Search This Blog

Spent Nuclear Fuel

The nuclear waste problem of today will be an energy solution in the future. Turning highly active waste into energy! Recycling the metallic fuel! Duh! 

The spent nuclear fuels from old reactors can be recycled, turned into new fuels, put into a breeder reactors, and this kind of closed fuel cycle produces dramatically less waste, enough that each nuclear plant would be reasonably able to fit all the resulting recycling wastes in existing cooling pools, where spent fuel rods are currently sitting, awaiting an intelligent solution. In this case the obvious choice is fuel recycling. Recycling the spent nuclear fuel is the only intelligent thing to do with it.
breeder reactor is not restricted to using recycled plutonium and uranium. It can employ all the actinides, closing the nuclear fuel cycle and potentially multiplying the energy extracted from natural uranium by about 60 times. I wish I could get this kind of performance out of the gasoline I used in my cars. 60X more energy, holy SHIT! Where are the breeder reactors? It feels like society as a whole is intelligent in some ways and horribly incompetent in others. We know what to do with the spent fuel, reprocess it, put it into a breeder reactor, but waste time and energy trying to figure out some cat brained long term storage solution, as if someone had a crystal ball, no one know what is going to be happening 10,000 years from now! Lets deal with problems now, that we have the ability to deal with using existing technologies!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Multi Material Storage Solution

So what about the remaining hard to deal with waste. Vitrification into glass. High Nickel Chromium Stainless steel protect the glass. The entire container is dipped into hot plastic to waterproof it, a recyclable plastic. In the distant future, the glass, steel, plastic storage vessels can be recycled, once fusion power liberates energy of galactic scale in future human energy systems. Once fusion power becomes a commercial technology, human society as a whole will be completely transformed into an energy abundant utopia, where outrageous recycling of everything becomes possible because of the nearly limitless cheap abundant energy that fusion power provides 24 hours a day, 7 days per week, continuous base loading capacity on the multi gigawatt scale. Fusion reactions will be disruptive to all conventional grid energy sources, solars major advantage will be leveraged on root tops, where the power is produced at the point of use, it just makes good rational sense. Battery energy storage will work with Solar power systems to make micro-generation distributed power systems that make all grid connected system more reliable, where loads on the grid system can be stabilized by all the grid interactive battery energy storage solar systems.

Glass, Steel, Plastic

Yes, we can solve the nuclear fuel cycle problem with recycling! Trying to store waste for 100,000,000 years is impossible given the current state of our technology. Our best bet is to vitrify the waste into glass, load the glass into protective containers made of corrosion resistant steel, titanium, or whatever metal is most corrosion resistant, special corrosion resistant alloys of iron, then the entire glass core steel container is dipped into water proofing, a hot thermoplastic like a heat vat of polypropylene PP. The plastic keeps water from storm systems, drainage, flooding, or any other source of water from corroding the steel. The steel container protects the brittle glass inside. This is a multilateral storage container solution that we can do right now. We can also reprocess spent nuclear fuel rods, recycling the energetic matter, breeding it, more reprocessing, repeat, use, repeat, use, so forth! This knowledge is already well distributed, why there is any debate about where to store the spent fuel mystifies people who are thinking clearly.

Humans did a lot of hard work to produce nuclear fuels from the earth, mining, processing. and spent nuclear fuel is made of metals that can be recycled into new fuel, over and over again.

From the World Nuclear Association: 

"Reprocessing technologies are being developed to be deployed in conjunction with fast neutron reactors which will burn all long-lived actinides, including all uranium and plutonium, without separating them from one another."

"A significant amount of plutonium recovered from used fuel is currently recycled into MOX fuel."
Recycling technology is the key to solving the nuclear waste problem.

A key, nearly unique, characteristic of nuclear energy is that used fuel may be reprocessed to recover fissile and fertile materials in order to provide fresh fuel for existing and future nuclear power plants. Several European countries, Russia, China and Japan have policies to reprocess used nuclear fuel, although government policies in many other countries have not yet come round to seeing used fuel as a resource rather than a waste.

Over the last 50 years the principal reason for reprocessing used fuel has been to recover unused plutonium, along with less immediately useful unused uranium, in the used fuel elements and thereby close the fuel cycle, gaining some 25% to 30% more energy from the original uranium in the process. This contributes to national energy security. A secondary reason is to reduce the volume of material to be disposed of as high-level waste to about one-fifth. In addition, the level of radioactivity in the waste from reprocessing is much smaller and after about 100 years falls much more rapidly than in used fuel itself.

These are all considerations based on current power reactors, but moving to fourth-generation fast neutron reactors in the late 2020s changes the outlook dramatically, and means that not only used fuel from today’s reactors but also the large stockpiles of depleted uranium (from enrichment plants, about 1.5 million tonnes in 2015) become a fuel source. Uranium mining will become much less significant.

Another major change relates to wastes. In the last decade interest has grown in recovering all long-lived actinides* together (i.e. with plutonium) so as to recycle them in fast reactors so that they end up as short-lived fission products. This policy is driven by two factors: reducing the long-term radioactivity in high-level wastes, and reducing the possibility of plutonium being diverted from civil use – thereby increasing proliferation resistance of the fuel cycle. If used fuel is not reprocessed, then in a century or two the built-in radiological protection will have diminished, allowing the plutonium to be recovered for illicit use (though it is unsuitable for weapons due to the non-fissile isotopes present).

* Actinides are elements 89 to 103, actinium to lawrencium, including thorium, protactinium and uranium as well as transuranics, notably neptunium, plutonium, americium, cerium and californium. The minor actinides in used fuel are all except uranium and plutonium.

Reprocessing used fuela to recover uranium (as reprocessed uranium, or RepU) and plutonium (Pu) avoids the wastage of a valuable resource. Most of it – about 96% – is uranium, of which less than 1% is the fissile U-235 (often 0.4-0.8%); and up to 1% is plutonium. Both can be recycled as fresh fuel, saving up to 30% of the natural uranium otherwise required. The RepU is chiefly valuable for its fertile potential, being transformed into plutonium-239 which may be burned in the reactor where it is formed.

So far, some 90,000 tonnes (of 290,000 t discharged) of used fuel from commercial power reactors has been reprocessed. Annual reprocessing capacity is now about 4500 tonnes per year for normal oxide fuels, but not all of it is operational.

Between 2010 and 2030 some 400,000 tonnes of used fuel is expected to be generated worldwide, including 60,000 t in North America and 69,000 t in Europe.

Recycling  = Metal Mineral Mining Process 

Conceptually, processing used fuel is the same as processing the concentrate of any metal mineral to recover the valued metals contained in it. Here the ‘ore’ (or effectively the concentrate from it) is hard ceramic uranium oxide with an array of other elements (about 4% in total), including both fission products and actinides formed in the reactor.

There are three broad kinds of metallurgical treatment at metal smelters and refineries:
Pyrometallugy using heat to initiate separation of the metals from their mineral concentrate (e.g. copper smelting to produce blister copper, lead smelting).
Electrometallurgy using electric current to separate the metals (e.g. alumina smelting to produce aluminium).
Hydrometallurgy using aqueous solutions that dissolve the metal, with sometimes also electrolytic cells to separate them (e.g. zinc production, copper refining).

The main historic and current process is Purex, a hydrometallurgical process. The main prospective ones are electrometallurgical – often called pyroprocessing since it happens to be hot. With it, all actinide anions (notably U & Pu) are recovered together.

Used fuel contains a wide array of nuclides in varying valency states. Processing it thus inherently complex chemically, and made more difficult because many of those nuclides are also radioactive.

The composition of reprocessed uranium (RepU) depends on the initial enrichment and the time the fuel has been in the reactor, but it is mostly U-238. It will normally have less than 1% U-235 (typically about 0.5% U-235) and also smaller amounts of U-232 and U-236 created in the reactor. The U-232, though only in trace amounts, has daughter nuclides which are strong gamma-emitters, making the material difficult to handle. However, once in the reactor, U-232 is no problem (it captures a neutron and becomes fissile U-233). It is largely formed through alpha decay of Pu-236, and the concentration of it peaks after about 10 years of storage.

The U-236 isotope is a neutron absorber present in much larger amounts, typically 0.4% to 0.6% – more with higher burn-up – which means that if reprocessed uranium is used for fresh fuel in a conventional reactor it must be enriched significantly more (e.g. up to one-tenth more) than is required for natural uraniumb. Thus RepU from low burn-up fuel is more likely to be suitable for re-enrichment, while that from high burn-up fuel is best used for blending or MOX fuel fabrication.

The other minor uranium isotopes are U-233 (fissile), U-234 (from original ore, enriched with U-235, fertile), and U-237 (short half-life beta emitter). None of these affects the use of handling of the reprocessed uranium significantly. In the future, laser enrichment techniques may be able to remove these isotopes.

Reprocessed uranium (especially from earlier military reprocessing) may also be contaminated with traces of fission products and transuranics. This will affect its suitability for recycling either as blend material or via enrichment. Over 2002-06 USEC successfully cleaned up 7400 tonnes of technetium-contaminated uranium from the US Department of Energy.

Most of the separated uranium (RepU) remains in storage, though its conversion and re-enrichment (in UK, Russia and Netherlands) has been demonstrated, along with its re-use in fresh fuel. Some 16,000 tonnes of RepU from Magnox reactors in UK has been usedc to make about 1650 tonnes of enriched AGR fuel. In Belgium, France, Germany and Switzerland over 8000 tonnes of RepU has been recycled into nuclear power plants. In Japan the figure is over 335 tonnes in tests and in India about 250 t of RepU has been recycled into PHWRs. In Russia RepU is used in all fresh RBMK fuel, and over 2500 tonnes has been recycled thus. Allowing for impurities affecting both its treatment and use, RepU value has been assessed as about half that of natural uranium.

Plutonium from reprocessing will have an isotopic concentration determined by the fuel burn-up level. The higher the burn-up levels, the less value is the plutonium, due to increasing proportion of non-fissile Pu isotopes (and minor actinides), and depletion of fissile plutonium isotopesd. Whether this plutonium is separated on its own or with other actinides is a major policy issue relevant to reprocessing (see section on Reprocessing policies below).

Most of the separated plutonium is used almost immediately in mixed oxide (MOX) fuel. World MOX production capacity is currently around 200 tonnes per year, nearly all of which is in France (see page on Mixed Oxide (MOX) Fuel). In future the Russian REMIX fuel may become established for recycling, though whether minor actinides remain with wastes or are recycled with REMIX depends on the reprocessing procedure.

History (fuel reprocessing) 

A great deal of hydrometallurgical reprocessing has been going on since the 1940s, originally for military purposes, to recover plutonium for weapons (from low burn-up used fuel, which has been in a reactor for only a very few months). In the UK, metal fuel elements from the Magnox generation gas-cooled commercial reactors have been reprocessed at Sellafield for about 50 yearse. The 1500 t/yr Magnox reprocessing plant undertaking this has been successfully developed to keep abreast of evolving safety, occupational hygiene and other regulatory standards. From 1969 to 1973 oxide fuels were also reprocessed, using part of the plant modified for the purpose, and the 900 t/yr Thermal Oxide Reprocessing Plant (THORP) at Sellafield was commissioned in 1994.

In the USA, no civil reprocessing plants are now operating, though three have been built. The first, a 300 t/yr plant at West Valley, New York, was operated successfully from 1966-72. However, escalating regulation required plant modifications which were deemed uneconomic, and the plant was shut down after treating 650 tonnes of used oxide and metal fuel using the Purex process. The second was a 300 t/yr plant built at Morris, Illinois, incorporating new technology based on the volatility of UF6 which, although proven on a pilot-scale, failed to work successfully in the production plant. It was declared inoperable in 1974. The third was a 1500 t/yr Purex plant at Barnwell, South Carolina, which was aborted due to a 1977 change in government policy which ruled out all US civilian reprocessing as one facet of US non-proliferation policy. In all, the USA has over 250 plant-years of reprocessing operational experience, the vast majority being at government-operated defence plants since the 1940s.

The main one of these is H Canyon at Savannah River, which commenced operation in 1955. It historically recovered uranium and neptunium from aluminium-clad research reactor fuel, both foreign and domestic. It could also recover Np-237 and Pu-238 from irradiated targets. H Canyon also reprocessed a variety of materials for recovery of uranium and plutonium both for military purposes and later high-enriched uranium for blending down into civil reactor fuel. In 2011 reprocessing of research reactor fuel was put on hold pending review of national policy for high-level wastes. Currently it is preparing plutonium for use in the new MOX plant at Savannah River.

In 2014, H Canyon completed reprocessing the long-stored uranium-thorium metal fuel from the 20 MWt Sodium Reactor Experiment (SRE), which had a high proportion of U-233. The sodium-cooled graphite-moderated SRE operated in California over 1957-64 and was the first US reactor to feed electricity to a grid. The uranium and actinides will be vitrified.

In France a 400 t/yr reprocessing plant operated for metal fuels from gas-cooled reactors at Marcoule until 1997. At La Hague, reprocessing of oxide fuels has been done since 1976, and two 800 t/yr plants are now operating, with an overall capacity of 1700 t/yr.

French utility EDF has made provision to store reprocessed uranium (RepU) for up to 250 years as a strategic reserve. Currently, reprocessing of 1150 tonnes of EDF used fuel per year produces 8.5 tonnes of plutonium (immediately recycled as MOX fuel) and 815 tonnes of RepU. Of this about 650 tonnes is converted into stable oxide form for storage. EDF has demonstrated the use of RepU in its 900 MWe power plants, but it is currently uneconomic due to conversion costing three times as much as that for fresh uranium, and enrichment needing to be separate because of U-232 and U-236 impurities. The presence of the gamma-emitting U-232 requires shielding and so should be handled in dedicated facilities; and the presence of the neutron-absorbing U-236 isotope means that a higher level of enrichment is required compared with fresh uranium.

The plutonium is immediately recycled via the dedicated Melox mixed oxide (MOX) fuel fabrication plant. The reprocessing output in France is co-ordinated with MOX plant input, to avoid building up stocks of plutonium. If plutonium is stored for some years the level of americium-241, the isotope used in household smoke detectors, will accumulate and make it difficult to handle through a MOX plant due to the elevated levels of gamma radioactivity.

India has two 100 t/yr oxide fuel plants operating, one at Tarapur since 1982, with another at IGCAR Kalpakkam, and a smaller one at BARC Trombay. Japan is starting up a major (800 t/yr) plant at Rokkasho while having had most of its used fuel reprocessed in Europe meanwhile. To 2006 it had a small (90 t/yr) reprocessing plant operating at Tokai Mura.

Russia has an old 400 t/yr RT-1 oxide fuel reprocessing plant at Ozersk (near Chelyabinsk, Siberia), the main feed for which has been VVER-440 fuel, including that from Ukraine and Hungary. The partly-built 3000 t/yr RT-2 plant at Zheleznogorsk in Siberia has been redesigned and first stage completion of 700 t/yr is expected about 2025. Another 800 t/yr is planned for 2028. This is apparently Purex though that is not confirmed. An underground military reprocessing plant there is decommissioned.

Compatible with Existing Reactors 

In today's reactors, reprocessed uranium (RepU) needs to be enriched, whereas plutonium goes straight to mixed oxide (MOX) fuel fabrication. This situation has two perceived problems: the separated plutonium is a potential proliferation risk, and the minor actinides remain in the separated waste, which means that its radioactivity is longer-lived than if it comprised fission products only.

As there is no destruction of minor actinides, recycling through light water reactors delivers only part of the potential waste management benefit. For the future, the focus is on removing the minor actinides along with uranium and plutonium from the final waste and burning them all together in fast neutron reactors. (The longer-lived fission products may also be separated from the waste and transmuted in some other way.) Hence the combination of reprocessing followed by recycling in today’s reactors should be seen as an interim phase of nuclear power development, pending widespread use of fast neutron reactors.

All but one of the six Generation IV reactors being developed have closed fuel cycles which recycle all the actinides. Although US policy has been to avoid reprocessing, the US budget process for 2006 included $50 million to develop a plan for "integrated spent fuel recycling facilities", and a program to achieve this with fast reactors has become more explicit since.

In November 2005 the American Nuclear Society released a position statement4 saying that it "believes that the development and deployment of advanced nuclear reactors based on fast-neutron fission technology is important to the sustainability, reliability and security of the world's long-term energy supply." This will enable "extending by a hundred-fold the amount of energy extracted from the same amount of mined uranium". The statement envisages on-site reprocessing of used fuel from fast reactors and says that "virtually all long-lived heavy elements are eliminated during fast reactor operation, leaving a small amount of fission product waste which requires assured isolation from the environment for less than 500 years."

In February 2006 the US government announced the Global Nuclear Energy Partnership (GNEP) through which it would "work with other nations possessing advanced nuclear technologies to develop new proliferation-resistant recycling technologies in order to produce more energy, reduce waste and minimise proliferation concerns." GNEP goals included reducing US dependence on imported fossil fuels, and building a new generation of nuclear power plants in the USA. Two significant new elements in the strategy were new reprocessing technologies at advanced recycling centres, which separate all transuranic elements together (and not plutonium on its own) ­starting with the UREX+ process (see section on Developments of PUREX below), and 'advanced burner reactors' to consume the result of this while generating power.

GE Hitachi Nuclear Energy (GEH) is developing this concept by combining electrometallurgical separation (see section on Electrometallurgical 'pyroprocessing' below) and burning the final product in one or more of its PRISM fast reactors on the same site. The first two stages of the separation remove uranium which is recycled to light water reactors, then fission products which are waste, and finally the actinides including plutonium.

In mid-2006 a report5 by the Boston Consulting Group for Areva and based on proprietary Areva information showed that recycling used fuel in the USA using the COEX aqueous process (see Developments of PUREX below) would be economically competitive with direct disposal of used fuel. A $12 billion, 2500 t/yr plant was considered, with total capital expenditure of $16 billion for all related aspects. This would have the benefit of greatly reducing demand on space at the planned Yucca Mountain repository.

Boston Consulting Group gave four reasons for reconsidering US used fuel strategy which has applied since 1977:
Cost estimates for direct disposal at Yucca Mountain had risen sharply and capacity was limited (even if doubled)
Increased US nuclear generation, potentially from 103 to 160 GWe
The economics of reprocessing and associated waste disposal have improved
There is now a lot of experience with civil reprocessing.

Soon after this the US Department of Energy said that it might start the GNEP (now IFNEC) program using reprocessing technologies that "do not require further development of any substantial nature" such as COEX while others were further developed. It also flagged detailed siting studies on the feasibility of this accelerated "development and deployment of advanced recycling technologies by proceeding with commercial-scale demonstration facilities."

In 2007 the US Nuclear Regulatory Commission’s Advisory Committee on Nuclear Waste and Materials published a report on Background, Status, and Issues Related to the Regulation of Advanced Spent Nuclear Fuel Recycle Facilities, which canvassed the advantages of reprocessing US civil spent fuel. The report states: “The DOE’s current program for implementing SNF recycle contemplates building three facilities: an integrated nuclear fuel recycle facility, an advanced reactor for irradiating Np, Pu, Am, and Cm, and an advanced fuel cycle research facility to develop recycle technology. The first two of these are likely to be NRC-licensed.” The report is a thorough overview of reprocessing but does not provide conclusions or recommendations.

The NRC report points out how the Purex process had been greatly improved since its military origins, but still suffered the drawback of producing a separated pure plutonium stream. It points to the virtues of the UREX processes.
Reprocessing today – PUREX

All commercial reprocessing plants use the well-proven hydrometallurgical PUREX (plutonium uranium extraction) process, which separates uranium and plutonium very effectively. This involves dissolving the fuel elements in concentrated nitric acid. Chemical separation of uranium and plutonium is then undertaken by solvent extraction steps (neptunium – which may be used for producing Pu-238 for thermo-electric generators for spacecraft – can also be recovered if required). The Pu and U can be returned to the input side of the fuel cycle – the uranium to the conversion plant prior to re-enrichment and the plutonium straight to MOX fuel fabrication.

Alternatively, some small amount of recovered uranium can be left with the plutonium which is sent to the MOX plant, so that the plutonium is never separated on its own. This is known as the COEX (co-extraction of actinides) process, developed in France as a 'Generation III' process, but not yet in use (see next section). Japan's new Rokkasho plant uses a modified PUREX process to achieve a similar result by recombining some uranium before denitration, with the main product being 50:50 mixed oxides.

In either case, the remaining liquid after Pu and U are removed is high-level waste, containing about 3% of the used fuel in the form of fission products and minor actinides (notably Np, Am, Cm). It is highly radioactive and continues to generate a lot of heat. It is conditioned by calcining and incorporation of the dry material into borosilicate glass, then stored pending disposal. In principle any compact, stable, insoluble solid is satisfactory for disposal.

No comments:

Post a Comment