Concept and Development Work for the LANL Materials Test Station

Concept and Development Work
for the LANL Materials Test Station

Eric Pitcher
Los Alamos National Laboratory
Presented to:
ESS Bilbao Initiative Workshop
17 March 2009

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 module
target module
beam mask

backstop

ESS Bilbao Initiative Workshop 16-18 March 2009 2

The MTS target consists of two spallation target
sections separated by a “flux trap”
materials sample cans
spallation target
test fuel rodlets
• Neutrons generated through
spallation reactions in tungsten
• 2-cm-wide flux trap that fits 40
rodlets

Beam pulse structure:
750 µs 7.6 ms

16.7 mA

Delivered to: left right left right
target 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


A sharp beam edge is key to maximizing the
neutron flux in the irradiation regions
• Two technologies facilitate

materials irradiation region
a sharp beam edge:

fuels irradiation region
– Beam rastering
– Design and testing by
Shafer et al. for APT at LANL
15 mm
– 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

Beam transport system produces a horizontal
focus at the target front face

25 mm wide
target face

15 mm nominal
footprint width

Beamletis
3 mm horizontal
x 8 mm vertical
(FWHM)

Vertical slew
covers 60 mm
nominal footprint
height in 750 µs
macro-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 40
vol% coolant outperforms
LBE
• MTS maximum coolant
volume fraction is 19%
• Neutron production density LBE supply plenum
with tungsten is 60% greater
than for LBE alone

Target is fabricated through multiple diffusion
bonding steps
• Fuel module housing and target Channels for
fuel pins
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
Ta front face
• No welds are used near the
proton beam


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
Copper Test Section
Surface Heat Flux
Peak ~600 W/cm2

1 mm x 18 mm
Channel
Flow Channel
Flow Rate
10 m/s

Test Goals:
• Determine single-phase HTC
Cartridge
• Identify plate surface temperature Heaters
@ 600 W/cm2
• Measure subcooled flow boiling
pressure drop
Cartridge heaters in tapered copper
• Investigate effect of plate surface
block will simulate beam spot heat
roughness
flux

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


Experimental results match test data using
Handbook heat transfer coefficient

Thermocouple
Locations Water flow

Temperature (°C)


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


LBE temperature is controlled with variable-area,
double-wall, shell and tube heat exchangers

LBE

100 Tubes
0.875” OD

LBE level in
intermediate annulus
sets heat transfer

water
surface area

Flowing LBE (primary coolant)
reservoir
gas/vac Static LBE
Inlet water manifold
Outlet water manifold

LBE-to-water heat exchanger is sufficiently
novel as to merit a confirmatory experiment
109 cm

Flowing LBE
(primary coolant)
Static LBE

Inlet water
manifold

Outlet water
manifold


Target lifetime will be limited by damage to the
target front face
• Experience base:
ISIS (SS316 front face): 3.2×1021 p/cm2 = 10
dpa
SINQ (Pb-filled SS316 tubes): 6.8×1021 p/cm2 = 22 dpa
MEGAPIE (T91 LBE container): 1.9×1021 p/cm2 = 6.8 dpa
LANSCE 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


Towards higher beam power:
Which is better—more energy or more current?
• If target lifetime and
coolant volume
fraction is
preserved, higher
beam current
3.6MW
1.8 MW
1
requires larger
beam spot

MTS Beam Footprint on Target


Peak neutron flux goes as Pbeam0.8

~ Ebeam0.8ibeam0.8
pk

Ebeam = 0.8 GeV ibeam = 1 mA

~ ibeam0.8 ~ Ebeam0.8
pk
pk


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


Concept and Development Work for the LANL Materials Test Station

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