It’s not a Three Mile Island situation yet, let alone a Chernobyl, and given the fact that the reactors are covered with containment vessels (which Chernobyl wasn’t), it’s unlikely to get quite that bad. But Dow Jones is now reporting that the local electric company says it’s “lost control over pressure in the reactors,” and stories on the wires an hour ago claimed that radiation levels in the control room at the plant have reached 1,000 times their normal level. And so one of the worst days in Japanese history may be about to turn worse still.

This Reuters piece explains the problem concisely. In a nutshell, the reactors are overheating because they can’t pump coolant into them. So massive was the quake that virtually all of the plant’s power sources are offline; no power means no pump means no coolant, which means the cores are going to get hotter and hotter. As you’ll see below, they do have emergency diesel systems available to get some coolant in there, but it sounds like that may succeed only in slowing the pace of the overheating, not reversing it. Potentially, it may get so hot that it melts down; in the near term, the heat in the chamber will produce radioactive steam, which will have to be released into the atmosphere or else the chamber could blow.

Unbelievable:

If the outage in the cooling system persists, eventually radiation could leak out into the environment, and, in the worst case, could cause a reactor meltdown, a nuclear safety agency official said on condition of anonymity, citing sensitivity of the issue.

Another official at the nuclear safety agency, Yuji Kakizaki, said that plant workers were cooling the reactor with a secondary cooling system, which is not as effective as the regular cooling method.

Kakizaki said officials have confirmed that the emergency cooling system — the last-ditch cooling measure to prevent the reactor from the meltdown — is intact and could kick in if needed.

“That’s as a last resort, and we have not reached that stage yet,” Kakizaki added…

“They are busy trying to get coolant to the core area,” Sheehan said. “The big thing is trying to get power to the cooling systems.”

There was some confusion earlier when Hillary declared that the U.S. had sent some emergency coolant to Japan and the Air Force said, er, no we didn’t. But at the moment it’s immaterial — the problem isn’t finding coolant to pump, it’s pumping in the already available supply. Meanwhile, apparently some radioactive material was already released into the sea when the quake hit and four reactors automatically shut down. Japanese officials say it’s not a threat to anyone and insist that they’re not at crisis stage yet, but 3,000 people in a two-mile radius have already been evacuated and those who remain within a seven-mile radius have been told to stay indoors. Gulp.

We’re bound to have updates of some kind on this story later, so watch this space. Exit question: Will Japanese engineering ingenuity prevent a total catastrophe here the same way it did with those swaying skyscrapers in Tokyo? Quote:

Mark Hibbs, a nuclear expert at the Carnegie Endowment for International Peace, told Reuters that there is serious concern in Japan whether the cooling of the core and removal of residual heat could be assured. “If that does not happen, if heat is not removed, there is a definite danger of a core melt … fuel will overheat, become damaged and melt down.”

“Even if fuel rods melt and the pressure inside the reactor builds up, radiation would not leak as long as the reactor container functions well,” Tomoko Murakami, leader of the nuclear energy group at Japan’s Institute of Energy Economics, told Reuters.

Update: The emergency cooling system is running on battery power right now, and the batteries are running down. Once all the juice is gone, it’ll be only hours until meltdown.

Officials are now considering releasing some radiation to relieve pressure in the containment at the Daiichi plant and are also considering releasing pressure at Daini, signs that difficulties are mounting. Such a release has only occurred once in U.S. history, at Three Mile Island.

“(It’s) a sign that the Japanese are pulling out all the stops they can to prevent this accident from developing into a core melt and also prevent it from causing a breach of the containment (system) from the pressure that is building up inside the core because of excess heat,” said Mark Hibbs, a nuclear expert at the Carnegie Endowment for International Peace.

While the restoration of power through additional generators should allow TEPCO to bring the situation back under control, left unchecked the coolant could boil off within hours. That would cause the core to overheat and damage the fuel, according to nuclear experts familiar with the Three Mile Island accident in Pennsylvania in 1979.

It could take hours more for the metal surrounding the ceramic uranium fuel pellets in the fuel rods to melt, which is what happened at Three Mile Island.

A horrifying quote from a nuclear waste specialist who spoke to ABC: “Given the large quantity of irradiated nuclear fuel in the pool, the radioactivity release could be worse than the Chernobyl nuclear reactor catastrophe of 25 years ago.”

Update: Cliche though it may be, this is indeed a race against time. The batteries powering the cooling pumps can run for about eight hours. After that…

U.S. Secretary of State Hillary Rodham Clinton said the U.S. Air Force is assisting in flying in backup generators, and Japanese ground forces are also trucking generators and batteries to the site, according to media reports. Time is critical, according to experts. Once power to the cooling supply is interrupted, all the coolant could boil off in as little as an hour, Kamps said.

If there is a meltdown at Fukushima, “the containment building is the last line of defense,” Kamps added. The reactor is 40 years old and the original ventilation system had to be retrofitted to allow radioactive gasses to be vented so that pressure would not build up and cause an explosion that would spread radioactivity over a much wider area.

Update: Not sure what this means yet for cooling down the reactors, but it’s cause for hope. From the IAEA:

Japanese authorities have informed the IAEA’s Incident and Emergency Centre (IEC) that officials are working to restore power to the cooling systems of the Unit 2 reactor at the Fukushima Daiichi nuclear power plant. Mobile electricity supplies have arrived at the site.

Japanese officials have also reported that pressure is increasing inside the Unit 1 reactor’s containment, and the officials have decided to vent the containment to lower the pressure. The controlled release will be filtered to retain radiation within the containment.

Update: Turns out that IAEA alert is six hours old. And yet, I saw no mention of it in the various stories I read fretting about a lack of power supplies at the plant. Very strange.