|Joined: ||Mon Mar 10th, 2008|
|Location: ||Seattle, USA|
|| Posted: Thu May 26th, 2011 01:49 pm||
|Damage to Fukushima Plants Worse Than Previously Reported
More Fuel Exposure; Breach of Reactor Vessel; Potential Damage from Earthquake
May 25, 2011, 2:47 AM EDT
By Yuji Okada and Tsuyoshi Inajima
May 25 (Bloomberg) -- Tokyo Electric Power Co. said the containment chambers of damaged reactors at its Fukushima nuclear plant were likely breached, identifying additional source of radiation leaks that may exceed Chernobyl.
Computer simulations of the meltdowns of three reactors in March indicates holes formed in chambers, the company known as Tepco said in a report.
The analysis confirms what independent researchers have said occurred after the March 11 earthquake and tsunami hit the plant. The report to the government raises fresh questions about how Tepco, which took more than two months to acknowledge fuel rods had melted, is handling the crisis, a nuclear researcher said.
“Unfortunately I can’t find any consistency in the report,” Hironobu Unesaki, a nuclear engineering professor at Kyoto University, said by phone. “Tepco hasn’t released sufficient radionuclide analysis of leaked contaminated water. Now they’ve confirmed fuel rods melted, they should also release more data including plutonium and uranium readings.”
Containment chambers surround the reactor vessel, which holds the fuel rods, and are meant to stop radiation and coolant leaks in the case of overheating.
Japan’s government in April raised the severity rating of nuclear crisis at the Fukushima Dai-Ichi nuclear plant to the highest, matching Chernobyl in 1986. At the time Tepco officials said the crippled plant may release more radiation than the Chernobyl.
...Tepco’s analysis shows the No. 1 chamber has one hole and the No. 2 unit has two breaches, according to a report filed to a Japanese nuclear watchdog. Cooling systems may have been breached at the No. 3 reactor at the site, Tepco said.
“The breaches were created awhile ago, so they won’t cause rapid increases in radiation doses,” said Ken Nakajima, a professor of nuclear engineering at Kyoto University who specializes in reactor safety. “However, I’m concerned about a possible increase in tainted water leaking from the holes, which may lead to contamination of groundwater and seawater.”
Tepco yesterday confirmed meltdowns of fuel rods in the No. 2 and 3 reactors at the station north of Tokyo, which has been emitting radiation since an earthquake and tsunami knocked out power and cooling systems on March 11.
It revised the time the No. 1 reactor melted to within 15 hours of the quake, an hour earlier than it gave last week when it announced the damage to the reactor was worse than thought.
--With assistance from Taku Kato in Tokyo. Editors: Aaron Sheldrick, Peter Langan
also see WS Journal:
By MITSURU OBE and PHRED DVORAK in Tokyo and REBECCA SMITH in San Francisco
One of the reactors at Japan's Fukushima Daiichi nuclear plant likely suffered a substantial meltdown of its core, operator Tokyo Electric Power Co. said Thursday, offering a fresh assessment of the reactor that suggests it came closer than the operator had previously revealed to a catastrophic meltdown.
... It is likely that the fuel rods that form the core of Reactor No. 1 had more than half melted in March, Tepco spokesman Junichi Matsumoto said Thursday. That assessment came after Tepco this week determined that both of the vessels that surround the reactor core may be damaged, leaking water that is supposed to be keeping the core cool.
The reactor core is still contained inside those vessels, Mr. Matsumoto said, and the temperature is stable. That indicates the accident didn't reach the most severe level, where fuel rods melt through those vessels and release massive amounts of radioactive material to the outside.
The findings raise a host of questions about the chain of events that led to the damage and have implications for future plant regulation in Japan and beyond. It also suggests that radioactive water has leaked into the reactor's basement in greater-than-believed quantities, likely dealing additional delays to the stricken plant's cleanup.
Tepco's assessment came after workers entered the reactor building this week and fixed a faulty water-level gauge. They determined that the reactor's pressure vessel—the cylindrical steel container that houses the fuel rods—had only about half the level of cooling water as previously thought.
That suggested Reactor No. 1 is likely more severely damaged than Tepco believed and could be leaking large amounts of highly radioactive water. It also shows that the area enclosing the fuel rods wasn't mostly submerged in cooling water, as Tepco had thought, but was instead high and dry.
The finding spurred experts to ask whether leaks or holes could have been caused by the 9-magnitude earthquake that struck Japan's northeastern coast on March 11. Tepco has said the damage at Fukushima Daiichi resulted from the subsequent tsunami, which cut power to the plant's cooling systems, causing reactor temperatures and pressure to rise to damaging levels.
If it turns out that Reactor No. 1's vessels were in fact damaged by the quake, that would lead to a wholesale review of earthquake standards for nuclear plants, warned Ken Nakajima, a professor of nuclear engineering at the Research Reactor Institute, Kyoto University.
In the U.S., 23 reactors have designs similar to the reactors at the Fukushima Daiichi site. Findings about possible damage caused by the earthquake, independent of the tsunami, will be incorporated into an analysis of seismic hazards in the eastern and central U.S. being conducted by NRC, said Scott Burnell, spokesman for the U.S. Nuclear Regulatory Commission.
Some U.S. experts said Tepco simply has acknowledged what U.S. nuclear experts already believed was the case—that severe core damage has occurred which allowed radioactive material to migrate outside the thick steel walls of the pressure vessel. One indication of this breakdown in normal protective barriers has been the high radiation readings in the containment area and reactor building.
Last edited on Thu May 26th, 2011 01:52 pm by sydneyst
|Joined: ||Mon Mar 10th, 2008|
|Location: ||Seattle, USA|
|| Posted: Mon Mar 28th, 2011 05:56 pm||
|Greenpeace Answers Questions About Nuke Worst-Case Outcome
excerpt from Q and A:
What is the worst case scenario? How bad can it be? And how close are we (or did we) come to this?
While it is difficult in this situation to rule out further earthquakes and other factors, at the moment the worst case could arguably be ongoing dramatic overheating in reactor number two where the containment vessel is already breached. This could lead to more radioactive material being released into the environment from the nuclear fuel elements. The spent nuclear fuel pools at all four reactors are exposed to the air and in unit four there are reports that the cooling water is boiling. This Scientific American article has more details.
What harmful effects have already happened? What are the possible long term impacts on soil, animals, agriculture etc.?
It is a disaster but the full extent is unknown. The question is not whether this qualifies as a disaster, it's a question of how big, how many people are effected and how long it will take to get under control. Only then can we start talking about remediation.
Already the authorities have reported radioactive contamination outside the reactors site, at the moment most attention is being focused on two radioactive elements: Iodine-129 and Caesium-137 contamination in particular.
Here is Time magazine on on iodine contamination:
When thyroid cells absorb too much radioactive iodine — either through the air or through contaminated food — it can increase the risk for thyroid cancer, says the American Thyroid Association. Babies and young children are at highest risk as their thyroid glands are most radiation-sensitive. People over 40 are at less risk.
Here is the US Environmental Protection Agency on Caesium-137 contamination:
People may ingest caesium-137 with food and water, or may inhale it as dust. If caesium-137 enters the body, it is distributed fairly uniformly throughout the body's soft tissues, resulting in exposure of those tissues. Slightly higher concentrations of the metal are found in muscle, while slightly lower concentrations are found in bone and fat. Compared to some other radionuclides, caesium-137 remains in the body for a relatively short time. It is eliminated through the urine. Exposure to cesium-137 may also be external (that is, exposure to its gamma radiation from outside the body).
also visit crisis page: http://www.greenpeace.org/usa/en/campaigns/nuclear/Fukushima-nuclear-disaster/
Last edited on Mon Mar 28th, 2011 06:07 pm by sydneyst
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