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Thorium and MSR Fuel Strategies
Kirk Sorensen, Flibe Energy
Oak Ridge National LaboratoryOctober 5, 2016
The production of long-lived nuclear waste has been a potent focus ofopposition to nuclear power for many years.
Because of the failure of the US government to take custody of spentnuclear fuel, it remains at the same site at which it was produced.
This was once the site of the Connecticut Yankee reactor. Even after anuclear power plant site has been decommissioned, the "orphaned"
spent nuclear fuel remains on site in casks.
These spent fuel casks cannot legally be moved from thedecommissioned reactor site and prevent its release for unlimited use.
They also require continuous security.
For millions of people each year, receiving a diagnosis of cancer is aterrifying moment that leads to profound uncertainty.
Targeted therapies look very promising against cancer, especially againstdispersed cancers like leukemia and lymphoma. They seek out cancer cells,destroying them with chemicals or radiation while leaving healthy cells alone.
Targeted Alpha Therapy using Bismuth-213
Bismuth-213 has a 45-minute half-life (perfect) and decays fromactinium-225, which has a 10-day half-life (perfect). It is near the endof its decay chain, and can be suitably chelated (wrapped in achemical cage) and attached to an antibody that will hunt down andattach to a bloodborne cancer cell. When it decays, the alpha particleit emits will kill the cancer cell.
This is called targeted alpha therapy (TAT).
TAT is a Smart Bomb Against Cancer
ExplosivePayload
PrecisionGuidance &
Delivery System
SpecificTarget
TargetDestruction
213Bi monoclonal antibody cancer cell programmed cell death(apoptosis)
232Th14.1 Gyr
α
7.282b
24.8mb 100.00%
233U159.2 kyr
α
51.31b
530b
91.2%
8.6mb
233Pa27.0d
β−
38.29b
7.2mb
233Th22.3m
β−
1.500kb
15.0
0b
1.0%
Glenn Seaborg first created uranium-233 from thorium in April 1941 andcorrectly predicted that it was the first of a new family of radioactive materials.
Candidate Alpha Emitters on the Decay Chains
Radon
Francium
Radium
Bismuth
Polonium
Astatine
Thallium
Lead
Actinium
Thorium
Protactinium
Uranium 238
234 230
226
222
218
214 210 206
234
234
214
214
210
210
233
229
225
225
221
217
213
209
209
213
209
Thorium (+0) Neptunium (+1)
235
231
231
227
223
215
211
211
207
227
223
219
207
Uranium (+2) Actinium (+3)
232
228
228
228
224
220
216
212
212
212
208
208
232
211
211
207
Actinium-225
Bismuth-213
Astatine-211
Bismuth-212
Bismuth-213 is formed from the decay of Uranium-233
A million grams of uranium-233 will produce about 4 grams ofthorium-229 each year. This thorium-229 will then produce
alpha-emitting medicines (actinium-225 and bismuth-213) forthousands of years.
Possible Nuclear Fuels
Natural Thorium100% thorium-232
Natural Uranium99.3% uranium-2380.7% uranium-235
Only a small fraction of natural uranium is fissile. Most uraniumand all thorium is "fertile" and can be converted to fissilematerial through neutron absorption.
Nuclear Conversion Reactions
Thorium
neutron
Uranium233
neutron
FissionProduct
FissionProduct
9,000 MWh(e)/kg2.3 (net) neutrons
time for
decay
Thorium and uranium-238 both require two neutrons to release their energy:one to convert them to fissile fuel and another to release their energy throughfission. But only thorium produces sufficient neutrons (2.3) in thermalreactors to sustain energy release.
Uranium238
neutron
Plutonium239
neutron
FissionProduct
FissionProduct
9,000 MWh(e)/kg1.9 (net) neutrons
time for
decay
Energy from thorium
232Th14.1 Gyr
α
7.282b
24.8mb 100.00%
233U159.2 kyr
α51.31b
530b
91.2%
8.6mb
233Pa27.0d
β−
38.29b
7.2mb
233Th22.3m
β−
1.500kb
15.0
0b
1.0%
I Abundant, natural thorium is thestarting point in the process
I Thorium absorbs a neutron,forming short-lived thorium-233.
I Thorium-233 quickly decays inprotactinium-233, which ischemically distinct from thorium.
I After a little more than a month,protactinium-233 will decay intouranium-233, which is the bestnuclear fuel.
I The fission of uranium-233releases energy and sufficientneutrons to continue the process.
Nuclear Conversion Reactions
Uranium238
neutron
Plutonium239
fast neutron
FissionProduct
FissionProduct
9,000 MWh(e)/kg2.3+ (net) neutrons
time for
decay
Using fast neutrons improves the performance of the uranium fuel cyclesufficiently to allow sustained further conversion and fission reactions. Thishas been the basis of global interest in fast-spectrum reactors for nearly 70years.
Thermal vs. fast neutron cross-sections
Uranium can be a sustainable fuel in a fast reactor, but using fast neutronscomes at a substantial price. Neutron cross-sections are much smaller forfast neutrons than for thermal (slowed-down) neutrons. To a thermal neutron,one atom of plutonium-239 is the equivalent of nearly 700 atoms ofplutonium-239 to a fast neutron. This is why thermal reactors have a farlower fuel inventory than fast reactors, and why almost every reactor inthe world today is a thermal reactor.
Starting with Uranium is Inevitable
Uranium235
Uranium238
Plutonium239
fissionneutrons
transmute
decay
Starting with uranium is inevitable since uranium-235 is the onlynatural fissile material. A well-designed reactor will essentially"burn out" its uranium-235 inventory while producingchemically-separable plutonium. Depending on the exposureduration small amounts of other transuranics will also form.
Today’s nuclear fuel is fabricated with extraordinary precision, like a fine watch.
But it is that precision that makes it difficult to recycle and to refabricate. A newapproach is needed that is more versatile and less expensive.
Spent Nuclear Fuel Composition
Very-low radioactivity, unused uranium fuel
Very-low radioactivity, unused uranium
Highly radioactive, but rapidly decaying fission products with a variety of potential applications
Low-lived, fairly radioactive “transuranic” isotopes, with potential for consumption in a reactor; drives disposal concerns
0%
1%
2%
3%
4%
5%
6%
Fresh fuel 1 year 2 years 3 years
The Traditional Plan for Nuclear Utilization
Uranium235
Uranium238
Plutonium239
fissionneutrons
tr ansmute
decay
Plutonium239
Uranium238
Plutonium239
fissi
onne
utro
ns
trans
mut
ede
cay
recycle
Phase 2: Plutonium breeding
Phase 1: Uranium-235 consumption
Sustainable Use of Thorium is the Ultimate Goal
Uranium233
Thorium232
Uranium233
fissionneutrons
transmute
decay
recycle
Uranium-233 alone produces sufficient neutrons per thermalneutron to match or exceed its consumption. In this way, U-233is the "catalyst" to sustainable energy production from thoriumand can almost eliminate transuranic production. But very littleU-233 presently exists, and not enough for a major rollout ofthorium reactors.
Decay Salt (HDLiF-BeF2-ThF4-PaF4)Blanket Salt (HDLiF-BeF2-ThF4)Fuel Salt (HDLiF-BeF2-UF4)Coolant salt (HDLiF-BeF2)Higher-pressure CO2 (200 bar)Lower-pressure CO2 (77 bar)Cooling Water
BismuthF2UF6-F2
HF-H2H2
Reactor Containment Boundary
DrainTank
Freeze valve
PrimaryHX
600 MW
1
2
3
4
GasHeater
600 MW5
6
7
Turbine384 MW
CompressorLo-temp39 MW
CompressorMed-temp
75 MW
Generator270 MW
Hi-Temprecuperator
986 MW
Lo-Temprecuperator
399 MW
Gas Cooler322 MW
14
1516
17
18
9
10
12
11
13
19
8 WetCooling
20
21
UF6
Reduction
HF
Electro
Rede x
1
Rede x
2
Electro
Fluor inator1
DecayTank
Fluorinator2
Rede x
3
51
52
31
32
39
43
42
5037
ThF4
makeup
38
36
40
33
3334
35
35
41
44
45
47
48
46
49
53 54
Liquid-Fluoride Thorium Reactors (LFTR) are reactors that useuranium-233 as their fuel, generated from abundant natural thorium.By using uranium-233, they also form the medicinal precursorsneeded for targeted alpha therapy.
Under the leadership of Alvin Weinberg, Oak Ridge National Laboratory ledthe effort to develop thorium as an energy source. Uranium-233 generated
from thorium was first used to power a reactor in 1968, and ORNL has beenthe home to the US supply of uranium-233 every since.
Uranium-233 Inventories in DOE
There are valuable materials atINL and ORNL that couldgreatly accelerate thoriumreactor development. Inparticular, the inventory ofThO2/233UO2 fuel developed forthe 1978 “Light Water BreederReactor” contains:
I 351 kg of 233UI 14,000 kg of thorium
This fuel could be fluorinatedinto ThF4 and UF4 andcombined with LiF-BeF2 salts toform the fuel and blanket saltsof a reactor that wouldthereafter produce ~300 MWeof sustainable powergeneration.
Consume Plutonium or Generate More Plutonium?
Plutonium239
Uranium238
Plutonium239
fissionneutrons
tr ansmute
decay
recycle
Plutonium239
Thorium232
Uranium233
fissionneutrons
tr ansmute
decay
Plutonium is theinevitable result ofthe first stage ofnuclear utilization.
WIth uranium, itcannot make morefissile than itconsumes (inthermal reactors).
But with thorium,plutonium fissiongenerates the U-233that is the key tosustainability.
Use Thorium for Transition from Plutonium
Plutonium239
Thorium232
Uranium233
fissionneutrons
transmute
decay
So consuming plutonium as fuel in a reactor with thorium canproduce the uranium-233 needed to "bridge" to sustainablethorium-fueled reactors.
Three-Phase Plan to Sustainability
Uranium235
Uranium238
Plutonium239
fission neutrons
transmute decay
Plutonium239
Thorium232
Uranium233
fission neutrons
transmute decay
Uranium233
Thorium232
Uranium233
fission neutrons
transmute decay
recycle
Phase 3Thorium consumption
Phase 2U-233 production
Phase 1U-235 consumption
Better Fuel Strategies for MSRs
Plutonium239
Uranium238
Plutonium239
fissionneutrons
tr ansmute
decay
recycle
Uranium235
Thorium232
Uranium233
fissionneutrons
tr ansmute
decay
A chloride MSR (fastspectrum) couldbreed more fuel thanit consumes, usingthe U-Pu cycle. Thishas been proposedfor fast chlorideMSRs.
Fission of U-235(essentially HEU)could permanentlyconsume it while theneutrons form U-233from thorium. Thisapproach couldskip to Phase 3.
Best Fuel Strategies for MSRs
Uranium233
Thorium232
Uranium233
fissionneutrons
tr ansmute
decay
recycle
Plutonium239
Thorium232
Uranium233
fissionneutrons
tr ansmute
decay
U-233 fuelirradiating Th-232can breed in thethermal spectrumand almost eliminatetransuranicproduction. This isPhase 3.
Consuming TRU inthe presence ofTh-232 forms U-233while permanentlydestroying TRU.This is Phase 2.
LFLEUR chemical processing
DrainTank
Freeze valve
Bi(Th)Bi(Pa,U)
Bi(Li)Bi(TRU)
Bi(Li)Bi(FP)
DecayTank
Waste
Fluorinator
Hydrofluorinator
RotaryVoloxidizer
H2
Reduction
Scrub
KOH
metallicTh feed
fluor
inat
edTR
U+
FP
purified UF6
barren fuel salt + FP
metallicHDLi feed
decontaminateduranium tetrafluoride
for conversion to U3O8and disposal
was
tesa
lt
waste
salt+FP
fuel powder
chopped and decladdedspent nuclear fuel
HF
barrencarriersaltflu
orin
ated
spen
tnuc
lear
fuel
Voloxidation
Spent nuclear fuel is first oxidized with nitrogen dioxide which causesit to pulverize into a fine powder. Xenon, krypton, tritium, iodine, andCO2 are removed as gases and purified and separated.
3UO2 + 2NO2 → U3O8 + 2NO2NO + O2 → 2NO2
Hydrofluorination
Next the powdered fuel is reduced with hydrogen andhydro-fluorinated to replace all oxides with fluorides. The constituentmaterials change from oxides (ceramics) to fluorides (salts) asoxygen in the spent fuel is removed as water vapor.
(U,Zr)O2 + 4HF → (U,Zr)F4 + 2H2O(Rb,Cs)2O + 2HF → 2(Rb,Cs)F + H2O
(Sr,Ba)O + 2HF → (Sr,Ba)F2 + H2OLn2O3 + 6HF → 2LnF3 + 3H2OMoO3 + 6HF → MoF6 + 3H2O
FluorinationUranium is removed from the salt mixture through fluorination togaseous uranium hexafluoride. Several other constituents also formgaseous hexafluorides, but most do not. Fluorination is one of themost challenging chemical processes because of its severity on anycontainer material.
UF4 + F2 → UF6
NpF4 + F2 → NpF6
Fluorination using NF3Alternatively, nitrogen trifluoride (NF3) might be used for fluorinationinstead of gaseous fluorine (F2). NF3 is much less aggressivetowards container materials.
2UO3 + 4NF3 → 2UF6 + 2N2 + 3O2
3NpO2 + 4NF3 → 3NpF4 + 2N2 + 3O2
2Ln2O3 + 4NF3 → 4LnF3 + 2N2 + 3O2
2MoO3 + 4NF3 → 2MoF6 + 2N2 + 3O2
LFLEUR chemical processing
DrainTank
Freeze valve
Bi(Th)Bi(Pa,U)
Bi(Li)Bi(TRU)
Bi(Li)Bi(FP)
DecayTank
Waste
Fluorinator
Hydrofluorinator
RotaryVoloxidizer
H2
Reduction
Scrub
KOH
metallicTh feed
fluor
inat
edTR
U+
FP
purified UF6
barren fuel salt + FP
metallicHDLi feed
decontaminateduranium tetrafluoride
for conversion to U3O8and disposal
was
tesa
lt
waste
salt+FP
fuel powder
chopped and decladdedspent nuclear fuel
HF
barrencarriersaltflu
orin
ated
spen
tnuc
lear
fuel
Flibe Energy was formed in order to develop liquid-fluoridereactor technology and to supply the world with affordable and
sustainable energy, water and fuel.
Through liquid-fluoridereactor technology,thorium will become theworld’s dominant energysource, and this will be thekey economic driver of thetwenty-first century.
And likely beyond.