Molten-Salt Technology and Fission Product Handling

Kirk Sorensen Flibe Energy, Inc.

ORNL MSR Workshop October 4, 2018 2018-10-16 rnilsaegnrlt otnsl ecosa whole. a the as of reactors many molten-salt on handling, to that be general product will are fission form focus principles reactor a my molten-salt While in on another. work fuel from our nuclear one separate, unburned to with difficult was in products which systems, fission solid-fueled to mixed fission contrast of a handling such intelligent represented the It for gave products. it today that technology options you reactor of array molten-salt with the to was One me talk attracted reactors. initially to molten-salt that like things in the I’d handling of their and and Sorensen products fission Kirk about is name my Hello, Fundamental Nuclear Reactor Concept

In its simplest form, a nuclear reactor generates thermal energy that is carried away by a coolant. That coolant heats the working ﬂuid of a power conversion system, which generates electricity from part of the thermal energy and rejects the remainder to the environment.

coolant working ﬂuid

fresh fuel electricity Power Nuclear Heat Conversion Reactor Exchanger System spent fuel heated water or air

coolant working ﬂuid

The primary coolant chosen for a nuclear reactor determines, in large part, its size and manufacturability. The temperature of the coolant determines the efﬁciency of electrical generation. Fundamental Nuclear Reactor Concept

coolant working ﬂuid

fresh fuel electricity Power Nuclear Heat Conversion Reactor Exchanger System Fundamental Nuclear Reactor Concept spent fuel heated water or air

coolant working ﬂuid

The primary coolant chosen for a nuclear reactor determines, in large

2018-10-16 part, its size and manufacturability. The temperature of the coolant determines the efﬁciency of electrical generation.

All fission reactors turn fissile material like uranium or plutonium into an array of fission and activation products (such as plutonium or neptunium). These fission and activation products have a wide variety of physical and chemical properties.

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UF6 and Reduction

UF6

Fluoride Fluoride Vacuum Volatility Volatility Distillation

Fertile Fuel Salt Fission Salt Product Waste

Recycle Recycle Fertile Salt Reactor Fuel Salt core

Reactor blanket Uranium Absorption UF4

UF6 and Reduction

UF6

Fluoride Fluoride Vacuum Volatility Volatility Distillation

Fertile Fuel Salt Fission Salt Product Waste

Recycle Recycle Fertile Salt Reactor Fuel Salt core

2018-10-16 Reactor blanket

A fluid-fueled reactor also has attractive options for the long-term management of fission products. They can be chemically isolated and sep- arated from the fuel salt in a manner analogous to the way that the kid- ney processes and removes waste products from the bloodstream. A variety of different approaches to the removal of fission/activation products have been proposed for liquid-fluoride nuclear reactors. These include distillation of the fuel salt itself leaving the fission/activation products in the heel. Another proposed method is to selectively pre- cipitate certain neutron-absorbing fission products by overwhelming the salt with another material transparent to neutrons, such as cerium.

2018-10-16 sinpout rmfloieslst metals. to salts reduce fluoride con- preferentially from will is products that salt fission reductant fuel chemical the metallic a here with process, tacted another yet is extraction Reductive ORNL two-fluid reactor chemical processing

lne atmnsPaF minus blanket salt

Bi(Th) Extractor Blanket

Th0 Reductant 0 Li Addition

-UF

Bi(Th,Pa,U) m H2-HF ˙

= ea Fluorinator Decay Hydroﬂuorinator

F Reduction UF6 Decay HF-H

Tank 2

F2 H2

ulFluorinator Fuel Freeze valve carrier salt Drain makeup Tank Distillation

to final fluorination and disposal ORNL two-fluid reactor chemical processing

lne atmnsPaF minus blanket salt

Bi(Th) Extractor Blanket

Th0 Reductant 0 Li Addition

-UF

Bi(Th,Pa,U) m H2-HF ˙

= ea Fluorinator Decay Hydroﬂuorinator

F Reduction UF6 Decay HF-H

Tank 2

F2 H2 ORNL two-ﬂuid reactor chemical processing Bi

ulFluorinator Fuel Freeze valve carrier salt Drain makeup Tank Distillation

F2 2018-10-16

to ﬁnal ﬂuorination and disposal

The MSRE considered distillation as a viable approach since it appears simple in concept. The high temperatures required for the distillation of a carrier salt of LiF-BeF2 (FLiBe) from a fuel salt are challenging. There is also the inefficiency issue of repeatedly attempting to boil a large inventory of carrier salt away in an attempt to concentrate a small inventory of fission products. Inevitably some of the valuable carrier salt will follow the fission products into the waste stream.

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2018-10-16 e.Z,U u a n te ciie edt euefo atin salt a from exception. reduce notable to a tend is actinides Thorium other lanthanides. the and sys- to Pa, LiF-BeF2-ThF4 preference Pu, the U, from Zr, are tem. species various overview extractable the substantially provides how be figure to This of tend products. actinides fission the the con- of than "noble" and noble nature first, most more salt the the remove fuel But to the tend of pretreatment. stituents will it any that without operate is extraction salt could reductive fuel that fuel the employed the be from on would products directly reactor fission liquid-fluoride of a removal of the salt for technique a Ideally, 2018-10-16 n hr rnu stedmnn ciieseis ouint the thorium to contain solution not a itself. species, does present actinide that may dominant challenge salt the fuel prod- is a fission uranium imagine lanthanide where can the and than one salt if fuel But the ucts. from propen- lower removed even be an which has to blanket Thorium sity salt breeder rep- products. the in fission which present lanthanide be europium, would of and class neodymium larger the the the from resent removed than be mixture to susceptible salt more fluoride all not are actinides graph minor this in other depicted several and plutonium, uranium, Zirconium,

2018-10-16 oepoutvl ormv sinproducts. much fission employed remove be to could could productively extraction neptunium, salt more reductive the uranium, and in removed present the largely non-metals extraction, and be metals, reductive transition the at of attempt many an undertaken be to hexafluo- could fluorination prior plutonium If but unstable. hexafluorides thermodynamically is volatile ride Neptunium form state. do tetravalent plutonium or fluo- trivalent and be fluorina- a also from the oxidized will on and/or actinides Depending rinated other temperature, UF6. and state liquid- agent fluorinat- gaseous a tion/oxidizing a in its found of to UF4 use reactor typically the fluoride uranium, is convert evaluate to to agent propose ing/oxidizing we which approach The ORNL one-fluid reactor chemical processing

H2 to purge columns H2 (10 scfm) (95%) (5%) Al O Sorber Charcoal Sorber 2 3 Vent to Stack (SeF6-TeF6) (Kr-Xe)

H makeup 2 Drawoff to Waste Evaporation and Salt Mine Storage H2 + HF from Hydroﬂuorinators Caustic Lithium Addition and Purge Columns H2 + HF Scrub (53g mole/day) (14.9 scfm) Salt Makeup H2 Bismuth KOH (HBr-HI) RE2+ BeF (74.8g mole/day) (10.5 scfm) (0.6 gal/day) 2 HF Accumulation ThF (100.3g mole/day) UF6 (2 gal/min) 4 Distillation in Bismuth Reduction KOH H2 Reservoir RE 2

Carrier Salt Discard (2.38 gal/day) + Bi-Li-RE2+ Drawoff Stripper (LiF-BeF2-ThF4) 2+ Bismuth (0.95 scfm) F2 to Bi-50 at.% Li-RE (50g mole Li/day) Removal 6 Fluorinators H2 (0.17 gal/min) (0.6 gal/day) + UF 2 + 3 F Fluorine HF Fission Product Lithium Addition

Cell ,RE (65g mole/day) Rare-Earth + Transfer 2 Extraction to LiCl (0.66 gal/day) 3+ Bismuth (12.4 gal/min)

Bi,RE RE Salt Cleanup HF to (5.7 gal/day) + + (Br-Kr-I-Xe, volatile metal ﬂuorides) Accumulation and U3 /U4 Hydroﬂuorinators H -HF to in Bismuth 2 Valence Recycle Adjustment F2 + UF6 Bi-Li-RE3+ Drawoff RE Fuel Salt Return (50g mole Li/day) 3

to Reactor +

Stripper (5.7 gal/day) (0.87 gal/min) UF6 Product Secondary Removal Hydro- Fluorination (165g U/day) LiCl (RE2+,3+) Fluorination

Salt from Reactor F (32.3 gal/min) 2 HF-H2 LiF-BeF2-ThF4-UF4 30-min Bi-5 at.% Li-RE3+ 71.7-16.0-12.0-0.3 mole% Salt Pa (8 gal/min) (0.87 gal/min) Holdup Extraction Tank Primary H2-HF to Fluorination Recycle Pa Storage and Decay Fission Product and LiF-ThF4-ZrF4-PaF4 Waste Salt Accumulation Bismuth Lithium addition F (71.0-26.0-2.8-0.2 mole%) 2 (Li-Th-Zr-U-Pa) (3.14 gal/day) 150-175 ft3 (371g mole/day) (0.9 scfm) (0.13 gal/min) Batchwise Discard 3 Hydro- (25 ft /220 days)220-day LiF-BeF -ThF -UF 2 4 4 Fluorination Pa Decay Ultimate Disposal in Bismuth F Salt Mine after LiCl 2 HF-H2 (0.78 gal/min) 9-yr decay period UF6-F2 LiF-ThF4-ZrF4-PaF4 ORNL one-ﬂuid reactor chemical processing

H2 to purge columns H2 (10 scfm) (95%) (5%) Al O Sorber Charcoal Sorber 2 3 Vent to Stack (SeF6-TeF6) (Kr-Xe)

Cell ,RE (65g mole/day) Rare-Earth + Transfer 2 Extraction to LiCl (0.66 gal/day) 3+ Bismuth (12.4 gal/min)

to Reactor +

Stripper (5.7 gal/day) (0.87 gal/min) UF6 Product Secondary Removal Hydro- ORNL one-ﬂuid reactor chemical processing Fluorination (165g U/day) LiCl (RE2+,3+) Fluorination Salt from Reactor F (32.3 gal/min) 2 HF-H2 LiF-BeF2-ThF4-UF4 30-min Bi-5 at.% Li-RE3+ 71.7-16.0-12.0-0.3 mole% Salt Pa (8 gal/min) (0.87 gal/min) Holdup Extraction Tank Primary H2-HF to Fluorination Recycle Pa Storage and Decay Fission Product and LiF-ThF4-ZrF4-PaF4 Waste Salt Accumulation Bismuth Lithium addition F (71.0-26.0-2.8-0.2 mole%) 2 (Li-Th-Zr-U-Pa) (3.14 gal/day) 150-175 ft3 (371g mole/day) (0.9 scfm) (0.13 gal/min) Batchwise Discard 3 Hydro- (25 ft /220 days)220-day LiF-BeF -ThF -UF 2 4 4 Fluorination Pa Decay Ultimate Disposal in Bismuth F Salt Mine after LiCl 2 HF-H2 (0.78 gal/min) 9-yr decay period 2018-10-16 UF6-F2 LiF-ThF4-ZrF4-PaF4

The appeal of fluorination as a technique for the removal of uranium from fluoride fuel salt has been noted for many years and fluorination formed an integral part of most of the chemical processing flow- sheets that were developed at Oak Ridge National Laboratory under the Molten-Salt Reactor Program from 1957 to 1976. Fluorinators were envisioned at a variety of locations in the chemical processing, universally under the assumption that they would remove uranium from the fuel salt. Despite the prevalence of fluorination as an envisioned chemical processing technique, the actual amount of development that was undertaken on continuous fluorination was surprisingly small.

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UF4 + F2 → UF6

NpF4 + F2 → NpF6 Fluorination Uranium is removed from the salt mixture through fluorination to gaseous uranium hexafluoride. Several other constituents also form gaseous hexafluorides, but most do not. Fluorination is one of the most challenging chemical processes because of its severity on any container material.

UF4 + F2 → UF6

NpF4 + F2 → NpF6 Fluorination 2018-10-16

At the heart of the challenge of fluorination is the nature of the gaseous species used. F2 is a very assertive, hazardous, highly corrosive, oxidation agent which effectively converts materials to their fully fluorinated, highest oxidation state. That behavior is simultaneously its advantage and its risk. Even ceramic (oxide) materials can be fluorinated; indeed this is how uranium oxides mined from the earth are prepared for enrichment, by first being fluorinated to uranium tetraflu- oride then uranium hexafluoride.

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2UO3 + 4NF3 → 2UF6 + 2N2 + 3O2

3NpO2 + 4NF3 → 3NpF4 + 2N2 + 3O2 2Ln2O3 + 4NF3 → 4LnF3 + 2N2 + 3O2

2MoO3 + 4NF3 → 2MoF6 + 2N2 + 3O2 Fluorination using NF3 Alternatively, nitrogen trifluoride (NF3) might be used for fluorination instead of gaseous fluorine (F2). NF3 is much less aggressive towards container materials.

2UO3 + 4NF3 → 2UF6 + 2N2 + 3O2

3NpO2 + 4NF3 → 3NpF4 + 2N2 + 3O2 2Ln2O3 + 4NF3 → 4LnF3 + 2N2 + 3O2 Fluorination using NF3 2MoO3 + 4NF3 → 2MoF6 + 2N2 + 3O2 2018-10-16

In the years since the MSRE concluded in 1976, alternative fluorination agents have been advanced for consideration. Most notable among these is NF3. NF3 has been considered for rocket propulsion and is extensively used in the electronics industry to clean and etch mi- croelectronic silica chips. It is minimally hazardous and not corrosive at temperatures below 70C and is likely less corrosive than other fluorinating agents. It is not known to react with moisture, is thermally stable at room temperature, and has been demonstrated by PNNL to be an effective, thermally-tunable fluorination/oxidation agent for spent nuclear fuel constituents. By controlling the treatment temperature, NF3 will selectively fluorinate/oxidize spent nuclear fuel constituents. The different temperature sensitivities and NF3 concentration effects for the fluorination/oxidation of the different constituents potentially provides mechanisms to effect separations of the volatile fluorides.

2018-10-16 fF,wihwl niciiaeycnetseist hi oaieforms exists). volatile form their a to such species behavior (if convert the from indiscriminately departure will notable which a F2, is of This salt. molten lan- the dis- earths, in remain solved will alkaline plutonium, The including metal actinides, remaining transition fluorides. and volatile the thanides, fluorina- form of effective many that an and products fission NpF4, is liquid- UF4, NF3 a for (600C), agent which tion/oxidation operate at temperatures would the reactor as fluoride such temperatures, higher At 600 MWt LFTR-23 flow diagram

Saturated 54◦C Exhaust Air (1067.0 m3/s) sCO2 Power Conversion System Main Electrical Main Turbine Generator RecompressorCompressor 368.9 MW 257.7 MW 61.06 MW 44.88 MW

57◦C Cooling Water 24◦C Inlet Air 550C 453C 147C 62C 32C (30% rel. humidity)

408C 141C 61C High-Temp Low-Temp Gas Cooler 27◦C Cooling Water Recuperator Recuperator 337.0 MW Gas Heater 1.211 GW 397.8 MW 600.0 MW Fuel Salt HF-H2 Blanket Salt

2Reduction H2 Coolant salt Decay Salt Waste Salt Fresh Offgas 1-day Offgas Bi(Pa,U) 3-day Offgas 90-day Offgas H2 Helium ea Fluorinator Decay ulFluorinator Fuel UF6-F2

Freeze Valve NF3 HF-H2 Decay H2 Tank Bi(Th,FP) Bismuth 200-bar CO2 77-bar CO2 NF3 Fuel-Salt NF3 Chemical Processing Water Drain Tank Long-Term Short-Term Gas Holdup Gas Holdup 600 MWt LFTR-23 ﬂow diagram

Saturated 54◦C Exhaust Air (1067.0 m3/s) sCO2 Power Conversion System Main Electrical Main Turbine Generator RecompressorCompressor 368.9 MW 257.7 MW 61.06 MW 44.88 MW

57◦C Cooling Water 24◦C Inlet Air 550C 453C 147C 62C 32C (30% rel. humidity)

408C 141C 61C High-Temp Low-Temp Gas Cooler 27◦C Cooling Water Recuperator Recuperator 337.0 MW Gas Heater 1.211 GW 397.8 MW 600.0 MW Fuel Salt HF-H2 Blanket Salt

2Reduction H2 Coolant salt Decay Salt Waste Salt 600 MWt LFTR-23 ﬂow diagram Fresh Offgas 1-day Offgas Bi(Pa,U) 3-day Offgas 90-day Offgas H2 Helium ea Fluorinator Decay ulFluorinator Fuel UF6-F2

Freeze Valve NF3 HF-H2 Decay H2 Tank 2018-10-16 Bi(Th,FP) Bismuth 200-bar CO2 77-bar CO2 NF3 Fuel-Salt NF3 Chemical Processing Water Drain Tank Long-Term Short-Term Gas Holdup Gas Holdup

The hazard level, and chemical reactivity attributes potentially make NF3 a very attractive fluorinating/oxidizing agent for managing the composition of the fuel salt in a liquid-fluoride reactor where uranium is the dominant or even exclusive fissile material. Fluorination/oxidation of the fuel salt with NF3 would produce UF6 and remove uranium from the salt. Reductive extraction could then be employed to remove non- volatile fission and activation products from the salt. Hydrogen could be used to reduce UF6 back to UF4 and reconstitute the salt for return to the reactor. Conclusions

I Fuel burnup in MSRs is limited by fission products I Reductive extraction can remove fission products, so long as actinides are removed first. I Fluorination can remove uranium and neptunium effectively from fluoride salts. I Fluorination using NF3 might be more practical than previously suggested approaches. Conclusions

I Fuel burnup in MSRs is limited by fission products I Reductive extraction can remove fission products, so long as actinides are removed first. I Fluorination can remove uranium and neptunium effectively from fluoride salts. Conclusions I Fluorination using NF3 might be more practical than previously suggested approaches. 2018-10-16

Flibe Energy and our partner Pacific Northwest Nuclear Laboratory are excited to take some of the first steps towards the handling of fission products in a molten-salt reactor as part of work recently announced for funding by the Department of Energy. Hopefully we can return next year and share some initial results of our work.