Appendix 2-2

Report from the Working Group
Working Group for the External Expert Panelon the Radioactive Material Leak Accident at
the Hadron Experimental Facility of J-PARC

Planning
g of safety
y measures(Countermeasures against recurrence of similar accidents)

The 3rd External Expert Panel Meeting
to Review the Radioactive Material Leak Accident
at the Hadron Experimental Facility of J-PARC at
KKR Hotel Tokyo on 20 June 2013
1

Main causes of the radioactive material leakage andcountermeasures against recurrence of a similar
accidents
The accident is dissected in five stages for which preventive measures are developed.

Stage 1: Delivery of abnormal beam
Stage 4: Leakage of radioactive material into the
Hadron experimental hallStage 2: Damage of thegold target
Stage 3: Leakage of radioactive material
into the primary beamline

Stage 5: Leakage of radioactive
material into the environment
outside the HD Facility
2

Stage1: Preventive measures against recurrence of the malfunction of theEQ (extraction quadrupole) system
In normal operation

75A

In the accident

159A

 Causes
The power supply for magnets, which control the slow beam
extraction, did not properly respond to the command signal in thedesignatedgpperiod of beam spill,
p and then it abruptly
p y broughtg a largegcurrent to the magnets.
 Behavior of the EQ power supply in the accident
・It returned no response to the command signal for the first ~0.3
seconds of the intended beam extraction .
・While the response was restored in 0.3 seconds, the power supply
control unit acted as if it was responding to an abrupt stepcommand of 159 A. This set off alarms of an overvoltage condition
and a tracking error
error.
・The investigation confirmed later that the power supply would
behave in the way as it did in the accident, when a step commandof 159 A is given.
・The
The reason for the lack of response in the first 0
0.3
3 seconds is still
under investigation.
 Countermeasures against recurrence of similar accidents

340A

Subject

Present

Tracking error of magnet
supply current

Display of the error・status in
the control system window.

FutureImmediate shutoff of thepower supply.
Halting of continuous beam
operation

340 A

120 A

> 6 ms< 1 msMaximum current allowed on
the EQ power supply
Response time to an
emergency stop signal of thepower supply

Tracking error：
Excessive deviation of themeasured current of amagnet power supply from3
its set valueCountermeasures against the risks of shortpulse extraction
Possibilities

Measures

Continuous beam operation:
Unintended firing of FX (fast extraction)
ki k magnett
kickerRearrange the timing of the pulser
charge-up, such that it is readied “rightb f
beforecompletionl ti off an SX (slow( lextraction)”, rather than “right before startup of an SX”.

Continuous beam operation:
Emergency stop of defocussing
quadrupole magnets

Focusing quadruple magnets will beturned off when a signal for an emergency
stop of defocussing magnets is detected
detected.

Beam study of accelerators

Lead beam to a beam dump in the hadron
hall directly, not go through a hadron target

FX kicker: A kicker magnet for fast beam extraction, which is used to dump left-over beam during
slow
lb
beam extraction.
t ti
4

Stage 2: Damage of the gold target
Stage 3: Leakage of radioactive material into the primary beamline
Causes :・The beam with a diameter of ~1mm deposited a large amount of energy when it penetrated through thetarget over a short period of 5 ms, locally heating up the gold target to a very high temperature.
・The gold target was not enclosed in a hermetic container.
Preventive measures against recurrencesof the accident :Exhaust stack

Machine room((radiation controlled area))・Fill the target container with an inert gas
whose flow is controlled by a circulation
system.
・Monitor the gas pressure and theconcentration of radioactive material within
the gas.
・Shorten the time interval of measurementof the target temperature and optimize the
alarm
l
th
threshold.
h ld
・Monitor the yield of secondary particles
・Take the target off the beam during
accelerator studies.
studies・Improve the monitors and stop beam
operation when an abnormal signal isdetected.

Primary beamline

Filter・An airtight target container.

Newly installation

Gas circulation system
Inert ggas circulator
Radiation monitor
Pressure monitor
Air storage
bag foremergency

Redirection
in case of
emergency

Pure water circulation pump
Heat exchanger
Demineralizer
PH regulator

TargetInstall an airtight target
container

Cooling water system
Present installation

Schematic of the new target system

5Stage 4: Leakage of radioactive material into
the Hadron experimental hall
Causes: Air-tightness of the radiation shielding wall was insufficient for containing
the radioactive material released in this accident.

Preventive measures: Reinforcement of the air-tightness of radiation shields for the primary
beamline Cover widely two shielding-block
shielding block layers of a ceiling of the primary-beamline
primary beamline with anairtight sheet
 Introduction of an extra bulkhead at openings for secondary beam transport lines
gof cable p
penetrations
 Reinforcement of air-tightness

 Install a radioactivity monitor for the air in the primary beamline area
 Stop the beam operation when abnormal signatures are detected.

6For stage4: Reinforcement of air-tightness ofthe primary beamline
Reinforcement of air-tightness of the ceiling area ofthe shielding blocks covering the primary beamline
・Coverage of the entire ceiling by a double-layered
airtight sheet (yellow part)・Sealing between the airtight sheet and the concrete
walls with a caulking compound• Plain view

P2

P1

P3

P4

P5

Reinforcement of air-tightness of cable
penetrations
・Sealing between the shielding wall andaperturesReinforcement of air-tightness of openings tosecondary beam transport lines
・Introduction of an extra bulkhead at openings forsecondary beam transport lines
・Sealing between the plastic sheets on the ceiling andconcrete walls with a caulking compound
7

Stage 5: Leakage of radioactive material into
the environment outside the HD Facility
Causes:The leakage resulted from operations of ventilation fansPreventive measures:・Existing ventilation fans are to be closed and sealed off.
・Air ventilation from the hall will be done through an
exhaust stack after filtering while monitoring the radiationlevel.
part of the pprotection
・Radiation monitors in the hall will be p
system which stops beam operation when an abnormalp
to separatepradiation level is detected. ((It is important
false alarms caused, for instance, by a radon isotope.)

8

For stage 5: Improvement of the Hadron experimental hall
Machine building No.3

Machine building No.2
Existing ventilation fansare closed and sealed off

Ventilation fan(s)( ) witha filterContamination inspection room

Air inlet

These doors are one-way
locked and designated as
emergency exits

Exhaust monitor

An exhaust stack will be
installed on a moundabove the switch-yard
and will be used until the
Machine Building No.3 isreadied・New air monitors in the hallContamination inspection room

Inward air flow

Existing ventilation fansare closed and sealed off

Tent-yard for equipment entry

9

Improvement of radiation safety management
First step actions (draft)

Second step actions (draft)

・Add
Add alarm functions on all
monitors provided by KEK・Add status displays to provide
the shift crew and relevant staff
with monitor information

Enhanced sharing of monitoring
information on the control system
network, in close collaboration witheach of the facilities at JJ-PARC
PARC

Station for shift crew

new scheme of data sharing

Monitor safety
information

Additionalradiation monitors

Displays ofoperating status

Radiation monitor
display

Data display
Alarm

Data display
Shift crew

Alarm

Existing
radiation
monitoring
systemPersonal Protection System(t b(tobe renovated)t d)Data transmission(with added functions)
Existing Control network

Schematics of the monitor system

10Case studies of heavy accidents at the Hadron Exp. Facility① In case of melt or evaporation of the target metal due to an
accidental, instantaneous exposure to a high-power beam
・An airtight target container to prevent leakage of radioactive
material to the primary beamline area
・Integrity
I t it off th
the ttargett containert i
iis tto beb maintainedi t i d even ini casethe entire target material evaporates, since the maximum
pressure rise in the target container will stay under 100 Pa.

② In case of additional breakage of the vacuum seal of thetarget container
・Radioactive material will leak into the vacuum duct of the
primary beamline.
・Valves on vacuum valves are to be closed, minimizing theleakage of radioactive material leakage into the housing forthe primary beam line. The primary beam line housing has
an airtight structure to prevent leakage into the experimental
hall.
・A large vacuum box, with a volume more than ten-fold larger
than the target container
container, is placed immediately downstream
downstream,
minimizing the risk of breakage of other vacuum seals further
downstream.

Even if several
vacuum seals arebroken, radioactive
material is confined to
an inside of the
primary beam line.
Vacuum seal
※atmospheric pressure in the target container③ (a) In case of additional breakage on the bulkheads of K1.8
and K1.1
・Radioactive
Radioactive material will leak into a vacuum duct of thesecondary beamline downstream
・Mitigate leakage to the experimental hall by returning exhaust
air from the vacuum pump to the primary beamline area

③ (b) In case of additional damage on the vacuum seal infront of the KL or in front of the beam dump
primaryy beamline
・Radioactive material will leak into the parea or into the beam dump area
・Airtight structure of the primary beamline area and thebeam dump area will prevent leakage into the experimental
1
hall and into the environment
1

Summary of countermeasures against
the recurrence of similar accidents
Safety measures developed in examination of each stage of this accident
 Stage 1: Delivery of abnormal beam
• Measures taken on the EQ magnet• Prevent delivery of an excessively large current; Rigorously detect abnormal conditions, etc.
• Countermeasures against the risks of short pulse extraction
 Stage 2: Damage of the gold target
Stage 3: Leakage of radioactive material into the primary beamline• An airtight target container, Circulated inert gas to fill the container• Monitoring the gas pressure and the concentration of radioactive material• Shorten the time interval of measurement of target temperature, etc.
 Stage 4: Leakage of radioactive material into the Hadron experimental hall
• Reinforcement of the air-tightness of radiation shields for the primary beamline• Install a radioactivity monitor of the air →Stop the beam operation when abnormal signatures aredetected Stage 5: Leakage of radioactive material into the environment outside the HD Facility• Seal-off existing ventilation fans
• Ventilation of the air of the hall will be through a stack after filtering and monitoring radiation level, etc.
 Consolidation of status displays with improved radiation safety management system
12Appendix ２－３－１

R
Reportt ffrom th
the W
Workingki
Group
G
Working Group for the External Expert
Panel to Review the Radioactive Material
Leak Accident at the Hadron Experimental
Facility of the J-PARC

Problems in the safety management
system and in the emergency
procedures,, etc.
p
The 3rd External Expert
Meeting held at KKR HotelTokyo on July 20, 2013
1

Issues pointed out at the 2nd meeting of
the External Expert Panel
•

•
•
•
•

•

Safetyy managementgsystemyhas to respondp
to symptoms
y p
before they turn into incidents.
– Actions to be triggered by symptoms– Symptoms
S
t
to
t be
b identified
id tifi d b
by iinquisitivenessi iti
Well thought-out safety measures to minimize unanticipatedpproblems
Close sharing of information and judgment
Authorization of facility operation belongs to the radiation
safetyf t management,t nott to
t theth acceleratorlt division
di i i
Empowerment of on-site facility managers– Keep in mind: Uniqueness of J-PARC
J PARC, where a variety of visiting
users conduct experiments
Protocol has to be clarified for delegation of responsibilities
when
h the
th manager ini chargehisi off-site.
ff it2

Problems in responding to the leak accident
at the Hadron Experimental Facility• Many early symptoms did not lead to appropriate actions.
– Target damage and subsequent leak of radioactive material were
not part of consideration.
– No procedures were defined to respond to early symptoms.
– No scheme for information sharing was in place for the pertinent
people.

• Delay in recognition of the accident led to late reporting.
– Ambiguous understanding of the criteria for issuing the statutory
report.
– Safety Division Head was solely responsible for judgment in
issuing reports• Procedures for conducting user evacuation wereiincomplete.
l t• The facility manager in charge was off-site at the time of
the incident.
incident3

Appendix 2-4

Report from the Working Group
Working Group for the External Expert Panelon the Radioactive Material Leak Accident at
the Hadron Experimental Facility of J-PARC
Evaluation of the soundness of the other facilities of J-PARC
 Materials and Life Science Experimental Facility Neutrino Experimental Facility Accelerator Facility
The 3rd External Expert Panel Meeting
to Review the Radioactive Material Leak Accident
at the Hadron Experimental Facility of J-PARC at
KKR Hotel Tokyo on 20 June, 2013
1

Materials and Life Science Experimental
Facility (MLF)• Area Classification― Target area: Class 1 radiation controlled area
― Experimental halls: Class 2 radiation controlled area
• Prevention of leakage of radioactive material at area boundaries―The
The target area is separated from the eexperimental
perimental halls b
by concrete walls,
alls which
hich arepart of the building structure.
―Zoned pressure controls within the radiation controlled areas―Air
Ai ventilation
til ti iis ddone ththroughh filtfilters with
ith ththe radioactivity
diti it bbeing
i monitored.
it d• Prevention of leakage of radioactive material due to damage on the neutron target― ScheduledS
replacement beforefoccurrence off damages― Precautions against damages
・Multiple layers of protection against leakage of mercury and an early detection system.
・Shutting off the exhaust ventilation will confine the radioactive material• Prevention of leakage of radioactive material due to damage on the muon target―The target installed in a vacuum chamber for protection in worst-case scenarios―Vacuum pump lines will be shut off and the pumps will be turned off, in case of
emergency.

2

Zoned pressure controls in the MLF
Class 2 radiation
controlled area

experimental halls
work area and passageways
machine rooms

Class 1 radiation
controlled area

Neutron target

Muon target

Uncontrolledarea

1st experimental
p
hall

３ＮＢＴ

Ｍ１

storage for radio-activatedmaterials
h t ll ((working
hot-cellki area withithradio-activated（ホットセル）materials)

storage for radio-activatedmaterials

Ｍ2
Hot cellRadiation shielding wall

2ndd experimentalit l hallh ll
Uncontrolled
非管理区域
area

Shielding blocks and walls

First floor

Basement level#3

No ventilation is done during beam operation.

The similar zoned pressure control is arranged at the 2nd and 3rd floors

Multiple protection of the mercury target
 The mercury target vessel consists of a mercury vessel and a safety hullhull.
 The mercury target vessel is covered by a steel vessel filled with helium, which in turn is housed ina neutron target station consisting of an outer liner and hermetic plates, forming a multi-layered
barrier.
 The mercury circulation system is placed in a hot cell under a negative room pressure.
 A multi-level detection system, including radiation monitors and leak detectors, is installed.
 radiation level in air ventilation is continually monitored before exhausting the air through a stack.
Monitor radiation level

MLF building
Neutron target station

Beamwindowi d

FilterHelium vessel
Safety hull
Primary
cooling water
Helium layer

Hot cellHeat exchanger(double-wall type)Mercury circulation
systemMercuryy

Mercury target

Protonbeam
Monitorradiationlevel

Helium layer

Secondary coolingwater

Leak detector of
mercury
Leak detector of
mercury

Radiation
containment

Monitorad a oradiationlevel
Mercury drain
tank4

Multiple protection of the muon target
Vacuum flange Vacuum chamber for the target
Experimental hall

Muon target
Coolingwater

Airtight bulkhead

Muon target

Flow meter

B
Beamlineli vacuum zone
Differential pressure switch

Proton beam
Airtight foil
and gate valve

M1M2 tunnell

Secondarybeamline
Ai ti ht partition
Airtight
titiExperimental hall

Emergency isolation
valve
Vacuum flange

To the neutron
Thermocouple fortargettemperature
measurement ofcooling water

Thermocouple for measurement

Emergency isolation of target temperature
valve
Differential ppressure switch: alarm

Muon experimental area

Thermocouple: MPS
Flow meter: MPS

・Muon target (2 cm-thick graphite) is contained in a vacuum chamber.
gy isolation valve and the ggate valve will be shut off when the vacuum is
・The emergency
deteriorated.
・The boundaries between the MLF experimental hall and the M1M2 tunnel are sealed
airtight.

Neutrino Experimental Facility• Area classification―TargetTt area, etc.
t (underground( d
d level):ll) ClClass 1 radiationdi ti controlled
t ll darea―Utilityy and machine buildingsg (g(ground surface level):) Class 1 radiation
controlled area
• Prevention of leakage of radioactive material at areaboundaries―Underground level construction has a sealed structure―Surface portion between the underground area and uncontrolledareas is under negative pressure control―Air exhaustion from the surface portion is done through filtersand stacks with the radiation level continuously monitored
monitored.
• Prevention of leakage of radioactive material due to damage ofthe target―The target is confined in a helium vessel.
6―Watch any leak of radioactive material from the helium vesselMultiple protection of Neutrino Experimental Facility
Target station building

NU No. 3Building

Negativepressurecontrol

Negative pressure control

Negativepressurepcontrol-10Pa

NU No. 2 Buinding

-10Pa

-20Pa

Surface part
Underground partPrimary beamline
tunnel（concrete shielding wall）

Beam
dump

targetProton beamfrom MR

Helium vessel(iron/ aluminum)
Airtight container for the target Helium
with cooling capability
container

E
Emergency
stop
t valvel
Gate valve

Beam window
Targetg station and beam dump
pp
parts of the target
g vessel are awelded structure of 100-200 mm-thick steel plates. The decay
volume part of the vessel is a welded structure of 16 mm-thicksteel plates surrounded by 6 m-thick concrete walls.
Earthquake-resistant structure is designed to withstand 650 Gal.
No damage occurred in the Great East Japan Earthquake.

•
Multiple layered airtight systems:
Multiple-layered―Both the target container and the helium container are helium–tight.
―Isolation of air between surface and underground levels•
Negative pressure control and controlled exhaustion at the surface level―Reference
R fnegativeti pressures: -10
10 P
Pa ffor TS/NU3 and
d -20
20 P
Pa ffor NU2―The air is exhausted through HEPA filters from a stack, after checking the concentration of radioactive material.
•
Protection system designed to prevent leakage of radioactive material in case of target of horn damages (worst case incident)
7

Prevention of leakage of radioactive material
at the target station
Exhaust device at thesurface level ( with filter)

・The entire building, including the surface-level part, is designated a class 1
radiation controlled area .
・In the surface-level part, the air is exhausted continuously and the leakage isprevented by negative pressure control.
・Radiation level of all exhausted air is continuously monitored.

Surface level
Exhaust stack

Exhaust monitor

Building frame
During beam operation no
personnel is allowed in theunderground area and the
air circulation is confinedwithin the area.

Caulking + airtight sheet

Movable concrete shielding wall
Service pit

Helium circulatory system

Helium circulatory system

TargetCooling water circulatory(circulation?) system

Magnetic horns

Storage

Cooling water circulatory(circulation?) system

Helium vessel
Underground machineroom

Air monitor(Capable of detecting leakage of radioactive material from helium vessel)8

Accelerator Facility• Area classification― Accelerator tunnels: Class 1 radiation controlled area
・During beam operations the air dampers are fully closed.
・Air is recirculated within class 1 controlled area.
― Sub-tunnels: Class 1 radiation controlled area
• Prevention of leakage of radioactive material at site boundaries― Accelerator ttunnels
nnels are air
air-tight.
tight― Interconnection areas between an accelerator tunnel and class
2 or uncontrolled areas are kept under negative room pressureand exhausted.
stack, with― The air is filtered and exhausted through a stackmonitoring the radiation level.
9

Prevention of leakage of radioactive material
at Linac
Linac building structure (cross section)

The klystronygallerygy(a class 2 radiation
controlled area)
Radiofrequency source

The intermediate tunnel(a class 1 radiation controlled area)
The accelerator tunnel(a class 1 radiation controlled area)

Fi controll and
Fire
d air
i sealingliLinear accelerator

At 3 GeV synchrotron the zoned negative pressure control at the boundaries isconducted to prevent the leakage.

10

Prevention of leakage of radioactive material
at 50 GeV synchrotron
R di ti h t
Radiation-hot
machine room

Negative roompressure

EV hall

Accelerator tunnel
connection tunnel

Shielding door
To accelerator tunnel

Negative roompressure

MR Machine Bldg. No. 2(cross section)

MR Utility Bldg. No.2
(cross section)

Evacuation Bldg. No.3((cross section))
Negative roompressure
Accelerator tunnel

Negative roompressure
Accelerator tunnel
connection
tunnelPower supply building
No.1 (cross section)

The same negative pressure control and exhaustion of interconnection areas
are conducted at other boundaries.
11

An accident in worst-case scenario
at Linac during beam operation
 Envisioned incident
A beam duct made of SUS was exposed to a continuous direct hit by the beam. A
partt off radio-activatedditi t d beamb
d t was sublimed
duct
bli d andd was releasedld iin ththe accelerator
l ttunnel. As no one noticed it, air exhaustion was started two hours after beam
operation stopped.
Beam energy: 400 MeV
Average current: 333 μA
Period of beam exposure: one hour
Period of cooling down: two hours
Area of leakage: L3BT tunnel (2500 m3)
Material of beam duct: SUS
Radioactive nuclides to be produced, theirconcentrations (absolute and relative values normalized
by statutory limits), and their sum (two hours after beamirradiation)
Ratio
normalized
li dby statutory
limit
-1

Typicalyp
produced
nuclideConcentrationCt ti（Bq/cc）

Mn 56
F 52
Fe
Mn 52
etc.

4.7×10-4 4.7×10
7 1×10-66 3.6×10
7.1×10
3 6×10-22-6
3.1×10
3.5×10-2-----

Total of the ratios

7.0×10-1 ＜ 1

400MeV
333μA
One hourBeam

Beam duct
SUS

Even if all the radioactive material produced inthis case was released to the environment (outof the radiation controlled area) through onetime exhaustion, the ratio of each nuclide
concentration normalized byy statutoryy limit staysyless than 1.
The total sum of the ratios above is still less than
121.

Summary Materials and Life Science Material Experimental Facility
・Area classification: The areas for neutron and muon targets are classified to a class 1 radiation
controlled area.
・Prevention of leakage of radioactive material at site boundaries
Zoned negative pressure control
・Prevention radioactive material leak due to the damage of the neutron target (worst-case scenario)
・Prevention
Prevention radioactive material leak due to the damage of the muon target (worst-case(worst case scenario) Neutrino Experimental Facility
・Area classification: The target area is classified to a class 1 radiation controlled area
・Prevention
Prevention of leakage of radioactive material at site boundaries
Underground level part is hermetic structure, and area between underground level and general area at surface
level is exhausted continuously and controlled by negative pressure.
・Prevention radioactive material leak by the damage of the target (worst-case scenario) Accelerator Facility
・Area classification: Accelerator tunnels are classified to a class 1 radiation controlled area
・Prevention of leakage of radioactive material at site boundaries
Accelerator tunnels are air-tight.
air tight. Interconnection areas between an accelerator tunnel and an unclassified
general area are continuously exhausted and are controlled negative pressure
We conclude that the area classification, measures to prevent leakage of radioactive material at site boundaries
and measures to p
prevent leakage
g of radioactive material due to the damage
g of a target
g at these facilities aremaintained sound and healthy.
13Appendix 2‐5Report from the Working Group
Working group of the Radioactive
Material Leak Accident at the Hadron
Experimental Facility of J-PARC

On observation of the target
 Reasons why
y direct observation of the target
g isneeded Status of removal of iodine isotope
p in the air
The 3rd External Expert Panel Meeting
to Review the Radioactive Material Leak Accident
at the Hadron Experimental Facility of the J-PARC
At KKR Hotel Tokyo on 20 June 2013
1

Reasons why direct observation of
the target is needed
1. We would like to confirm our analysis on the cause of the accident which ispresently
tl presumed
d as follows:f ll“Th“The protont b
beam was extractedt t d iin a periodi dmuch shorter than the normal operating condition and was delivered to thegold target. This caused partial melting or evaporation of the target, which
resulted in release of radio
radio-active
active material therein
therein.” For detailed designs ofpreventive measures, we would like to conduct direct observation especiallytaking heed on the following points:
–
–
–
–
–

Condition of the target damage in its downstream part (determination of the extent
of damage)Slit condition between target gold blocks (emission pathway from the target)
Condition of bonding between gold and copper block
Condition of interior of the target container and the surrounding environment (lines
of evidence for melting, vaporization and an emission pathway)
Status of beryllium film on the downstream side (possible damage)

2. We would like to investigate the extent of contamination in the area aroundthe target and its neighborhood, learn the pathway for the leak and utilize
the information for development of countermeasurescountermeasures.
2Status of removal of iodine isotope
in the air
Prior to investigation of the gold target, wehave to reduce the concentration of radioactive
material in the air to prevent spreading of thecontamination. For this ppurposep
the air in thetunnel was circulated through charcoal filters
while the concentration was monitored.

3

Layout of machine buildings
MR ExitBldg. No. 1

MR Carry-in
Bldg. No. 2

MR Power Supply
Bldg. No. 3

Neutrino
beamlinetoKamioka

MR Machine
Bldg. No. 2

HadronMachineBldg. No. 2

Hadron Primary Beamline(near the gold target)

Hadron Exp.
Facility

MR Machine
Bldg. No.3

HadronMachineBldg. No. 1

50 GeV synchrotron (MR)MR ExitBldg. No. 2

MR Power Supply
Bldg. No. 1

Switch Yard
MR Power Supply
Bldg. No. 2
MR ExitBldg No
Bldg.
No. 3

MR Machine
Bldg. No. 1

MR Carry-in
Carry inBldg. No. 1

Circumference: 1.6 km•

On July 11, 2013, HEPA filters were replaced by charcoal filters at the
Hadron Machine Bldg. No. 1.

•

On July 14, 2013, HEPA filters of other machine buildings were replaced4by charcoal filters.

Radioactivity density in the sampled air (I-125, [Bq/cm3])
MR-M1

MR-M2

MR-M3

HD-M1

Before using
charcoalhl filtfilters

1.6×10-7(J l 10(July
10, 2013)

1.5×10-7(J l 9(July
9, 2013)

1.7×10-7(J l 9(July
9, 2013)

2.4×10-7( JJuly
l 8
8, 2013)

July 11, 2013

―

―

―

July 12, 2013

―

―

―

July 16, 2013

July 17, 2013

July 18
18, 2013

8.2×10-8( 3 hours circulation))

7.1×10-8( 11 hours circulation)

5.8×10-8

1.1×10-7

7.0×10-8

1.2×10-7( 3 hours circulation)( 5 hours circulation)( 5 hours circulation)( 14 hours circulation)

3.3×10-88<1.8×10-88

4.0×10-88

4.4×10-88( 7 hours circulation)( 11 hours circulation)( 11 hours circulation)( 38 hours circulation)

1.6×10-8

1.9×10-8

2.2×10-8

2.8×10-8( 31 hours circulation)( 35 hours circulation)( 35 hours circulation)( 62 hours circulation)・Charcoal filters have been found to be quite effective* Th
The numbersb
iin parentheseshiindicateditheh totall air
i circulationi l i times
iafter
f startingi thehuse of charcoal filters

I-125 radioactivity density

Radioactivity ddensity (Bqq/cm3)

1.0E‐06

MR‐M1
MR‐M2

1.0E‐07

MR‐M3
HD‐M1(SY)

1 0E‐08
1.0E‐08
‐5

5

15

25

35

Circulation time [h]

45

55

65

75