A Radiatively Cooled A Radiatively Cooled ADS Beam WindowADS Beam Window

Caroline Mallary, Physics MQPCaroline Mallary, Physics MQP

20072007

What is ADS?What is ADS?

AAccelerator ccelerator DDriven riven SSystemystem– A means of transmuting A means of transmuting

nuclear waste, ornuclear waste, or– A new type of fission A new type of fission

reactor, orreactor, or– BothBoth

Runs on a sub-critical Runs on a sub-critical pile: reaction cannot run pile: reaction cannot run awayaway

Can be designed to burn Can be designed to burn existing nuclear wasteexisting 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)

What is ADS?What is ADS? How?How?

– Some of the Some of the “afterheat” of spent “afterheat” of spent nuclear fuel can be nuclear fuel can be captured in a power captured in a power generator, instead of generator, instead of a mountaina mountain Goal is 95% of MA & Goal is 95% of MA &

LLFPs transmutedLLFPs transmuted 250 kg/300 days250 kg/300 days

– But, reaction needs a But, reaction needs a catalystcatalyst

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)

The ConceptThe Concept

Proton accelerator creates neutrons by Proton accelerator creates neutrons by spallatingspallating high-Z target nuclei (smashing them to bits)high-Z target nuclei (smashing them to bits)

Spallation neutrons used to maintain fission Spallation neutrons used to maintain fission reaction where not normally possiblereaction where not normally possible– Subcritical pilesSubcritical piles– In waste actinidesIn waste actinides– Chain reaction can’t exist w/o accelerator: To stop, just Chain reaction can’t exist w/o accelerator: To stop, just

unplug itunplug it

Some FacilitiesSome Facilities Current generation of Current generation of

experiments focus on experiments focus on spallationspallation– J-PARC’s TEF is planning J-PARC’s TEF is planning

work with U, Pu, and minor work with U, Pu, and minor actinidesactinides

Experimental FacilitiesExperimental Facilities– Oak Ridge Nat’l Oak Ridge Nat’l

Laboratories, Tennessee Laboratories, Tennessee (SNS, April 2006 [sns.gov])(SNS, April 2006 [sns.gov])

– J-PARC, Japan (TEF, J-PARC, Japan (TEF, October 2006 [j-parc.jp])October 2006 [j-parc.jp])

– SINQ, Switzerland SINQ, Switzerland (MEGAPIE, August 2006 (MEGAPIE, August 2006 [megapie.web.psi.ch])[megapie.web.psi.ch])

A ProblemA Problem

Proton accelerator is BIGProton accelerator is BIG– ~1 GeV protons needed for spallation~1 GeV protons needed for spallation– Proton fluences >10Proton fluences >101414 /s /cm /s /cm22 needed to make power needed to make power

generation practicalgeneration practical– That kind of radiation can damage any material, besides That kind of radiation can damage any material, besides

which…which…– This beam melts most things you put in front of itThis beam melts most things you put in front of it

Accelerator needs to be kept at high vacuum Accelerator needs to be kept at high vacuum (<10(<10-9-9 atm) atm)– How do you make the window that the beam How do you make the window that the beam

comes out of?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)

One SolutionOne Solution

Liquid-metal coolingLiquid-metal cooling– Mercury or Lead-Bismuth Mercury or Lead-Bismuth

Eutectic targets, in direct contact Eutectic targets, in direct contact with windowwith window Liquid metal removes heat fastLiquid metal removes heat fast Can be used to cool core as wellCan be used to cool core as well Flows: no accumulated radiation Flows: no accumulated radiation

damagedamage Most popular designMost popular design

– Direct contact with target Direct contact with target damages windowdamages window CorrosiveCorrosive Pulsed beams cause shock-waves Pulsed beams cause shock-waves

and pitting … dT/dt ~ 10and pitting … dT/dt ~ 1077 K/s!* 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)

Other SolutionsOther Solutions

Windowless designWindowless design– Liquid metal can evaporate into accelerator Liquid metal can evaporate into accelerator

vacuumvacuum Multiple beamsMultiple beams

– Reduces power needed per beamReduces power needed per beam Gas-cooled windowGas-cooled window

– Much more difficult to cool than with liquid metalMuch more difficult to cool than with liquid metal– Core should have separate, passive liquid cooling Core should have separate, passive liquid cooling

systemsystem Radiative coolingRadiative cooling

– Window must be thin & stable at high temperaturesWindow must be thin & stable at high temperatures

Radiative CoolingRadiative Cooling

Thicker window Thicker window greater greater heat deposition by beamheat deposition by beam

Window melts if it receives Window melts if it receives more heat than it can more heat than it can radiate awayradiate away

High temperatures & long-High temperatures & long-term stresses weaken term stresses weaken metalsmetals

To radiate, must have: To radiate, must have: Window Equilibrium Temperature > Ambient Window Equilibrium Temperature > Ambient TemperatureTemperature

Thinner window Thinner window higher stress for higher stress for same ambient pressuresame ambient pressure

It’s an Optimization Problem

Alloy bases examined:Alloy bases examined:

WantWant– Maximal proton fluxMaximal proton flux– Window strong enough Window strong enough

Assume must hold back 1 Assume must hold back 1 atmatm

– Heating by Beam = Power Heating by Beam = Power Emitted Emitted Temperature remains Temperature remains

constantconstant– Good radiation tolerance Good radiation tolerance

Experiments neededExperiments needed Some calculations possibleSome calculations possible

Material InvestigationMaterial Investigation

Aluminum Chromium Zirconium TantalumTitanium Iron Niobium

TungstenVanadium Nickel Molybdenum Rhenium

For each material there is an ideal thickness & operating temperatureFor each material there is an ideal thickness & operating temperature

Material Properties ConsideredMaterial Properties Considered– Tensile Strength = Tensile Strength = f f (T, t)(T, t)– Electronic Stopping Power Electronic Stopping Power DensityDensity

( MeV( MeV cmcm22/g ) /g ) (g/cm(g/cm33) = MeV/cm of thickness) = MeV/cm of thickness

– Oxidation ResistanceOxidation Resistance– Emissivity reviewed but Emissivity reviewed but not not usedused

Assume is feasible to blacken to 90% of BlackbodyAssume is feasible to blacken to 90% of Blackbody

ProcedureProcedure– Literature ReviewLiterature Review– Lots of SpreadsheetsLots of Spreadsheets– Irradiation experiment (to be completed)Irradiation experiment (to be completed)

Material InvestigationMaterial Investigation

Sample Spreadsheet* : For V-40Ti-5Al-0.5CSample Spreadsheet* : For V-40Ti-5Al-0.5CDensity = 5.3 g/cc; Stopping Power = 1.62 MeV cmDensity = 5.3 g/cc; Stopping Power = 1.62 MeV cm22 /g; /g;Ambient Pressure = 1 atm; Ambient Temp = 300 K; Window Radius = 10 Ambient Pressure = 1 atm; Ambient Temp = 300 K; Window Radius = 10 cmcm

Material InvestigationMaterial Investigation

TemperaturTemperature (K)e (K)

UTS (MPa):UTS (MPa):

100-hr rupture100-hr ruptureTotal Emitted Total Emitted Power (W)Power (W)

Center Center Thickness 4 Thickness 4 safety (mm)safety (mm)

Flux/cmFlux/cm2 2 at at CenterCenter

673673 920920 632632 0.0150.015 1.0 1.0 10 101515

773773 772772 11191119 0.0180.018 1.5 1.5 10 101515

873873 283283 18361836 0.0480.048 8.9 8.9 10 101414 Window is 1.5Window is 1.5 as thick at edge, hemispherical as thick at edge, hemispherical Beam is continuous, not pulsedBeam is continuous, not pulsed Beam profile is adjusted so that heating is even across windowBeam profile is adjusted so that heating is even across window

Total Proton Flux = (Flux/cmTotal Proton Flux = (Flux/cm22 at Center) at Center) (314 cm (314 cm22) ) 0.519 0.519

*Data Source: Rostoker. *Data Source: Rostoker. The Metallurgy of Vanadium,The Metallurgy of Vanadium, 1958 1958

Low TemperatureLow Temperature– Can be run in airCan be run in air____________________________________________________________

Best MaterialsBest Materials RefractoryRefractory

– Higher flux possibleHigher flux possible– May anneal rad. May anneal rad.

damagedamage– Harder to blacken?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.

Best MaterialsBest Materials

MaterialMaterial Max total Max total flux flux

(p / s), [mA](p / s), [mA]

ThicknesThickness (mm)s (mm)

Op.TemOp.Temp (C)p (C)

Safety factor; max Safety factor; max lifetime data foundlifetime data found

1. Moly-TZM1. Moly-TZM 1.3 101.3 101818 [200][200]

0.0360.036 13161316 4; 100-hr rupture, 4; 100-hr rupture, but v. stable (NASA)but v. stable (NASA)

2. W-ThO2. W-ThO22 1.5 101.5 1018 18

[240][240]0.0100.010 10931093 2; 1,000-hr rupture2; 1,000-hr rupture

3. Inconel-3. Inconel-718718

4.6 104.6 101717 [73] [73] 0.0120.012 650650 4; none given4; none given

4. Udimet 4. Udimet 901901

4.5 104.5 101717 [70] [70] 0.0130.013 649649 2; 1,000-hr rupture2; 1,000-hr rupture

5. V-40Ti-5. V-40Ti-5Al-0.5C5Al-0.5C

2.4 102.4 1017 17 [39][39] 0.0180.018 500500 4; 100-hr rupture4; 100-hr rupture

6. 31HT 6. 31HT SteelSteel

1.8 101.8 101717 [28] [28] 0.0250.025 595595 1; 100,000-hr 1; 100,000-hr rupture rupture

7. 316 Steel7. 316 Steel 1.7 101.7 101717 [27] [27] 0.0200.020 538538 1; 10,000-hr 1% 1; 10,000-hr 1% creepcreep

Assume:Assume:– 30 spallation neutrons / proton30 spallation neutrons / proton– 97% critically w/o spallation neutrons97% critically w/o spallation neutrons– 10101717 1-GeV protons/second (16 mA, 16 MW beam) 1-GeV protons/second (16 mA, 16 MW beam)– Beam is 15% power efficientBeam is 15% power efficient

Calculation:Calculation:i.i. 3% free neutrons are from spallation3% free neutrons are from spallationii.ii. (30 n/p) (30 n/p) (10(101717 p/s) / (0.03) = 10 p/s) / (0.03) = 1020 20 free neutrons/sfree neutrons/siii.iii. If 80% of free neutrons cause a 200 MeV fission, then have 1.6 If 80% of free neutrons cause a 200 MeV fission, then have 1.6

10102222 MeV/s. MeV/s.iv.iv. If generation system is 30% efficient have 4.8 If generation system is 30% efficient have 4.8 10102121 MeV/s = 770 MeV/s = 770

MWMWv.v. 770MW - 16 MW/0.15 = 770MW - 16 MW/0.15 = 660 MW plant660 MW plant

Conclusion:Conclusion:– Any of the best window material can be run below max flux and Any of the best window material can be run below max flux and

still sustain a commercial-size power plantstill sustain a commercial-size power plant

Is it Enough?Is it Enough?

Solid target better hereSolid target better here– Would require core redesignWould require core redesign– Can neutron brightness be maintained?Can neutron brightness be maintained?– May still want reactor cooling system to be liquid metalMay still want reactor cooling system to be liquid metal

Window may be meters away from target & coreWindow may be meters away from target & core– Greatly reduces damage from neutrons & gammas, Greatly reduces damage from neutrons & gammas,

but…but…– How do exotic materials respond to proton irradiation How do exotic materials respond to proton irradiation

damage?damage? SpallationSpallation Transmutation Gases (H & He embrittlement)Transmutation Gases (H & He embrittlement) Crystal DamageCrystal Damage 1 1 dpadpa = = 0.40.4S(N)S(N)fluxflux

tt TDE TDE zz

Radiative ADS IssuesRadiative ADS Issues

Some FormulasSome Formulas Heating Temperature Emissivity Level (90% Heating Temperature Emissivity Level (90%

Bb) Bb)

Some FormulasSome Formulas

Load on the windowLoad on the window– Only the part of the window facing outwards Only the part of the window facing outwards

matters…Approximate as a discmatters…Approximate as a disc

Disc approximation works for radiative area, tooDisc approximation works for radiative area, too

Some FormulasSome Formulas

Z =Z = Safety factor x R x Ambient Safety factor x R x Ambient PressurePressure

2 x Strength x 1.52 x Strength x 1.5 Max Flux =Max Flux = Emitted Emitted

. . Density x Stopping Power x Density x Stopping Power x

Thickness x 1.602 x 10Thickness x 1.602 x 10-13-13

SNS ImageSNS Image