All Use of Spent Nuclear Fuel
It seems to me quite interesting to deal with the economics of spent nuclear fuel (SNF). There are few things on Earth with such complex economic duality: SNF is also a very dangerous waste with extremely expensive disposal, and at the same time a source of many unique elements and isotopes that cost a lot of money.
This duality gives rise to a complex choice about the future of spent nuclear fuel - for many decades now, the vast majority of countries possessing nuclear energy cannot decide whether to dispose of spent nuclear fuel or recycle.
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In this text, if possible, I will carefully try to calculate the expenditure and revenue side of the SNF economy.
Terms and abbreviations used:
Fissile materials (DM) - the actual nuclear fuel that supports the fission chain reaction (Pu239, U235, Pu241, U233). What is called a fuel, in fact, besides DM, usually contains other materials — oxygen, uranium 238, and fission products.
Fission products - fragmentation elements, formed from the DM as a result of fission reaction. Usually radioactive isotopes from 70 to 140 numbers of the periodic table.
PWR / VVER - the most common type of nuclear reactors in the world, with pressurized water (not boiling) in the primary circuit, with a thermal neutron spectrum.
BN is another type of reactor, with a fast neutron spectrum and sodium as a coolant.
CNFC - the closure of the nuclear fuel cycle , a promising method for expanding the fuel base of nuclear energy. This implies the use of BN or BREST reactors.
BREST is another type of reactor with a fast neutron spectrum and lead coolant, which theoretically is more secure than a BN. No such reactor has yet been built.
The cost of spent nuclear fuel begins at the NPP operator when it leaves the in- situ holding pool and goes either to the dry or to the wet storage. Hereinafter, it is convenient to recalculate all costs into unit costs per kilogram of heavy metals of SNF, so if sent to a dry storage facility, such expenses range from 130 to 300 dollars per kg of SNF and are determined mainly by the cost of storage containers or the building that houses the SNF. Of this amount, from 5 to 30 dollars accounted for transportation operations.
Loading into the shipping container is probably the most expensive SNF in the world - from the surviving holding pool 4 units of the Fukushima nuclear power plant
These amounts are, in fact, negligible. A kilogram of SNF, when it was still fuel, produced (if you take the PWR / VVER) from 400 to 500 MW * h of electricity, costing about 16 ... 50 thousand dollars, i.e. Moving to intermediate storage is not worth it and 1% of revenues from the production of atomic electricity.
However, intermediate storage is intermediate and that it should have some continuation. This can be either direct disposal of SNF unchanged or processing.
Dry container storage is the cheapest option for intermediate storage of SNF today - no building is needed if the site is located on the NPP territory - even additional security is not needed. The gigawatt unit uses about 2.5 such containers for a year, each costing $ 0.5-1 million per unit.
Deep disposal of spent nuclear fuel is now being implemented in the form of specific projects in Finland , Sweden, the United States and Switzerland and is being investigated for different sites in another two dozen countries. The example of Finland and Sweden shows that the cost of direct disposal will most likely be around $ 1,000 per kilogram of SNF or slightly lower - and the total costs by the time of the final removal of the issue from the SNF from the NPP operator’s shoulders will be, accordingly, something like $ 1000-1200 on kilogram. Interestingly, this amount is about half the cost of fresh fuel.
Containers for final geological disposal. The technology requires an exposure of 20-30 years before performing this disposal, however today in many countries there are no problems with the search for spent nuclear fuel, which has been stored for 30+ years
However, the cost of direct disposal is similar to the cost of recycling - maybe by extracting valuable materials, you can reduce overall costs, or even get a plus?
The main motive for radiochemical reprocessing of spent nuclear fuel is the new nuclear fuel accumulated in it, and a little wider - in general, fissile materials. The cost of these recoverable materials is an anchor in the whole processing economy, in other words, it is definitely the most valuable thing that can be extracted from SNF. Comparing with the cost of U235, extracted from natural uranium (approximately 25 thousand dollars per kg), one can quickly figure out whether the game is worth the effort.
If you look for information on the cost of reprocessing, you can find figures from $ 700 to $ 2,000 per kilogram of heavy metals from SNF (without taking into account the weight of the metal parts of the fuel assembly with fuel, which you also have to mess with, and oxygen, because the fuel is mostly in the form of oxide) . The spent nuclear fuel of the atomic energy industry - PWR / VVER reactors contains from 1.5 to 2.5% of fissile materials (the first figure refers to modern fuel designs, of which they are squeezed to the maximum, the second to old spent SNF).
Overloading of a new transport container TUK-141 with the fuel from the Balakovo NPP reactors in September this year - the beginning of the processing process
You can multiply. Spending from 700 to 2000 dollars we get 25000h1.5-2.5% = 375 ... 625 dollars of fissile materials. The situation worsens even more if we recall the isotopic composition of fissile materials extracted from PWR / VVER spent nuclear fuel - uranium will be contaminated with neutron poison U236, and plutonium almost half consists of non-fissioning isotopes (Pu240, Pu242). In addition, subsequent fabrication of fresh SNF with fairly radioactive plutonium is also more expensive than working with “organic” enriched natural uranium product.
And here in the slender (I hope) narrative on the economics of spent nuclear fuel, which is today, it is worth taking a step aside and also looking at the cost of the fuel cycle in relation to fast reactors and CNFC - what experts considered in the 60s and 70s as the future of the industry.
The simplified (really simplified) scheme of the fuel cycle with reprocessing without fast reactors is rather meaningless, as discussed below.
And the situation will immediately improve. First, the fast neutron spectrum requires a much larger amount of fissile materials in the core, which is achieved by increasing their concentration: up to 20–30% plutonium or 235 uranium, as opposed to 4–5% for reactors with a thermal spectrum. Those. to obtain the same amount of Pu239, we need to recycle 5-6 times less SNF. In addition, we all remember that fast reactors are breeders, and they contain more DM in the SNF than in fresh fuel!
There is one more aspect, if we compare the DM from SNF and natural uranium. When the concentration of DM in fresh fuel BN, say, 27%, burns out of this no more than 11%. Those. â…” Extracted natural uranium without reprocessing will go to the dump, which catastrophically drops the economy of fast reactors without reprocessing spent nuclear fuel (for example, BN-600). The situation is actually the reverse of the VVER.
But let's count. If we extract 300 grams of plutonium from a kilogram of spent nuclear fuel, then in the equivalent of natural uranium our profit is $ 7,500, which is certainly more than the cost of processing this kilogram of $ 2,000. Here the truth must be remembered that in the next cycle it burns about â…“ of the extracted quantity, i.e. revenue is reduced to $ 2,500 per kilogram of SNF.
In fact, this means that the cost of reprocessing spent nuclear fuel — the fabrication of new fuel for fast reactors is equivalent to the fabrication of fuel from natural uranium — the reprocessing “tail” ceases to be a burden.
In fact, of course, I simplify. all sorts of things, such as minor actinides, the disposal of fission products pull the economy of processing down, and the real result is highly dependent on technology. For example, below are the calculated figures for the output of various unpleasant things when processing SNF in France (for 6 different scenarios for the development of this reprocessing) in an amount covering SNF from 100 to 150 gigawatts of capacity.
Below is a table that shows the reduction in demand for natural uranium through the use of fissile materials from recycled fuels.
And now let's see if there is anything else useful in the SNF, which could improve the economy of reprocessing as a whole. Here it is necessary to recall that the fission products of uranium and plutonium are about 70 isotopes of 25 elements. Some nuclides - stable and radioactive, in principle, are of commercial interest.
Palladium Each ton of fission products accounts for approximately 5% of palladium of complex isotopic composition. Those. About 5 kilograms of palladium can be extracted from each ton of SNF of BN containing 100 kilograms of fission products, and 800 grams of tonne of WWER SNF. Unfortunately, palladium will be radioactive due to the Pd-107 isotope (about 14% of all palladium isotopes in SNF), which has a half-life of 6.5 Ma, i.e. wait for its collapse will not work. The specific activity of palladium extracted from SNF will be about 1.2 MBq / g, which is quite a lot. NRB-99 sets the limit for the safe annual supply of palladium of such activity to 1.45 grams per year.
Theoretically, if this radioactive palladium is used (in some industrial catalysts, say) and its price is equal to the price of natural (~ $ 30,000 per kg!), Palladium extracted from SNF will replenish 1-2% of the cost of SNF reprocessing.
Rhodium . Another platinum group metal. 1.2 kg of rhodium can be extracted from a ton of spent nuclear fuel, and about 500 grams from a ton of WWER spent fuel. The longest-lived radioactive isotope Rh-102 with a half-life of 3.74 years, Somewhere in 50 years of exposure, the radioactivity of rhodium will drop to values ​​after which it can be considered non-radioactive. The cost of rhodium is about the same (now even more) than that of palladium, respectively, rhodium extracted from SNF will compensate for 0.3-0.5% of the cost of reprocessing.
Ruthenium . In addition to the infamous Ru-106, among the fission products there are also stable isotopes of this element. Ruthenium in mass in SNF is about 25% more than palladium, and not radioactive (after the collapse of the main amount of Ru-106), it becomes in about 40 years of exposure. Unfortunately, the cost of ruthenium is 6 times lower than palladium, therefore, it also adds only 0.2-0.4% of the cost of spent nuclear fuel reprocessing.
Silver . Among the fission fragments, its share is approximately 0.8%. Those. from this ton of its fragments will be about 8 kg. It has two relatively long-lived radioactive isotopes. Ag-110m with a half-life of 250 days and Ag-108m with a half-life of 418 years. The second isotope is formed with a relatively low yield. The residual activity after 30 years of exposure will be 2.9 ÎĽCi / g, slightly higher than the radioactivity of natural uranium, but comparable. Suitable for technical use, but due to the relatively low cost is hardly economically feasible.
Xenon This is the most common of the fragments of uranium or plutonium - only stable isotopes make up about 12% of the mass of fission products. Despite its low, against the background of palladium or ruthenium, the cost (~ $ 50 per kg) is the fact that xenon is a noble gas that makes it interesting. When any SNF reprocessing, xenon is released in gaseous form, therefore, no special radiochemistry is needed to obtain it, which drastically reduces the cost. There is, however, one problem - although there are no long-lived xenon isotopes (a gift of nature!), It is always accompanied by krypton, the Kr-85 isotope of which is a long-lived radioactive element.
Nevertheless, cryogenic rectification can help to obtain pure xenon, which is now increasingly used in spacecraft ion engines, in anesthesia, etc. In spite of this, I did not manage to find traces of the practice of xenon conservation during the reprocessing of spent nuclear fuel - it is usually simply dumped into the atmosphere.
Technically, there are still a few elements that may be of interest in the future for extraction from SNF, for example tellurium. However, the current cost of these materials, as in the case of silver, does not justify their extraction from SNF.
Shares of various elements in fission products U235
The result is that, at best, when barriers to the use of weakly radioactive palladium are removed, precious metals can return about 2-2.5% of the cost of processing SNF, and at worst, about 0.5%, which means that removing them from no one will deal with the fragmentation mass.
Finishing the description of this section, it must be said that the wait-and-see position on disposal is also explained by the possible emergence of new methods for the reprocessing of spent nuclear fuel, such as the electrofusion of the spent nuclear fuel proposed by BREST or the more exotic spent nuclear fuel rectification or plasma separation. Theoretically, the reprocessing of spent nuclear fuel can be noticeably cheaper, winning the total cost of the disposal scenario. However, the position of the United States, which in every way impedes the development of spent nuclear fuel reprocessing in the world, and technical difficulties hinder the development of this theory.
Returning to the economy: seeing the big picture, I want to consider another option - endless “intermediate” storage. If you look at the estimates of the operating costs of the storage site, we will see there figures of 5-15 dollars per kilogram of fuel per year, with 90% of this amount due to the cost of protecting the site. It turns out that the difference between the cost of direct disposal and the accumulated value of storage is selected for 50-100 years, for which dry storage containers or storage buildings are usually calculated.
It turns out the following gradation of actions - it is cheaper to “intermediately” store, but this process runs the risk of dragging out (as it happens in the USA, where national disposal of spent nuclear fuel has been under discussion for 40 years) and become a significant factor in the overall life cycle cost of nuclear fuel. The best instant decision in terms of cost is the fastest possible disposal of SNF in deep geology. Well, if there is hope for the development of nuclear energy in the direction of the CNFC - then it is necessary to develop the processing of nuclear fuel.
By the way, see a cool video about the creation and testing of a concrete cork for the tunnels of the Finnish burial Onkalo.
This duality gives rise to a complex choice about the future of spent nuclear fuel - for many decades now, the vast majority of countries possessing nuclear energy cannot decide whether to dispose of spent nuclear fuel or recycle.
')
In this text, if possible, I will carefully try to calculate the expenditure and revenue side of the SNF economy.
Terms and abbreviations used:
Fissile materials (DM) - the actual nuclear fuel that supports the fission chain reaction (Pu239, U235, Pu241, U233). What is called a fuel, in fact, besides DM, usually contains other materials — oxygen, uranium 238, and fission products.
Fission products - fragmentation elements, formed from the DM as a result of fission reaction. Usually radioactive isotopes from 70 to 140 numbers of the periodic table.
PWR / VVER - the most common type of nuclear reactors in the world, with pressurized water (not boiling) in the primary circuit, with a thermal neutron spectrum.
BN is another type of reactor, with a fast neutron spectrum and sodium as a coolant.
CNFC - the closure of the nuclear fuel cycle , a promising method for expanding the fuel base of nuclear energy. This implies the use of BN or BREST reactors.
BREST is another type of reactor with a fast neutron spectrum and lead coolant, which theoretically is more secure than a BN. No such reactor has yet been built.
Debit
The cost of spent nuclear fuel begins at the NPP operator when it leaves the in- situ holding pool and goes either to the dry or to the wet storage. Hereinafter, it is convenient to recalculate all costs into unit costs per kilogram of heavy metals of SNF, so if sent to a dry storage facility, such expenses range from 130 to 300 dollars per kg of SNF and are determined mainly by the cost of storage containers or the building that houses the SNF. Of this amount, from 5 to 30 dollars accounted for transportation operations.
Loading into the shipping container is probably the most expensive SNF in the world - from the surviving holding pool 4 units of the Fukushima nuclear power plant
These amounts are, in fact, negligible. A kilogram of SNF, when it was still fuel, produced (if you take the PWR / VVER) from 400 to 500 MW * h of electricity, costing about 16 ... 50 thousand dollars, i.e. Moving to intermediate storage is not worth it and 1% of revenues from the production of atomic electricity.
However, intermediate storage is intermediate and that it should have some continuation. This can be either direct disposal of SNF unchanged or processing.
Dry container storage is the cheapest option for intermediate storage of SNF today - no building is needed if the site is located on the NPP territory - even additional security is not needed. The gigawatt unit uses about 2.5 such containers for a year, each costing $ 0.5-1 million per unit.
Deep disposal of spent nuclear fuel is now being implemented in the form of specific projects in Finland , Sweden, the United States and Switzerland and is being investigated for different sites in another two dozen countries. The example of Finland and Sweden shows that the cost of direct disposal will most likely be around $ 1,000 per kilogram of SNF or slightly lower - and the total costs by the time of the final removal of the issue from the SNF from the NPP operator’s shoulders will be, accordingly, something like $ 1000-1200 on kilogram. Interestingly, this amount is about half the cost of fresh fuel.
Containers for final geological disposal. The technology requires an exposure of 20-30 years before performing this disposal, however today in many countries there are no problems with the search for spent nuclear fuel, which has been stored for 30+ years
However, the cost of direct disposal is similar to the cost of recycling - maybe by extracting valuable materials, you can reduce overall costs, or even get a plus?
Credit
The main motive for radiochemical reprocessing of spent nuclear fuel is the new nuclear fuel accumulated in it, and a little wider - in general, fissile materials. The cost of these recoverable materials is an anchor in the whole processing economy, in other words, it is definitely the most valuable thing that can be extracted from SNF. Comparing with the cost of U235, extracted from natural uranium (approximately 25 thousand dollars per kg), one can quickly figure out whether the game is worth the effort.
If you look for information on the cost of reprocessing, you can find figures from $ 700 to $ 2,000 per kilogram of heavy metals from SNF (without taking into account the weight of the metal parts of the fuel assembly with fuel, which you also have to mess with, and oxygen, because the fuel is mostly in the form of oxide) . The spent nuclear fuel of the atomic energy industry - PWR / VVER reactors contains from 1.5 to 2.5% of fissile materials (the first figure refers to modern fuel designs, of which they are squeezed to the maximum, the second to old spent SNF).
Overloading of a new transport container TUK-141 with the fuel from the Balakovo NPP reactors in September this year - the beginning of the processing process
You can multiply. Spending from 700 to 2000 dollars we get 25000h1.5-2.5% = 375 ... 625 dollars of fissile materials. The situation worsens even more if we recall the isotopic composition of fissile materials extracted from PWR / VVER spent nuclear fuel - uranium will be contaminated with neutron poison U236, and plutonium almost half consists of non-fissioning isotopes (Pu240, Pu242). In addition, subsequent fabrication of fresh SNF with fairly radioactive plutonium is also more expensive than working with “organic” enriched natural uranium product.
And here in the slender (I hope) narrative on the economics of spent nuclear fuel, which is today, it is worth taking a step aside and also looking at the cost of the fuel cycle in relation to fast reactors and CNFC - what experts considered in the 60s and 70s as the future of the industry.
The simplified (really simplified) scheme of the fuel cycle with reprocessing without fast reactors is rather meaningless, as discussed below.
And the situation will immediately improve. First, the fast neutron spectrum requires a much larger amount of fissile materials in the core, which is achieved by increasing their concentration: up to 20–30% plutonium or 235 uranium, as opposed to 4–5% for reactors with a thermal spectrum. Those. to obtain the same amount of Pu239, we need to recycle 5-6 times less SNF. In addition, we all remember that fast reactors are breeders, and they contain more DM in the SNF than in fresh fuel!
There is one more aspect, if we compare the DM from SNF and natural uranium. When the concentration of DM in fresh fuel BN, say, 27%, burns out of this no more than 11%. Those. â…” Extracted natural uranium without reprocessing will go to the dump, which catastrophically drops the economy of fast reactors without reprocessing spent nuclear fuel (for example, BN-600). The situation is actually the reverse of the VVER.
But let's count. If we extract 300 grams of plutonium from a kilogram of spent nuclear fuel, then in the equivalent of natural uranium our profit is $ 7,500, which is certainly more than the cost of processing this kilogram of $ 2,000. Here the truth must be remembered that in the next cycle it burns about â…“ of the extracted quantity, i.e. revenue is reduced to $ 2,500 per kilogram of SNF.
In fact, this means that the cost of reprocessing spent nuclear fuel — the fabrication of new fuel for fast reactors is equivalent to the fabrication of fuel from natural uranium — the reprocessing “tail” ceases to be a burden.
In fact, of course, I simplify. all sorts of things, such as minor actinides, the disposal of fission products pull the economy of processing down, and the real result is highly dependent on technology. For example, below are the calculated figures for the output of various unpleasant things when processing SNF in France (for 6 different scenarios for the development of this reprocessing) in an amount covering SNF from 100 to 150 gigawatts of capacity.
Below is a table that shows the reduction in demand for natural uranium through the use of fissile materials from recycled fuels.
And now let's see if there is anything else useful in the SNF, which could improve the economy of reprocessing as a whole. Here it is necessary to recall that the fission products of uranium and plutonium are about 70 isotopes of 25 elements. Some nuclides - stable and radioactive, in principle, are of commercial interest.
Palladium Each ton of fission products accounts for approximately 5% of palladium of complex isotopic composition. Those. About 5 kilograms of palladium can be extracted from each ton of SNF of BN containing 100 kilograms of fission products, and 800 grams of tonne of WWER SNF. Unfortunately, palladium will be radioactive due to the Pd-107 isotope (about 14% of all palladium isotopes in SNF), which has a half-life of 6.5 Ma, i.e. wait for its collapse will not work. The specific activity of palladium extracted from SNF will be about 1.2 MBq / g, which is quite a lot. NRB-99 sets the limit for the safe annual supply of palladium of such activity to 1.45 grams per year.
Theoretically, if this radioactive palladium is used (in some industrial catalysts, say) and its price is equal to the price of natural (~ $ 30,000 per kg!), Palladium extracted from SNF will replenish 1-2% of the cost of SNF reprocessing.
Rhodium . Another platinum group metal. 1.2 kg of rhodium can be extracted from a ton of spent nuclear fuel, and about 500 grams from a ton of WWER spent fuel. The longest-lived radioactive isotope Rh-102 with a half-life of 3.74 years, Somewhere in 50 years of exposure, the radioactivity of rhodium will drop to values ​​after which it can be considered non-radioactive. The cost of rhodium is about the same (now even more) than that of palladium, respectively, rhodium extracted from SNF will compensate for 0.3-0.5% of the cost of reprocessing.
Ruthenium . In addition to the infamous Ru-106, among the fission products there are also stable isotopes of this element. Ruthenium in mass in SNF is about 25% more than palladium, and not radioactive (after the collapse of the main amount of Ru-106), it becomes in about 40 years of exposure. Unfortunately, the cost of ruthenium is 6 times lower than palladium, therefore, it also adds only 0.2-0.4% of the cost of spent nuclear fuel reprocessing.
Silver . Among the fission fragments, its share is approximately 0.8%. Those. from this ton of its fragments will be about 8 kg. It has two relatively long-lived radioactive isotopes. Ag-110m with a half-life of 250 days and Ag-108m with a half-life of 418 years. The second isotope is formed with a relatively low yield. The residual activity after 30 years of exposure will be 2.9 ÎĽCi / g, slightly higher than the radioactivity of natural uranium, but comparable. Suitable for technical use, but due to the relatively low cost is hardly economically feasible.
Xenon This is the most common of the fragments of uranium or plutonium - only stable isotopes make up about 12% of the mass of fission products. Despite its low, against the background of palladium or ruthenium, the cost (~ $ 50 per kg) is the fact that xenon is a noble gas that makes it interesting. When any SNF reprocessing, xenon is released in gaseous form, therefore, no special radiochemistry is needed to obtain it, which drastically reduces the cost. There is, however, one problem - although there are no long-lived xenon isotopes (a gift of nature!), It is always accompanied by krypton, the Kr-85 isotope of which is a long-lived radioactive element.
Nevertheless, cryogenic rectification can help to obtain pure xenon, which is now increasingly used in spacecraft ion engines, in anesthesia, etc. In spite of this, I did not manage to find traces of the practice of xenon conservation during the reprocessing of spent nuclear fuel - it is usually simply dumped into the atmosphere.
Technically, there are still a few elements that may be of interest in the future for extraction from SNF, for example tellurium. However, the current cost of these materials, as in the case of silver, does not justify their extraction from SNF.
Shares of various elements in fission products U235
The result is that, at best, when barriers to the use of weakly radioactive palladium are removed, precious metals can return about 2-2.5% of the cost of processing SNF, and at worst, about 0.5%, which means that removing them from no one will deal with the fragmentation mass.
Balance
Finishing the description of this section, it must be said that the wait-and-see position on disposal is also explained by the possible emergence of new methods for the reprocessing of spent nuclear fuel, such as the electrofusion of the spent nuclear fuel proposed by BREST or the more exotic spent nuclear fuel rectification or plasma separation. Theoretically, the reprocessing of spent nuclear fuel can be noticeably cheaper, winning the total cost of the disposal scenario. However, the position of the United States, which in every way impedes the development of spent nuclear fuel reprocessing in the world, and technical difficulties hinder the development of this theory.
Returning to the economy: seeing the big picture, I want to consider another option - endless “intermediate” storage. If you look at the estimates of the operating costs of the storage site, we will see there figures of 5-15 dollars per kilogram of fuel per year, with 90% of this amount due to the cost of protecting the site. It turns out that the difference between the cost of direct disposal and the accumulated value of storage is selected for 50-100 years, for which dry storage containers or storage buildings are usually calculated.
It turns out the following gradation of actions - it is cheaper to “intermediately” store, but this process runs the risk of dragging out (as it happens in the USA, where national disposal of spent nuclear fuel has been under discussion for 40 years) and become a significant factor in the overall life cycle cost of nuclear fuel. The best instant decision in terms of cost is the fastest possible disposal of SNF in deep geology. Well, if there is hope for the development of nuclear energy in the direction of the CNFC - then it is necessary to develop the processing of nuclear fuel.
By the way, see a cool video about the creation and testing of a concrete cork for the tunnels of the Finnish burial Onkalo.
Source: https://habr.com/ru/post/371211/
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