Radiation Protection at J-PARC Neutrino Experimental Facility and - - PowerPoint PPT Presentation

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 Ishida Neutrino Section, J-PARC Center, KEK

1

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

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/exhaust Disposal of tritiated cooling water

2

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

J-PARC Neutrino Experimental Facility

3

J-PARC, Tokai

N

TS: Targt Station, NU: Neutrino Utility building

Beam Dump Extraction Point Muon Monitors 110m 280m 295km To Kamioka Target Horns

 



Decay Volume Near Neutrino Detectors

MLF RCS

NU1 NU2 TS NC NU3 NM NA

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

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 Dump Pit Muon Pit

Pipe/Duct Shaft Passage

Neutrino Utility Building #3 (NU3) Beam

10.2m 1m 4m 6m

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

0.05Bq/cc TS exhaust 01:50 07:50 NU3 exhaust 0.07

Exhaust monitor signal (Dec.24, 2009)

The first continuous (only 20kW) beam NU3 exhaust signal: Alert level= 0.05Bq/ cc(Raw data) ⇔ Observed 0.06 Bq/ cc

Beam operation w as lim ited w ithin only ~ 3 0 m in due to the radiation in the exhaust air.

5

0.05Bq/cc 20min 25min 30min 20min 25min 30min

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

Smoke Test

6

• 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 pit PS/DS B1

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

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

Flow of the Irradiated Air at NU3

7

900mBq/cc 400mBq/cc 30mBq/cc

Exhaust monitor 50mBq/cc (Raw data) Service hatch Super-hot Machine Room (B1F) Machine room (1F)

Dump pit Cooling loop Mupit cooling 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

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

Air tightening (NU3)

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

8

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

Degasifier in BD/DV cooling water circuit

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

9

DV BD

Hollow fiber membrane

T.I shida J-PARC 2 0 1 4 : The 2 nd I nternational Sym posium on Science at J-PARC, Jul.1 5 , 2 0 1 4

Target Station (TS)

1 0

10.6m Baffle

Graphite Collimator

Horn-1 Horn-2 Horn-3

Beam window Ti-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

1 1

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

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

TS 1F Bypass Ventilation

1 2

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 HEPA 排気ファン 給気ファン

OA

スタックへ

スタックへ OA EA HEP 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/cc 0.1mBq/cc(190kW) ⇒ 950kW acceptable !

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

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.

1 3

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

Nested negative pressure control

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

1 4

Negative pressure Control (- 20Pa ) Pressure: As-Is Negative pressure Control (-20Pa) Deeper Negative pressure (-40Pa) Very long duct (decay) Past CENF facility design

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

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  390GBq x ~2 larger than current capability

1 5

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

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

Radioactive cooling water drainage@ NU2

Upgrade water dilution tanks to x ~3 larger volume (84m3234m3)

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

2.0m 4.0 m 1.5 m 5.0 m

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

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

Summary

For 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.

1 7