Radiation Protection at J-PARC Neutrino Experimental ...

T.Ishida | High Power Targetry R&D Roadmap WS, FNAL, 31 May 2017

Radiation Protection at J-PARC Neutrino Experimental Facility

and Lessons Learnt

Taku IshidaNeutrino Section, J-PARC

Center, KEK

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Radiation Protection: Critical Limiting Factor on HPT

Facility Operation

On the way of designing J-PARC neutrino facility, we thought capacity of beam intercepting devices - target, beam window, electromagnetic horns and beam dump - will limit the acceptable beam power and operation.However in reality, radiation protection / safety issues become comparable or even severer limiting factors. As examples I will describe tough lessons learnt at J-PARC neutrino facility:

Radioactive air ventilation/exhaustDisposal of tritiated cooling water

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J-PARC Neutrino Experimental Facility

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J-PARC, Tokai

N

TS: Targt Station, NU: Neutrino Utility building

BeamDump

ExtractionPoint

MuonMonitors

110m

280m

295kmTo Kamioka

TargetHorns

DecayVolume

Near NeutrinoDetectors

MLF

RCS

NU1

NU2

TS

NC

NU3

NMNA


NU3: Neutrino Utility Building #3

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

Beam

1st FL

B1+ 4.5 stand

B1 FL

B2 FL

[Super Hot]

[Hot Machine Room]

18.5

m

4

Decay Volume Beam DumpPit

MuonPit

Pipe

/Duc

t Sha

ft

Pass

age

Neutrino Utility Building #3(NU3)

Beam

10.2m 1m 4m

6m


0.05Bq/ccTS exhaust

01:50 07:50

NU3 exhaust 0.07

Exhaust monitor signal (Dec.24, 2009)

The first continuous (only 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.

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0.05Bq/cc

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


Smoke Test

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• 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 !


Flow of the Irradiated Air at NU3

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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. [Most probably from degasifier of radioactive cooling water ]The air is going into 1F through service hatch and cable penetrations

Negative Pressure control [-20Pa]

Cable penetrations

Clean air

Contained, As-Is Pressure


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

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Degasifier in BD/DV cooling water circuit

Guess: Exhaust from pumps (evacuating hollow fiber membrane filters) may contain radioactive gas from cooling water

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DV BD

Hollow fiber membrane

T.Ishida J-PARC 2014 : The 2nd International Symposium on Science at J-PARC, Jul.15, 2014

Target Station (TS)

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10.6

m

BaffleGraphiteCollimator

Horn-1 Horn-2Horn-3

Beam windowTi-alloy

DV collimator

3 electromagnetic horns / a baffle are supported from the wall of vessel by support modules. Apparatus on the beam-line are highly irradiated after beam. Remote maintenance is the key issue.

OTR Target

Beam

Horn dock

Storage area

Service pit

T.Ishida | High Power Targetry R&D Roadmap WS, FNAL, 31 May 2017 11

Chimney stack

【Negative pressure control】

外気13,000m3/h

Ventilation【 closed 】Service pit

【circulating ]

Superhot Machine room

Jan. 2010 20kW beam

~1.5mBq/cc

900mBq/cc 300mBq/cc

⇔ law：0.5mBq/cc[ 3month average ]

Flow of the Irradiated Air at Target Station

Storage area

Caulking to block gap Sheemles balloon sheet

Add cyricone

Air-tightened duct And dumper


TS 1F Bypass Ventilation

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13,000m3/h

Total 13,000m3/h

1,300m3/h

Reduce ventilation flow to 10% w/o changing total flow ⇒41Ａｒ(110 min) to decay signal×0.3

EA

入口除塩フィルタ

HEPA排気ファン

給気ファン

OA

スタックへスタックへ

OA

EA

HEPA

給気ファン

（インバータ）軸流ファン

（インバータ）

排気ファン

2012年1月

Exhaust signal ：0.4mBq/cc@130 kW ⇒ 0.13mBq/cc0.1mBq/cc(190kW) ⇒ 950kW acceptable !


Stop of ventilation system by single event upset(2010 April)

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 2010, summer.

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Nested negative pressure control

It can be very standard idea at reactor facilities (JAEA ?) Worth to introduce to J-PARC

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Negative pressure Control (- 20Pa )

Pressure: As-Is

Negative pressure Control (-20Pa)

Deeper Negative pressure (-40Pa)

Very long duct (decay)

Past CENF facility design


Although radioactive nuclear ions (7Be..) can be removed using ion-exchange resins, there is no way to extract tritiated water (HTO) . Disposal after dilution under control of Radiation Hazard Prevention Act Based on the working procedures by current drainage system, it is very hard to deal tritiated water from 750kW operation within the same year.

750kW x 107sec (116 days) = 15.6x1020pot 390GBqx ~2 larger than current capability

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Radioactive cooling water drainage @ NU2

8.4x1020 pot / year(400kW x 107sec)25GBq HTO produced per 1x1020POT

In Horn/TS He Vessel/Decay Volume Cooling Water

11.5GBq

13.5GBq

3.5GBq x 60disposal/year = 210GBq

210 / 25 = 8.4

84m3 x 42 Bq/cc (70% of 60Bq/cc limit)= 3.5GBq/disposal


Radioactive cooling water drainage@ NU2

Upgrade water dilution tanks to x ~3 larger volume (84m3234m3)

Piles of the building are not strong enough.New facility building with larger tanks ?

3 urgent improvements:1. Frequency of drainage (every 3d/ 60 times

2d/90 : 600kWx107s)2. Takeover by tank truck (+150kWx 107s)3. Shortcut in the circulation system and

apply partial dilution

Rehearsal of tank-truck takeover at NU3.

(Dec. 2015)

1st real takeover took place on Jan. 2016

2.0m4.0m

1.5m

5.0m

(5m x 5m x 2m) x 2tanks (5m x 5m x 5m) x 2tanks


SummaryFor J-PARC neutrino facility, currently most severe limiting factor on beam power (400kW x 107sec/year) is from limitation on total amount of tritiated water drainage.

Improvement scenario is under consideration, which will count for > 700kW operation.In the future MW operation we need new facility building with larger tank.Or, to carry forward (part of) tritiated water to following years by keeping them in the system (risk when water leak happens)

Radioactive exhaust air is another limiting factor (upgrade successful to accept ~1MW beam)

Nested negative pressure control may solve the problem.

It should be worth to emphasize that facility design wrt. radiation protection, safety, and waste treatment are of vital importance to maximize the benefit of high power target facility.

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Radiation Protection at J-PARC Neutrino Experimental ...

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