Concept and Development Work for the LANL Materials Test Station
Eric PitcherLos Alamos National Laboratory
Presented to:ESS Bilbao Initiative Workshop
17 March 2009
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The Materials Test Station will be a fast spectrum fuel and materials irradiation testing facility
• MTS will be driven by a 1-MW proton beam delivered by the LANSCE accelerator
• Spallation reactions produce 1017 n/s, equal to a 3-MW reactor
fuel moduletarget module
beam mask
backstop
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The MTS target consists of two spallation target sections separated by a “flux trap”
spallation targettest fuel rodletsmaterials sample cans• Neutrons generated through
spallation reactions in tungsten
• 2-cm-wide flux trap that fits 40 rodlets
Beam pulse structure:
16.7 mA
750 µs 7.6 ms
Delivered to: left right left righttarget target target target
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Spatial distribution of the proton flux shows low proton contamination in the irradiation regions
fuels irradiation region
materials irradiation regions
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The neutron flux in the fuels irradiation region exceeds 1015 n/cm2/s and has low spatial gradient
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• Two technologies facilitatea sharp beam edge:– Beam rastering
– Design and testing by Shafer et al. for APT at LANL
– Imaging the beam spot on target– VIMOS by Thomsen et al. for
SINQ at PSI– Imaging methods for SNS under
study by Shea et al. at ORNL
• MTS will rely on rastering plus beam spot imaging to produce a 15-mm-wide beam spot only 4 mm from the irradiation regions
A sharp beam edge is key to maximizing the neutron flux in the irradiation regions
15 mm
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Beam transport system produces a horizontal focus at the target front face
15 mm nominalfootprint width
25 mm widetarget face
Beamletis3 mm horizontal x 8 mm vertical (FWHM)
Vertical slew covers 60 mm nominal footprint height in 750 µsmacro-pulse
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The MTS target is tungsten cooled by liquid lead-bismuth eutectic (LBE)
• Neutron production density is proportional to target mass density– W density = 19.3 g/cc
LBE density = 10.5 g/cc� tungsten diluted by 40vol% coolant outperformsLBE
• MTS maximum coolantvolume fraction is 19%
• Neutron production density with tungsten is 60% greater than for LBE alone
LBE supply plenum
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Target is fabricated through multiple diffusion bonding steps
• Fuel module housing and target sidewalls are T91
• Ta front face and W target plates have 0.1- to 0.2-mm T91 clad diffusion bonded on each face
• Target plates are diffusion bonded to the fuel module and target sidewalls
• No welds are used near the proton beam
Channels for fuel pins
Ta front face
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A tungsten target with heat flux up to 600 W/cm2 can be cooled by water
• For single-phase D2O:
– 10 m/s bulk velocity in 1mm gap (series pressure drop � 5.5 bar)
– Heat transfer coefficient � 5.4 W/cm2-K
– 70 µA/cm2 beam current density on 4.4-mm-thick W plate produces 600 W/cm2 at each cooled face
– At 600 W/cm2, Tsurf�110 ºC above bulk coolant temp
– Tcoolant,inlet = 40 ºC,Tcoolant,exit = 105 ºC,Tsurface.exit = 215 ºC
– Static pressure at inlet is 26 bar to suppress boiling
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An experiment was conducted to validate the target thermal-hydraulic performance
Surface Heat FluxPeak ~600 W/cm2
1 mm x 18 mmFlow Channel
CartridgeHeaters
Copper Test Section
ChannelFlow Rate
10 m/s
Cartridge heaters in tapered copper block will simulate beam spot heat flux
Test Goals:
• Determine single-phase HTC
• Identify plate surface temperature @ 600 W/cm2
• Measure subcooled flow boiling pressure drop
• Investigate effect of plate surface roughness
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Thermal-hydraulic experiments using water coolant confirm heat-transfer correlations
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Experimental results match test data using Handbook heat transfer coefficient
Temperature (°C)
ThermocoupleLocations Water flow
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Heavy water can cool the spallation target, but LBE provides the required higher temperature operation
• LBE coolant offers a number of advantages over water:– Easy to control and monitor fuel clad temperature at 550 ºC– Can accommodate fuel pin bowing and swelling– Very high heat transfer coefficient �parallel flow okay– Liquid to very high temperature �low pressure operation– No risk of tungsten-steam reactions releasing radioactive inventory
• Disadvantages of LBE coolant:– Potentially corrosive at elevated operating temperature (>550 ºC)– Not a liquid at room temperature (piping must have race heaters)– Loop components (pumps, valves, etc.) are more expensive than
for water loops– Polonium release at elevated temperature
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water
LBE temperature is controlled with variable-area,double-wall, shell and tube heat exchangers
100 Tubes0.875” OD
Flowing LBE (primary coolant)Static LBEInlet water manifoldOutlet water manifold
LBE
reservoirgas/vac
LBE level in intermediate annulus sets heat transfer surface area
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LBE-to-water heat exchanger is sufficiently novel as to merit a confirmatory experiment
109 cm
Flowing LBE(primary coolant)
Static LBE
Inlet watermanifold
Outlet watermanifold
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Target lifetime will be limited by damage to the target front face
• Experience base:ISIS (SS316 front face): 3.2×1021 p/cm2 = 10
dpaSINQ (Pb-filled SS316 tubes): 6.8×1021 p/cm2 = 22 dpa
MEGAPIE (T91 LBE container): 1.9×1021 p/cm2 = 6.8 dpaLANSCE A6 degrader (Inconel 718): 12 dpa
• MTS design, annual dose (70µA/cm2 for 4400 hours):(T91-clad tantalum front face): 6.9×1021 p/cm2 = 23 dpa
• Fast reactor irradiations at the tungsten operating temperature (700 ºC) yielded 1.5% swelling at 9.5 dpa
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The MTS would benefit from increased beam power on target
• At 4 MW, the peak fast neutron flux in MTS would be equal that of JOYO
• MTS could meet (at 1.8 MW) or exceed (at 3.6 MW) IFMIF peak damage rates for fusion materials studies
1 MW 1.8 MW 3.6 MW
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Towards higher beam power:Which is better—more energy or more current?
• Above ~800 MeV, target peak power density increases with beam energy
• Addressed by:– Higher coolant volume
fraction for solid targets– Higher flow rate for liquid
metal targets– Bigger beam spot
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• If target lifetime and coolant volume fraction is preserved, higher beam current requires larger beam spot
Towards higher beam power:Which is better—more energy or more current?
1 MW1.8 MW3.6 MW
MTS Beam Footprint on Target
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�pk ~ Ebeam0.8ibeam
0.8
Peak neutron flux goes as Pbeam0.8
ibeam = 1 mA
�pk ~ Ebeam0.8
Ebeam = 0.8 GeV
�pk ~ ibeam0.8
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Summary
• Beam rastering and target imaging are key to the successful realization of high neutron flux in MTS
• A water- or metal-cooled stationary solid target is viable beyond 1 MW– Solid targets have higher neutron production density than liquid
metal targets– Replacement frequency is determined by target front face
radiation damage, and is therefore the same as for a liquid metal target container if the beam current density is the same
– A rotating solid target will have much longer lifetime than stationary targets
• Target “performance” ~ (beam power)0.8
– Does not depend strongly on whether the power increase comes from higher current or higher energy