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Lessons for the Liquid-Fluoride Thorium Reactor (from history)

Lessons for the Liquid-Fluoride Thorium Reactor (from history). Kirk Sorensen July 20, 2009 Mountain View, California. Executive Summary. Energy Generation Comparison. 230 train cars (25,000 MT) of bituminous coal or, 600 train cars (66,000 MT) of brown coal,

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Lessons for the Liquid-Fluoride Thorium Reactor (from history)

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  1. Lessons for the Liquid-Fluoride Thorium Reactor(from history) Kirk Sorensen July 20, 2009 Mountain View, California

  2. Executive Summary

  3. Energy Generation Comparison 230 train cars (25,000 MT) of bituminous coal or, 600 train cars (66,000 MT) of brown coal, (Source: World Coal Institute) = or, 440 million cubic feet of natural gas (15% of a 125,000 cubic meter LNG tanker), 6 kg of thorium metal in a liquid-fluoride reactor has the energy equivalent (66,000 MW*hr electrical*) of: *Each ounce of thorium can therefore produce $14,000-24,000 of electricity (at $0.04-0.07/kW*hr) or, 300 kg of enriched (3%) uranium in a pressurized water reactor.

  4. 2007 World Energy Consumption The Future: Energy from Thorium 5.3 billion tonnes of coal (128 quads) 31.1 billion barrels of oil (180 quads) 2.92 trillion m3 of natural gas (105 quads) 6600 tonnes of thorium (500 quads) 65,000 tonnes of uranium ore (24 quads)

  5. Today’s Uranium Fuel Cycle vs. Thoriummission: make 1000 MW of electricity for one year 35 t of enriched uranium (1.15 t U-235) Uranium-235 content is “burned” out of the fuel; some plutonium is formed and burned • 35 t of spent fuel stored on-site until disposal at Yucca Mountain. It contains: • 33.4 t uranium-238 • 0.3 t uranium-235 • 0.3 t plutonium • 1.0 t fission products. 250 t of natural uranium containing 1.75 t U-235 215 t of depleted uranium containing 0.6 t U-235—disposal plans uncertain. Within 10 years, 83% of fission products are stable and can be partitioned and sold. One tonne of natural thorium One tonne of fission products; no uranium, plutonium, or other actinides. Thorium introduced into blanket of fluoride reactor; completely converted to uranium-233 and “burned”. The remaining 17% fission products go to geologic isolation for ~300 years.

  6. How it all began…

  7. Thorium was discovered in 1828 by the Swedish scientist Jons Jacob Berzelius. Berzelius named thorium after Thor, the Norse god of thunder. There was little to say about thorium when it was first discovered apart from its specific weight and its high-temperature capabilities. “thallium, thorium, thulium…” The Discovery of Thorium

  8. In 1898, Marie Curie made a remarkable discovery: Thorium and uranium were radioactive! But with a 15 billion-year half-life (older than the universe), it didn’t decay very often and had very low radioactivity… Eventually thorium decays to lead-208. Thorium is Radioactive

  9. Natural Decay Chains • There are four natural decay chains, three of which still exist on Earth. The fourth is extinct due to rapid decay. “Uranium” (4n+2) Lead 206 Pb,Bi,Po 210 Pb,Bi,Po 214 Polonium 218 Radon 222 Radium 226 Thorium 230 Th,Pa,U 234 Uranium 238 21 yr 26 min 3 min 3.8 day 1600 yr 80000 yr 247 kyr 4.5 Gyr “Actinium” (4n+3) Tl,Pb 207 Pb,Bi 211 Polonium 215 Radon 219 Fr,Ra 223 Ac,Th 227 Th,Pa 231 Uranium 235 36 min 0.0018 sec 4 sec 11 days 21 yr 32500 yr 700 Myr “Thorium” (4n) Tl,Pb 208 Pb,Bi,Po 212 Polonium 216 Radon 220 Radium 224 Ra,Ac,Th 228 Thorium 232 10 hr 0.15 sec 55 sec 3.64 day 6.7 yr 14.1 Gyr “Neptunium” (4n+1) Tl,Pb,Bi 209 Bi,Po 213 Astatine 217 Francium 221 Ra,Ac 225 Thorium 229 Pa,U 233 Neptunium 237 162 kyr 2.14 Myr 47 min 0.032 sec 10 days 7340 yr 5 min 207 208 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 229 230 231 232 233 234 235 236 237 238 206 209 228

  10. Three Conceptual Breakthroughs Nuclear Fission (1939)—Otto Hahn and Lise Meitner discover that neutrons cause uranium atoms to split, releasing energy. The true nature of the nucleus (1935)—Hideki Yukawa hypothesizes that the nucleus consists protons and neutrons bound together by a “nuclear force” that overcomes the inherent repulsion of the protons to one another. Radioactivity (1896)—Henri Becquerel discovered that some elements (uranium and thorium) emit particles spontaneously.

  11. Lesson for LFTR:Once you’ve figured out how matter really works, you realize that if you’re looking for a dense source of energy, nuclear fission is your answer.

  12. Three basic options for fission The fission of U-235 was discovered by Otto Hahn and Lise Meitner in 1938. Uranium-235 (0.7% of all U) Pu-239 as a fissile fuel was discovered by Glenn Seaborg in March 1941. Uranium-238 (99.3% of all U) Plutonium-239 U-233 as a fissile fuel was discovered by Seaborg’s student John Gofman in February 1942. Thorium-232 (100% of all Th) Uranium-233

  13. Could weapons be made from the fissile material? Uranium-235 (“highly enriched uranium”) Natural uranium Isotope separation plant (Y-12) Hiroshima, 8/6/1945 Depleted uranium Isotope Production Reactor (Hanford) Pu separation from exposed U (PUREX) Trinity, 7/16/1945 Nagasaki, 8/9/1945 PROBLEM: U-233 is contaminated with U-232, whose decay chain emits HARD gamma rays that make fabrication, utilization and deployment of weapons VERY difficult and impractical relative to other options. Thorium was not pursued. Isotope Production Reactor uranium separation from exposed thorium Thorium?

  14. U-232 decays into Tl-208, a HARD gamma emitter Thallium-208 emits “hard” 2.6 MeV gamma-rays as part of its nuclear decay. These gamma rays destroy the electonics and explosives that control detonation. They require thick lead shielding and have a distinctive and easily detectable signature. 232U 14 billion years to make this jump Some 232U starts decaying immediately 1.91 yr 1.91 yr 1.91 yr 3.64 d 3.64 d 3.64 d Uranium-232 follows the same decay chain as thorium-232, but it follows it millions of times faster! This is because 232Th has a 14 billion-year half-life, but 232U has only an 74 year half-life! Once it starts down “the hill” it gets to thallium-208 (the gamma emitter) in just a few weeks! 55 sec 55 sec 0.16 sec

  15. U-232 Formation in the Thorium Fuel Cycle

  16. Lesson for LFTR:Thorium’s no good for nuclear weapons.Of course, if it’s wartime, this fact isn’t going to help you get developed.

  17. The “chain-reaction”

  18. Nuclear Criticality: A Condition of Balance 10,000 fissions lead to 9999 fissions… the reactor is subcritical and the fission rate will decrease. 10,000 fissions lead to 10,000 fissions… the reactor is critical and the fission rate will stay the same. 10,000 fissions lead to 10,001 fissions… the reactor is supercritical and the fission rate will increase.

  19. Self-controlling Fission Reactors are Possible Analogy: mass-spring system Implementation: fission reactor • It was clear that achieving perfect criticality (multiplication factor of 1.00000000000000000) was impossible by any active control • But natural effects could be used to “tune in” the reactor to perfect criticality • Expansion of water (reduced moderation) • Expansion of fuel (reduced fuel) • Increased neutron absorption in fuel (Doppler coefficient) • This is the principle of the “temperature coefficient of reactivity”, which needs to be prompt, negative and strong The rate of fission governs the amount of heat added to the water…but the density of the returning water governs the fission rate (through moderation) Gravity pulls downward on the mass...but the spring’s force is proportional to its extension.

  20. 1942: The First Nuclear Reactor – CP1

  21. Lesson for LFTR:You want a reactor with a negative, prompt, and strong temperature coefficient of reactivity.

  22. Enrico Fermi argued for a program of fast-breeder reactors using uranium-238 as the fertile material and plutonium-239 as the fissile material. His argument was based on the breeding ratio of Pu-239 at fast neutron energies. Argonne National Lab followed Fermi’s path and built the EBR-1 and EBR-2. Eugene Wigner argued for a thermal-breeder program using thorium as the fertile material and U-233 as the fissile material. Although large breeding gains were not possible, THERMAL breeding was possible, with enhanced safety. Wigner’s protégé, Alvin Weinberg, followed Wigner’s path at the Oak Ridge National Lab. 1944: A tale of two isotopes…

  23. Fission/Absorption Cross Sections

  24. Lesson for LFTR:Only thorium can be fully consumed in a thermal spectrum reactor.To fully consume uranium you MUST have a fast spectrum reactor.

  25. Protactinium-233 Thorium-233 decays quickly to protactinium-233 Protactinium-233 decays slowly over a month to uranium-233, an ideal fuel Uranium-233 Thorium-233 Uranium-233 fissions, releasing energy and neutrons to continue the process Natural thorium absorbs a neutron from fission and becomes Th-233 Thorium-232

  26. 1944: A tale of two isotopes… “But Eugene, how will you reprocess the fuel fast enough to prevent neutron losses to protactinium-233?” “We’ll build a fluid-fueled reactor, that’s how…”

  27. Th-232 in FertileTh-232 blanket Chemical separator FissileU-233 core Chemical separator n n New U-233 fuel Fission products out Heat

  28. Lesson for LFTR:In fluid form, many of the drawbacks of thorium can be overcome.In fluid form, the xenon-135 can be removed continuously.

  29. 1951: Experimental Breeder Reactor 1 In 1951, Fermi’s protégé Walter Zinn and his Argonne team successfully operated the first liquid-metal-cooled fast spectrum breeder reactor at a site in Idaho. The reactor produced enough power to light a few light-bulbs, but was heralded as the first power-producing reactor in the world.

  30. 1952: Homogeneous Reactor Experiment - 1 In 1952, Weinberg’s ORNL team duplicated this accomplishment by building the first aqueous homogenous reactor (HRE-1), which produced about 100 kWe of electrical power. The HRE was not a thorium breeder (yet) but was intended to prove the technology for one.

  31. 1958: Homogeneous Reactor Experiment - 2 HRE-2 was built to a thermal power of 5 megawatts and further developed AHR technology.

  32. ORNL Fluid-Fueled Thorium Reactor Progress (1947-1960) 1947 – Eugene Wigner proposes a fluid-fueled thorium reactor 1950 – Alvin Weinberg becomes ORNL director 1952 – Homogeneous Reactor Experiment (HRE-1) built and operated successfully (100 kWe, 550K) 1959 – AEC convenes “Fluid Fuels Task Force” to choose between aqueous homogeneous reactor, liquid fluoride, and liquid-metal-fueled reactor. Fluoride reactor is chosen and AHR is cancelled. Weinberg attempts to keep both aqueous and fluoride reactor efforts going in parallel but ultimately decides to pursue fluoride reactor. 1958 – Homogeneous Reactor Experiment-2 proposed with 5 MW of power

  33. Aircraft Nuclear Program Between 1946 and 1961, the USAF sought to develop a long-range bomber based on nuclear power. The Aircraft Nuclear Program had unique requirements, some very similar to a space reactor. • High temperature operation (>1500° F) • Critical for turbojet efficiency • 3X higher than sub reactors • Lightweight design • Compact core for minimal shielding • Low-pressure operation • Ease of operability • Inherent safety and control • Easily removeable

  34. Aircraft Nuclear Program allowed ORNL to develop reactors It wasn’t that I had suddenly become converted to a belief in nuclear airplanes. It was rather that this was the only avenue open to ORNL for continuing in reactor development. That the purpose was unattainable, if not foolish, was not so important: A high-temperature reactor could be useful for other purposes even if it never propelled an airplane… —Alvin Weinberg

  35. Radiation Damage Limits Energy Release • Does a typical nuclear reactor extract that much energy from its nuclear fuel? • No, the “burnup” of the fuel is limited by damage to the fuel itself. • Typically, the reactor will only be able to extract a portion of the energy from the fuel before radiation damage to the fuel itself becomes too extreme. • Radiation damage is caused by: • Noble gas (krypton, xenon) buildup • Disturbance to the fuel lattice caused by fission fragments and neutron flux • As the fuel swells and distorts, it can cause the cladding around the fuel to rupture and release fission products into the coolant.

  36. Ionically-bonded fluids are impervious to radiation • The basic problem in nuclear fuel is that it is covalently bonded and in a solid form. • If the fuel were a fluid salt, its ionic bonds would be impervious to radiation damage and the fluid form would allow easy extraction of fission product gases, thus permitting unlimited burnup.

  37. The Birth of the Liquid-Fluoride Reactor The liquid-fluoride nuclear reactor was invented by Ed Bettis and Ray Briant of ORNL in 1950 to meet the unique needs of the Aircraft Nuclear Program. Fluorides of the alkali metals were used as the solvent into which fluorides of uranium and thorium were dissolved. In liquid form, the salt had some extraordinary properties! • Very high negative reactivity coefficient • Hot salt expands and becomes less critical • Reactor power would follow the load (the aircraft engine) without the use of control rods! • Salts were stable at high temperature • Electronegative fluorine and electropositive alkali metals formed salts that were exceptionally stable • Low vapor pressure at high temperature • Salts were resistant to radiolytic decomposition • Did not corrode or oxidize reactor structures • Salts were easy to pump, cool, and process • Chemical reprocessing was much easier in fluid form • Poison buildup reduced; breeding enhanced • “A pot, a pipe, and a pump…”

  38. The Aircraft Reactor Experiment (ARE) In order to test the liquid-fluoride reactor concept, a solid-core, sodium-cooled reactor was hastily converted into a proof-of-concept liquid-fluoride reactor. The Aircraft Reactor Experiment ran for 100 hours at the highest temperatures ever achieved by a nuclear reactor (1150 K). • Operated from 11/03/54 to 11/12/54 • Liquid-fluoride salt circulated through beryllium reflector in Inconel tubes • 235UF4 dissolved in NaF-ZrF4 • Produced 2.5 MW of thermal power • Gaseous fission products were removed naturally through pumping action • Very stable operation due to high negative reactivity coefficient • Demonstrated load-following operation without control rods

  39. The “Fireball” The “Fireball”, or Aircraft Reactor Test, was the culmination of the ANP effort at ORNL. • 235UF4 dissolved in NaF-ZrF4 • Designed to produce 60 MW of thermal power • Core power density was 1.3 MW/L • NaK used to transport heat to jet engines at 1150 K • 1500 hours (63 days) design life • 500 hours (21 days) at max power • The “Fireball” pressure shell was only 1.4 meters in diameter! • Contained core, reflector, and primary heat exchanger inside The “Fireball” was considered the superior design for the ANP, but the program was cancelled in 1961 before it was built.

  40. Lesson for LFTR:Sometimes the right answer comes from an unexpected direction.Fluoride fuel is the only practical way to build a high-temperature, high-power-density reactor.

  41. Weinberg wanted a civilian fluoride reactor program “Until then I had never quite appreciated the full significance of the breeder. But now I became obsessed with the idea that humankind’s whole future depended on the breeder.” —Alvin Weinberg

  42. MSBR’58 Reactor Plant Isometric Image source: ORNL-2634: MSRP Status Report, pg 3

  43. Fluorination made separating UF4 and ThF4 easy • Fluorination was a basic chemical advantage of the fluoride-fueled approach • UF4 (in solution) + F2 → UF6 (gaseous) • Bred uranium-233 could be easily removed from a thorium fluoride mixture using this approach.

  44. Lesson for LFTR:Nature is sometimes kind.The ability to separate uranium from thorium under high radiation and at high temperatures argues strongly for a fluoride fueled reactor.

  45. A chance meeting leads to the MSRE By the end of 1959, our engineering development program had proceeded far enough that we felt justified in proposing an MSR experiment (MSRE), but getting money and permission appeared difficult. Then one day I heard a rumor that Frank Pittman, who had succeeded Ken Davis as director of the DRD, had expressed interest in funding as many as four “quick and dirty” reactor experiments provided that each one should cost less than a million dollars. As I remember it, I wrote a proposal that night and submitted it through channels the next day. I outlined the general features of the reactor, and by analogy with another reactor system for which a cost estimate had been made. I came up with a cost estimate of $4.18 million. The proposal was accepted, although by the time the design had been detailed the cost estimate had doubled. —H.G. “Mac” MacPherson from “The Molten-Salt Adventure”

  46. Conceptual Framework of the Molten-Salt Reactor Experiment The conceptual design of the MSRE was arrived at as follows. To keep the reactor simple we intended to simulate only the fuel stream of a two-fluid breeder reactor, so that no thorium fluoride was included. We wanted the neutron spectrum to be near thermal, as it would be in a commercial reactor, and since graphite was the moderator, this dictated the minimum physical size. The moderator was in the form of a 1.37-m-diam x 1.62-m-high right circular cylinder. Had it been smaller, the neutron leakage would have caused the neutron spectrum to be more energetic than we wished. We would have liked to have a higher power density, but cost considerations limited us to ~10 MW of heat. There was also another reason for limiting the power of the reactor. The AEC accounting rules at the time allowed us to build a 10-MW reactor as an experiment, using operating funds. A higher power reactor would have required us to obtain a capital appropriation and would have limited our freedom to make changes. Actually we miscalculated the heat transfer characteristics and the reactor operated at only 8 MW. —H.G. “Mac” MacPherson from “The Molten-Salt Adventure”

  47. Molten Salt Reactor Experiment (1965-1969)

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