From the University of California – San Diego via Eurekalert
First quantitative measure of radiation leaked from Fukushima reactor
Observations of radioactive sulfur that formed when seawater was used to cool reactors and spent fuel ponds reveal the amount of radiation leaked from damaged fuel
Atmospheric chemists at the University of California, San Diego, report the first quantitative measurement of the amount of radiation leaked from the damaged nuclear reactor in Fukushima, Japan, following the devastating earthquake and tsunami earlier this year.
Their estimate, reported this week in the early, online edition of the Proceedings of the National Academy of Sciences, is based on a signal sent across the Pacific Ocean when operators of the damaged reactor had to resort to cooling overheated fuel with seawater.
“In any disaster, there’s always a lot to be learned by analysis of what happened,” said senior author Mark Thiemens, Dean of the Division of Physical Sciences at UC San Diego. “We were able to say how many neutrons were leaking out of that core when it was exposed.”
On March 28, 2011, 15 days after operators began pumping seawater into the damaged reactors and pools holding spent fuel, Thiemens’ group observed an unprecedented spike in the amount of radioactive sulfur in the air in La Jolla, California. They recognized that the signal came from the crippled power plant.
Neutrons and other products of the nuclear reaction leak from fuel rods when they melt. Seawater pumped into the reactor absorbed those neutrons, which collided with chloride ions in the saltwater. Each collision knocked a proton out of the nucleus of a chloride atom, transforming the atom to a radioactive form of sulfur.
When the water hit the hot reactors, nearly all of it vaporized into steam. To prevent explosions of the accumulating hydrogen, operators vented the steam, along with the radioactive sulfur, into the atmosphere.
In air, sulfur reacts with oxygen to form sulfur dioxide gas and then sulfate particles. Both blew across the Pacific Ocean on prevailing westerly winds to an instrument at the end of the pier at UC San Diego’s Scripps Institution of Oceanography where Thiemens’ group continuously monitors atmospheric sulfur.
Using a model based on NOAA’s observations of atmospheric conditions the team determined the path air took on its way to the pier over the preceding 10 days and found that it led back to Fukushima.
Then they calculated how much radiation must have been released. “You know how much seawater they used, how far neutrons will penetrate into the seawater and the size of the chloride ion. From that you can calculate how many neutrons must have reacted with chlorine to make radioactive sulfur,” said Antra Priyadarshi, a post-doctoral researcher in Thiemens’ lab and first author of the paper.
After accounting for losses along the way as the sulfate particles fell into the ocean, decayed, or eddied away from the stream of air heading toward California, the researchers calculated that 400 billion neutrons were released per square meter surface of the cooling pools, between March 13, when the seawater pumping operation began, and March 20, 2011.
The trace levels of radiation that reached the California coast never posed a threat to human health. “Although the spike that we measured was very high compared to background levels of radioactive sulfur, the absolute amount of radiation that reached California was small. The levels we recorded aren’t a concern for human health. In fact, it took sensitive instruments, measuring radioactive decay for hours after lengthy collection of the particles, to precisely measure the amount of radiation,” Thiemens said.
Concentrations a kilometer or so above the ocean near Fukushima must have been about 365 times higher than natural levels to account for the levels they observed in California.
The radioactive sulfur that Thiemens and his team observed must have been produced by partially melted nuclear fuel in the reactors or storage ponds. Although cosmic rays can produce radioactive sulfur in the upper atmosphere, that rarely mixes down into the layer of air just above the ocean, where these measurements were made.
Over a four day period ending on March 28th, they measured 1501 atoms of radioactive sulfur in sulfate particles per cubic meter of air, the highest they’ve ever seen in more than two years of recordings at the site.
Even intrusions from the stratosphere – rare events that bring naturally produced radioactive sulfur toward the Earth’s surface – have produced spikes of only 950 atoms per cubic meter of air at this site.
The nuclear reaction within the cooling seawater marked sulfur that originated in a specific place for a discrete period of time. That allowed researchers to time the transformation of sulfur to sulfur dioxide gas and sulfate particles, and measure their transport across the ocean, both important factors for understanding how sulfate pollutants contribute to climate change.
“We’ve really used the injection of a radioactive element to an environment to be a tracer of a very important process in nature for which there are some big gaps in understanding,” Thiemens said.
The event also created a pulse of labeled sulfur that can be traced in the streams and soils in Japan, to better understand how this element cycles through the environment, work that Thiemens and colleagues in Japan have already begun.
###
I’ve located what should have been in the press release, and added the graph above too:
Reference
- Priyadarshi, A. , Dominguez, G. & Thiemens, M. H. Proc. Natl Acad. Sci. USA http://www.pnas.org/content/early/2011/08/11/1109449108.abstract (2011).
Full paper: http://www.pnas.org/content/early/2011/08/11/1109449108.full.pdf+html
Data Supplement:
NOTE: I originally published this at 1PM today, but Willis also published a story right about the same time, so I put this one on hold after it had been up for two minutes in deference to Willis new article since this could keep a few hours. So if anybody wonders why there was a difference in Tweet and Facebook timings, and the story, that’s why. – Anthony
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
Why is spent nuclear fuel stored in ponds next to the reactor? Why not just reprocess the fuel and reuse it like France does.
As if it matters but is an interesting point
A PNAS article with a big press release?
hmmm…..
http://latimesblogs.latimes.com/nationnow/2011/08/radioactive-isotope-detected.html
As far as I understand, Japan does reprocess their spent nuclear fuel. However, all nuclear fuel must be stored in a pool near the reactor building for quite a time before the radioactivity has decayed enough to make for safer handling and transport. I think the wait time is about 5 years. Mostly because the decay heat being produced by the fuel would require the transport casks to have cooling. The casks used to transport the fuel are made of very thick concrete. They are impervious to external damage. They can be hit by a locomotive, burned for hours and submerged with no leakage of radiation. A cooling system on the casks would make them extremely vulnerable.
When a refueling a reactor, the fuel must always be under water. In a BWR, like Fukushima, the concrete lid is removed from above the reactor vessel, then the reactor vessel lid is removed. Finally, the area above is flooded with water to match the level of the fuel pool and then fuel can be safely moved. It’s very simple so the fuel can go directly from the reactor to the pool. In a PWR where I worked, the fuel pool is outside of the containment building. The reactor vessel is flooded and a tunnel connects the fuel pool to the reactor vessel. There’s a carriage assembly that shuttles the fuel back & forth. It’s much more complicated. I can completely understand the point of keeping the system as simple as possible.
From what I can tell, the spent fuel pools were probably not the source of any significant radiation. Whether or not the fuel was intact, the neutrons would still activate the sea water. Course throughout the event, I began to wonder if a better course of action would have been to completely cease cooling the reactor vessels with sea water. I figured the cores were pretty early on molten lumps which is not conducive to efficient heat transfer. And, that the amount of sea water being injected was probably inadequate to flood the core. I would guess that most of the seawater was flashing to steam as it hit the hot reactor vessel thus helping the radioactive elements to be lifted into the atmosphere. There was no way they were going to save the reactors, so their duty became to protect the health and safety of the public. Perhaps the safer approach would have been to hold off on cooling water injection until a few days later into the accident when the decay heat would have been significantly less. It will be interesting to see how the reactor vessels held up to that extreme damage. I know this is an extremely bizarre idea, but it certainly should be considered as a means to reduce contamination and exposure to the public.
If true (not saying it is or not) this implies very bad things.
Neutron radiation is only released in large quantities during ACTIVE nuclear fission, this implies that there was an extended uncontrolled nuclear criticality ongoing during the seawater cooling. This is a far worse accident (extended uncontrolled criticality) than even the meltdowns we know happen (which is even further cause for skepticism about the report).
@tarpon Even if you go with nuclear fuel reprocessing, you still need to store fresh spent fuel in a water pool, it’s just to darn hot (thermally and radioactively) to work with until the short-lived fission products decay (a few years, not decades).
That would imply that there was still fission occurring. Everything I have read says fission stopped when the reactor was shut down during the quake. It isn’t likely that “fuel melt” would have been the cause of this because that would have continued, there would be nothing to stop that fission reaction short of running out of fissionable material. The graph would not show a sharp spike and then a decay like that, it would show a spike up and remain there if there was a fission reaction occurring from damaged fuel. Steam was being vented more or less continually. Sea water was not, to the best of my knowledge, injected while there was a fission reaction still occurring. Yes, there might have been some delayed neutrons but those should have been emitted long before sea water was injected.
Spontaneous fission from accumulated Pu240?
Spacing of the rods in the ponds is carefully regulated. Did the earthquake disturb that? The fresh water in the ponds was polluted with seawater altering the effective spacing, regardless of what the earthquake may have done. It seems it was all very much at risk from the time it existed only on paper until the day the earth shook. In hindsight the Fukushima reactors should never have been built.
And the accuracy of their conclusions is …. +/- what?
I do not wish to stop people from thinking, but you have the following only-slightly knowns:
1) the amount of seawater pumped in,
2) the ratio of sulphur atoms rising into the general atmospheric circulation vs that falling in the immediate area,
3) the dilution ratio for the contaminated air heading towards the States,
4) the drop-out rate,
5) the dilution through “eddies” along the way,
6) the dilution effect of dropping the contaminated air to the sensor altitude,
67 the measurement precision,
8) the accuracy of the calculation of initial sulphur atoms created under the actual chaotic condition of the semi-open reactor.
Bet the result has 3 significant figures in it, though. Good to get a grant going, including fieldwork in Japan. Not that this is a bad thing, but Mann has taught us a thing or two about limits to knowledge, right?
Oh there is even more than that. You have to take into account the salinity of the water on those particular days and take into account that we are talking about three reactors and three spend fuel pools so those numbers have to be spread across six different sources. So it isn’t like those neutron counts would have happened at one specific source. That is the total count (they estimate) of neutrons across all potential sources. Still, it seems “fishy” to me.
Having moved my fair share of fuel (new and spent) these guys are so full of it. Uranium, plutonium and a myriad of fission products naturally decay and release neutrons. In the SFP (spent fuel pool) each spot where a fuel rod assembly is stored (yes under water) has a lining of boron impregnated plate. Boron absorbs neutrons. If the SFP or the core was flooded with seawater (at least 1 reactor was undergoing a refueling outage so the core was not enclosed in the vessel) seawater would be in betweeen the boron plates and fuel ass’y. Thereby exposed to neutrons. Fuel gets reused in later cycles and is stored on site for that purpose as well. 400 billion neutrons…whoa…they could dance with several angles on a pinhead.
I like this attitude:
““We’ve really used the injection of a radioactive element to an environment to be a tracer of a very important process in nature for which there are some big gaps in understanding,” Thiemens said.”
That’s insanity. They’re not being precise enough. My calculations are closer to 392,644,917,606 +- 10.
For a little while there, it was “in style” to be “detecting” radiation from Fukushima. I wonder how these same people would have been handling the open-air detonation of nuclear bombs, like the Bikini tests, or the fallout from Hanford (near me).
Unfortunately, Geiger tubes (which we need where I work) have been in critically short supply since March, while a large number of people suddenly needed to try to measure Fukushima. Sad.
“The levels we recorded aren’t a concern for human health…”
How many cells needs to be initially affected to lay the foundation of cancer? How many radioactive particles does it take to be unsafe? Sulfur is a key component in most human proteins, so even small molecules or particles are readily absorbed by the body. Once absorbed, the radioactive sulfur will keep radiating the body from the inside, and in a localized fashion – thus increasing the chance of a cancer or other illness developing.
35S will decay to 35Cl emitting a beta particle, and has a half life is 87 days, so it will basically be all gone in approximately 3 years…
…about 365 times higher…
about? ROFL
Having worked with radioactive sulphur, admittedly some forty years ago and for other reasons, I cannot think of a more unreliable measurement technique. It is highly reactive and just too easily adsorbed to the point that it was almost impossible to ensure that even carefully calibrated supplies in storage cylinders were not wildly out within hours of filling let alone days. Even calibration at the cylinder head as supplies were drawn from it could not be relied on as the piping and reaction chamber itself adsorbed the stuff and even using calibration samplers side by side with the test piece did not provide adequate control. The only thing i know of with similar or indeed worse problems is eth ox: oddly the subject of your next post.
I do not doubt the instrument readings merely what relevance, if any, they have to the nuclear release at the site.
Kindest Regards
The bogey man of radiation propagated by the anti nuke mob in the sixties and seventies ain’t necessarily so. In naturally occurring high radiation areas people tend to live healthier and longer lives.
If the radiation is so bad and so long lived there should be not a soul left alive in Japan after two big dirty bombs. People in Japan tend to be healthy and long lived.
Many chemical pollutants are more insidious and do not have a half life. Remember the fifties and sixties with bombs going of every where like fire crackers, we must be all dead or mutant.
Feeble nonsense.
Thor, unless you are in a lead lined safe about ten feet thick, in deep intergalactic space, you are going to be exposed to radiation. Cancer happens in the human body quite frequently, it’s just that your immune system stops it for the vast majority of the time before it can take hold.
Please just go eat a banana while leaning up against a granite countertop and plan your airplane flight. Sure, those three things expose you to radiation, but they aren’t even close to dangerous. Perspective man!
@Patrick
Outside the Earths magenetic field there is no protection whatsoever from cosmic radiation and particles carried out of the solar system by the solar wind. You are safer on earth, especially in a bunker wich is located somewhere underground.
Still you won’t be proctected from the ±4400 Bq of radioactive decay per seccond wich is produced in your own body.
Over a four day period ending on March 28th, they measured 1501 atoms of radioactive sulfur in sulfate particles per cubic meter of air, the highest they’ve ever seen in more than two years of recordings at the site.
crosspatch says:
August 15, 2011 at 5:35 pm
the researchers calculated that 400 billion neutrons were released per square meter surface of the cooling pools
That would imply that there was still fission occurring. Everything I have read says fission stopped when the reactor was shut down during the quake. It isn’t likely that “fuel melt” would have been the cause of this because that would have continued, there would be nothing to stop that fission reaction short of running out of fissionable material. The graph would not show a sharp spike and then a decay like that, it would show a spike up and remain there if there was a fission reaction occurring from damaged fuel.
================ah but if ypou limit the time you collect data you can manage to sort of…hide the ONGOING problems…see the FOUR day limit..above.
There are some really wild comments on here today – seems like we still can’t get over the fear of anything radioactive!
Thanks to those people who have pointed out that neutrons are produced all the time from fissile material and that these levels of radioactive elements are meaningless in terms of human health.
Nice comments from people who actually know something about re-fuelling reactors. The reason behind the cooling being in the reactor building and up on the 4th floor had not been explained (to me) before. Remember these were 40 year old reactors so more modern designs have changed this with gravity-fed cooling systems, although probably with more complicated re-fuelling procedures.
Interesting arguments from Lisa K as well about cooling with water (producing steam) verses letting them cool on their own. I guess the worry (at the time) was the potential for exposure of the fuel itself (with release of heavier elements) if they let the reactor core and the the fuels rods in the cooling ponds melt completely. It is questions and discussions like this that will inform the next round of reactor design and emergency procedures.
Bottom line is still that these reactors stood up to an earthquake and tsunami well above their design specifications – even after a lifetime of producing electricity. It is about time we gave the nuclear industry some credit for the job they have done (and are doing) instead of the knee-jerk reaction of ‘close it down’ every time time a nuclear plant is in the news.
I’m a little confused by Some Guy and others. NEUTRON radiation is natural radiation everyone is exposed to from rocks, etc.. When active fission is occurring, you are getting PROTON radiation, which is quite different as it means the strong force has been broken in a nucleus of an atom. Neutrons come off of atoms all the time, you don’t want a lot of exposure to it, but you can handle quite a bit of it over your lifetime. Proton sources are quite bad for human life, avoid them.
So, as far as I know it the fact that NEUTRONS were being released in large numbers is not indicative of active fission occurring when seawater was being used to cool it. This is a masters in physics speaking here, so if there’s someone who works in nuclear power who knows better, feel free to correct me.
I too, was wondering about where the activating neutrons came from. I consulted one of our nuclear engineers and he said, just as I remembered and others have indicated here, that the thermal neutron flux in a scrammed reactor goes to zero. There are then “delayed” neutrons that result from fission product decays, but they have a very small population and half lives measured in seconds. The first sea water was not admitted to the reactors until 2 days after the tsunami, leaving plenty of time for the delayed neutron population to decay off. I am having trouble reconciling the results of the study and this information.
And BTW, Japan does recycle their fuel, by sending it to France for reprocessing. Unit 3 at Fukushima had some of this reprocessed fuel, called mixed oxide or MOX.
400 billion neutrons per square meter in 7 days is 100 thousand or 100 million events per second per square meter, depending on whether the billion is a thousand million or a million million. Even the high number means that only a tiny fraction of the core has been exposed, and I’m talking grammes here, not kilogrammes.
“Quantitative?” – maybe.
Indirect and fraught with an incredible amount of approximations and assumptions – certainly.
‘Measuring’ the radioactivity released at Fukushima via sulfate isotope measurements thousands of miles downwind, depending on ocean currents, winds, intervening atmospheric conditions, etc. – is a lot like measuring the global CO2 emissions with a thermometer.
Ed, in America, Billion means 1,000,000,000. The million-million isn’t used here.
Also, don’t forget, these are emission monitoring people. They are used to back-tracing things on this order of magnitude. How else would Texas power plants contribute to pollution in one county of Illinois but not in Oklahoma, Kansas, Missouri, or Nebraska (for those from elsewhere, those are the states in between).
Finally, look at their concentration. 1500 molecules per cubic meter of gas? That is a detection limit of 1 in 100 hextillion. I thought that it was bad when they were detecting dioxin emissions in the parts per quintillion, but this is just plumb ridiculous.