A Small Mobile Molten Salt Reactor SMMSR For Underdeveloped Countries and Remote Locations

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A Small Mobile Molten Salt Reactor (SM-MSR)For
Underdeveloped Countries and Remote Locations

• William A. Casino
• Kirk F. Sorensen
• Christopher A. Whitener
• April 25, 2007

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Overall Design Goals

• Develop a portable 100 MWe reactor suitable for
  deployment in remote regions.
• Design for a 30-year lifetime between refueling.
• Include non-proliferation attributes.
• Employ passive and inherent safety features
  wherever feasible.
• Reduce complexity in design, development,
  operation, staffing, accident handling.
• Secondary design goals
• Learn from each other (neutronics, hydraulics,
  fuel cycle)
• Become fantastic reactor designers who open new
  career opportunities
• Have fun!

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Overall Design Trades

• Spectrum fast
• Fuel solid
• Coolant liquid-metal
• Sustenance breeding
• Decay heat pool
• PCS steam turbine
• Xenon fast spectrum

• Spectrum (epi)thermal
• Fuel liquid fluoride
• Coolant liquid fluoride
• Moderator graphite
• Sustenance simple refuel
• Decay heat drain tank
• PCS He gas turbine
• Xenon removal

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Chosen Design Solution

• To achieve inherent safety, long operational
  lifetime, and extreme simplicity, we chose a
  fluoride reactor design using a once-through
  enriched uranium fuel cycle.
• Fuel is UF4 dissolved in a matrix of 7LiF-BeF2.
• Graphite moderator and reflector.
• Blanket region is fuel salt downcomer and
  neutron/gamma shield.
• Core vessel is Hastelloy-N.
• Power density chosen to allow 30-year graphite
  lifetime.

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Chosen Power Conversion System

• Power conversion system uses helium gas turbines
  in a closed-cycle configuration.
• Helium gas turbines can take advantage of
  high-temperature capabilities of reactor to
  achieve high conversion efficiencies (40-50,
  depending on design).
• Turbomachinery size can be adjusted by altering
  minimum cycle pressure with little penalty.
• Helium gas turbine technology must be developed
  but has broad application across Gen-4 concepts.
• Also compatible with dry cooling approach at a
  small loss in efficiency.

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Reactor Performance Features

• High temperature operation at low pressures in
  the core.
• Excellent electrical conversion efficiency
  possible.
• Potential for thermochemical hydrogen generation.
• Lightweight core vessel and core graphite can be
  transported without fuel salt.
• Ease in operation and fueling.
• Reactor is passively stable and can withstand
  severe accidents and operator error without
  radiation release.
• Excess reactivity can be minimized and new fuel
  added continuously.
• No xenon transients at shutdown.
• Xenon and other gases come out of solution during
  operation of the reactor, allowing improvement in
  k-eff and elimination of xenon transients.
• Reactor capable of following electrical load
  naturally.

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Reactor and PCS Transportation

• Reactor vessel and primary heat exchanger shipped
  in a single piece.
• Helium turbomachines and secondary heat
  exchangers shipped in multiple pieces and
  connected on site.

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Natural Circulation Design
25 meters structure height -7 meters from grade
level
Heat Exchanger Shell with Integral Surge Reservoir
Heat Exchanger Matrix
Fuel Salt Cold Leg
Fuel Salt Hot Leg
Containment Structure
Moderator Chamber (Active Core Region)
Freeze Valve
Core Safety Dump Tank
0 meters structure height -32 meters from grade
level
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Reactor Safety Features

• Fluoride reactor design is passively safe against
  reactivity excursions due to large negative
  temperature coefficient of reactivity
• When salt is heated, it expands out of moderated
  core region
• Reactor design is passively safe for decay heat
  removal
• Complete loss of coolant, loss of power accident
  leads the freeze plug in the bottom of the
  reactor to thaw, draining fuel salt into a
  passively cooled configurationallows reactor to
  downshift heat removal system without
  intervention.
• Reactor design allows excess reactivity to be
  minimized.
• Fuel is continuously added to reactor at a very
  low level through UF6 reduction.
• No excess reactivity allows elimination of
  burnable poisons, boron, and control rods.
• Chemically stable fuel and coolantno liquid
  metal reactions.
• No radiation damage to fuelionic bonds are
  impervious.
• No issues with rod expulsion or rod positionno
  rods!
• No salt pumpsnatural circulation employed.

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Passive Decay Heat Removal thru Freeze Valve
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Fluoride Fuels and Coolants

• Fluorides of lithium and beryllium can dissolve
  fluorides of uranium, fission products, and
  actinides.

• They are stable at high temperatures and low
  pressures.

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Graphite Lifetime Limits Fluence

• The primary consideration for reactor lifetime is
  the graphite distortion, which is a strong
  function of fluence and temperature.

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Neutronic Modeling in KENO
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Primary and Secondary Heat Exchangers
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Reactor Design Sequence
1. Core Salt
7LiF-BeF2-UF4
2. Core Salt Liquidus
772. K
3. Coolant Fluid
LiF-BeF2 (66-34)
4. Coolant Fluid Liquidus
732. K
5. Core Outlet Temperature
1000. K
6. Thermal Margin
27. K
7. Core Inlet Temperature
799. K
8. Salt/Salt HX DT
20. K
9. Salt/Helium HX DT
20. K
10. Gas Heater Inlet Temperature
759. K
11. Gas Heater Outlet Temperature
960. K
12. Power Conversion System
helium gas turbine
13. Conversion Efficiency
42.2
14. Helium Net Work
1.35 MW/kg/s
15. Electrical Power
100. MWe
16. Core Thermal Power
237. MWt
17. Helium Mass Flow Rate
76. kg/s
18. Coolant Fluid Mass Flow Rate
507. kg/s
19. Core Salt Mass Flow Rate
423. kg/s
20. Graphite Temperature
1050. K
21. Graphite Design Fluence
2.6822 n/cm2
22. Core Lifetime
30.0 yr
23. Core Power Density
5.2 kW/L
24. Core Volume
45529. L
25. Core Diameter
300. cm
26. Core Length
644. cm
27. Core Height/Diameter
214.7
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Temperature-Entropy Diagram of Cycle
1000 K
8
10
12
960 K
7. Hi-press regenerator outlet / Preheater inlet
900 K
8. Preheater outlet / Turbine 1 inlet
9. Turbine 1 outlet / Reheater 1 inlet
10. Reheater 1 outlet / Turbine 2 inlet
11. Turbine 2 outlet / Reheater 2 inlet
12. Reheater 2 outlet / Turbine 3 inlet
800 K
13. Turbine 3 outlet / Lo-press regenerator inlet
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7
9
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700 K
600 K
0. Lo-press regenerator outlet / Precooler inlet
500 K
1. Precooler outlet / Compressor 1 inlet
2. Compressor 1 outlet / Intercooler 1 inlet
3. Intercooler 1 outlet / Compressor 2 inlet
4. Compressor 2 outlet / Intercooler 2 inlet
5. Intercooler 2 outlet / Compressor 3 inlet
0
400 K
6. Compressor 3 outlet / Hi-press regenerator
inlet
2
4
6
300 K
1
3
5
300 K
20.0
22.0
24.0
26.0
28.0
30.0
32.0
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Power Conversion System Design
1. Working Fluid
Helium
2. Gas Model
Helmholtz
3. Gas Heater Outlet Temperature
960. K
4. Gas Heater Inlet Temperature
759. K
5. Turbine Efficiency
92.0
6. Regenerator Delta-T
25. K
7. Number of Reheaters
2
8. Turbine Pressure Ratios

9. Number of Intercoolers
2
10. Heat Exchanger Pressure Drop
1.0 per 100K of HX
11. Heat Exchanger Pressure Ratios

12. Total Compression Ratio
7.481
13. Compressor Pressure Ratios

14. Compressor Inlet Temperature
300. K
15. Compressor Efficiency
88.0
16. Initial Pressure
2.00 MPa
17. Compression State Points

18. Expansion State Points

19. Ideal (Ericcson) Cycle
68.8
20. Cycle Efficiency
43.5
21. Net Work
1353. kJ/kg
22. Electrical Power
100.0 MW
23. Generator Efficiency
97.0
24. Mass Flow Rate
76.2 kg/s
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Conclusions

• The selection of a fluoride reactor and a helium
  gas turbine power conversion system enables a
  portable, long-lived power reactor.
• Preliminary analyses of reactor systems were
  conducted.
• Core design
• Neutronics
• Thermal hydralics
• Depletion and fuel cycle
• Power conversion
• Further work would refine and improve the design,
  possibly including alternate development
  directions.