In 2020, the US Congress directed the Department of Energy (DOE) to write a report within 180 days about the potential of thorium and uranium-233 as fuels for future nuclear reactors.

Not later than 180 days after the date of enactment of this Act, the Secretary shall, after consulting with relevant entities, including National Laboratories, institutions of higher education, and technology developers, submit to Congress a report identifying any and all options for providing nuclear material, containing isotopes other than the uranium-235 isotope, such as uranium-233 and thorium-232 to be used as fuel for advanced nuclear reactor research, development, demonstration, or commercial application purposes.

On May 19, 2022, Senator Tommy Tuberville of Alabama reminded Energy Secretary Granholm about the obligation to report on thorium and uranium-233.

TUBERVILLE: In fact, in 2008, the report calls U-233 an irreplaceable natural resource. Congress has asked for answers on this, are you familiar with that? We’ve asked for answers. Okay. The appropriations bill in ’21 required the DOE to inform Congress about the potential of 233. Do you know when this report was due, Ms. Granholm?

GRANHOLM: When was it due?

TUBERVILLE: 2021. I do not know why but this report is still not finished. And to me, it’s a very important report. If we’re going to do away with gas and we’re going to try to cut back on our oil supply, we have got to find some way to generate more power in this country. Clean power. We’re all for that. My colleague, Senator Warren, and I do not see eye to eye on a lot of things, but we do agree on how egregious the mismanagement and disregard for civilian oversight is within our Department of Energy.

I have previously reported on this reaction. Almost a year later DOE released the report.

 

Alternate Fuels: Thorium and Uranium-233 (PDF, 2.4MB)

March 2023

This report is perplexing; although the report covers a highly technical topic and is the result of over two years of work it has significant oversights and inaccuracies. My overall takeaway from the document is that the report is internally inconsistent. Although the report acknowledges several benefits of thorium these benefits are later listed as concerns and do not lead to the rational conclusion that the U.S. should pursue a domestic thorium MSR program. The report fails to fulfill the 2022 House request to report on thorium MSRs. The report switches between solid and liquid core reactors with little consistency. The report should separate these two technologies instead of attributing the weakness of solid-fuel reactors to thorium MSRs. Furthermore, the report does not acknowledge the significant difficulties and lack of HALEU, instead attributing the benefits of LEU to all Uranium technology.

Perhaps even more troubling, the report does not fulfill the original 2020 Energy Act request to consult “with relevant entities, including National Laboratories, institutions of higher education, and technology developers,” based on the exclusion of National Laboratory and technology developer collaborations. The report fails to fulfill the stated goal of the 2020 request to identify “any and all options” for use of thorium and uranium-233. This misleads Congress and makes it difficult for Congress to determine the future of the 233U currently stored at ORNL. The report also erroneously asserts that the destruction of 233U is required to harvest the medical benefits of actinium-225 and bismuth-213 when these elements can be easily harvested while preserving this valuable resource, allowing the U.S. to save taxpayer dollars, expand science, support medical advances, and produce clean energy from a material currently designated as waste.

As I go through the report I note a number of inaccuracies and oversights that I will rebut below.

page 10

“The Molten Salt Thorium Research Reactor at Oak Ridge National Laboratory (ORNL) in Tennessee was a demonstration MSR that used fissile thorium and produced U-233 as the main fissile driver in its second campaign.”

ORNL called the demonstration the Molten-Salt Reactor Experiment, and it used U-233 created in another reactor as its fissile fuel in its second campaign. It never had thorium in the salt.

page 11

“In 1973 the United States effectively discontinued thorium-related nuclear research because uranium-fueled reactors were a proven, efficient technology and thorium’s breeding ratio in LWRs [Light Water Reactors] was considered to be too low to produce enough fuel to support development of a commercial nuclear industry.”

This statement is untrue. The United States discontinued Thorium MSR work to provide more funds for the sodium fast-breeder reactor effort (LMFBR). The LMFBR was supported at the highest levels of government and industry at that time. The Nixon White House perceived the program to have remarkable inertia and the they requested that the Atomic Energy Commission (AEC) focus their efforts on one breeder reactor instead of four breeder reactor. The AEC, under Glenn Seaborg, believed the claims by LMFBR developers that the LMFBR design would have a higher breeding ratio than the thorium MSR approach. That higher breeding ratio claim, in turn, fueled the belief that the “doubling time” of the LMFBR would be much shorter than that of other reactors. Both of those claims turned out to be far afield of reality. AEC never perceived Uranium-fueled reactors as proven and efficient. Even in the early 1960s Seaborg and his agency clearly understood that they were a stop-gap measure at best. The U.S. undertook the LMFBR effort because they knew that a transition away from LWRs was necessary due to their inefficient use of uranium, and the belief that a national buildout of LWRs would rapidly exhaust U.S. uranium reserves. However, the LMFBR development failed and the government cancelled the main project, the Clinch River Breeder Reactor, in the late 1970s, briefly restored it under Reagan, and then cancelled it again in the early 1980s. France and Japan continued with their large LMFBRs but both failed expensively. Nevertheless, the successor to the AEC, the DOE, has poured money into the sodium-fast-reactor concept ever since. The most recent example is the ARDP funding a fast-sodium reactor that is even more fuel-inefficient than LWRs. The cost has already ballooned from $2B to $4B even before any construction. It also requires HALEU fuel that, as of now, can only be obtained from Russia.

“For most countries, including the United States, uranium is relatively abundant so that the deployment of thorium-based power reactors has been limited.”

Neither uranium abundance nor scarcity has ever been the motivation for a thorium MSR. The motivation for thorium, the reason why it has always held appeal, is that thorium holds the potential for a more efficient use of nuclear resources and the near elimination of transuranic waste. Putting that aside, geographic distribution of uranium might suggest that the U.S. is blessed with abundant uranium deposits. However, the amount of uranium within national borders should not be the relevant measure. What is relevant is whether that uranium can be extracted at commercially competitive costs. Uranium mines in the United States are not competitive with those in Canada, Kazakhstan, Niger, or many other countries. Further, mined uranium alone cannot power LWRs. It must be converted from oxide to hexafluoride form and then enriched, deconverted back to oxide, and then fabricated into pellets. The United States has only one conversion facility which was built in 1958. The U.S. has only one enrichment facility which is entirely foreign-owned and can only meet 40% of U.S. annual enrichment needs. The United States has no HALEU enrichment capability. The United States is not well-suited to support a uranium fuel supply chain.

Returning to the problem of waste from the uranium fuel cycle, other countries observed the failure of the US and other developed nations to license and open geologic repositories. The fact that a thorium MSR, if properly designed and operated, will not produce long-lived transuranic waste, represents a powerful motivator for many countries to investigate a thorium MSR. The policies of the current coalition government in the Netherlands illustrates this. They have reversed long-standing opposition to nuclear energy and have set aside EUR 5 billion as initial funding for two new nuclear reactors. The government worked with the leading technical university, TU Delft, to issue the report: “A Vision for a Nuclear and Radiation Ecosystem in the Netherlands.” The report prominently highlights the potential for Thorium MSRs to provide the long-term nuclear waste solution for the Netherlands. The Netherlands already has a solution for its nuclear waste for the next one hundred years as represented by the impressive COVRA facility. COVRA puts the Netherlands well ahead of the U.S. when it comes to addressing the waste issue and yet the country is looking beyond a hundred years to secure a truly permanent solution such as the thorium MSR. In contrast, DOE-NE instead elects to put taxpayer money behind uranium-fueled designs that require HALEU enrichment and/or TRISO fuels, both of which will exacerbate, rather than mitigate, the existing waste challenge.

pages 11-19

The DOE-NE discusses international thorium efforts and lists a number of private companies that work on various thorium-based fuels.

pages 20-25

“The DOE-EN describe its own limited efforts to fund various small studies on thorium reactor work. This work ranges from thorium in LWRs to a handful of GAIN vouchers around thorium MSRs.”

Section III of this report describes “historical U.S. Thorium Reactor Programs”. The report fails to include Flibe Energy’s efforts to develop thorium reactors in this section, even though Flibe Energy began in 2011. In section IV, the DOE  describes DOE-NE work related to thorium reactors. However, the report fails to mention the 150-page proposal submitted to the DOE-NE under the Advanced Reactor Development Program by Flibe Energy. Nor does the report mention the Industry FOA award to Flibe Energy around the removal of uranium from a molten-salt reactor. The report does briefly mention two GAIN awards to Flibe Energy. The report fails to give a clear description of the breakthroughs in fissile security that resulted from one of those GAIN awards with ORNL. Congress instructed the DOE to “consult with technology developers” but I can tell you that no conversations whatsoever have taken place between FEI and the DOE-NE relative to this report.

Moreover, DOE-NE failed to reference the extensive EPRI report on the LFTR design, published in 2015. Additionally, the researchers either failed to mention, or missed, the hundereds of public presentations Flibe has given. Additionally, Flibe Energy met with high level personnel at the DOE on June 24, 2021 and inquired about the report and an opportunity for input. The DOE was familiar with the report. On October 26, 2021 Flibe Energy corresponded with another person at the DOE and followed up on the report requesting an opportunity to provide information but these efforts yielded no opportunity, despite the congressional instruction that the DOE consult with “technology developers.”

page 28

“No current U.S. infrastructure to support thorium fuel utilization exists.”

Thorium MSR does not require the same extent of infrastructure as uranium and plutonium. The report already makes it clear that thorium is available from monazite tailings. Thorium is mono-isotopic and so does not require “enrichment”. Thorium only needs a one-time chemical conversion from thorium dioxide to thorium tetrafluoride, and that conversion is chemically favorable. Molten-salt reactors do not require the fabrication of pellets, or their aggregation into rods, or their accumulation into assemblies.

Finally, it is worth highlighting that thorium’s infrastructure requirements compare extremely favorably with DOE’s favored reactor designs. Nine of the ten ARDP awardees have designs that require HALEU fuel (>5% enrichment). Some even require HALEU in metal form, which, like HALEU deconversion, is much more expensive at higher enrichments than at the standard enrichments below 5%. HALEU also faces further challenges associated  with transport containers and licensing. Currently no infrastructure exists in the U.S., or elsewhere in the world outside of Russia, to enrich, deconvert, or transport HALEU levels of enrichment.

“In the United States, thorium research and development has been minimal for more than 30 years, so that DOE laboratory experience would have to be gained and/or enhanced.”

DOE labs are not required to develop new fuel, either thorium or other advanced fuel.

“The U.S. laboratories and nuclear industry does not have the required infrastructure to fabricate, ship, or use thorium-based fuels.”

Thorium-based fuel (LiF-ThF4) does not present a unique challenge to ship particularly as compared to HALEU. It has almost no radioactivity and no chemical hazard. The U.S. nuclear industry does not have the required infrastructure to enrich (not needed in thorium), deconvert (not needed in thorium), metallize (not needed in thorium), fabricate, ship, or use HALEU-based fuels. These arguments more easily disqualify the use of HALEU than of thorium.

page 29

“The NRC would need to perform confirmatory research experiments and develop sufficient information to approve potential thorium-fueled reactor designs and fuel cycle facilities.”

The NRC would need to approve a facility that handled larger amounts of thorium, just as they have to do for HALEU, for TRISO, and for all sorts of technical elements embedded in the designs DOE selected in the ARDP program.

“Not every thorium fuel design is self-sustaining.”

This is true, but the Flibe Energy LFTR design that IS self-sustaining. A LFTR started on U-233 would reach equilibrium very quickly. Flibe Energy modeled this in the GAIN effort with ORNL however, this design is not mentioned in the report.

“Thorium fuel radioactive decay products and created fissile U-233 could pose unique hazards and proliferation issues.”

The formation of U-232 is not a problem, but rather a solution. Its decay products generate gamma rays that makes the material far less attractive for proliferation diversion. This is the biggest reason the Manhattan Project shelved thorium technology for weapons applications during their research. I covered this in my masters’ thesis.

“The U-233 fuel can be used in nuclear weapons, which eliminates the main reason for transitioning to this technology for many in the first place, i.e., reduction of Pu isotopes from uranium-only fuel.”

All of today’s reactors produce plutonium, which can be used in nuclear weapons, and unlike U-233, plutonium HAS been used in thousands of nuclear weapons. Futhermore, today’s nuclear reactors produce tens of metric tonnes of plutonium every year, material which HAS and IS being used in nuclear weapons unlike U-233.

“Thorium fuel reprocessing is more difficult than uranium fuel reprocessing.”

This statement only considers thorium dioxide fuels, mentioning their difficulty in dissolution into nitric acid. Thorium dioxide fuels are very difficult to reprocess. However, the thorium MSR uses a LiF-ThF4 based fuel which can be “processed” without changing form. Unlike solid fuel, liquid fuel need not be dissolved in nitric acid and shifted from an oxide-based formulation to a nitrate-based formulation. The recent GAIN work with ORNL describes how thorium fuel would be electrolytically processed to remove bred protactinium and uranium.

“The high gamma radiation associated with the short-lived daughter products of U-232, which is always associated with U-233, necessitates remote handling, reprocessing, and refabrication of fuel.”

Thorium MSRs do not require fuel refabrication.

“The protactinium formed in thorium fuel cycle also causes reprocessing problems, which need to be resolved.”

Protactinium presents an opportunity as covered in the GAIN work.

“Research into thorium energy is limited. Historically, thorium fuel research and thorium reactor deployment has been limited because of the possible proliferation concerns over U-233 production.”

Thorium research was limited because the U.S. ended it in favor of the sodium fast-breeder, a reactor that could make electrical power AND weapons-grade plutonium simultaneously. Other nations followed suit. Plutonium proliferation is a more immediate and vastly greater threat than U-233 proliferation.

page 30

“Molten salt reactors pose unique technology challenges.”

Every reactor poses “unique technology challenges” but not all have the promising solutions of the thorium MSR. Molten salt “can be corrosive” however, the Oak Ridge work showed how to put the right molten salts into the right materials to address these challenges.

“Continuous chemical cleanup systems are needed to remove contaminants and fission products that parasitically absorb neutrons and create corrosion issues.”

Every reactor today uses continuous chemical processing to keep corrosion under control; a molten-salt reactor is no different. But a molten-salt reactor can realize great advantages from its chemical processing system, namely, the ability to utilize thorium fuel 200 times more efficiently than uranium.

“Chemical extraction and diversion of U-233 using these chemical cleanup systems can lead to proliferation problems.”

To clarify, the United States can never “proliferate”; we already have nuclear weapons. We have tens of metric tonnes of surplus weapons-grade plutonium that we are attempting to destroy at great cost. We will never attempt to “pilfer” U-233 from a thorium reactor and make weapons with it. Even if we did, we would merely add a few more weapons to a stockpile that already numbers in the thousands of weapons. There is absolutely nothing about the operation of a thorium MSR that would change the fact that the US is a nuclear-weapons state and has thousands of nuclear weapons. The U.S. will never undergo any effort to add U233-based weapons to our existing plutonium and HEU-based weapons. The building of HALEU-based reactors and spreading that technology around the world poses thousands of times the threat to global anti-proliferation efforts than a thorium reactor would.

“Thorium fuel fabrication, reactor deployment, recycling, and utilization may cost more than uranium.”

A thorium MSR does not require fuel fabrication. The recycling of the fuel is simplified tremendously relative to uranium reactors and part of the reactor design itself. U.S. uranium reactors are based on uranium mined outside of the country, uranium enriched outside of the country, and fuel that is fabricated and irradiated with no disposition path. I do not know how the DOE arrived at this development number, but Flibe Energy has worked on development costs and challenges for over a decade and I’m sure they would happily share their experience.

“Standard fuel rods may have waste storage challenges and high fabrication costs, but even with current technology, it is still cheaper to generate power with uranium fuel rods than it would be to fabricate thorium fuel for energy production.”

Thorium MSRs contain no fuel rods.

page 32

“Table 5-1. Comparison of Closed U/Pu fuel cycle costs versus Th fuel cycle costs. The transition thorium fuel cycle would require significantly larger amounts of natural uranium and separative work units (SWU) than for the standard uranium cycle for the same energy output, dependent on reactor type, burn-up, and fuel management.”

Flibe Energy modeled these same factors and come to the opposite conclusion.

“For thorium-based cycles, the cost associated with using recycled fissile material (plutonium or U-233) heavily depends on the back end of the chosen fuel cycle.”

Flibe Energy described this technology in the EPRI report, and uses a very different method.

page 33

“Homogeneous thorium/uranium LWR fuel cycle studies have shown that these fuel cycles are not economically competitive over conventional uranium cycles with current fuel management strategies.”

This report is very inconsistent when discussing thorium, here the report references a LWR instead of discussing a thorium MSR. A revised report treating thorium MSRs separately from reactors using solid fuel would provide more useful comparisons.

“If fissile U-233 is used for closing the thorium fuel cycle, radioactive daughter products of U-232 would require remote operations.”

All recycled fuels require remote operations. In molten-salt fuels remote operations are an insignificant factor unlike with solid fuel pellets.

“High-level long-lived waste would require permanent disposal. No significant economic difference between uranium and thorium cycles would be seen, especially if it is assumed here that only residual waste from reprocessing would be disposed.”

This ignores the fact that liquid fuel allows for individual extraction of daughter products, allowing for productive uses of the rare elements produced. Additionally, this statement compares liquid fuel cycles to reprocessed uranium, which the U.S. does not currently practice.

page 34

“Development of new thorium-based fuels or new reactor concepts is a time- and resource-consuming process.”

This makes it fortunate to have a company that has been developing thorium-based fuels and reactor concepts for 12 years.

“Any thorium fuel design would require the use of uranium/plutonium fissile “driver” fuel until enough U-233 is produced by neutron irradiation to make the fertile thorium cycle self-sustaining.”

Luckily, the U.S. has U-233 available for use, but will need to stop the down-blending of this valuable element.

“The key factor governing the rate at which U-233 could be produced from the introduction of Th/Pu or Th/U/Pu fuel is the amount of Pu available.”

And luckily the U.S. has designated over 50 MT of plutonium as surplus and committed by treaty to dispose of over 34 MT of this plutonium in a manner that makes it unsuitable for use in nuclear weapons. This initiative has already cost our country tens of billions of dollars but could instead create valuable energy in a thorium MSR.

“The development of a fully self-sustaining closed thorium/U-233 fuel cycle would also require the development of industrial-scale reprocessing capabilities to recover the U-233 from spent fuel along with fuel fabrication facilities to prepare the material for reuse.”

The LFTR design accomplishes this step by using equipment that would fit in the volume of a small closet. This solution is simple, continuous, rad-hardened, and secure from diversion.

“Major impediments…The thorium extraction (THOREX) process has been only demonstrated in laboratory facilities but has yet to reach the maturity of the commercial plutonium uranium reduction extraction (PUREX) process. Alternative conceptual processes could be investigated but would take years to develop.”

The development of THOREX is irrelevant to a thorium MSR. The THOREX process is based on using concentrated nitric acid to dissolve thorium dioxide fuel pellets, turning them into thorium nitrate. The thorium in an MSR is in the form of thorium tetrafluoride, and in some cases, thorium tetrachloride. Both would already be in a liquid form in their respective molten-salt solutions. There would be no reason to attempt to convert them to an inferior chemical form like thorium nitrate. One of the biggest advantages of a thorium molten-salt reactor is the fact that chemical separations can be undertaken in the native fuel form of the reactor. No chemical shift, such as from oxides to nitrates as is proposed in the THOREX process, is necessary or desirable.

“Major impediments…recycling U-233 produced in irradiated thorium fuel is the presence of radioactive U-232.”

Molten-salt reactors do not require fuel fabrication like solid-fueled reactors do, and so the presence of strongly radioactive U-232 does not concern molten-salt reactor operation.

“Major impediments…Thorium fuel technologies may require significant R&D.”

To provide some context, the DOE told Congress that they need more than four billion dollars for new HALEU enrichment. By contrast these thorium technologies can be developed for the tens of millions of dollars.

“Major impediments…Advanced dedicated thorium/uranium breeder/burner reactor designs that may be able to utilize a closed thorium/U-233 fuel cycle are still in the early conceptual design study phase. Breeding U-233 from thorium in a thermal neutron spectrum reactor is slow and would require extensive reprocessing.”

These designs are far beyond conceptual. U-233 will breed from thorium immediately and will sustain the nuclear reaction. DOE reports from the ORNL GAIN research confirm this.

“Major impediments…MSRs may offer the prospect of using thorium fuels with online uranium extraction (U-233) and/or recovery and reuse systems; however, the design, development, licensing, and construction of such novel separation systems is a major, costly, and long-term undertaking. Such on-line uranium chemical separation systems could also lead to U-233 extraction creating proliferation issues.”

Flibe Energy’s interaction with the DOE on the ORNL GAIN report comes to totally different conclusions.

page 35

“In summary…the benefits of a thorium fuel cycle are modest[.]”

The report fails to explain why the benefits of reduced waste and a closed fuel cycle are “modest”. The billions that DOE-NE has spent over the last fifty years on Sodium fast reactors achieved something far more “modest”.

Figures 5-1 and 5-2 are lifted directly from Moir and Hargraves paper without discussion.

page 37

Proliferation, Safeguards, Security, and Criticality Safety Issues

Prefacing the discussion of these issues, let us note that the United States, by definition, cannot “proliferate” nuclear weapons in one sense of the word, and will not “proliferate” nuclear weapons in the other sense of the word. The United States already possesses a large arsenal of nuclear weapons. The United States is a nuclear weapons state. No addition of nuclear weapons will change this status, even if fashioned from a novel fissile material like uranium-233.

The United States does not and will not help other countries that are not weapons states to become weapons states.  The U.S. will not “proliferate” nuclear weapons technologies to other countries. Thus the entire notion of “proliferation” emerging from the United States is completely non-sensical.

Apparently, the United States once tested a nuclear weapon that contained uranium-233. It was the “Teapot Military Effects Test”, detonated on April 15, 1955. The Teapot MET used a “composite” core of plutonium and U-233 based on the plutonium/U-235 pit from the TX-7E, a prototype Mark 7 nuclear bomb design used in the 1951 Operation Buster-Jangle Easy test. It produced a yield of 22kt (comparable to the Fat Man plutonium-only weapon that exploded over Nagasaki), but significantly less than the expected amount. As a military effects test, the DoD specified that the device should have a calibrated yield within 10% of ratings. However, weapon designers at Los Alamos substituted the experimental core without notifying the DoD. The unexpected lower yield, 33% less than the DoD expected, ruined many of the military’s tests. In simpler terms, Teapot MET was a “dud” that was not repeated. Its existence does not constitute “proliferation” because the U.S. already had nuclear weapons, and it offered no advantages over highly-enriched uranium or plutonium and the U.S. did not purse further uranium-233-based weapons. These facts provide important context for any proliferation or security discussion.

Thorium contains no fissile isotopes; it is purely fertile. Fission reactions are necessary to create the neutrons that will convert thorium into U-233. If a non-weapons state aspires to produce nuclear weapons, they would need to possess fissile material to irradiate the thorium in a reactor. If they possessed this fissile material already there would be no reason to make yet another fissile material for a weapon. Natural uranium can be isotopically enriched to the level where nuclear weapons can be produced from highly-enriched uranium that would result from that process. Alternatively, natural uranium can be arranged into a critical configuration using heavy water or graphite as a moderator and irradiate the uranium-238 that forms 99.3% of natural uranium in order to produce chemically-separable plutonium. The U.S. used both processes to produce the first nuclear weapons as did every other weapons state. To produce uranium-233 would require the consumption of some of this enriched uranium or plutonium, an inefficient further step that fails to advance the objectives of the would-be proliferator.

During the Manhattan Project, Glenn Seaborg, the discoverer of plutonium and uranium-233, pressed for General Leslie Groves to allow him to examine U-233 as a possible substitute for plutonium as a fissile material. After Groves gave him permission, Seaborg examined the production pathways to U-233 and found that no matter which path he pursued, unacceptably large amounts of uranium-232 would form. Seaborg then petitioned Groves to end investigation of U-233 for weapons despite having originally advocated for it. His arguments against U-233 for weapons use remain as relevant today as they were in 1945. The underlying physics and chemistry remains unchanged. Across all nations, a tiny number of weapons tests with U-233 have taken place, but no nation has developed or deployed an operational U-233 weapon.

“The United States explored the possibility of using Th-232 as a source to produce U-233 for nuclear weapons and concluded that it could be a very potent weapon when the first U-233 bomb was tested in 1955.”

No, the Teapot MET test was a “dud” and  the U.S. did not pursue U-233 for weapons development.

page 38

“Eventually, scientists were able to obtain U-233 by using a variety of chemical separation methods to extract protactinium 233 (Pa-233) from irradiated Th-232 fuel and allowing the Pa-233 to radioactively decay into isotopically pure U-233.”

The very first way that Glenn Seaborg and his group obtained U-233 in 1942 was from protactinium extraction.

“Protactinium separations and decay provide an easy pathway for obtaining highly attractive weapons-grade U-233 from thorium fuel cycles.”

Although I dispute the ease of protactinium separations, one must already have uranium or plutonium to irradiate thorium to produce U-233. An actor with uranium or plutonium has much easier paths to a nuclear weapon than to add another complicated layer and develop a weapon from a U-232 contaminated material with completely undefined detonative properties relative to HEU and plutonium designs.

“The Nuclear Suppliers Group Part 1 Guidelines (the “Trigger List”) and the Zangger Committee control thorium as source material in section 1.1 and 2a, respectively, and U-233 as special fissionable material in section 1.2 and 2b, respectively. These controls require that states apply fundamental principles for safeguards and export controls before transferring these materials for peaceful purposes to any non-nuclear-weapon State.”

Yes, and context here is appropriate. Those same definitions apply to plutonium as a “special nuclear material” and uranium-238 as a source material. All uranium-based reactors generate plutonium, a special nuclear material that operators must safeguard and control. Yet the U.S. promotes and exports uranium-based reactors that are making plutonium.

“In the United States, the export of thorium and U-233 are subject to the NRC’s export control regulations and the terms of an agreement for cooperation pursuant to Section 123, recognizing their inherent proliferation risk.”

This also applies to uranium and plutonium.

“Section 123 of the Atomic Energy Act requires that any such civil nuclear cooperation agreements include nine robust nonproliferation commitments from the international partner designed to ensure the highest level of safeguards, security, and nonproliferation controls.”

Yet the DOE signed a 123 agreement with communist Vietnam that “permitted” them to enrich uranium and reprocess plutonium.

“Safeguarding commercial spent fuel reprocessing is complicated for any type of fuel cycle, and the thorium fuel cycle is no exception and not “intrinsically” proliferation resistant as some proponents have stated, nor does it necessarily have an increased proliferation resistance, given the proclivity of U-233 for nuclear weapons use.”

Natural uranium can be enriched to HEU without ever touching a reactor. It is radiologically “ice-cold” even after that enrichment and practically indetectable, because it is still composed of the natural isotopes of uranium, just at a different composition. Plutonium is an alpha-emitter that is easily shielded. But U-233 is always contaminated with more or less U-232 which renders it a screaming gamma source and easy to detect. It is inherently resistant to diversion, as previously admitted in this section. There is no “proclivity” for nuclear weapons use, again as demonstrated by its conspicuous absence from the nuclear stockpiles of the world. These statements have no supporting evidence. Uranium-233 is very challenging to make into a weapon and such a weapon would be easily detectable and difficult to shield and handle. Any uranium-233 weapons program would have undergo many years of testing, improvement, and iteration to be fashioned into a credible deterrent. The US and other weapons states already have large nuclear arsenals and no interest or temptation to add hypothetical U-233 weapons to their arsenals.

“The importance of protactinium extraction chemistry in thorium fuel reprocessing needs to be recognized and addressed by measurement accountability safeguards technologies to reduce the chances that such a route would be employed by would-be proliferators for acquiring weapons-usable U-233 from irradiated thorium fuel.”

The ORNL GAIN work, which the DOE has mentioned in this report accomplished this. ORNL worked out a method of operating a thorium MSR that makes illicit diversion nearly impossible.

“As thorium fuel can be irradiated in commercial nuclear plants and produce U-233, it is a requirement of the international safeguards system of the IAEA that thorium and the entire thorium fuel cycle be safeguarded.”

Commercial nuclear plants can, and do, irradiate natural uranium and produce plutonium. Those materials require the same safeguards.

page 39

“Effective safeguards, security, and export control regimes must detect: (a) the diversion or theft of fissile materials (U-233) from thorium-fueled reactor facilities,”

Thorium MSRs are breeder reactors and operate with a bare minimum of excess reactivity which makes diversion difficult. They depend on a constant replenishment of U-233 from the blanket in order to operate. If proliferators diverted material, the reactor’s reactivity would fall, not replenish, and the reactor would shut down. In addition, a non-trivial amount of U-232 would contaminate the U-233  which would decay and emit a considerable gamma signature, greatly facilitating detection of any theft.

“(b) the misuse of facilities, equipment and technology that handle irradiated thorium fuel from declared purposes, e.g., clandestine operations at fissile U-233 production and reprocessing facilities,”

If an operator attempted to divert U-233 from its use in the reactor that diversion would manifest itself quickly by a fall in reactor reactivity and eventual shutdown. The report mentioned earlier that thorium reactors do not have much breeding gain, and the accumulation of a significant quantity (SQ) of U-233 would be difficult to achieve since all the bred U-233 needs to go into the reactor to keep it operating.

“(c) the transfer of nuclear technology and skills to illicit purposes.”

The recent DOE-NE push for HALEU makes this problem much worse, because a country that gets a HALEU-fueled reactor from the U.S. has a credible argument to require such enrichment levels. Nations will by necessity, require the enriched fuels to run these reactors.

“Non-proliferation for a nuclear reactor or fuel system can be evaluated by assessing the relative effectiveness of diversion “barriers” designated as either as: (a) intrinsic material and technical features, or (b) extrinsic safeguards and institutional measures used to avoid proliferation.”

Yes, and only uranium-233 has an intrinsic material barrier in the form of U-232. No such barrier exists in enriched uranium. No such barrier exists in plutonium. Furthermore, plutonium cannot be isotopically denatured. Uranium-233 has an intrinsic barrier AND can be instantly denatured by natural uranium if desired.

“Table 6-1 shows the proliferation resistance parameters for uranium versus thorium fuel in LWRs. Table 6-2 shows the materials barriers proliferation resistance capability of uranium versus thorium fueled LWRs.”

The Energy Act of 2020 required the DOE to report on all alternative fuels to uranium 235, specifically mentioning thorium 232 and uranium 233. The House Appropriations Act added the requirement that the report specifically address a domestic thorium MSR program, not a thorium LWR program.

“Without appropriate international safeguards measures in place, any misuse of thorium fuel could go undetected.”

This is also true for uranium reactors, except that that diversion will be much easier to catch in a thorium MSR situation. Right now, unsavory actors could simply acquire enriched uranium fuel, run it in a reactor for a few months, shut down “unexpectedly”, remove the fuel, process it via proven PUREX techniques, and harvest substantial amounts of weapons-grade plutonium.

“Current detection and intrinsic safeguards methods are focused on uranium and plutonium fuel cycles and may not be adequate for thorium fuel, particularly for reprocessing activities or monitoring chemical clean-up systems in liquid molten salt reactors.”

ORNL studied this very problem and determined how to monitor these activities.

“Different types of detection and safeguards methods for three thorium-based fuel cycles would be needed: (1) transition to thorium fuel for LWRs, (2) Th/U/Pu fuel in fast reactors using sodium coolant, and (3) thorium deployment in MSRs with liquid fuel.”

The U.S. does not need to develop all three of these methods simultaneously, if at all. Currently, the U.S. only needs to examine method (3) and ORNL has done so.

“Development of specific thorium cycle detection, non-destructive assay techniques, and safeguards methods at high technology readiness levels will be required before thorium-fueled reactors are deployed.”

That development is underway.

“Significant gamma shielding and remote handling is required for any irradiated thorium fuel processing.”

Yes, and the gamma rays that require this common sense precaution also allow for the straightforward detection of any diversion.  But MSRs can process their thorium fuel in its native chemical form in the reactor and that does not require external facility or the typical processes associated with solid fuels.

“The presence of U-232 in irradiated thorium fuel is often cited as providing self-protection against proliferation, because of its decay product gamma emissions, in particular, Thallium-208 emits a strong 2.6 MeV gamma ray when it decays. The level of proliferation resistance and self-protection that U-232 gamma emissions provide, however, depends on the proliferation threat scenario, i.e., on the capacity of proliferators to build or acquire shielded facilities and/or willingness to expose themselves or personnel to high radiation doses.”

The amount of U-232 contamination needed to generate a lethal dose to a would-be diverter is shockingly low. The proliferators would face significant difficulties with transportation due to radiation poisoning even with a willingness to expose themselves. Plutonium is much easier to steal and shield.

“Several types of thorium fueled reactors enable the production of protactinium to generate U-233. Three intermediate protactinium isotopes are produced when thorium 232 is irradiated, namely Pa-231, Pa-232, and Pa-233, that eventually form U-233.”

Only Pa-233 decays to U-233. Pa-232 decays to U-232, whose gamma-emitting daughters will strongly discourage diversion. Pa-231 has a high neutron absorption cross-section, which will cause it absorb a neutron, form Pa-232, and decay to U-232. So two paths lead to U-232 and one leads to U-233. Glenn Seaborg used this logic that  to convince General Groves not to pursue a U-233 weapon, even after he labored for years to convince Gen. Groves to do precisely the opposite.

“Pa-233 can be chemically separated from thorium and decays into U-233 with a half-life of 27 days:”

This is true, however, all of the protactinium isotopes will come out with that separation, not just Pa-233. And the trajectories of those other protactinium isotopes negatively impact the ultimate attractiveness of any diverted material, since two out of three lead to U-232.

page 40

“The half-lives of the three protactinium isotopes work in the favor of potential proliferators. Because Pa-232 decays faster than Pa-233, the isotopic purity of Pa-233 increases with time.”

This is not quite correct. In the time it takes for Pa-232 to decay to acceptable levels, a substantial amount of Pa-233 has decayed away as well. Pa-232 has a half life of 1.32 days, while Pa-233 has a half-life of 27 days. If one assumes ten half-lives on Pa-232 to reduce its presence in the extracted protactinium, then 13 days will have elapsed on Pa-233 decay and a substantial fraction of the Pa-233 (30%) will have decayed away to U-233 at the time at which the would-be diverters “make a cut” and remove U-232 contaminated uranium from the material they wish to steal. At this point they will be down 30% from the material they might have diverted. Any diversion of future fuel from the thorium MSR will begin degrading its reactivity and will become noticeable. The would-be thieves have less and less time and less and less material the more determined they become to obtain “pure” U-233. If they wait a month to ensure all the Pa-232 has decayed away, they will have lost half of their eventual haul of U-233. And they still have many more months to wait until the Pa-233 has decayed to U-233. If they want all of it they’re looking at nearly a year of waiting. Any of these would-be thieves would be far better served applying their considerable insight into the decay properties of fissile materials to the theft of HEU or plutonium, neither of which have any of these problems.

“If the protactinium is carefully separated from its uranium decay products a second time, this protactinium will decay into very pure weapons-usable U-233 over the next few months with a very low U-232 concentration.”

Yes, it will take many months for the U233 thieves to “wait out” the decay of U233 and begin their clandestine program of weapons development. Ten half-lives of Pa-233 is ten months.

“Many chemical methods exist for the aqueous separation of protactinium from thorium and uranium oxides, including the commonly proposed THOREX process.1,2,3 Once dissolved in acid, protactinium can simply be adsorbed onto glass or silica beads, exploiting the same chemical mechanism used by Meitner and Hahn to isolate protactinium from natural uranium a century ago.”

The report emphasized earlier how difficult the THOREX process is. The report also suggests here “many ways” exist to do a thing that later it asserts is exceptionally difficult and will require years of research with little possibility of success.

“Molten salt reactors with fissile and fertile fuel isotopes flowing in the salt coolant can be used to breed U-233 and extract protactinium by using chemical clean-up systems with resin beads and THOREX extraction chemistry.”

No, it is much easier than that to extract protactinium from molten salt. An electrolytic cell, akin to a battery, will likely make it possible. But this system will extract all the isotopes of protactinium, not just one of them like the report previously asserted. And unless that material is returned to the reactor in a timely manner it will lose reactivity and shut down. The system conceived during the ORNL GAIN effort immediately back-extracts this protactinium and uranium into a volume of fuel salt from the reactor core, which already has uranium and fission products in it. These form an intense radiation field that discourages diversion of the material. After several half-lives of Pa-233 (several months) the now-decayed mixture is gradually returned to the reactor, sustaining reactivity.

“Fixed thorium oxide “blanket” fuel assemblies irradiated on the periphery of a HWR can be aqueously reprocessed to extract irradiated protactinium and U-233.”

Operators can also process fixed uranium oxide “blanket” fuel assemblies on an HWR or an LWR using proven and well-understood aqueous techniques like PUREX to extract weapons-grade plutonium. Indeed, the U.S. and every other nation used this method to get the weapons-grade plutonium from which they built their nuclear arsenals. This argument applies equally well to traditional methods as well as thorium, except that aqueous processing of thorium/uranium dioxide (THOREX) is much more difficult than the same processing in uranium/plutonium dioxide (PUREX), as the report previously pointed out.

“Many HWRs include continuous refueling operations, which means that irradiated thorium can be removed quickly and often, without shutting the reactor down.”

True but this statement lacks context. The same thing can and does happen with uranium and plutonium every day. Using thorium would probably make this less likely than it is now. Every day bundles of natural uranium move through CANDU reactors and are discharged with plutonium with high isotopic quality, suitable for weapons use, able to be processed using PUREX.

“The irradiated thorium “blanket” radioactivity would be lower than the main core, so blanket fuel could be reprocessed immediately.”

This is also true for the uranium fuel cycle. The Canadians apply PUREX to their CANDU bundles at any time and use the resulting material to make weapons. But they do not and we do not worry about it, even though many countries have CANDU reactors.

“Reprocessing of irradiated thorium fuel in India’s civilian and military HWRs creates unique safeguard challenges since India is not a member of the Nuclear Non-Proliferation Treaty.”

India is not a member of the NNPT but China and Russia are. NNPT membership has not made China or Russia any less of a nuclear threat. Because India already possesses nuclear weapons this argument does not specifically apply to thorium.

“India has abundant thorium resources and is highly motivated to develop thorium reactors that can breed U-233.”

Yes, yet all of India’s weapons are still made from plutonium.

page 41

“Thorium fuel cycles produce weapons-usable U-233, so natural or depleted uranium (U-235 and U-238) could be added to “denature” the thorium fuel to make it difficult to separate out U-233 produced during irradiation from the other existing uranium isotopes during reprocessing.”

No, thorium fuel cycles do not produce weapons-usable U-233. Neither the U.S. nor any other nation designs weapons to use U-233. No one makes U-233 for weapons. Denaturing U-233 with U-238 will lead to the production of plutonium. Unlike U-233, plutonium is weapons-usable, weapons exist that use plutonium, and past production supplied plutonium for weapons.

“In contrast to reactors fueled only with uranium where there is no natural means to “denature” the resulting plutonium isotopes, adding U-235 and U-238 to unirradiated thorium fuel produces an effective deterrent for separating U-233 from irradiated thorium.”

A “denatured” thorium MSR, operating on a mixture of U-233 and U-238, will still make protactinium that is chemically distinct from thorium, uranium, and plutonium and which could be chemically isolated and then allowed to decay to U-233. Denaturing U-233 in the reactor with U-238 does not improve things, it makes them worse, because now the reactor also makes chemically separable plutonium that is weapons-usable.

“Furthermore, adding some natural or depleted uranium to thorium fuel improves safeguards detectability since it produces a unique U-232 radiation signature and higher spontaneous neutron emissions from U-238.”

No U-232 exists in natural or depleted uranium and adding natural or depleted uranium does not enhance that detectability. I agree that the presence of U-232 helps, but that benefit does not come from natural or depleted uranium. Additionally, U-238 has no appreciable spontaneous neutron emissions.

“Denaturing U-233 by adding U-238 would also assist in lowering the proliferation risk, but this approach would offset the benefits of reduced plutonium production.”

It would not lower proliferation risk. The single greatest factor that lowers proliferation risk in the United States is the simple fact that we actively oppose other countries developing nuclear weapons.

“Thorium-based fuel cycles require fissile containing driver fuels, using either depleted, natural or low-enriched uranium (LEU) enriched up to 20 weight percent U-235, or plutonium and causes additional proliferation concerns.”

No, thorium reactors need U-233 as their driver fuel. The report is internally inconsistent by first advocating adding uranium to thorium and then detailing this as a proliferation concerns.

“U-233 has a smaller critical mass than does either U-235 or Pu-239 and has other nuclear properties that are also significantly different from other fissile isotopes, so that U-233 has unique criticality safety processing and disposal issues.”

Slightly smaller but not significantly so. Yes, U233 has different nuclear properties which is why an effort to forge U-233 into an operational nuclear weapon would be exceptionally difficult and costly. It would also present considerable opportunity cost relative to embarking on the same effort with enriched uranium or plutonium, both of which are known to work and are the basis of the world’s nuclear arsenals.

“To avoid U-233 nuclear criticality issues, it was found that one part U-233 needs to be diluted with 188 parts by weight of DU (0.2 weight percent U-235), to ensure subcriticality in water and in dry conditions.”

Adding thorium avoids criticality issues, and it that addition that could be reversed chemically. Lithium is a superior addition than thorium or U-235. Storing U-233 in a lithium-fluoride, uranium-fluoride form would arrest criticality concerns.

“Thus, 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 percent, thus creating an effective barrier to diversion of U-233.”

No one wants to steal U-233 because of the radiation risk of U-232 and the immaturity of weapons designs that could use the material.

“More depleted or natural uranium would be required if other fissile uranium or plutonium isotopes are present, so that detailed criticality safety analysis would be required to ensure nuclear safety during fuel fabrication, reprocessing and disposal activities.”

While the report recommends diluting uranium-233 to render it unusable, no such solution exists for plutonium. Yet we have reactors that make hundreds of kilos of plutonium every day.

“The DOE inventory of U-233 at ORNL is currently being down-blended for final disposition.”

This is a travesty and a crime against the future of our nation. U-233 should be preserved to take advantage of the benefits of Thorium MSRs including reduced waste, lower diversion risk, and access to rare isotopes.

“Several stakeholders have suggested that DOE halt the disposition of U-233 inventories stored in Building 3019A at ORNL because they consider U-233 a national asset.”

DOE should halt the downblending and recognize U-233 as the national asset it is.

“In correspondence with Congress in 2021, NE responded to requests for additional information on alternatives for this U-233, expressing the view that DOE can achieve its mission to advance nuclear power to meet the Nation’s energy, environmental, and national security needs without having a domestic inventory of U-233.”

Of course DOE asserts this, because DOE makes no effort to develop thorium reactors. But the facts do not support DOE’s assertion, as I have described herein.

“Currently, DOE’s Office of Environmental Management (EM) manages the U-233 disposition program at ORNL, as part of the ORNL cleanup activities. EM has received regular appropriations from Congress to continue the disposition program and has contracted with Isotek to provide for disposition of the U-233.”

Congress only appropriated these funds to the DOE because the DOE told Congress it was worthless and dangerous when instead U-233 is a valuable national resource. With accurate information these appropriations would not occur. The downblending should be stopped to preserve U-233 and the valuable resources it produces.

“In turn, Isotek has a separate but related agreement with TerraPower that makes the byproduct of the U-233 disposition processing available as a medical isotope.”

Isotek harvests thorium-229, the immediate decay product of U-233. If the the DOE did not downblend and destroy the U-233, it would go on making this valuable decay product for hundreds of thousands of years. But DOE is allowing Isotek to make a one-time harvest of the Th-229, then permanently destroying the source.

page 43

“The continuation of this agreement enables the production of vital material for targeted alpha therapy, which is a form of cancer treatment.”

U-233 does not have to be downblended in order to harvest Th-229. These two agreements are severable allowing for the preservation of both resources.

“DOE performed a preliminary assessment of U-233 shipment and possible storage options at INL and associated costs in November 2019.”

Currently, Congress is asking the DOE to transfer the material to the US Army at Redstone Arsenal.

“This preliminary assessment indicated that, should a private Thorium reactor developer express any interest in retaining the U-233 inventory for up to 5 years, it could cost up to $500 million.”

The budget to downblend the U-233 is more than $500 million. Transferring U-233 to the Army is a cheaper option.

“This cost estimate was a preliminary rough order of magnitude because no thorium reactor developer has approach DOE with a specific plan or proposal on how to manage the inventory of U-233.”

DOE has U-233 on a disposal list. DOE-NE will not pull it off that list. Only Congress can do that and that is why the Congress is asking for the truth about U-233 however this report is full of inaccuracies.

“The development of new regulatory information and licensing changes required for any thorium-fueled reactor deployment will be very resource- and time-consuming.”

This is true of almost all advanced reactor designs, yet NRC has an order to modernize it’s licensing requirements and make them technology agnostic. The directive to adapt current regulations to allow for advanced designs did not exclude thorium.

“Fuel and reactor vendors may have many hurdles to overcome to obtain the experimental data needed to be able to have their specific designs licensed by the NRC.”

Molten-salt fuel does not need to be qualified like a solid fuel would. Additionally, this argument applies to most advanced designs.

“The NRC will need fundamental irradiation experimental data, post-irradiation examination information, and transient fuel performance experience to be able to license and regulate specific thorium fuel and reactor designs.”

This might be the case for solid thorium dioxide fuels, but not thorium MSRs. As a fundamentally different fuel cycle many of these requirements apply differently.

“The most likely near-term application of thorium is in currently operating U.S. LWRs or in Generation IV LWRs, where fuel designs would : (a) use homogeneously mixed thorium with uranium (UO2 + ThO2) fuel pins, (b) add separate fertile thorium (ThO2) fuel pins to LWR UO2 fuel assemblies, or (c) use mixed plutonium and thorium (PuO2 + ThO2) fuel pins in LWR UO2 fuel assemblies.”

No, none of these applications will be near-term because thorium offers no advantages over uranium in existing light-water reactors. Thorium’s advantages are manifested in properly-designed MSRs.

page 44

“Those phenomena associated with thorium fuel that are different when compared to typical UO2 fuel include melting temperature, fission gas release, decay heat, and safety performance parameters (e.g., reactivity coefficients).”

The report needs to distinguish between thorium MSRs and LWRs, this applies to LWRs.

page 45

“The NRC’s regulatory and evaluation processes would likely need to be developed specifically for each type of thorium-fueled reactor concept, for the thorium infrastructure changes, shipping, fuel fabrication, in-reactor fuel performance and safety analyses issues, spent fuel handling and storage.”

Yes, and the simplicity and safety of the thorium MSR make this task much more straightforward.

“Irradiation of prototypical thorium fuel in the INL ATR and testing in the INL Transient Reactor Test Facility (TREAT) may be needed to determine thorium fuel performance.”

This does not apply to thorium molten salts.

“Because of a lack of experiential knowledge of using thorium in modern LWRs, the uncertainties would be greater than for LWRs using UO2-only fuels. Thorium-bearing LWR fuel may have larger uncertainties that would impact operating margins in the reactor, especially in terms of technical specification limits. The fuel vendors and licensees would need to address these uncertainties with experiments, computer code validations, etc., to reduce uncertainties and answer NRC questions.”

Congress specifically asked the report to address thorium MSRs not thorium LWRs. I agree that thorium LWRs are a bad idea. However, thorium MSRs are a great idea.

“The radiological dose associated with radionuclide releases (i.e., source terms) during severe accidents depends on the ability of fuel to retain fission product gases.”

Molten salt reactors constantly handle their fission product gas inventory and there is no gas inventory to inadvertently release during severe accidents, which in molten-salt reactors are still simple to accommodate due to the liquid fuel form.

page 46

“Peak power locations, power peaking in radial blanket regions, local inside pin power distributions, pellet rim effects with the increase of fissile isotopes in thorium fuel will differ from uranium fuel and depend on the entire core design.”

Molten salt reactors constantly homogenize their fuel and blankets and this simplifies core analysis and modeling by orders-of-magnitude relative to solid fuels. The reactor does not include pellets or pins, or cladding to undergo edge effects or damage, just a fluid pumped through the reactor and assuming a uniform composition on every pass. This argument alone should  sufficiently compel the DOE-NE to want to develop molten-salt reactors.

“The buildup of U-233 in fertile and fissile fuel assemblies/pins, size of the blanket region, and changes in fissile core content may alter the stability of the core and induce power oscillations during particular anticipated operational transients or accident conditions.”

A thorium MSR design addresses all of these concerns via the chemical processing system, yet another reason to pursue thorium MSRs rather than thorium LWRs, and why Congress asked about thorium MSRs.

“The addition of thorium to the core may also impact characteristics after the reactor is shut down. The U-233 produced from the decay of Pa-233 (half-life of 27 days) could impact refueling operations and intermediate spent fuel pool storage.”

Another solid-fueled problem. One of many.

page 47

“Specialized computer simulation codes that can model the complex fuel flowing in salt coolant MSRs or DMSRs and that can predict the isotopic concentrations, fuel movement, burnup, and conversion of the fissile and fertile fuel over the reactor lifetime may need to be developed by reactor vendors and require actual experimental data to benchmark their models.”

I agree and encourage DOE to assist in this effort with their funding from Congress to develop alternative fuels.

“Removal of fission product species in the online chemical cleanup systems will need to be modelled as well. Novel computer simulation models will be required for operational conditions and accident analyses.”

DOE can help with these efforts rather than encouraging sodium fast reactor or gas cooled reactors.

“In order to use thorium in LWRs, the uranium fuel must be more highly enriched than in a conventional UOX fuel fueled, e.g., 10 percent–20 percent U-235 instead of up to 5 percent in a PWR with standard uranium fuel because of the neutron-absorbing characteristics of thorium.

Yes, using thorium in a non-breeding LWR does not work because thorium just displaces uranium-238 and requires higher enrichments for the remaining uranium. Thorium LWRs do not make sense to pursue.

“These changes would require major modifications to the existing fresh fuel infrastructure (e.g., fabrication, shipping casks, etc.) to address the higher enrichments and the related criticality issues, in addition to any licensing issues associated directly with the use of thorium.”

This is correct and it is a problem that DOE needs to address because 9 of the 10 ARDP winners use HALEU fuel. Outside of Centrus Energy’s HALEU demo cascade, which is not yet up and running, and will only produce non-commercially significant amounts of HALEU, no HALEU enrichment exists outside Russia. Furthermore, there is no deconversion of HALEU enrichments, no metallization of HALEU, and no licensed transport containers. These major modification are required for many advanced reactor designs.

page 48

“MSRs were originally developed as thermal spectrum breeder reactors with recycling and the denatured MSR (DMSR) concept was developed as an alternative to reduce proliferation risk by eliminating online chemical processing and to operate the DMSR as a once-through thorium/uranium system.”

The decision to denature thorium MSRs does not reduce proliferation risk but only degrades the ability of the MSR to use thorium efficiently.

page 49

“As a fertile material, thorium generally requires recycling to increase its fuel utilization and to recover U-233.”

Yes, and the marvelous thing about a thorium MSR is that the required chemical processing can be done in the blanket fluid, in the chemical state in which it operates, without alteration. This is a superlative advantage over every other thorium-based reactor concept.

“Reactor systems supporting thorium fuel cycles can operate as converters or breeders. Converters require additional fissile material to operate (e.g., U or Pu), but breeders would eventually be self-sufficient on thorium and U-233 alone.”

Yes, and breeders are the whole point.

“If the recycling method separates thorium from uranium in a THOREX process, then this separated uranium typically has a high U-233 fissile content and therefore represents a proliferation risk[.]”

A thorium MSR does not use THOREX and I addressed the lack of a U-233 content proliferation risk above.

“however, the production of U-232 along with U-233 provides some proliferation protection[.]”

This is correct that U-232 acts as a deterrent against fissile theft.

“Should thorium recovery and U-233 recycling be considered, then new NRC regulations, guidance, and proliferation resistance safeguard standards would have to be developed not only for the recycling process, but also for the U-233 bearing fuel fabrication, shipping, handling, and in-reactor safety issues.”

Ideally this statement would have been followed by page after page of detailed description of how such a system might operate. Arguably this is exactly what Congress asked for when they requested this report.

page 52

“Currently the domestically produced supply of actinium-255 and bismuth-233 is limited by the availability of the parent radionuclide, Th-229, which is derived from U-233 produced in nuclear reactors by irradiating natural Th-232. Appendix A Figure A-3 shows how actinium-255 and bismuth-233 can be produced from irradiating thorium and producing U-233, and through the radioactive decay chain.”

It is bismuth-213 not bismuth-233. Altogether, this section skips very briefly over an exceptionally compelling topic. Thorium reactors produce U-233, and tiny bit of this decays into the precursors for cancer-fighting drugs. This reason alone more than justifies a thorium reactor program.

page 53

On this page, instead of describing obscure radionuclide dating methods using thorium, a discussion of the LFTR design would have served to answer Congress’s request.

The report goes on to describe how thorium-229 can help make super-accurate atomic clocks. This same Th-229 comes from the decay of U-233, the same U-233 the DOE is currently downblending and destroying.

page 54

Yes, I agree, thorium is an easily-obtained byproduct of rare-earth mining.

page 55

“Monazite is a good source of REEs but extracting REEs from monazites is not economical mainly because the radioactive byproduct thorium would have to be stored indefinitely.”

The earth holds an abundant amount of thorium and the thorium could be diluted and filled into the mines. Additionally, thorium MSRs will utilize the thorium to provide abundant, carbon-free energy.

page 58

“Clean non-nuclear energy technologies require REEs for their deployment.”

And clean, nuclear energy technology requires thorium.

page 59

“If ever needed in the distant future, direct dedicated thorium mining is generally easier than mining uranium.”

That is true, but the U.S. will never need to directly mine thorium. The rare-earth mines required for non-nuclear energy will supply all the thorium-bearing ore needed.

“The overall abundance of thorium is not an issue for any short to medium term deployment of thorium-fueled nuclear power plants. If thorium-based fuel cycles were to be pursued worldwide, the quantities of thorium available as a by-product of the extraction of other minerals (rare earths, titanium, phosphates) would be able to provide enough quantities of thorium for its use in the nuclear industry for this purpose.”

Agreed. This fact strongly encourages adoption of thorium MSRs.

“The extraction of REEs from existing phosphate monazite mining mill tailings would be better facilitated by the removal of thorium to reduce radioactivity levels during the REE recovery process. The thorium extracted could be safely and separately stored for fueling future nuclear reactors and for use in non-nuclear applications, such as high-temperature ceramics, melting tanks, catalysts, welding electrodes and metal alloys.”

Exactly. The United States should do this.

“The only near-term economic benefit of considering future thorium fuel utilization may be that by removing and storing the naturally radioactive thorium that contaminates monazite wastes, valuable REEs can be safely extracted.”

I can think of far more near-term benefits to considering future thorium utilization than that.

“REEs refined from mining waste streams would meet the industrial demands for essential rare earth materials in strategic industries, including advanced technologies, carbon-free energy production, transportation, manufacturing, and defense and security needs. But REEs and thorium are linked at the mineralogical, regulatory, and geopolitical level.”

This provides reason enough to pursue a thorium reactor development effort.

“U.S. NRC and international safety regulations pertaining to the radioactivity of natural thorium have contributed to market distortions related to REEs. The proliferation of regulations reflecting international standards regarding the definition of nuclear “Source Material” eliminated these high value REEs from the value chain for most of the world.”

Yes and this has had terrible consequences for the U.S. and has not enhanced global security. It has only moved rare-earth supply chains to China where they have proceeded without environmental considerations and have poisoned thousands of people.

pages 60 through 64

These appear to be taken directly from promotional literature from John Kutsch.

page 64

“It should be noted that while DOE monitors thorium-fueled reactor research, development, and deployments internationally, NE is not currently working with any other nations to develop TMSR programs.”

Indeed, DOE-NE should work with the prime domestic developer of thorium MSR: Flibe Energy. Flibe Energy would have made a valuable partner on this report given Congress’ instructions to engage with technology developers and consider domestic development of thorium MSRs.

page 65

“The U.S. does not have any existing thorium fuel cycle infrastructure.”

The US can make thorium tetrafluoride and that is all that a thorium MSR needs.

“Scientists have suggested that it would take at least 5 years and $25 billion to design and deploy a viable thorium demonstration reactor.”

Flibe Energy spent months on a development plan that was submitted to the DOE-NE under the Advanced Reactor Development Program. This plan and its development and cost estimates are not mentioned although they are far lower than $25 billion.

“Building a U.S. thorium fuel cycle infrastructure to support thorium fueled reactors would be very expensive and would take many years to license and deploy.”

Untrue and unsupported, and at any rate, not a determination for the DOE-NE to make. However, the more industry struggles to address the HALEU challenge, the more the following statement rings true. “Building a U.S. HALEU fuel cycle infrastructure to support HALEU fueled reactors would be very expensive and would take many years to license and deploy.”

“The economic benefit for nuclear fuel vendors and utilities to potentially use thorium fuel in future yet-to-be-licensed reactor designs is a significant impediment when uranium fuel is relatively inexpensive, has been licensed for years, and more advanced accident tolerant uranium fuel designs are becoming available soon.”

DOE-NE has built the nation’s entire future nuclear technology portfolio around HALEU, a material only available from Russia, and is now going to the Congress, hat-in-hand, to demand $4B for HALEU enrichment infrastructure for use in yet-to-be licensed reactor designs.

“Thorium fuel utilization poses some significant challenges. Currently no thorium infrastructure exists in the U.S.”

This point lacks support. Repetition does not make it more true. Furthermore, the lack of HALEU infrastructure in the U.S. did not prevent the DOE-NE from building their entire ARDP plan around HALEU.

“Building a new thorium infrastructure that includes thorium fuel fabrication, fuel shipments, reactor licensing especially for mixed uranium and thorium and Th/U/Pu core designs, spent fuel recycling and processing in heavily shielded hot cells, spent fuel storage and shipping, etc., may cost much more than just continuing to use uranium-only fuel.”

That statement might be true if one considered only solid thorium-dioxide fueled light-water reactors, but it is definitely not true when considering thorium MSRs.

“If irradiated thorium fuel is reprocessed to recover fissile U-233 for subsequent Th/U-233 reactor fuel loadings, then THOREX processing could be used.”

Molten-salt reactors do not require THOREX processing.

“DOE does not advocate any fuel reprocessing at this time.”

The DOE needs to more specifically define reprocessing to exclude chemical treatment of fuel actively circulating in a reactor.

“However, if fuel reprocessing were to be considered, the THOREX process used to remove thorium from spent fuel is more complicated than using either the UREX process used to recover U-235 or the PUREX process used to recover U-235 and Pu isotopes together for MOX fuel fabrication.”

I agree, and THOREX is not required, because molten salt processing is so much easier.

“Irradiating thorium fuel produces fissile U-233 which presents a significant proliferation problem.”

The existence of U-233 will not cause the United States to decide to proliferate nuclear weapons to other countries. The United States does not currently proliferate U-233 to other countries based on the few hundred kilograms we currently possess. Additionally, the U.S. also has vast amounts of surplus plutonium and we do not proliferate that material to other countries despite the fact it would be far more straightforward to fabricate weapons of known designs from plutonium.

“Although thorium can be “denatured” by adding depleted or natural uranium, irradiation of thorium isotopes produces three protactinium isotopes Pa-231, Pa-232, and Pa-233, that eventually decay into pure U-233.”

Only Pa-233 decays into U-233. Pa-232 decays into U-232, and Pa-231 decays very slowly into Ac-227.

“Protactinium isotopes can be easily chemically separated from irradiated thorium fuel. Pa-233 with its 27 day half-life decays into pure U-233, so isolating Pa-233 produced during thorium irradiation may pose a serious proliferation issue.”

I addressed this assertion above.

“Significant gamma shielding and remote handling is required for any irradiated thorium fuel storage and reprocessing.”

Molten salt thorium fuel obviates these concerns.

“Thorium fuel may be useful for future Generation IV reactor designs, including advanced MSRs that would use natural and/or depleted uranium with its fissile U-235 content to “denature” fertile thorium fuel that would produce fissile U-233 as Th-232 is irradiated over the core lifetime.”

Denatured MSR designs would be far worse than designs that use thorium and U-233 efficiently. They would produce plutonium while changing the chemical separability of protactinium. The efforts that Flibe Energy and ORNL have undertaken address concerns around fissile security and provide concrete solutions.

page 66

“U.S. thorium demand for nuclear and non-nuclear applications may be aided by removing thorium during REEs extraction from monazite mining wastes.”

Yes, please do that.

References:

ORNL-TM-2022-2394, Safeguards for the Lithium Fluoride Thorium Reactor: A Preliminary Nuclear Material Control and Accounting Assessment, Richard L. Reed, Louise G. Evans, Donald N. Kovacic, August 2022.

Technical Report 3002005460, Program on Technology Innovation: Technology Assessment of a Molten Salt Reactor Design, Electric Power Research Institute, October 2015.