Nuclear Meltdown

NRC: No water in spent fuel pool of Japan plant

(Agencies)
Updated: 2011-03-17 09:16

WASHINGTON -?The chief of the US Nuclear Regulatory Commission said Wednesday that all the water is gone from one of the spent fuel pools at Japan's most troubled nuclear plant. But Japanese officials denied it.

"There is no water in the spent fuel pool and we believe that radiation levels are extremely high, which could possibly impact the ability to take corrective measures," NRC Chairman Gregory Jaczko said at a House Energy and Commerce subcommittee hearing.

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If Jaczko was correct, this would mean there was nothing to stop the fuel rods from heating and ultimately melting down. The outer shell of the rods could also ignite with enough force to propel the radioactive fuel inside over a wide area, widening the potential reach of any nuclear fallout.

That country's nuclear safety agency and Tokyo Electric Power Co., which operates the six-unit Fukushima Dai-ichi complex, denied Jaczko's statements that the water is gone from the pool.

Utility spokesman Hajime Motojuku said the "condition is stable" at Unit 4, which was shut when the earthquake and tsunami hit last week.

After the hearing, Jaczko left some wiggle room. If he is wrong, it would represent a very embarrassing moment for the US government.

"My understanding is there is no water in the spent fuel pool," he said. "I hope my information is wrong. It's a terrible tragedy for Japan."

Jaczko said the information came from NRC staff and experts in Tokyo who are working with the utility in Japan. He said NRC staffers continue to believe the spent fuel pool is dry. "They believe the information they have is reliable," he said.

In another troubling development, the International Atomic Energy Agency in Vienna said temperatures in units 4, 5 and 6 have been rising. The temperature in Unit 4 on Monday and Tuesday was given as 183 degrees Fahrenheit (84 Celsius). For Wednesday, the IAEA report for Unit 4 stated, "no data."

Also alarming was the information at units 5 and 6, which were in cold shutdown when the earthquake hit and had not been known to be of any concern. Also, the fuel rods in use when those two reactors were shut for maintenance remain inside their reactor vessels.

In Unit 5, the pool temperature was 139 degrees Fahrenheit (59.7 Celsium) on Monday, 141 degrees Fahrenheit (60.4 Celsius) on Tuesday and 145 degrees Fahrenheit (62.7 Celsius) on Wednesday.

Temperatures at Unit 6 also rose Tuesday and Wednesday. The latest temperature was 140 degrso.

Unlike fuel rods in reactor cores protected by 6-inch (15-centimeter)-thick steel walls, the spent fuel pools are considerably more vulnerable - located on the top floor of each reactor's containment building, without any extraordinary protection. Plus, the containment building of Unit 4 has a big hole in a wall.

But a key question is just how much of the radioactive material decayed inside the rods before they were transferred to the storage pool.

"For the time being, the greatest concern is the spent fuel pools because there is a clear pathway for release of radioactivity from the pools into the environment," said Ed Lyman, a physicist at the Union of Concerned Scientists, an activist group.

Fuel rods consist of a zirconium outer casing and highly radioactive uranium pellets inside. Experts say the casings of the spent fuel rods in Unit 4's pool have likely already overheated and cracked, allowing radioactive gases to vent into the air. That radiation is hindering the efforts to control the developing catastrophe at the reactor complex.

Officials have acknowledged that the cores of units 1, 2, and 3 have begun to melt down, but no one has said the walls of the reactor vessels have been breached. Radiation has been leaking from the reactor structures, though.

Even at those units, the spent fuel pools could spell an even more severe problem. Explosions at units 1 and 3, which were operating at the time of the earthquake and tsunami, have left those spent fuel pools exposed to the open air.

The pools and those at units 5 and 6 - which also were shut at the time the qu decades. This type of cesium, known as cesium-137, emits what is known as a hard gamma ray which is strong enough to penetrate human skin.

"You don't have to breathe it in to be affected," Lyman said. The release of cesium could render the area around a plant uninhabitable. The size of the area would depend on the amount of material released and the direction and strength of the wind at the time of release.

Cesium was the largest source of radiation around the Chernobyl reactor in the Ukraine, which suffered the fuel, allowing radioactive contents to escape in the air in smoke, said David Lochbaum, nuclear safety chief at the Union of Concerned Scientists. He said a fire would spew "a whole gamut of nasty materials." In addition to cesium, he cited krypton, strontium and ruthenium.

"You have the potential for significant long-term land area contaminations," said Robert Alvarez, a senior scholar at the Institute for Policy studies in Washington and a former Department of Energy official.