not to eat spinach and other leafy green
Whether the salt is adding to the problems or not, Sherry says it would be helpful to get rid of it.
"Ultimately, you want to flush out the seawater altogether and re-establish the usual chemical
conditions operating in the reactor system," he says.
There are encouraging signs that this process may be under way. By yesterday, power had been
restored to all six reactor units at Fukushima, and the lights in the control rooms switched on in
units 1 and 3. Previously, workers had been contending with complete darkness.
More importantly, workers were also close to testing a cooling pump that for the first time would
inject fresh water rather than seawater into reactor unit 3.
There was a cost to the operation, however: Two workers were hospitalised after having to wade
through radioactively contaminated water while installing cabling in the basement of reactor unit 3.