ESS-Bilbao Initiative Workshop. Status of JSNS and R&D on mercury target.
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Transcript of ESS-Bilbao Initiative Workshop. Status of JSNS and R&D on mercury target.
![Page 1: ESS-Bilbao Initiative Workshop. Status of JSNS and R&D on mercury target.](https://reader033.fdocuments.net/reader033/viewer/2022051412/549ea8acac79593d768b47d0/html5/thumbnails/1.jpg)
Status of JSNS and
R&D on mercury target
J-PARC
Neutron Source SectionLeader
M. Futakawa
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@AMNCOPQR
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STUV:W'XL8YI8ZH
First observation of neutrons at JSNS
t~9.2ms, l~2.6A, E~12meV
Congratulation !
TOF result shows the design of our neutron source
is appropriate.
On 30th May 2008
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Resume at 5kW
Begin user program
20kW beam delivery
100kWeuiv. beam delivery
RFQ became instable
(As of Feb. 19, 2009)
MLF Proton Beam History in FY2008
AC power supply fault at RCS
RUN19 in Oct. was dedicated to RFQ conditioning
Birth of neutron beam
Technical problem in
LH2 cryogenic system at MLF
Birth of muon beam
RFQ conditioning
First beam at 25Hz
Resume
at 5 kWResume at 181 MeV
Begin user
program
20 kW Beam20 kW 20 kW
100 kW
equivalent
for short
period
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Proton Beam Transport Facility
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! s:TH'Z_HH^kk^_`^`V'kWTUW:n'_`'L8'cT\o:U\'i^UkW'g:TH'km_W'iU_H'TZZ:j:UTW_U'm^W'H:UZ[U\'WTUV:WWmU_[Vm'I8b'HTV`:Wk'_o:U'LIt"H'j_`V'g:TH'j^`:
! s:TH'hU_i^j:'T`n'h_k^W^_`'_`'WTUV:WkH__Wm'hU_i^j:u'`_'W^jW
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Target station
Target trolley
Mercury target
Proton beamwindow
Beam duct
Target station at JSNS
Irradiatedcomponentshandlingroom
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JSNS Mercury Target System
Hg target : Cross-flow type, Multi wall vessel
Hg leak detectors (Electric circuit, Gas monitoring)
All components of circulation system on target trolley:
EM pump, Compact heat exchanger, Surge tank, etc.
Hot cell : Hands-on maintenance
Vibration measuring system due to pressure wave
Length 12 m
Height 4 m
Width 2.6 m
Weight 315 ton
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JSNS Mercury Target Vessel
Cross flow type
Length 2 m
Weight 1.4 ton
Hg flow velocity 0.7 m/s
Hg inventory 1.5 m3
Heavy water
Mercury
Mercury
Flow vanes
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90kW-Motor
Mercury duct
Magnets
18
20
mm
840 mm
50 m3/h
0.2 MPa
Optimization of duct design FEM analysis on pressure, Lorentz force & Hg flow
Inner wall :3mm
Outer wall :5 mm with ribs
JSNS PM pump
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Maintenance in Hot CellDose Estimation
• Several maintenance ! Done by hands-on
– Longer than 10 years interval
• Dose estimation– Considering residual Hg in piping and valves after Hg drain
– Less than 100 µSv/h at > 12 m
• 203Hg mainly contributes to the dose.
• Hot cell entry is possible.
Hands-on maintenance area
Target vessel
exchange truck
In-cell filter
Handling
Device of
MRA
Estimation in the Hot cell dose
100 µSv/h
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Maintenance in Hot CellMeasurement and Future Entry
• Separation products selectivelyadhere to the piping.– 188Ir, 185Os was strongly observed
unexpectedly.
– Dose rates for 188Ir, 185Os wereincreased during Hg drain.
– Dose rate after drain is higher thanbefore that.
• Our dose estimation was so muchunderestimated.
• Hot cell entry in future !Additional shield of iron with 20cm thickness will be prepared.
Variation of the counting rates
during Hg drain
Additional Shield
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0.4TP
0.8TPLaser Doppler Vibrometer
Range : ±0.1m/s
Accuracy : 5x10-7 m/s < 300kHz
First observation of vibarational signal
related to pressure waves at target
Mirror assembly A
Laser beam
Mirror assembly B
Target
Inner plug
Micro-multi-prism
Measured vibration
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Flow guide
Hg
Proton beam
Mercury targetPressure dynamicresponse in mercury
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What is cavitation bubbles
in mercury
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R&D on mitigation technology
Violently bubble collapsing
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Inventory : 5 L
Stagnant
Flow : 0.3m/s
+Bubble ca.0.1%
Off-line test on pitting damage by MIMTM
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Futakawa, at al; J. Nucl. Sci. Tech. 40(2003) 895-904
Pitting formation
Off-beam test by MIMTM
103
104
105
106
107
Isolate pits
Combined pits
Crack
20µm
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Fatigue strength degradation by pitting damage
25µm4E7
1E8
400
600
800
1000
1200
1400
1600
102
103
104
105
106
107
108
109
Kolsterise As receivedKolsterise 4e7Kolsterise 1e8316LN20%CW As received316LN20%CW 5e7
Ben
din
g s
tress
, M
Pa
Number of cycles to failure, Nf
0.7 !f
0.6 !f
0.3 !f
w/o pits
with pits after 4e7
Cracks
Futakawa, at al; Nucl Mat. 356(2006) 168-177
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Lifetime estimation of target vesseltaking account of pitting and irradiation damages Pitting damage
Radiation damage
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0
2000
4000
6000
8000
10000
0
2000
4000
6000
8000
10000
0.33 0.45 0.6 0.8 1
Tim
e to
5 d
pa
, h
Tim
e to 1
0 %
Pf , h
Power, MW
0
25
50
75
100
0.33 0.45 0.6 0.8 1
Fail
ure
pro
bab
ilit
y P
f , %
Power, MW
Pitting damage reduces lifetime of target
The lifetime at 10 % failure probability
under 1 MW will be reduced to ca 30 hrs
by pitting damage: fatigue and radiation
damages. 300 hrs for 0.8 MW, 2400 hrs for
0.6 MW.
Pitting damage
Time to 5 dpa
Futakawa, at al ; NIM Vol 562(2006), 676-679
Beam profile
2500 hr at 25 Hz
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Stagnant Flow Flow+Bubble
-25
-20
-15
-10
-5
0
0 50 100 150 200 250
Stagnant_1Stagnant_2Stagnant_3Stagnant_4Stagnant_5
Dep
th, m
m
Distance, µm
-25
-20
-15
-10
-5
0
0 50 100 150 200 250
Flow_1Flow_2Flow_3Flow_4Flow_5
Dep
th, m
m
Distance, µm
-25
-20
-15
-10
-5
0
0 50 100 150 200 250
Flow+bubble_1Flow+bubble_2Flow+bubble_3Flow+bubble_4Flow+bublle_5
Dep
th, m
m
Distance, µm
250!m
Ae/A0=0.1 Ae/A0=0.04 Ae/A0=0.02
Damage dependency on flowing condition
5000 cycles, Flow velocity 0.3 m/s, Gas/Hg 10-3
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Effect of flowing on bubble collapse behavior
Micro-jet impact angle is inclined,
because the growth behavior
affected by the flowing. Tanaka, et al, CAV2006CAV2006 (2006) (2006)
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Effect of micro-jet impact angle
on pit formationMicro-jet impact angle determined by cavitation bubble collapsing
behavior that is affected by mercury flowing condition.
Pit depth is affected by jet-angle. Almost 1/5 at 45 degree.
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0
2000
4000
6000
8000
10000
0
2000
4000
6000
8000
10000
0.33 0.45 0.6 0.8 1
Tim
e to
5 d
pa
, h
Tim
e to 1
0 %
Pf , h
Power, MW
Stagnant
Time to 5 dpa
0
25
50
75
100
0.33 0.45 0.6 0.8 1
Fa
ilu
re p
rob
ab
ilit
y P
f , %
Power, MW
Flowing improves lifetime ?
Flowing decreases the failure
probability due to the pitting
damage, so that, increase the
lifetime of target.
StagnantFlowing
Flowing
Beam profile
2500 hr at 25 Hz
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Kinetic
energy
Thermal
energy
Contraction
Thermal diffusion
Attenuation of the pressure
waves due to the thermal
dissipation of kinetic energy
Pressure
wave
Thermal
expansion
Absorption of the thermal
expansion of mercury due to the
contraction of micro bubbles
A
BC
A B
Suppression against cavitationbubble by compressivepressure emitted from gas-bubble expansion.
C
3 mechanisms for each region Center of thermal shock : A
Absorption
Propagation path : B
Attenuation
Negative pressure field : C
Suppression
Absorption Attenuation Suppression
Mechanisms of bubbling mitigation
Bubble<50 µm
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10-3
10-2
10-1
100
0.1 1 10 100 1000
Single phase
!=0.05%
!=0.10%
!=0.30%
!=0.50%
!=1.00%
No
rma
lize
d p
eak
pre
ssu
re,
Pv/P
s
Bubble radius, µm
Ps=25MPa
Pressure reduced by micro-gas-bubbles
Expected pressure reduction by absorption and attenuation
Okita Okita et alet al., ., CAV2006CAV2006 (2006); (2006); J Fluid Sci TechnolJ Fluid Sci Technol 33 (2008) 116 (2008) 116
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Bubbles < 50 µm, that is most effective to reduce pressure waves,
is successfully generated by using in swirl bubbler.
Venturi
Bubblers applicable to targetto mitigate the pressure waves
Venturi, Needle, Swirl bubblers were investigated in mercury
He gas supply
Venturi
Needle
Swirl
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Bubble distribution in target vesselvNumerical simulation Spherical bubble
Homogeneous bubble size distribution
Assumed bubble size distribution
Bubble distribution is very dependent on
the position of bubbler, which is affected
by flow pattern.
vExperiment in water and mercury Curving flow channel effect
Bubble coalescence effect
Verification of conventional codes; Star-CD, Fluent, etc.
Mercury loop test at TTF
Water loop test at JAEA
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Improvement in target system
Bubbler
Gas supplying system to control gas pressure
and flow rate
Compact target to reduce waste volume
and install bubblers
Gas supply unit
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Summary
vAt MLF in J-PARC, the first proton beam was injected into
mercury target to yield neutrons on 30th May 2008.
vIn mercury target for pulsed spallation neutron sources, the
cavitation damage induced by pressure waves is a top
issue to increase power level to MW-class.
vOne of prospective techniques to mitigate pressure waves is
to inject micro-bubbles into the mercury.
vSwirl bubbler can generate bubbles <50 µm in mercury, that
is expected to effectively mitigate pressure waves.
vCollaboration with SNS is important. Mockup tests of target
vessel with bubblers will be carried out using TTF loop to
evaluate bubbles’ distribution in target vessel.
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Flow guide
Hg
Proton beam
Mercury target
5 mm
0.5 mm
0.05 mm
1m/s
Bubble distribution in Hg flowing
Bubbling position dependency on distribution:
B+D positions for bubbles to reach around
window and max. peak position.
A
B
C
D
Rising effect on bubble distribution
By FLUENT
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On-beam test was carried out by using WNR facility to investigate the bubbling effect
on the pressure waves caused by proton beam injection. The displacement velocity
measured by a Laser Doppler Vibrometer L.D.V. was reduced by bubbling.
Pressure wave mitigation
by A & B mechanisms
Hg loop with bubbler
Proton beam
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0 0.2 0.4 0.6 0.8 1.0
W/O BubblingBubbling
Vel
oci
ty,
m/s
Time, ms
SNS/JSNS collaboration on pressure wave issue
2005 WNR test for bubble mitigation technology