Concept and Development Work for the LANL Materials Test Station

Concept and Development Work for the LANL Materials Test Station

Eric PitcherLos Alamos National Laboratory

Presented to:ESS Bilbao Initiative Workshop

17 March 2009

ESS Bilbao Initiative Workshop 16-18 March 2009 2

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


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


Spatial distribution of the proton flux shows low proton contamination in the irradiation regions

fuels irradiation region

materials irradiation regions


The neutron flux in the fuels irradiation region exceeds 1015 n/cm2/s and has low spatial gradient


• 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


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


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


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


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


Thermal-hydraulic experiments using water coolant confirm heat-transfer correlations


Experimental results match test data using Handbook heat transfer coefficient

Temperature (°C)

ThermocoupleLocations Water flow


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


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


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


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


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


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


• 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


�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


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

Technology

Concept and Development Work for the LANL Materials Test Station