RIKEN Accel. Prog. Rep. 50 (2017)

Research Activities 1991–2016

Safety management at Nishina Center since 1990
∗1∗1,∗2Uwamino,N.
Y.Y.Uwamino,
N.Nakanishi,Nakanishi,∗2∗2S.S.Fujita,
Fujita,∗2∗2S.S.Ito,
Ito,∗3∗3H.
H.Sakamoto,
Sakamoto,∗2∗2R.
R.Higurashi,
Higurashi,∗2∗2H.H.Mukai,
Mukai,∗2∗2
∗2
∗2
∗2
∗2
∗2
∗2
∗2
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∗2
A. Akashio, K. Tanaka,
Okayasu, N.
N. Fukunishi,
Fukunishi, andand M.
M. KaseKaseTanaka, T. Okayasu,

tions of radiation-relating aﬀairs.
Based on the measured neutron production data,shielding calculation was performed using a discrete
ordinates transport code, and the shield thicknessesof the RIBF building were determined. The results
were investigated by a radiation safety committee led
by Dr. Kamitsubo. The committee ﬁrstly discussed
the criteria of radiation levels in and around the facility. It also discussed the safety measure for induced
radioactivity in accelerator components and in air andwater. The committee held 6 meetings over 4 years
and approved the design.
The RIBF project and its safety design 3) were explained to the mayor and the municipal government
and assembly. After they acknowledged the project,
we explained to the residents successfully.
The personal safety interlock system (HIS) was built
several years before the installation, and its logic wastested using a simulation device. HIS was a separated
system from those of Nishina and Linac buildings, andits logic was comparably simple.
During the construction of RIBF, we applied for thelicense of uranium acceleration at the old accelerators.
On the day when we submitted the application form
to the government oﬃce, a radioisotope source was illegally found outside of radiation-controlled area. Webrought this accident to the notice of the same oﬃceimmediately. We received a special inspection by theoﬃce and sent many documents on the facts of the accident and on measures to prevent a similar accident
from occurring again. We luckily could obtain the license within a normal period.
The ﬁrst beam was extracted from the superconducting cyclotron (SRC) on December 28, 2006. After the tuning of accelerators, a 86 Kr beam was transported to the experimental area in the very early morning on March 15, 2007, and we measured the radiationlevels in and around the facility before daybreak. Thegovernment inspection of the facility was conductedon the same day in reference to our measured radiation data. The pass certiﬁcate was issued on March22, and we could start the experiment. The accelerator staﬀ soon succeeded in the acceleration of 238 U byusing the ﬁxed-frequency ring cyclotron (fRC), and wepassed the government inspection for the whole facilityby the end of March 2007.

The most impressive development since 1990 has
been the construction of the radioactive-isotope-beamfactory (RIBF). It included the decommissioning of theold 160-cm cyclotron, safety design of the new facility,and its commissioning.
The 160-cm cyclotron was the facility built ﬁrst
when RIKEN moved from central Tokyo, Komagome,to the present campus. The operation started in 1966and ended in 1990. It accelerated particles ranging
from protons to Ne ions with energies of several tensof MeV. A hot laboratory was adjoined, and several
points of it were contaminated since it was used fora long period. Decontamination was performed by an
external company. Some parts of the accelerator wereradioactivated, and the activated parts were removed
and stored in the radioactive waste storehouse. The
main part of the accelerator is displayed in front of
the main research building of the campus, as shown in
Fig. 1. However, coils and pole pieces were replacedwith mock-ups since these parts were activated.
When the safety design of RIBF started, we did nothave any data or computer codes for the shielding calculation. Fortunately, a similar-energy heavy-ion facility, Heavy Ion Medical Accelerator in Chiba (HIMAC),
started operation. We could measure the neutron production data at a thick target bombarded by heavy
ions in collaboration with Tohoku University.1) The
measured data were not only used as a source term of
the high-energy neutron shielding calculation of RIBF,
but they also contributed to the development of a computer code, Particle and Heavy Ion Transport CodeSystem 2) (PHITS), which is widely used for estima-References
1) T. Kurosawa et al., J. Nucl. Sci. Technol. 36, 41 (1999).
2) T. Sato et al., J. Nucl. Sci. Technol. 50, 913 (2013).
3) Y. Uwamino et al., Radiat. Prot. Dosim. 115, 279(2005).

Fig. 1. The old 160-cm cyclotron displayed in front of themain research building.
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Directorof Safety
SafetyManagement
ManagementGroup,
RIKEN Nishina
Director ofGroup(2006–present)
Center
RIKEN(2006–present)
Nishina Center
RIKEN
Nishina
CenterWako Safety
Center,
RIKEN
Wako Safety Center, RIKEN

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