Testing Options for Nuclear Thermal Propulsion Systems

1
Testing Options for Nuclear Thermal Propulsion
Systems
Presented to Nuclear and Emerging Technologies
for SpaceNETS 2009
James E. Werner Idaho National Laboratory
June 16, 2009
2
NERVA Program

• Four reactor test series to demonstrate
  Basic nuclear technology
• KIWI
• Phoebus
• Pewee-1
• Nuclear Furnace-1
• KIWI, Phoebus, and Pewee-1 open cycle systems
  and exhausted their effluent into the atmosphere
• Nuclear Furnace-1 used an effluent treatment
  system
• Between 1959 and 1972, the Space Nuclear
  Propulsion Office oversaw 23 reactor tests

3
Why Build a Nuclear Rocket?

• Three times the ISP of chemical engines
• its have been shown to be
• Faster
• Reduced Transit times for long stay missions
• Reduced round trip times for short stay missions
  for the same initial mass to low earth orbit
  (IMLEO)
• Cheaper
• Reduced IMLEO requirements for the same mission
  duration
• Greater mission flexibility for VSE Mars (cargo
  and especially piloted) missions with respect to
  departure windows
• Fewer launches required
• Fewer supplies, equipment, power needed
• Better
• One propulsion system capable providing a step
  change capability in meeting many exploration
  mission needs
• Technology within developmental timeframe
• Reduced exposure for manned missions

4
Basic Options

• Ground test with the US
• Ground test remotely (i.e. in an ocean)
• No ground test

5
Elements of a Ground Test Facility

• Facilities
• Containment Building
• Control Building
• Test Cell
• Exhaust Treatment System
• Hydrogen Supply System
• Cold Engine Assembly Building
• Hot Engine Disassembly Building
• other support systems and buildings
• Dependent on size (thrust), thermal power level
  and duration
• NTR engine physical size modestly affects size of
  containment building

6
Test Facility Concepts

• Above Ground Effluent Treatment System (ETS)
• Subsurface Active Filtration of Exhaust (SAFE)
  Test Facility
• Other?

7
Effluent Treatment Systems Needs

• Cooling the hydrogen effluent
• Removing particles from the gas flow stream
• Further reduction of the temperature
• Removing the water and dissolved fission products
  
• Removing the noble gases
• Flaring the exiting hydrogen stream (containing
  no detectable fission products)

8
SNTP Effluent Treatment Systemfor 550 MWt
9
Parametric Estimation of ETS Costs
Cost Factors Based on NTP Thrust Normalized
for 25klbf NTR
10
Subsurface Active Filtration of Exhaust (SAFE)
Test Facility

• Filtration of the engine exhaust using the NTS
  alluvium soil / rock as the holdup and active
  filtration medium
• relies upon the alluvial soil characteristics to
  filter the effluents from the NTR exhaust
• Nozzle exit is sealed at the surface
• Exhaust pressure will drive exhaust and water
  vapor into the porous soil or rock at a rate
  equal to the NTR mass flow
• Could be operated for long periods over a wide
  range of engine thrust levels

11
SAFE Facility Description

• Uses a borehole 8 feet in diameter by 1200 feet
  deep
• Upper 100 feet would be steel encased
• Cooling water would be sprayed into the borehole
  to limit the exhaust temperature
• Maximum back pressure buildup in the borehole
  would be 36 psi
• Independent study by the Desert Research
  Institute (DRI) Some radionuclides would reach
  the surface within several years after injection
  but, at acceptably allowable levels for the NTS

12
Comparison between ETS and SAFE

• ETS
• Pros
• No large quantity of contaminated liquid effluent
  will be generated.
• Altitude simulation may be possible with this
  system.
• A center for ground testing with dedicated test
  facilities could be established for NTP systems
  up to the design rating.
• Performance of the system will be well
  characterized after initial testing.
• Cons
• Large quantities of liquid hydrogen will be
  required for each test.
• Large, complex effluent filtration systems have
  not yet been demonstrated.
• Public acceptance of once through exhaust
  treatment with discharge to the atmosphere may be
  challenging.
• Containment isolation system during abnormal
  events may be complex.

13
Comparison between ETS and SAFE

• SAFE
• Pros
• No active effluent treatment system required.
• Existing boreholes are available.
• Less hydrogen will be required per test.
• Potential for significant costs savings
• Cons
• Further studies could show the need for waste
  coolant water removal and a filtration system.
• Boreholes may have limited reuse capability and
  require relocation of certain GTF assets, (e.g.,
  portable containment structure).
• Monitoring of borehole alluvial soil performance
  during and after testing will be required.

14
Next Steps

• Fuel Development - driving force for the design
  of the effluent treatment system will be the
  integrity of the fuel under normal operating and
  abnormal operating conditions. Limited
  information available as to how much of the
  halogen or noble gases can be retained in the
  fuel (needed for both ETS and SAFE)
• Demonstration of Subsurface Filtration System - a
  subscale proof of concept test is needed
• Gas would be spiked with Krypton-85 to permit
  monitoring of the gas permeation in the alluvial
  soils
• ambient and elevated temperature tests could be
  performed