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A Radiatively Cooled ADS Beam Window

A Radiatively Cooled ADS Beam Window. Caroline Mallary, Physics MQP 2007. What is ADS?. A ccelerator D riven S ystem A means of transmuting nuclear waste, or A new type of fission reactor, or Both Runs on a sub-critical pile: reaction cannot run away

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A Radiatively Cooled ADS Beam Window

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  1. A Radiatively Cooled ADS Beam Window Caroline Mallary, Physics MQP 2007

  2. What is ADS? • Accelerator Driven System • A means of transmuting nuclear waste, or • A new type of fission reactor, or • Both • Runs on a sub-critical pile: reaction cannot run away • Can be designed to burn existing nuclear waste Fig 1. Concept of a Power & Transmutation system for long-lived radioactive nuclides byJAERI. From Y. Kurata, T. Takizuka, T. Osugi, H. Takano,JNM301, 1, (2002)

  3. What is ADS? • How? • Some of the “afterheat” of spent nuclear fuel can be captured in a power generator, instead of a mountain • Goal is 95% of MA & LLFPs transmuted • 250 kg/300 days • But, reaction needs a catalyst Fig 2. Radioactive power from decay of fission products and actinides. This decay-power results from the waste of 1 mo. of operation of a 1000-MW power plant. Solid curve is the sum of contributions of individual isotopes. From B.L. Cohen, Rev. Mod. Phys 49, 1 (1977)

  4. The Concept • Proton accelerator creates neutrons by spallating high-Z target nuclei (smashing them to bits) • Spallation neutrons used to maintain fission reaction where not normally possible • Subcritical piles • In waste actinides • Chain reaction can’t exist w/o accelerator: To stop, just unplug it

  5. Some Facilities • Current generation of experiments focus on spallation • J-PARC’s TEF is planning work with U, Pu, and minor actinides • Experimental Facilities • Oak Ridge Nat’l Laboratories, Tennessee (SNS, April 2006 [sns.gov]) • J-PARC, Japan (TEF, October 2006 [j-parc.jp]) • SINQ, Switzerland (MEGAPIE, August 2006 [megapie.web.psi.ch])

  6. A Problem • Proton accelerator is BIG • ~1 GeV protons needed for spallation • Proton fluences >1014 /s /cm2 needed to make power generation practical • That kind of radiation can damage any material, besides which… • This beam melts most things you put in front of it • Accelerator needs to be kept at high vacuum (<10-9 atm) • How do you make the window that the beam comes out of? One of the window designs considered for SNS. Note domed central portion. From Proceedings of the Particle Accelerator Conference, ORNL team (2003)

  7. One Solution • Liquid-metal cooling • Mercury or Lead-Bismuth Eutectic targets, in direct contact with window • Liquid metal removes heat fast • Can be used to cool core as well • Flows: no accumulated radiation damage • Most popular design • Direct contact with target damages window • Corrosive • Pulsed beams cause shock-waves and pitting … dT/dt ~ 107 K/s!* Fig 3. Pitting in an annealed 316LN window (SNS). From J. Hunn, B. Riemer, C. Tsai, JNM318, pg. 102, (2003) *John R. Haines. Target Systems for the Spallation Neutron Source, PowerPoint (2003)

  8. Other Solutions • Windowless design • Liquid metal can evaporate into accelerator vacuum • Multiple beams • Reduces power needed per beam • Gas-cooled window • Much more difficult to cool than with liquid metal • Core should have separate, passive liquid cooling system • Radiative cooling • Window must be thin & stable at high temperatures

  9. Radiative Cooling It’s an Optimization Problem Thicker window  greater heat deposition by beam Window melts if it receives more heat than it can radiate away High temperatures & long-term stresses weaken metals Thinner window  higher stress for same ambient pressure • To radiate, must have: • Window Equilibrium Temperature > Ambient Temperature

  10. Material Investigation • Alloy bases examined: • Want • Maximal proton flux • Window strong enough • Assume must hold back 1 atm • Heating by Beam = Power Emitted • Temperature remains constant • Good radiation tolerance • Experiments needed • Some calculations possible Aluminum Chromium Zirconium Tantalum Titanium Iron Niobium Tungsten Vanadium Nickel Molybdenum Rhenium • For each material there is an ideal thickness & operating temperature

  11. Material Investigation • Material Properties Considered • Tensile Strength = f (T, t) • Electronic Stopping Power Density • ( MeVcm2/g ) (g/cm3) = MeV/cm of thickness • Oxidation Resistance • Emissivity reviewed but not used • Assume is feasible to blacken to 90% of Blackbody • Procedure • Literature Review • Lots of Spreadsheets • Irradiation experiment (to be completed)

  12. Material Investigation • Sample Spreadsheet* : For V-40Ti-5Al-0.5C Density = 5.3 g/cc; Stopping Power = 1.62 MeV cm2 /g; Ambient Pressure = 1 atm; Ambient Temp = 300 K; Window Radius = 10 cm • Window is 1.5 as thick at edge, hemispherical • Beam is continuous, not pulsed • Beam profile is adjusted so that heating is even across window Total Proton Flux = (Flux/cm2 at Center)  (314 cm2)  0.519 *Data Source: Rostoker. The Metallurgy of Vanadium, 1958

  13. Best Materials • Refractory • Higher flux possible • May anneal rad. damage • Harder to blacken? ______________________________ • Low Temperature • Can be run in air ______________________________ Inconel-718 or Udimet 901 (Nickel-based) Vanadium - 40Ti - 5Al - 0.5 C 31HT or 316 Steel Inconel-718 was the best but little data was available: 1 short-time elevated temperature strength and no lifetime data. Used factor of 4 safety in window thickness to compensate Molybdenum TZM Thoriated Tungsten Molybdenum-TZM (Mo-0.5Ti-0.08Zr, Stress-Relieved) has v. good lifetime but should not be run in air at high temperatures.

  14. Best Materials

  15. Is it Enough? • Assume: • 30 spallation neutrons / proton • 97% critically w/o spallation neutrons • 1017 1-GeV protons/second (16 mA, 16 MW beam) • Beam is 15% power efficient • Calculation: • 3% free neutrons are from spallation • (30 n/p) (1017 p/s) / (0.03) = 1020 free neutrons/s • If 80% of free neutrons cause a 200 MeV fission, then have 1.6 1022 MeV/s. • If generation system is 30% efficient have 4.8 1021 MeV/s = 770 MW • 770MW - 16 MW/0.15 = 660 MW plant • Conclusion: • Any of the best window material can be run below max flux and still sustain a commercial-size power plant

  16. Radiative ADS Issues • Solid target better here • Would require core redesign • Can neutron brightness be maintained? • May still want reactor cooling system to be liquid metal • Window may be meters away from target & core • Greatly reduces damage from neutrons & gammas, but… • How do exotic materials respond to proton irradiation damage? • Spallation • Transmutation Gases (H & He embrittlement) • Crystal Damage • 1 dpa = 0.4S(N)flux t TDE  z

  17. Some Formulas • Heating Temperature Emissivity Level (90% Bb)

  18. Some Formulas • Load on the window • Only the part of the window facing outwards matters…Approximate as a disc Disc approximation works for radiative area, too

  19. Some Formulas • Z =Safety factor x R x Ambient Pressure 2 x Strength x 1.5 • Max Flux = Emitted . Density x Stopping Power x Thickness x 1.602 x 10-13

  20. SNS Image

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