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Related: About this forumForensic Analysis of One of the Earliest Weapons Grade Plutonium Samples Ever Prepared.
Recently I've been studying - because some excellent articles on the topic have been showing up in the scientific journals I routinely scan and or read - the interesting chemistry of the clean up of one of the most radioactively contaminated sites in the world, the Hanford Reservation near Richland, Washington.
Here for instance, is one such paper on this topic, on which I may comment in the future in this space: 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 381396)
I am always interested in radiochemistry, since I believe understanding it represents the last best hope of the human race.
Coincidentally, I've been going through old papers that I collected years ago but never read to sort them into appropriate directories, and I came across an interesting paper relating to one of the earliest known samples of plutonium ever prepared, prepared in the early days of the Manhattan project. The paper is here: Nuclear Archeology in a Bottle: Evidence of Pre-Trinity U.S. Weapons Activities from a Waste Burial Site (Schwantes et al., Anal. Chem., 2009, 81 (4), pp 12971306)
The Hanford site, which is where most of the plutonium for America's nuclear weapons was made, for most of its history as a production plant, operated on what its operators considered to be "emergency" conditions, extreme conditions of races against real and putative enemies, in both hot and cold war. The mentality was not focused at all on the long term other than potential post apocalyptic scenarios in which our enemies nuked us before we could nuke them. In such a mentality, so far as radioactive fission products as well as toxic chemicals were concerned, they were handled in a way that in our more distant time we would regard as extremely cavalier. In the earliest years, nuclear by products, often referred to as "nuclear waste," were often disposed of in open trenches, to be replaced later by single shell tanks, some of which famously leaked, and then in double shell tanks. Poor records and inventories were kept, but again, the remediation of this site has some fascinating chemistry and the clean up shows as much ingenuity as the creation of these materials did.
By the way, the existence of the Hanford Site has not lead to a death toll that even remotely approximates the number of people who have been killed by the by products of combustion of dangerous fossil fuels and biomass, which approximates about 7 million people a year, every year, which is roughly the equivalent of nuking and completely wiping out a city the size of Hong Kong every year, without stop. There are people, not very bright people, who wish to represent Hanford as the worst environmental problem that has ever existed, scientifically illiterate journalists for example. The 55,000 citizens of Richland, Washington are leading useful lives - many are scientists at Pacific Northwest National Laboratories - and are not dropping dead in the streets.
But no matter.
Anyway...Nuclear Forensics and the earliest plutonium samples:
From the opening text of the paper:
Background
The Hanford Site in Washington became the location for U.S. plutonium production during World War II. The Pu produced at this site was used in the first Pu nuclear weapon dropped on Nagasaki, Japan, on August 10, 1945, and in Trinity, the name given to the worlds first test of a nuclear weapon on July 16, 1945. In December 2004, a safe containing several hundred milligrams of extremely low burnup Pu (a term typically associated with Pu produced as part of a weapons program) in a one gallon glass jug was unearthed by Washington Closure Hanford (WCH) personnel while excavating the 618-2 burial ground in the 300-area of Department of Energys Hanford site.(8, 9) The jug contained ?400 mL of slurry characterized as a white precipitate in a clear liquid. Pictures in Figure 1 document this find. In-field ? analysis conducted on the container detected the presence of only 239Pu. The minimum 239,240Pu/238Pu and 239Pu/241Am ratios were estimated to be at least 320:1, and 1000:1, respectively, based upon the detection limits of this analytical technique, indicating the Pu was produced from extremely low exposure fuel, consistent with early military reactor operations at Hanford. The absence of ?-emitting U or fission product isotopes in the spectra also suggested the Pu had been separated and purified prior to its disposal. Considering the potential historical significance of the find, WCH personnel coordinated with staff at Pacific Northwest National Laboratory (PNNL) to conduct further analysis of the sample. All of the liquid and ?2% of the solid from the container were repackaged into two 1 L polypropylene bottles on May 10, 2006, with one of the two bottles being transferred to PNNL. The majority of the solid material remained, caked to the walls of the original glass jug and was earmarked for disposal. We have coined the process of characterizing this sample as nuclear archeology.
Here's a photograph of the safe and the bottle in it in which the plutonium was found:
The caption:
Apparently the process utilized to isolate the plutonium used a lanthanum fluoride carrier. It must have been the case that there was very little plutonium available at the time of the isolation, which is not surprising. In 1944, a chemist named Don Mastick broke a test tube in such a way as to end up eating what was then the world supply of the element; and many years later, as an old man was interviewed on the subject before dying in 2007 at the age of 87.
The scheme for analyzing the contents of the bottle is shown in the following graphic, also from the paper:
One of the interesting things about this paper which surprised me - this after more than 3 decades of reading about nuclear science - was that there was enough Na-22, a radioactive isotope of sodium in the sample to use it as a kind of tracer of the history of the bottle. As it is a radioactive isotope that is neutron deficient, as opposed to neutron rich, it's not an isotope I ever bothered thinking much about. It arises from the interaction of fluorine, a monoisotopic element with a mass number of 19, with alpha particles:
You learn something every day. This might be of interest to all those people working on MSRs (Molten Salt Reactors) utilizing the "FLIBE" or "FLINAK" salts. It's probably not a serious drawback, but one probably requiring some attention.
Some additional comment from the authors on the role of Na-22 in their analysis:
Figure 4:
The caption:
Further elaboration is in the text of the original paper about how to use isotopes like 22Na (or similar secondary nuclear reactions) to determine whether the same contains all of the plutonium originally available from its source, or only a fraction of it.
By the way, the plutonium in this sample was almost pure Pu-239, a grade of plutonium that today would be considered an extreme weapons grade material. This is unsurprising, since the Manhattan project had no way of knowing the effect of plutonium-240 would have on their weapons, and probably went to great lengths to avoid its accumulation. This requirement, regrettably greatly increased the volume of waste in order to isolate it, and this remained an issue, even after it was understood that weapons grade plutonium could tolerate more Pu-240 than was realized. Weapons grade plutonium is still not at all like reactor grade plutonium.
The caption:
Using the ratio, the authors determined that the source of the plutonium was not Hanford's more famous B-reactor, but rather the X-reactor, which was not located at Hanford, but rather at Oak Ridge.
This is explicated in the full text.
Interesting stuff, I think.
I wish you a pleasant rest of the weekend.