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  1. 1. Rohan Chakraborty Indus world school Raipur [C.G]
  2. 2. Failings of Previous Fuel Types <ul><li>Brittleness of materials </li></ul><ul><ul><li>Engine vibrations cracked the fuel apart </li></ul></ul><ul><ul><li>Thermal instability, cracking, and coefficient of thermal expansion </li></ul></ul><ul><li>Hydrogen erosion of carbide fuels at high temperatures </li></ul><ul><ul><li>Carbide coatings provided insufficient protection </li></ul></ul><ul><li>Loss of fission products in exhaust </li></ul>
  3. 3. Cladding Failure of Early NTR Designs
  4. 4. Fuel Endurance
  5. 5. Tungsten Cermet <ul><li>Hot hydrogen compatibility </li></ul><ul><li>Better thermal conductivity </li></ul><ul><li>Potential for long life reactors </li></ul><ul><ul><li>High melting point (~3700 K) </li></ul></ul><ul><ul><li>Resistance to creep at high temperatures </li></ul></ul><ul><li>Smaller reactor core then carbide fuels </li></ul><ul><li>Good radiation migration properties </li></ul><ul><li>“ Cladding” from same metallic material </li></ul><ul><ul><li>Contains fission products and uranium oxide in fuel </li></ul></ul><ul><li>More radiation resistant than carbon </li></ul>W
  6. 6. Lifetime of Cermet Fuels <ul><li>Not limited by erosion of tungsten-cermet fuels </li></ul><ul><li>Actual limitation </li></ul><ul><ul><li>Quantity of nuclear material </li></ul></ul><ul><ul><li>Integrity of non-nuclear rocket components </li></ul></ul><ul><ul><li>Poison buildup </li></ul></ul><ul><ul><li>Possible space-cold effects (ductile to brittle transition) </li></ul></ul><ul><ul><li>Operation temperature (max I sp of ~950 s) </li></ul></ul>
  7. 7. Future of Cermet Fuel <ul><li>Bi-modal design for power production </li></ul><ul><li>Reusable nuclear rocket engines </li></ul><ul><ul><li>Orbital/Space Station refueling </li></ul></ul><ul><ul><li>LANTR (LOX-Augmented NTR) concept </li></ul></ul><ul><li>Develops technology for high performance fission surface power </li></ul><ul><li>Fuel and engine testing would enable Mars missions and beyond </li></ul>
  8. 8. Fuel Additives <ul><li>Tungsten compatible materials </li></ul><ul><ul><li>Provide desirable mechanical properties </li></ul></ul><ul><ul><ul><li>Reduce brittleness, improve toughness </li></ul></ul></ul><ul><ul><ul><li>Adjust ductile to brittle transition </li></ul></ul></ul><ul><ul><li>Stabilizers </li></ul></ul><ul><ul><ul><li>Decrease fission product migration </li></ul></ul></ul><ul><ul><ul><li>Reduce UO 2 fuel inventory </li></ul></ul></ul><ul><li>Candidate materials </li></ul><ul><ul><li>Examples: Re, Mo, ThO 2 , Gd 2 O 3 </li></ul></ul>
  9. 9. Cross Section (Probability) <ul><li>Various modifiers </li></ul><ul><ul><li>Particle energy </li></ul></ul><ul><ul><li>System temperature </li></ul></ul><ul><ul><li>Target atom </li></ul></ul><ul><li>Types of interactions </li></ul><ul><ul><li>Scattering </li></ul></ul><ul><ul><ul><li>Elastic </li></ul></ul></ul><ul><ul><ul><li>Inelastic </li></ul></ul></ul><ul><ul><li>Capture </li></ul></ul><ul><ul><ul><li>Absorption </li></ul></ul></ul><ul><ul><ul><li>Fission </li></ul></ul></ul>
  10. 10. Fission Cross Section
  11. 11. Design Benefits of a Fast Reactor <ul><li>Greater power density </li></ul><ul><li>Lighter core design than thermal reactors </li></ul><ul><li>Burn-up of transuranics generated in the reactor </li></ul><ul><li>Reflectors instead of moderating material </li></ul><ul><li>Fast reactors can be controlled using the reflector systems with control drums </li></ul>
  12. 12. Maintaining Thermal Subcriticality <ul><li>Boron-carbide control drums absorb excess neutrons </li></ul><ul><li>Melting of the core would put it in a non-critical state </li></ul><ul><li>Loss of the beryllium reflector ensures the reactor cannot go critical </li></ul><ul><li>Addition of tungsten and rhenium absorb neutrons at the thermal energies 4 to 5 orders of magnitude greater than carbon </li></ul>
  13. 13. Thermal Poison: Rhenium-187
  14. 14. Fuel Element Design (Past & Present) 19-Hole Design (2 mm) 5-Fin Design (3 mm) Dumbo Design
  15. 15. Cooling the Reactor System
  16. 16. 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
  17. 17. Rocket Operation Parameters <ul><li>Single Reactor </li></ul><ul><li>Specific Impulse = 850 s </li></ul><ul><li>Thrust = 150 kN (34 klbf) </li></ul><ul><li>Temperature = 2300 – 2500 K </li></ul><ul><li>Hydrogen Flow Rate = 18.0 kg/s </li></ul><ul><li>Thermal Power = 650 MW </li></ul><ul><li>Cermet: W-Re(6.5 w/o)-UO 2 (60 v/o, 93% HEU) </li></ul>
  18. 18. Specific Impulse Comparison
  19. 19. Reactor Controls <ul><li>Requires semiautonomous controls </li></ul><ul><li>Requires knowledge of real-time status </li></ul><ul><ul><li>Neutron or gamma flux </li></ul></ul><ul><ul><li>Power level </li></ul></ul><ul><ul><li>Dose </li></ul></ul><ul><ul><li>Temperature </li></ul></ul><ul><ul><li>Propellant flow </li></ul></ul><ul><ul><li>Strain/deformation </li></ul></ul>
  20. 20. Measuring Flux, Power, and Dose <ul><li>Direct detection </li></ul><ul><ul><li>Requires detector to differentiate between neutrons and gammas </li></ul></ul><ul><ul><li>Gamma detectors </li></ul></ul><ul><ul><ul><li>Correlated to neutron flux and power level </li></ul></ul></ul><ul><li>Indirect detection </li></ul><ul><ul><li>Neutron thermometer </li></ul></ul><ul><ul><ul><li>Interpolation from temperature gradient information </li></ul></ul></ul><ul><ul><li>Gamma thermometer </li></ul></ul><ul><ul><ul><li>Only viable candidate for in-core detection </li></ul></ul></ul>
  21. 21. Temperature Measurements <ul><li>Require temperature profile of core, propellant, and fuel elements </li></ul><ul><li>Thermocouples can function in high temperature, high radiation environments </li></ul><ul><li>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) </li></ul><ul><li>Higher temperatures use platinum-rhodium and tungsten-rhenium thermocouples (>2700 K) but decalibrate with neutron exposure </li></ul><ul><ul><li>Johnson noise thermometry </li></ul></ul><ul><ul><ul><li>Mean kinetic energy of atomic ensemble </li></ul></ul></ul><ul><ul><ul><li>Needs preamplifier electronic development </li></ul></ul></ul>
  22. 22. Propellant Flow <ul><li>Flow from storage tanks </li></ul><ul><li>Flow through turbomachinery </li></ul><ul><li>Propellant flow necessary for rocket thrust </li></ul><ul><li>Also necessary for cooling non-fuel reactor components to prevent damage </li></ul><ul><li>Extensive modeling available through programs such as FLUENT </li></ul>
  23. 23. Strain/Deformation <ul><li>Important for k eff – expansion yields negative reactivity and contraction yields positive reactivity </li></ul><ul><li>In ground vacuum chamber testing, can use CCD camera to measure </li></ul><ul><li>Gleeble testing of components </li></ul><ul><li>Luna Innovation’s fiber optics can also measure strain – only tested at low temperatures </li></ul>
  24. 24. Nuclear Dosimetry using MCNP5 <ul><li>Turbomachinery – SS </li></ul><ul><ul><li>Neutron </li></ul></ul><ul><ul><ul><li>1.2 ± 0.3x10 9 cm -2 *s -1 </li></ul></ul></ul><ul><ul><ul><li>2.1 ± 0.4x10 4 rem*hr -1 </li></ul></ul></ul><ul><ul><li>Photon </li></ul></ul><ul><ul><ul><li>3.4 ± 0.3x10 9 cm -2 *s -1 </li></ul></ul></ul><ul><ul><ul><li>6.8 ± 0.7x10 3 rem*hr -1 </li></ul></ul></ul><ul><li>Payload – H 2 O </li></ul><ul><ul><li>Neutron </li></ul></ul><ul><ul><ul><li>0 </li></ul></ul></ul><ul><ul><li>Photon </li></ul></ul><ul><ul><ul><li>0 </li></ul></ul></ul>ZH 2
  25. 25. Summary <ul><li>Tungsten-Cermet fuels demonstrate potential for long-lived, high Isp, nuclear rockets with high-integrity containment of uranium and fission products </li></ul><ul><li>Fuels development and testing necessary to confirm potential of tungsten-cermet fuels in reactors for NTRs </li></ul>W