Tungsten
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Tungsten

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@bout wolfram W [tungsten]

@bout wolfram W [tungsten]

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Tungsten Tungsten Presentation Transcript

  • Rohan Chakraborty Indus world school Raipur [C.G]
  • Failings of Previous Fuel Types
    • Brittleness of materials
      • Engine vibrations cracked the fuel apart
      • Thermal instability, cracking, and coefficient of thermal expansion
    • Hydrogen erosion of carbide fuels at high temperatures
      • Carbide coatings provided insufficient protection
    • Loss of fission products in exhaust
  • Cladding Failure of Early NTR Designs
  • Fuel Endurance
  • Tungsten Cermet
    • Hot hydrogen compatibility
    • Better thermal conductivity
    • Potential for long life reactors
      • High melting point (~3700 K)
      • Resistance to creep at high temperatures
    • Smaller reactor core then carbide fuels
    • Good radiation migration properties
    • “ Cladding” from same metallic material
      • Contains fission products and uranium oxide in fuel
    • More radiation resistant than carbon
    W
  • Lifetime of Cermet Fuels
    • Not limited by erosion of tungsten-cermet fuels
    • Actual limitation
      • Quantity of nuclear material
      • Integrity of non-nuclear rocket components
      • Poison buildup
      • Possible space-cold effects (ductile to brittle transition)
      • Operation temperature (max I sp of ~950 s)
  • Future of Cermet Fuel
    • Bi-modal design for power production
    • Reusable nuclear rocket engines
      • Orbital/Space Station refueling
      • LANTR (LOX-Augmented NTR) concept
    • Develops technology for high performance fission surface power
    • Fuel and engine testing would enable Mars missions and beyond
  • Fuel Additives
    • Tungsten compatible materials
      • Provide desirable mechanical properties
        • Reduce brittleness, improve toughness
        • Adjust ductile to brittle transition
      • Stabilizers
        • Decrease fission product migration
        • Reduce UO 2 fuel inventory
    • Candidate materials
      • Examples: Re, Mo, ThO 2 , Gd 2 O 3
  • Cross Section (Probability)
    • Various modifiers
      • Particle energy
      • System temperature
      • Target atom
    • Types of interactions
      • Scattering
        • Elastic
        • Inelastic
      • Capture
        • Absorption
        • Fission
  • Fission Cross Section
  • Design Benefits of a Fast Reactor
    • Greater power density
    • Lighter core design than thermal reactors
    • Burn-up of transuranics generated in the reactor
    • Reflectors instead of moderating material
    • Fast reactors can be controlled using the reflector systems with control drums
  • Maintaining Thermal Subcriticality
    • Boron-carbide control drums absorb excess neutrons
    • Melting of the core would put it in a non-critical state
    • Loss of the beryllium reflector ensures the reactor cannot go critical
    • Addition of tungsten and rhenium absorb neutrons at the thermal energies 4 to 5 orders of magnitude greater than carbon
  • Thermal Poison: Rhenium-187
  • Fuel Element Design (Past & Present) 19-Hole Design (2 mm) 5-Fin Design (3 mm) Dumbo Design
  • Cooling the Reactor System
  • Accident Scenarios for Homogenous Core Design  k = 0.003 k is normalized to critical configuration Configuration k eff Basic Core Criticality -- Boron Drums Closed 0.931 Bare Core 0.696 Configuration k eff Reflectors w/ Drums Closed -- Freshwater 0.977 Seawater* 0.976 Dry Sand 0.985 Fused Silica (Dry, 5-m) 0.995 Wet (Freshwater) Sand 0.986 Wet (Seawater) Sand* 0.983 Configuration k eff Without Reflectors -- Freshwater 0.955 Seawater* 0.926 Dry Sand 0.980 Fused Silica (Dry, 5-m) 1.065 Wet (Freshwater) Sand 1.000 Wet (Seawater) Sand* 0.985
  • Rocket Operation Parameters
    • Single Reactor
    • Specific Impulse = 850 s
    • Thrust = 150 kN (34 klbf)
    • Temperature = 2300 – 2500 K
    • Hydrogen Flow Rate = 18.0 kg/s
    • Thermal Power = 650 MW
    • Cermet: W-Re(6.5 w/o)-UO 2 (60 v/o, 93% HEU)
  • Specific Impulse Comparison
  • Reactor Controls
    • Requires semiautonomous controls
    • Requires knowledge of real-time status
      • Neutron or gamma flux
      • Power level
      • Dose
      • Temperature
      • Propellant flow
      • Strain/deformation
  • Measuring Flux, Power, and Dose
    • Direct detection
      • Requires detector to differentiate between neutrons and gammas
      • Gamma detectors
        • Correlated to neutron flux and power level
    • Indirect detection
      • Neutron thermometer
        • Interpolation from temperature gradient information
      • Gamma thermometer
        • Only viable candidate for in-core detection
  • Temperature Measurements
    • Require temperature profile of core, propellant, and fuel elements
    • Thermocouples can function in high temperature, high radiation environments
    • Fiber Bragg Gratings as developed by Luna Innovations deal with relatively high temperatures (~1100 °C) and high dose (8.7 x 10 8 Gy gamma)
    • Higher temperatures use platinum-rhodium and tungsten-rhenium thermocouples (>2700 K) but decalibrate with neutron exposure
      • Johnson noise thermometry
        • Mean kinetic energy of atomic ensemble
        • Needs preamplifier electronic development
  • Propellant Flow
    • Flow from storage tanks
    • Flow through turbomachinery
    • Propellant flow necessary for rocket thrust
    • Also necessary for cooling non-fuel reactor components to prevent damage
    • Extensive modeling available through programs such as FLUENT
  • Strain/Deformation
    • Important for k eff – expansion yields negative reactivity and contraction yields positive reactivity
    • In ground vacuum chamber testing, can use CCD camera to measure
    • Gleeble testing of components
    • Luna Innovation’s fiber optics can also measure strain – only tested at low temperatures
  • Nuclear Dosimetry using MCNP5
    • Turbomachinery – SS
      • Neutron
        • 1.2 ± 0.3x10 9 cm -2 *s -1
        • 2.1 ± 0.4x10 4 rem*hr -1
      • Photon
        • 3.4 ± 0.3x10 9 cm -2 *s -1
        • 6.8 ± 0.7x10 3 rem*hr -1
    • Payload – H 2 O
      • Neutron
        • 0
      • Photon
        • 0
    ZH 2
  • Summary
    • Tungsten-Cermet fuels demonstrate potential for long-lived, high Isp, nuclear rockets with high-integrity containment of uranium and fission products
    • Fuels development and testing necessary to confirm potential of tungsten-cermet fuels in reactors for NTRs
    W