exhaust monitor signal & improvements for air-tightness ventilation system trouble by neutrons

Ver. 1.1 [Nov.09] NBI2012, CERN, Geneva, Switzerland, 6th – 10th November 2012

Ishida et al. J-PARC/KEK

T2K Radioactivity in the

Exhaust AirT.Ishida, Y.Yamada, M.Tada &

Y.OyamaNeutrino Experimental Facility

GroupJ-PARC / KEK

[CONTENTS] 1. Exhaust monitor signal & improvements for air-tightness

2. Ventilation system trouble by neutrons

3. Bypass line installation and operation

4. Summary 1


Ishida et al. J-PARC/KEK Radiation Monitors

2

TSNU2

NU3

BLUE311G

Exhaust air monitor (gamma): 3 pairs(S/BG)NaI (TI) scintillation counterLevel of exhaust at upstream of the exhaust chimney stack.Should be no signal during beam< 0.5 mBq/cc for 3 month average

Environment air monitor (gamma): 3 NaI (TI) Scintillation counter level of environment at pits/machine rooms at TS / NU3Entry prohibited with signal > 10mBq/ccNU2 exhaust is also monitored.

Area monitor (gamma/n): 4 pairsIonization chamber / 3He counterNear the boarders of rad. controlled areaGamma: < 0.3uSv/h [alert 0.8uSv/h]Neutron: < 0.01uSv/h [alert 0.5uSv/h]Integration over every 1 hour is used for PPS: limit: 0.5uSv/h x 1hr.


Ishida et al. J-PARC/KEK Radiation monitors at TS

3

Exhaust monitor

Environment monitor

Area monitor

NU3 also has the monitors

10L （ 3atm ） , 50mm thick Pb3inφx3in NaI 　

41L （ 1atm ） 30mm thick Pb2inchφx2inch NaI

10atm 1inchφ×10inch He-3 Prop. Counter

YEL301

YEL302

BLU302

BLU312

2 cells (A/B) for signal / B.G.

Exhaust chimney stack



0.05Bq/ccTS exhaust

01:50 07:50

NU3 exhaust 0.07

Exhaust monitor signal (Dec.24, 2009)

MR R#28: The first continuous (20kW) beamNU3 exhaust signal: Alert level= 0.05Bq/cc(Raw data) ⇔ Observed 0.06 Bq/cc

Beam operation was limited within only ~30min due to the radiation in the exhaust air.

4

0.05Bq/cc

20min 25min 30min 20min 25min 30min



Flow chart of NU3 Air Conditioning

(Beam Operation Mode)

If air tightness of the pits / rooms are bad, irradiated air in BD can go to the hot machine room We started to investigate air flow / air tightness of pits / rooms

5

mupit

BeamDump

Hot machine room(1F)

polution test room (1F)

Stair room

Super-hot machine room (B1F)

-20Pa

Exhaust monitor

Env. monitor

Leak-tightened damper

OUR GUESSExhaust chimney stack



NU3: Neutrino Utility Building #3

Beam Dump Pit /μPit

Water circulation system for downstream half of DV and BD [B1] Air circulation system for BD / MuPit [B1+4.5]

Decay Volume Beam DumpPit

MuonPit

Pipe

/Duc

t Sha

ft

Pass

age

Neutrino Utility Building #3(NU3)

Beam

Beam

1st FL

B1+ 4.5 stand

B1 FL

B2 FL

[Super Hot]

[Hot Machine Room]

Cross section of NU3

18.5

m

10.2m 1m 4m6m

6


Ishida et al. J-PARC/KEK Drain water pit at muon pit

The drain port connecting to dump pit was closed by a flange with thinner pipe.

2010/1/6

1/18

Dump pit mpit

End of pipe under water level

7


Ishida et al. J-PARC/KEK Smoke Test

8

• B2 PS/DS smoke around heat-retention of square-ducts ⇒ / penetration of cable bundles • B1 around service hatch / penetration of cable bundles ⇒

@ pipe/duct shaft(B2) 1/14

Dump pitPS/DS

B1

Test with a smoke machine, normally used for theater plays !



Air tightening (NU3)

Remove insulation around ducts seal with thin iron plates and caulkingLiquid silicone glue for the cable penetrations Seal edges of concrete blocks at the delivery entrance to downstairsDoors sealed with tape, repeat smoke tests to find remaining leaks

9


Ishida et al. J-PARC/KEK Jan. 23-24 （ MR Run#29 ）

NU3 exhaust monitor signal becomes much smaller TS exhaust becomes 0.05Bq/cc with 2 hours of beam operation

10

TS Exhaust 0.05Bq/cc

NU3 exhaust

0.05Bq/cc



Flow of the Irradiated Air at NU3(beam commissioning mode)

11

900mBq/cc

400mBq/cc

30mBq/cc

Exhaust monitor50mBq/cc

(Raw data)

Servicehatch

Super-hotMachineRoom (B1F)

Machineroom (1F)

Dump pitCooling loop

Mupitcooling loop

Environment air monitor suggests that irradiated air was leaked into super-hot machine room from (air-tightened) dump pit cooling loop.The air is going into 1F through service hatch and cable penetrations

Negative Pressure control[-20Pa]Cable

penetrations

Clean air



Flow of the Irradiated Air at TS

12

Service pit / storage area covered with concrete blocks.

ServicePit

Super hot Machine room

chim

ney

stac

k

Cooling loop

negative pressure

Clean air

300mBqcc

900mBq/cc

Exhaust line(closed)

• Duct /pipe/ cable penetrations, including horn power cables.

The job was much much

harder


Ishida et al. J-PARC/KEK Ex.Monitor Measurements

13

0.5mBq/cc

3 mBq/cc

0

BLU302A （ Signal)

BLU302B （ BG)

Exhaustto enter into TS

0.06Bq/cc

0.045Bq/cc

Both A(cell with 3 atm. exhaust air) and B(closed, BG cell) have signalGamma ray from 1F environment (outside of the cell) air is observed as common signal.

Radiation level in Exhaust = [ {A – Pedestal} - {B – Pedestal} ] / 3 (atm.)1mBq/cc~1.5mBq/cc law limit ＜　 0.5mBq/cc 　 [3-month average]January: 3 days operation / 30days 0.5m x 10 = 5mBq/cc acceptable.

Exhaustto enter into TS

（ R#29, Jan.2010)


Ishida et al. J-PARC/KEK TS air tightening （ Feb.15-22 ）

Stop air flow coming out between concrete blocks by backup material and caulking

14

We now learn how to sense tiny air leak by hand !

Smoke tester

Need to do after every summer maintenance !


Ishida et al. J-PARC/KEK Cable penetration

•

15

HornPower Cables

Two SignalCable trays

Two square opernings

Not only by smoke, but also by smell of smoke, we can find leak…

apply neg.pressure to 1F:-100Pa


Ishida et al. J-PARC/KEK R#29 Jan.30~Feb.6 R#30 Feb.22~Mar.1

1.0 0.5mBq/cc (20kW, factor 2 reduction) 0.5~0.8mBq/cc (27kW)

16

0.5mBq/cc



Add MVDs in the Underg. Vent Line

(Mar.30~Apr.2,2010)

We doubted leak in the ducts to vent undergr. rooms17

Chim

ney

stac

k

New Motorized Volume Dumpers

To exhaust monitor

Inlet Filter Unit

Outlet HEPA Filter Unit

Inlet Filter Unit

VentilationFANS (outlet)

VentilationFAN(inlet)

MVDroom press.

control


Ishida et al. J-PARC/KEK Install MVD 　 Mar.30~Apr.2

Add air-tightened MVDs (bought for NU3..) Later replaced to bigger ones / install the small ones to NU3

18

Normal damperAir-tightened dumper

Air-tightenedWelding thick platesNormal thin duct


Ishida et al. J-PARC/KEK Cover Shield Block Surface

During ventilation, sheets swollen by the air, leaking through the sealed block floor..

19



Mar.19-25(R#31)Apr.14-21 (R#32)

Signal (A-B) highly reduced (but not perfect) 0.07 +- 0.09mBq/cc (40kW)

0.5mBq/cc

20


Ishida et al. J-PARC/KEK Air under the cover

Radiation level under the cover: ~ 90mBq/cc21

Ar40(n,γ)Ar41 (1.83hrs)K40 (1460keV)

N-14 (n, 2n) N-13 (9.97 m)O-16 (n, p) N-16 (7.3 s)



Sudden Stop of TS Ventilation System

[Apr.20-21, 2010]

The control panel was located in B1F machine room, since limitation of 1F floor space. Later we noticed it was around the level of target.. “Single event upset” on a CPU unit of the PLC by beam-induced fast neutrons.As temporary fix during Run-1, extract / relocate the CPU unit by 10m to area with less neutrons, then covered with LG blocks.Whole control panels of air-conditioning/cooling water at TS moved to the ground floor in 2009, summer.

22



Install MVDs (Jun.2~4, 2010)

TS/NU3 underg rooms separated by the dumpers2010Jun: 　 0.1~0.15mBq/cc @ ~50kW

23

TS NU3


Ishida et al. J-PARC/KEK 2011 Feb.~Mar.

24

We have introduced the second layer of sheets to shield floor. ~0.3mBq/cc for 145kW : ⇒ hit 0.5mBq/cc limit with 240kW beam1 month average for Jan.:0.14mBq/cc ⇒ 1/28~2/28: 0.32mBq/cc



Bypass line: Idea & Expectation

25

13,000m3/h

Total 13,000m3/h

1,300m3/h

Use TS 1F volume as a reservoir of irradiated air to decay.

Airflow in the room / Total

• 41Ar x0.29 11C x0.14 13N x0.12 15O

x0.10

Now

T1/241Ar ： 110 min11C ： 20 min13N ： 10 min15O ： 2 min

10%

0

20

40

60

80

100

120

140

160

180

200

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Rat

io (1

F ra

diat

ion

leve

l)

• 41Ar x2.9 11C x1.4 13N x1.2 15O x1.0

Airflow in the room / Total Now10%

Rat

io (e

xh. r

adia

tion

leve

l) Idea by Oyama-san


Ishida et al. J-PARC/KEK Design

26

10~100%

90~ 0%

TS 1F

VAV ： Variable Air Volume CAV ： Constant Air Volume Inverter control for inlet fans

Bypass line



ConstructionDec.2011-Jan.2012

Duct: 600x1,000 4D=4m straight section needed fro VAV/CAV. Works completed on Jan.13, 2012. Bypass flow set to zero for Jan. beam.Flow control was carefully tuned on February.

27

To chimney

To 1F

1F return

HEPA

Inlet Filter VAV(1F)

VAV(Bypass)

CAV

Inv.fan Inv. fan



Tuning for Air Flow Control(Feb., 2012)

28

VAV opening ratio (%)

1F In 1F Out

Bypass

Negative pressureControl

Bypass 0% 100%

0m3/h

13,000m3/h

Bypass1F

Total


Ishida et al. J-PARC/KEK Mar.~Apr. 2012

0.4m(127kW)0.13mBq/cc(140-150kW) with 90% bypassMarch beam: 145/ 0.13 x0.5=558kW acceptableApril beam: 176/ 0.16 x0.5=550kW acceptable

29



Balloon Sheet Installation(Apr.2012)

Improve shield cover: Continuous 2-layer sheets for balloon was installed in Apr.2012 during beam.Radiation level after installation

reduced by factor ~2 ~0.1mBq/cc for 190kW

30* Photo taken on Nov.2, 2012

• The radiation level in the 1F w bypass• 50mBq/cc ⇒ 　 (70+-5)mBq/cc [w/o beam:

35mBq/cc]• Still low compared to regulation

[<500mBq/cc]


Ishida et al. J-PARC/KEK Summary

Observed Acceptable <0.5m2010 Jan.-Feb. 1.5mBq/cc (20kW) ~7kW* Air tightening for floor blocks, seal cable penetration holes, & smoke tests 2010 Feb.-Mar. 0.5(20)0.8(27kW) ~17kW

* Add MVDs for ducts to underground rooms / cover block floor by water-proof sheets 2010 Jun. 0.1~0.15(50kW) 170kW* Add blocks to gaps at shield floor, upgrade of air-tightened doors 2010 Nov.~2011 Feb. 0.28(105)0.4(125kW) 160kW

* Add second layer of sheets2011 Mar. 0.3(145kW) 240kW* Install bypass line to 1F vent line2012 Mar.~Apr. 0.13(145)0.16(176kW) 550kW

* Balloon sheet installation2012 May.~Jun. 0.1mBq/cc(190kW) 950kW

31

Acceptable beam is being improved by 2 order, now ~ 1MW

Radiation in exhaust air of TS was being the bottleneck of our beam power



Backups

32


Ishida et al. J-PARC/KEK Regulations on Radiation

Radiation level, ( ) = J-PARC design rule• Boundary of radiation control area: <0.5mSv/h (<0.25mSv/h)• Accessible area for radiation worker: <25mSv/h (<12.5mSv/h)• (Boundary between building and underground soil: <5mSv/h)

Radioactivity in disposed water• 3H: <60 Bq/cm3

• 7Be: <30 Bq/cm3

• 22Na: <0.3 Bq/cm3

Radioactivity in exhausted air through a stack• 3H: <5 mBq/cm3 in three months average• 41Ar: <0.5 mBq/cm3 in three months average

33


Ishida et al. J-PARC/KEK Additional Concrete Shields

(2010 Summer)

Blocks should be sealed and covered after every summer maintenance !

34

Air-tightened door upgraded


Ishida et al. J-PARC/KEK 2010 Jun.2010 Nov.~Dec.

2010Jun: 　 0.1~0.15mBq/cc @ ~50kW 2010Nov.~Dec: 0.28mBq/cc @105kW 0.36mBq/cc@115kW

Signal levels of A/B were reduced, but not for B-A… 35

Nov.~Dec.Jun. 2010


Ishida et al. J-PARC/KEK 2011 Jan.~Feb.

Smoke test on Jan.13, fix some leaks at cable penetration holes.0.5mBq/cc when the additional shields were removed (105kW) 0.4mBq/cc with shields(105kW), 0.4mBq/cc for 125kW

36

W/o additional concrete shields

exhaust monitor signal & improvements for air-tightness ventilation system trouble by neutrons

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