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.