There was confusion last night after the chief of the US nuclear watchdog said all the water had gone from one of the spent fuel pools at Japan's most troubled nuclear plant.
But Japan's nuclear safety agency and Tokyo Electric Power, which operates the Fukushima Daiichi complex, denied the water had gone. Utility spokesman Hajime Motojuku said the “condition is stable” at the Unit 4 reactor.
If the liquid evaporates, it would mean there was nothing to stop the fuel rods getting hotter and ultimately melting down.
The outer shell of the rods could also ignite with enough force to blast the radioactive fuel inside over a wide area.
US Nuclear Regulatory Commission boss Gregory Jaczko did not say how his information was obtained, but the NRC and US department of energy both have experts on site at the Fukushima complex of six reactors.
He said officials believe radiation levels are extremely high, and that could affect workers' ability to stop temperatures rising.
Japanese riot police yesterday joined the fight to stop the badly damaged nuclear plant from going into meltdown, bringing in a water cannon truck to cool an overheating reactor.
The deployment of the police last night heightened fears that the plant operator, Tokyo Electric Power (Tepco), is quickly running out of options.
Technicians at the nuclear plant who had been using seawater and helicopters to dump water on the crippled facility were pulled out yesterday for over an hour after radioactivity levels spiked. Tepco later sent more than 100 men in protective suits back inside.
Reactor 3 has reportedly been leaking radiation since an explosion damaged its containment system, and Tepco has refused to rule out the threat of “criticality” — a potentially catastrophic fission explosion in Reactor 4.
The riot police will try to bring the situation under control by spraying pressurised water into a storage pool for spent nuclear fuel inside the No 4 reactor, says state broadcaster NHK.
Meanwhile, in the first sign that international frustration at the Japanese government's reticence on the status of the stricken power plant has reached a critical moment, the director general of the International Atomic Energy Agency issued a thinly veiled rebuke to Prime Minister Naoto Kan's administration.
“We do not have all the details of the information so what we can do is limited,” said Yukiya Amano, who is Japanese himself. “I am trying to further improve the communication.”
As it struggles to gain control of a nuclear crisis and to feed and shelter the thousands left homeless by last week's devastating tsunami, the Japanese government is facing growing criticism over its handling of the crisis, the the depth of which was underlined yesterday in a rare TV appearance by Emperor Akihito, who said he was “deeply concerned” by the tragedy enveloping his country. “I hope from the bottom of my heart that the people will, hand in hand, treat each other with compassion and overcome these difficult times,” he said in a televised address.
Five nuclear workers have reportedly died since the quake and tsunami hit on Friday, knocking out diesel-fuelled cooling systems.
Two more are missing with at least 20 injured. The unheralded technicians, who are virtually the only firewall in the nuclear crisis, were put at further risk on Tuesday when the health ministry doubled their radiation-exposure limit to 250 millisieverts.
The Fukushima crisis has overshadowed the plight of about 450,000 refugees, mainly in the decimated north-east of the country. The government said yesterday that the death toll had climbed to 3,700 but thousands more are missing.