16 Years of (Radioactive) Cesium Recovery Processing at Hanford's B Plant.
Last edited Sun Apr 8, 2018, 09:10 AM - Edit history (4)
If you want to get a rise out of people with a modicum of understanding of environmental issues, and certain primitive ideas about it, one can mention the Hanford "Nuclear Waste" tanks on the Hanford Reservation, the location of the Pacific Northwest National Laboratories.
This plant was the site of production for the majority of the plutonium used in the production of the American Nuclear Weapons arsenal, an arsenal that I personally believe to need that "swords into ploughshares" approach. Operations began there in the early 1940's, and plutonium production at the site continued until 1987, when the N-reactor - a nuclear reactor with a basic design similar to the Chernobyl reactor, although unlike Chernobyl reactor the N reactor featured a negative void coefficient - was shut and the United States announced it had all the plutonium it would ever need.
(This, by the way, in my opinion, is an incorrect statement. My view is that we need more plutonium, not less of it, the idea behind this view being to ban most mining for energy for several centuries, until some future generation, unlike ours, gets it head on straight. Converted to plutonium, the uranium (and thorium) already mined and isolated could supply all of humanity's energy needs for centuries, but no matter.)
Understandably, since almost everything about the "new" element, plutonium, was unknown - even though some of the best minds in the United States (and elsewhere) were studying it - the chemical processing of plutonium was more or less ad hoc, conducted on the fly, without much long term environmental thinking, or, in fact, much long term thinking about anything.
Macroscopic quantities of plutonium can only be made in a nuclear reactor; and this requirement dictates that when formed it will always be formed in the presence of fission products. In commercial nuclear reactors, the mass ratio of plutonium formed to fission products is roughly 1:4.
At Hanford, these fission products - for almost the entire history of nuclear energy fission products have been arbitrarily assigned the term, "nuclear waste" - were dumped into a series of now famous "waste" tanks, tanks which are now being "cleaned up" at a cost of billions of dollars because they are leaking radioactive stuff.
Oh my God!!! They're leaking!!!
Many fission products have relatively short half-lives and decay to stable isotopes while still in the reactor, generating about 3% of the heat utilized - in commercial nuclear reactors - the heat that drives the turbines. Examples of such products are all of the fission products having a mass number of 133, or a mass number of 138, or a mass number of 127, or mass number 98...
Others famously do not.
Some radioactive isotopes will not decay to stable isotopes in the lifetime of the planet. For instance, fission isotopes having a mass number of 115 will decay into the radioactive (and apparently toxic) element indium, Indium is one of the only radioactive elements - along with tellurium and rhenium - to possess a stable isotope (in the case of indium it's the 113 isotope) which is present in quantities smaller than the radioactive isotope in all of its mined ores. In fact, natural indium contains only roughly 4% stable indium-113, and roughly 96% radioactive indium-115. If you have a cell phone in your pocket, you have radioactive indium in your pocket.
The reason that there isn't much stable indium on the planet is because all of the world's cadmium is radioactive, and contains the radioactive isotope Cd-113, the precursor of In-113, blocking the formation of Indium-113 from the primordial nuclear events that created all the heavy elements on this planet. Cd-113 has been decaying into indium since the formation of this planet, and it will be doing so around the time the sun reaches red giant stage and eats this planet whole. However it is decaying very slowly: It's half life is 77 quadrillion years, and it has survived since the formation of the earth and makes up about 23% of "natural" cadmium.
As is the case with the long lived isotope uranium-238 - so called "depleted uranium" - the chemical toxicity of both radioactive naturally occurring cadmium and radioactive naturally occurring indium vastly outstrips the radiotoxicity, which in all three cases is trivial, but not zero.
Cadmium, Indium, and Tellurium (again, in the same class as indium with respect to ratios of stable to radioactive isotopes) are all used in solar cells, meaning that the chemotoxic wastes that into which they will all be transformed will all be radioactive waste as well, much like the thorium containing mine tailings for all the lanthanides mined to make electric cars and wind turbines. However, the longer an isotope's half-life, the smaller its radiologic risk will be. The radioactivity of cadmium, indium, cadmium and thorium probably account for less than 10 deaths (out of tens of millions of deaths) each year.
As far as I can tell, nobody in the general public cares very much about cadmium or indium in Hanford's tanks, apart from the scientists involved in the clean up who realize that these elements must be there, because, um, they're scientists.
What really get's the public imagination going is the element cesium, the same stuff that prominently leaked, generating millions of barely literate news stories and internet posts - out of the Chernobyl and Fukushima reactors. Those old enough to remember, will recall that cesium isotopes also generated huge panics during the era of open air nuclear testing many years before Chernobyl and Fukushima. Cesium's most famous radioactive isotope is the 137 isotope, which has a half-life of 30.23 years and is very, very, very radioactive and in secular equilibrium with an even more radioactive isotope, Ba-137m, which exists a few minutes before decaying into stable nonradioactive Ba-137.
If you were born after 1945, you have lived your entire life being exposed to Cs-137 in amounts that grew continuously until roughly 1963, and have tapered off since, with a few spikes from Chernobyl and Fukushima. Up until 1963, with rare exceptions thereafter, the stuff was routinely vaporized in the planetary atmosphere, and somehow did less damage than the currently ongoing practice of vaporizing coal on a far more massive scale. Vast quantities of coal are being vaporized today.
I have been reading about the chemistry and physics of radioactive elements associated with nuclear energy, as well about topics in nuclear engineering, for more than 30 years, relying heavily on the primary scientific literature to do so. And while I am always interested in the geochemistry of radioactive materials that have been added to the environment from nuclear fuel reprocessing, nuclear accidents, nuclear weapons testing, and nuclear war - the number of nuclear wars being one, in contrast to the number of oil wars, which is considerably greater than one - I can't say that it amounts to more than 10% of my readings on nuclear issues. Readings about Hanford, in general, represent in turn only a small percentage of that 10%. The truth is that I am far more interesting in the processing and use of fission products than their environmental fate, since as environmental issues go the effects of radiation are trivial when compared to the effects of air pollution and climate change.
Whenever I've been presented with idiotic stuff about Hanford - a recent example consisted of a very stupid interaction with a commentator about the collapse of a tunnel at Hanford, this on a planet where 19,000 people will die today from air pollution - I am usually dismissive: I like to note that even if the 44,000 people living in Richland, WA, the "home town" of the Pacific Northwest National Laboratory at Hanford, were all wiped out by Hanford "nuclear waste," the disaster would amount to a little over two days worth of deaths from air pollution. Of course, Hanford hasn't been wiped out by radioactive stuff, and frankly, it won't be.
Whenever I hear or read about cesium plumes under leaky Hanford tanks, I generally sigh to myself, without paying much attention, "Why the hell don't they just run that crap through an ion exchange resin and be done with it?"
Recently in my regular reading in one of the journals I regularly read, I came across a paper that has increased my attention to the fascinating issue of the Hanford tanks, specifically, this one: Review of the Scientific Understanding of Radioactive Waste at the U.S. DOE Hanford Site (Peterson et al, Environ. Sci. Technol., 2018, 52 (2), pp 381–396).
The paper is so interesting that I did something that is somewhat unusual, I downloaded pretty much every scientific reference in the paper, with a few inaccessible omissions, and then references in the references.
I won't talk more about this paper itself in this post although I may do so in the future here, but will instead site one of the references, a document entitled, "Sixteen Years of Cesium Recovery Processing at Hanford's B Plant" (RHO-RE-SA-169). You can find this document in full on the internet, but it took me a while to find it before downloading it, and I'm too lazy to find it again, so I won't link it here.
"Why the hell don't they just run that crap through an ion exchange resin and be done with it?..."
Well, it appears that they pretty much did that.
The text referring to RHO-RE-SA-169 from the Peterson paper cited above is this:
Strontium-90 (t1/2 = 28.6 y) and 137Cs (t1/2 = 30.2 y) are major contributors to the heat generated from nuclear fission wastes. These isotopes also have potential commercial value 90Sr as a source of 90Y used in medical applications,18?20 and 137Cs as a source of ? rays (through decay of its daughter 137mBa, which emits a 662 keV ? ray) for sterilization applications.21 Megacuries of these two isotopes have been separated from acidic process solutions and from tank waste at Hanford.22
The cited reason that Cs-137 is valuable, by the way, is somewhat superficial. Cs-137 can be and is used for sterilization, but this is only a tiny reflection of its utility. Gamma radiation can solve some otherwise very intractable environmental problems, in particular those involving pollution with legacy (for example DDT, CFC and PCBs) and ongoing chemical pollution of the atmosphere and bodies of water, among other things. Regrettably this utility is vastly under explored and utilized.
Following references in reference 22 leads one to the "Sixteen years" report, which was published based on a talk given at a meeting of the American Nuclear Society at Niagara Falls, NY, in September 1986, a little more than 5 months after Chernobyl blew up. Chernobyl was the event that lead me to serious reading about nuclear energy, and the more I read, the more I found reason to change my mind about lots and lots and lots of things, only one of which involved the question of whether nuclear energy was a bad thing or a great thing.
The "Sixteen Years" document refers to operations at Hanford to recover Cs-137 that began shortly after Christmas in 1967 and was ended after 1979, with processing of the recovered cesium continuing for several years after that, continuing until 1984.
The separation process, was, in fact, an ion exchange process.
"Why the hell don't they just run that crap through an ion exchange resin and be done with it?..."
By the way, the events described in "Sixteen Years" were not the first attempt to separate cesium from the fission products that went into the Hanford tanks.
In 1957, near Kyshtym in the former USSR, there was a chemical explosion at the Soviet nuclear weapons plant in the closed city Mayak, which served the exact same function for the Russian nuclear weapons program that Hanford played for the Americans. The explosion is said to have involved nitrates used in the separation plants. Although this was a chemical explosion similar to the explosion that the domestic terrorist Timothy McVeigh used to strike Oklahoma City and not a nuclear explosion, it took place in a storage tank that was more or less the equivalent of the Hanford tanks, a highly radioactive mishmash of fission products. It is estimated to have released 20 million curies of radioactivity, two of which were aerosols and were distributed over a wide area.
Nitrates were also used in American operations, but along with something else, nickel ferricyanide. The heavy group one elements potassium, rubidium and cesium all form insoluble salts with iron and nickel cyano complexes, in the iron case referred to as ferrocyanides. (Ferroferricyanide salt is a chemical compound formerly used as a dye known as "Prussian Blue," which was sometimes used as a wet analytical test for iron.)
In the early 1950's ion exchange technology, while known, was in its infancy. In 1954 a flow sheet was published for the removal of cesium-137 from fission products in order to reduce the heat load in the Hanford Tanks being filled at that time. (cf HW-30399, AEC Research and Development Report, 1954.)
Decades later, when the contents of the tanks were being investigated, scientists recognized that the material dumped into the tanks from this process, along with hot radioactive materials might well explode. Between 1954 and 1958 about 140 metric tons of ferricyanide found its way into 18 Hanford tanks.
At the same time, nitrate wastes - nitric acid was widely used in the PUREX plutonium separation process to recover plutonium - also found their way into the tanks.
A very exothermic reaction between sodium nitrate and nickel ferricyanide in which the two compounds react explosively to form nitrogen gas, sodium carbonate, nickel (II) oxide, iron (II) oxide and carbon dioxide. This reaction releases 9 MJ of energy per kg. (cf. HNF-SA-3126-FP, Resolution of the Hanford Ferricyanide Safety Issue.) This implies that were the ferricyanide evenly distributed among each of the 18 tanks, that each tank would contain about 7.8 tons of ferricyanide, and the chemical explosion in a tank would release about 73 GJ of energy, equivalent to a 17 "Megaton" chemical explosion.
That would have been bad.
It turns out that the cyanide in the tanks was radiolytically decomposed resulting in a much milder reaction that essentially ate up all that dangerous stuff.
And now about the "Sixteen Years."
Three forms of ion exchange were utilized. The first one of which was Linde AW-500, an aluminosilico zeolite. The uptake of cesium was recorded in a straight forward manner. The "waste" solutions were passed over columns at a rate of about 40 gallons per minute, and the radioactivity of the eluent was monitored. When radioactivity began to show up, it the resin was fully loaded, and the elution was stopped and the cesium removed from the resin by elution with ammonium carbonate, evaporated, and sent for processing. When the Linde AW-500 was found to show poor long term stability under radiation loads, it was replaced with Norton Zeolon 900, also an aluminosilicate zeolite. When this too showed poor long term stability under radioactive loading, they were ultimately replaced with an organic ion exchange resin, Duolite ARC-359, a sulfonated phenolic formaldehyde resin.
Apparently over 116 million curies of cesium-137 was recovered in this way, almost six times the amount of radioactivity released in the Mayak disaster.
All of this cesium was immobilized in the form of a cesium phosphotungstate having a ratio of sodium to cesium of 10:1 and encapsulated into 1500 stainless steel containers, in which they remain today, with some having been distributed to licensees for use.
The 116 million curie figure is kind of ambiguous, since the cesium was undergoing radioactive decay throughout the 16 year process. It may refer to the amount loaded or the final amount at the end of the campaign in 1986. For simplicity, I will assume the latter.
In 1986, 116 million curies of cesium-137 - given the specific activity of cesium at 4.4 hundred trillion Becquerel per mole, would amount to 1.34 tons of the stuff.
In equilibrium with Barium-137m, it can be shown that in 1986, 116 million curies of cesium would be putting out about 1.26 MW of power.
By 2018, this material has decayed to 47.8% of the original amount, and now represents about 683 kg, putting out about 604 kW of power.
My kid is in his first year of college and is taking a course in differential equations and another in the thermodynamics of materials. I asked him to set up an equation and solve it to demonstrate what volume of the water contaminated with PCB's in the Hudson River superfund site, which is now being dredged even though there is actually no safe place to put the dredgings, could be heated and boiled off in a reactor heated with this much energy, in the process destroying and mineralizing the PCB's.
He blew me off. I don't blame him. He's busy. Anyway a soxhlet type arrangement extracting the PCB out of the dredgings with isopropanol would be superior for this purpose, and the thought experiment actually proposed a dumber idea than a practical use.
The point I wanted to make for him, since his generation will need to clean up our mess since we didn't give a shit about future generations when we made this mess, is that these kinds of radioactive materials can be very useful for this purpose. He didn't solve the problem - which has a simpler solution actually than one involving differential equations - but he got the point.
In fact, not all of the cesium remains at Hanford. Recently I got to see a photograph of one of the canisters while attending a lecture on radiologically stable artificial muscles (which were ultimately tested in space, where the radiation field is constant) but before being flown in the space station were subjected to ground based gamma radiation.
A video of that lecture is here: Science on Saturday: Synthetic Muscle for Deep Space Travel
Here's something interesting to ponder if you actually made it through this too long post: The Hanford clean-up is a mess that a previous generation left for our generation to clean up. It's likely very possible to clean it up by the way, challenging, expensive if interesting, but clearly possible.
The ultimate death toll of the Hanford tanks will be thankfully small, probably not zero, but certainly not more than the equivalent of a few hours - if that - of air pollution deaths.
Our generation is leaving all future generations fracking fields bleeding all sort of chemicals and elements, some of which, chiefly radium and its daughters, are highly radioactive. No one is cleaning it up. We're pretending it's not there, just like the people who were working at Hanford didn't worry about the long term consequences of what they were doing.
Much worse than the fracking fields is the condition of our atmosphere. This week, after years of jaw boning, we're at 410 ppm of carbon dioxide in the planetary atmosphere, and rising, rising fast.
I spend a lot of time wondering if it is even possible to clean up the mess we're leaving, a mess that dwarfs Hanford, dwarfs Chernobyl, dwarfs Fukushima, and is not limited to specific geographical areas but involves the entire planet.
If we complain about the indifference of the people who filled the Hanford tanks, we will be Trumpian in our hypocrisy. We will be Trump scale liars, because what we are doing is far worse, and far less possible to solve, even with hundreds of trillions of 2018 dollars.
I wish I lived in a time where people, in general, could get beyond emoting and simply think.
Simply think...
Enjoy the rest of the weekend.
= new reply since forum marked as read
