Status of a Cryogenic System for J-PARC Neutrino · PDF fileStatus of a Cryogenic System for...

Status of a Cryogenic System for J-PARC Neutrino

- Availability, Tritium creation, Volatilization of the ammonia etc. -

KEK：Y. Makida, H. Ohata, O. Araoka, M. Iida T. Ogitsu, N. Kimura, T. Okamura, T. Nakamoto,

K. Sasaki, M. Iio, M. Yoshida

Contents

1. J-PARC and T2K Overview. 2. Cryogenic Plant for T2K. 3. Status of Cryogenic Plant.

– History and Rate of Operation – Initial Failure at Turbine and Pump – Watching Impurities and Unexpected Volatilization . – Creation of Tritium and Radiation Control

4. Conclusion

J-PARC (Japan Proton Accelerator Research Complex)

Linac 330 m

3 Gev rapid cycle synchrotron (RCS) 350 m circ. , 25 Hz

Main synchrotron 1500 m circ., 25 Hz

30 GeV (in future 50GeV)

Neutrino Facility To Super - Kamiokande

Hadron Experimental Facility Material and Life Science

Facility

Transmutation Experimental Facility (in future)

The J-PARC accelerator complex consists of 3 accelerators, a linear accelerator, a rapid cycle synchrotron (RCS, 3GeV) and a 50 GeV (Max) synchrotron. Each accelerator provides the experimental faculties (materials and life science, hadron physics, neutrinos, transmutation) with a high intensity beam. The secondary particles, such as neutrons, mesons as well as neutrinos from these mesons, are produced by bombarding a target with an intense proton beam.

Jan, 2007, 181 MeV

Nov, 2007 3 GeV

Dec, 2008 MR beam

Apr., 2009 Neutrino Beam

Purpose of T2K experiment

http://www-nu.kek.jp/jhfnu/index_e.html

• The T2K (Tokai to Kamioka) experiment is a neutrino-oscillation experiment to study nature of neutrinos.

• Artificial neutrino beam generated in the J-PARC is shoot toward the 50kton water Cherenkov detector, Super-Kamiomande, which is located about 1000m underground in Kamioka mine (Gifu) and is 295km away from Tokai.

• http://t2k-experiment.org/

5

Preparation Section

SC combined func mags

Target-Horn System Target Station

Decay Volume Beam Dump

Final Focusing Section

Muon Monitoring Pit

Near Neutrino Detector

295km to Super-Kamiokande

100m

T2K neutrino facility in J-PARC http://j-parc.jp/Neutrino/en/nu-facility.html

• P beams accelerated up to 30 GeV are directed westward through the Primary Part . • P collide with a graphite target and produce π-mesons, which decay into neutrinos. • A string of SC. Mag is a core part in the Primary Part.

30 GeV (50 GeV)

Present status of T2K

20kW, upto 240 kW 65x1019 for physics analysis

• Although two long shut-down periods due to an earthquake and a radiation accident respectively, T2K resumed data taking. Statistic of P beam became enough to announce its experimental result.

• The international T2K collaboration announced a definitive observation of muon neutrino to electron neutrino transformation on July 2013.

• T2K saw its first event in antineutrino beam mode on June 2014.

Electron-neutrino candidate in Super Kamiokande

HD hall radiation accident

History of accumulated proton number and beam power improvement

Contents



4. Conclusion

8 8

Primary line components - One string of Superconducting Magnet -

The neutrino beam line has a bending section with a radius of 105 m, where single string of 28 superconducting magnets has been installed. The magnet design is very unique. It has a combined function of 2.6 T dipole field with 19.6 T/m quadrupole field gradient by a left-right asymmetric distribution of conductors.

Cryogenic Plant overview

LN2 CE

S.C. Magnet MCP, CB, Sub-cooler, CLB

Cryogenic devices, 4 He tanks, 1 LN2 CE, a compressor, a cold box, a sub-cooler and a current lead box, are set on surface. The magnets are at -12 m under ground and coolant SHE is transported between them.

He Tank

Pacific Ocean (5m Tsunami arrived)

10 m

Overall Layout (Ground Plan) Neutrino Beam Line Superconducting Magnet Arc in main tunnel at -12m level Radius 105m, Length 150m

Cold Box、Subcooler SHE Max 300 g/s 4.5 K LHe pot : 800 ℓ C/L flow : 1 g/s

Main Compressor (MCP) : 570 kW, 1.4 MPa, 150g/s

Buffer Vessel (for MCP) Volume 100m3×1

LN2: 20000 ℓ Only pre-cooling & cold purification 18000 ℓ/day @ pre-cool 300 – 100 K

Magnet String & Transfer Line Inventor 3900 ℓ, Cold mass 225 ton(Fe) 90 m transfer line with SC bus Heat Leak 220 W + Beam Loss max 150 W

Recovery Vessel (for Quench) As Storage Vessel for Inventory Volume 100m3×3

Conceptual Flow Diagram @ excitation

A cascade refrigerating system , composed a Claude cycle refrigerator with a centrifugal pump , supplys 4.5 K, 0.4 MPa, 300 g/s She.

Turbine flow goes through radiation shield cooling line in the magnet .

LN2 is consumed for pre-cooling and gas purification.

1.4MPa, 150 g/s He gas is supplied by the compressor. 70 g/s flow expands and works at turbines, and the rest expand at JT valve in the sub-cooler.

Conceptual Flow Diagram @ excitation

A pair of cooling gas flow for the current leads is divided from the SHE supply line simply. SC cables directly enter the SHE line

SHE pump outlet is connected with the inlet of JTV. The pressure in this connection line is kept at 0.4 MPa by the JTV. This control scheme spontaneously complements the current leads cooling gas which falls out from the pumped circulation.

Refrigerator capacity 1500 W need the 900 W offset by using LHe level control heater.

Saving refrigerator capacity by reducing unloader and supply pressure results in lower power consumption at the compressor.

Power saving mode.

Saving 1.5 Yen/month

Contents



4. Conclusion

History and Rate of Operation

FY2011 FY2012 Earthquake 11/3

• After MSS Miss Trigger trouble is solved, Nu cryogenic system has cased no interruptions of T2K experiment.

• Rate of operation (availability) is beyond 0.99. • Although cryogenic system did not stop, some devices did

abnormal movement. It was only lucky.

11/12

7/3 15/3

6/5 17/5

4/12

8/12

8/12

History and Rate of Operation FY2014 FY2013

HD Radioactive Material Leak Accident on 23/May

• About HD radiation material leak accident please refer http://j-parc.jp/HDAccident/HDAccident-e.html • To restart J-PARC operation, Radiation control management became severe. • Nu cryogenic facility and its maintenance method were examined in radiation

evaluation committee. • T2K experiment resumed on April 2014.

J-PARC operation was not admitted until improved radiation management was established.

http://j-parc.jp/HDAccident/HDAccident-e.html

Contents



4. Conclusion

Notches in Turbine • We found some notches at 2nd turbine blades by

the visual inspection after 2009 autumn operation. • We observed abnormal start movement of 2nd

turbine. • Lined TED turbine needs bearing gas supply

during only start-up. And bearing gas stops, when the rotation reach to normal speed.

• But 2nd turbine could not start with bearing gas, and it could start when bearing gas stopped.

• Once start-up, 2nd turbine rotated normal condition during the beam operation, and cooling power did not degrade.

• Measured mechanical strength of the turbine material is rather low.

• Linde also reported that the bearing gas pressure at 14 bar in Nu cold box is higher than its design pressure of >10 bar in standard liquefiers.

• New turbine made with inspected material was set. • Pressure reducing valve was installed into the

bearing gas supply line.

Remade 2nd Turbine and 1st Turbine

PRV addition into bearing line

HP

LP

MAG CP

Rubbing of SHE pump

Cold bearing is Exchanged annually by Taiyo Nippon Sanso, Main contract of Nu cryogenics . And removed bearing is inspected by Barber Nichols to analyze its operation life.

• We found burrs on the pump impeller blades by the visual inspection after 2010 autumn -> 2011 winter operation.

• We heard abnormal large and shrill noise during the operation.

• But flow rate of 300 g/s at nominal rotation improved 310 g/s.

• So, the operation continued. • Lower position of the pump

impeller caused scratch of the impeller blades with the pump housing.

• New tool and gage to set the blade at the design position are prepared.

Cold Bearing

Tuning Bolt of Rod Length

Contents



4. Conclusion

Watching and measuring impurities • Inner Detectors (Measured gas go to the LP line)

– Dew-point meter : MICHLL Ins. Water detection < - 60 ◌۫C ( before cool down ), -90 ◌۫C (usually)

– Discharge light spectrometer : KEK original N2, < 1 ppm

– Gas chromatograph : SHIMAZU → LINDE multi component detector

N2, O2, CO, CO2 < 1 ppm • Gas sampling

– Quadruples mass spectrometer : ULVAC & JAEA H2 < 1 ppm H2 from polymers in the magnets by beam irradiation.

– Liquid scintillator : Radiation Control Equipment HT < 7 Bq/cc, HTO < 5 mBq/cc (Radiation control criteria) 3Helium ↔ Tritium is transmutation

Oil separation check

Oil return Solenoid valve with Counter and Action signal

Oil must be ≦0.001vol.ppm

Level Switch Sight Glass

Action Signal

Controller Counting Interval check

Screw Compressor

5th Separator Molecular Sieve Adsorption

4th Separator Active Charcoal Adsorption

1st Separator Demister Separation

Water Cooler

2nd & 3rd Separator Filter Element Coalescence

Controller checks oil return valve action interval. If the interval become longer, that means filter elements are saturated.

Filter element selection is important. Activity of DOMINICK HUNTER is short. This element caused RIKEN Oil diffusion accident. TAIHEIYOU filter is activate longer. So, filters in 2nd separator were exchanged.

Oil check sampling annually. Daily check through sight glass.

Unexpected Volatilization : Ammonia from Magnet

Glass-reinforced Phenolic Thermosets Rin=102 mm, t=20 mm, L= 100 mm *PM9640 by Sumitomo Bakelite, Arisawa

Ammonia Origin

Ammonia Properties

Molecular Formula NH3

Molecular Mass 17.031 g/mol

Density 0.86 kg/m3 (1.013 bar at boiling point) 681.9 kg/m3 at −33.3 ℃ (liquid)

Melting point −77.73 °C (195.42 K)

Boiling point −33.34 °C (239.81 K)

• We found that irritant odor in vent helium gas from the magnet at maintenance.

• Gas analyzing showed that the odor material is ammonia.

• Search found the plastic spacer is its origin. • Why the Nu refrigerator was not blocked up?

• Molecular Sieve (Crystalline Zeolite) in 5th oil separator can adsorb large quantity of ammonia.

• 5th separator has large enough quantity of MS, which can adsorb 79 kg ammonia.

• And MS can be re-activate by heating at 150 ℃.

Atmosphere Atmosphere

Ammonia Detector

Pump

Dew point mater

MS (13X) Adsorb

He Recovery

N2 gas for reactivation

He + 100 ppm NH3 to watch adsorption

He for carburation

Thermo-meter

Heater

Contents



4. Conclusion

HT (Bq/L) HTO (Bq/L) Beam P (kW) May/2010 0 0.082 ~ 80 July/2010 0 0 ~ 80 Sep./2012 48.2 2.4 ~ 200 Dec./2012 28 0 ~ 220 Mar./2013 19 0 ~ 230 May/2013 40.5 0 ~ 230 Aug./2013 37.5 0 ~ 230 July/2014 40.5 0 ~ 250

Measurement Record of Tritium (HT & HTO)

• Sample gas is analyzed by Liquid scintillater with precision of 5Bq/L.

• Analysis is done at RT, AP.

Radiation Management in J-PARC require

Larger Beam Power may produce more tritium.

HT (BP 25K) and HTO inside MAG @ Beam Time -> Sampling at > 25 K, @ Return from MAG

25

HT HTO Boiling Point (K) 25 373

Melting Point (K) 20.4 277.5

A. Limit * (Bq/L) 7000 5 * Allowable limit in discharging gaseous radioactive waste

Law Concerning Prevention from Radiation Hazards due to Radio‐Isotopes, etc. (≈ ICRP90)

Regulation << A. Limit

• Gaseous waste must be vent through authorized vent stack with radiation monitor. Even small gas vent from maintained equipment must follow the guideline.

• The work place, where gaseous waste is vent, is set as a radiation management area temporally.

Same Operation and Modified Maintenance due to Tritium

But Radiation Management in J-PARC accept • Nu cryogenic system, which is designed and is inspected by High Pressure

Gas Regulation, holds enough air-tightness to prevent tritium leakage. • Consequently, Nu cryogenic area on surface need not become radiation

management area parmanetly. It is only set, when the helium gas part is exposed.

Temporal Radiation Management Area

Cryo. Room Tank Yard Air

Vent Stack

Tank

Evaporator

Tank

Tank

Evaporator

MCP

Oil Separator

CB

Subcooler

C/L Box

Otherwise

Air

Guide Line of Temporal Radiation Management

MCP Surface

Vacuum Vessel

Sub- Cooler CB Tank CL

BOX

Vac. Pump

Existing Vent Stack

Cryogenics Room = Temporal Backup Seal

Radiation Monitor

Beam Pipe

Under Ground Radiation Management

He V

ent L

ine

0.1 mm Metal Mesh 1 mm Metal Mesh

Magnet

Temporal Vent Line Temporal 1st Seal

Backup Seal

Actual Method : Filter Exchange at 2nd,3rd Oil Separator

1st seal Oil Separator Unit is covered by an air-tight plastic sheet room. Backup seal Cryogenic Room becomes radiation management area.

400 m3/h blower exhausts air from the room to the vent line.

Oil Filter Exchange

Radiation Safety Check By gas sampling and smearing.

Analysis takes 1day

Setting Management Area

Radiation Safety Check By smearing. Analysis takes 1day

Cancel Management Area

Actual Method : Relief Valve Exchange at outdoor Tanks

RV RV vent

Stop Valve He must be vent before RV removal

Rope set management area . Rope is back-up seal ???

Wrench is kept inside plastic bag as 1st seal. Back up seal is rope.

Radiation Safety Check By smearing. Analysis takes 0.5day

Setting Management Area

Radiation Safety Check By smearing. Analysis takes .5day

Cancel Management Area

Removed RV Smear Inspection

Send RV to maker for calibration

CONCLUSION • After initial troubles were solved, Nu cryogenic system has

been stable since FY2012 autumn. • It was not expected that volatilization of the ammonia from

the magnet, but fortunately, molecular sieve in the 5th oil separator can adsorb a gross quantity.

• Tritium of 40 Bq/cc has been detected in refrigerant. In spite of lower value than its allowable limit of 7000 Bq/cc, Nu cryogenic operation and maintenance method were examined in radiation evaluation committee.

• Helium vent must be through authorized line and stack after radiation measurement. Fortunately vent line from RV and the vacuum pumps had been constructed. Gas monitor and metal filters were installed into the vent line additionally.

• Some maintenance works, RV and oil filter etc. exchange, need setting of temporal radiation management area and complicated procedures.

Backup Slied

Specifications of each component in the cryogenic plant(1). Component Item Specification Compressor Type Oil injected two stage screws compression

Manufacture / Model name MAYEKAWA/HE3225MSC-KLBM Discharge pressure 1.4 MPa Discharge stream 160 g/s Oil separation 5 stages, Demister , 2 stage Coalescer,

Activated charcoal, Molecular sieve Refrigerator Type Claude cycle

Manufacture/Model name LINDE/ TCF200S Refrigeration power without LN2 @ Supplied gas pressure of 1.4 MPa Return gas pressure of 0.12 Mpa

1500 W at 4.5 K for pumped SHE stream + 2400 W at 80 K for radiation shields + 1.1 g/s from 4.5 K for current leads

Turbine type Dynamic bearing expansion turbine Turbine and JT stream at steady state 70 g/s, 80 g/s Shield stream 70 g/s (equal with turbine stream )

Sub-cooler Manufacture JECC TORISHA Phase separator ( LHe reservoir) capacity 1600 ℓ Stored LHe volume at steady state 800 ℓ SHE pump manufacture Barber-Nichols SHE pump bearing type Ball bearing Nominal pumped flow rate 300 g/s Available pressure head at nominal flow 100 kPa

Specifications of each component in the cryogenic plant(2).

Component Item Specification

LN2 cold evaporator Volumetric capacity Operation pressure

20000 ℓ (stored volume 18000 ℓ) 0.5 MPa

Manufacture CRYO-ONE Dryer Moisture absorber Synthetic zeolite

Amount of throughput 200 Nm3/h ×24 h Absorption ability Outlet impurity 1.2 ppm, dew point -75 ◌۫C

Cryogenic purifier Impurity absorber Amount of throughput

Activated carbon 200 Nm3/h ×24 h

Absorption ability Outlet impurity 1.2 ppm Pressure vessel Volume 100 m3 ×4, one for buffer, others for

storage Operation pressure 1.5 MPa COP, FOM 0.0026, 16 %

• External set of a dryer and a cryogenic purifier is installed, because large amount of moisture and air from magnet electric insulator were predicted. The capacity of this purification unit is large enough for the 1000 ppm inventory.

• Impurities in helium gas was actually removed in two days before cooling down, so the rate of operation of the dryer and the purifier is very low.

Effort of Power Saving Mode

before after High (discharge) pressure control MPaG 1.3 1.1 Refrigerator cycle flow rate g/s 155 125

LHe level control heater W 900 400

Refrigerator capacity W 1500 1000

Lower unloader posision % 100 95

Compressor power consumption kW 570 430

Power cost per month (¥15/kwh) K YEN 6,156 4,644 CO2 emission per month (0.555kg/kWh)* ton(CO2) 228 172

SHE flow (just for information) g/s 300 300

Saving 1.5 MYen/month, 55 ton CO2/month

BufferTank

Main Compressor

LN2 CE

Sub-cooler

Beam Line Tunnel

S.C. Magnets

Subtunnel B (Connection)

LHe

Multi Transfer Line

Mag

net C

oolin

g w

ith B

us

Purifier

Radiation Shield

JT

Mag

net C

oolin

g R

etur

n

SHEPump

Currnt Leads

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 22 23 21 24 25 26 27 28

Surface

Shie

ld C

oolin

g R

etur

n

Shie

ld C

oolin

g Su

pply

Rad

uatu

i Shi

eld

Tube GasTrailer

>20000 L

Turbine

100 m3

100 m3

QuenchRevcovery

Tank

Oil Separators

to Atm

End Box

Feed Box

100 m3

100 m3

Cold Box

Quench Exhausion

VacuumPump

Quench Exhausion

CB&SC pre-cooling

Magnet Pre-cooling

Gas transport

Shield Pre-cooling

Conceptual Flow Diagram @ pre-cooling

The cooling He gas circulation through the magnets is driven by the compressor.

The shield circulation is driven by the compressor, too.

The pump circulation is bypassed for its pre-cooling.

Magnets is cooled down for 8 days.

Liquefaction

Gas Recovery

Shield Cooling

Quench Emergent Exhaustion

C/L Cooling

Pump Protection

BufferTank

Main Compressor

LN2 CE

Sub-cooler

Beam Line Tunnel

S.C. Magnets

Subtunnel B (Connection)

LHe

Multi Transfer Line

Mag

net C

oolin

g w

ith B

us

Purifier

Radiation Shield

JT

Mag

net C

oolin

g R

etur

n

SHEPump

Currnt Leads

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 22 23 21 24 25 26 27 28

Surface

Shie

ld C

oolin

g R

etur

n

Shie

ld C

oolin

g Su

pply

Rad

uatu

i Shi

eld

Tube GasTrailer

>20000 L

Turbine

100 m3

100 m3

QuenchRevcovery

Tank

Oil Separators

to Atm

End Box

Feed Box

100 m3

100 m3

Cold Box

Quench Exhausion

VacuumPump

Quench Exhausion

CP 0.45MPa

Conceptual Flow Diagram @ Quench

At quench, the pump circulation quickly switch to the bypass line and is isolated from the magnets. The quenched magnet pressure is released to the storage tanks through the exhaustion lines directly.

Tritium Estimation at 1W/m beam Loss ( in case of All beam loss in the SC )

• After 4000 h 1w/m loss – Beam Tube Periphery

• 180 Bq/cc * 5 litter – Cooling Hole

• 25 Bq/cc * 10 litter

– Press Shoulder etc • 10 Bq/cc * 15 litter

– End Space • 50 Bq/cc * 40litter

– 3He to tritium • 7 Bq/cc* (5+10+15+40)

litter – Total

• 54 Bq/cc

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