NuclearPowered FullyMobile Lunar Outpost

1
Nuclear-Powered Fully-Mobile Lunar Outpost

• Aaron Craft, Natasha Glazener, Rick Henderson,
  Logan Sailer, and Josh Valentine
• Presented to INL
• July 28, 2008

2
Overview

• Project description
• The FSP
• Challenges to Being Mobile
• Radiator Analysis
• In-situ Resources
• Neutronics Model of FSP
• Shielding

3
Overview

• Project description
• The FSP
• Challenges to Being Mobile
• Radiator Analysis
• In-situ Resources
• Neutronics Model of FSP
• Shielding

4
Project Description

• NASAs current plan is the US Space Exploration
  Policy (was Vision for Space Exploration)
• Return humans to the Moon and then to Mars
• The current plan allows for 5-10 Sorties
• Placing a few humans on the lunar surface for 2
  weeks at different locations
• Then placing a lunar outpost somewhere that
  houses 6 humans for 6 weeks

5
Project Description, cont.

• Included is a rover that will allow astronauts to
  travel 300 km in 3 days
• Estimated power 2kWe
• Unshielded against lethal solar flares
• Adding shielding against solar flares adds 2
  tons
• Required power 10-20kWe
• A completely mobile base would
• Reduce number of costly sorties
• Allow long stay times
• Provide shielding from lethal solar flares

6
Project Description, cont.

• AFSPS (FSP) used in stationary base designs
• Use FSP for mobile reactor as well
• Determine if shield and radiator can be designed
  to fit on a 3x10m, 10t cart
• This enables a train of cars to travel the lunar
  surface

7
Overview

• Project description
• The FSP
• Challenges to Being Mobile
• Radiator Analysis
• In-situ Resources
• Neutronics Model of FSP
• Shielding

8
Fission Surface Power System

• AFSPS Study initiated in April 2006 by NASA and
  the DOE
• Determine features and costs of FSP
• Team consisted of members from several NASA field
  offices and DOE National Labs
• Low risk chosen over high performance and/or low
  mass system
• Top-level screening studies used as a basis

9
FSP Design
Images Mason et al. System Concepts for
Affordable Fission Surface Power 2008
10
FSP Main Components

• Reactor
• Shielding
• Power Conversion
• Power Conditioning and Distribution
• Heat Rejection

Image Mason et al. System Concepts for
Affordable Fission Surface Power 2008
11
Reactor Design

• Stainless steel vessel and clad
• Low Temperature (900K fuel-clad temp)?
• UO2 Fueled 85 fuel pins(93 enriched)?
• Liquid-metal Cooled (78 - Na, 22 - K)?
• Six radial beryllium (Be) reflector drums provide
  reactivity control

12
Shielding

• Above surface
• Alternating layers of W and LiH with boral bottom
  plate to limit back scatter
• 90 limit radiation to 5 rem/yr at 2 km
• 270 sized for 50 rem/yr at 2 km
• B4C in a stainless steel container

Image Mason et al. 2006
Image Mason et al. 2008
13
Shielding, cont.

• B4C in a stainless steel container providing both
  neutron and gamma attenuation
• W and LiH top shield with boral liner placed in
  excavated location
• Reduces radiation lt 5 rem/yr at 6m

Image Mason et al. 2006
Image Mason et al. 2008
14
Power Conversion System

• Opposing coupled free-piston Stirling power
  converters (Thot 830K, Tcold 415K)?
• Low power (50kWe, 175kWt) 8 x 6 kWe
  alternators
• Affordability
• Off the shelf
• Within experience base for free-piston Stirling
  technology

Image Mason et al. 2008
15
Alternative PCSs

• Low temperature reactor
• Thermoelectric, Thermophotovoltaic, Thermoionic
• AMTEC
• Rankine
• Brayton
• Stirling
• High Temperature Reactor

16
Brayton vs. Stirling PCS

• Low power
• High power

• Efficiency and heat rejection
• Weight

ImageMason et. al. 2006
17
Heat Rejection

• Tin 420K, Tout 390K, H2O
• TRAD 387K, T8 317K
• 4m tall, 34m wide, 175m2 radiative surface area
• 7kg/m2, 615 kg total weight

Image Mason et al. System Concepts for
Affordable Fission Surface Power Jan. 2008
18
Concepts Taken from FSP

• Off-the-shelf/Affordability
• Reactor Design
• PCAD
• Stirling PCS
• Examine other options for radiator
• New shield design

19
Overview

• Project description
• The FSP
• Challenges to Being Mobile
• Radiator Analysis
• In-situ Resources
• Neutronics Model of FSP
• Shielding

20
Mobility Requirements

• Mass lt 10,000 kg (ATHLETE max load)
• Reactor cart
• Dose lt 5 rem/yr to astronauts
• Dose to Stirling lt 1E14 nvt and 2 MRad gamma
• Lifetime (8 yr operation)
• Place Stirling engines behind shield
• Radiator must withstand motion induced loading
• Cart 3 m wide and 10 m long

21
Power Mobility

• Multiple mobility options for mobile reactor
  base
• Mobile, inhabited base reactor
• Coupled during transit, uncoupled when stationary
• Permanently coupled
• Mobile, uninhabited base reactor
• Coupled during transit, uncoupled when stationary
• Solo reactor module (10 t)

22
Power Mobility

• AFSPS 40 kWe
• 120 kWt rejection
• Accomplished with 175 m2 of radiating area (87 m2
  heat-pipe radiators)
• Required Power
• 0.050-0.080 We-hr/km/kg
• For inhabited module, 10 kWe constant load
• Mobile base masses from 30-100 t

23
Power Mobility

24
Power Mobility

• Power Dependent
• Reactor Power
• Dependant on Heat Dissipation
• Fractional power
• Supplemental Power
• Solar simple, passive
• Fuel Cell proven, rechargeable
• H2O
• Alternative
• Emergency power

25
Power Mobility - Fractional
26
Mobility Options Wagon

• Habitation Modules
• Radiator/Storage Carts
• Reactor Cart

Reactor at Full Power In Transit
27
Mobility Options Wagon

• Habitation Modules
• Radiator/Storage Cart
• Reactor Cart

Reactor at Half Power In Transit
28
Mobility Options Train

• Habitation Modules
• Radiator Cart
• Reactor Cart

Reactor at Half Power In Transit
29
Mobility Options

• Constraints
• Mass 10 t per cart
• Power Velocity 0.080 We-hr/km/kg
• Heat dissipation Radiative area
• Options
• 2 habitation modules
• 1-2 Radiator storage carts
• Reactor cart
• Fractional power Fuel Cells

30
Overview

• Project description
• The FSP
• Challenges to Being Mobile
• Radiator Analysis
• In-situ Resources
• Neutronics Model of FSP
• Shielding

31
Mobile Radiator Design

• Challenge Putting 175 m2 on a 3 x 10 meter cart
• 1-sided - Horizontal Orientation
• 2-sided - Vertical Orientation
• Types to consider
• Heat pipe
• Liquid sheet
• Liquid drop
• Fountain

ImagesSiamidis, 2006
32
Mobile Radiator Design, cont.

• Liquid sheet
• Conventionally too large would require 150 0.5m
  x 5m sheets
• Spherical configuration over sized
• Would require two 6 meter diameter spheres to
  reject required heat

ImagesBrandhorst et al. 2006
33
Mobile Radiator Design, cont.

• Liquid drop
• A mass savings exists
• Area would require large number of carts
• Fountain configuration would require a spray
  nearly 30 meters high

Image Tagliafico, 1997
34
Mobile Radiator Design, cont.

• 1-sided can eliminate view factor (horiz.)?
• 2-sided can reduce size (vert.)?
• Running reactor at lower power
• 4 m x 11 m deployed vertical HP radiator
• Additional 4 m x 11m stowed radiator

35
Mobile Radiator Design, cont.

• Conestoga wagon configuration
• 2.5m sides, 3m diameter dome, 4m tall
• Consume two carts, but allow storage and provide
  full power and heat rejection 93 m2 per cart

36
Mobile Radiator Summary

• Liquid drop and sheet increase radiating area
• Fountain requires extreme height
• Domed configuration most feasible
• Full radiating area Full power
  Max speed
• Vertical radiator with partial stowed
• Partial radiating area, requires reduced speed
  and power
• Full power when stationary

37
Overview

• Project description
• The FSP
• Challenges to Being Mobile
• Radiator Analysis
• In-situ Resources
• Neutronics Model of FSP
• Shielding

38
In-situ Resources

• Utilizing resources already present on the moon
• Less mass launched
• Sulfur in lunar regolith (0.81 wt)
• Oxygen in lunar regolith (46 wt)

39
Why It Is Important

• Minimize the supplies required
• Self sufficient outpost
• Having backup power supply
• Ability to generate oxygen

40
Molten Salt Reduction of O2

• Oxygen is needed for the fuel cycle as well as
  life support.
• Regolith is 43.6 oxygen by mass.
• A mixture of CaCl2 (or other Salts) and the
  regolith is heated to 700C.
• CaCl2 has good reductive potential.
• Using a cathode and anode the oxygen can be
  harvested from the various oxides in regolith.

41
Sulfur

• Regolith contains 810 grams of sulfur per metric
  ton of regolith
• On earth, sulfur is mined by simply using heat
• Sulfur is liquid at 115.2C at 1 atm.
• The liquid sulfur can be collected in a bucket
• 99.8 pure
• The pure sulfur can be stored for later use

42
Sulfur, cont.
Structure of solid sulfur
43
Sulfur, cont.

• Sulfur rings form straight chains when heated
• This will cause viscosity to decrease up to 155C
• Above 159C, the chains will form S16 and S24
• These longer chains will cause viscosity to
  increase until 200C
• Above 200C there is enough energy to break the
  longer chains and viscosity will decrease

44
Sulfur-Oxygen Fuel Cell

• A fuel cell is an electro chemical conversion
• Requires a catalyst
• Utilizes a constant supply of fuel
• S O2 SO2
• .89 V theoretical power production
• 0.45 Volts electrical at 50 efficiency

45
Sulfur-Oxygen Fuel Cell, cont.
46
Problems with S-O Fuel Cell

• Sulfur hinders most known electrode materials
• Sulfur results in up to 80 loss of power
• Some studies have shown that various alloys
  eliminate or minimize this problem.
• Sulfur is about 7 times more viscous than water
• Viscosity increases with temperature after
  melting
• The sulfur fuel must be very pure
• Any deviation from purity results in power loss

47
Combustion Engine
48
Sulfur Combustion Engine

• Potential to use off the shelf engine
• May need to slightly modify the valves
• Sulfur melts at 115C
• The sulfur needs to be atomized
• The sulfur fuel supply will need to be heated
• Sulfur will auto-combust above 290C (i.e.
  diesel)
• Testing needs to be done to define other
  conditions

49
Future Work

• Test the auto combustion of sulfur
• Prove the concept of a sulfur combustion engine
  in a vacuum
• Prove the concept of sulfur mining from regolith
• Prove the concept of electro-chemical separation
  of oxygen using molten salts
• Continue development electrode materials that are
  not hindered by the presence of sulfur (i.e.
  develop a sulfur fuel cell)

50
Overview

• Project description
• The FSP
• Challenges to Being Mobile
• Radiator Analysis
• In-situ Resources
• Neutronics Model of FSP
• Shielding

51
MCNP Model of FSP

• MCNP model obtained from Dr. Poston (LANL)
• Model originally buried in lunar regolith

52
MCNP Model of FSP, cont.

• Model was modified
• Original cross-section libraries used (.30c and
  .40c)
• Cross-section libraries changed to .66c (Poston ?
  )
• Cold/clean, full excess model used

53
MCNP Model of FSP, cont.
54
Overview

• Project description
• The FSP
• Challenges to Being Mobile
• Radiator Analysis
• In-situ Resources
• Neutronics Model of FSP
• Shielding

55
Shield Requirements

• SIZE
• 3m x 10m cart
• 3m maximum diameter
• MASS
• 10,000 kg total cart mass
• 7400 kg available for shield

56
Previous vs. Mobile Shield

• Existing stationary design
• 5 rem/yr at 1000m
• Shield mass 6200 kg (8800 kg total)
• Mobile design
• 5 rem/yr at 15m
• Shield mass 7400kg (10,000 kg total)
• Must attenuate 4500 times more dose
• Must optimize shield design

Image Mason et al. 2008
57
Radial Shield Study Process

• Collect materials to consider - down selection
• Size shield to provide required neutron dose
• Add gamma shielding for neutron attenuators
• Find optimal position/amount of gamma attenuator
• Compare shield configurations by size and mass

58
Materials Considered

• Water / BH2O (0.78 wt)
• LiH and Li6H (95 enriched)
• HfH2
• YH
• ZrH
• ThH2
• B4C, tungsten, regolith

59
Method of Down Selection

• Add shield mass until 1000x decrease in n-dose
• Does not include gamma dose
• Neutron attenuators being compared

60
Shield Masses
61
Shield Volume
62
Dose Contributions
63
Observations

• BH2O less volume than pure water (10)
• Li6H - lighter and smaller than natural LiH (14)
• ZrH - lightest heavy-metal hydride
• HfH2 - requires less volume but heavy
• Li6H and BH2O require gamma shielding
• Consider H2O, BH2O, LiH, Li6H and ZrH

64
Updated Model

• Includes 20 partial protection

65
Radial Shield Thickness

• Dose vs. thickness is desired for each material
• Thickness intervals every 10 cm
• Expect e-µx relationship
• Use to design shield for 5 rem/yr

66
Dose vs. Shield Thickness

67
Using the Results

• Gamma dose vs. thickness was also found and
  included in thickness calculations
• Used data to find thickness for 5 rem/yr at 100m,
  15m and x-shield

68
Radial Shield Volumes
69
Radial Shield Masses

• H2O, B-H2O, LiH and Li6H do not include gamma
  attenuator mass (tungsten)

70
Observations

• These masses are for a 360 shield
• Considering 70, 180 and 360 shields
• ZrH too massive for 360 shield but useful where
  compact shielding is needed
• Li6H is the lighter and smaller than BH2O
  Leading shielding material

71
Adding Gamma Shielding

• H2O, B-H2O, LiH and Li6H need gamma shielding
• Tungsten is a solid gamma shielding material
• Two studies
• 1. Find gamma dose vs. thickness for tungsten
• 2. Find optimal position within shield
• Not simple e-µx relationship due to (n, ?)

72
Gamma Dose vs. W-Thickness

• Next, find optimal position and use this data to
  find required thickness

73
Finding Optimal Position

• Move same mass of tungsten through shield at 5cm
  increments (0-50cm)

74
Finding Optimal Position, cont.

• See increased gamma dose due to (n, ?) reaction,
  which is due to fast neutrons
• The further the tungsten from the core
• Less (n, ? ) reaction (fewer fast
  neutrons)
• Thinner tungsten layer (less attenuation)
• The further the tungsten from the core, the more
  massive the shield

75
Optimal Position
76
Using the Results

• Add tungsten at optimal position for required
  dose
• Use previous data
• Create 70, 180 and 360 shields for BH2O and
  Li6H
• Compare by size and mass

77
70 Radial Shields
78
180 Radial Shields
79
360 Radial Shields
80
Smart Shields
81
Radial Shield Comparison
82
Radial Shield Summary

• Li6H-W shield lighter than BH2O-W shield
• BH2O makes possible the Smart Shield
• More BH2O can be brought on later missions to
  fill more shield
• Option BH2O 360 shield (70 _at_15m and 180
  _at_100m)
• 7080 kg for W and inner BH2O
• Later 7150 kg for outer BH2O

83
Ground Scatter

• Height of Reactor off Regolith
• Reflected Radiation
• Direct Radiation
• Bottom Shielding
• Thickness
• Geometry
• Scattered Radiation

Regolith
Shield
84
Ground Scatter

• Relate Dose vs. Height using MCNP5 models
• Tally totally dose, as well as reflected dose
• Compare at different heights off regolith
• Varied Tally Surfaces
• Outer Shield Surface
• 2 m and 10 m radial surfaces, 1.7 m height
• At shield and 15 m radial surfaces, 1.7 m height

85
Ground Scatter MCNP5
VOID
VOID
VOID
LIGHT REGOLITH
DENSE REGOLITH
86
Ground Scatter

• ZrH
• Rounded Bottom Shield

87
Ground Scatter

• Not unexpectedly, dose increases with increased
  height
• Particles scattering out of lower shield
• Line-of-sight to dose surfaces
• Model Limitations
• Flagged regolith cells located directly below
  primary shield

88
Ground Scatter

• ZrH with HfH seat
• Cylindrical Bottom Shield, Extended Primary
  Shield

HfH
89
Ground Scatter

• Further modeling resulted in unexplained or
  random behavior
• HIGH STANDARD DEVIATIONS (0.17 - 0.28)
• Increased regolith thickness
• Increased shield thickness
• Solution weighted cells and more particles

90
Ground Scatter

• Significant radiation scatter
• Necessitates large lower shield
• Significantly increases system mass
• Future work required
• Tungsten placement
• Radial extension alternative
• Complete optimization of lower shielding with
  current radial shield configuration

91
Ways to Reduce Shield Mass

• Smart Shield
• Void Shielding
• Chamfer Outside Surfaces

92
Void Shielding

• Idea deflect radiation rather than attenuate
  them
• Less thermal stress on shield
• Lower shield mass

93
Shield Opening Angle
94
Material Scattering
95
Mirrors and Mass
96
Vacuum Space
97
Void Shield Future Work

• Optimization
• Crystals / nanotubes
• Vertical void shield sections

98
Chamfer Shield

• Outside corners attenuate little dose
• Make the outside of the shield spherical
• Shown to significantly decrease mass (up to 9)

99
Shield Summary

• Optimal materials used
• Optimal radial shield conditions found
• Shielding required beneath core
• There are ways to reduce the shield mass
• Some shield configurations fit within size and
  mass constraints, not inhibiting mobile outpost
• Use Li6H or BH2O and tungsten shield
• Place tungsten at optimal position
• Required shielding for 70 _at_15m

100
Proposed Mobile Lunar Base

• Habitation Modules
• Radiator/Storage Carts
• Reactor Cart

Reactor at Full Power In Transit
101
Summary

• Expanding the research base for the FSP
• Radiator area shield mass are largest
  challenges
• Use a separate radiator cart
• Shielding at 15m is possible for lt7400 kg
• High-T nuclear heat makes in-situ resource
  utilization viable

102
Acknowledgements

• Dr. Steven Howe INL, CSNR
• Dr. Mike Houts NASA
• Dr. Dave Poston LANL
• Kristi Bailey Delisa Rogers INL, CSNR
• INL Technical Library Staff

103
References
Bennett, G.L., Radar Men on the MoonA Brief
Survey of Fission Surface Power Studies, in the
Proceedings of the Space Technology and
Applications International Forum (STAIF2008),
edited by M.S. El-Genk, AIP Conference
Proceedings, Melville, New York, 2008. Eagle
Engineering, Inc. Lunar Surface Transportation
Systems Conceptual Design Lunar Base Systems
Study Task 5.2 Report. EEI Report 88-188. July 7,
1988. Carrier, W. David, III. The four things
you need to know about the Geotechnical
Properties of Lunar Soil. Lakeland, FL Lunar
Geotechnical Institute, 2005. Campos, Arturo B.
Apollo Experience ReportLunar Module Electrical
Power Subsystem. NASA TN D-6977. Washington
D.C. NASA, 1972. Greenspan, E., High
Effectiveness Shielding Materials and Optimal
Shield Design, Journal of Testing and Evaluation.
Jan, 1992. Hellem, S. and Williams, A., The Rate
of Combustion of Single Droplets of Sulfur,
Combustion and Flame 20, 133-135, 1973.
104
References
Heiken, Grant H., David T. Vaniman, Bevan M.
French. Lunar Sourcebook A Users Guide to the
Moon. Houston Cambridge University,
1991. Karchmer, J. H., The Analytical Chemistry
of Sulfur and its Compounds Part I, Wiley
Interscience 1970. Kowash, B. R., 2nd
Lieutenant., Parameter Study for Optimizing the
Mass of a Space NuclearPower System Radiation
Sheild. Air Force Institute of Technology, March
2002. Lamarsh, J. R. and Baratta, A. J.,
Introduction to Nuclear Engineering, 3rd Edition.
Prentice Hall, Upper Saddle River, NJ. 2001. Lee,
L., W., Shield Analysis of a Small Compact Space
Nuclear Reactor, Air Force Weapons Laboratory,
Kirtland AF Base, NM. August 1987. Lide, D. R.,
CRC Handbook of Chemistry and Physics, 88th
Edition (Internet Version 2008), CRC Press/Taylor
and Francis,Boca Raton, FL.
105
References
Mason, L, Poston, D.I., Qualls, L., System
Concepts for Affordable Fission Surface Power,
in the Proceedings of the Space Technology and
Applications International Forum (STAIF2008),
edited by M.S. El-Genk, AIP Conference
Proceedings, Melville, New York, 2008. Mason, L,
A Comparison of Fission Power System Options for
Lunar and Mars Surface Applications, in
proceedings of Space Technology and Applications
International Forum (STAIF-2006), edited by M. S.
El-Genk, AIP Conference Proceedings 813,
Melville, New York, 2006. MatWeb,
www.matweb.com Mueller, W., M. and Blackledge,
J., P. Review of Metal Hydrides for Nuclear
Reactor Applications, New York, Metullurgical
Society of the American Institute of Mining,
Metallurgical and Petroleum Engineers, vol.7.10,
pp47-50, 1960. NNDC Nuclear Wallet,
http//www.nndc.bnl.gov/wallet, National Nuclear
Data Center, Jan 18, 2008.
106
References
Poston, D.I., Kapernick, R.J., Marcille, T.F.,
Sadasivan, P., Dixon, D.D., and Amiri, B.W.,
Comparison of Reactor Technologies and Designs
for Lunar/Martian Surface Reactor Applications,
in proceedings of the 2006 International Congress
on Advances in Nuclear Power(ICAPP '06), American
Nuclear Society, La Grange Park, IL,
2006. Poston, D.I., Kapernick, R.J., Dixon, D.D.,
Amiri, B.W., and Marcille, T.F., Reference
Reactor Module for the Affordable Fission Surface
Power System, in the Proceedings of the Space
Technology and Applications International Forum
(STAIF2008), edited by M.S. El-Genk, AIP
Conference Proceedings, Melville, New York,
2008. Tagliafico , L. A. and Fossa , M.,
Lightweight Radiator Optimization for Heat
Rejection in Space. Heat and Mass Transfer 32
(1997) 239244 Ó Springer-Verlag, 1997. Web
Elements, www.webelements.com.
107
Questions