Part 2
Disposing of dangerous waste
One of the the features of the Molten Salt Reactor system is its organic ability to reprocess dangerous nuclear products from its fuel. We will see elsewhere that fission products can be continuously processed out of nuclear fuel. The withdraw of some fission products makes a positive contribution to the operational qualities of molten salt reactors in addition to making them safer. We will also see that both stable and unstable fission products separated out of a MSR fuel salts represent a potential revenue stream for the reactor owner. The ultimate solution for the so called problem of nuclear waste is that “nuclear waste” is transformed into an above ground mine for mineral resources.
One advantage to the two fluid MSR design is that the recovery of fissionable yield from nuclear breeding is kept separate from from recovery of fission products. It is thus possible to keep all operations related to new fuel recovery and processing within the reactor hot cell, which becomes a significant barrier to nuclear proliferation.
The IFR technology used by the ARC-100 requires that its fuel be removed and batch processed outside the reactor. The metallic fuel is mechanically removed from the reactor and them disolved in a molten salt bath, and uranium and TRUs are separated from fission products, and then reformed into metallic fuel elements, and returned to the reactor. There are in efficiencies in this process, and up to 3% of the plutonium present in the reprocessed fuel may be lost to the process. It would be unacceptable for plutonium to contaminate recovered fission products. In addition, the potential for large plutonium losses in the recovery process could lead to accounting issues that could mask plutonium diversions for weapons purposes.
Transportation requirements
Professor Andrew Kadak,, who teaches nuclear engineering at MIT, has pointed out what happens when labor is transferred to the construction site to the factory.
“Building a reactor in a factory should save construction time, says Kadak. He estimates that what takes eight hours to do in the field could be done in just one hour in a factory. Once the reactor is manufactured, it would then be shipped to the site of a power plant along with the necessary containment walls, turbines for generating electricity, control systems, and so on.”
In order to take full advantage of the labor and cost saving potential of factory manufacture of reactors, the final product must be broken down into a relatively few, transportable and easily and quickly assembled components. Thus the successful factory manufactured reactor should be relatively compact. Reactors such as the PBMR have very large cores, and thus require considerable onsite assembly. They are not conspicuously less expensive than larger light water reactors manufactured by onsite assembly of factory manufactured kits. A Le Blanc tube MSR core would not only be very inexpensive to manufacture, but it would also be easily transportable. If the design of the MSR heat exchange can be kept to a transportable size, easy transportation and rapidly assembly of Le Blanc MSRs would be possible.
In contrast the small “factory built” mPower reactor would still require a few million hours of onsite labor and 2 years of onsite construction. It is not clear how much onsite manufacturing will be required for the ARC-100. Although its core is small, the sodium pool required by the IFR safety philosophy requires a much larger containment vessel, and its fuel handling machinery is fairly complex. It appears that the final assembly of the ARC-100 will be a larger and more complex task than MSR final assembly, but a great deal more should be known before final judgement n the matter is possible.
Self sustaining fuel cycles
The success of the nuclear technology of the 1950's is currently a curse to the nuclear industry. The short comings of 50's technology continue to offer grounds for opposition to nuclear power, while the the once through uranium fuel cycle cannot be sustained as the primary source of global energy. This circumstances was actually foreseen during World War II by Manhattan project scientist. Alvin Weinberg recored,
“At the April 28, 1944, meeting of the New Piles Committee, Phil Morrison had reported the known reserves of uranium at workable concentration to amount to only about 20 000 tons. With so little fuel, nuclear energy based only on the 0.7 per- cent of uranium-235 in natural uranium could hardly amount to much. Morrison also pointed out at this meeting that the vastly larger amount of residual uranium in the granites could be burned with a positive energy balance—but only if used in a breeder.”
According to Weinberg, Morrison added that
“more work should be done on the nuclear development of thorium because of its greater availability and also suggested experiments, . . .”
Weinberg records Morrison's excitement when,
“Morrison showed me his calculations . . .”
What Morrison demonstrated to Weinberg was that,
“if uranium (was) burned in a breeder (reactor), the energy released through fission exceeded the energy required to extract the residual 4 ppm of uranium from granitic rocks.”
Later Weinberg was to reduce this key to sustainable nuclear power to a single slogan, “burn the rocks.”
Later Eugene Wigner and Alvin Weinberg came to prefer thorium breeding to uranium breeding. Both preferred the advantages of fluid core reactors. Eugene Wigner, who was still in Chicago, had become interested in breeder reactors, and their siblings, converter reactors. Wigner became intrigued by the potential of a thorium breeding cycle. Wigner concerned about future uranium supplies envisioned a reactor that would burn Pu239 and would be surrounded by a blanket of Th232. The reactor would produce U-233, a fissionable nuclear fuel. But, it was noted that the cost of fuel reprocessing for such a reactor would make it not competitive with coal as a power source.
At that point Wigner and Harold Urey realized that the aqueous homogeneous reactor offered a solution to the problem of fuel reprocessing costs. Unlike Fermi who was strictly a classical physicist, Wigner was trained as a chemical engineer. For Wigner, the fluid fuel approach meant that the fuel could be withdrawn without difficulty from the reactor, reprocessed, and returned in a process that would cost much less than the cost of reprocessing solid reactor fuel. It is a tribute to the genius of Eugene Wigner, that he understood the problem that would create nuclear waste in conventional civilian power reactors, and that started the process of developing a solution to the problem.
Wigner, and his bright young assistant, Alvin Weinberg, together with engineer Gale Young, wrote a report outlining the concept in the spring of 1945. Thus the notion that the aqueous homogeneous reactor could serve as a basis for a civilian power industry remained a focus of Wigner for some time. Weinberg, both a research director and later as general director of Oak Ridge National Laboratory, championed Oak Ridge research on the aqueous homogeneous reactor until the end of the 1950’s.
Critics of nuclear power often depict nuclear scientists, as lacking in vision or a concern for human well being, and impractical. In fact the opposite is the case. Eugene Wigner was a scientist who could look long into the future and anticipated resource shortages. He was practical enough to see that low cost power was highly desirable, and as someone who had actually worked as a chemical engineer, he applied a sound chemical engineering approach to the reprocessing of nuclear fuel, and worked that approach back into the design of the reactor. Alvin Weinberg, Wigner’s young assistant, was to learn from Wigner’s long vision, and was to elaborate it during the coming years.
Eventually the Chemist Raymond C. Briant convinced Alvin Weinberg that the Molten Salt Reactor held more promise as a thorium cycle nuclear breeder than the aqueous homogeneous reactor.
Molten Salt Reactors are a reality. Two were built and successfully tested in the 1950's and '60's at Oak Ridge. A 1980's reactor experiment at Shippingport, Pennsylvania demonstrated that breeding thorium was possible. There appear to be no killer technological obstacles to the development of the Molten Salt Thorium Breeder, the LFTR. But can the LFTR be built at a cost that is significantly less than the cost of conventional reactors?
There is probable cause to believe that the answer is yes, but this is less than certain without further investments. There are financial risks for all forms of post carbon energy including for renewables, whose goose, according to T. Boone Pickens, would be cooked without very large government subsidies.
It certainly is no more certain that the AEC-100 or the mPower Reactor can be built for less than conventional reactors, and even less likely that either can be built for less than factory manufactured LFTRs.
Nuclear proliferation issues
In a famous essay, Hyman Rickover wrote about the difference between paper reactors and real reactors. A real reactor is one for which the challenges of implementation have been meet. Paper reactors is a reactor whose design only exists on paper. There are also real and paper proliferation routs. A real proliferation route is one which nations acquire nuclear weapons, contrary to international treaties. Paper routes to nuclear proliferation, are routes that no nation has actually used to acquire nuclear weapons, but which academic nuclear proliferation “experts” imagine might be used.
Academic Nuclear proliferation reactor specialist Frank von Hippel apparels to have invented a paper route to nuclear proliferation by dropping a sentence from an anthologized paper by nuclear weapons designer J. Carson Marks. The paper was on the explosive qualities of reactor grade plutonium (RGP), that is the the plutonium that found in “spent” reactor fuel. In his original paper, Marks had noted that while reactor grade plutonium was not weaponozable. In a later republication of Marks' paper, edited by von Hippel, the sentence stating that RGP was not weaponizable was dropped. Von Hippel then went on to postulate that RGP was weaponizable, offering as his authority Marls's (redacted) paper, thus creating a wholly paper route to the treaty violating development of nuclear weapons.
At the same time nuclear weapons have spread to a number of nations by routes wholly unforeseen by von Hippel and his academic and policy making followers. The actual routes to nuclear proliferation followed by real proliferators, have many advantages over the paper routes suggested by von Hippel and Company. The use of Generation IV reactor technology as a nuclear proliferation tool, would appear to be more paper routes to proliferation. Nuclear proliferation experts who express concern about the use of Generation IV nuclear technology would appeal place concern about such paper routes over proven proliferation routes. Contrary to the usual assumption, the development and use of Generation IV technologies would not make proliferation more likely.
The LFTR, which can be designed to only breed its own replacement fuel and nothing more, is a very unlikely proliferation too. In addition, by tweaking the LFTR fuel formula by adding U-238, separating out fissionable U-233 from the LFTR fuel would become very difficult.
The ARC-100 is another unlikely proliferation tool. If the ARC -100 is started with large amounts of RGP, even by running its fuel through short cycles before reprocessing will not produce plutonium of weapons grade purity. If an ARC-100 is started with weapons grade plutonium or HEU, then the would be proliferator already posses nuclear proliferation tools.
It should thus be concluded that the LFTR and the ARC-100 are paper proliferation risks, are not realistic proliferation options, and are highly unlikely to increase the probability that rogue states or terrorist groups will acquire nuclear weapons.
Manufacturing speed and cost
The construction of Light Water Reactors typically takes from 3 to 6 years and requires more that 10,000,000 hours of highly skilled labor. On average over two hours of each workers labor time is lost every day, due to project disorganization. Reactors are largely constructed on site, Modules typically weigh 40 tones. The AP-1000 is designed to be built from a kit which includes close to 300 40 ton modules, in addition to much more massive parts including pressure vessels and steam generators. There is much more to AP-1000 assembly besides connecting the modules like so many lego blocks.
Shifting from the construction of large reactors in the field, to manufacturing small reactors in factories, potentially holds the promise of a considerable labor savings. Technology changes might save even more labor and on other aspects of reactor manufacture as well. For Example, The Le Blanc tube MSR/LFTR core would be quite simple, and would require little labor compared to core manufacture for conventional reactors. Other parts of MSR/LFTR type reactor are also relatively simple, and probably could ber mass produced easily and cheaply. There are thus probable cause arguments that LFTRs can be factory manufactured cheaply and at low cost, and that their final assembly would be quick and inexpensive. There are also cautionary tales about quick, easy and inexpensive technology schemes. If cost certainty is an over riding goal in future energy technology development, we face a deeply troubling future.
There are however, reasons to believe that the factory manufacture of major LFTR components can don in a relatively short period of time. There would also be cost advantages to manufacturing large numbers of LFTRs. Hence there is a rational for mass production of LFTRs in factories, if the deployment logistics can be worked out. David Walters has proposed a the use of naval yards for LFTR factories, and this is an attractive proposal.
The mass deployment of LFTRs would require the creation of a karge number of deployment teams. A rapid deployment cycle would lead to deployment teams that were highly experienced, and hence final assemble would be involve far fewer problems than conventional
reactor field manufacturing. It thus would certainly not impossible for LFTRs to progress from order to criticality in under 6 months.
In contrast, the construction of a more conventional mPower reactor can, according to information from Babcock & Wilcox, be expected to take two years. How Long ARC-100 manufacture will take is unknown.
Cooling
One of the allegations offered by critics of nuclear power is the “we are running out of water” story. The story says that reactors require too much water, and that we face a water shortage, thus we cannot supply enough water to cool reactors. Hence it is a waste of money to build them. This story is ironic because the tale teller is usually also a solar thermal advocate, and never has considered the water issues of solar thermal power. In fact the greatest future water shortages will be in the desert southwest, the area of the country where solar thermal power looks attractive. The “we are running out of water” story is far more telling for the Colorado River Basin, than for any other water shed in the United States. Hense, water shortages are going to be far more of a problem for renewable energy than for nuclear power. Nuclear power plants, can draw cooling water from the sea. In fact, California nuclear power plants can be located by the sea, and their water cooling system can also serve as be a desalinization system.
Most of the water used in reactor cooling is returned to its natural source, although a small percentage will be lost through evaporation. Reactors can be air cooled. The B&W mPower small reactor is designed to be either air or water cooled, with air cooling extracting a small efficiency penalty. The original Molten Salt Reactors were air-cooled, and there would be no major problems designing LFTRs for air cooling. Thus water shortages are not an obstacle to reactor deployment any where in the world.
Rapid and Massive Deployment
Significant problems, including AGW, and the decline of conventional oil sources will require a significant transition away from 20th century energy technologies during the next 40 years. For nuclear power to play a significant role in this transition, it will require both rapid and massive deployment of power generating reactors globally. The use of small factory produced reactors can facilitate this mass rapid deployment, because factory produced reactors can be built with greater labor efficiency and very likely at a lower cost compared to traditional reactor manufacturing technologies. In particular, Molten Salt type reactors including the LFTR have attractive features which would ease their mass production and mass deployment problems. These include:
When ORNL researchers compared the potential costs of Molten Salt Breeder Reactors (a LFTR) with that of Light Water Reactors in the early 1970's, they found that the likely costs of the MSBR would be about the same as that of a LWR. However the costs of LWRs rose significantly later in the 1970's and 1980's. Much of that cost increase was dure to added LWR safety features, that would not be necessary for a LIFTR. Thus there is reason to suspect that a LFTR, even with fuel reprocessing will cost less to build than conventional reactors. If fuel reprocessing and cleaning systems are mas produced, their cost will be relatively low, thus for the LFTR, massive deployment would probably tend to lower component costs.
The prospects for massive deployment of small, factory produced LWR s such as the B&W mPower are far less certain. Fuel availability will be a major issue, and compared to the LFTR, the mPower is far more complex and therefore likely to be more expensive and require a significantly longer time to build.
Finally, too few details have been offered about the ARC-100 to even speculate about its costs. However, If the primary source of ARC-100 and LFTR start up charges is Reactor Grade Plutonium, 10 thermal LFTRs can be started for every 1 ARC-100. In addition the breeding ration of the ARC-100 would be probably be similar to that of the LFTR. Thus the ARC-100 could well be significantly handicapped in the race to provide massive deployment potential.
Fuel efficiencies
Both the LFTR and the ARC-100 offer significantly greater fuel efficiency than conventional reactors. Both are capable of 1 to 1 fuel conversion and both are capable of breeding. Both designs are consistent with a sustainable nuclear economy.
Fuel reprocessing
Both the LFTR and the ARC-100 offer integral fuel reprocessing technologies. The LFTR's technology offers some advantages and may cost less to manufacture and operate. Both technologies appear to offer fuel reprocessing at a lower cost than traditional reprocessing technologies. The ARC-100's reprocessing technology could loose as much as 3% of the plutonium present in reprocessed fuel, to its waste stream. The losse ration for the LFTR is unknown,
Long term nuclear waste
Both the LFTR and the ARC-100 could meet the 99% reduction of nuclear waste target. In addition both could be effective tools for reducing the amount of TRU fount in spent light water reactor fuel.
In Part 3 I intend to argue the probable case that Generation IV reactors can be produced and deployed at a sufficiently rapid rate to meet global carbon emission reduction goals by 2050. I will also argue the cost of Generation IV reactors is likely to be significantly lower than the cost of conventional reactors, Finally I will argue that Generation IV reactors represent sustainable energy technology, and thus represent a long term solution to meeting human energy needs,
Safety
The issue of nuclear safety has already been addressed elsewhere in this white paper. There are three different philosophies of nuclear safety. They are:
A. Defensive safety which involves preventing the emissions of radioactive isotopes from a reactor through the use of a system of barriers to that spread. The barriers can also be barriers to prevent loss of cooling in the event of a loss of coolant accident. finally barriers may be barriers to dangerous human behavior that could could lead to radioisotope emissions. Both operator error and the actions of terrorists belong in this barrier category.
B. Natural or passive safety. this catigory of safety relies on the laws of nature to keep a reactor safe. One example would be the use of natural water circulation or thermal syphoning to keep coolant water circulating through a reactor core. With natural circulation one does not need to worry about the consequences of a pump failure.
A second natural safety system would involve the gravity feed of emergency coolant water into a LWR core, in the event of a loss of coolant accident.
In Integral Fast Reactors, the use of a coolant pool, the use of fuel metal expansion to create a negative coefficient of reactivity, and the use of natural convection coolant circulation all use the laws of nature to automatically provide safety without human intervention. Finally in molten fluoride salt the thermal expansion of the carrier/fuel salt, cause by increased reactor temperature automatically begins to expel nuclear fuel from the core. The hotter the reactor gets, the more nuclear fuel is automatically expelled until the reactor is unable to sustain a chain reaction and shuts down. This feature operates in an entirely automatic fashion and is not controlled by operators. Finally if a MSR core overheats, a drain plug at the bottom of the reactor automatically melts, and the core drains into drain tanks. the tanks are in turn cooled by the natural convection of air, and a chimney effect draws fresh air into the reactor chamber at the bottom and expelles hot air at the top of a chimney.
C A third philosophy of nuclear safety might be called precautionary or offensive safety. This approach is only possible in fluid core reactors. In particular it was investigated at Oak Ridge National Laboratory for the Molten Salt Breeder Reactor. Precautionary safety involves the removal of highly radioactive fission products from the nuclear core. These include the gasses xenon(Xe), and krypton (Kr),. and the volatile fission products, iodine(I), tellurium(Te), cesium(Cs), and rubidium(Rb). In particular it is considered highly desirable from the standpoint of reactor control to continuously bubble xenon out of the liquid salt core fluids, with krypton following the xenon out. They can then be captured and stored. Removing the volatile fission products enhances nuclear safety, nut solves some materials problems with MSR. Tellurium is a particular problem because it contributes to some materials problems in the MSR core. The removal of the noble metals,
The removal of the noble gases, volatile fission products, and Nobel metals can be justified by safety benefits as a step designed to increase nuclear safety while lowering overall nuclear costs. In addition the continuous removal of fission products will offer significant benefits to reactor designers.
Thus Molten Salt Reactors have unique precautionary safety features, that involve the removal of radioactive isotopes. Combining the precautionary safety removal of radioactive gasses, and volatile fission products with an underground location location would mean in practice that further defenses against radioisotope release in the event of a nuclear accident would be unnecessary because gravity would serve as a sufficient barrier to the movement of against the movement of non-volatile radioisotopes away from the reactor hot cell. In addition, MSRs including the Liquid Fluoride Thorium reactor (LFTR) can be designed to operate with a negative coefficient of thermal reactivity, which protects the reactor from a loss of control over criticality as internal temperature rises.
MSRs can be designed to completely shut down before rising temperatures become a serious problem. In addition freeze core drain plugs offer a fall back passive safety feature that prevents reactor overheating. As core salt temperature rises past a certain point a plug of frozen salt is melted by simple heat transfer from the fluid core salt to the frozen plug salt. Once the plug melts the core salt drains into a tank or series of tanks shaped to prevent criticality. A passive air cooling system can insure that heat from the radioactive decay of the remaining fission products in the core salts will not become a problem.
The ARC-100, a proposed 100 MWe Integral Fast Reactor would share with other IFRs a negative temperature coefficient of reactivity. A large tank of liquid sodium located in close proximity to the reactor core would then serve as a thermal reservoir to prevent overheating due to the radioactive decay of the fission products embedded with in the fuel. A passive air cooling system will prevent the core and sodium tank from overheating. The ARC-100 breeding ratio is unlikely high enough to pose a void wort problem, and even if it did, Argonne National Laboratory research indicates that the IFR negative temperature coefficient of reaction feature of IFRs would shut down the fission process in the ARC-100 core before the core is damaged.
Thus both the LFTR and other factory produced MSTs as well as the ARC-100 would offer outstanding levels of safety. In particular MSR safety could offer a major route to lowering reactor price, because massive safety structures would be unnecessary.
Disposing of dangerous waste
One of the the features of the Molten Salt Reactor system is its organic ability to reprocess dangerous nuclear products from its fuel. We will see elsewhere that fission products can be continuously processed out of nuclear fuel. The withdraw of some fission products makes a positive contribution to the operational qualities of molten salt reactors in addition to making them safer. We will also see that both stable and unstable fission products separated out of a MSR fuel salts represent a potential revenue stream for the reactor owner. The ultimate solution for the so called problem of nuclear waste is that “nuclear waste” is transformed into an above ground mine for mineral resources.
One advantage to the two fluid MSR design is that the recovery of fissionable yield from nuclear breeding is kept separate from from recovery of fission products. It is thus possible to keep all operations related to new fuel recovery and processing within the reactor hot cell, which becomes a significant barrier to nuclear proliferation.
The IFR technology used by the ARC-100 requires that its fuel be removed and batch processed outside the reactor. The metallic fuel is mechanically removed from the reactor and them disolved in a molten salt bath, and uranium and TRUs are separated from fission products, and then reformed into metallic fuel elements, and returned to the reactor. There are in efficiencies in this process, and up to 3% of the plutonium present in the reprocessed fuel may be lost to the process. It would be unacceptable for plutonium to contaminate recovered fission products. In addition, the potential for large plutonium losses in the recovery process could lead to accounting issues that could mask plutonium diversions for weapons purposes.
Transportation requirements
Professor Andrew Kadak,, who teaches nuclear engineering at MIT, has pointed out what happens when labor is transferred to the construction site to the factory.
“Building a reactor in a factory should save construction time, says Kadak. He estimates that what takes eight hours to do in the field could be done in just one hour in a factory. Once the reactor is manufactured, it would then be shipped to the site of a power plant along with the necessary containment walls, turbines for generating electricity, control systems, and so on.”
In order to take full advantage of the labor and cost saving potential of factory manufacture of reactors, the final product must be broken down into a relatively few, transportable and easily and quickly assembled components. Thus the successful factory manufactured reactor should be relatively compact. Reactors such as the PBMR have very large cores, and thus require considerable onsite assembly. They are not conspicuously less expensive than larger light water reactors manufactured by onsite assembly of factory manufactured kits. A Le Blanc tube MSR core would not only be very inexpensive to manufacture, but it would also be easily transportable. If the design of the MSR heat exchange can be kept to a transportable size, easy transportation and rapidly assembly of Le Blanc MSRs would be possible.
In contrast the small “factory built” mPower reactor would still require a few million hours of onsite labor and 2 years of onsite construction. It is not clear how much onsite manufacturing will be required for the ARC-100. Although its core is small, the sodium pool required by the IFR safety philosophy requires a much larger containment vessel, and its fuel handling machinery is fairly complex. It appears that the final assembly of the ARC-100 will be a larger and more complex task than MSR final assembly, but a great deal more should be known before final judgement n the matter is possible.
Self sustaining fuel cycles
The success of the nuclear technology of the 1950's is currently a curse to the nuclear industry. The short comings of 50's technology continue to offer grounds for opposition to nuclear power, while the the once through uranium fuel cycle cannot be sustained as the primary source of global energy. This circumstances was actually foreseen during World War II by Manhattan project scientist. Alvin Weinberg recored,
“At the April 28, 1944, meeting of the New Piles Committee, Phil Morrison had reported the known reserves of uranium at workable concentration to amount to only about 20 000 tons. With so little fuel, nuclear energy based only on the 0.7 per- cent of uranium-235 in natural uranium could hardly amount to much. Morrison also pointed out at this meeting that the vastly larger amount of residual uranium in the granites could be burned with a positive energy balance—but only if used in a breeder.”
According to Weinberg, Morrison added that
“more work should be done on the nuclear development of thorium because of its greater availability and also suggested experiments, . . .”
Weinberg records Morrison's excitement when,
“Morrison showed me his calculations . . .”
What Morrison demonstrated to Weinberg was that,
“if uranium (was) burned in a breeder (reactor), the energy released through fission exceeded the energy required to extract the residual 4 ppm of uranium from granitic rocks.”
Later Weinberg was to reduce this key to sustainable nuclear power to a single slogan, “burn the rocks.”
Later Eugene Wigner and Alvin Weinberg came to prefer thorium breeding to uranium breeding. Both preferred the advantages of fluid core reactors. Eugene Wigner, who was still in Chicago, had become interested in breeder reactors, and their siblings, converter reactors. Wigner became intrigued by the potential of a thorium breeding cycle. Wigner concerned about future uranium supplies envisioned a reactor that would burn Pu239 and would be surrounded by a blanket of Th232. The reactor would produce U-233, a fissionable nuclear fuel. But, it was noted that the cost of fuel reprocessing for such a reactor would make it not competitive with coal as a power source.
At that point Wigner and Harold Urey realized that the aqueous homogeneous reactor offered a solution to the problem of fuel reprocessing costs. Unlike Fermi who was strictly a classical physicist, Wigner was trained as a chemical engineer. For Wigner, the fluid fuel approach meant that the fuel could be withdrawn without difficulty from the reactor, reprocessed, and returned in a process that would cost much less than the cost of reprocessing solid reactor fuel. It is a tribute to the genius of Eugene Wigner, that he understood the problem that would create nuclear waste in conventional civilian power reactors, and that started the process of developing a solution to the problem.
Wigner, and his bright young assistant, Alvin Weinberg, together with engineer Gale Young, wrote a report outlining the concept in the spring of 1945. Thus the notion that the aqueous homogeneous reactor could serve as a basis for a civilian power industry remained a focus of Wigner for some time. Weinberg, both a research director and later as general director of Oak Ridge National Laboratory, championed Oak Ridge research on the aqueous homogeneous reactor until the end of the 1950’s.
Critics of nuclear power often depict nuclear scientists, as lacking in vision or a concern for human well being, and impractical. In fact the opposite is the case. Eugene Wigner was a scientist who could look long into the future and anticipated resource shortages. He was practical enough to see that low cost power was highly desirable, and as someone who had actually worked as a chemical engineer, he applied a sound chemical engineering approach to the reprocessing of nuclear fuel, and worked that approach back into the design of the reactor. Alvin Weinberg, Wigner’s young assistant, was to learn from Wigner’s long vision, and was to elaborate it during the coming years.
Eventually the Chemist Raymond C. Briant convinced Alvin Weinberg that the Molten Salt Reactor held more promise as a thorium cycle nuclear breeder than the aqueous homogeneous reactor.
Molten Salt Reactors are a reality. Two were built and successfully tested in the 1950's and '60's at Oak Ridge. A 1980's reactor experiment at Shippingport, Pennsylvania demonstrated that breeding thorium was possible. There appear to be no killer technological obstacles to the development of the Molten Salt Thorium Breeder, the LFTR. But can the LFTR be built at a cost that is significantly less than the cost of conventional reactors?
There is probable cause to believe that the answer is yes, but this is less than certain without further investments. There are financial risks for all forms of post carbon energy including for renewables, whose goose, according to T. Boone Pickens, would be cooked without very large government subsidies.
It certainly is no more certain that the AEC-100 or the mPower Reactor can be built for less than conventional reactors, and even less likely that either can be built for less than factory manufactured LFTRs.
Nuclear proliferation issues
In a famous essay, Hyman Rickover wrote about the difference between paper reactors and real reactors. A real reactor is one for which the challenges of implementation have been meet. Paper reactors is a reactor whose design only exists on paper. There are also real and paper proliferation routs. A real proliferation route is one which nations acquire nuclear weapons, contrary to international treaties. Paper routes to nuclear proliferation, are routes that no nation has actually used to acquire nuclear weapons, but which academic nuclear proliferation “experts” imagine might be used.
Academic Nuclear proliferation reactor specialist Frank von Hippel apparels to have invented a paper route to nuclear proliferation by dropping a sentence from an anthologized paper by nuclear weapons designer J. Carson Marks. The paper was on the explosive qualities of reactor grade plutonium (RGP), that is the the plutonium that found in “spent” reactor fuel. In his original paper, Marks had noted that while reactor grade plutonium was not weaponozable. In a later republication of Marks' paper, edited by von Hippel, the sentence stating that RGP was not weaponizable was dropped. Von Hippel then went on to postulate that RGP was weaponizable, offering as his authority Marls's (redacted) paper, thus creating a wholly paper route to the treaty violating development of nuclear weapons.
At the same time nuclear weapons have spread to a number of nations by routes wholly unforeseen by von Hippel and his academic and policy making followers. The actual routes to nuclear proliferation followed by real proliferators, have many advantages over the paper routes suggested by von Hippel and Company. The use of Generation IV reactor technology as a nuclear proliferation tool, would appear to be more paper routes to proliferation. Nuclear proliferation experts who express concern about the use of Generation IV nuclear technology would appeal place concern about such paper routes over proven proliferation routes. Contrary to the usual assumption, the development and use of Generation IV technologies would not make proliferation more likely.
The LFTR, which can be designed to only breed its own replacement fuel and nothing more, is a very unlikely proliferation too. In addition, by tweaking the LFTR fuel formula by adding U-238, separating out fissionable U-233 from the LFTR fuel would become very difficult.
The ARC-100 is another unlikely proliferation tool. If the ARC -100 is started with large amounts of RGP, even by running its fuel through short cycles before reprocessing will not produce plutonium of weapons grade purity. If an ARC-100 is started with weapons grade plutonium or HEU, then the would be proliferator already posses nuclear proliferation tools.
It should thus be concluded that the LFTR and the ARC-100 are paper proliferation risks, are not realistic proliferation options, and are highly unlikely to increase the probability that rogue states or terrorist groups will acquire nuclear weapons.
Manufacturing speed and cost
The construction of Light Water Reactors typically takes from 3 to 6 years and requires more that 10,000,000 hours of highly skilled labor. On average over two hours of each workers labor time is lost every day, due to project disorganization. Reactors are largely constructed on site, Modules typically weigh 40 tones. The AP-1000 is designed to be built from a kit which includes close to 300 40 ton modules, in addition to much more massive parts including pressure vessels and steam generators. There is much more to AP-1000 assembly besides connecting the modules like so many lego blocks.
Shifting from the construction of large reactors in the field, to manufacturing small reactors in factories, potentially holds the promise of a considerable labor savings. Technology changes might save even more labor and on other aspects of reactor manufacture as well. For Example, The Le Blanc tube MSR/LFTR core would be quite simple, and would require little labor compared to core manufacture for conventional reactors. Other parts of MSR/LFTR type reactor are also relatively simple, and probably could ber mass produced easily and cheaply. There are thus probable cause arguments that LFTRs can be factory manufactured cheaply and at low cost, and that their final assembly would be quick and inexpensive. There are also cautionary tales about quick, easy and inexpensive technology schemes. If cost certainty is an over riding goal in future energy technology development, we face a deeply troubling future.
There are however, reasons to believe that the factory manufacture of major LFTR components can don in a relatively short period of time. There would also be cost advantages to manufacturing large numbers of LFTRs. Hence there is a rational for mass production of LFTRs in factories, if the deployment logistics can be worked out. David Walters has proposed a the use of naval yards for LFTR factories, and this is an attractive proposal.
The mass deployment of LFTRs would require the creation of a karge number of deployment teams. A rapid deployment cycle would lead to deployment teams that were highly experienced, and hence final assemble would be involve far fewer problems than conventional
reactor field manufacturing. It thus would certainly not impossible for LFTRs to progress from order to criticality in under 6 months.
In contrast, the construction of a more conventional mPower reactor can, according to information from Babcock & Wilcox, be expected to take two years. How Long ARC-100 manufacture will take is unknown.
Cooling
One of the allegations offered by critics of nuclear power is the “we are running out of water” story. The story says that reactors require too much water, and that we face a water shortage, thus we cannot supply enough water to cool reactors. Hence it is a waste of money to build them. This story is ironic because the tale teller is usually also a solar thermal advocate, and never has considered the water issues of solar thermal power. In fact the greatest future water shortages will be in the desert southwest, the area of the country where solar thermal power looks attractive. The “we are running out of water” story is far more telling for the Colorado River Basin, than for any other water shed in the United States. Hense, water shortages are going to be far more of a problem for renewable energy than for nuclear power. Nuclear power plants, can draw cooling water from the sea. In fact, California nuclear power plants can be located by the sea, and their water cooling system can also serve as be a desalinization system.
Most of the water used in reactor cooling is returned to its natural source, although a small percentage will be lost through evaporation. Reactors can be air cooled. The B&W mPower small reactor is designed to be either air or water cooled, with air cooling extracting a small efficiency penalty. The original Molten Salt Reactors were air-cooled, and there would be no major problems designing LFTRs for air cooling. Thus water shortages are not an obstacle to reactor deployment any where in the world.
Rapid and Massive Deployment
Significant problems, including AGW, and the decline of conventional oil sources will require a significant transition away from 20th century energy technologies during the next 40 years. For nuclear power to play a significant role in this transition, it will require both rapid and massive deployment of power generating reactors globally. The use of small factory produced reactors can facilitate this mass rapid deployment, because factory produced reactors can be built with greater labor efficiency and very likely at a lower cost compared to traditional reactor manufacturing technologies. In particular, Molten Salt type reactors including the LFTR have attractive features which would ease their mass production and mass deployment problems. These include:
A. The absence of massive steel components which are featured in water cooled reactors.The fuel and blanket salt cleaning and reprocessing systems of LFTR add both to their direct cost and the complexity of the LFTR. But even here we have a mixed picture, because fuel salt cleaning and reprocessing are safety and “Nuclear waste handling” features, that perform functions that are external for solid core reactors. In particular fuel cleaning may lower other safety related reactor construction expenses, blanket salt reprocessing would substitute for uranium enrichment in conventional reactors.
B. Very simplified cooling system compared to LWRs.
C. Simplified instrumentation system,
D. Flexible materials choices.
E. Relatively few parts.
F. Relative light weight of at least some major components.
When ORNL researchers compared the potential costs of Molten Salt Breeder Reactors (a LFTR) with that of Light Water Reactors in the early 1970's, they found that the likely costs of the MSBR would be about the same as that of a LWR. However the costs of LWRs rose significantly later in the 1970's and 1980's. Much of that cost increase was dure to added LWR safety features, that would not be necessary for a LIFTR. Thus there is reason to suspect that a LFTR, even with fuel reprocessing will cost less to build than conventional reactors. If fuel reprocessing and cleaning systems are mas produced, their cost will be relatively low, thus for the LFTR, massive deployment would probably tend to lower component costs.
The prospects for massive deployment of small, factory produced LWR s such as the B&W mPower are far less certain. Fuel availability will be a major issue, and compared to the LFTR, the mPower is far more complex and therefore likely to be more expensive and require a significantly longer time to build.
Finally, too few details have been offered about the ARC-100 to even speculate about its costs. However, If the primary source of ARC-100 and LFTR start up charges is Reactor Grade Plutonium, 10 thermal LFTRs can be started for every 1 ARC-100. In addition the breeding ration of the ARC-100 would be probably be similar to that of the LFTR. Thus the ARC-100 could well be significantly handicapped in the race to provide massive deployment potential.
Fuel efficiencies
Both the LFTR and the ARC-100 offer significantly greater fuel efficiency than conventional reactors. Both are capable of 1 to 1 fuel conversion and both are capable of breeding. Both designs are consistent with a sustainable nuclear economy.
Fuel reprocessing
Both the LFTR and the ARC-100 offer integral fuel reprocessing technologies. The LFTR's technology offers some advantages and may cost less to manufacture and operate. Both technologies appear to offer fuel reprocessing at a lower cost than traditional reprocessing technologies. The ARC-100's reprocessing technology could loose as much as 3% of the plutonium present in reprocessed fuel, to its waste stream. The losse ration for the LFTR is unknown,
Long term nuclear waste
Both the LFTR and the ARC-100 could meet the 99% reduction of nuclear waste target. In addition both could be effective tools for reducing the amount of TRU fount in spent light water reactor fuel.
In Part 3 I intend to argue the probable case that Generation IV reactors can be produced and deployed at a sufficiently rapid rate to meet global carbon emission reduction goals by 2050. I will also argue the cost of Generation IV reactors is likely to be significantly lower than the cost of conventional reactors, Finally I will argue that Generation IV reactors represent sustainable energy technology, and thus represent a long term solution to meeting human energy needs,
Posts
No comments:
Post a Comment