Martian Surface Reactor Group December 3, 2004

1. Martian Surface Reactor GroupDecember 3, 2004

2. Motivation for Mars • “We need to see and examine and touch for ourselves” • “…and create a new generation of innovators and pioneers.”

3. Motivation for MSR

4. Nuclear Physics/Engineering 101

5. Nuclear Physics/Engineering 101

6. 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

7. MSR Components • Core • Nuclear Components, Heat • Power Conversion Unit • Electricity, Heat Exchange • Radiator • Waste Heat Rejection • Shielding • Radiation Protection

8. 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

9. Habitat Reactor Proposed Mission Architecture

10. CORE

11. Core - Design Concept • Design criteria: • 100 kWe reactor on one rocket • 5 EFPY • Low mass • Safely Launchable • Maintenance Free and Reliable

12. 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

13. Fuel Pin Heatpipe Tricusp Material Core - Pin Geometry • Fuel pins are the same size as the heat pipes and arranged in tricusp design.

14. 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)

15. 88 cm Fuel Pin Reflector and Core Top-Down View 10 cm Reflector Control Drum Reflector 42 cm Fuel Core 10 cm Reflector Zr3Si2 Reflector Total Mass: 2654kg Radial Reflector Core – Reactivity Control • Reflector controls neutron leakage • Control drums add little mass to the system and offer high reliability due to few moving parts

16. Core - Smear Composition

17. Core - Power Peaking

18. Operation over Lifetime BOL keff: 0.975 – 1.027 = 0.052 EOL keff: 0.989 – 1.044 = 0.055

19. 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

20. Launch Accident Results • 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

21. 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

22. 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

23. PCU

24. 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

25. 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

26. 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

27. PCU – Heat Pipes (2) • Possible Limits to Flow • Entrainment • Sonic Limit • Boiling • Freezing • Capillary • Capillary force limits flow:

28. 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

29. PCU – Thermionics Design

30. 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

31. 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

32. PCU – Heat Exchanger to Radiator • Heat Pipe Heat Exchanger

33. 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%

34. PCU – Future Work • Improving Thermionic Efficiency • Material studies in high radiation environment • Scalability to 200kWe and up • Using ISRU as thermal heat sink

35. Radiator

36. Objective • Design a radiator to dissipate excess heat from a nuclear power plant located on the surface of the Moon or Mars.

37. Goals • Small mass and area • Minimal control requirement • Maximum accident safety • High reliability

38. Decision Methodology • Past Concepts • SP-100 • SAFE-400 • SNAP-2 • SNAP-10A • Helium-fed • Liquid Droplet • Liquid Sheet

39. Component Design • Heat pipes • Carbon-Carbon shell • Nb-1Zr wick • Potassium fluid • Panel • Carbon-Carbon composite • SiC coating

40. Structural Design • Dimensions • Height 3 m • Diameter 4.8 m • Area 39 m2 • Mass • Panel 200 kg • Heat pipes 60 kg • Supports 46 kg

41. Support • Supports • Titanium • 8 radial beams • 3 circular strips

42. Analysis • Models • Isothermal • Linear Condenser • Comparative Area • Moon 39 m2 • Mars 38.6 m2

43. Future • Analysis of transients • Model heat pipe operation • Conditions at landing site • Manufacturing

44. Shielding

45. 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

46. Shielding - Constraints • Weight limited by landing module (~2 MT) • Temperature limited by material properties (1800K) Courtesy of Jet Propulsion Laboratory

47. Shielding - Design Choices Neutron shielding Gamma shielding boron 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

48. Shielding - Dose w/o shielding • Near core, dose rates can be very high • Most important component is gamma radiation

49. Shielding - Neutrons

50. Shielding - Neutrons (2)