liquid fluoride thorium reactors

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
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:
is the fissionable material providing the power
 This choice of fissionable material has many advantages
 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
South Africa
Other countries
World total
Reserve Base
+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
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
233 Pa
233 U
~0.08 fractional
takeoff for
next reactor
 fission
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)
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,
 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)
 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
 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
6 kg of thorium metal
Energy for 3 MWe days
The United States has buried 3200 metric
tonnes of thorium nitrate in the Nevada
There are 160,000 tonnes of economically
extractable thorium in the US, even at
today’s “worthless” prices!

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