More bad nuclear news --- and good news for a victim

A third explosion in four days rocked the earthquake-damaged Fukushima Dai-ichi nuclear plant in northeast Japan early Tuesday, the country's nuclear safety agency said.

The blast at Dai-ichi Unit 2 followed two hydrogen explosions at the plant — the latest on Monday — as authorities struggle to prevent the catastrophic release of radiation in the area devastated by a tsunami.

The troubles at the Dai-ichi complex began when Friday's massive quake and tsunami in Japan's northeast knocked out power, crippling cooling systems needed to keep nuclear fuel from melting down.

The latest explosion was heard at 6:10 a.m. Tuesday (2110 GMT Monday), a spokesman for the Nuclear Safety Agency said at a news conference. The plant's owner, Tokyo Electric Power Co., said the explosion occurred near the suppression pool in the reactor's containment vessel. The pool was later found to have a defect.

International scientists have said there are serious dangers but not at the level of the 1986 blast in Chornobyl.

Concerns about a radiation release from the Fukushima Daiichi [1] power facility have focused on its stricken nuclear reactors, but the plants of that design also store highly radioactive spent fuel in pools outside the protective containment structure that surrounds the reactor itself.

Opponents of nuclear power have warned for years that if these pools drain, either by accident or terrorist attack, it could lead to a fire and a catastrophic release of radiation. Now, there have been hydrogen explosions [2] at two of the reactor buildings housing spent fuel pools at Fukushima.

This diagram [3] shows where spent fuel pools are typically located in the 1970s-vintage GE Mark I reactor design in use at Fukushima units 1, 2 and 3, where officials suspect reactor fuel has melted...

The concern is that if the water in the pools ever drops too low, the zirconium cladding that holds the radioactive fuel pellets would begin to heat up and eventually burn. And if it did, the smoke from the fire could carry radiation away from the plant because the pool is outside the containment.