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LEGO Reactor - ICAPP 2008
1. A Basic LEGO Reactor
Design for the Provision of
Lunar Surface Power
John Darrell Bess
Nuclear Engineer/Reactor Physics
ANS Annual Meeting/ICAPP
June 12, 2008
Research performed as part of the
Center for Space Nuclear Research at INL
2. 2
Objective
Develop a lunar nuclear reactor
¤ Modular, safe, and reliable
¤ Can be optimized for lunar-base
power demand
¤ Implemented, and later evolved,
using lunar-regolith*
*lunar-regolith:
“blanket rock”, the layer of loose,
heterogeneous material scattered across the lunar surface
3. 3
Lunar Surface Power is Essential
Sustained human and robotic presence
¤ Life-support systems
¤ Communications
¤ Transportation
¤ Scientific missions
¤ Development of
innovative space
technologies and
knowledge
¤ Lunar colonization*
and in situ resource
mining and manufacturing
*Eventual development of tourism,
commercialization, and a lunar society ( )
4. 4
Space Reactor Heritage
U.S. has launched one SNAP-10A reactor
Russia has launched over 30 space reactor systems
Various concepts have been proposed over the past 50 yrs
¤ Heatpipe Operated Mars/Moon Exploration Reactor (HOMER)
¤ Affordable Fission Surface Power System (AFSPS)
¤ Submersion Subcritical Safe Space (S^4) Reactor
¤ Space Power Annular Reactor System (SPARS)
¤ Space Nuclear Steam Electric Energy (SUSEE)
¤ Safe and Affordable Fission Engine (SAFE)
¤ Sectored Compact Reactor (SCoRe)
¤ Mars Surface Reactor (MSR)
¤ SP-100
6. 6
LEGO Reactor Design Features
Lunar regolith Failure of single
functions as both subunit does not cause
shielding and reflector complete reactor failure
material Versatility in placement
Reactor subunits are of new reactor systems
subcritical in design Potential for Lunar
Decreased neutron evolution of design (in
fluence = reduced situ)
material damage
Reduced thermal loads
Modularity
8. 8
Reactor Subunit Description - II Heat
Transfer
SS-316 monolithic, and Power
hexagonal core
Conversion
¤ 2.94-cm (1.16”) pitch
Systems
¤ 23.8-cm (9.37”) diameter
core
¤ 1.64-cm (0.64”) diameter
External
holes
Heatpipes
49-cm (19”) fueled height
106-cm (42”) heatpipe
extension from core
170-cm (67”) primary
subunit length Reactor
Core
Base
Support
9. 9
LEGO Reactor Cluster
30 kWe system power
Bulk Regolith
Subunits placed 60-cm
Regolith Melt
apart
Interstitial Control Rods
¤ nat-B4C
¤ 10-cm (4”) diameter
¤ 49-cm (19”) height
¤ SS-316 chamber
Reactor Control
Subunit Rod Unit
10. 10
Mass Estimate for Unshielded Subunit
Mass (kg) Component Estimate Source
207.16 Reactor Core, Fuel, and Heatpipes MCNP5
10.15 Secondary Heat Transfer (Potassium Boiler) HOMER-25
35.71 Free-Piston Stirling Convertor 140 W/kg
29.07 Waste-Heat Rejection (Heatpipe Radiator) 688 W/kg
12.50 Power Management and Distribution HOMER-25
6.25 Cabling HOMER-25
72.53 Control Rod and Shaft MCNP5
373.37 Subtotal --
74.67 20% Mass Contingency --
448.04 Total without Shielding --
Each subunit contains 88 kg HEU.
Maximum shielding mass would not increase total
mass above ~1 metric ton.
11. 11
Specific Mass Comparison
Space Power Unshielded Specific Mass
Reactor (kWe) Mass (kg) (kg/kWe)
HOMER-25 25 1564 62.6
LEGO Reactor 25 2240 89.6
Space Power Unshielded Specific Mass
Reactor (kWe) Mass (kg) (kg/kWe)
AFSPS 40 2916 72.9
LEGO Reactor 40 3584 89.6
12. 12
Overall LEGO Reactor Design
Potassium Boiler
0.5 m
Uranium Dioxide /
Stainless Steel Core Hex-Conical
0.51 m Carbon-Carbon
Composite Heat-
pipe Radiators
6.45 m * 0.5 m D
Free-Piston Stirling
Space Converter
0.26 m
Sodium / Stainless Overall Dimensions
Steel Heatpipes 8.77 m High
1.06 m 0.50 m Diameter
Stainless Steel
Base Support
0.12 m * 0.24 m
14. 14
LEGO Reactor Evolution - I
Fuels Development Axial Reflector/Shield
¤ Nitride Fuels ¤ Be or BeO
¤ Other Fissile Reactor Control
Isotopes ¤ B4C Tri-Shades
ﻬPu-239
ﻬTh-232/U-233
ﻬCm-245/-244*
ﻬAm-242m*
* Not Available in kg quantities
16. 16
Potential Applications
Non-Lunar, Irradiation Research
Extraterrestrial and Development
Surfaces ¤ Neutron Flux-Trap
¤ Mars, Mercury, ¤ Radioisotope
Moons, Asteroids Breeding
Symbiosis with Lunar ¤ Component Testing
Manufacturing
¤ Regolith Analyses
Thorium Breeding
Terrestrial Develop of
Modular Reactors for
Rural and Developing
Areas
17. 17
Conclusions
A LEGO Reactor Thermodynamic and
cluster can provide the heat transfer analysis
30+ kWe for a lunar will be necessary to
base completely characterize
the LEGO Reactor
Means for waste-heat
rejection may represent Further technological
the limiting factor development may
evolve the LEGO
¤ coupling distance
reactor into a more
¤ maximum power competitive design
Subunit mass of
~500kg
23. 23
Power Conversion
Potassium Boiler Heatpipe Radiator
Stirling Engine ¤ Redundancy in design
¤ Optimal for ≤40 kWe ﻬFin failure
¤ Developing 5 kWe free- ﻬLoop failure
piston, space convertor ¤ Carbon “armor”
for NASA
Heater Displacer Alternator
Head Drive Assembly
Assembly Assembly
24. 24
Concern for Launch Safety
Subunit must remain Current methods for
subcritical (keff < 0.985) maintaining a subcritical
reactor
¤ Prior to launch
¤ Poison control rods
¤ During launch
or drums
¤ Upon accidental
¤ Removable beryllium
impact
reflectors
¤ When submerged
¤ Incorporated spectral
in moderator and/or
shift absorbers (Re,
reflector material
B4C, Gd2O3)
¤ When immersed
¤ Fuel reactor in-orbit
in fire
(or on the lunar
¤ i.e. Always surface)
26. 26
Lunar Regolith Composition
Engineering, Construction and Operations in Space IV,
American Society of Chemical Engineering, pp. 857-866, 1994.
27. 27
Rock-Melt Drilling
Also known as Subterrene
or Subselene drilling
High temperature
application with heat pipes
to melt rock
Melted material is forced
into porous rock
Results in a glassy finish
with no debris
4-9 kWth power requirement
29. 29
Coupling Analysis
Avery’s coupling coefficients
Coefficients determined between all units in the
hexagonal cluster
¤ Adjacent: kij = 0.1121±0.0025
¤ 2-Away: kij = 0.1374±0.0026
¤ Cross-Cluster: kij = 0.1411±0.0025
“Infinite” coupling: kij = 0.1496±0.0025
Reactor system is very loosely coupled
Tightly coupled systems typically have kij values in the thousandths decimal place.
30. 30
Drafting Board Launch Pad
Thorough
thermodynamic and
heat transfer analysis
Ground testing
Confirmation of final
design for “flight”
testing
Safety and security
measures
31. 31
Faring Limits Faring Limits
Launch Vehicles
<13.8-m H, <5-m D 10.5-m H, 7.5-m D
Proposed (~20-21 mT)
Current (~7-9 mT)
¤ NASA’s Exploration
¤ Delta IV Heavy System Architecture
Study (ESAS)
¤ Atlas V Heavy
Launch Vehicle
(HLV)