Status of JSNS and

R&D on mercury target

J-PARC

Neutron Source SectionLeader

M. Futakawa

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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

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

Proton Beam Transport Facility

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Target station

Target trolley

Mercury target

Proton beamwindow

Beam duct

Target station at JSNS

Irradiatedcomponentshandlingroom

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

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

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

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

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

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

Flow guide

Hg

Proton beam

Mercury targetPressure dynamicresponse in mercury

What is cavitation bubbles

in mercury

R&D on mitigation technology

Violently bubble collapsing

Inventory : 5 L

Stagnant

Flow : 0.3m/s

+Bubble ca.0.1%

Off-line test on pitting damage by MIMTM

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

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

Lifetime estimation of target vesseltaking account of pitting and irradiation damages Pitting damage

Radiation damage

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

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

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)

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.

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

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

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

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

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

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

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.

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

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