Appendix 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

1. Progress report
2 M
2.
Main
i causes off th
the radioactive
diti materialt i l lleakagek
3. Problems in the safety management system
The Second External Expert Panel Meeting toReview the Radioactive Material Leak Accident atth Hadron
theH dEExperimental
it lF
Facilityilit off th
the JJ-PARC
PARCat KKR Hotel Tokyo on July 5, 2013
1

１．Progress report
Subjects of discussion at the 1st and 2ndWorking Group meetings• Safety management system
Extraction of issues and problems, causes for the delay in the statutory
report procedures for reporting,report,reporting user support
support, safety training
training, etcetc.

• Experimental facilities:( ) accelerators and beam transport(1)
p system,y, ((2)) detailed investigation
gof
the malfunction of the power supply system, (3) gold target: design
specifics and history, (4) plans of site investigation for the gold target,(5) present set-up
set up of radiation controlled areas
areas, integrity of air-tightness
air tightness
and air exhaustion and (6) overall monitoring and control systems for
managing unusual situations• Countermeasures against recurrence of similar accidents• Review of the integrity of other facilities at J-PARC
2

2. Main causes of the radioactive material leakage
The sequence of the accident is dissected into five stages
where the causes therein are analyzed
StStage1
1: D
Deliveryli
off abnormalblb
beamStage 4: Leakage of radioactive material
into the Hadron experimental hallStage 2: Damage of the gold target
Stage 3: Leakage of radioactive
material into the primary beamline

Stage 5: Leakage of radioactive
material into the environment
outside the HD Facility
3

2. Main causes of the radioactive material leakage

Stage 1: Delivery of abnormal beam
 At around 11:55 of May 23, 2013, due to a malfunction of theslow extraction system of the 50 GeV Synchrotron (MR), a
proton beam consisting of 2×1013 protons was delivered to
the gold target within a very short period (5/1000 of a second)second).
 Normally 3×1013 protons are slowly and evenly extracted
and delivered to the gold target over a period of 2 seconds
seconds.

No. ofprotons Normal beam
2 seconds

No. ofprotons

250 times higher peakintensity than the normal(designed) beam delivery

Abnormal beam

Malfunction
5/1000 of a second(5 milliseconds)
illid )TimeTime

42. Main causes of the radioactive material leakage

Stageg 1: Delivery
y of abnormal beam
Record of a normal beam shot
Normal beam
shot pprofile
正常ショット#297302

Record of the abnormal beam shot profile
Abnormalshot withMPS #298939
EQ MPSbeamショット
5/23EQ
11:55

EQ: instantaneous high current output

The monitor display for beam extraction

Cause:
A power supply for driving a magnet, which
controls the slow beam extraction
extraction, did notproperly respond to the control signal during thefirst fraction of a second in the period of beam
spill, and then it abruptly brought a large currentt thetoth magnet.
t• The accelerator operation was automatically
stopped by detecting the malfunction of thepower supply
ppp y and the signals
gfrom the beamloss monitors.
• While the operation staff of the accelerator
misunderstood that it had been due to amalfunction of the fast extraction kicker
kicker. A large
fraction of the proton beam in fact wasdelivered to the target in HD Facility.
• The accelerator staff did not recognize theincident as one that had led to any possibility ofpartial melting of the gold target.
red line: intensity monitor for the circulating-beamlight blue line: beam spill monitor
green line: preset value for the EQ power supply
blue line: output current of the EQ power supply
pink line: preset value for the RQ power supply
olive-green line: output current of the RQ power supply

52. Main causes of the radioactive material leakage

Stage 2: Damage of the gold target
The target was instantaneously heated up to a very high temperature and was partially damaged,
causingg dispersion
pof radioactive material in the air of the target
g container.
銅ブロック
Copperblock

Gold(□6 mm×L66 mm)
金(□6mmx L66mm)

熱電対
Thermocouples
Coolingg water tubing
g
冷却水配管

Close
Close-up
up of the gold target
金標的部の拡大

Cause:
When the beam with a diameter of ~1mm penetrated the target, a large amount of energy wasdeposited within a short period of 5 ms,ms resulting a very high temperature within the goldgold.
• A volume of ~1 mm in diameter and ~40 mm in length is presumed melted. The estimate above
is based on simulation, which needs to be verified with site investigation that requires reductionof ambient dose rate in the neighborhood
gof the target
g as well as understanding
g of local
authorities and local residents.
• Leak of radioactive material has not been aggravated by subsequent operation of the6accelerator.

2. Main causes of the radioactive material leakage

Stage 3 : Leakage of radioactive material
into the primary beamline
Radioactive material was released from the damaged target spread into the space ofthe primary beamline surrounded by concrete shielding blocks.
Cause:
 The target container was not hermetically sealed.
− Operation with the designed proton beam power assumed use of a water-cooled
rotating nickel disk in a container that can be hermetically sealedsealed.
− In present operation with the beam power lower than the original design, thetarget design was revised to use platinum or gold for increasing the yield of
secondary particles such as K-mesons.
K mesons. The target was stationary and air
air-cooledcooled
or water-cooled, and is placed in an non-hermetic atmospheric environment
where no specific considerations were given for possible damages in abnormal
beam conditions that had occurred in this accident or alike.
 Use of unsealed targets is not uncommon at high-energy proton synchrotron
facilities, while risk hazards associated with beam-incurred target damages are ashared notion at cyclotron facilities and high-intensity
high intensity electron accelerators.
72. Main causes of the radioactive material leakage

Stageg 3 : Leakage
g of radioactive material
into the primary beamline
History of the T1 target at the HD Facility
Beam power

1.2 kW

5 kWOperation
Otiperiod

Jan. 7 to Feb
JanFeb.
28, 2009

Targetmaterialnickel(54 mm)

Cooling
methodAir-cooledrotating disk

Air-cooled(convection)

yes

no50 kW

Oct .1,
1 2009 to Oct
Oct. 1 to Nov.
Nov JanJan. 7 to Jul
Jul. 22, Dec.14,
D 14 2012
Mar. 2, 201016, 2010
2012
to Jun. 28, 2013
platinum (60 mm) platinum (60 mm)
platinum (60 mm)
nickel (54 mm)
nickel (54 mm)

gold (66 mm)

nickel (54 mm)

Directly water –Air-cooled Indirectly water- Indirectly watercooled rotating(convection)
cooledcooleddisk

Appearancepp

Airtightstructurenononoyes8

2. Main causes of the radioactive material leakage

Stageg 4: Leakage
g of radioactive material
into the Hadron experimental hallRadioactive material in the target assembly area leaked into the Hadronexperimental hall.
Cause:
 Air tightness of a radiation shielding wall, made of concrete or steel
shieldinghi ldi blocks,
bl k was iinsufficientffi i t ffor thi
this iincident.
id t− Rubber sheets are inserted in space between the blocks. Putty filling isapplied
ppin ggaps
p at ppenetrations of ducts and tubes.
− The provisions above are sufficient for containing Argon-41 that is
produced from radioactivation of the air during normal operation.
− The provisions above could prevent radioactive material leakage dueto the target damage if the target were hermetically sealed.
− The provisions above are not sufficient in case of an accident involving
damages to the non-sealed target as in this accident.
9

2. Main cause of the radioactive material leakage

Stageg 4: Leakage
g of radioactive material
into the Hadron experimental hall
The radiation shielding walls in the HD hall
Ventilation fansg blocks
Hadron Concrete shielding
Servicespaceexperimental hall
Steel shielding
blocksGold target

Concrete structurePrimary beamline tunnel

Cross section

TrenchEExteriori view
ioff theh radiation
di i shielding
hi ldi wallll
10

2. Main causes the radioactive material leakage

Stageg 5: Leakage
g of radioactive material into
the environment outside the HD Facility
Radioactive material leaked out to the environment outside the building.
Ventilation fans

Delivery of proton beam
was halted by MPS

Operation of ventilation fans

Operation of ventilation fans

Cause: The leakage is resulted from operations ofventilation fans
 Operation of ventilation fans
1st instance: to confirm the soundness of area monitors in the HD hall
2nd instance: to reduce radiation exposure to users
 Since the radiation dose rate in the HD hall was below the legal limit, the environmental effect associatedwith operation of ventilation fans was considered negligible.
 Lack of integration of information including data from radiation monitors in the hall and those at otherfacilities for adequate assessment of the situation.
 Failure in making rational and logical judgment, leading to personnel’s radiation exposure and delays in
11reporting.

3. Problems in the safety management system:

Human factors
 When the interlock alarm went off, the persons in charge considered it
as a hardware
h diissue, not as a potential
i l radiation
di i safety
fiissue.
 Insufficient communication among the persons in charge caused a
didisorganized
i d response tot theth accident.
id t It was not clearly understood among the persons in charge as to “whois responsible for reporting the accident and for initiating the respondingprocess”.
 The Safety Division HeadHead, who is responsible for decision making on asafety issue, was not available on-site to make suitable decisions.
 The safety manual was not sufficiently specific and the organization forfacility-wide information sharing and decision-making procedures werenot clearly laid out.
 Emergency drills did not include case studies of radioactive materialleakage.

12

3. Problems in the safety management system:

Monitoring devices
 The radiation monitoring system was not available in ways
to allow sharing of all the information among the personnel
at distributed locations
locations.
 The layout of the radiation monitoring screen did not deliver
information in straightforward ways to use in intermediatesituations between hardware alarms and radiation
alarms (Difficulty in transition of recognition from hardware
alarms.(Difficulty
alarm situations to radiation alarm situations.)
 Not
N t a sufficientffi i t numberb off radiationdi ti monitors
itwere availableil blat locations with possible leakage of radioactive material.
13

3. Problems in the safety management system:

Accident of radiation exposure andaccident of radioactive material leakage
 Safety management of accelerator-related facilities, such as at KEK,
hhavebbeen stipulated
ti l t d iin accordancedwith
ith RRadiationdi ti HHazarddP
Prevention
ti A
Act.
t Facilities of JAEA have been managed in accordance with Nuclear
Reactor Regulation as well as Radiation Hazard Prevention Act, and astricter law (i.e., Nuclear Reactor Regulation) is applied in case ofaccidents.
J-PARC under joint management of KEK and JAEAg
 Combination of the experiences and expertise of the two organizations
could result in a more effective safety management system.
 Information sharing and work coordination between the two organizations
were insufficient,insufficient leading to inappropriate judgment and actions taken in
response to the radioactive material leakage in J-PARC.
 We expect reconsideration of the organizational relation between bothparent organizations and the J-PARC Center concerning the radiation
14
safety management.