Posted on 03/21/2011 11:22:58 AM PDT by SeekAndFind
For more than a week the world has watched the escalating crisis at Japan’s Fukushima Daiichi nuclear power plant slide from one catastrophic episode to a seemingly graver one, often upending assurances from the Japanese and adding to the fear and confusion about how it all might end.
Are we on a slow-motion path to a six-reactor meltdown? Or will Fukushima stop short of being the worst nuclear power disaster ever, and squeeze somewhere behind Chernobyl and alongside Three Mile Island in infamy?
While there can be no definitive answers amid a still-unfolding disaster, ProPublica spoke with seven top nuclear engineers and scientists to at least establish some boundaries for the disaster’s potential health and environmental impacts.
The rough consensus: The long-term and most severe effects from radiation at the plant, where four of six reactors are in crisis [1] and hundreds of tons of spent fuel is a risk, will be largely contained to the area around the plant, affect a relatively limited population and will likely not spread outside Japan.
Even in the worst case, the crisis should not lead to the level of health and environmental destruction that followed the 1986 Chernobyl disaster [2], the experts say. Unlike Chernobyl, the potential for an explosion large enough to carry contaminants high into the atmosphere and to far away areas appears remote.
A complete loss of control of the Fukushima plant, followed by total meltdowns at multiple reactors and fires in the spent fuel [3] stocks, would be an extraordinary development leading to very high radioactive emissions and contamination of the surrounding landscape that could last for decades.
Such a scenario [4] is now less probable, in part because the fuel rods in the reactors are expected to continue to cool each day. Even a sustained fire in the spent fuel that sits on the top level of the reactors is unlikely to result in “criticality,” or a new nuclear chain reaction and reheating of that spent fuel.
The New York Times reported [5] that Japanese officials remain concerned that criticality is possible in some of the troubled reactors or spent fuel. But even if it were to happen, the process can eventually be interrupted.
Experts interviewed by ProPublica said that even if a meltdown scenario unfolded unabated, the contamination would likely remain localized and would not affect a large population because evacuations have already been ordered. There remains uncertainty about whether worst-case contamination could reach as far as Tokyo, about 150 miles from the Fukushima plant, but few believe there is any chance of dangerous levels of contamination spreading offshore.
“The events that have happened, and the speculation for what could happen is not on the same scale as the release from Chernobyl,” said Peter Caracappa, a nuclear engineer at Rensselaer Polytechnic Institute, in Troy, N.Y. “Based on all the available information, the risk to any of the places far from the plant … would be too small to calculate with any confidence. We’re not talking intercontinental effects.”
Odds of Total Meltdown Diminish
There are two aspects to the ongoing risk at the Fukushima Daiichi [6] plant in Japan: the fate of the reactors themselves, and the condition of the millions of pounds of spent fuel rods stored in open pools atop the reactor structures.
A total meltdown would occur if the fuel rods inside a reactor continue to overheat and break down, spilling the uranium or uranium-plutonium pellets inside them into a heap on the reactor floor. The core of the reactor containing the fuel rods is encased in a steel vessel that is then surrounded by a huge reinforced-concrete containment structure.
As the fuel consolidates, there is less space for cooling water to circulate among the pellets, which can heat into a molten substance. The hotter that molten slurry gets, the greater the possibility that it can burn through the fortified steel containment vessel meant to isolate whatever happens inside the reactor.
A breach of the reactor vessel would normally be the most critical danger. If a meltdown did happen, experts say the fuel could leak out and spread through cracks in the concrete containment, sear through a second metal liner and then flow out in the open air toward the perimeter of the plant.
“That’s the event that changes this situation from a horrible situation to a nightmare of unprecedented proportion,” said Kenneth Bergeron, a physicist who worked on nuclear reactor accident simulations at Sandia National Laboratories.
Officials have said they believe there has been a partial meltdown at least two of the four troubled reactors. But it has now been seven days since the reactors were shut down following a 9.0 earthquake that rocked the islands of Japan and triggered the devastating tsunami that swamped the power plant.
Tokyo Electric Power Company, which runs the plant, continues to work to control the temperature inside the reactors and has been injecting sea water laced with boron, which short-circuits the nuclear reaction, into the reactors to maintain cooling. Experts believe that by now, the reactors should have cooled substantially. And with each day that passes, they say, the temperature drops further and the possibility of a full meltdown diminishes.
“That doesn’t seem very likely now,” said Louis Lanese, a nuclear engineer who worked on the Three Mile Island crisis in 1979 and now is a partner with Panlyon Technologies, a nuclear energy-services firm in Flanders, N.J. “It’s cooled down. They have water over the core. Every day makes the consequences a little bit better.”
For those cores to melt now, Lanese said, there would have to be a complete loss of water, and fuel rods would have to sit for some time – days or even weeks. Even then, he said, “I don’t know if there is enough energy in that fuel to even get out of the reactor vessel.”
Spent Fuel Is Less Potent
The greater risk may now lie with the spent fuel sitting in storage pools on top of the reactors. Those pools contain very large quantities of old fuel, at least some of which still contains significant amounts of uranium, and they are not in containment like the reactor cores.
The spent fuel rods generate residual heat and must be cooled by water, but water levels have been precariously low in at least one pool – Unit 3 – and may have dried up altogether in the pool at Unit 4. The danger is that the zirconium cladding that contains the fuel pellets, when exposed to the air, can catch fire and burn intensely and leave the fuel pellets exposed.
Twice, reports have emerged of smoke and a possible fire in the pool atop Unit 4, but it has been difficult to confirm exactly what is taking place. Those reports have also stoked concerns that spent fuel could also melt down, and because it is not contained, release large amounts of radioactivity.
But much of the most dangerous material has already been spent, or has begun to degrade. Lanese said that if the cooling water has already evaporated from the pool in Unit 4 without a significant fire erupting, it is a sign that convection cooling from exposure to the air is enough to keep the rods stable.
Explosions remain a risk at the site. When nuclear fuel is hot enough, it can split the water molecules, releasing hydrogen, a flammable gas. Should spent fuel become molten, it could melt through the floor of the pool. When doused again with water, it could create hydrogen and an explosion that released radioactive contaminants. If reactor fuel were to melt down, it could fall into an area that contains water.
There have already been three hydrogen explosions at the Fukushima Daiichi plant – a gas buildup in the reactor buildings of Units 1, 2 and 3 destroyed the exterior walls. But unlike Chernobyl, the worst explosion believed possible at the Japanese plant would not push tens of thousands of feet into the atmosphere and would be a momentary event.
That explosive power is the key difference.
In Chernobyl [7], the reactor burst in a fiery ball while running at full capacity. The Chernobyl plant was also an entirely different design. It did not have a containment vessel to hold the fuel inside, and the core of the reactor contained graphite. The graphite burned like coal and sustained a roaring fire for two weeks, pushing radioactive particles miles into the atmosphere. That is how some of Chernobyl’s radioactive fallout ended up in Northern Europe.
Radiation Risk Mostly Local
If there is open-air exposure of molten fuel at Fukushima Daiichi, there does not appear to be a mechanism for carrying large quantities of radioactive byproducts over wide areas or great distances. A fire or hydrogen blast could carry contaminants into the lower atmosphere, but only for a relatively short way, scientists say.
The exposed fuel rods or molten slurry emit large amounts of radiation and present a serious health risk to workers inside the plant. But the radiation itself doesn’t extend very far. To affect people outside the Fukushima facility, radioactive material has to be spread around.
Long-term radiation risks result from people swallowing or breathing in tiny particles that continue to be radioactive inside the human body and continue to emit radiation as they break down over time. The radionuclides of most concern include cesium 137 – which has been detected around the Fukushima Daiichi plant – as well as strontium 90 and plutonium 239.
“A fuel melt doesn’t necessarily lead to a big disaster, any more than what we have,” said Gilbert Brown, a professor in the nuclear engineering program at the University of Massachussetts in Lowell. “Even if it’s a fuel melt, you have to have a mechanism to get all that radiation to people, to get hurt by it.”
Bergeron estimates that even after the worst kind of explosion at the Fukushima Daiichi plant, contamination might be detectable 200 miles away, with the most serious contamination within a 100-mile radius.
“That, although striking and horrible, is something described as manageable,” Bergeron said.
An evacuation has cleared out part of the area around the plant. Experts say the largest environmental impact, outside the facility, is potential contamination of the surrounding landscape. Fallout could affect groundwater and surface water supplies, as well as render much of the nearby farmland too dangerous for use.
Some of that environmental contamination can be cleaned up, but agriculture and food supplies could be affected for decades. Human health exposure can be limited by both evacuations and other precautions.
“I don’t think we are going to kill a lot of people,” said Victor Gilinsky, a former commissioner of the U.S. Nuclear Regulatory Commission and a former head of the physical sciences department at the Rand Corporation. “But you could have a tremendous amount of land contamination. Depending on the half life, it could be many time more than 30 years before you could go there.”
Much uncertainty remains about what will happen next at the Fukushima Daiichi plant. Experts caution that if there has been any lesson thus far, it is that assumptions can be easily proved wrong. But with every day that Japanese responders hold wholesale deterioration at bay – however tenuously – the health and environmental impacts should be less severe.
“I’ve worked almost 40 years in this business to keep anything even remotely like this from happening,” said Lanese. “But strange as it is, these situations tell me that these plants have even more resilience than I had expected.
“This is what an 9.0 earthquake and an eight-foot Tsunami does?” he asked. “It’s unprecedented. And those nuclear reactors are still there and still hanging in there.”
-- Michael Grabell and Nick Kusnetz of ProPublica contributed to this report.
Worse than TMI, but not NEARLY as bad as Chernobyl.
Much closer to TMI than to Chernobyl, in other words.
When all is said and done, this was a huge story about little.
The real tragedy is the quake and the tsunami, but apparently “reality” isn’t good enough for the lame stream media,
If this turns out to be true, this will deeply sadden FR’s resident Drama Queens.
The MSM sure is pushing the worst case views about radiation sickness and contamination, and radiation clouds and all that.
The enviro liberals will not let this crisis go to waste. They will use it to clamp down on any further nuclear expansion.
They'll just move on to the next crisis as the MSM leads them.
The gullibility around here is quite thick these days.
Is your count down clock started yet?
One of the worst things about the nuclear problem at Fukishima is that it distracts from the horrific toll from the earthquake and tsunami and certainly hampered relief efforts.
Well i don´t know but the radiation in tokio has raised from 14 cpm (yesterday) to 25 cpm right now.
And the wetter forecast says that in the next hours the wind will change and blows straight to tokio + rain is expected.
But as said 25 cpm is not much (for example the US starts warning when 126 cpm are reached).
But the levels will definitely raise when it starts to rain in the next hours.
btw. here is a live geiger counter from Tokio.
http://www.ustream.tv/channel/%E3%82%AC%E3%82%A4%E3%82%AC%E3%83%BC%E3%82%AB%E3%82%A6%E3%83%B3%E3%82%BF
won’t staying indoors and sealing the windows keep people from the worst of it?
They'll just have to get over it.
Is your count down clock started yet?
Not yet...I'll wait until I'm at about 30 days. Or at least until I have my flight itinerary. :)
I am very much looking forward to being home for a while.
On April 27, 1953, at the Rensselaer Polytechnic Institute in Troy, New York, Professor Herbert Clark and his students entered a metal shack that served as a laboratory for their radiochemistry class. All the Geiger counters were registering radiation many times the normal rate. The students carried the radiation measuring devices to areas on campus noting the high readings. Assuming the previous night's heavy rains had washed some atmospheric radiation onto the campus, Dr. Clark contacted John Harley, an associate at the U.S. Atomic Energy Commission's Health and Safety office in New York City. Dr. Clark summarized the details of campus measurements from his class. Gamma radiation on the ground was ten to five hundred times normal; beta ray radiation was even higher and hot spots of even high readings were found in rainspouts and puddles.
Later that day, Dr. Clark learned there had been an atomic bomb test conducted by the AEC in the Nevada desert two days earlier. The mushroom cloud had reached 40,000 feet into the atmosphere then drifted 2,300 miles across the United States in a northeasterly direction. It passed over Utah, Colorado, Kansas, Missouri, Illinois, Indiana, Ohio and Pennsylvania before being caught up in a storm that dropped rain on upstate New York, southern Vermont and parts of Massachusetts.
Dr. Clark's students took their geiger counters on the road and began measuring the radioactivity on the ground, roof shingles and vegetation wherever they stopped in Albany, Saratoga Springs, and Schenectady, New York. Typical readings were twenty to one hundred times higher than normal. This has become known as "the Troy incident."
Surprisingly, they found that it was comparable to that reported the previous year by the AEC’s New York Laboratory for fallout in desert areas only 200 to 500 miles from the point of detonation at the Nevada test site itself.
For what it’s worth;
http://www.freerepublic.com/focus/news/2691725/posts?page=46#46
Days to receive dose for increase cancer risk of 1 in a 1,000
432 (at 100 CPM)
86 (at 500 CPM)
28 (at 1,500 CPM)
4 (at 10,000 CPM)
Days for earliest onset of radiation sickness
25,937 (at 100 CPM)
5,187 (at 500 CPM)
1,729 (at 1,500 CPM)
259 (at 10,000 CPM)
Well at least this will protect you from a dirrect radioactive contamination (if this happens because its not a given fact that this will definitely happen).
But for example some elements like caesium 137 haf a “half life” of 30 years. So you won´t escape this one once it get into the ground.
(Yay only about 5 years here then half of the caesium we got (1200 km away from tschernobyl “but it rained heavily when the radioactive clouds passed by”) will go away ;-)
I wonder if the radiation at the plant itsself is any indication of what will spread. In other words how can radiation be worse than anywhere but at the plant itself?? If any want to know what actual radiation levels are at the plant check these links;
http://www.tepco.co.jp/en/press/corp-com/release/index-e.html
http://www.nisa.meti.go.jp/english/
Watch these sites for current radiation levels which right now are around 500 micro Sv or .5 m/Sv.
Here’s the latest information about the radiation levels at a location inside the plant itself; http://www.nisa.meti.go.jp/english/files/en20110321-1.pdf
Note that Iodine-131 has a half-life of 8.02 days meaning it’s radiation hazard will diminsh very quickly.
Interesting and good catch.
The difference between atomic bomb testing and Fukushima Daiichi is Fukushima Daiichi did not punch a bunch of radiation into the upper atmosphere - it’s not up there to come down in the form of rain.
Just for example this maps shows some of the radiation in the USA right now. You will see in some places (and this radiotion exists since years) is even higher than in tokio right now. So nothing to worry at the moment. Btw. all the yellow numbers are cpm
If the Ruskies dropped a nuke on Dallas and you lived in Fort Worth, I would say it would be a good plan. But for this, it would have meant you missed being outdoors on such a nice day. And what a waste of tape.
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