RARE -- CHAPTER 6 -- CREATED IN A NUCLEAR REACTOR

CHAPTER 6 – CREATED IN A NUCLEAR REACTOR

·         This chapter gives a description of how rare metals and scarce radioactive elements can be synthesized in small but usable amounts in fuel rods.  Examples of these are technetium, rhodium, palladium, ruthenium, californium, and curium.  These new elemental substances are recovered along with left over uranium during the reprocessing of spent fuel rods.  To recover these elements, the spent fuel rods are broken into smaller pieces and subjected to a strong acid to dissolve the uranium oxide pellets while the metals remain solid.  The author points out the downsides of nuclear reprocessing:  it is labor- and time-intensive, the uranium and plutonium fuel can still form localized hotspots and may reach critical mass, storage is vulnerable to theft, etc.  Presidents Ford and Carter stopped the reprocessing of fuel to prevent the spread of nuclear material.  President Reagan lifted this ban and from there went back-and-forth in a start-stop policy that rests now on President Obama.  At present, reprocessing of reactor fuel used to generate energy for public consumption is not being done in the US.  The fear of radioactive waste being acquired by nefarious groups to use for detonating dirty bombs was reiterated by President Obama in 2014, claiming that this is a more real danger than the reconstitution of the Russian Federation.  As the author opines, this will probably put an end to the promise of reclaiming rare metals from fuel rods.  One last downside of reprocessing is the additional volumes of waste created by the strong acids and carcinogenic solvents used in recovering the uranium and plutonium.  While dilute in radioactive substance, these volumes of waste nevertheless need to be stored for a long time for the radioactivity to die down.  The author also brings up the point that because many of these synthetic products are radioactive or can be induced to become radioactive by irradiation, they must be safely stored for a period of time to allow the radioactivity to diminish.  A rule of thumb is that 7 half-lives must pass before 99% of the radioactive material has decayed.  Half-lives can vary by size, from 30 seconds for rhodium-106 to 39 days and 368 days respectively for ruthenium-103 and ruthenium-106 to 6.5 million years for palladium-107.  The author concedes that reprocessing and subsequent storage with its downsides can be a costly alternative to mining these rare metals and scarce radioactive elements.  During critical times of need or due to issues of national security, recovering 4-5 kg of rare metals in a metric ton of fuel rod waste may make it worthwhile alternative.  Nevertheless, the author shares the belief that being able to recover precious rare metals is an added value that can provide a financial advantage to compensate for the high cost of waste management.

·         Atoms of rare metals are good at absorbing neutrons, thus their use in fuel control rods in nuclear power plants.

·         Many rare metals are created during these nuclear reactions taking place in power plants, enough for actual sale and industrial use, an example of which is rhodium.

·         There are 38 known naturally radioactive elements with plutonium and uranium the most well-known.

·         Element 84 all the way to 118 are radioactive.  Of these 36 elements [should be 35?], only 12 exist in large enough reserves to be usable.

·         Elements synthesized in fuel rods:  californium, curium, rhodium, palladium, ruthenium, technetium.

·         To initiate a stable chain reaction, most new nuclear plants can simply place a used fuel rod in the reactor.  As an alternate, mixing polonium, an alpha emitter, with beryllium will release enough neutrons from the beryllium to start reactions in the fuel rods.

·         Spent uranium fuel rods:  no longer sufficient to sustain nuclear reactions; the physical distribution of uranium atoms does not support a sustained stable chain reaction; other metals and molecules have been formed.

·         Spent fuel rods can be reprocessed to take usable leftover uranium and extract newly formed rare metals and scarce radioactive elements.  A strong acid is used to dissolve the uranium pellets while rhodium and other new metals formed remain solid.  These clumps of new metals are separated and further concentrated to isolate pure samples of the individual metals.

·         The author points out the downsides of nuclear reprocessing:  it is labor- and time-intensive, the uranium and plutonium fuel can still form localized hotspots and may reach critical mass, storage is vulnerable to theft, etc.

·         Presidents Ford and Carter stopped the reprocessing of fuel to prevent the spread of nuclear material.  President Reagan lifted this ban and from there went back-and-forth in a start-stop policy that rests now on President Obama.  At present, reprocessing of reactor fuel used to generate energy for public consumption is not being done in the US.  The fear of radioactive waste being acquired by nefarious groups to use for detonating dirty bombs was reiterated by President Obama in 2014, claiming that this is a more real danger than the reconstitution of the Russian Federation.  As the author opines, this will probably put an end to the promise of reclaiming rare metals from fuel rods.

·         One last downside of reprocessing is the additional volumes of waste created by the strong acids and carcinogenic solvents used in recovering the uranium and plutonium.  While dilute in radioactive substance, these volumes of waste nevertheless need to be stored for a long time for the radioactivity to die down.

·         Individual elements created in fuel rods can be formed as different isotopes.  Some of these newly synthesized istotopes are radioactive, like curium and americium.  In addition, these radioactive elements can irradiate non-radioactive elements and cause them to become radioactive.  On the positive side, the half-lives of some of these, e.g. the major isotopes of palladium, ruthenium, and rhodium, are relatively short.

·         If not reprocessed or reused, the author discussed briefly the existence of geological repositories in which the spent fuel and other waste is buried.  One of these is in New Mexico, 2,000 feet under State Road 128 consisting of non-airtight 50-plus football size rooms built to store waste for tens of thousands of years.

·         Reclaimed metals need to be stored for decades in order for decay rate to decrease to a safer level before the metals are sold or used for commercial purposes.  These include nonradioactive palladium, ruthenium, and rhodium because of their irradiation.  A rule of thumb is that 7 half-lives must pass before 99% of the radioactive material has decayed.  Half-lives can vary by size, from 30 seconds for rhodium-106 to 39 days and 368 days respectively for ruthenium-103 and ruthenium-106.  It would take 9 months for the 103 isotope and 7 years for the 106 isotope before they are deemed reasonably safe to use.

·         Ruthenium-106 is used for experimental treatment of certain forms of cancer including uveal melanoma.

·         17% of salvaged palladium is the radioactive Pd-107 isotope with a half-life of 6.5 million years.  It is a low-energy beta emitter that perhaps can one day be used by researchers for tracing purposes.

·         The author concedes that reprocessing and subsequent storage with its downsides can be a costly alternative to mining these rare metals and scarce radioactive elements.  During critical times of need or due to issues of national security, recovering 4-5 kg of rare metals in a metric ton of fuel rod waste may make it worthwhile alternative.

·         Other radioactive elements for mostly academic research use are manufactured in particle accelerators, namely curium, berkelium, neptunium, californium, mendelevium, and others, at a very steep cost with low yields.

·         Synthesis of transmuted elements from natural nuclear reactors:  Oklo in Central Africa is the site for 16 natural nuclear reactor sites that have operated for the last 500 million years.  It was discovered when ore from the region was analyzed and found to contain a much lower concentrations of uranium-235 than naturally found.  These reactors, on the average, produced only a small amount of energy, about 100 kW, 0.01% of the output of a commercial reactor.  Only traces of synthetic elements are thought to exist as many of them have long decayed to other more stable elements (Tc to Ru and Pu to U, e.g.).