1. Nuclear Engineering Department Massachusetts Institute of Technology M artian S urface R eactor Group Martian Surface Reactor Group December 3, 2004

2. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 2 OVERVIEW Need for Nuclear Power Fission 101 Project Description Description and Analysis of the MSR Systems –Core –Power Conversion Unit (PCU) –Radiator –Shielding Conclusion

3. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 3 Motivation for MSR

4. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 4 Need for Nuclear Power

5. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 5 Fission 101

6. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 6 MSR Mission Nuclear Power for the Martian Surface –Test on Lunar Surface Design Criteria –100kWe –5 EFPY –Works on the Moon and Mars

7. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 7 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 –Scalability

8. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 8 MSR System Overview Core (54%) –Nuclear Components, Heat Power Conversion Unit (17%) –Electricity, Heat Exchange Radiator (4%) –Waste Heat Rejection Shielding (25%) –Radiation Protection Total Mass ~8MT

9. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 9 CORE

10. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 10 Core – Goals and Components Goals –1.2 MWth –1800K Components –Spectrum –Reactivity Control Mechanism –Reflector –Coolant System –Encapsulating Vessel –Fuel Type/Enrichment

11. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 11 Core - Design Choices Overview Design ChoiceReason Fast Spectrum, High TempHigh Power Density UN Fuel, 33 w / o enriched High Temperature/Breeding Lithium CoolantPower Conversion Re Cladding/Internal StructurePhysical Properties Zr 3 Si 2 Reflector material Neutron “Mirror” Rotating Drums Autonomous Control Hafnium Core VesselAccident Scenario Tricusp Fuel ConfigurationSuperior Heat Transfer

12. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 12 Heatpipe Fuel Pin Tricusp Material Core - Pin Geometry Fuel pins are the same size as the heat pipes and arranged in tricusp design. Temperature variation 1800-1890K

13. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 13 Core – Design Advantages UN fuel, Ta absorber, Re Clad/Structure high melting point, heat transfer, neutronics performance, and limited corrosion Heat pipes pumps not required, excellent heat transfer, small system mass Li working fluid operates at high temperatures necessary for power conversion unit (1800K)

14. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 14 Core – Dimensions and Control Reflector controls neutron leakage Small core, total mass ~4.3 MT Reflector Core Fuel Pin Fuel Reflector 42 cm 89 cm 10 cm Reflector

15. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 15 Core - Composition

16. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 16 Core - Power Peaking

17. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 17 Operation over Lifetime BOL k eff : 0.975 – 1.027 EOL k eff : 0.989 – 1.044 = 0.052 = 0.055

18. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 18 Launch Accident Analysis Worst Case Scenario: –Oceanic splashdown assuming Non-deformed core All heat pipes breached and flooded

19. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 19 Launch Accident Results Reflectors StowedReflectors Detached WaterK eff =0.970K eff =0.953 Wet SandK eff =0.974K eff =0.965 Inadvertent criticality will not occur in any conceivable splashdown scenario

20. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 20 Core Summary UN fuel, Re clad/structure, Hf vessel, Zr 3 Si 2 reflector Relatively flat fuel pin temperature profile 1800-1890K 5+ EFPY of 1.2 MW th, ~100 kW e, at 1800K Autonomous control by rotating drums over entire lifetime Subcritical for worst-case accident scenario Mass : ~4MT

21. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 21 PCU

22. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 22 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

23. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 23 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

24. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 24 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

25. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 25 PCU – Heat Pipes (2) Possible Limits to Flow –Entrainment –Sonic Limit –Boiling –Freezing –Capillary Capillary force limits flow:

26. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 26 PCU - Thermionics Thermionic Power Conversion Unit –Mass: 240 kg –Efficiency: 10%+ 1.2MWt -> 125kWe –Power density: 10W/cm 2 –Surface area per heat pipe: 100 cm 2

27. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 27 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 T E = 1800K, T C = 950K

28. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 28 PCU – Thermionics Design

29. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 29 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

30. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 30 PCU – Heat Exchanger to Radiator Heat Pipe Heat Exchanger

31. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 31 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%

32. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 32 Radiator

33. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 33 Objective Dissipate excess heat from a power plant located on the surface of the Moon or Mars.

34. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 34 Environment Moon –1/6 Earth gravity –No atmosphere –1360 W/m 2 solar flux Mars –1/3 Earth gravity –1% atmospheric pressure –590 W/m 2 solar flux

35. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 35 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

36. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 36 Component Design Heat pipes –Carbon-Carbon shell –Nb-1Zr wick –Potassium fluid Panel –Carbon-Carbon composite –SiC coating

37. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 37 Component Design (2) Supports –Titanium beams 8 radial beams 1 spreader bar per radial beam –3 rectangular strips form circles inside the cone

38. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 38 Structural Design Dimensions –Conical shell around the core –Height 3.34 m –Diameter 4.8 m –Area 41.5 m 2 Mass –Panel 360 kg –Heat pipes 155 kg –Supports 50 kg –Total: 565 kg

39. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 39 Shielding

40. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 40 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

41. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 41 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

42. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 42 Shielding - Constraints Weight limited by landing module (~2 MT) Temperature limited by material properties (1800K) Courtesy of Jet Propulsion Laboratory

43. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 43 Shielding - Design Choices Neutron shielding Gamma shielding boron carbide (B 4 C) shell (yellow) Tungsten (W) shell (gray) 40 cm12 cm Total mass is 1.97 MT Separate reactor from habitat –Dose rate decreases as 1/r 2 for r >> 50cm - For r ~ 50 cm, dose rate decreases as 1/r

44. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 44 Shielding - Dose w/o shielding Near core, dose rates can be very high Most important components are gamma and neutron radiation

45. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 45 Shielding - Neutrons MaterialReason for Rejection H2OH2OToo heavy LiToo reactive LiHMelting point of 953 K BBrittle; would not tolerate launch well B 4 CAlPossible; heavy, needs comparison w/ other options Boron Carbide (B 4 C) was chosen as the neutron shielding material after ruling out several options

46. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 46 Shielding - Neutrons (3) One disadvantage: Boron will be consumed over time

47. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 47 Shielding - Gammas MaterialReason for Rejection Z < 72 Too small density and/or mass attenuation coefficient Z > 83 Unstable nuclei Pb, Bi Not as good as tungsten, and have low melting points Re, Ir Difficult to obtain in large quantities Os Reactive Hf, Ta Smaller mass attenuation coefficients than alternatives Tungsten (W) was chosen as the gamma shielding material after ruling out several options

48. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 48 Shielding - Design Two pieces, each covering 40º of reactor radial surface Two layers: 40 cm B 4 C (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

49. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 49 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

50. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 50 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

51. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 51 MSR Assembly Sketch

52. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 52 MSR Mass Bottom Line: ~82g/We

53. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 53 Mass Reduction and Power Gain 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 potentially 900kWth –Gain mass of heat pipes to transport heat to ISRU (depends on the distance of reactor from plant) –Loose 515kg of Radiator Mass Bottom Line: ~60g/We

54. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 54 MSR Mission Plan Build and Launch –Prove Technology on Earth Earth Testing –Ensure the system will function for ≥ 5EFPY Lunar / Martian Landing and Testing –Post Landing Diagnostics Startup Shutdown

55. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 55 MSR Group Expanding 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

56. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 56 Additional Slides

57. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 57 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

58. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 58 PCU – Decision Methodology BraytonSterlingThermionics Small Mass and Size (Cost) - 1.35 Actual PCU213 Outlet Temperature333 Peripheral Systems (i.e. Heat Exchangers, A to D converter)111 Launchable/Accident Safe - 1.13 Robust to forces of launch123 Fits in rocket333 Controllable - 1.14222 High Reliability and Limited Maintenance - 1.00 Moving Parts123 Radiation Resistant231 Single Point Failure123 Proven System222 Inlet Temperature331 Total23.7726.5528.51

59. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 59 PCU – Future Work Improving Thermionic Efficiency Material studies in high radiation environment Scalability to 200kWe and up Using ISRU as thermal heat sink

60. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 60 Radiator Future Work Analysis of transients Model heat pipe operation Conditions at landing site Manufacturing

61. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 61 Analysis Models –Isothermal –Linear Condenser Comparative Area –Moon 39.5 m 2 –Mars 39 m 2

62. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 62 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.

63. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 63 Shielding - Alternative Designs Three layer shield –W (thick layer) inside, B 4 C middle, W (thin layer) outside –Thin W layer will stop secondary radiation in B 4 C shield –Putting thick W layer inside reduces overall mass

64. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 64 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

65. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 65 MRS Design Advantages Robustness Redundancy Scalability

66. Nuclear Engineering Department Massachusetts Institute of Technology MSR Group, 12/3/2004 Slide 66 MSR Cost Rhenium Procurement and Manufacture Nitrogen-15 Enrichment Halfnium Procurement