News got worse overnight from Japan’s stricken Fukushima Daiichi nuclear power plant.  The containment pools covering the fuel rods now appear to be boiling in the reactors that have already been shut down, and storage pool walls have been damaged.  Earlier today, Japan took the unusual step of ordering nearby residents to seal themselves in their homes — 140,000 people:

Dangerous levels of radiation leaking from a crippled nuclear plant forced Japan to order 140,000 people to seal themselves indoors Tuesday after an explosion and a fire dramatically escalated the crisis spawned by a deadly tsunami.

In a nationally televised statement, Prime Minister Naoto Kan said radiation has spread from the four stricken reactors of the Fukushima Dai-ichi nuclear plant along Japan’s northeastern coast. The region was shattered by Friday’s 9.0-magnitude earthquake and the ensuing tsunami that is believed to have killed more than 10,000 people, plunged millions into misery and pummeled the world’s third-largest economy.

Japanese officials told the International Atomic Energy Agency that the reactor fire was in a storage pond and that “radioactivity is being released directly into the atmosphere.” Long after the fire was extinguished, a Japanese official said the pool, where used nuclear fuel is kept cool, might be boiling.

The order applies to people living within a 19-mile radius of the plant.  They have been ordered to stay inside and seal doors and windows and “make your homes airtight,” which will be nearly impossible, and unsustainable after a few days even if it weren’t.  Eventually, people will need to exchange the stale air in their homes with the outside to maintain proper oxygen levels, and will have to find water and food as well.

Radiation levels south of the plant are now 100 times normal levels, which isn’t a problem for short-term exposure but could be a big problem for people who live there.  Their fear now is less the radiation leaking at the moment, and more that the containment vessels won’t hold and the fuel rods will explode into the atmosphere.  That will generate fallout that could poison the area for years.

However, the biggest issue facing Japan’s population may not be radiation, but a lack of heat and water.  With electricity and with oil distribution disrupted, the cold winter presents immediate problems:

When Japan lost a large chunk of its electricity-generating capacity to the one-two punch of earthquake and tsunami, the narrative in parts of one of the world’s most technologically advanced societies was transformed overnight into one of Third World hardship.

For most Japanese, the rolling outages instituted in the wake of the twin disasters translate to inconvenience, sacrifice and economic loss. But for tens of thousands who are now homeless and huddled in evacuation centers in the hard-hit northeast, the stakes are much higher.

“Evacuation centers have half a million people in centers and schools that don’t have water, electricity and oil,” said Sheila Smith, senior fellow for Japan Studies at the Council on Foreign Relations. “And the temperatures are near freezing. … (In some places) it is snowing. The immensity of this crisis cannot be understated.”

The crisis at Fukushima Daiichi has occupied the attention of nuclear-power experts, for obvious reasons, but that means that Japan cannot get its other undamaged reactors back on line quickly.  Japan gets 35% of its electricity from nuclear plants, and there wouldn’t be enough excess capacity in other sources to cover that kind of loss.  Other power sources need imported raw materials, which would be difficult to distribute internally in this crisis anyway.  The shortage has required power companies to ration electricity through rolling blackouts until their supplies can reliably stay on line.

Update (AP): Both the Journal and the Times report that the situation at reactor number two has stabilized in some respects, with a core group of 50 emergency workers remaining behind to pump sea water into the containment vessel. Radiation levels near the plant are reportedly down sharply after soaring following the explosion at reactor two. As Ed noted, the major concern right now appears to be the possibility of spent fuel rods boiling over; according to the NYT, that area is now so dangerous that workers can’t approach it.

Update (Ed, 10:41 am): The Boss Emeritus has followed reports on Twitter that a quake measuring 6.2 magnitude struck the center of Japan today, hitting Tokyo.  That’s within manageable range, but may complicate matters for responders if more damage occurs — or if this was a foreshock of a larger quake coming.

Update (Ed, 2:11 pm): I conflated two different alerts.  The quake that hit today and rattled Tokyo was in the center of Japan, not off the west coast; that was an earlier quake report.  I’ve fixed the headline and the last update.