專家警告往廢棄燃料棒上澆水可能使之進入臨界狀態
專 家警告往廢棄燃料棒上澆水可能使之進入臨界狀態，引發更大核災難。
Analysis: Japan nuclear crisis reaches new levels
NEW YORK |
Tokyo Electric Power Co (TEPCO), the operator of the six-reactor complex, was considering spraying water into the spent fuel pools through the holes in the roof by helicopter but later canceled that mission.
Arnie Gundersen, a 29-year veteran of the nuclear industry who has worked on reactors similar to the Daiichi plant and is now chief engineer at Fairewinds Associates Inc, warned that dropping water on the spent fuel pool could make matters worse.
"It's a bad idea to drop water onto the fuel racks. You could get an inadvertent criticality. That means you could have a nuclear reaction, similar to that in a reactor core, in the fuel pool," Gundersen said.
MORE RADIATION
"There is more radiation in the spent fuel pool - which is about ten stories in the air -- than in the reactor core," Gundersen said, noting used rods contain more dangerous radioactive materials than new rods, including elements cesium, strontium and plutonium.
Plutonium, in particular, is a very nasty isotope and could cause cancer in very small quantities if ingested, he said.
The uranium fuel is burned in the reactor for three to six years before being placed into the pool. About one third of the fuel is removed from the reactor core to the pool every 18 to 24 months during refueling outages.
Used fuel rods must sit in the spent fuel pool for at least five years. Though, much to the consternation of environmental and anti-nuclear groups, the rods usually sit in the pool much longer while waiting for either reprocessing or storage in dry casks.
Gundersen also said he recommended evacuating children and pregnant women to more than 50 miles away from the plant to avoid the radiation risk.
In a sign that other spent fuel rod pools could be in a deteriorating condition, the NRC Chairman Jaczko said he also believed the pool at the No. 3 reactor may also have a leak.
"Every day it seems like things may be stabilizing but you wake up the next morning and it seems like things have not stabilized or maybe gotten worse," said Brian Woods, nuclear engineering associate professor at Oregon State University and a former engineer for the U.S. Department of Energy.
Woods said that it may be time to think of encasing the complex in some kind of protective material.
"More than likely you're probably looking at some kind of external containment," he said.
(Reporting by Scott DiSavino, David Sheppard, Matt Daily and Ben Berkowitz in New York, Timothy Gardner in Washington, Bernie Woodall in Detroit and Eileen O'Grady in Houston; Editing by Martin Howell)
