Present Status of Neutron Source at J PARC MLF Katsuhiro Haga On - - PowerPoint PPT Presentation

J‐PARC Symposium 2019 2019/9/23‐26

Present Status of Neutron Source at J‐PARC MLF

Katsuhiro Haga On behalf of MLF team (Neutron Source Section)

1‐MW spallation neutron source at J‐PARC

Cryogenic hydrogen system Proton beam 3 GeV, 1MW, 25 Hz Neutron beam lines (23) 21: in operation Mercury target system

5m

Moderators

2

Year

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 #1 #2 #3 #4 #5 #6 #7 #8 #9 120 ~ 310 kW, 2050 MWh 330 ~ 513 kW, 670 MWh Failure in outer water shroud 210 ~ 150 kW, 1048 MWh

History of target operation at J‐PARC

20 ~ 220 kW, 471 MWh 6 times target replacements to date 300 ~ 525 kW, 1812 MWh 300 ~ 535 kW, 2120 MWh

Improved robust design

• Max. 505 kW, 170 MWh

Failure in inner water shroud

3

Work plan in FY2019

• Neutron source operations for 8 run cycles (176 days) with an

availability over 90%

• Target operations with a beam power of 500 kW or higher.
• Replacement to the target vessel of new design, termed as

constrain‐free structure, which has minimum coupling between water shroud and mercury vessel during summer

• shutdown. ‐> The replacement work is going on.
• Completion of a new target vessel.
• Completion of the transportation of a used target vessel from

MLF building to another storage building (Radio‐Activated Materials Building). ‐> finished on July 22

4

10 20 30 40 50 60 70 80 90 100 100 200 300 400 500 600 700 800 900 1000 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

Beam Power [kW] Operational Efficiency [%]

Beam Operations with #8 and #9 Targets

• Stable and long term beam operation of more than 500kW was achieved

with high average efficiency of more than 90%.

• 1MW beam study at the end of user beam operations was successful.
• Average efficiency in the case of target #9 was over 98%!

1MW study (1 hour) 2018 2019

5

1MW study (10.5 hour)

Target #8

Beam power

Target #9

Summer shutdown (target replacement) Average operational efficiency per run#

1MW Target Study of Target #9

10 20 30 40 50 60 200 400 600 800 1000 Temperature rise of mercury vessel, ℃ Beam power, kW 5 10 15 20 25 30 200 400 600 800 1000 Temperature rise of mercury, ℃ Beam power, kW

Mercury Mercury temperature Mercury vessel temperature

 Heat deposition of 50%

• f beam power into

mercury was assumed.  Temperature riser of mercury showed good agreement with the analytical prediction.  Temperature rise of mercury vessel at 1 MW was a little bit less than the analytical prediction.  The effect of beam profile can be one of the reasons.

Proton beam

20 40 60 80 100 120 200 400 600 800 1000

11:00 13:00 15:00 17:00 19:00 21:00

Temperature trend at 1MW study

Mercury vessel Mercury at outlet Mercury at inlet Beam power

Analytical prediction Analytical prediction 1MW Study

Study data of #9 target Study data of #8 target

1MW study

Temperature [ºC] Beam power [kW]  Temperatures reached almost stable values in two hours.

Facility data of steady state under 1 MW beam condition could be obtained for the first time.

Critical Issues of Target Vessel for High‐power Operation

1.Improvement of the target vessel design to have sufficient reliability and robustness. 2.Mitigation of pitting damage at the beam window

• f the target vessel.

7

1050mm

3mm Diffusion bonding Water channels End plate

Design improvements of target vessel

1st～7th (previous)

8th, 9th(current)

constraint‐free

High robustness and reliability can be obtained.

10th,11th,12th

Made with diffusion bonding and many welds which can be the cause of initial defects. Monolithic structure

• f water shroud &

Hg vessel Monolithic structure of water shroud Water shroud Bolts Hg vessel Water shroud Hg vessel Water shroud Hg vessel

Constraints between vessels cause high thermal stress which limits beam power.

 No coupling between vessels.  Fabrication techniques were improved.

Welds were drastically reduced. 8

9

Fabrication of Constraint-free Type Target

Mercury vessel Water shroud He layer（Gap:3mm）

 By the high accuracy fabrication and welding techniques with little deformation, the 3 mm gap of helium layer could be maintained.  By the intensified non‐destructive inspection, tiny defects can be detected in the fabrication process to minimize the possibility of target failure during the beam operation.  The constraint‐free type target is ready to be used from this November.

Suppression of welding deformation is the key issue. Water shroud Reinforcement rib Back plate Back plate Dial gauges

Fabricated with the combination of TIG welding and Electron Beam welding.

Pulsed proton beam Mercury vessel Pitting damage of the wall by the cavitation Actual pitting damages Beam window (Thickness : 3 mm)

Most vulnerable to pitting damage

#1 SNS target 3055 MWh Mercury Abrupt heating

• f mercury

Pressure wave Thermal expansion Φ 50 mm #1 J‐PARC target 471 MWh

• Nov. 2011
• Max. pit depth :

0.25 mm

(D. McClintock, JNM 2012)

Pitting Damage by Pressure Wave

Schematic images of pitting damage generation

Mercury Wall Cavitation bubble

Cavitation bubble inflates by the mercury negative pressure. Cavitation bubble shrinks rapidly. Shrink energy concentrates to one point and damage is formed.

Micro‐jet

Proton beam

Mercury

Rapid flow in narrow channel Micro‐bubble injection Outer wall

P

2mm Inner wall

50 mm

Stagnant 250μm Flow

Laboratory experiment in JAEA

A B

A:Center of thermal shock B:Propagation path

Absorption of thermal expansion of mercury by bubble contraction Attenuation of pressure waves by thermal dissipation of kinetic energy

Technologies for Pitting Damage Mitigation

Micro‐bubble injection into mercury

Proton beam Bubbler

Rapid mercury flow in narrow channel

Mirror

Laser Doppler Vibrometer(LDV)

Target vessel

Microphone

• 0.3
• 0.2
• 0.1

0.1 0.2 0.3 0.4 2 4 6 8 10 12 14

Time, ms

w/o bubbles

Proton beam : 300 kW

w/ bubbles

Displacement velocity, m/s

Monitoring the Efficacy of Bubble Injection

0.2 0.4 0.6 0.8 1 20 40 60 80 100 Velocity amplitude, m/s PQ

0.5 1 1.5 200 400 600 800 1000

Beam power [kW]

Normalized peak value of sound signal

Vibration of target vessel #8

Study data in the past 1MW study data Analytical prediction

 P, Q and vibration velocity amplitude are related well by the parameter PQ.  The parameter showed good agreement with the analytical prediction. P: beam power Q: heat density , : constant

Sound signal of target vessel

Data of target #9 Data of target #8  Because of inadequate welding, Mirror dropped

• ff the target #9 by

pressure wave vibration.  Efficacy of bubble injection was monitored by sound signal recorded by a microphone.  The sound data showed good linearity and agreement between #8 and #9 targets.

13

Cutting Specimens from Beam Window of Target Vessel

Target No. 8 (Oct. 2017 — Jul. 2018) Total energy : 1812 MWh

• Av. beam power : 434 kW@25 Hz

Total pulses : ca. 3.76×108 shots

70 mm

Cut two locations (center and off‐center)

 Specimens were cut out at the center and off‐ center locations of the beam window of target #8.  Quantitative damage data on the bulk side of the inner wall protected by microbubble injection was

• btained for the first time.

Mercury vessel Water shroud

4 layers window (3+3+3+5 mm)

Center Off‐center

Hole saw

Cavitation Damage of Target #8

φ50 mm

Beam ① Outer wall inside ③ Inner wall inside ② Inner wall

• utside

Center Off‐center

① Outer wall inside ③Inner wall inside (Bulk side) (Narrow channel) Center Off‐center

Dose rate: ~200 Sv/h

②Inner wall outside

 Damage on the narrow channel side was much less than that on the bulk side, which is

advantageous to protect the outer wall, i.e. mercury boundary.

 No‐visible damages were observed on the off‐center specimens.  Soundness of the inner wall is also important since damage penetration through the

inner wall from the bulk side would hamper the damage mitigation effect in the narrow channel. Dmax: ~15 µm Dmax: ~250 µm

15

Cavitation bubble behaviors in flow and narrow gap

Experimental verification

Flow

Electrode diameter: 1 mm

Gap : 10 mm Gap : 3 mm Stagnant Flowing 1.7 m/s

Stagnant Flowing

Cavitation bubble

Microjet Microjet Narrow gap Microjet 200 kfps 200 kfps 200 kfps 200 kfps

 Flow velocity and gap width dependency (confirmed)

• Damage is reduced as the flow velocity increases.
• Damage changes depending on gap width.

 Power dependency of cavitation damage in narrow channel has not clarified yet.

• Effect of wall boundary on cavitation growing and collapsing behavior
• Pressure gradient strongly affects in narrow gap, which should be verified

through experiments and numerical simulation

Influence of a Hole of Inner Wall on Flow Velocity

• Basic water experiments of double flow to understand flow pattern around beam window
• Effects of opening diameter in narrow channel on reduction of downstream velocity

‐‐‐wall curvature on flow pattern ‐‐‐cross flow for bubble distribution, bubble coalescence in narrow channel, etc.

• Basic flow examination ‐> Simulation ‐> Mockup model ‐> Mercury simulation and examination

Pump Surge tank Nozzles for tracer bubbles Flow meter Rectangular and curvature test section Flow meter Compressor

• M. H. lamp

High-speed video camera Acrylic channel(70x70) Cross flow test section

Curvature model Curvature model Rectangular model

Bubbles for tracer Camera

Water Experiment

Analytical Design of a New Target Vessel (Tentative)

Mercury flow velocity Mercury temperature Helium bubble particle flow trace :  80 μm [m/s] [deg C] Bubbler position of current target Mercury vessel temperature [deg C]

JFY 2016 JFY 2017 JFY 2018 JFY 2019 JFY 2020 100 200 300 400 500 600 700 800 900

1000

MLF beam power (kW)

#2 (200 kW)

#2 (150 kW)

#8 (300 ~ 500 kW)

1‐MW test

Lifetime estimation based on pitting damage observation Operation

Outlook of operational beam power upgrade

• Beam power will be increased step by step to keep stable operation.
• Observation results of pitting damage will be decisive factor of beam power.

Further development of pitting‐damage mitigation‐technology will be continued for high power stable target operation. #9 (> 500 kW)

1‐MW test

Constraint free type target

Summary

• Stable and long term beam operation of more than 500kW was achieved

with high average efficiency of more than 90%.

• 1MW beam study at the end of user beam operations was successful.
• Fabrication of the target vessel of constrain‐free structure is finished and

will be installed next month.

• The pitting damage in narrow channel of target #8 and #9 was much less

than that on the bulk side, which is advantageous to protect the mercury boundary, but beam power will be increased step by step to keep stable

• peration.
• Further development of pitting‐damage mitigation‐technology will be

continued for stable target operation at higher power.

19