Appendix 3

Investigation on the Gold Target
July 2013
J-PARC Center

1J-PARCJ
PARC Facilities Layout

2Overview of the Investigation
Plain view

Side view

NorthEast
Beam dump

West

Shieldingblocks

Beam

Upper shielding blocks

EastB
Beamddump

Beam

G ld target
GoldttPrimary proton
beamline tunnel

SouthL
Lower
shieldinghi ldi blocks
bl kGold target

Service tunnel

Primary proton beamline tunnel A large number of protons were delivered to the gold target within an
unexpectedly short period (5 milliseconds). As a result, it is consideredthat the gold target was damaged and radioactive material leaked out
from the target assembly area into the Hadron experimental hall (HDhall) and also outside the boundaries of the radiation controlled area ofthe Hadron Experimental Facility (HD Facility).
 To determine the cause(s) of this accident, we need to directly observe
the gold target by using a fiberscope or other methods in close proximity.
3

Preparation for the Investigation (1/2)• The gold target is housed in a primary beamline tunnel in the HD hall. The tunnel iscovered by shielding blocks made of concrete or steel. For observation, it isg blocks above the goldgtarget
g to make annecessaryy first to remove the shielding
opening for a fiberscope.
• It is known that the radioactive material has leaked into a tunnel of the 50 GeVythat is adjacentjto the p
primaryy beamline tunnel of the HD hall.
synchrotron• To prevent further spread of the radioactive material, the investigation is planned
as follows:(Step 1)
By continuously circulating the ambient air in the tunnel through the activated charcoal
filters to be newly installed, reduce the concentration of radioactive material in the air as
much as possible.
N t mostt off theNote:th radioactive
diti nuclides
lid observed
bd right
i ht after
ft th
the accident
id t hhave ddecayeddb
by now, andd th
thedominant airborne radioactive material in the tunnel, at this moment, is iodine-125 (125I). Activatedcharcoal filters act as a very effective trap for 125I.

(Step 2)After confirming the radiation level to be sufficiently low in the tunnel, the tunnel air will be
exhausted through HEPA (High-Efficiency Particulate Air) filters installed at MR Machine
Buildings No.1, 2 and 3 and Hadron Machine Buildings No.1 and 2. During this process
the radiation level will be monitored
monitored.
Note: After the accident, the HD hall has been re-classified as a class 1 radiation controlled area and astrict curfew has been imposed against leakage of any radioactive material from the building.
4Preparation for the Investigation (2/2)
Schematic Diagrams of Filtering Procedures
Exhauststack

Circulation Operation:pcontinued sufficiently
y to remove 125I andother radioactive material
Activated Charcoal filter

OutsideTunnel/Switch Yard
Part of the air goes througha charcoal filter during thecirculation operation

Exhauststack

Exhaustion Operation: initiated when radioactive material
concentrations become negligibly small
HEPA filter
OutsideTunnel/Switch Yard

Machine Building

The air goes through an
HEPA filter during theexhaustion operation
5Locations of Machine Buildings
Emergency ExitServiceEntrance
MR Power Supply
Building No
No.3
3

Neutrino
Beamline
toKamioka
MR Machine
Building NoNo.3
3

MR Machine
Building No.2

MR tunnel
50 GeV Synchrotron

MR Power SupplyB ildi N
Building
No.1
1Emergency Exit

HadronMachine
gBuilding
No.2

Hadron Primary Beamline(near the gold target)

Hadron Machine
Building No.1

Switch Yard
MR Power Supply
Building No.2

Emergency Exit
MR Machine
Building No.1

Circumference: 1.6 km
ServiceEntrance

6Concentration of Radioactive Material in the Tunnels
3)
Table 1: Concentrations of radioactive material in air samples
pfrom the tunnels ((Bq/cmq50 GeV Synchrotron Tunnel
125I

4.1x10Primary Beamline Tunnel of HD Hall

−7

1.4x10−4

Table 2: Estimated concentrations of radioactive material in the exhaust air, averaged over 3months, when the air in the tunnel is exhausted as it is(Bq/cm3)
50 GeV Synchrotron Facility
125I

7.3x10

Hadron Experimental Facility−11

1.1x10−8

Legal limit of the maximum concentration of 125I in the exhaust air: 8x10−6 Bq/cm3• Table 2 shows the averaged concentrations of radioactive material in an exhausted air when air
exhaustion is continued for 3 months as it is. The averaged concentrations are expected to be well
below the legal limit.
• Before the tunnel air go through a usual exhaustion route, we will use activated charcoal filters tofurther lower the concentration on case.
• Exhaustion of the air from the tunnel won’t start unless the airborne radiation level there to become
sufficiently low. The air will be discharged through HEPA filters at MR Machine Buildings No.1- No.3
and Hadron Machine Buildings No.1 and 2 while monitoring the radiation levels to ensure that they stay
below the legal limit.
• 125I is most off the radioactive nuclides observed right afterf the accident have decayed by now and thedominant airborne radioactive material in the tunnel at this moment. Activated charcoal filters act as avery effective trap for 125I.
7

Procedure to open a gap by moving radiation
shieldingg blocks above the goldgtargetgWestNorthSouth

Temporary storage area will becovered with plastic sheets
Removing shielding blocks
to temporary storage

Temporary storage for ironshielding blocks

Temporary storage area will becovered with plastic sheets

Survey area

Temporary storage for upperconcrete shielding blocks

Temporary storage area will becovered with plastic sheets

Gold target

East8Removal p
procedure of radiation shielding
g blocks• Utmost care is taken to prevent the spread ofcontamination and to ensure the safety for all workers.
– Radiation
R di ti shielding
hi ldi bl
blocks:k withith removall off eachh bl
block
k llayer,
the surface contamination is surveyed and the ambient air issa p ed
sampled.
– Workers wear a special protection gear and a mask.
– Plastic sheets are used everywhere
yto preventpthe spread
pofcontamination.
– Use of air purifiers.
– Use of portable air exhaust systems.

9Removal of shielding blocks
at the top layerWith removal of each block layer, the ambient
air is sampled.

Shieldingblocks

Wire

Each block, after removal, is checked forsurface contamination with a survey
meter and by smear tests

Plastic sheets

East

West~10cm

TapingDust sampling horse
Dust sampling unit

10Removal of shielding blocks
att theth topt layerl
Crane

Covering sheets

Taping
12 m

Rubber sheets placed between layers of shielding blocks

height10 m

Opening area

8m

Shielding blocks to be moved

Service tunnel

6m
5m
3m
West

Gold target

East
11Air samplingAir sampling

Covering sheets

12 mheight

10 m
8m
6m
5m
3m
West

East
12

Air sampling
Crane

12 m

height

10 m

8m
6m
5m
3m
East

West
13

Air sampling

To the survey area
for checking surface
contamination

Covering sheets

12 mheight

10 m
8m
6m
5m
3m
West

East
14

Removal process of shielding blocks of lower layers
Two-stepp measures to p
prevent spread
pof radioactive material• Exhaustion of contaminated air in the primary beamline tunnel• Use of air purifiers• Portable exhaust unit with a filter

Crane

Framed p
plastic sheets
Opening area is covered withextra sheets during break

12 m
Portable exhaust unit with a filter

Air purifies

height10 m
8m

Taping
Air flo
flow

6m
5m
3m
East

Gold target

WestTo the HD Machine Building

Primary beamline tunnel

15

Air flow in the Hall while moving shielding blocks
The Hadron experimental hall(cross section)
Exhauststack

Air flow

Air flow

FilterMachineBuilding

Air flow
Air flow

Ai flflow
AirGoldtarget
g16

Removal of shielding blocks of lower layers
Portable exhaust unit with a filter

Crane
12 m
Air purifies

height

10 m
8m
Air flo
flow

6m
5m
3m

East

Gold targetgW tWest
To the HD Machine Building

Primary beamline tunnel

Removal of shielding blocks oflower layers
yCrane17

To the survey area
for checking surface
contamination

Portable exhaust unit with afilter

12 m

Air purifies

height

10 m
8m
Air floflow

6m
5m
3m
West
To the HD Machine Building

EastGold target

Primary beamline tunnel

18Temporary (shield) opening on the topof the gold target
North
Framed plastic sheets

During crane
operation, only thesheets required tomake necessary
opening are removed

West
East19SouthWhen a suitable access path is prepared, the gold target is
examined by using a fiberscope, etc. guided through an L-shaped
tubing.
L-shaped guide tube

45m
4.5
Tubular scaffolding
for a fiberscope

Slit opening: gap width 84 mm x length 500 mm

1m
20

②①

Step 1: observe the gold
target by adjusting thelocation of the tip of theL-shaped
p gguide
Step 2: observe from theother side, if possible.

50 cm

21

The fiberscope to be used22

Practice run with a dummy target
mock-up scaffolding (4.5 m high)The dummy target andmock guide pipe

unlighted video scope image

up close image obtained with digital zooming

23

Schedule of Investigation of the Gold Target
Needs about 4 weeks for preparation after starting air exhaustion
Air exhaustion through MR Machine
Buildings No.1-3 and Hadron Machine
Building No.1
Air exhaustion through Hadron Machine
B ilding No
Building
No.2
2
Air exhaustion from primary beamline
tunnel of the HD hallRemoval of shielding blocks from theprimary beamline of the HD hallInstallation of the fiber scope
Investigation of the gold target
Restoring the shielding blocks to their
original positions

About 2 weeks

Actual schedule may vary.

About 2 weeks
24