Reactor No. 3 is a major concern to Japanese officials because its fuel is a mixture of enriched uranium and plutonium, known as mox. Mox is considered more hazardous than just enriched uranium alone, according to Prof. Burton Richter, PhD, an expert in nuclear reactors at Stanford. Dr. Richter received the Nobel Prize for Physics in 1976 and served as director of the Stanford Linear Accelerator Center.
"It is very nasty," Richter said about mox. The presence of plutonium, he says, poses a greater biological hazard.
Japanese officials have been concentrating their efforts on Reactor No. 3, while U.S. experts have been expressing more concern about Reactor No. 4, which has enriched uranium. Dr. Richter believes there is a difference in facts behind this. Gregory Jaczko, chairman of the U.S. Nuclear Regulatory Commission, told members of Congress on Wednesday that his information indicates fuel rods are exposed inside Reactor No. 4.
Keeping them submerged in water, according to experts we've consulted, is essential to cool them down over a three to four year period until the radiation risk is reduced. Out of water, they can melt down and release lethal radiation. However, Japanese officials from Tokyo Electric, operator of the plant, and from Japan's Nuclear and Industrial Safety Agency, said they can't get close enough to determine if the rods are exposed.
"It's basically a big swimming pool and in this case it's not in the primary containment. When you blew the roof off as we saw on Monday, it's essentially out in the open," UC Berkeley nuclear engineer professor Dr. Peter Hoseman said.
Radiation levels have risen to about 250 millisievert an hour, 100 feet above the plant, according to Japanese officials. That is the exposure limit in the U.S. for public safety and emergency workers.
"It's like a squirt gun, using a squirt gun against a raging forest fire. They don't know what to do. They're clueless," ABC News consultant and physicist Michio Kaku said.
Despite that difference, Jaczko from the NRC told reporters at the White House today that the U.S. is receiving good cooperation from the Japanese. The U.S. has 11 expert technicians on-site.