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Nuclear Engineering Department
Massachusetts Institute of Technology
Martian Surface Reactor Group
Martian Surface Reactor GroupDecember 3, 2004
MSR Group, 12/3/2004Slide 2
Nuclear Engineering Department
Massachusetts Institute of Technology
Motivation for Mars
• “We need to see and examine and touch for ourselves”
• “…and create a
new generation of
innovators and pioneers.”
MSR Group, 12/3/2004Slide 3
Nuclear Engineering Department
Massachusetts Institute of Technology
Motivation for MSR
10/15/2004 Slide 1Competition Sensitive – Do not distribute outside of NASA / Draper / MIT team
Bill Nadirbnadir@mit.edu
NASA Concept Exploration and Refinement Study
Surface Power
Lunar Surface Power Options
Fission Reactor
Fission Reactor + Solar
Radioisotope + Solar
Solar
Chemical
Duration of use
Ele
ctric
Po
we
r L
eve
l (kW
e)
Martian Surface Power Options
- Solar power becomes much less feasible
- Mars further from Sun(45% less power)
- Day/night cycle- Dust storms- Too-short Lifetime for
Martian missions
- Nuclear Power dominates curve for Martian missions.
MSR Group, 12/3/2004Slide 4
Nuclear Engineering Department
Massachusetts Institute of Technology
Nuclear Physics/Engineering 101
MSR Group, 12/3/2004Slide 5
Nuclear Engineering Department
Massachusetts Institute of Technology
Nuclear Physics/Engineering 101
MSR Group, 12/3/2004Slide 6
Nuclear Engineering Department
Massachusetts Institute of Technology
Goals
• Litmus Test– Works on Moon and
Mars– 100 kWe – 5 EFPY – Obeys Environmental
Regulations– Safe
• Extent-To-Which Test– Small Mass and Size– Controllable – Launchable/Accident
Safe– High Reliability and
Limited Maintenance
– Scalability
MSR Group, 12/3/2004Slide 7
Nuclear Engineering Department
Massachusetts Institute of Technology
MSR Components
• Core
– Nuclear Components, Heat
• Power Conversion Unit
– Electricity, Heat Exchange
• Radiator
– Waste Heat Rejection
• Shielding
– Radiation Protection
MSR Group, 12/3/2004Slide 8
Nuclear Engineering Department
Massachusetts Institute of Technology
MSR Mission
• Nuclear Power for the Martian Surface
– Test on Lunar Surface
• Design characteristics of MSR
– Safe and Reliable
– Light and Compact
– Launchable and Accident Resistant
– Environmentally Friendly
MSR Group, 12/3/2004Slide 9
Nuclear Engineering Department
Massachusetts Institute of Technology
Proposed Mission Architecture
Habitat Reactor
MSR Group, 12/3/2004Slide 10
Nuclear Engineering Department
Massachusetts Institute of Technology
CORE
MSR Group, 12/3/2004Slide 11
Nuclear Engineering Department
Massachusetts Institute of Technology
Core - Design Concept
• Design criteria:
– 100 kWe reactor on one rocket
– 5 EFPY
– Low mass
– Safely Launchable
– Maintenance Free and Reliable
MSR Group, 12/3/2004Slide 12
Nuclear Engineering Department
Massachusetts Institute of Technology
Core - Design Choices
• Fast Spectrum, High Temp• Ceramic Fuel – Uranium
Nitride, 33.1 w/o enriched
• Lithium Heatpipe Coolant• Tantalum Burnable Poison• Hafnium Core Vessel• External Control By Drums
• Zr3Si2 Reflector material
• TaB2 Control material
• Fuel Pin Elements in tricusp configuration
MSR Group, 12/3/2004Slide 13
Nuclear Engineering Department
Massachusetts Institute of Technology
Heatpipe Fuel Pin
Tricusp Material
Core - Pin Geometry
• Fuel pins are the same size as the heat pipes and arranged in tricusp design.
MSR Group, 12/3/2004Slide 14
Nuclear Engineering Department
Massachusetts Institute of Technology
Core – Design Advantages
• UN fuel, Ta poison, Re Clad/Structure high melting point, heat transfer, neutronics performance, and limited corrosion
• Heat pipes no pumps, excellent heat transfer, reduce system mass.
• Li working fluid operates at high temperatures necessary for power conversion unit (1800 K)
MSR Group, 12/3/2004Slide 15
Nuclear Engineering Department
Massachusetts Institute of Technology
Core – Reactivity Control
• Reflector controls neutron leakage• Control drums add little mass to the system and offer high
reliability due to few moving parts
Radial Reflector
Control Drum
Reflector and Core Top-Down View
Reflector
Core
Fuel Pin
Fuel
Reflector
Zr3Si2 ReflectorTotal Mass:
2654kg
42 cm
88 cm
10 cm
10 cmReflector
MSR Group, 12/3/2004Slide 16
Nuclear Engineering Department
Massachusetts Institute of Technology
Core - Smear Composition
Material Purpose Volume Fraction7Li Coolant 0.07275946915N Fuel Compound 0.353381879
NatNb Heatpipe 0.076032901181Ta Poison 0.037550786NatRe Cladding/Structure 0.110216571235U Fissile Fuel 0.116593812238U Fertile Fuel 0.233464583
MSR Group, 12/3/2004Slide 17
Nuclear Engineering Department
Massachusetts Institute of Technology
Core - Power PeakingPeaking Factor, F(r)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
-22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22
Core Radius (cm)
F(r
)
31.1InDrumsRPPR 24.1OutDrumsRPPF
MSR Group, 12/3/2004Slide 18
Nuclear Engineering Department
Massachusetts Institute of Technology
Operation over Lifetime
keff over Core Lifetime
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
0 1 2 3 4 5 6
Years at Full Power
keff
BOL keff: 0.975 – 1.027
EOL keff: 0.989 – 1.044
effk = 0.052
effk = 0.055
MSR Group, 12/3/2004Slide 19
Nuclear Engineering Department
Massachusetts Institute of Technology
Launch Accident Analysis
• Worst Case Scenarios:– Oceanic splashdown
assuming• Non-deformed core • All heat pipes
breached and flooded
– Dispersion of all 235U inventory in atmosphere
MSR Group, 12/3/2004Slide 20
Nuclear Engineering Department
Massachusetts Institute of Technology
Launch Accident Results
Reflectors Stowed Reflectors Detached
Water Keff=0.97081±0.00092 Keff=0.95343±0.00109
Wet Sand Keff=0.97387±0.00095 Keff=0.96458±0.00099
•Total dispersion of 235U inventory (104 kg) will increase natural background radiation by 0.024%•Inadvertent criticality will not occur in any conceivable splashdown scenario
MSR Group, 12/3/2004Slide 21
Nuclear Engineering Department
Massachusetts Institute of Technology
Core Summary
•UN fuel, Re clad/structure , Ta poison, Hf vessel, Zr3Si2 reflector
•Low burn, 5+ EFPY at 1 MWth, ~100 kWe,
•Autonomous control by rotating drums over entire lifetime
•Flat temperature profile at 1800K
•Subcritical for worst-case accident scenario
MSR Group, 12/3/2004Slide 22
Nuclear Engineering Department
Massachusetts Institute of Technology
Future Work
• Investigate further the feasibility of plate fuel element design
• Optimize tricusp core configuration
• Examine long-term effects of high radiation environment on chosen materials
MSR Group, 12/3/2004Slide 23
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU
MSR Group, 12/3/2004Slide 24
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU – Mission Statement
Goals:
– Remove thermal energy from the core
– Produce at least 100kWe
– Deliver remaining thermal energy to the radiator
– Convert electricity to a transmittable form
Components:
– Heat Removal from Core
– Power Conversion/Transmission System
– Heat Exchanger/Interface with Radiator
MSR Group, 12/3/2004Slide 25
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU – Design Choices
• Heat Transfer from Core
– Heat Pipes
• Power Conversion System
– Cesium Thermionics
• Power Transmission
– DC-to-AC conversion
– 22 AWG Cu wire transmission bus
• Heat Exchanger to Radiator
– Annular Heat Pipes
MSR Group, 12/3/2004Slide 26
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU – Heat Extraction from Core
• Heat Pipes from Core:
– 127 heat pipes
– 1 meter long
– 1 cm diameter
– Rh wall & wick
– 400 mesh wick
– 0.5mm annulus for liquid
– Li working fluid is Pressurized to boil @ 1800K
MSR Group, 12/3/2004Slide 27
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU – Heat Pipes (2)
• Possible Limits to Flow– Entrainment– Sonic Limit– Boiling– Freezing– Capillary
• Capillary force limits flow:
Qmax
llL K A
w
21re
lg l ( )sin
l
ll
MSR Group, 12/3/2004Slide 28
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU - Thermionics
• Thermionic Power Conversion Unit
– Mass: 240 kg
– Efficiency: 10%+
• 1.2MWt -> 125kWe
– Power density:
10W/cm2
– Surface area
per heat pipe:
100 cm2
MSR Group, 12/3/2004Slide 29
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU – Thermionics Design
MSR Group, 12/3/2004Slide 30
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU - Thermionics Issues & Solutions
– Creep @ high temp
• Set spacing at 5 mm
• Used ceramic spacers
– Cs -> Ba conversion due to fast neutron flux
• 0.01% conversion expected over lifetime
– Collector back current
• TE = 1800K, TC = 950K
134134133 ),( BaCsnCs
MSR Group, 12/3/2004Slide 31
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU – Power Transmission
– D-to-A converter:• 25 x 5kVA units • 360kg total• Small
– Transmission Lines:• AC transmission• 25 x 22 AWG Cu wire bus• 500kg/km total• 83.5:1 Transformers increase voltage to 10,000V
– 1,385kg total for conversion/transmission system
MSR Group, 12/3/2004Slide 32
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU – Heat Exchanger to Radiator
• Heat Pipe Heat Exchanger
MSR Group, 12/3/2004Slide 33
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU – Failure Analysis
• Very robust system
– Large design margins in all components
– Failure of multiple parts still allows for ~90% power generation & full heat extraction from core
• No possibility of single-point failure
– Each component has at least 25 separate, redundant pieces
• Maximum power loss due to one failure – 4%
• Maximum cooling loss due to one failure – 0.79%
MSR Group, 12/3/2004Slide 34
Nuclear Engineering Department
Massachusetts Institute of Technology
PCU – Future Work
• Improving Thermionic Efficiency
• Material studies in high radiation environment
• Scalability to 200kWe and up
• Using ISRU as thermal heat sink
MSR Group, 12/3/2004Slide 35
Nuclear Engineering Department
Massachusetts Institute of Technology
Radiator
MSR Group, 12/3/2004Slide 36
Nuclear Engineering Department
Massachusetts Institute of Technology
Objective
• Design a radiator to dissipate excess heat from a nuclear power plant located on the surface of the Moon or Mars.
44s TTσεAQ
MSR Group, 12/3/2004Slide 37
Nuclear Engineering Department
Massachusetts Institute of Technology
Goals
• Small mass and area
• Minimal control requirement
• Maximum accident safety
• High reliability
MSR Group, 12/3/2004Slide 38
Nuclear Engineering Department
Massachusetts Institute of Technology
Decision Methodology
• Past Concepts
– SP-100– SAFE-400– SNAP-2– SNAP-10A– Helium-fed– Liquid Droplet– Liquid Sheet
MSR Group, 12/3/2004Slide 39
Nuclear Engineering Department
Massachusetts Institute of Technology
Component Design
• Heat pipes– Carbon-Carbon shell– Nb-1Zr wick– Potassium fluid
• Panel– Carbon-Carbon
composite– SiC coating
Fin
Heat Pipe
3 mm
Thermal Radiation
5 mm
Wick Vapor Channel
MSR Group, 12/3/2004Slide 40
Nuclear Engineering Department
Massachusetts Institute of Technology
Structural Design
• Dimensions– Height 3 m
– Diameter 4.8 m
– Area 39 m2
• Mass– Panel 200 kg
– Heat pipes 60 kg
– Supports 46 kg
Core & Shield
2.0 m
0.5 m 0.5 m
0.60 m
2.4 m
2.54 m
Radiator Panel
Heat Pipe
1.45 m
MSR Group, 12/3/2004Slide 41
Nuclear Engineering Department
Massachusetts Institute of Technology
Support
• Supports– Titanium– 8 radial beams– 3 circular strips
Core
Radiator Panel
1.5 m
1.25 m
Support Anchor 6.54°
Strips
MSR Group, 12/3/2004Slide 42
Nuclear Engineering Department
Massachusetts Institute of Technology
Analysis
• Models– Isothermal– Linear Condenser
Radiating Area needed to Reject 900 kW
0
10
20
30
40
50
60
70
80
700 800 900 1000 1100 1200 1300 1400
Radiator Temperature (K)
Rad
iato
r A
rea
(m2 )
• Comparative Area– Moon 39 m2
– Mars 38.6 m2
MSR Group, 12/3/2004Slide 43
Nuclear Engineering Department
Massachusetts Institute of Technology
Future
• Analysis of transients
• Model heat pipe operation
• Conditions at landing site
• Manufacturing
Nuclear Engineering Department
Massachusetts Institute of Technology
Martian Surface Reactor Group
Shielding
MSR Group, 12/3/2004Slide 45
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Design Concept
• Dose rate on Moon & Mars is ~14 times higher than on Earth
• Goal: – Reduce dose rate to
between 0.6 - 5.7 mrem/hr
• Neutrons and gamma rays emitted, requiring two different modes of attenuation
MSR Group, 12/3/2004Slide 46
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Constraints
• Weight limited by landing module (~2 MT)• Temperature limited by material properties (1800K)
Courtesy of Jet P
ropulsion Laboratory
MSR Group, 12/3/2004Slide 47
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Design Choices
Neutron shielding Gamma shieldingboron carbide (B4C) shell (yellow) Tungsten (W) shell (gray)
40 cm 12 cm
• Total mass is 1.97 MT
• Separate reactor from habitat
– Dose rate decreases as
1/r2 for r >> 50cm
- For r ~ 50 cm, dose rate decreases as 1/r
MSR Group, 12/3/2004Slide 48
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Dose w/o shielding
• Near core, dose rates can be very high• Most important component is gamma radiation
MSR Group, 12/3/2004Slide 49
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Neutrons
Material Reason for Rejection
Z > 5 Inefficient neutron slowing; too heavy
H2O Too heavy
Li Too reactive
LiH Melting point of 953 K
B Brittle; would not tolerate launch well
B4CAl Possible; heavy, needs comparison w/ other options
MSR Group, 12/3/2004Slide 50
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Neutrons (2)
Material Maximum thickness for 1 MT
shield (cm)
Dose Rate at shielding
edge (mrem/hr)
Dose rate at 10 m
(mrem/hr)
Unshielded N/A 2.40*107 26.8*103
Boral (B4CAl) 20.3 1.24*105 323.2
Borated Graphite (BC)
22.7 4.28*104 111.1
Boron Carbide (B4C)
21.1 3.57*104 92.9
MSR Group, 12/3/2004Slide 51
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Neutrons (3)
• One disadvantage: boron will be consumedDose vs. Distance at t=0 and t=5 years
0
2
4
6
8
10
12
14
16
18
20
5 10 15 20 25 50 75 100 125 150 175 200 225 250
meters
mre
m/h
r
Dose after 5years ofoperationDose at 0 yearsof operation
MSR Group, 12/3/2004Slide 52
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Gammas
Material Reason for Rejection
Z < 72 Too small density and/or mass attenuation coefficient
Z > 83 Unstable nuclei
Pb, Bi Possible, but have low melting points
Re, Ir Difficult to obtain in large quantities
Os Reactive
Hf, Ta Smaller mass attenuation coefficients than alternatives
MSR Group, 12/3/2004Slide 53
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Gammas (2)
Material Maximum thickness for 3 MT shield (cm)
Dose rate at 90 cm (mrem/hr)
Unshielded N/A 2.51*106
Pb 17.1 594.66
Bi 19.4 599.88
W 10.6 480.00
MSR Group, 12/3/2004Slide 54
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Gammas (3)
• Depending on mission parameters, exclusion zone can be implemented
MSR Group, 12/3/2004Slide 55
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Design
• Two pieces, each covering 40º of reactor radial surface
• Two layers: 40 cm B4C (yellow) on inside, 12 cm W (gray) outside
• Scalable– @ 200 kW(e) mass is
2.19 metric tons– @ 50 kW(e), mass is
1.78 metric tons
MSR Group, 12/3/2004Slide 56
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Design (2)
• For mission parameters, pieces of shield will move – Moves once to align shield with habitat– May move again to protect crew who need to enter
otherwise unshielded zones
MSR Group, 12/3/2004Slide 57
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Alternative Designs
• Three layer shield– W (thick layer) inside,
B4C middle, W (thin layer) outside
– Thin W layer will stop secondary radiation in B4C shield
– Putting thick W layer inside reduces overall mass
MSR Group, 12/3/2004Slide 58
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding -Alternative Designs (2)
-The Moon and Mars have very similar attenuation coefficients for surface material
-Would require moving 32 metric tons of rock before reactor is started
MSR Group, 12/3/2004Slide 59
Nuclear Engineering Department
Massachusetts Institute of Technology
Shielding - Future Work
• Shielding using extraterrestrial surface material:
– On moon, select craters that are navigable and of appropriate size
– Incorporate precision landing capability
– On Mars, specify a burial technique as craters are less prevalent
• Specify geometry dependent upon mission parameters
– Shielding modularity, adaptability, etc.
MSR Group, 12/3/2004Slide 60
Nuclear Engineering Department
Massachusetts Institute of Technology
MSR Assembly Sketch
• Breathtaking Figures Goes Here
MSR Group, 12/3/2004Slide 61
Nuclear Engineering Department
Massachusetts Institute of Technology
MSR Mass
Component Mass (kg)Core 4310PCU 1385Radiator 306Shielding 1975Total 7976
Bottom Line: ~80g/We
MSR Group, 12/3/2004Slide 62
Nuclear Engineering Department
Massachusetts Institute of Technology
MSR Cost
• Rhenium Procurement and Manufacture
• Nitrogen-15 Enrichment
• Halfnium Procurement
MSR Group, 12/3/2004Slide 63
Nuclear Engineering Department
Massachusetts Institute of Technology
Mass Reduction
• Move reactor 2km away from people
– Gain 500kg from extra transmission lines
– Loose almost 2MT of shielding
• Use ISRU plant as a thermal sink
– Gain mass of heat pipes to transport heat to ISRU (depends on the distance of reactor from plant)
– Loose 360kg of Radiator Mass
Bottom Line: ~60g/We
MSR Group, 12/3/2004Slide 64
Nuclear Engineering Department
Massachusetts Institute of Technology
MRS Design Advantages
• Robustness
• Safety
• Redundancy
• Scalability
MSR Group, 12/3/2004Slide 65
Nuclear Engineering Department
Massachusetts Institute of Technology
MSR Mission Plan
• Build and Launch
– Prove Technology on Earth
• Earth Orbit Testing
– Post Launch Diagnostics
• Lunar / Martian Landing and Testing
– Post Landing Diagnostics
• Startup
• Shutdown
MSR Group, 12/3/2004Slide 66
Nuclear Engineering Department
Massachusetts Institute of Technology
MSR GroupExpanding Frontiers with Nuclear Technology
“The fascination generated by further exploration will inspire…and create a new generation of innovators and pioneers.”
~President George W. Bush
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