liquid fluoride thorium reactors
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Transcript 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
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!