lftr proliferation concerns

LFTR Proliferation Concerns Is a Liquid Fluoride Thorium Reactor proliferation resistant? By David Amerine

2 LFTR PROLIFERATION CONCERNS

Table of Contents

Abstract ...................................................................................................................... 3

Background ................................................................................................................. 5

Controversy ............................................................................................................... 10

Conclusions ................................................................................................................ 19

About the Author ....................................................................................................... 20

LFTR PROLIFERATION CONCERNS 3

THORIUM MOLTEN SALT REACTOR ASSOCIATION

Abstract The LFTR and the Thorium fuel cycle are highly proliferation resistant. Thorium and its derivative fuel, uranium-‐233 (U-‐233), are highly unsuitable for nuclear weapons due to inherent production of other undesirable isotopes. LFTR is unique in its ability to meet both energy generation and non-‐proliferation mandates. In the traditional light-‐water reactor uranium-‐235/238 (U-‐235/238) nuclear reactions generate a byproduct, pultonium-‐239 (Pu_239), a radioactive isotope used to make weapons. However, when thorium is consumed (converted to uranium-‐233) in the LFTR, much less plutonium is produced and the vast majority of this is Pu-‐238. Pu-‐238 is highly valuable for use in nuclear batteries and is completely unsuitable for weapons use. The bottom line is that if U-‐233 was useful in making nuclear bombs, nuclear countries with large deposits of Thorium, like the United States or India, would have already done it. However, none of the thousands of warheads in the world's arsenals are based on the thorium fuel cycle.

The LFTR resists diversion of its fuel to nuclear weapons in four ways:

1. First, the thorium-‐232 breeds by converting first to protactinium-‐233, which then decays to uranium-‐233. If the protactinium remains in the reactor, small amounts of U-‐232 are also produced. U-‐232 has a decay chain product (thallium-‐208) that emits powerful, dangerous gamma rays. These are not a problem inside a reactor, but in a bomb, they complicate bomb manufacture, harm electronics, and reveal the bomb's location.

2. Second, another proliferation resistant feature comes from the fact that LFTRs

produce very little plutonium, around 15 kg per gigawatt-‐year of electricity (this is the output of a single large reactor over a year). This plutonium is also mostly Pu-‐238, which makes it unsuitable for fission bomb building, due to the high heat and spontaneous neutrons emitted.

3. Third, a LFTR does not make much spare fuel. It produces at most 9% more fuel

than it burns each year, and it is even easier to design a reactor that makes 1% more fuel. With this kind of reactor, building bombs quickly will take power plants out of operation, and this is an easy indication of national intentions.

4. Finally, use of thorium can reduce or even eliminate the need to enrich uranium.

Uranium enrichment is one of the two primary methods by which states have obtained bomb-‐making materials.


Addressing the proliferation concerns from a slightly different perspective leads to the same conclusion:

1. Thorium is generally accepted as proliferation resistant compared to U-‐Pu cycles. The problem with plutonium is that it can be chemically separated from the waste and perhaps used in bombs. It is publicly known that even reactor-‐grade plutonium can be made into a bomb if done carefully. By avoiding plutonium altogether, thorium cycles are superior in this regard.

2. Besides avoiding plutonium, Thorium has additional self-‐protection from the hard gamma rays emitted due to U-‐232 as discussed above. This makes stealing Thorium based fuels more challenging. Also, the heat from these gammas makes weapon fabrication difficult, as it is hard to keep the weapon pit from melting due to its own heat. Note, however, that the gammas come from the decay chain of U-‐232, not from U-‐232 itself. This means that the contaminants could be chemically separated and the material would be much easier to work with. U-‐232 has a 70-‐year half-‐life so it takes a long time for these gammas to come back.

3. The one hypothetical proliferation concern with Thorium fuel though, is that the Protactinium can be chemically separated shortly after it is produced and removed from the neutron flux (the path to U-‐233 is Th-‐232 -‐> Th-‐233 -‐> Pa-‐233 -‐> U-‐233). Then, it will decay directly to pure U-‐233. By this challenging route, one could obtain weapons material. But Pa-‐233 has a 27-‐day half-‐life, so once the waste is safe for a few times this duration, weapons are out of the question. So concerns over people stealing spent fuel are largely reduced by Th, but the possibility of the owner of a Th-‐U reactor obtaining bomb material is not.



Background The choice of nuclear power as a major contributor to the future global energy needs must take into account acceptable risks of nuclear weapon proliferation, in addition to economic competitiveness, acceptable safety standards, and acceptable waste disposal options. The main goal is to strengthen the proliferation resistance of the civilian nuclear fuel cycle such that it remains the less preferred route to nuclear weapon development. The primary link between civilian nuclear power and nuclear weapons is nuclear material, i.e. materials, which either are, or could be processed into, weapon-usable material. The general proliferation risks associated with civilian nuclear power systems include:

• misuse of nuclear materials through its diversion or theft, • misuse of facilities, equipment, and technology, • transfer of nuclear skills and technology.

Non-proliferation or “proliferation-resistance” is assessed by analyzing the diversion “barriers” associated with a given nuclear system. The proliferation resistance of a given system is not an absolute value. It is, therefore, important to develop a methodology that can compare existing and proposed reactor/fuel cycle systems with respect to their proliferation resistance. An assessment of proliferation resistance–general approach requires an overall methodology providing an integrated assessment that combines the effectiveness of:

• material/technical features–designated as intrinsic barriers; and • safeguard/institutional measures–designated as extrinsic barriers.

Material barriers are those material qualities that make it difficult to produce a nuclear explosive and may be related to isotopic composition of the material, isotopic separation/processing required, radiation hazard and signature, and detectability and difficulty of movement of the mass/bulk required. Additional intrinsic barriers are related to the elements of the fuel cycle itself, difficulty of gaining access to materials, or misuse of facilities to obtain weapon-usable material. These and other features of a given fuel cycle may be described as attributes of a given system. A systematic accounting of such attributes may serve as a framework for a methodology integrated assessment of the proliferation resistance.


The Nuclear Energy Research Advisory Committee (NERAC) of Department of Energy, USA has summarized the relative importance of various barriers to a selected threat as shown in the Table below. Sophisticated Sophisticated Unsophisticated Subnat'l State -‐ Overt State -‐ Covert State -‐ Covert Group Material Barriers Isotopic Low Low High High Chemical Very Low Very Low High High Radioligical Very Low Low Moderate High Mass/Bulk Very Low Low Low Moderate Detectable Very Low Low Moderate High Technical Barriers Facility Very Low Low Low Moderate Accessibility Very Low Low Low Moderate Avail. Mass Moderate Moderate High High Skills Low Low Moderate Moderate Time Very Low Very Low Moderate High Institutional Barriers Safeguards Moderate High High Moderate Access & Very Low Low Moderate Moderate Security Location Very Low Very Low Low Low The first two types of barriers (material and technical) are intrinsic and the last barrier (institutional) is extrinsic. The NERAC report suggests several guidelines/comments for implementation of the proliferation resistance assessment methodology:

• barriers are not absolute, but are engineering challenges that may be overcome by a combination of technology and weapon design, • barriers do not act independently, and the effect of multiple barriers can be greater than the sum of their individual effects, • the barriers approach avoids the difficulty of the risk-based method, which requires quantitative (numerical) risk probabilities, • the barriers approach requires only an assessment of the relative effectiveness of individual barriers, resulting in qualitative and transparent comparisons of various systems concepts and options, • effectiveness of different barriers can not be aggregated into a single parameter, • qualitative effectiveness of a barrier is graded in five categories:

1. ineffective or very low – I, 2. low – L, 3. medium or moderate – M, 4. high – H, and



5. very high – VH. A consistent comparison of different systems requires consideration of all steps of the fuel cycle. Many of the barriers, related to mining, milling, and conversion, as well as, extrinsic barriers, have similar proliferation resistance characteristics for all fuel cycles, and thus, do not significantly affect relative comparisons of most fuel cycles. To compare different options the comparative effectiveness of each barrier, divided in categories must be considered and graded into one of the five categories listed above. In order to address the impact of introducing Thorium-based fuel cycles, two prevalent factors should be clearly stated:

• Utilization of Thorium-based fuel will influence mainly the material barriers, • Material barriers are important for the proliferation threats posed by the covert effort undertaken by an unsophisticated state and a subnational group. This statement is based on the assumption that technical barriers will be less effective for the proliferation threat posed by a sophisticated country.

The light water reactor (LWR) with the once-through fuel cycle is likely to remain the main technology direction in the near term, with heavy water reactors as a secondary route. Thus, the LWR once-through cycle may serve as a “reference” case for assessment of evolutionary improvements in the proliferation resistance of more advanced reactor designs and fuel cycles, such as Thorium-based fuels. The proliferation resistance advantages of the Thorium-based fuels are realized through:

• extended fuel burnup, which could result in the reduction of the quantity and quality of plutonium (Pu) produced, reduction in the number of refuelings, and the number of spent fuel assemblies, and • significant reduction in the quantity and quality (isotopic composition) of the discharged fuel as a result of a partial replacement of U-238 by Th-232 as a fertile component of the fuel.

For the proliferation resistance effect of introducing Th–based fuel the fissile material weapon quality is evaluated by considering three properties:

• The critical mass is different for different isotopic composition of Pu; • Weapon yield degradation due to pre-initiation caused by spontaneous fission neutrons; • Weapon stability degradation caused by heat emission.

Thorium-based fuel may be introduced in all reactor systems of current technology and advanced designs. With respect to LWR’s, there are two main design options:


• A homogeneous mixture of ThO2 and UO2 • Several heterogeneous designs, where Th and U parts of the fuel are spatially

separated Several fuel cycle performance parameters related to the proliferation resistance are summarized in Table below. Proliferation resistance parameters PWR Th-Homogeneous Th-Heterogeneous Total Pu Discharged, 250 150 70-90 kg/GW(e)-year Spontaneous Fission Source, (crit.mass-sec)-1 1.6*106 3.0*106 4.0*106

Decay Heat Emission, watts/crit.mass 90 200 350 Note: The data in the table are approximate, representative values derived on the basis of several homogeneous and heterogeneous Th–based designs. As an example, the qualitative assessment of the proliferation barriers presented below is related to the heterogeneous Th–based fuel design (seed blanket). The following Table presents an example of the qualitative comparison of the standard (all–U) fuel cycle with the Thorium– based fuel cycle for the LWR reactor of current technology. Comparison of proliferation resistance of all-Uranium vs. Thorium cycles for LWR (subnational group threat) All-U fuel Th–based fuel Material Barriers Isotopic High Very High Chemical High High Radiological High Very High Mass and Bulk Moderate Moderate Detectability High Very High Thorium produces through a nuclear reaction the fissile isotope U-233. U-233 has been determined to be at least as efficient as U-235 as a weapon material. Therefore, a relatively small amount of natural (or enriched) uranium can be added to thorium in order to dilute the generated U-233 below the proliferation level of 12%, thus creating an effective barrier to diversion of U-233. It should be noted that grading of the all–U case presented in the Table just above is based on the values adopted in the NERAC report and should be considered as a guideline only. The justification of the corresponding values for the Th–based case are discussed below:

• Isotopic barrier grade increased from high to very high,



• Amount of fissile material in spent fuel decreased by a factor 2–4, • Critical mass for Pu composition is increased by 30–50%, • Fresh fuel enrichment below 20%, i.e. low enrichment, • Spontaneous neutron generation is increased by a factor of 2–2.5, • Heat-generation rate (Pu-238) is increased by a factor of 2.5–4, • Radiological barrier grade increased from high to very high, • Pu-238 + Pu-240 + Pu-242 content increased by a factor of 1.5–2, • U-232 present only in Th–based fuel, • Detectability barrier grade increased from high to very high, • Passive delectability increased due to an increase in spontaneous fission, • Hardness and uniqueness of the radiation signature increased (U-232).

The objective of thorium fuel cycle should be to ensure ‘proliferation-resistance’ of ‘fissile’ material and at the same time produce minimum quantities of ‘radiotoxic waste’. The radiotoxicity of the waste can be significantly reduced if the bred U-233 is separated and recycled but the disadvantage associated with this strategy is that U-233 is ‘fissile’ and constitutes the proliferation problem. The U-233 can be rendered proliferation-resistant through mixing with U-238 and denaturing. However, on recycling such denatured fuel, a new source of radiotoxicity is introduced in the fuel cycle. The proliferation/toxicity dilemma of thorium based fuel cycle can be resolved in combination with one of the following family of accelerated driven Energy Amplifiers (EA):

• completely thermalized neutron (graphite moderator) #1, • partially thermalized neutron (pressurized water moderator) #2 • fast neutron (lead cooled) #3

U-232 is always present in ‘fissile’ U-233 and has the daughter product Tl-208, which emits highly penetrating 2.6 MeV gamma photons. The fractional quantity (ppm) of U-232 in the recycled uranium from spent thorium fuel as function of burnup is significant. Burnup #1 #2 #3 40 GWd/t 200 ppm 3100 ppm 500 ppm 80 GWd/t 200 ppm 5000 ppm 900 ppm 160 GWd/t not applicable not applicable 2200 ppm


The gamma activity provides adequate barrier to diversion, particularly when the U-232 content is in the higher range. However, the presence of U-232 will pose problem during reprocessing and re-fabrication because of the need of very thick lead shielding to reduce the gamma dose. The lead shielding thickness in cm is necessary to reduce the gamma dose rate. This is not a factor with the LFTR since the fuel and its daughter particles are consumed in the reactor. In contrast to uranium-fuelled reactors (U-238+U-235), where there is no natural denaturant for plutonium isotopes, U-238 is an effective denaturant for the bred U-233 in thorium (Th-232) cycle. A possible solution to safeguard the reactor grade U-233 is to denature with U-238. Denaturing the reactor-grade uranium with a equal quantity of U-238 should be regarded as the lower limit for non-proliferation. The resulting radiotoxicity is a factor 50 lower than that obtained by using U-238 as the breeder fuel. Depending on which system is used, different levels of the isotopes U-232 will be produced. Through its high gamma active Tl-208 daughter product, one will require shielding in any recycling/fabrication stages. However, this gamma activity will also allow one to monitor movements of the material and possible diversion. Th-232 /U-233 offers potentially significant advantages over U-238/U-235/Pu-239, in terms of lesser transuranic actinide waste and adequate proliferation-resistance.

Controversy In January 2009, the Institute for Energy and Environmental Research (IEER) and Physicians for Social Responsibility (PSR) issued a “fact sheet” called “Thorium Fuel: No Panacea for Nuclear Power.” The authors of this sheet were Arjun Makhijani and Michele Boyd:

Thorium fuel cycles are promoted on the grounds that they pose less of a proliferation risk compared to conventional reactors. However, whether there is any significant non-proliferation advantage depends on the design of the various thorium-based systems. No thorium system would negate proliferation risks altogether. Neutron bombardment of thorium (indirectly) produces uranium-233, a fissile material, which can be used in nuclear weapons (1 Significant Quantity of U-233 = 8kg).

The USA has successfully tested weapon/s using uranium-233 cores. India may be interested in the military potential of thorium/uranium-233 in addition to civil applications. India is refusing to allow safeguards to apply to its entire 'advanced' thorium/plutonium fuel cycle, strongly suggesting a military dimension.

The possible use of highly enriched uranium (HEU) or plutonium to initiate a thorium-232/uranium-233 reaction, or proposed systems using thorium in



conjunction with HEU or plutonium as fuel, present risks of diversion of HEU or plutonium for weapons production as well as providing a rationale for the ongoing operation of dual-use enrichment and reprocessing plants. Thorium fuelled reactors could also be used to irradiate uranium to produce weapon grade plutonium.

Kang and von Hippel conclude that "the proliferation resistance of thorium fuel cycles depends very much upon how they are implemented". For example, the co-production of uranium-232 complicates weapons production but, as Kang and von Hippel note, "just as it is possible to produce weapon-grade plutonium in low-burnup fuel, it is also practical to use heavy-water reactors to produce U-233 containing only a few ppm of U-232 if the thorium is segregated in "target" channels and discharged a few times more frequently than the natural-uranium "driver" fuel."

One proposed system is an Accelerator Driven Systems (ADS) in which an accelerator produces a proton beam, which is targeted at target nuclei (e.g. lead, bismuth) to produce neutrons. The neutrons can be directed to a subcritical reactor containing thorium. ADS systems could reduce but not negate the proliferation risks.

Last year, Dr. Alexander Cannara wrote a letter to IEER/PSR pointing out errors and omissions in the “fact sheet” and requesting IEER/PSR to implement corrections. To the best of my knowledge no amendment or correction was ever issued.

This is an extended rebuttal of the claims made about thorium by Makhijani and Boyd; the entirety of their original statement is included in the rebuttal and denoted by italics.

Thorium “fuel” has been proposed as an alternative to uranium fuel in nuclear reactors. There are not “thorium reactors,” but rather proposals to use thorium as a “fuel” in different types of reactors, including existing light-‐water reactors and various fast breeder reactor designs.

It would seem that Mr. Makhijani and Ms. Boyd are unaware of the work done at Oak Ridge National Laboratory under Dr. Alvin Weinberg from 1955 to 1974 on the subject of fluid-‐fueled reactors, particularly those that used liquid-‐fluoride salts as a medium in which to sustain nuclear reactions. The liquid-‐fluoride reactor was the most promising of these fluid-‐fueled designs, and indeed it did have the capability to use thorium as fuel. It was not a light-‐water reactor, nor was it a fast-‐breeder reactor. It has a thermal (slowed-‐down) neutron spectrum that made it easier to control and vastly improved the amount of fissile fuel it needed to start. It operated at atmospheric pressure rather than the high pressure of water-‐cooled reactors. It


was also singularly suited to the use of thorium due to the nature of its chemistry and the chemistry of thorium and uranium.

Thorium, which refers to thorium-‐232, is a radioactive metal that is about three times more abundant than uranium in the natural environment. Large known deposits are in Australia, India, and Norway. Some of the largest reserves are found in Idaho in the U.S. The primary U.S. company advocating for thorium fuel is Thorium Power (www.thoriumpower.com). Contrary to the claims made or implied by thorium proponents, however, thorium doesn’t solve the proliferation, waste, safety, or cost problems of nuclear power, and it still faces major technical hurdles for commercialization.

Mr. Makhijani and Ms. Boyd may wish to update their document since “Thorium Power” is now called “Lightbridge” and no longer advocates for the use of thorium, whereas the community of supporters of liquid-‐fluoride thorium reactors (LFTR) still maintains strong support for the use of thorium because it is indeed a solution to the issues of proliferation, waste, safety, and cost that accompany the present use of solid-‐fueled, water-‐cooled reactors.

Thorium is not actually a “fuel” because it is not fissile and therefore cannot be used to start or sustain a nuclear chain reaction. A fissile material, such as uranium-‐235 (U-‐235) or plutonium-‐239 (which is made in reactors from uranium-‐238), is required to kick-‐start the reaction. The enriched uranium fuel or plutonium fuel also maintains the chain reaction until enough of the thorium target material has been converted into fissile uranium-‐233 (U-‐233) to take over much or most of the job. An advantage of thorium is that it absorbs slow neutrons relatively efficiently (compared to uranium-‐238) to produce fissile uranium-‐233.

On the contrary, thorium is very much a fuel because in the steady-‐state operation of a LFTR, it is the only thing that is consumed to make energy. Makhijani and Boyd are correct that any nuclear reactor needs fissile material to start the chain reaction, and the LFTR is no different, but the important point is that once started on fissile material, LFTR can run indefinitely on only thorium as a feed—it will not continue to consume fissile material. That is very much the characteristic of a true fuel. “Burning thorium” in this manner is possible because the LFTR uses the neutrons from the fissioning of uranium-‐233 to convert thorium into uranium-‐233 at the same rate at which it is consumed. The “inventory” of uranium-‐233 remains stable over the life of the reactor when production and consumption are balanced. Today’s reactors use solid-‐uranium oxide fuel that is covalently-‐bonded and sustains radiation damage during its time in the reactor. The fluoride fuel used in LFTR is ionically-‐bonded and impervious to radiation damage no matter what the exposure duration. LFTR can be used to consume uranium-‐235 or plutonium-‐239 recovered from nuclear weapons and “convert” it, for all intents and purposes, to uranium-‐233



that will enable the production of energy from thorium indefinitely. Truly this is a reactor design that can “beat swords into plowshares” in a safe and economically attractive way.

The use of enriched uranium or plutonium in thorium fuel has proliferation implications. Although U-‐235 is found in nature, it is only 0.7 percent of natural uranium, so the proportion of U-‐235 must be industrially increased to make “enriched uranium” for use in reactors. Highly enriched uranium and separated plutonium are nuclear weapons materials.

Since so many nuclear weapons have already been built and are being decommissioned, one might assume that Makhijani and Boyd would welcome a technology like LFTR that could safely consume these sensitive materials in an economically-‐advantageous way, beating swords into plowshares and using material that was once fashioned as a weapon as a material that can provide light and energy to billions. Enriched uranium or plutonium can’t simply be “thrown away”. LFTR puts these materials to productive use as they are destroyed in the reactor and uranium-‐233 is generated.

In addition, U-‐233 is as effective as plutonium-‐239 for making nuclear bombs. In most proposed thorium fuel cycles, reprocessing is required to separate out the U-‐233 for use in fresh fuel. This means that, like uranium fuel with reprocessing, bomb-‐making material is separated out, making it vulnerable to theft or diversion. Some proposed thorium fuel cycles even require 20% enriched uranium in order to get the chain reaction started in existing reactors using thorium fuel. It takes 90% enrichment to make weapons-‐usable uranium, but very little additional work is needed to move from 20% enrichment to 90% enrichment. Most of the separative work is needed to go from natural uranium, which has 0.7% uranium-‐235 to 20% U-‐235.

In a fluoride reactor, all of the fuel processing equipment will be located in a containment region containing the reactor and its primary heat exchangers, under very high radiation fields, and under the high heat needed to keep the fuel liquid. Once the system is properly designed to direct uranium-‐233 created in the outer regions of the reactor (the “blanket”) to the central regions of the reactor (the “core”) there will be no possibility of redirection of the material flow. Such a redirection would necessitate a rebuild of the entire reactor and would be vastly beyond the capabilities of the operators. Furthermore, the nature of U-‐233 removal and transfer from blanket to core involves the operation of an electrolytic cell that will allow very precise control and accountability of the material in question. Unlike solid-‐fueled reactors the uranium-‐233 never needs to leave the secure area of the containment building or come in contact with humans in order to continue the operation of the reactor. This is another important point that the authors have failed to distinguish as they have ignored the existence or implications of fluid-‐fueled


thorium reactors.

To claim that uranium-‐233 is just as effective as plutonium-‐239 for nuclear weapons is gross simplification bordering on outright deception. They have similar values for critical mass, but this leaves out a very important point. The nuclear reactions that consume uranium-‐233 also produce small amounts of uranium-‐232, a contaminant that will later be mentioned by the authors but ignored at this stage of the criticism. U-‐232 has a decay sequence that includes the hard gamma-‐ray-‐emitting radioisotopes bismuth-‐212 and thallium-‐208. Indeed, the half-‐life of U-‐232 is short enough that this decay chain begins to set up within days of the purification of the uranium, and within a few months that gamma-‐ray flux from the material is intense. These gamma rays destroy the electronics of a nuclear weapon, compromise the chemical explosives, and clearly signal to detection systems where the fissile material is located. This is one of the key reasons why no operational nuclear weapons have ever been built using uranium-‐233 as the fissile material.

It has been claimed that thorium fuel cycles with reprocessing would be much less of a proliferation risk because the thorium can be mixed with uranium-‐238. In this case, fissile uranium-‐233 is also mixed with non-‐fissile uranium-‐238. The claim is that if the uranium-‐238 content is high enough, the mixture cannot be used to make bombs without a complex uranium enrichment plant. This is misleading. More uranium-‐238 does dilute the uranium-‐233, but it also results in the production of more plutonium-‐239 as the reactor operates. So the proliferation problem remains either bomb-‐usable uranium-‐233 or bomb-‐usable plutonium is created and can be separated out by reprocessing.

In my opinion, mixing uranium-‐238 with uranium-‐233 during the normal operation of a LFTR is a bad idea because it compromises the capability of the reactor to “burn” thorium to a degree that it then becomes necessary to add fissile material to keep the reactor running. This is because uranium-‐238 will absorb many of the neutrons that would otherwise convert thorium into uranium-‐233, instead converting uranium-‐238 into plutonium-‐239. Plutonium-‐239 is a poor fuel in a LFTR due to the limited solubility of plutonium trifluoride (PuF3) and the poor performance of plutonium in a thermal-‐neutron spectrum (only 2/3 of the plutonium-‐239 will fission when struck by a neutron).

But something is possible in the fluid fuel of a LFTR that is impossible in the solid fuel of a conventional reactor with regards to the “downblending” of uranium. Under extreme scenarios, it may be desireable to have a separate supply of uranium-‐238 inside the reactor containment that could be irreversibly mixed with the uranium-‐233 in the core. This would have the effect of making the reactor unable to restart, and despite the contention of Makhajani and Boyd, there is no feasible way to isotopically separate uranium-‐233 (contaminated with uranium-‐



232) from uranium-‐238 because of the severe gamma radiation that would be emitted during any attempt to separate the isotopes. This approach to “just-‐in-‐time” downblending is only possible with fluid fuel, and its absence of consideration in the document again shows that the authors are unaware of the fluid fuel option and its implications.

Further, while an enrichment plant is needed to separate U-‐233 from U-‐238, it would take less separative work to do so than enriching natural uranium. This is because U-‐233 is five atomic weight units lighter than U-‐238, compared to only three for U-‐235. It is true that such enrichment would not be a straightforward matter because the U-‐233 is contaminated with U-‐232, which is highly radioactive and has very radioactive radionuclides in its decay chain. The radiation-‐dose-‐related problems associated with separating U-‐233 from U-‐238 and then handling the U-‐233 would be considerable and more complex than enriching natural uranium for the purpose of bomb making. But in principle, the separation can be done, especially if worker safety is not a primary concern; the resulting U-‐233 can be used to make bombs. There is just no way to avoid proliferation problems associated with thorium fuel cycles that involve reprocessing. Thorium fuel cycles without reprocessing would offer the same temptation to reprocess as today’s once-‐through uranium fuel cycles.

Makhijani and Boyd really betray a fundamental lack of understanding of the nature of uranium isotope separation facilities with their simplistic and cursory description of U-‐233 separation from U-‐238. Such a process would be so difficult due to the presence of U-‐232 that it simply would not be considered, even by the hypothetical “suicide” operators that they postulate. Anyone who had invested the large sums of money into a uranium isotope separation system would never risk permanently crippling its ability to operate by introducing U-‐232-‐contaminated feed into the system.

Proponents claim that thorium fuel significantly reduces the volume, weight and long-‐term radiotoxicity of spent fuel. Using thorium in a nuclear reactor creates radioactive waste that proponents claim would only have to be isolated from the environment for 500 years, as opposed to the irradiated uranium-‐only fuel that remains dangerous for hundreds of thousands of years. This claim is wrong. The fission of thorium creates long-‐lived fission products like technetium-‐99 (half-‐life over 200,000 years). While the mix of fission products is somewhat different than with uranium fuel, the same range of fission products is created. With or without reprocessing, these fission products have to be disposed of in a geologic repository.

Again, the authors make blanket statements about “thorium” but then confine their examination to some variant of solid thorium fuel in a conventional reactor. In a LFTR, thorium can be consumed with exceptionally high efficiency, approaching completeness. Unburned thorium and valuable uranium-‐233 is simply recycled to


the next generation of fluoride reactor when a reactor is decommissioned. The fuel is not damaged by radiation. Thus thorium and uranium-‐233 would not enter a waste stream during the use of a LFTR.

All fission produces a similar set of fission products, each with roughly half the mass of the original fissile material. Most have very short half-‐lives, and are highly radioactive and highly dangerous. A very few have very long half-‐lives, very little radioactivity, and little concern. A simple but underappreciated truth is that the longer the half-‐life of a material, the less radioactive and the less dangerous it is. Technetium-‐99 (Tc-‐99) has a half-‐life of 100,000 years and indeed is a product of the fission of uranium-‐233, just as it is a product of the fission of uranium-‐235 or plutonium-‐239. Its immediate precursor, technetium-‐99m (Tc-‐99m), has a half-‐life of six hours and so is approximately 150 million times more radioactive than Tc-‐99.

Nevertheless, it might come as a surprise to the casual reader that hundreds of thousands of people intentionally ingest Tc-‐99m every year as part of medical imaging procedures because it produces gamma rays that allow radiography technicians to image internal regions of the body and diagnose concerns. The use of Tc-‐99m thus allows physicians to forego thousands of exploratory and invasive surgeries that would otherwise risk patient health. The Tc-‐99m decays over the period of a few days to Tc-‐99, with its 100,000 half-‐life, extremely low levels of radiation, and low risk.

What is the ultimate fate of the Tc-‐99? It is excreted from the body through urination and ends up in the municipal water supply. If the medical community and radiological professionals intentionally cause patients to ingest a form of technetium that is 150 million times more radioactive than Tc-‐99, with the intent that its gamma rays be emitted within the body, and then sees no risk from the excretion of Tc-‐99 into our water supply, where is the concern? It is yet another example of fear, uncertainty, and doubt that Makhijani and Boyd would raise this issue as if it represented some sort of condemnation of the use of thorium for nuclear power.

If the spent fuel is not reprocessed, thorium-‐232 is very-‐long lived (half-‐life:14 billion years) and its decay products will build up over time in the spent fuel. This will make the spent fuel quite radiotoxic, in addition to all the fission products in it. It should also be noted that inhalation of a unit of radioactivity of thorium-‐232 or thorium-‐228 (which is also present as a decay product of thorium-‐232) produces a far higher dose, especially to certain organs, than the inhalation of uranium containing the same amount of radioactivity. For instance, the bone surface dose from breathing an amount (mass) of insoluble thorium is about 200 times that of breathing the same mass of uranium.



Statements like this really cause me to wonder if Makhijani and Boyd understand the nature of radioactivity. Yes, thorium-‐232 has a 14-‐billion-‐year half-‐life, which means that the radioactivity of thorium is exceptionally low. It will rise as the decay chain of Th-‐232 begins to form, but it is still at a very low level. To be concerned with the radioactivity of thorium in spent fuel, while neglecting to mention the five billion kilograms of thorium contained in each meter of the Earth’s continental crust again appears to be another example of fear, uncertainty, and doubt levied unfairly against the use of thorium. The buildup of thorium-‐228 as part of the decay of thorium will happen on a scale within the Earth’s crust so titanically in excess of any activity on the part of man so as to render that point utterly immaterial to any discussion of thorium as a nuclear fuel.

Since both thorium and uranium are natural and common constituents of the Earth’s crust, discussing a bone surface dose obtained by breathing insoluble thorium—a very strange exposure pathway—and contrasting it with uranium is again utterly immaterial to the use of thorium as a nuclear fuel. Do Makhijani and Boyd mean to say that it would be preferable to be breathing uranium instead? The criticism seems to have no structure.

Furthermore, LFTR will not reject thorium to a waste stream nor generate “spent fuel” in the conventional sense. Thorium remains in the reactor until consumed for energy. At shutdown, unconsumed thorium is transferred to the next generation of reactor.

Finally, the use of thorium also creates waste at the front end of the fuel cycle. The radioactivity associated with these is expected to be considerably less than that associated with a comparable amount of uranium milling. However, mine wastes will pose long-‐term hazards, as in the case of uranium mining. There are also often hazardous non-‐radioactive metals in both thorium and uranium mill tailings.

Thorium is found with rare-‐earth mineral deposits, and global demand for rare-‐earth mining will inevitably bring up thorium deposits. At the present time, we in the US have the strange policy of considering this natural material as a “radioactive waste” that must be disposed at considerable cost. Other countries like China have taken a longer view on the issue and simply stockpile the thorium that they recover during rare-‐earth mining for future use in thorium reactors. In addition, the United States has an already-‐mined supply of 3200 metric tonnes of thorium in Nevada that will meet energy needs for many decades. The issues surrounding thorium mining are immaterial to its discussion as a nuclear energy source because thorium will be mined under any circumstance, but if we use it as a nuclear fuel we can save time and effort by avoiding the expense of trying to throw it away.


Research and development of thorium fuel has been undertaken in Germany, India, Japan, Russia, the UK and the U.S. for more than half a century. Besides remote fuel fabrication and issues at the front end of the fuel cycle, thorium-‐U-‐233 breeder reactors produce fuel (“breed”) much more slowly than uranium-‐plutonium-‐239 breeders. This leads to technical complications. India is sometimes cited as the country that has successfully developed thorium fuel. In fact, India has been trying to develop a thorium breeder fuel cycle for decades but has not yet done so commercially.

Thorium/U233 reactors like LFTR produce sufficient U-‐233 to make up for U-‐233 consumed in the fission process. This may be what the authors meant by “breeding more slowly”, but since they consider plutonium a dangerous substance and eschew the use of nuclear power, it is a wonder why they would consider a reactor that does not produce plutonium as having some sort of deficiency. They neglect to elaborate on what sort of “technical complications” this very attractive feature would entail.

The thorium effort in India has been centered around the use of thorium in solid-‐oxide form, and has suffered from the deficiencies of using this approach, which are transcended through the use of thorium in liquid fluoride form. This is further evidence that the authors are unaware of the implications of the liquid-‐fluoride thorium reactor.

One reason reprocessing thorium fuel cycles haven’t been successful is that uranium-‐232 (U 232) is created along with uranium-‐233. U-‐232, which has a half-‐life of about 70 years, is extremely radioactive and is therefore very dangerous in small quantities: a single small particle in a lung would exceed legal radiation standards for the general public. U-‐232 also has highly radioactive decay products. Therefore, fabricating fuel with U-‐233 is very expensive and difficult.

Previously I mentioned the implications of the presence of uranium-‐232 contamination within uranium-‐233 and its anti-‐proliferative nature with regards to nuclear weapons. U-‐232 contamination also makes fabrication of solid thorium-‐oxide fuel containing uranium-‐233-‐oxide very difficult. In the liquid-‐fluoride reactor, fuel fabrication is unnecessary and this difficulty is completely averted.

Thorium may be abundant and possess certain technical advantages, but it does not mean that it is economical. Compared to uranium, thorium fuel cycle is likely to be even more costly. In a once-‐through mode, it will need both uranium enrichment (or plutonium separation) and thorium target rod production. In a breeder configuration, it will need reprocessing, which is costly. In addition, as noted, inhalation of thorium-‐232 produces a higher dose than the same amount of uranium-‐238 (either by radioactivity or by weight). Reprocessed thorium creates even more risks due to the highly radioactive U-‐232 created in the reactor. This makes worker protection more



difficult and expensive for a given level of annual dose.

The liquid-‐fluoride thorium reactor has an exceptionally simple and self-‐contained fuel cycle that has every promise of being less-‐expensive than today’s wasteful and complicated “once-‐through” approach to uranium fuel utilization. Makhijani and Boyd try to assign thorium to the wasteful “once-‐through” fuel cycle, point out deficiencies, and then condemn thorium as having no promise. This might analogous to putting diesel fuel in a gasoline-‐powered car and then pointing out how deficient diesel fuel is when the car will no longer operate. It is disingenuous and deceptive, and the kindest thing that can be said is that Makhijani and Boyd are ignorant of the implications of the liquid-‐fluoride thorium reactor and its fuel cycle, which they should not be if they presume to issue a “position paper” such as this.

Finally, the use of thorium also creates waste at the front end of the fuel cycle. The radioactivity associated with these is expected to be considerably less than that associated with a comparable amount of uranium milling. However, mine wastes will pose long-‐term hazards, as in the case of uranium mining. There are also often hazardous non-‐radioactive metals in both thorium and uranium mill tailings.

This is a repeat of the issue previously considered, as is immaterial as a factor for or against the use of thorium in nuclear powered reactors since thorium will be mined anyway during the mining of rare-‐earth minerals. The only question will be whether the mined thorium will be wasted or not.

Conclusions In conclusion, Makhijani and Boyd fail to consider the implications of the liquid-‐fluoride thorium reactor on all aspects relating to the benefits of thorium as a nuclear fuel. They fail to consider its strong benefits with regards to nuclear proliferation, since no operational nuclear weapon has ever been fabricated from thorium or uranium-‐233. They fail to consider how LFTR can be used to productively consume nuclear weapons material made excess by the end of the Cold War. They fail to consider the reduction in nuclear waste that would accompany the use of LFTR. They fail entirely to account for the safety features inherent in a LFTR—how low-‐pressure operation and a chemically-‐stable fuel form allow the reactor to have a passive safety response to severe accidents. They fail to account for the improvement in cost that would be realized if LFTRs were to efficiently use thorium, reduce the need for mining fossil fuels, and increase the availability of energy.

The authors of the rebuttal concluded with the following statement: "Mr. Makhijani and Ms. Boyd should retract this statement in its entirety as flawed and deceptive to a public that needs clear and accurate information about our energy future."


About the Author

David Amerine David Amerine has 45 years of experience in the nuclear industry. He began his career in the U.S. Navy, after graduating from the United States Naval Academy and obtained a Masters in Management Science from the Naval Post Graduate School while in the Navy. After leaving the Navy, he joined Westinghouse at the Department of Energy (DOE) Hanford Site. There he worked as a shift operations manager and then as the refueling manager for the initial core load of the Fast Flux Test Facility, the nation’s prototype breeder reactor. Mr. Amerine furthered his career in the commercial nuclear power industry throughout the 1980’s, first as the Nuclear Steam Supply System (NSSS) vendor, Combustion Engineering, Site Manager at the Palo Verde Nuclear Generating Station during startup of that three-‐reactor plant and then as Assistant Vice President Nuclear at Davis-‐Besse Nuclear Power Station. There he led special, interdisciplinary task forces for complex problem resolutions involving engineering and operations during recovery period at that facility back in the late 1980’s.



Davis-‐Besse was the first of eight nuclear plants where he was part of the leadership team or the leader brought in to restore stakeholder confidence in management and/or operations. In the DOE Nuclear Complex these endeavor recoveries included the Replacement Tritium Facility, the Defense Waste Processing Facility, and the Salt Waste Processing Facility projects. In addition to Davis-‐Besse in the commercial nuclear industry, in 1997 he was brought in as the Vice President of Engineering and Services at the Millstone Nuclear Power Station where he was instrumental in leading recovery actions following the facility being shut down by the Nuclear Regulatory Commission (NRC). His responsibilities included establishing robust Safety Conscious Work Environments (SCWE) programs. In 2000, Mr. Amerine assumed the role of Executive Vice President of Washington Government, a $2.5 billion business unit of Washington Group International (WGI). In this role, Mr. Amerine was responsible for integrated safety management, conduct of operations, startup test programs, and synergies between the diverse operating companies and divisions that made up WGI Government. Mr. Amerine was then selected as the Executive Vice President and Deputy General Manager, CH2M Hill Nuclear Business Group, where he supported the President in managing day-‐to-‐day operation of the group, which included six major DOE sites, three site offices, and numerous individual contracts in the international nuclear industry. He was charged with improving conduct of operations and project management, expenditures and staffing oversight, goal setting, performance monitoring, and special initiatives leadership. Mr. Amerine came to B&W in 2009 where he was subsequently selected as President of Nuclear Fuel Services in early 2010 after the NRC had shut down that facility which is vital to the security of the United States since it is the sole producer of fuel for our nuclear Navy. He led the restoration of confidence of the various stakeholders including the NRC and Naval Reactors. The plant was restored to full operation under Mr. Amerine’s leadership. He retired from NFS in 2011.

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