Summary of the Report from the Working Groupfor The External Expert Panel on the Radioactive Material Leak Accident
at the Hadron Experimental Facility of J-PARC
July 29, 2013
At around 11:55 on May 23, 2013, the electromagnets for slow extraction of proton beams
from the 50-GeV synchrotron (MR) malfunctioned, and then an intense peaked beam beyond
a designed value was delivered to the gold target in the Hadron experimental hall (HD hall).
Part of the gold target was damaged and the radioactive material dispersed from the goldtarget. It leaked into the environment outside of the radiation controlled area of the Hadron

Experimental Facility (HD facility) due to a series of incidents beyond expectations and afailure in grabbing ongoing situations properly.

The working group investigated andanalyzed causes of the accident and matters of the safety management system.

We

considered preventive measures against recurrence of similar accidents and examined thesoundness of the facilities other than the HD facility in J-PARC.
The accident of the radioactive material leakage occurred through the following fivestages.
1) Due to the malfunction of electromagnets, intense peaked proton beam exceeded adesigned value was delivered to the gold target.
2) The target was instantaneously heated up to a very high temperature and was partiallydamaged, causing vaporization of gold and dispersion of radioactive material in gold.
3) The radioactive material leaked into the primary beamline room because the target
container was not hermetically sealed.
4) Since airtightness of the primary beamline room was not sufficient, the radioactive
material leaked into the HD hall and workers were exposed to radiation.
5) Due to operation of ventilation fans in the HD hall, the radioactive material wasreleased into the environment outside of the radiation controlled area of the HD facility.
Thirty-four out of 102 people who entered the HD hall at the time of the accident, wereinternally exposed to radiation.

They had a whole-body counter measurement, and themaximum amount of their radiation doses was 1.7 mSv. Medical examination confirmed theabsence of any adverse effects due to the radiation exposure.

The total amount ofradioactive material released into the HD hall was estimated with a simulation based on
actual data of the airborne sample that had been collected at HD hall and readings of the area
monitors in the HD hall, being found to be ~20 billion Bq (2×1010 Bq). The radiation dose of
the site boundary at the location closest to the HD facility was estimated below 0.29 µSv asreported in the first statutory report and it has little effect on the environment.
1Based on the analysis of this accident, here we summarized preventive measures againstrecurrence of similar accidents from standpoints of “the prevention of the radioactive
material leakage”, “the prevention of radioactive exposure” and “ensuring soundness of thefacilities”. The frameworks for the measures are as follows: 1) preventive measures against
the malfunction of electromagnets, 2) ensuring of air-tightness, 3) management of exhaust
ventilation, and 4) reinforcement of monitoring radioactivity, etc. It is very important todecrease a frequency of a malfunction of the power supply system. However, we found that
it is impossible to completely eliminate a malfunction through an examination of a various
preventive measures. Essentials of the preventive measure against the radioactive material
leakage are reinforcement of airtightness of the target container and exhaustion of the air
through filters from a stack after checking concentration of radioactive material.
Correspondence of envisioned case studies of severe accidents was examined and then we
confirmed that it would be able to prevent recurrence of the leakage accident of radioactive
material at the HD facility. Direct observation of the target has not yet been conducted.
Although the incidents could have been almost figured out based on simulations, direct
observation of the target and the circumstances is required to draw a final conclusion.
Direct observation, however, is not an essential in considering the preventive measuresagainst recurrence of similar accidents.
In addition to the preventive measures against the hardware aspect, the safety
management system was also verified. Inadequacy of safety management system of theJ-PARC Center led to delay in reporting and incorrect judgments, and they could not preventthe radioactive material leakage and radiation exposure, which should be able to prevent
under appropriate conditions. The impletion is summarized in the following two points: 1)
inadequacy of the safety management system to respond to emergency situations and 2)
inadequacy of the review system from the aspect of radiation safety. Regarding the safety
management system, the following matters will be particularly improved: (a) clarification of ahierarchy for officers in charge, of which Director of the J-PARC Center is a top and has thehighest responsibility; (b) arrangement of their authorities and a chain of commands; (c)establishment of a new “alert status” to collect necessary information and to respond to an
incident at a stage when any indication of an abnormality is observed; and (d) enforce theclarification of the criteria for judgments and the revision of operation manuals. This newsystem will be established with incorporating users. Regarding the inadequacy of theradiation safety review system, the measures to enforce functions of a committee wherediscusses radiation safety issues has been proposed.

The measures include new

appointments of committee members to provide an opportunity for intensive and fruitful
discussions. To maintain and improve individual safety awareness, it is very important toprovide continuous safety education and training. In this accident, there were many users2

who recognized increases in radiation readings but did not leave the HD hall. Therefore, it
is important to provide a safer experimental environment to users through conducting more
efficient safety education and training.
J-PARC consists of, besides the HD facility, the Materials and Life Science ExperimentalFacility (MLF), the Neutrino Experimental Facility and the Accelerator Facility.

These

facilities were examined on their validity of a classification of radiation controlled areas andsafety management equipment, and the safety of instruments and devices. As a result, it
turned out that the classification of radiation controlled areas and the radiation control wereconducted adequately and also it was confirmed that the instruments and devices were highly
safe at the three facilities above.

3

Table1: Correspondence table of incidents and preventive measures
Incidents

Preventive measures

Damage to thetarget• Prevent abnormal beam extraction by improving the operation
condition of EQ magnet power supply system• Improve monitors for target temperature• Retract the target off the beam orbit during accelerator studies

Leakage ofradioactivematerial• Make the target container air-tight and install radiation monitors• Reinforce airtightness in the primary beamline room and implementmonitoring function• Exhaust the air through filters from a stack, after checking
concentration of radioactive material

Lack of sharing
radiation
monitoring
information• Unify radiation safety management equipment• Improve interlock system

Table 2: Issues and measures from the viewpoints of safety management and procedures to becarried out in emergency situations
IssuesMeasures

Organizational setup forresponding to incidents wasincomplete.

• Introduce three levels of status in response to incidents:“the normal status”, “the alert status”, and “theemergency status”. A uniquely identified commander to
conduct information collection and sharing, reporting,actions in incident site, and evacuation conduct.

Organizational setup for safety
review was insufficient.

• Internal Radiation Safety Committee will bereorganized into J-PARC Radiation Safety Review
Committee.

Periodical reviews of education/training and safety standards
were insufficient.

• Continual education and training including users• Bidirectional education processes and exercises forradiation-related accidents• Periodical reviews of the criteria and procedures, etc. toprevent stereotypical responses

4