A Tale of Two (or More) Nuclides: the Potential for Nuclear Power from Fission Reactors Using Abundant Thorium Physics Colloquium, NMSU, 1 March 2012 Engineering Conference, El Paso Electric Company Thursday, TBA, Spring 2012 By Vince Gutschick Global Change Consulting Consortium Inc. Las Cruces, NM 88011 (575) 571-2269 gcconsortium.com With material taken from diverse sources (attributions and additional detail available; see printed pages of references) Focus on molten salt reactors Primarily, the liquid fluoride thorium reactor (LFTR) The basics of a LFTR: 233U is the fissionable material providing the power This choice of fissionable material has many advantages Alvin Weinberg 233U is bred from abundant and cheap natural thorium, 232Th Using 1 (and a fraction) of the 2.48 neutrons liberated in fission of 233U In a favored and tested design, both the 233U and the Th are dissolved in molten salts, as fluorides. Molten salt is the coolant, fuel repository, and moderator The attraction of LFTRs: 1. For energy policy World Thorium Resources Country Australia India USA Norway Canada South Africa Brazil Other countries World total Reserve Base (tons) 340,000 300,000 300,000 180,000 100,000 39,000 18,000 100,000 1,400,000 +600,000 Lehmi Pass Cost The breedable fuel, Th is: Abundant why? nucleosynthesis Available in many nations; US has vast reserves Burnable to ca. 95%, vs. several % for U Used without costly enrichment The Source: U.S. Geological Survey, Mineralreactor is: Commodity Summaries, January 2008 Smaller/simpler than PBWRs and many Gen IV reactors Safety (clearly a plus for utilities, too) Passively safe: negative reactivity change on overheating Near-zero pressurization of nonreactive, nongaseous coolant Major reduction of life-cycle radioactive hazards Mining effort very low; low radon exposure (1/1200 as much ore) Almost zero transuranics – non-production, high burnup …and more: The attraction of LFTRs: 1. For energy policy - continued Energy security Large reserves in US…and in many nations Non-proliferation No enriched 235U or Pu (233U is hard to weaponize) 233U / Th mix emits hard gammas from 208Tl– can’t carry it away! (though 208Tl can be reduced in concentration in certain reactor designs) Low-carbon energy Only significant CO2 emissions are in reactor construction Neutral feature: Cooling water demand similar to current-generation reactors The attraction of LFTRs: 2. For utilities Known performance & engineering demands ORNL reactor (6 MW) ran 5 years Added design: FLIBE; Japan-Russia-US collaborations; Chinese plans for reactors by 2016) Inherent safety already noted Chemistry & metallurgy of thorium are very well known Coolant easy to handle and safe (very low chemical reactivity) Load following! Negative reactivity change with T jet engines, even 60-second lag time Essentially no xenon reactivity and no transients / oscillations (Chernobyl!) Simple control No xenon oscillations No fuel-rod distortions Geological storage more acceptable: 300 years …and more: The attraction of LFTRs: 2. For utilities - continued Efficient power generation High-T coolant suited to Brayton-cycle gas turbines Construction cost lower No high-pressure coolant lines Simpler containment vessel Waste storage reduced in volume and in time 1/30 of PBWR waste volume Neutral feature: On-site processing of fuel needed(extraction of 233U, 135Xe, perhaps metals) However, it’s simpler than pooled reprocessing of PBWR fuels So, why was it not commercialized? It did not create Pu for nuclear weapons during the Cold War Adm. Rickover needed a nuclear sub reactor ASAP and stuck with it afterward • Nixon administration decided to favor the liquid metal fast breeder reactor over the LFTR as a thermal reactor Legacy of PBWR / vested interests has delayed development Now: one of the Gen IV candidates Along with 2 other thermalized-neutron reactors: Very-high-T reactor, esp. pebble-bed, and supercritical water reactor And 3 fast reactors Gas-, sodium-, or lead-cooled How does a LFTR work?: 1. The physics Natural thorium is basically pure 232Th; long-lived: 13-14 Gy No isotopic enrichment needed, unlike that for U Fission unknown 233U from several other types of breeder reactors, for a start Fissionable; generates the neutrons for power+breeding Yet, very little production of Np, Pu, unlike 235U + 238U fuel 232 Th 1.08 n 233 Th β 233 Pa β 233 U ~0.08 fractional takeoff for next reactor fission n 2.48 n Maintain loss of 0.4 n (to Xe, walls, etc.) Side reactions (not shown, for clarity): Production of 232U by 3 reactions – 0.13% of 233U – makes 208Tl, “safekeeper” Minor production of 234U, which is mostly just accumulates (poorly fissionable) Moderation What does one of these molten salt reactors look like? Interesting fuel / salt composition and properties Salt as coolant, moderator: 7LiF (*) + BeF2 Good liquid temperature range (paratectic) High solubility for nuclides as fluorides Good moderator (low-mass nuclides) Very small neutron absorption cross-section Highly radiation resistant Very minor production of radioactive products (small amt. tritium) Excellent heat capacity and heat transfer capacity Low corrosiveness for metal piping (misinformation persists) High thermal expansion coefficient negative reactivity Retains metallic fission products Gaseous fission products can be sparged from it for removal Low chemical toxicity (even with Be) and chemical reactivity 48% thorium / 1% U by mass, 15% / 0.3% by mole fraction Ratio compensates for the 50-fold higher n cross-section of Th How does a LFTR work?: 2. Engineering Fuel loads: for 150 MWe, 13.5 tonnes Th, 270 kg 233U (1:48) Thermal output 350 MW Salt volume for same: 13.5 cubic meters Core diameter 2 m Flow speed 0.15 m/s Outlet T ≈ 700 °C ≈ 970 K ; T rise through reaction zone = 135 K; Brayton-cycle theoretical η ≈ (970-400)/970 = 69% (real: 55%) Modified Hastelloy piping Reprocessing loops for 135Xe removal and 233U recovery On-site storage of 135Cs, 3H, and 233U the hot one Design decision: remove 234Pa? t1/2 = 32,760 y Drain tanks for meltdowns / shutdowns How does a LFTR work?: 3. Economics Construction cost: projected at ½ that for PBWR coal! Can it run in a mode to cover base load and variable load, economically? It can follow the load, but… What is the amortization of fixed costs in mixed mode? How does it compare to standard base-load + peaking combos? Mixed optimization (D. Leblanc, 2010): Power production: net cost Burnup of transuranics, esp. from PBWR and other U reactors Overall safety Proliferation resistance Resource utilization Ecological economics: net carbon balance (capital construction) Challenges Permitting – less challenging than for other Gen IV Commercialization – market penetration time Avoiding the mistakes of Gen I’s diverse designs Engineering On-site reprocessing (has been done on smaller scales) Scaling up the core Alloys for corrosion resistance (probably solved; perception must be corrected) Gamma shielding Decay heat handling by passive cooling on “meltdown” Safe storage of 233U, 135Cs, 3H, 85Kr Preventing loss of the fuels Plan to dispose of the Th stocks! (& short stock of 233U in US?) Plan to blend down 233U into other enriched U stocks! Developing the technology before we have to buy it back from China Selling it globally – need many (too) years of operational experience here? The end…of the talk. A restart for LFTRs References available See also energyfromthorium.com sites.google.com/site/ rethinkingnuclearpower/aimhigh www.thoriumenergyalliance.com/ 6 kg of thorium metal Energy for 3 MWe days The United States has buried 3200 metric tonnes of thorium nitrate in the Nevada desert. There are 160,000 tonnes of economically extractable thorium in the US, even at today’s “worthless” prices!