Fukushima and Cesium
Fukushima and Cesium
(A summary of the facts concerning the radioactive Cesium at the Fukushima Daiichi nuclear station. The synopsis comes from postings in the Fukushima Updates and Commentary blogs of this website. This shows that the Cesium risks have been exaggerated and much contrary “evidence” has been intentionally presented out of context.)
a. How Hazardous is Cesium-137?
Analysis of the decontaminated waters at F. Daiichi show a Cesium concentration of roughly 2.5 Becquerels per cubic centimeter in waste storage tanks. There is more than 400,000 tons of this wastewater in large tanks which cover a large portion of the F. Daiichi station’s property. In addition, there are more than 3,000 spent fuel bundles in storage at Fukushima Daiichi. Each of these used fuel bundles contain a numerically large volume of radioactive Cesium isotopes, which is one of the by-products of fissioning Uranium: specifically the isotopes Cesium-137 (Cs-137) and Cs-134. We will take a rational look at the risk posed by radioactive Cesium in part 1, and the risk with F. Daiichi’s spent fuel in part 2.
The sum-total of Fukushima’s Cesium has been touted by antinuclear extremists to be an apocalyptic nuclear accident waiting to happen, resulting in widespread fears. But one question is routinely avoided by both nuclear critics and the Press…just how hazardous is radioactive Cesium?
Cesium is often touted to be a “bone-seeker” by nuclear critics and some of the world’s Press. Allegedly, it stays in the skeleton for long periods of time, eventually causing bone cancer. However, there is no actual evidence to support the “bone-seeker” notion relative to Cesium itself. In most cases, the bone-seeking concept comes from the occasionally-posted misunderstanding that Cesium is chemically similar to Calcium - the major element in our bones. This is simply not true. A quick look at Chemistry’s Periodic Chart of the Elements shows it is not in group II with Calcium, but is actually located in group I with Sodium. We also find Potassium in the same chemical group with Sodium and Cesium. All three are thereby chemically similar. Their properties are different from group II elements.
At this point, it should be mentioned that another of the radioactive elements found in reactor fission products is Strontium (Sr-90). Strontium is in the same chemical group II as Calcium, with similar bio-chemical properties. Sr-90 can be called a “bone seeker”. It seems Strontium and Cesium have been confused relative to their properties.
Back to the topic at hand… the properties of Cesium and the other group I elements. Our bodies cannot store Sodium and Potassium, which is why we must continually keep replenishing these necessary nutritional minerals through the foods we eat. All ingested elements have what’s called a “biological half-life”, which is used to estimate how long they will stay in our systems before being removed along with physiological wastes. For Potassium, the half-life is about thirty days. That means half of the Potassium we consume today will be gone in a month. Half of the remainder will be purged after two months…and so on. The rule-of-thumb is that after 10 half-lives (300 days, in the case of Potassium), today’s ingested volume will be gone from the body. Of course, Potassium is continually being taken-in via our foods, so there is almost always a constant amount of the nutritional element in our bodies.
The biological processing of Cesium through our system is similar to what happens with K-40, but it has a biological half-life of about 100 days. The Cesium ingested today will be totally purged after about 2.5 years (~1,000 days) by natural bodily processes. The biological half-life can be reduced through medication (e.g. Prussian Blue) to about 30 days, just like Potassium. Thus, a comparison between reactor Cesium and Potassium is bio-chemically strong…not identical, but strong.
However, some people might say that Potassium isn’t as radioactive as reactor Cesium, so no realistic comparison can be made. This is another misconception. Potassium in our food necessarily contains isotope 40 (K-40) which is naturally radioactive. It doesn’t come from nuclear power plants: it is not a fission by-product. K-40 is produced in the cores of stars and dispersed throughout the galaxy by supernovae. Its half-life is a little over a billion years, which means it’s will be around for a very long time.
But, how much radioactivity does K-40 actually produce since it’s only about .01% of all the Potassium found in nature? Well, there’s a lot of Potassium in the world…one of the most abundant non-gaseous elements on the Earth’s surface. It’s found everywhere in the soils of the world and is part of the earth-grown foods we eat; broccoli, peas, beans, potatoes, some fruit (like bananas), and nuts, just to name a few. It’s safe to say that we all ingest some K-40 every day, have ingested it since birth, and will continue to do so for the rest of our lives. Ingestion of K-40 is unavoidable. But, how radioactive does K-40 make the soil? Dirt typically contains ~10 Becquerels per kilogram (1 Becquerel = 1 radioactive emission per second) and tends to concentrate in plants as they grow. Because we are constantly ingesting K-40 in our food, it is an ever-present naturally-occurring radioactive constituent inside everyone’s bodies. How radioactive does it make each of us? At any given moment there are about 3,400 Becquerels of K-40 inside each person on our planet; 3,400 internal radioactive emissions every second.
Some might further object that K-40 and reactor Cesium produce different kinds of radiation. That’s somewhat true. To begin, both emit Beta (β) radiation. A β is a high-speed electron. When it comes in contact with anything (even air) the β quickly gets absorbed into the outer electron shell of another atom, ionizing the atom. A β cannot penetrate very well…most βs are totally absorbed by a thin piece of tin foil. It happens that fast. It should be noted that high-energy βs need a few millimeters of aluminum to be attenuated, but these energy levels are not typical of what we find with K-40 and reactor Cesium: both are much less energetic and thus have less penetrating ability. Your outer layers of skin (which are dead) are an excellent β radiation shield with energy levels below about 1.5 MeV (Million electron Volts), which is the case with reactor Cesium βs. If βs are released inside living tissue, the ionization occurs in the tissue-itself and can cause localized harm, nearly all of which is counteracted by cellular repair mechanisms. The energy level of the Cs-137 β is 1.17 MeV, Cs-134 at 0.7 MeV, while the β from K-40 is actually a bit higher than both at 1.31 MeV. But, for all intents and purposes the three are relatively equal energy-wise with relatively weak penetrating properties.
One difference between the two is that K-40 also emits a Gamma ray of 1.46 MeV about 11% of the time: Cs-137 emits β and a much-weaker Gamma than K-40 at about 0.67 MeV. Cs-134 a β plus occasionally a Gamma at 0.67 MeV. Does this mean K-40 is more hazardous than reactor Cesium? No. Here’s why…a β is actually a high speed, sub-atomic particle ejected from the nucleus of a radioactive atom. A neutron in the nucleus suddenly becomes unstable, expunges the high energy electron (β) and turns into a proton. When this happens to a Cs-137 nucleus, it is no longer Cesium. It instantly becomes Barium-137.
Ba-137 is about 12% of all the naturally-occurring Barium found on our planet, and it is not typically radioactive. However, if it has been freshly formed by Cs-137 β-decay, then it is briefly radioactive. It literally has too much energy in the nucleus to be stable and must give off some of it in the form of Gamma radiation. It releases the Gamma at an energy level of 0.7 MeV and loses the radioactive potential. It only happens once and cannot happen a second time to the same atom. Ba-137 has a radioactive half-life of 2.6 minutes, so it will be gone no more than 26 minutes after it is formed, with a 50% chance of it being gone 2.6 minutes after it forms. It doesn’t stick around very long.
Barium is a group II element…chemically similar to Calcium. Thus, it can be called a “bone-seeker”, per se. However, it typically takes longer than 26 minutes for radioactive Ba-137 spawned by Cs-137 to “find” some bone in our systems. Bodily-retained Cesium tends to concentrate in muscle tissue, which is why it has a longer biological half-life than Potassium. Thus, the Ba-137 is released into muscle and not bone. Although biologically lodged in muscle when it is transmuted from Cs-137, there is a small but finite probability that some of the Cesium-spawned radioactive Ba-137 will find bone to irradiate. If this happens, bone exposure will occur for a very short time due to Ba-137’s very short half-life, but not long enough or in sufficient concentration to cause cancer.
Because of the Cesium-Barium connection and Cesium’s longer biological half-life than Potassium, the bodily-retained limit for Cesium-137 is many times lower than the recommended (but not regulated) bodily-retained limit for K-40. We would have to continually eat a LOT of Potassium-rich food to reach the recommended K-40 limit…more than 10 bananas or a 5lb. bag of potatoes every day. By the same token, we would have to eat 100 grams (about 4 ounces) of reactor Cesium-contaminated food, at Japan’s 100 Bq/kg limit, every day for a year to reach its regulatory limit in Japan, which is several times more restrictive than the rest of the world.
<Comment – I found out how radioactive bananas are when working at an American nuclear power plant. I eat a banana every morning with breakfast to boost my Potassium level and avoid painful night cramps in my calves. One morning, I decided to cut up two bananas on my breakfast cereal, instead of one, because I had experienced a calf-cramp in the middle of the previous night. As it turned out, I was scheduled for my annual “whole body” scan that morning, that checked for radioactive isotopes which might be in my system due to working at an operating nuke plant. After the scan was over, I was ushered to a “clean room” and interrogated about where I had been. My body’s radiation level had set off the scanner’s alarm. In the midst of the questioning, a technician came into the room and asked me what I had for breakfast because the alarm was due to an unusually-high K-40 level. When I said “two” and explained I eat a banana every morning, they suggested I skip the banana regimen on my scheduled day the following year. – End comment.>
Taking all of the above into consideration, I want to ask two questions. First, are the levels of reactor Cesium in the stored decontaminated waters (~2.5 Bq/cc) at F. Daiichi really “highly radioactive”, as is always stated in Japanese (and many international) news media reports? Second, is reactor Cesium as hazardous as the Press and hard-core nuclear critics make it out to be?
References for part a. -
- Situation of storage and treatment of accumulating water including highly concentrated radioactive materials at Fukushima Daiichi Nuclear Power Station; Tepco News; October 31, 2012; http://www.tepco.co.jp/en/press/corp-com/release/2012/10/index-e.html
- Potassium; Argonne National Laboratory; http://www.ead.anl.gov/pub/doc/potassium.pdf
- Cesium; Argonne National Laboratory; http://www.evs.anl.gov/pub/doc/cesium.pdf
- General Information about K-40; Oak Ridge Associated Universities; January, 2009; http://www.orau.org/ptp/collection/consumer%20products/potassiumgeneralinfo.htm
- Periodic Chart of the Elements; Web Elements; http://www.webelements.com/
- Interactive Chart of the Nuclides; National Nuclear Data Center; Brookhaven National Laboratory; http://www.nndc.bnl.gov/chart/reCenter.jsp?z=19&n=21
b. How Hazardous is Cesium in Fukushima’s Spent Fuel Pools?
We will now look at how reactor Cesium has been used to exaggerate risk relative to the spent fuel pools at Fukushima Daiichi.
As said earlier, reactor Cesium is a by-product of the fission process that occurs inside nuclear power plant fuel bundles. There are actually 48 radioactive elements formed when the Uranium-235 in the fuel is fissioned, and more than a hundred of isotopes of those elements. Most have such short half-lives that they are gone within an hour after the chain-reaction stops. A nuclear weapon’s detonation also produces the same types of radioactive isotopes, plus numerous others not found in reactors. This is because of the intensely-concentrated high energy neutron field inherent to the detonation itself. Reactor fission products range from Zinc to Dysprosium on the Periodic Chart of the Elements. On the other hand, the bomb’s isotopic matrix is much, much wider with as many as 71 elements (and their isotopes), from Sodium to Lead on the Periodic Chart.
Relatively few of the bomb fallout isotopes come from nuclear fission. In fact, most radioactive materials in a bomb’s fallout are cause by the process called “neutron activation”. Neutrons are the only type of radiation that can make other atoms radioactive. The soils, buildings, and other materials pulverized by a bomb’s explosion are instantly engulfed in the neutron field caused by the detonation, making radioactive isotopes from those elements that were not radioactive before the blast. Some of the prominent bomb-fallout isotopes are Sodium-24, Chromium-51, Manganese-54, Iron-59, Cobalt-60, Copper-64, Antimony-122 and 124, Tantalum-180 and 182, and Lead-203.(1) The half-lives vary from as low as 8 hours (Ta-180) and as long as 5.3 years (Co-60). Just for the record, a small amount of Carbon-14 is formed by the bomb, but its quantity is miniscule. Regardless, none of the bomb-fallout isotopes listed above are produced by power plant reactors. By comparison, bomb-spawned Cs-137 is literally a trace relative to the volumes of the above-listed bomb fallout isotopes.
It is important to note that the above list of predominant bomb-spawned isotopes are contained in microscopic agglomerations of dust containing a wide variety of these isotopes, fused together by the enormous heat of the fireball. The tiny clumps are highly radioactive and are the source of the concept of “hot particles”. They are relatively heavy in relation to the fission-product isotopes produced by bombs. As a result, the “hot particles” will “fall out” of the cloud of debris carried downwind from the blast site. Thus, the majority of the bomb-spawned isotopes, especially those caused by neutron activation, will descend from the high level cloud and are seldom carried more than 100 miles from the blast site (although certain upper-level meteorological conditions might carry hot particles as far as 200 miles). The fission-product isotopes, however, are mostly independent of these relatively heavy hot particle agglomerations. They are much, much lighter than the hot particles so they are carried great distances by wind and weather. Thus, Cs-137 and Cs-134 (as well as Sr-90) are used as “tracers” to monitor the spread of bomb fallout around the world, in the atmosphere and in soils. Because Cs-137 is the tracer most often used for weapon’s fallout dispersal studies, and there is little or no public knowledge of bomb-spawned hot particles, it is a common misconception that radioactive Cesium is the main constituent of bomb fallout and the cause of fallout-spawned cancer deaths.
Both reactors and bombs produce the popularly-mentioned isotopes Iodine-131, Cs-137, and Sr-90 that populate the Press reports concerning Fukushima. I-131 has a half-life of 8.1 days, Cs-137 at 30.1 years, and Sr-90 at 29 years. As described earlier, the length of an isotope’s half-life indicates how long it will last, in ever-descending activity level, if we multiply it by ten. While the amount of Cs-137 spawned by a bomb is relatively minute, the amount made in a reactor over a period of years is much greater. However, the documented fatalities caused by bomb fallout were largely due to the spectrum of the isotopes produced in high amounts found in hot particles, but to imply that all fatalities were due to Cs-137 exposure is a gross exaggeration. (For more “hot particle” information, and its misuse relative to Fukushima, see the Dec. 27, 2013 Fukushima Commentary - The Fukushima Hot Particle Myth.)
Case in point – the Daigo Fukurayu Maru in 1954. The Maru was a Japanese fishing ship located about 130 kilometers (~80 miles) downwind from America’s largest-ever atmospheric nuclear weapon’s test, code-named Bravo, rated at 15 million tons of TNT – roughly 1,000 times more powerful than the bomb dropped on Hiroshima. The 40,000 ft.-high cloud was immediately visible to the Maru and the sound of the blast clearly heard by the startled crew. The Maru pulled in its fishing equipment and began to sail away. Unfortunately, they traveled into the path of the bomb fallout. Radioactive dust, soot and even larger hot particles rained down on the Maru and her 23-man company. The crew received high internal and external radiation exposure, estimated at an average of 3000 millisieverts (mSv) each. All experienced nausea and those on deck received superficial skin burns from the β-emitting elements contained in the fallout pouring down around them. One crew member died about six months later due to acute hepatitis, which is not considered to be a radiation-induced condition but was probably exacerbated by the radiation exposure which reduced the individual’s immune system function. All others recovered from their symptoms. Seventeen remain alive today. Regardless, the crew’s radiation exposure was due to the entire range of radioactive isotopes they were subjected to. No reputable research report attributes the crew’s illnesses to Cs-137 alone. (2, 3)
Let’s also look at the data relative to fallout from the bombings of Hiroshima and Nagasaki in 1945. It is estimated that some 201,000 people died as a result of Hiroshima/Nagasaki; 130,000 killed by the two explosions themselves, 70,000 due to radiation exposures caused by the enormous neutron and gamma exposures radiated by the two bursts, and about 1,000 due to latent effects resulting from internal and external fallout exposure by 1951.(4.5.6) The fallout-caused deaths are believed to have been the result of contact with and ingestion of the full spectrum of fallout isotopes, only a miniscule fraction of which was Cs-137. In other words, those who succumbed to Hiroshima/Nagasaki fallout exposure did not die of Cs-137 exposure alone: in fact, the tiny fraction of Cs-137 in the fallout probably didn’t kill any Japanese or even make them sick...the amount produced was just too small.
These unequivocal facts have not deterred hardened nuclear energy critics from making it seem as if Cs-137 was the sole culprit behind all weapon’s-fallout-related and Chernobyl accident effects. They do this to make Cs-137 exposure seem unfathomably hazardous, and use their deceptive rhetoric to predict apocalyptic consequences. At the forefront is American Arnie Gundersen, a maverick former nuclear engineer. Gundersen evokes fearful visions of a Fukushima-based, nuclear-weapons-level holocaust when he says, “There’s more cesium in that [Unit 4] fuel pool than in all 800 nuclear bombs exploded above ground…But of course it would happen all at once. It would certainly destroy Japan as a functioning country. Move south of the equator if that ever happened, I think that’s probably the lesson there.” (8) It should be added that another noteworthy American, Robert Alvarez, makes a similar exaggeration when he uses Chernobyl for his wildly-speculative assumptions about spent fuel pool accidents. He writes that there is 85 times more Cesium in the spent fuel stored at F. Daiichi than was released by Chernobyl, therefore “It [all Cs-137 being released] would destroy the world environment and our civilization.” (7)
It would be of little consequence if doom-sayers like Gundersen and Alvarez were merely preaching to the world’s antinuclear choir, but their predictions of a Cs-137-caused apocalypse due to the spent fuel bundles at Fukushima Daiichi have received wide news media coverage in Japan, frightening millions. And, their severely disingenuous speculations have received virtually no rebuttal in the Japanese Press. Are they “telling it like it is”, or are they successfully selling fear-inducing rhetoric to millions of Japanese who have no idea what the risks of Cs-137 really are?
From what we have just seen, it seems clear that the popularly-posted risks of radioactive Cesium at Fukushima have been severely over-blown. The Cesium exposures due to nuclear detonations have never been shown to have killed anyone, let alone made anyone ill. Predicting world-wide apocalypse from Fukushima’s inventory of Cesium, using nuclear weapons as “proof”, is horribly misleading.
References for part b. -