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

2. What is ADS? Accelerator Driven System 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 by JAERI. From Y. Kurata, T. Takizuka, T. Osugi, H. Takano, JNM 301, 1, (2002)

3. What is ADS? How? 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) 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 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 Current generation of experiments focus on spallation –J-PARC’s TEF is planning work with U, Pu, and minor actinides Experimental Facilities 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 Proton accelerator is BIG –~1 GeV protons needed for spallation –Proton fluences >10 14 /s /cm 2 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) 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 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 ~ 10 7 K/s!* * John R. Haines. Target Systems for the Spallation Neutron Source, PowerPoint (2003) Fig 3. Pitting in an annealed 316LN window (SNS). From J. Hunn, B. Riemer, C. Tsai, JNM 318, pg. 102, (2003)

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

9. Radiative Cooling 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 To radiate, must have: Window Equilibrium Temperature > Ambient Temperature Thinner window  higher stress for same ambient pressure It’s an Optimization Problem

10. Alloy bases examined: Alloy bases examined: Want 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 Material Investigation Material Investigation AluminumChromiumZirconiumTantalum TitaniumIronNiobiumTungsten VanadiumNickelMolybdenumRhenium For each material there is an ideal thickness & operating temperature For each material there is an ideal thickness & operating temperature

11. Material Properties Considered Material Properties Considered –Tensile Strength = f (T, t) –Electronic Stopping Power  Density  ( MeV  cm 2 /g )  (g/cm 3 ) = MeV/cm of thickness –Oxidation Resistance –Emissivity reviewed but not used  Assume is feasible to blacken to 90% of Blackbody Procedure Procedure –Literature Review –Lots of Spreadsheets –Irradiation experiment (to be completed) Material Investigation Material Investigation

12. Sample Spreadsheet* : For V-40Ti-5Al-0.5C Sample Spreadsheet* : For V-40Ti-5Al-0.5C Density = 5.3 g/cc; Stopping Power = 1.62 MeV cm 2 /g; Ambient Pressure = 1 atm; Ambient Temp = 300 K; Window Radius = 10 cm Material Investigation Material Investigation Temperature (K) UTS (MPa): 100-hr rupture Total Emitted Power (W) Center Thickness 4 safety (mm) Flux/cm 2 at Center 6739206320.015 1.0  10 15 77377211190.018 1.5  10 15 87328318360.048 8.9  10 14 Window is 1.5  as thick at edge, hemispherical Window is 1.5  as thick at edge, hemispherical Beam is continuous, not pulsed Beam is continuous, not pulsed Beam profile is adjusted so that heating is even across window Beam profile is adjusted so that heating is even across window Total Proton Flux = (Flux/cm 2 at Center)  (314 cm 2 )  0.519 *Data Source: Rostoker. The Metallurgy of Vanadium, 1958

13. Low Temperature Low Temperature –Can be run in air ______________________________ Best Materials Best Materials Refractory Refractory –Higher flux possible –May anneal rad. damage –Harder to blacken? ______________________________ 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 Best MaterialsMaterial Max total flux (p / s), [mA] Thickness (mm) Op.Temp (C) Safety factor; max lifetime data found 1. Moly-TZM 1.3 10 18 [200] 0.0361316 4; 100-hr rupture, but v. stable (NASA) 2. W-ThO 2 1.5 10 18 [240] 0.0101093 2; 1,000-hr rupture 3. Inconel-718 4.6 10 17 [73] 0.012650 4; none given 4. Udimet 901 4.5 10 17 [70] 0.013649 2; 1,000-hr rupture 5. V-40Ti-5Al- 0.5C 2.4 10 17 [39] 0.018500 4; 100-hr rupture 6. 31HT Steel 1.8 10 17 [28] 0.025595 1; 100,000-hr rupture 7. 316 Steel 1.7 10 17 [27] 0.020538 1; 10,000-hr 1% creep

15. Assume: Assume: –30 spallation neutrons / proton –97% critically w/o spallation neutrons –10 17 1-GeV protons/second (16 mA, 16 MW beam) –Beam is 15% power efficient Calculation: Calculation: i.3% free neutrons are from spallation ii.(30 n/p)  (10 17 p/s) / (0.03) = 10 20 free neutrons/s iii.If 80% of free neutrons cause a 200 MeV fission, then have 1.6  10 22 MeV/s. iv.If generation system is 30% efficient have 4.8  10 21 MeV/s = 770 MW v.770MW - 16 MW/0.15 = 660 MW plant Conclusion: Conclusion: –Any of the best window material can be run below max flux and still sustain a commercial-size power plant Is it Enough? Is it Enough?

16. Solid target better here 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 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 Radiative ADS Issues Radiative ADS Issues

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

18. Some Formulas Load on the window 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 Z = Safety factor x R x Ambient Pressure 2 x Strength x 1.5 2 x Strength x 1.5 Max Flux = Emitted. Max Flux = Emitted. Density x Stopping Power x Thickness x 1.602 x 10 -13 Density x Stopping Power x Thickness x 1.602 x 10 -13

20. SNS Image