martian surface reactor group december 3, 2004web.mit.edu/course/22/22.33/final report/12-8 final...
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Nuclear Science and Engineering DepartmentMassachusetts Institute of Technology Martian Surface Reactor Group
Martian Surface Reactor GroupDecember 3, 2004
MSR Group, 12/3/2004Slide 2Nuclear Science and Engineering Department
Massachusetts Institute of Technology
OVERVIEW
• The Need• Mission Statement• Project Organization• Goals• Project Description• Description and Analysis
of the MSR Systems– Core– Power Conversion Unit (PCU)– Radiator– Shielding
• Total Mass Analysis• Conclusion
MSR Group, 12/3/2004Slide 3Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Lunar Surface Power Options
Fission Reactor
Fission Reactor + Solar
Radioisotope + Solar
Solar
Chemical
Duration of use
Ele
ctric
Pow
er L
evel
(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.
Motivation for MSR
Comparison of Solar and Nuclear Power on the Moon
0.0E+00
5.0E+03
1.0E+04
1.5E+04
2.0E+04
2.5E+04
0 50 100 150 200 250
Power (kWe)
Mas
s (k
g)
SolarReactor
MSR Group, 12/3/2004Slide 4Nuclear Science and Engineering Department
Massachusetts Institute of Technology
MSR Mission Statement
• Nuclear Power for the Martian Surface– Test on Lunar Surface
• Design Criteria– 100kWe– 5 EFPY– Works on the Moon and Mars
MSR Group, 12/3/2004Slide 5Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Organizational Chart
Project Management
CoreTask Manager
PCUTask Manager
RadiatorTask Manager
Core Group
Shielding Task Manager
PCU Group Radiator Group Shielding Group
MSR Group, 12/3/2004Slide 6Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Decision Goals
• Litmus Test– Works on Moon and
Mars– 100 kWe – 5 EFPY – Obeys Environmental
Regulations
• Extent-To-Which Test– Small Mass and Size– Controllable – Launchable/Accident Safe– High Reliability and Limited
Maintenance
• Other– Scalability– Uses Proven Technology
MSR Group, 12/3/2004Slide 7Nuclear Science and Engineering Department
Massachusetts Institute of Technology
MSR System Overview
• Core – Fast, UN, Zr3Si2 reflector w/ drums, Hf vessel
• Power Conversion Unit – Cs Thermionics, Heat Pipes, D-to-A
• Radiator – Heat Pipe/Fin, 950K
• Shielding – 2mrem/hr, Neutron/Gamma
• Total Mass ~8MT
MSR Group, 12/3/2004Slide 8Nuclear Science and Engineering Department
Massachusetts Institute of Technology
CORE
MSR Group, 12/3/2004Slide 9Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Core – Challenges
• Fit on one rocket• Autonomous
control for 5 EFPY• High reliability• Safe in worst-case
accident scenario• Provide 1.2 MWth
MSR Group, 12/3/2004Slide 10Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Core - Design Choices Overview
Design Choice ReasonFast Spectrum, High Temp High Power DensityUranium Nitride Material Characterisitcs33.1% Enrichment BreedingHeatpipe with Li coolant Power ConversionHafnium Core Vessel Accident ScenarioTantalum Neutron Absorber Lower BOL kef f for accidentsRotating Drums Autonomous ControlZr3Si2 Reflector Less ThermalizationFuel Pins in Tricusp Heat Transfer
MSR Group, 12/3/2004Slide 11Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Core - Pin Geometry
• Fuel pins are the same size as the heat pipes and arranged in tricusp design.
• Highest centerline fuel pin temperature at steady state is 1890K.
UN fuel
Li heatpipe Re structure
MSR Group, 12/3/2004Slide 12Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Core – Design Advantages
• UN fuel, Ta absorber, Re Clad/Structure performance at high temperatures, heat transfer, effect on neutron economy, and limited corrosion
• Heat pipes no pumps required, excellent heat transfer, small system mass
• Li working fluid operates at high temperatures necessary for power conversion unit
MSR Group, 12/3/2004Slide 13Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Core – Dimensions and Control
Small core, total mass ~4.3 MT
Neutron Absorber
Control Drum
Top-Down ViewIsometric View
Reflector
Core
Fuel Pin
Fuel
Reflector
42 cm
88 cm10 cm
10 cmReflector
MSR Group, 12/3/2004Slide 14Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Core – Isotopic Composition
Material Purpose Volume Fraction7Li Coolant 0.07315N Fuel Compound 0.353
NatNb Heatpipe 0.076181Ta Neutron Absorber 0.038NatRe Cladding/Structure 0.110235U Fissile Fuel 0.117238U Fertile Fuel 0.233
MSR Group, 12/3/2004Slide 15Nuclear Science and 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 -18 -14 -10 -6 -2 2 6 10 14 18 22
Core Radius (cm)
F(r)
31.1=InDrumsRPPR 24.1=OutDrumsRPPF
MSR Group, 12/3/2004Slide 16Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Operation over Lifetime
BOL keff: 0.975 – 1.027
EOL keff: 0.989 – 1.044
effk∆ = 0.052
effk∆ = 0.055
Reactivity over Lifetime
0.97
1.00
1.03
1.06
0 1 2 3 4 5
Years of Operation
Kef
f
MSR Group, 12/3/2004Slide 17Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Launch Accident Analysis
• Worst Case Scenario– Oceanic splashdown
assuming• Non-deformed core • All heat pipes breached
and flooded• Problem: Large gap between
BOL keff and accident scenario
MSR Group, 12/3/2004Slide 18Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Accident Scenario: NatHf Vessel
• Introduce absorbing vessel– High thermal cross-section– Low fast cross-section
Core (24 cm) Vessel
Segment (1 cm)
0.0
1.0
2.0
3.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Energy (MeV)
Vess
el F
lux/
Cor
e F
lux
MSR Group, 12/3/2004Slide 19Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Launch Accident Results
Keff=0.965Keff=0.974Wet Sand
Keff=0.953Keff=0.970Water
DetachedStowedReflector Position
• Inadvertent criticality will not occur in conceivable splashdown scenarios
MSR Group, 12/3/2004Slide 20Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Accident Scenario Design Constraint
• NASA requires reactor to be subcritical in all launch accident scenarios
• Improvements– Higher enrichment– Flatten keff vs. lifetime
plots– Less mass
• Design freedom increases if this constraint is eased
MSR Group, 12/3/2004Slide 21Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Core Summary
• Core has UN fuel, Re clad/tricusp, Ta absorber, Hf vessel, Zr3Si2 reflector and TaB2 control material
• Relatively flat fuel pin temperature profile
• 5+ EFPY at 1.2 MWth, ~100 kWe,
• Autonomous control by rotating drums over entire lifetime
• Subcritical for worst-case accident scenario
MSR Group, 12/3/2004Slide 22Nuclear Science and Engineering Department
Massachusetts Institute of Technology
PCU
MSR Group, 12/3/2004Slide 23Nuclear Science and 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 24Nuclear Science and 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
Reactor
MSR Group, 12/3/2004Slide 25Nuclear Science and Engineering Department
Massachusetts Institute of Technology
PCU – Heat Extraction from Core
• How Heat Pipes Work– Isothermal heat transfer– Capillary action– Self-contained system
• Heat Pipes from Core:– 127 heat pipes– 1 meter long– 1 cm diameter– Niobium wall & wick– Pressurized Li working fluid, 1800K
MSR Group, 12/3/2004Slide 26Nuclear Science and 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
ρl σl L K Aw
⎛
⎝⎜⎜⎜
⎞
⎠⎟⎟⎟
− 2 1re
ρl g l ( )sin φ
σl
µl l
MSR Group, 12/3/2004Slide 27Nuclear Science and 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 28Nuclear Science and Engineering Department
Massachusetts Institute of Technology
PCU - Thermionics Issues & Solutions
– Creep at high temp• Set spacing at 0.13 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
βγ +→→ 134134133 ),( BaCsnCs
MSR Group, 12/3/2004Slide 29Nuclear Science and Engineering Department
Massachusetts Institute of Technology
PCU – Thermionics Design
MSR Group, 12/3/2004Slide 30Nuclear Science and 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• Transformers increase voltage to 10,000V
– ~1.4MT total for conversion/transmission system
MSR Group, 12/3/2004Slide 31Nuclear Science and Engineering Department
Massachusetts Institute of Technology
PCU – Heat Exchanger to Radiator
• Heat Pipe Heat Exchanger
MSR Group, 12/3/2004Slide 32Nuclear Science and 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: 3%• Maximum cooling loss due to one failure: 1%
MSR Group, 12/3/2004Slide 33Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Radiator
MSR Group, 12/3/2004Slide 34Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Objective
• Dissipate excess heat from a power plant located on the surface of the Moon or Mars.
( )44s TTσεAQ ∞
•
−=
MSR Group, 12/3/2004Slide 35Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Environment
• Moon– 1/6 Earth gravity– No atmosphere– 1360 W/m2 solar flux
• Mars– 1/3 Earth gravity– 1% atmospheric pressure– 590 W/m2 solar flux
MSR Group, 12/3/2004Slide 36Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Radiator – Design Choices
• Evolved from previous designs for space fission systems:
– SNAP-2/10A– SAFE-400– SP-100
• Radiates thermal energy into space via finned heat pipes
MSR Group, 12/3/2004Slide 37Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Concept Choices
• Heat pipes
• Continuous panel
• Carbon-Carbon composites
• One-sided operation
MSR Group, 12/3/2004Slide 38Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Component Design
• Heat pipes– Carbon-Carbon
shell– Nb-1Zr wick– Potassium fluid
• Panel– Carbon-Carbon
composite– SiC coating
Exterior of Panel
Thermal Radiation
Heat PipeVapor
Channel3 mm5 mm
MSR Group, 12/3/2004Slide 39Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Component Design (2)
• Supports– Titanium beams
• 8 radial beams• 1 spreader bar
per radial beam
– 3 rectangular strips form circles inside the cone
Core
Radiator Panel
1.5 m
1.25 m
Support Anchor 6.54°
Strips
MSR Group, 12/3/2004Slide 40Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Structural Design
• Dimensions– Conical shell around the core– Height 3.34 m– Diameter 4.8 m– Area 41.5 m2
• Mass– Panel 360 kg– Heat pipes 155 kg– Supports 50 kg– Total 565 kg
Core & Shield
2.34 m
0.5 m 0.5 m
0.60 m
2.4 m
2.97 m
Radiator Panel
Heat Pipe
0.918 m
MSR Group, 12/3/2004Slide 41Nuclear Science and Engineering Department
Massachusetts Institute of Technology
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)
Radi
ator
Are
a (m
2 )
Analysis: Models
• Models– Isothermal– Linear Condenser
• Variables– Power– Sky temperature– Emissivity– Panel width
940 K
25 m2
MSR Group, 12/3/2004Slide 42Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Analysis (2): Temperature
• Condenser model– Calculate sensible and latent heat loss– Length dependent on flow rate
Temperature (K)
Length (m)
950
9401 2
945 K
940 K
MSR Group, 12/3/2004Slide 43Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Analysis (3): Dust
• Dust Buildup– SiO2 dust has small
effect on Carbon-Carbon emissivity
– 5% emissivity loss predicted for 5 yrs
– Emissivity loss increases required area by 2 m2
Radiator Area with 0.85 Base Emissivity
0
2
4
6
8
10
39 40 41 42 43 44
Radiator Area (m2)
% E
mis
sivi
ty L
oss
Moon Mars
MSR Group, 12/3/2004Slide 44Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding
MSR Group, 12/3/2004Slide 45Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding - Design Concept
• Natural dose rate on Moon & Mars is ~14 times higher than on Earth
• Goal: – Reduce dose rate due
to reactor to between 0.6 - 5.6 mrem/hr
• 2mrem/hr– ALARA
• Neutrons and gamma rays emitted, requiring two different modes of attenuation
MSR Group, 12/3/2004Slide 46Nuclear Science and 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 47Nuclear Science and 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 48Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding - Dose w/o shielding
• Near core, dose rates can be very high• Most important components are gamma and neutron radiation
Dose (mrem/hr)
Distance (m)
20
10
2
1000500 2000
MSR Group, 12/3/2004Slide 49Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding - Neutrons
Possible; heavy, needs comparison w/ other optionsB4CAl
Brittle; would not tolerate launch wellB
Melting point of 953 K LiH
Too reactiveLi
Too heavyH2O
Reason for RejectionMaterial
• Boron Carbide (B4C) was chosen as the neutron shielding material after ruling out several options
MSR Group, 12/3/2004Slide 50Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding - Neutrons (3)
• Boron burnup is a resolvable issue
0
2
4
6
8
10
12
14
16
18
20
5 10 15 20 25 50 75 100 125 150 175 200 225 250meters
Dose after 5 years ofoperation
Dose at 0 years ofoperation
MSR Group, 12/3/2004Slide 51Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding - Gammas
Smaller mass attenuation coefficients than alternativesHf, Ta
ReactiveOs
Difficult to obtain in large quantitiesRe, Ir
Not as good as tungsten, and have low melting pointsPb, Bi
Unstable nucleiZ > 83
Too small density and/or mass attenuation coefficientZ < 72
Reason for RejectionMaterial
• Tungsten (W) was chosen as the gamma shielding material after ruling out several options
MSR Group, 12/3/2004Slide 52Nuclear Science and 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– at 200 kW(e) mass is
2.19 metric tons– at 50 kW(e), mass is
1.78 metric tons
MSR Group, 12/3/2004Slide 53Nuclear Science and 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 54Nuclear Science and Engineering Department
Massachusetts Institute of Technology
• Using a shadow shield requires implementation of exclusion zones:
• Unshielded Side:– 32 rem/hr - 14 m – 2.0 mrem/hr - 1008 m – 0.6 mrem/hr - 1841 m
• Shielded Side:– 32 rem/hr - inside shield– 400 mrem/hr – at shield
boundary– 2.0 mrem/hr - 11 m – 0.6 mrem/hr - 20 m
Shielding - Design (3)
core
MSR Group, 12/3/2004Slide 55Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding – Future Extensions
• 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 56Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding – Future Extensions (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
Distance (m)
Thickness (cm)
40
10
60 80 100
MSR Group, 12/3/2004Slide 57Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Summary
MSR Group, 12/3/2004Slide 58Nuclear Science and Engineering Department
Massachusetts Institute of Technology
MSR Assembly Sketches
MSR Group, 12/3/2004Slide 59Nuclear Science and Engineering Department
Massachusetts Institute of Technology
MSR Assembly Sketches (2)
MSR Group, 12/3/2004Slide 60Nuclear Science and Engineering Department
Massachusetts Institute of Technology
MSR Mass
Component Mass (kg)Core 4310PCU 1385Radiator 565Shielding 1975Total 8235
Bottom Line: ~82g/We
MSR Group, 12/3/2004Slide 61Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Mass Reduction and Power Gain
• Move reactor 2km away from people– Gain 500kg from extra transmission lines– Lose almost 2MT of shielding
• Use ISRU plant as a thermal sink– Gain potentially 900kWth– Gain mass of heat pipes to transport heat to ISRU
(depends on the distance of reactor from plant)– Lose 565kg of Radiator Mass
Bottom Line: ~67 g/We
MSR Group, 12/3/2004Slide 62Nuclear Science and Engineering Department
Massachusetts Institute of Technology
MSR Mission Plan
• Build and Launch– Prove Technology on Earth
• Earth Orbit Testing– Ensure the system will function for ≥ 5EFPY
• Lunar / Martian Landing and Testing– Post Landing Diagnostics
• Startup• Shutdown
MSR Group, 12/3/2004Slide 63Nuclear Science and 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
MSR Group, 12/3/2004Slide 64Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Additional Slides
MSR Group, 12/3/2004Slide 65Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Future Work – Core
• 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 66Nuclear Science and Engineering Department
Massachusetts Institute of Technology
MSR Fuel Pin Sketch
MSR Group, 12/3/2004Slide 67Nuclear Science and Engineering Department
Massachusetts Institute of Technology
MSR Core Top View
MSR Group, 12/3/2004Slide 68Nuclear Science and Engineering Department
Massachusetts Institute of Technology
180Hf Cross Section
MSR Group, 12/3/2004Slide 69Nuclear Science and Engineering Department
Massachusetts Institute of Technology
NatHf Cross Section
MSR Group, 12/3/2004Slide 70Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Radiological Hazard Mitigation
Hafnium Core VesselSplashdown Inadvertent Criticality
Inventory Reactivity Contribution Was Determined to be Negligible
Reentry Dispersal of Inventory
Use of Nuclear Safe OrbitOrbital Diagnostic Testing
Operational Procedures, Appropriate facilities and equipment
Pre-Launch and Launch
Mitigation StrategyHazard During
Radiological Hazards need not limit utilization of nuclear power in space!
MSR Group, 12/3/2004Slide 71Nuclear Science and 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 72Nuclear Science and Engineering Department
Massachusetts Institute of Technology
PCU – Decision Methodology
28.5126.5523.77Total
133Inlet Temperature
222Proven System
321Single Point Failure
132Radiation Resistant
321Moving Parts
High Reliability and Limited Maintenance - 1.00
222Controllable - 1.14
333Fits in rocket
321Robust to forces of launch
Launchable/Accident Safe - 1.13
111Peripheral Systems (i.e. Heat Exchangers, A to D converter)
333Outlet Temperature
312Actual PCU
Small Mass and Size (Cost) - 1.35
ThermionicsSterlingBrayton
MSR Group, 12/3/2004Slide 73Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Solid-State vs. Dynamic PCU
Power vs. Mass for Different PCU Options
0
10
20
30
40
50
60
70
80
0 200 400 600 800 1000 1200
Power (kWe)
Mas
s (M
T)
thermionics
stirling
• Stirling Assumptions:– At 100kWe, operating
at 10% efficiency– 4MT net gain in PCU
• Heat exchanger• 4x 800kg engines
– 1MT gain in radiator– Scales with gain in
efficiency, also gains radiator mass.
MSR Group, 12/3/2004Slide 74Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Solid State v. Dynamic (2)
54.270.81 MWe
20.228.8400 kWe
16.221300 kWe
14.214.4200 kWe
13.28.2100 kWe
SterlingThermionics
MSR Group, 12/3/2004Slide 75Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Radiator Future Work
• Analysis of transients
• Model heat pipe operation
• Conditions at landing site
• Manufacturing
MSR Group, 12/3/2004Slide 76Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Analysis (3): Location
• Environment– Moon closer to
sun, but has no atmosphere
• Comparative Area– Moon 39.5 m2
– Mars 39 m2
Radiator Area for Three Power Levels
30
40
50
60
70
80
90
0 100 200 300 400 500 600 700 800
Tinf (K)
Are
a (m
2 )
800 kW 900 kW 1000 kW
MSR Group, 12/3/2004Slide 77Nuclear Science and 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 78Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Radiation Interactions with Matter
• Charged Particles (α, β)– Easily attenuated– Will not get past core reflector
• Neutrons– Most biologically hazardous– Interacts with target nuclei – Low Z material needed
• Gamma Rays (Photons)– High Energy (2MeV)– Hardest to attenuate– Interacts with orbital electrons and nuclei– High Z materials needed
MSR Group, 12/3/2004Slide 79Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding - Dose Modeling
• Dose distance dependence is modeled as: – r0/r for r < 2 r0
– A* (r0/r) + B * (r0/r)2 for 2 r0 < r < 10 r0
– (r0/r)2 for r > 10 r0where r0 = core radius,A = -1/8 and B = 9/4
MSR Group, 12/3/2004Slide 80Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding - Neutrons (2)
0.03573.57*10421.1Boron Carbide (B4C)
0.04274.28*10422.7Borated Graphite (BC)
0.12421.24*10520.3Boral (B4CAl)10.292.40*107N/AUnshielded
Dose rate at 10 m
(mrem/hr)
Dose Rate at shielding
edge (mrem/hr)
Maximum thickness for 1 MT
shield (cm)
Material
MSR Group, 12/3/2004Slide 81Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Shielding - Gammas (2)
480.0010.6W
599.8819.4Bi
594.6617.1Pb
2.51*106N/AUnshielded
Dose rate at 90 cm (mrem/hr)
Maximum thickness for 3 MT shield (cm)
Material
MSR Group, 12/3/2004Slide 82Nuclear Science and Engineering Department
Massachusetts Institute of Technology
MSR Cost
• Rhenium Procurement and Manufacture
• Nitrogen-15 Enrichment• Hafnium Procurement
MSR Group, 12/3/2004Slide 83Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Mass Comparison
54
SP-100(100kWe)
2567082Specific Mass (g/We)
SAFE-400(100kWe)
SNAP-10A(650We)
MSR(100kWe)
MSR Group, 12/3/2004Slide 84Nuclear Science and Engineering Department
Massachusetts Institute of Technology
Motivation for Mars
• “We need to see and examine and touch for ourselves”
• “…and create anew generation of innovators and pioneers.”