Status of JSNS and R&D on mercury target Masatoshi Futakawa (J-Parc)

1. Status of JSNS
and
R&D on mercury target
J-PARC
Neutron Source Section
Leader
M. Futakawa

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3. First observation of neutrons at JSNS
t~9.2ms, l~2.6A, E~12meV
On 30th May 2008
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TOF result shows the design of our neutron source
is appropriate.

4. MLF Proton Beam History in FY2008
(As of Feb. 19, 2009)
RFQ became instable
20 kW Beam
20 kW 20 kW
Begin user
Birth of neutron beam
program
First beam at 25Hz
20kW beam delivery
Resume at 5kW
Birth of 100kWeuiv. beam delivery
muon beam
Begin user program
100 kW
equivalent
for short
period
Resume
Resume at 181 MeV at 5 kW
AC power supply fault at RCS
RFQ conditioning
Technical problem in
LH2 cryogenic system at MLF RUN19 in Oct. was dedicated to RFQ conditioning

5. Proton Beam Transport Facility
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6. Target station at JSNS
Target station
Irradiated
components
handling
Mercury target room
Proton beam
window
Beam duct Target trolley

7. 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 4m
Width 2.6 m
Weight 315 ton

8. JSNS Mercury Target Vessel
Heavy water
Cross flow type
Length 2 m
Mercury
Weight 1.4 ton
Hg flow velocity 0.7 m/s
Hg inventory 1.5 m3
Mercury
Flow vanes

9. JSNS PM pump
Optimization of duct design
FEM analysis on pressure, Lorentz force & Hg flow
Inner wall :3mm
Outer wall :5 mm with ribs
90kW-Motor
Magnets
50 m3/h
1820 mm
0.2 MPa
Mercury duct
840 mm

10. Maintenance in Hot Cell
Dose 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.
Estimation in the Hot cell dose
Hands-on maintenance area
Handling
Target vessel Device of
100 µSv/h
exchange truck MRA
In-cell filter

11. Maintenance in Hot Cell
Measurement and Future Entry
Variation of the counting rates
• Separation products selectively during Hg drain
adhere to the piping.
– 188Ir, 185Os
was strongly observed
unexpectedly.
– Dose rates for 188Ir, 185Os were
increased during Hg drain.
– Dose rate after drain is higher than
before that.
• Our dose estimation was so much
underestimated.
• Hot cell entry in future ! Additional Shield
Additional shield of iron with 20
cm thickness will be prepared.

12. First observation of vibarational signal
related to pressure waves at target
Laser Doppler Vibrometer Measured vibration 0.8TP
Range : ±0.1m/s
0.4TP
Accuracy : 5x10-7 m/s < 300kHz
Laser beam Inner plug
Mirror assembly A
Mirror assembly B
Micro-multi
-prism
Target

13. Pressure dynamic Hg
Mercury target
response in mercury
Flow guide
Proton beam

14. What is cavitation bubbles
in mercury

15. R&D on mitigation technology
Violently bubble collapsing

16. Off-line test on pitting damage by MIMTM
Inventory : 5 L
Stagnant
Flow : 0.3m/s
+Bubble ca.0.1%

17. Off-beam test by MIMTM
Isolate pits
103
104
Crack
Combined pits
105
Pitting formation
106
107
20µm
Futakawa, at al; J. Nucl. Sci. Tech. 40(2003) 895-904

18. Fatigue strength degradation by pitting damage
Kolsterise As received
Kolsterise 4e7
Kolsterise 1e8
1600
316LN20%CW As received
316LN20%CW 5e7
w/o pits
1400
Bending stress, MPa
1200
1000 with pits after 4e7
0.7 !f
800
0.6 !f
600
0.3 !f
400
Cracks
2 3 4 5 6 7 8 9
10 10 10 10 10 10 10 10
4E7 25µm
Number of cycles to failure, N f
1E8
Futakawa, at al; Nucl Mat. 356(2006) 168-177

19. Lifetime estimation of target vessel
taking account of pitting and irradiation damages Pitting damage
Radiation damage

20. 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.
Beam profile
2500 hr at 25 Hz
10000
10000
100
Time to 5 dpa
Failure probability P , %
Pitting damage 8000
8000
Time to 10 % Pf , h
f
75
Time to 5 dpa, h
6000
6000
50
4000
4000
25
2000
2000
0 0
0
0.33 0.45 0.6 0.8 1 0.33 0.45 0.6 0.8 1
Power, MW
Power, MW
Futakawa, at al ; NIM Vol 562(2006), 676-679

21. Damage dependency on flowing condition
Ae/A0=0.1 Ae/A0=0.04 Ae/A0=0.02
250!m
0
0 0
-5 -5 -5
Depth, mm
Depth, mm
Depth, mm
-10 -10 -10
-15 -15 -15
Stagnant_1 Flow_1 Flow+bubble_1
-20 Stagnant_2 -20 Flow_2
-20 Flow+bubble_2
Stagnant_3 Flow_3 Flow+bubble_3
Stagnant_4 Flow_4 Flow+bubble_4
Stagnant_5 Flow_5
Flow+bublle_5
-25 -25 -25
0 50 100 150 200 250 0 50 100 150 200 250
0 50 100 150 200 250
Distance, µm Distance, µm Distance, µm
5000 cycles, Flow velocity 0.3 m/s, Gas/Hg 10-3

22. Effect of flowing on bubble collapse behavior
Micro-jet impact angle is inclined,
because the growth behavior
affected by the flowing. Tanaka, et al, CAV2006 (2006)

23. Effect of micro-jet impact angle
on pit formation
Micro-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.

24. Flowing improves lifetime ?
Flowing decreases the failure
probability due to the pitting
damage, so that, increase the
Beam profile lifetime of target.
2500 hr at 25 Hz
10000
100 10000
Failure probability P , %
Time to 5 dpa
Stagnant
Stagnant 8000
8000
f
Flowing
Time to 10 % Pf , h
75 Flowing
Time to 5 dpa, h
6000
6000
50
4000
4000
25
2000
2000
0
0
0
0.33 0.45 0.6 0.8 1
0.33 0.45 0.6 0.8 1
Power, MW Power, MW

25. Mechanisms of bubbling mitigation
3 mechanisms for each region
Center of thermal shock : A
B
Absorption
C
A Propagation path : B
Attenuation
Negative pressure field : C
Suppression
Bubble<50 µm
C
B
A
Contraction
Thermal diffusion
Thermal Pressure Kinetic Thermal
expansion wave energy energy
Absorption of the thermal Suppression against cavitation
Attenuation of the pressure
expansion of mercury due to the bubble by compressive
waves due to the thermal
contraction of micro bubbles pressure emitted from gas-
dissipation of kinetic energy
bubble expansion.
Absorption Attenuation Suppression

26. Pressure reduced by micro-gas-bubbles
Normalized peak pressure, P v/Ps
Single phase
!=0.05%
100 !=0.10%
!=0.30%
!=0.50%
!=1.00%
10-1
10-2
Ps=25MPa
10-3
0.1 1 10 100 1000
Bubble radius, µm
Expected pressure reduction by absorption and attenuation
Okita et al., CAV2006 (2006); J Fluid Sci Technol 3 (2008) 116

27. Bubblers applicable to target
to mitigate the pressure waves
Venturi, Needle, Swirl bubblers were investigated in mercury
He gas supply
Venturi
Needle
Venturi
Swirl
Bubbles < 50 µm, that is most effective to reduce pressure waves,
is successfully generated by using in swirl bubbler.

28. Bubble distribution in target vessel
vNumerical 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.
Water loop test at JAEA
Mercury loop test at TTF

29. Improvement in target system
Gas supplying system Compact target
to reduce waste volume
to control gas pressure
and install bubblers
and flow rate
Bubbler
Gas supply unit

30. 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.

31. Bubble distribution in Hg flowing
Hg
Mercury target
A
By FLUENT
Flow guide
B
Proton beam
1m/s
5 mm
C
0.5 mm
D
Bubbling position dependency on distribution: 0.05 mm
B+D positions for bubbles to reach around
window and max. peak position.
Rising effect on bubble distribution

32. Pressure wave mitigation
by A & B mechanisms
0.6 W/O Bubbling
Bubbling
0.4
Velocity, m/s
0.2
0
Proton -0.2
beam
-0.4
Hg loop -0.6
0 0.2 0.4 0.6 0.8 1.0
with bubbler
Time, ms
SNS/JSNS collaboration on pressure wave issue
2005 WNR test for bubble mitigation technology
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.