THE NUCLEAR ENERGY INDUSTRY AND THE MSR
Many people quite reasonably feel that the nuclear industry should not continue operation without having a solution for the disposal of its highly radioactive waste, whether that waste is in the form of spent fuel or the results of other operations such as reprocessing. However, the industry has in fact developed the necessary technologies and implemented most of them. The remaining issue is an acceptable safe storage of long-lived, high-level radioactive material regardless of its format. Whatever the political path forward on this issue, the proposed solutions must be acceptable to the public. That requires a dedicated effort to educate the public on the safety of whatever path is chosen.
Today, safe management practices are implemented or planned for all categories of radioactive waste. Low-level waste (LLW) and most intermediate-level waste (ILW), which make up most of the volume of waste produced (97%), are being disposed of securely in near-surface repositories in many countries so as to cause no harm or risk in the long-term. This practice has been carried out for many years in many countries as a matter of routine.
High-level waste (HLW) is currently safely contained and managed in interim storage facilities. The amount of HLW produced (including Spent Nuclear Fuel (SNF) when this is considered a waste) is in fact, small in relation to other industry sectors. HLW is currently increasing by about 12,000 tonnes worldwide every year, which is the equivalent of a two-story structure, built on a basketball court and is miniscule compared with other industrial wastes. The use of interim storage facilities currently provides an appropriate environment in which to contain and manage this amount of waste. These facilities also allow for the heat and radioactivity of the waste to decay prior to long-term geological disposal. In fact, after 40 years there is only about one thousandth as much radioactivity as when the spent fuel is removed from the reactor. Interim storage provides an appropriate means of storing used fuel until a time when a country has sufficient fuel to make a repository development with economic and political and public acceptance of the repository, or a system to recycle the SNF.
In the long-term, however, appropriate disposal arrangements are required for HLW, due to its prolonged radioactivity. Disposal solutions are currently being developed for HLW that are safe, environmentally sound, and publicly acceptable. In the government sector, highly radioactive waste has been successfully immobilized in borosilicate glass, poured into stainless steel canisters, and safely (temporarily) stored in on-site concrete vaults since the middle 1990’s.
The current solution that is widely accepted as feasible is deep geological disposal, and repository projects are well advanced in some countries, such as Finland, Sweden, and the USA. In fact, in the USA a deep geological waste repository, the Waste Isolation Pilot Plant (WIPP), is already in operation in New Mexico for the disposal of transuranic waste (long-lived Intermediate Level Waste (ILW) contaminated with military materials such as Plutonium). The proposed Yucca Mountain repository for long-lived HLW in Nevada is showing classic NIMBY (Not In My Back Yard) resistance. These countries have demonstrated that political and public acceptance issues at a community and national level can be met.
With the availability of technologies and the continued progress being made to develop publicly acceptable sites, it is logical and important that construction of new nuclear facilities continue. Nuclear energy has distinct environmental advantages over fossil fuels. In fact, prior to consideration of the issue of containing and managing virtually all its wastes, it must be recognized that nuclear power stations do not cause any pollution. The fuel for nuclear power is virtually unlimited, considering both geological and technological aspects. There is plenty of Uranium in the Earth’s crust, and furthermore, well-proven (but not yet fully developed for commercial applications) technology, like liquid core molten salt reactors (LCMSR), has the potential to extract almost all the energy from nuclear fuels (which current reactors do not do) and produce no long-term waste and a very small amount of short-term nuclear waste. The current safety record of nuclear energy is better than for any other major industrial technology, and it will only continue to improve with new nuclear reactors such as LCMSRs. All these benefits should be taken into account when considering the construction of new facilities and in the consideration of the budget for long-term storage or for recycling nuclear waste.
Whether nuclear fuel is used only once or recycled for subsequent use, disposal of high-level radioactive byproducts in a fortified repository will be necessary. Underground disposal in specially designed facilities like Yucca Mountain or the Waste Isolation Pilot Plant in New Mexico is an essential element of a sustainable, integrated used nuclear fuel management program.
THE NUCLEAR WASTE POLICY ACT
In 1982, Congress passed the Nuclear Waste Policy Act directing the Department of Energy to build and operate a repository for used nuclear fuel and other high-level radioactive waste. The act set a deadline of 1998 for the Energy Department to begin moving used fuel from nuclear energy facilities to the repository.
To fund the federal program, the act established a Nuclear Waste Fund. Since 1983, electricity consumers have paid into the fund one-tenth of a cent for every kilowatt-hour of electricity produced at nuclear power plants. These fees continue to accumulate at a rate of $750 million a year, and the fund accrues more than $1 Billion in interest each year. The fund’s balance, as of May 2013, was more than $29 Billion. Without a high-level radioactive waste management program and annual congressional appropriations, these funds are not available for their intended purpose.
THE YUCCA MOUNTAIN PROGRAM
In 1987, Congress amended the Nuclear Waste Policy Act, directing the Department of Energy (DOE) to study exclusively Nevada’s Yucca Mountain, a remote desert location, as the site for a potential repository for geologic disposal of used nuclear fuel. After two decades of site studies, the federal government filed a construction license application in 2008 for a repository at Yucca Mountain.
However, President Obama in 2010 stopped the Yucca Mountain license review and empaneled a study commission to recommend a new policy for the long-term management of used fuel and high-level radioactive waste. In January 2012, the Blue Ribbon Commission on America’s Nuclear Future published its final recommendations, most of which are supported by the industry. DOE’s used fuel management strategy to implement the commission’s recommendations was issued in January 2013.
The Nuclear Waste Policy Act of 1982 to began requiring the Department of Energy to remove used fuel from reactor sites by 1998. The government’s failure to do so has resulted in nearly $2 Billion in court-awarded damage settlements being paid from the taxpayer-funded Judgment Fund to compensate energy companies for storing the used fuel onsite. Damages could reach more than $20 Billion by 2020, and up to $500 million annually after 2020.
RECYCLING NUCLEAR WASTE
The $29 billion sitting in the Nuclear Waste Management Fund is more than enough to finish the commercialization of two competing reactor technologies, the IFR (Integral Fast Reactor) and the LCMSR (Liquid Core Molten Salt Reactor), as well as the infrastructure needed to handle and process high level nuclear waste to be used as fuel for these technologies. These technologies could reduce current high-level nuclear waste levels by an expert-estimated 99%.
When technology is considered, there is no problem with nuclear waste. We have the technological know-how to recycle or store many types of nuclear waste in repositories very safely.
Spent Nuclear Fuel (SNF), otherwise commonly known as high-level nuclear waste or just simply nuclear waste, has long been reprocessed to extract fissile materials for recycling to provide fresh fuel for existing and future nuclear power plants. France has been recycling nuclear waste since the 1980’s.
The entirety of spent nuclear fuel is not waste. Plutonium and Uranium – which can be recycled – contribute about 98% of all the spent nuclear fuel stockpiles, and thus, only the remaining two percent of the spent fuel is waste that needs to be sequestered from the environment.
In the past, the main reason for reprocessing SNF has been to recover unused Uranium and Plutonium in the used fuel elements and, thereby, close the fuel cycle. This approach captures the vast amount of energy still remaining in the SNF.
The primary driver for the recycling of SNF is to increase utilization of available natural resources for energy generation. Waste management benefits are secondary, and advanced fuel cycle technologies are not needed for the safe disposal of used fuel and high-level waste.
In America, the current approach is, after being used once in the reactor, SNF is typically removed. After a period of onsite storage, it would be sent to a repository (for which Yucca Mountain was intended) for ultimate disposal. This approach is called an open fuel cycle. On the other hand, the recycling and reuse of nuclear fuel takes place in a closed cycle. This is an approach that captures the vast amount of energy still remaining in the SNF, as what is done in France.
While the recycling of Plutonium in light water reactors is a mature commercial technology, the current improvements in resource utilization are modest. Single-pass recycling, for example, only provides Uranium savings on the order of 12% to 15%. The uses of competing technologies like a LCMSR (Liquid Core Molten Salt Reactor) or IFR (Integral Fast Reactor) are technologies that could greatly increase the percentage of nuclear fuels recycled.
The full promise of recycling – that is, natural Uranium savings on the order of 95 per cent – can only be realized with the commercial-scale deployment of fast reactor and/or Molten Salt Reactor technologies.
THE INTEGRAL FAST REACTOR
The Integral Fast Reactor (IFR), a type of Generation IV Reactor, was developed at Argonne National Laboratory in the US, but was cancelled in 1994 for political reasons, just as demonstrations were being prepared after a decade of successful development.
Since then, interest has grown in recovering all long-lived actinides – together with Plutonium – to recycle them in the IFR so that they end up as short-lived fission products.
As can be deduced from the word “fast” in its name, the IFR is a type of reactor that allows neutrons to move at higher speeds by eliminating the moderating materials used in thermal reactors. The greater velocity of the neutrons results in a more energetic splitting, and thus a greater number of neutrons being liberated from the collisions. The result is that the fuel is utilized much more efficiently.
Whereas, a normal light water reactor utilizes about 1%of the fissionable material that was in the original ore, with the rest being treated as waste, a fast reactor can burn up virtually all of the Uranium in the ore. In addition, the fuel can be recycled on site in a process that removes the fission byproducts and incorporates the actinides from the spent nuclear fuel (SNF) into new fuel rods, which are then reloaded into the reactor. The resulting waste can then be stabilized by vitrification, and stored for thousands of years without fear of significant air or groundwater contamination.
The waste coming from an IFR does not have to be stabilized for nearly as long as waste from a traditional reactor. Unlike the waste from the thermal reactors used today, waste elements from IFRs have much shorter half-lives than the actinides that have been retained in the reprocessing and subsequently reloaded into the IFR’s core for further fissioning. With the actinides removed from the SNF, dealing with this new type of nuclear waste becomes easily manageable.
The Science Council for Global Initiatives (SCGI), an international Non-Governmental Organization (NGO) aiming to get the first commercial-demonstration IFR, claims that the 98% – 99% of the energy left in the spent fuel from traditional reactors can provide all the energy the world needs for a couple centuries.
“The IFR can be the solution to virtually all of the problems humanity faces today that are in any way connected to energy. Instead of recovering less than 2% of the energy in Uranium, IFRs can utilize nearly 100% of it, making them many times more efficient than conventional reactors. They leave behind no long-lived waste products, and the small amount left can be easily and safely disposed of,” the SCGI states.
Chairman of the Georgia Public Service Commission Tim Echols was recently heard saying that the mounting SNF being stored on the site of nuclear plants was like “constipation blocking the progress of the industry,” and that a better idea would be to recycle the fuel rods as the French do so that they can be used again. According to Echols, Nathan Deal, the governor of Georgia, has already given his support to a policy change and to locating a fuel-reprocessing plant in Georgia.
IF FRANCE CAN DO IT, WE CAN DO IT BETTER, RIGHT?
Areva, headquartered in France, has been at the forefront in spent nuclear fuel (SNF) recycling and has reached an industrial maturity that lends itself well to use elsewhere. However, other countries, such as the United States, have not adopted policies to adopt this technology. Areva has undertaken de-conversion of enrichment tails at Pierrelatte since the 1980s, and today, at its La Hague site, it operates the MELOX plant, a used-fuel recycling facility with capacity of 1,700 tons per year that has been working since 1995. It is also the world’s only operational large-capacity Mixed Oxide (MOX) fuel production plant.
Areva has proposed building a $20 billion plant in the US with a technology similar to the one it uses in France, where 17 per cent of electricity is derived from recycled SNF. According to Areva, the group has joined with Duke Energy, one of America’s largest nuclear power producers, to submit a proposal to the Department of Energy for the construction of a MOX-fuel fabrication plant to supply MOX fuel to reactors in the US. The MOX Fuel Fabrication Facility (MFFF), which will be used to recycle nuclear materials in weapons, is under construction at the Savannah River Site (SRS) in South Carolina but has experienced cost and schedule overruns primarily due to adapting the French approach to American standards and requirements.
A common question raised during discussions on reprocessing is, “If the French are reprocessing used fuel, why isn’t the US?”
In many ways, the U.S. and France represent opposite ends of the spectrum.
In France, the recycling of MOX in light-water reactors is a very mature, ongoing commercial practice supported by an existing industrial, commercial, and regulatory infrastructure. This situation has resulted from a deliberate, multi-decade national energy policy prioritizing energy security for a country with limited domestic natural energy resources. Accordingly, there would need to be a compelling reason for France to abandon its recycling program.
In the US, initial plans for building a recycling program were abandoned in the 1970s due to proliferation concerns. The accompanying infrastructure was not fully developed or ever completed. A compelling case would need to be made for launching a recycling program in the U.S. in the face of the additional expense needed for development and infrastructure.
THE US OUTLOOK FOR RECYCLING NUCLEAR WASTE
In the nearer term, the overriding considerations for nuclear power are safety, reliability, and affordability. Current Uranium projections indicate adequate fuel supplies for the remainder of the 21st century, and accordingly, departure from the once-through fuel cycle using current light water reactor technology will require a compelling business case.
Considering the capital-intensive infrastructure required to bring commercial recycling to the US, a number of conditions must be met to shift from the current once-through fuel cycle based on light-water reactor technology. These conditions include a stable national energy policy and strategic vision; maturity of the regulatory infrastructure; a proven fuel cycle technology and designs; and cost and schedule estimates.
Furthermore, several other criteria need to be met to justify transitioning from the current fuel cycle to one of reprocessing fuel for use in our present light water reactor fleet. Uranium prices much higher than they are today would be required to make such an approach financially appealing. Recycling of Plutonium (as MOX) could become economically feasible as long as reprocessing costs are competitive. The deployment of advanced reactors, like the IFR and LCMSR and other fuel cycle technologies could extend the fuel supply through better consumption and efficient use of nuclear fuel if Uranium resources become limiting.
Although the two terms “reprocessing” and “recycling” are often used interchangeably, reprocessing represents just one element, albeit a very important one, needed to support a recycling fuel cycle.
Given that the primary objective of building and operating a nuclear fuel cycle is for energy generation, the primary focus on research, development, and demonstration (RD&D) programs should be on the reactor, not spent nuclear fuel storage, as the key enabling technology, as that is the point where energy is generated. All other technologies and infrastructures exist to support the safe, reliable, and economic operation of the reactor.
AN INHERENTLY SAFE MOLTEN SALT REACTOR ACTINIDE BURNER
Thermal-spectrum molten salt reactors have long interested the nuclear engineering community because of their many safety benefits – inherent passive shutdown ability, low pressure piping, negative void and temperature coefficients, and chemically stable coolants – as well as their scalability to a wide range of power outputs.
MSRs (Molten Salt Reactors), including those using a liquid core approach, were originally developed at the Oak Ridge National Laboratory (ORNL) in the 1950s, 1960s, and 1970s, and working versions were shown to operate as designed.
The bulk of the early work on these MSR designs focused on component lifetime – specifically, developing alloys able to maintain their mechanical and material integrity in a corrosive, radioactive salt environment. Experimental tests running over several years at ORNL in the 1960s and 1970s showed that modified Hastelloy-N possesses the necessary chemical and radiation stability for long-term use in the fabrication of molten salt reactors.
Despite very promising progress on the MSR, the United States remained focused on light-water reactors for commercial use, primarily because of extensive previous operating experience with naval water-cooled reactors and early success with commercial light water power reactors.
Advocates of Thorium and increasing demand for small modular reactors have driven a renewed examination of molten salt reactors beginning in the 1990s. In 2002, the multinational Generation IV International Forum (GIF) reviewed approximately one hundred of the latest reactor concepts and selected molten salt reactors as one of the six advanced reactor types most likely to shape the future of nuclear energy “due to advances in sustainability, economics, safety, reliability, and proliferation-resistance.”
Nearly all currently operating commercial reactors use solid Uranium oxide as fuel. The Uranium oxide, which is in the form of solid pellets, is surrounded by a metal cladding that helps the fuel retain its shape within the reactor and provides a barrier to the release of fission products into the surrounding coolant.
In contrast, a Molten Salt Reactor, such as the design of Transatomic’s WAMSR (Waste Annihilating Molten Salt Reactor), uses liquid fuel instead of solid fuel. Transatomic’s WAMSR uses Uranium (or spent nuclear fuel [SNF]) dissolved in a molten fluoride salt, which acts as both fuel and coolant.
Liquid fuel offers significant advantages during normal operation. Primarily, it permits better heat transfer between the fuel and coolant, which in turn allows for higher reactor outlet temperatures. Higher outlet temperatures lead to higher overall thermal efficiency for the plant. Liquid fuel reactors also eliminate the need for fuel enrichment and fabrication, thereby greatly reducing the overall fuel cycle costs.
HIGHER OUTLET TEMPERATURES AND EFFICIENCY
In a commercial light water reactor, water is used as a working fluid to carry the heat away from the hot outer surface of the fuel cladding, typically at about 330°C, to the plant’s power conversion loop. A higher cladding temperature allows for a higher water temperature, which allows for a more efficient power production cycle. A problem with solid fueled reactors, however, is that the Uranium oxide material is a poor heat conductor. In most light water reactors it is not possible to increase the outer cladding temperature significantly beyond 330°C, because that would result in an unacceptably high fuel centerline temperature that would destroy the fuel assembly.
A liquid-fueled reactor does not have these problems, because the fuel and coolant are the same material. The fuel salt is a good heat conductor, and, therefore, can have both a lower peak temperature and a higher outlet temperature than a solid fueled reactor.
LCMSRS CAN ALSO USE THORIUM AS A FUEL
Molten Salt Reactors (MSRs), using liquid core designs, are usually geared toward the Thorium (Th-232) to Uranium (U-233) fuel cycle. They were developed initially when there was high emphasis on breeding. MSRs were conceived as near thermal reactors with a graphite moderator. The preferred salts are fluorides, including beryllium and lithium fluorides, because of their desired nuclear and thermodynamic properties. Both the beryllium and the fluorine cause significant neutron moderation. To achieve breeding with the soft neutron spectrum, it is necessary to select the Thorium cycle.
THE MOLTEN SALT REACTOR EXPERIMENT
The MSRE (Molten Salt Reactor Experiment) was operated initially with Uranium 235 at 35% enrichment as the fissile fuel. That operation spanned 34 months beginning in 1965 and included a sustained run of 188 days (partly at low power to accommodate the experimental program). All aspects of operation, including the addition of fissile fuel with the reactor operating at power, were demonstrated. Subsequently, the mixture of Uranium 235 and Uranium 238 was removed from the salts by on-site fluorination, and Uranium 233 was added to the fuel salt for the next phase of the operation. Plutonium produced during the Uranium 235-Uranium 238 operations remained in the salt during the Uranium 233 operation. Several fissile additions consisting of Plutonium (PuF3) were made for fuel makeup to demonstrate that capability. The Plutonium additions were made by adding capsules of PuF3 in the solid form to the reactor salt and allowing the Plutonium salt to dissolve. Thus, Plutonium from two sources was burned in the MSRE: the added Plutonium, and the Plutonium that was bred from the Uranium 238 in the initial operations.
The MSRE, without changes in design, operated successfully on all of the major fissile fuels: Uranium 235 and Uranium 233, and Plutonium mixed with Uranium. This property of the MSR provides the ultimate flexibility in the utilization of various fissile fuels.
The LCMSRs are fluid fuel reactors, and as such, they differ from all the current, common, solid fuel reactors. Fluid fuel can be transferred remotely by pumping through pipes connecting storage or reaction vessels (e.g., a reactor core). The relatively simple remote handling allows even the fresh fuel to be highly radioactive, which provides a strong diversion or proliferation inhibitor. Also, highly radioactive fuel can be detected easily. If the temperature of the fuel is allowed to drop, the fuel solidifies and again is difficult to manipulate, providing additional diversion protection.
The fluid fuel at operating reactor fissile concentrations provides inherent protection against criticality accidents during handling. In thermal designs, the graphite moderator is required for criticality so that criticality can occur only in the core. For other concepts, the design would have to exclude vessels that are not criticality safe for credible fuel mixtures.
Fuel prepared for an LCMSR can be conveniently shipped as a cold solid and re-melted just before it is added to the reactor system. For small additions, the reactor can be designed to accept the fuel in the frozen state, as in the MSRE. With a fluid fuel, the entire fuel element fabrication process is avoided. This saves a significant part of the head-end effort and cost. The absence of a solid fuel-manufacturing phase provides for enormous flexibility. The fuel can be blended into the reactor exactly as needed at any time. The amount of fuel added will depend on the type of fuel, its isotopic makeup, and its concentration. There is no need for exact long range planning that may be upset by variations on either the supply or the demand side. There is no need for long lead times and interim storage. These advantages are particularly important for fuel derived from weapons. The reactor can accommodate the rate and exact kind of fuel that becomes available. The fine-tuning of the composition can be done on an as needed basis at the site.
SAFETY OF MOLTEN SALT REACTORS
The Liquid Core Molten Salt Reactor (LCMSR) can potentially achieve almost any degree of safety desirable at a cost. Some extreme degrees of safety were summarized in the proposal for the Ultimate Safe Reactor. The MSRs using a liquid core approach possess many inherent safety properties. As a LCMSR uses a molten fuel, a “meltdown” is of no particular consequence. The fuel is critical in the molten state in the optimal configuration: in laymen’s terms, in normal operation it is already melted down. If the fuel escapes this environment or configuration because of relocation, it will become subcritical. Thus, re-criticality in any reasonable design cannot occur.
Fluid fuel has inherently a strong negative temperature coefficient of reactivity because of expansion of the fluid that results from removal of fuel from the core. This property is in addition to other spectral contributions to the negative reactivity coefficient. At the very extreme, the fuel would cause failure of the primary coolant boundary (without a serious pressure rise), in which case the fuel would automatically be returned to a critically safe configuration. Further, the ability to add fuel with the reactor on-line strongly limits the amount of excess nuclear reactivity that must be available in the system.
On-line processing reduces the amount of fission products retained in the system. This reduces both the risk of dispersal of radioactivity and the amount of decay heat that must be contended with during an accident. The fission product inventory, in an earlier concept of the Molten Salt Breeder Reactor, was planned to be a l0-day accumulation. A more recent proposal suggests reducing the fission products to a level where the entire afterheat can be contained in the salt without reaching boiling. There is a limit to the reduction of fission product inventory in the reactor. The limit is determined by several factors, two of which are economics and concentration of the fission products. The practical limit of the latter has not yet been determined and is not known. In practically all LCMSR concepts, the fission gases and volatiles are removed continuously, reducing significantly the potential radioactive source term, the length of time it is radioactive.
Fluid fuel also allows shutdown of the reactor by draining the core into subcritical containers from which any decay heat can be readily removed by conduction and natural convection.
The LCMSRs can be designed in an extremely safe manner with inherently safe properties that cannot be altered or tampered with. These safety attributes make the LCMSRs very attractive and may contribute to their economy by reducing the need for elaborate additional safety measures.
Nuclear waste is an important issue affecting the acceptability of any nuclear-related system, and reactors in particular. There is no way that a reactor that utilizes the fission process can eliminate the fission products. The LCMSRs, with their continuous processing and the immediate separation of the residual fuel from the waste, simplify the handling of the waste and contribute to the solution and acceptability of the waste issue.
The on-line processing can significantly reduce the transportation of radioactive shipments. There is no shipping between the reactor and the processing facility.
Storage requirements are also reduced, as there is no interim storage needed for either cool down or preparation for shipment. The waste, having been separated from the fuel, requires no compromise to accommodate the fuel for either criticality or diversion (proliferation) concerns. The waste shipments can be optimized for waste concerns alone. The actinides can be recycled into the fuel for burning, and thus eliminated from the waste. While further work is required to fully analyze this possibility, several design proposals to burn actinides (Spent Nuclear Fuel) to produce energy in an LCMSR have been made. The LCMSR designs with on-line processing lend themselves readily to recycling actinides in the fuel.
Eliminating the actinides from shipments and from the waste reduces the very long controlled storage time of the waste to more acceptable and reasonable periods of time than is the case today with traditional light water reactors. The on-site on-line processing allows for inclusion of some selected fission products along with the recycled actinides for transmutation in the reactor. For example, the long-lived iodine could be removed from the waste and retained in the core.
The fission products, already being in a processing facility and in a fluid matrix, can be processed to the optimal form desired. That is, they can be reduced in volume by concentration or diluted to the most desirable constitution. They can be further transformed into the most desirable chemical state, shape, size, or configuration to meet shipping and/or storage requirements. The continuous processing also allows making the shipments to the final disposal site as large or as small as desired. This can reduce to an acceptable level the risk associated with each individual shipment.
A 520 MWe light-water reactor would contain approximately 40 tons of solid fuel and generate 10 metric tons of SNF (Spent Nuclear Fuel) each year. The SNF contains materials with half-lives on the order of hundreds of thousands of years. Although reprocessing methods are available for partially reducing the waste mass, they are currently cost prohibitive in the U.S., and existing methods accumulate pure Plutonium as a byproduct.
The basics of how a 520 MWe Transatomic Waste Annihilating Molten Salt Reactor (WAMSR) reactor would operate are as follows: The reactor starts with 65 tons of SNF (Spent Nuclear Fuel) in its fuel salt. Each year, 0.5 tons of fission products are filtered from the system and a fresh 0.5 tons of fuel is added, keeping the fuel level steady. The fuel addition can occur in batches; it does not need to be added continuously. At reactor end of life, the inventory of fuel remaining in the reactor may be transported for use in another WAMSR reactor. Alternately, it may be inserted into a disposal cask and stored in a repository.
Compared to a similarly sized light-water reactor, the annual waste stream is reduced from 10 to 0.5 metric tons – which is 95% less waste. Furthermore, the vast majority of the waste stream has a relatively short half-life decay, on the order of a three hundred years or less. We believe mankind can easily store waste materials on these timescales, compared to the hundreds of thousands of years required for waste from LWRs. This changes a civilizational problem into a relatively straightforward engineering task.
BETTER INHERENT SAFETY
Molten salt reactors are a win for public safety. The main concern in a nuclear emergency is to prevent widespread release of radioactive materials. The Transatomic’s WAMSR materials and design greatly reduce the risk of reactor criticality incidents, shrink the amount of radioisotopes in the primary loop, eliminate driving forces that can widen a release, and provide redundant containment barriers for defense in depth. Because of these factors, a strong case can be made for the elimination, or at least the reduction in robustness by an order of magnitude, of the containment vessel, when compared to a traditional light water reactor. This would greatly reduce construction and operation costs.
As with light-water reactors, molten salt reactors have a strong negative void coefficient and negative temperature coefficient. In molten salt reactors, these negative coefficients greatly aid reactor control and act as a strong buffer against temperature excursions. As the core temperature increases, the salt expands. This expansion spreads the fuel volumetrically and slows the rate of fission. This stabilization is automatic and occurs even without operator action.
Online refueling and fission product removal primarily control reactivity in a WAMSR. In light water reactors, reactivity decreases over time as the fuel depletes and fission product poisons accumulate within the fuel rods. Therefore, a light water reactor core must initially have significant excess reactivity to ensure that the reactor remains critical for the entirety of the cycle. In WAMSRs, however, fuel can be added to the core continuously to counteract fuel depletion, and fission products are extracted – either continuously or in batches – to minimize the accumulation of fission product poisons. WAMSRs can, therefore, operate with very little excess reactivity.
The small amount of excess reactivity present during operation is controlled by a central neutron-absorbing control rod, which can be inserted to decrease reactivity or removed to increase reactivity. As there is little excess reactivity at all times during operation, there is very little coarse movement of this rod. There are two additional neutron-absorbing shutdown rods at the center of the core. These rods are fully inserted when the reactor is shut down, and are only moved in startup and shutdown procedures.
The power level is controlled primarily by operator adjustments to the turbine. Slowing the turbine extracts less heat from the salt, thereby increasing its temperature, which in turn decreases the thermal power generated in the core. Once the reactor reaches the desired power level where heat produced is equal to the turbine heat draw, the system re-stabilizes. These dynamics provide tight negative feedback loops and give the system inherent stability.
Furthermore, liquid fuel is not tightly constrained by the rate of power change in the reactor. In solid-fueled reactors, changing the power level too quickly can cause detrimental pellet-cladding interactions. Also, large power changes in LWRs result in significant fission product poison (Xenon) contraction or expansion, which is counter to the reactor power change desired, and must be compensated for by control rod manipulation, which is undesirable for several reasons.
Although the WAMSR is meant for baseload operation, the liquid fuel and the ability to control heat output via the turbine enables excellent load following operation, which is more difficult with light water reactors.
PASSIVE SAFETY AND INHERENT RESISTANCE TO BEYOND-DESIGN-BASIS EVENTS
A significant vulnerability common to all currently operating commercial light-water reactors is that typically they require external electric power to pump coolant over their cores to prevent a meltdown. By definition, a passively safe nuclear reactor is one that does not require operator action or electrical power, whether internal or external, to shut down safely in an emergency. It is a further goal that the reactor be able to cool safely during an extended station blackout without any outside emergency measures. An inherently safe reactor will be able to achieve these goals even in the face of events that have historically been considered beyond-design-basis.
The Transatomic WAMSR is a major advance over light-water reactors because it is passively safe (primarily because of its freeze valve) and can passively cool its drained core via cooling stacks connected to its auxiliary tank. If the freeze valve fails, the control rods may be inserted by operator action, or passively via an electromagnetic failsafe, thereby making the reactor subcritical. If the control rods or other active measures cannot be used, the hot fuel salt will simply remain in the reactor vessel. Heat will cause the salt to expand, thereby reducing reactivity. If the freeze valve fails and the salt continues to increase in temperature, the zirconium hydride moderator rods will decompose, with a minor release of hydrogen gas that is not adequate to pose an explosion threat because of the volume of the primary loop. The lack of neutron moderation brings the reactor to a sub-critical state.
If the salt increases in temperature enough to induce material failure in the vessel, then the salt will flow via gravity into a catch basin located immediately below the vessel. The catch basin in turn drains via gravity into the auxiliary tank. The reactor and its catch basin are sealed within a concrete chamber only accessible by hatch. Thus, even in this worst-case accident scenario, the system is confined, non-flammable, and shuts down passively. If fuel salt through some further circumstance escapes the primary containment surrounding the primary loop, it will still be inside the concrete secondary containment structure, which is located at least partially below grade.
An intermediate loop creates a buffer zone between the radioactive materials in the reactor and the non- radioactive water in the steam turbine (if a steam turbine is used). The steam is at a higher pressure than the intermediate loop, and the intermediate loop is at a higher pressure than the primary loop, so any leaks in heat exchangers will cause a flow toward the core rather than out of the core. Any small counter-pressure flow across the primary heat exchanger is trapped in the intermediate loop. The intermediate loop feeds into a steam generator, and both are also within the concrete secondary containment structure.
If the fuel salt, despite all existing safety mechanisms in the system, escapes the containment structure, it will return to solid form once it cools below approximately 500°C.
In sum, in today’s nuclear plants an explosion or steam rupture might have wide area consequences, so safety must be assured probabilistically through the use of multiple independent or redundant systems, adding construction time and materials, cost and complexity. Transatomic’s WAMSRs draw on these redundant techniques in places, but ultimately provide a more resilient safety foundation – molten salt is inherently less capable of a wide-area public disaster.
The $2 Billion price point for a WAMSR can greatly expand the demand for nuclear energy, because it is a lower entry cost than large-sized, solid core, nuclear power plants. The Vogtle 3 and 4 plants, each 1100 MWe and built in parallel, have a combined project cost of $14 Billion for about 4 times higher output. Even if the cost per watt were the same, a lower price for a smaller unit will still expand the number of utilities that can afford to buy nuclear reactors, better match slow changes in demand, allow greater site feasibility, and reach cash flow breakeven faster. The speed of construction and faster payback also reduce financing costs.
WAMSRs will also deliver a low levelized cost of electricity (LCOE). While most observers assume nuclear fuel costs are near zero, the Nuclear Energy Institute estimates the 2011 cost was actually $0.068 per kilowatt-hour. WAMSRs expect to produce far more electricity per ton of ore than the current fuel cycle, driving these costs down toward zero. The WAMSR is refueled continuously for a high capacity factor.
LOWERING THE HURDLES FOR A U.S. SPENT NUCLEAR FUEL REPOSITORY
The United States has set aside a $32 Billion trust for a repository and has 64,000 tons of spent nuclear fuel (SNF) to store – approximately $500 per kilogram of SNF. However, our country has not been able to agree on a location or final design for the repository.
Should the USA build a reprocessing facility? The cost to reprocess as the French do is likely $1,000 to $2,000 per kilogram of heavy metal, which is well above what is available in the U.S. Waste Disposal Trust Fund. Meanwhile, SNF can be held inside existing wet storage pools at near-negligible cost. As pools fill up, SNF older than 3-10 years can be placed in dry casks for roughly $100 per kilogram and stored for 40 years or longer, making this method a cost-effective stopgap. About one-quarter of US SNF has been loaded into dry-casks. The other 48,000 tons remain in wet pools, adding to the plant inventory of radionuclides.
The WAMSR can use fresh Uranium fuel or SNF. Utilities can currently only buy fresh Uranium from commercial suppliers. The business case for a utility using SNF is somewhat more complicated, because the SNF requires additional handling costs as compared to fresh fuel. A company would need to (1) transport and receive the radioactive spent fuel rods, (2) remove the cladding physically, and (3) dissolve the Uranium oxide into the molten salt or convert it to a gas that can be injected into the molten salt. The techniques are well known because the same three initial steps must be employed in reprocessing plants such as at La Hague in France or similar facilities existing at the Idaho National Laboratory. The WAMSR avoids all of the remaining chemical steps that are the main cost drivers of reprocessing work. If full reprocessing costs over $1,000 per kilogram, as in the case of France’s reprocessing, the WAMSR could potentially perform just the initial three steps for a fractional amount, perhaps in a small number of regional facilities that ship fuel directly to WAMSR reactors. Transatomic’s initial assessment is that a disposal charge of $500 per kilogram of SNF is achievable, affordable, and less expensive than French style reprocessing, and would be within the budget allowed by the U.S.
WASTE DISPOSAL TRUST FUND
The existing 64,000 tons of SNF contain an enormous amount of energy. If all U.S. light-water plants were replaced tomorrow by WAMSR reactors, it would still take 350 years to consume all of the existing SNF. Even if we expand the role of nuclear by also converting all coal plants to WAMSRs, we could still run for 150 years. The SNF needs to be stored in the meantime. Furthermore, the WAMSR would themselves create small amounts of short-lived waste to store. We, therefore, cannot use WAMSRs to avoid a U.S. repository entirely. WAMSRs do, however, allow us to build smaller and simpler repositories. SNF would only need to be stored for a few hundred years instead of hundreds of thousands of years. Furthermore, by avoiding a great deal of future SNF, we may avoid the need to ever build a second or third repository.
CO-LOCATION OFFERS MANY ADVANTAGES
Co-Locating LCMSRs (Liquid Core Molten Salt Reactors) with currently operating utility nuclear electricity generation plants offers utility providers many advantages. Currently, America operates a very safe, yet aging fleet of Light Water Reactors that accounts for almost 20% of U.S. electrical generation with just a few more than 100 generating units. Because SNF consuming LCMSRs can be made very small they could very easily be co-located onsite with retiring reactors. This could allow for much easier site licensing application, on site storage of nuclear waste, as well as utilization of the retiring reactor’s switchgear and steam turbine.
While many envision a LCMSR as not requiring a steam turbine in favor of a super-critical closed cycled Brayton turbine, which will be much more efficient when developed, the present reality is that economics and practicality may indeed drive the first generation of LCMSR to use the “hand me downs” of the legacy LWR fleet.
The SNF processing and logistic infrastructure from today’s light water reactors needed for a LCMSR fleet operation would not be trivial. A reprocessing plant capable of serving one hundred 1 Gigawatt plants, experts estimate, would cost $20 billion. If LCMSRs retired all of our light water reactors (which would more than likely never happen) and went on to replace Coal and Natural Gas, that would equate to a need for 5 reprocessing plants serving five hundred 1 Gigawatt plants.
Comparing the LCMSR or the IFR Integral Fast Reactor as a replacement for our traditional Nuclear power plants, Coal power plants, Natural gas power plants, and Renewable energy power plants and farms, a fleet of either of these advanced nuclear reactors offers better economics than any of the traditional power sources named here.
An IFR is expected to cost half ($5 billion) of a brand new 1 GW LWR (Light Water Reactor) newly sited ($10 billion). A 1GW LCMSR is expected to cost 1/10th of a 1 GW LWR ($1Billion). The IFR facility cost, however, includes the cost of reprocessing on-site, whereas the LCMSR facility cost does not.
Constructing 500 new LWRs would cost an estimated $10 Trillion
Constructing 500 IFRs would cost an estimated $5 Trillion.
Constructing 500 LCMSRs would cost an estimated $500 Billion plus $100 Billion in infrastructure and processing facilities.
Clearly LCMSRs have a long term economic edge over both new LWRs and IFRs.
Because of the need for a light water reactor fuel reprocessing facility that would make SNF usable in LCMSRs, many believe that the first LCMSRs will not consume SNF. Many imagine the progression of LCMSRs consuming fuel to start with Uranium, then Thorium, and then to a final design that uses SNF. This is owing to many experts’ belief that the reprocessing facility will need the commitment of a minimum of twenty LCMSRs consuming SNF as fuel to economically justify its construction.
Based on almost every conceivable metric, including the environment, economics, safety, proliferation resistance, and many others, Federal legislators should embrace the development of the LCMSR (Liquid Core Molten Salt Reactor) for reducing the nation’s nuclear waste while increasing the nation’s security and competition abroad. Legislators should consider using the Nuclear Waste Management Fund to develop LCMSR technology to produce less nuclear waste and to consume current nuclear waste stockpiles.
In addition to all their improvements to the production of electricity set forth here, liquid core molten salt reactors provide many other benefits. These include the production of nuclear isotopes for medical imaging and cancer research, and to power NASA’s deep space probes. They also include production of tremendous amounts of process heat for liquefaction of coal, municipal solid wastes, other carbon sources (including seawater) into liquid transportation fuels; desalination of seawater into potable water; creating the economic viability of extraction of presently unrecoverable near-solid heavy oil; and many manufacturing and industrial processes. All of this will be done at a very reduced cost compared with today’s methods, and with no pollution or carbon production whatsoever.