Reimagining Nuclear Energy with Molten-Salt Technology

Kirk Sorensen Flibe Energy

Nuclear Suppliers Workshop October 2, 2018 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. Water has been the most common reactor coolant but has several disadvantages. Coolant Choices for a Nuclear Reactor

atmospheric high-pressure pressure operation operation Metal Water

moderate temperature (250-450◦C)

Salt Gas

high temperature (650-900◦C) Volumetric Heat Capacity of Coolant Options

4,670 Of the four coolant 4,040 options, a fluoride salt (LiF-BeF2) has the greatest volumetric heat capacity (thermal energy per unit volume). It can 1,700 also carry this thermal 1,040 energy at a low—essentially ambient—operating 20 pressure.

2 lead water helium sodium LiF-BeF LiF-BeF2 fluoride salt is an excellent carrier for uranium (UF4) nuclear fuel. Today’s nuclear fuel is "ceramic"—consisting of uranium bound with oxygen to form uranium dioxide. Oxygen is very electronegative and forms strong bonds with metals, however fluorine, and only fluorine, is even more electronegative. Free energy differences (oxides/chlorides) at 1000 K

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−100 Free Energy Differences

−150 Cs Ba Sr La Pr Ce Gd Nd Pu Th U Zr Alkaline fission products are stable in chloride salt, and will not volatilize if introduced to air. Actinides may form oxides in air, but will not volatilize. Free energy differences (oxides/fluorides) at 1000 K

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−50

−100

−150 Free Energy Differences

−200 Cs Ba Sr La Pr Ce Gd Nd Pu Th U Zr In fluoride form all actinides and alkaline fission products, most notably cesium and strontium, remain in fluoride salt form in the presence of air, do not form volatile species. In molten salts, the first barrier to fission product release is the chemical form of the fuel salt, rather than the mechanical integrity of the fuel pin. Fluorine can replace oxygen in all minerals and transform ceramics (oxides) into salts (fluorides). Fluoride salts are safe and versatile Chemically stable in air and water

Unpressurized liquid with 1000◦C range of temperature MSR Material Compatibility

Through proper material choices, molten-salt reactors can operate in a state of fundamental chemical equilibrium. This was demonstrated by the MSRE with FLiBe salt, graphite, and Hastelloy-N alloy. This is very different than the environment inside PWRs. 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

Lanthanide Fission Products Development of NF3 fluorination takes place in the Radiological Processing Laboratory at Pacific Northwest Nuclear Laboratory in Washington state. NF3 Fluorination Research at PNNL

Using NF3, LiF-BeF2-UF4 salt will be fluorinated to demonstrate the removal of uranium. Unique Technology Intersection

Power-generating Medical-isotope- reactors generating reactors

LFTR

LWR, HWR, HTGR, NRU, HFR, OPAL, LMFBR, FHR, BR2, Safari, TRIGA, GFR SHINE, TRIUMF Fission product distribution

Strontium-90

Molybdenum-99 Lanthanides

Krypton Xenon

Promethium- 147 79 81 83 85 87 89 91 93 95 97 99 101 103 105 107 109 111 113 115 117 119 121 123 125 127 129 131 133 135 137 139 141 143 145 147 149 151 153 155 Conclusions

I MSRs feature circulating fuel dissolved in stable form in the coolant. I Molten salts chemically bind most fission products, but do not retain noble gas fission products at all, thus the standard operating approach for noble gases should bound potential accidents. I Properly chosen materials operate in chemical equilibrium with the coolant without stored energy terms or driving forces for radionuclide release. I Fission products can be extracted and purified during operation.