Japan races against time to prevent reactor meltdown

The only ideas we have right now are using a helicopter to spray water from above,or inject water from below, a power company official said at a news conference. We believe action must be taken by tomorrow or the day after.

Hydrogen bubbling up from chemical reactions set off by the hot fuel rods produced a powerful explosion on Tuesday morning that blew a 26-foot-wide hole in the side of Reactor 4 at the plant. A fire there may have been caused by machine oil in a nearby facility,inspectors from the US Nuclear Regulatory Commission said,according to an American official.

Concern remained high about the storage ponds at Reactors 4,5 and 6. None of these reactors was operating on Friday afternoon when the offshore earthquake now estimated at strength 9 and subsequent tsunami struck.

At least 750 workers evacuated Tuesday morning after a separate explosion ruptured the inner containment building at Reactor 2,which was crippled on Friday. The explosion released a surge of radiation 800 times more intense than the recommended hourly exposure limit in Japan.

Fifty workers stayed behind,struggling to keep hundreds of gallons of seawater a minute flowing through temporary fire pumps into the three stricken reactors,where overheated fuel rods continued to boil away the water at a brisk pace.

By early afternoon,radiation levels had plunged,according to the International Atomic Energy Agency in Vienna. Workers have been releasing surges of radiation each time they bleed radioactive steam from the reactors in an attempt to manage the pressure inside,but no high levels of radiation are yet being released on a sustained basis,Japanese officials said.

Japanese Prime Minister Naoto Kan warned in a nationally televised address late Tuesday morning of rising radiation. The chief cabinet secretary,Yukio Edano,urged people who live within about 18 miles of the plant to take precautions. Please do not go outside,please stay indoors,please close windows and make your homes airtight, he said. More than 100,000 people are believed to be in the area.

In Tokyo,the metropolitan government said Tuesday it had detected radiation levels 20 times above normal over the city,though it stressed that such a level posed no immediate health threat and that readings had dropped since then. The explosion in Reactor 2,a little after 6 am on Tuesday,particularly alarmed Japanese officials and nuclear power experts around the world because it was the first detonation at the plant that appeared to occur inside one of the primary containment buildings.

After a series of conflicting reports about how much damage was inflicted on the reactor after that blast,Yukio Edano said that there is a very high probability that a portion of the containment vessel was damaged.

Japanese officials subsequently said that the explosion had damaged a doughnut-shaped steel container of water,known as a torus,that surrounds the base of the reactor vessel inside the primary containment building.

Even if a full meltdown is averted,Japanese officials on Tuesday faced unpalatable options.

One was to continue flooding the reactors and venting the resulting steam,while hoping that the prevailing winds did not turn south towards Tokyo or west,across northern Japan to the Korean peninsula.

The other was to hope that the worst of the overheating was over,and that with the passage of a few more days the nuclear cores would cool enough to essentially entomb the radioactivity inside the plants,which clearly will never be used again. Both approaches carried huge risks.

While Japanese officials made no comparisons to past accidents,the release of an unknown quantity of radioactive gases and particles signs that the reactor cores were damaged from at least partial melting of fuel added considerable tension to the effort to cool the reactors.

Its way past Three Mile Island already, said Frank von Hippel,a physicist and professor at Princeton,referring to a 1979 nuclear accident in the US. The biggest risk now is that the core really melts down and you have a steam explosion.KEITH BRADSHER &

HIROKO TABUCHI