Japan No. 2 Core Melted Through Reactor VesselThe confidential assessment was submitted to the NRC on March 26, and its concerns centered around "mounting stresses placed on the containment structures as they fill with radioactive cooling water, making them more vulnerable to rupture" in aftershocks which continue to occur after the earthquake of March 11.
by Roberta Rampton and Ayesha Rascoe - Reuters, April 6, 2011
The core at Japan's Fukushima nuclear reactor has melted through the reactor pressure vessel, Democratic Congressman Edward Markey told a hearing on the nuclear disaster on Wednesday.
"I have been informed by the Nuclear Regulatory Commission that the core of Unit Two has gotten so hot that part of it has probably melted through the reactor pressure vessel," said Markey, a prominent nuclear critic in the House of Representatives.
U.S. Sees Array of New Threats at Japan’s Nuclear Plant
By JAMES GLANZ and WILLIAM J. BROAD - New York Times, April 6, 2011
United States government engineers sent to help with the crisis in Japan are warning that the troubled nuclear plant there is facing a wide array of fresh threats that could persist indefinitely... according to a confidential assessment prepared by the Nuclear Regulatory Commission.
It also "cites the possibility of explosions inside the containment structures due to the release of hydrogen and oxygen from seawater pumped into the reactors", which would lead to, well; stuff we don't want to think about. I stand by my earlier statement: It appears likely central Japan might want to go for pizza for 25,000 years.
My favorite part was where, as a result of hydrogen explosions at the Fukushima Daiichi reactor site after March 12, pieces of amazingly radioactive spent fuel were found blown (in one case) up to a mile away from the plant; in another, lying on the ground between two of the reactor buildings.
...If the fuel continues to heat and melt because of ineffective cooling, some nuclear experts say, that could also leave a radioactive mass that could stay molten for an extended period...
[After reviewing the confidential report, David A. Lochbaum, director of the nuclear safety project at the Union of Concerned Scientists, said] “I thought they were, not out of the woods, but at least at the edge of the woods... This paints a very different picture, and suggests that things are a lot worse...”
UPDATE: As usual, "We express regret":
TOKYO (Reuters) - Japan stopped highly radioactive water leaking into the sea on Wednesday from a crippled nuclear plant and acknowledged it could have given more information to neighboring countries about contamination in the ocean.Nice.
..."The original amount of radioactivity is very low, and when you dilute this with a huge body of water, the final levels will be even lower than legal limits," said Pradip Deb, senior lecturer in Medical Radiations at the School of Medical Sciences, Royal Melbourne Institute of Technology University.
..."What they are going to have to release is likely to be highly radioactive. The situation could politically be very ugly in a week," said Murray Jennex at San Diego State University, who specializes in nuclear containment.