The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

Decommissioning of CNS SF Cyclotron Facility
S.Watanabe\ N.Yamazaki•, Y.Ohshiro•, S.Kubota•, K.Kono·, S.Kubono•,
T.Katayama· , M.Sekiguchi", K.Masumotob, and K.Shodac"Center for Nuclear Study, University of TokyobRadiation Science Center, High Energy Accelerator Research Organizationc Nihon Kensetu Kogyo Co. Ltd
The CNS SF cyclotron facility was decommissioned at theThe paper discusses the decomend of August 2000.
missioning procedures of the CNS SF cyclotron facility,
especially describes the evaluation and separation of raThe analysis of residual radioactividioactive materials.
ties in shielding, and transportation of activated materials
are discussed.
1. Introduction
An operation of SF cyclotron was stopped at 13th Dec.
1999. Total amount of operation time was 36000 hours
from the begging of first beam experiments. On Dec.
1999, decommissioning schedule was planned and disassembling of beam transport line was started at the beginning of Jan. 2000. The dismantling of SF cyclotron wasfinished at the end of June. 2000. The decommissioning
program comprises, (1) a disassembling of SF cyclotron
and beam transport line, and (2) a separation of activatedmaterial from the instruments and building. There wereso many instruments in the SF cyclotron. Magnets, vacuum chambers, rf resonator, and their wiring and mechanical connection were tightly coupled with each other. Especially, SF cyclotron magnet was separated into fourpieces of magnet yokes after dismantling the rf acceleration
Dee. An identification and separation of radioisotope andtheir evaluation have been done on the basis of the"guide-line of decontamination for a particle accelerator".
The measuring instruments and their calibration are ruled
Which are basedin the radiation safety control manual.
on the guideline of IAEA, ICRP, and law of radiation protection in Japan [1-4].

Fig.l Lift-upped rf resonator of SF cyclotron to land on
the KEK. The acceleration Dee (left side) was covered with Pb shield.

Figure 1 shows rf resonator transported from CNS-Tanashi
campus. It is lift-upped to land on the KEK-Tsukuba. The
decommissioning also includes a cleaning of the radioactive isotope in a ferroconcrete for a radiation shield. The
radioactive isotope 60Co, '34Cs, and 152Eu are generated andcondensed in the ferroconcrete of the radiation shield. Especially, a fast neutron from the SF cyclotron activateswide area of the cyclotron room. The radioactive waste
was transferred to the JRIA (Japan Radio Isotope Association). So, the planning of decommissioning was concentrated to the quantitative estimation of the radioactive material in the CNS SF cyclotron facility and determination ofboth the area and depth of decontamination of ferroconcrete.
This paper discusses the decommissioning of SF cyThe severances and decontamination ofclotron facility.
the radiation shield are also discussed. A particle spectrometer was dismantled and has been moved to RIKEN.
Dismantling of the spectrometer is discussed in the elsewhere.
2. Decommissioning procedures
The decommissioning comprises the survey of radioactivematerials, disassembling the radioactive materials, severance of radioactive materials, transportation and storage of
There are so many raseparated radioactive materials.
For examples, adioactive materials in the SF cyclotron.
coaxial-type rf resonator, an acceleration Dee, a beam extraction channel, an axial injection system, a vacuum
chamber and beam probes were activated with the accelerated ion beam.
During the beam acceleration, accelerated ion beam
hit the electrodes such as the cone, Dee, deflector, andvacuum chamber at the exit of SF cyclotron. The beamhitting is a reason of the production of radioisotopes because of the gamma ray production and neutron capture.
Due to the absorption of fast neutron, radioisotope is generated and remained in not only the cyclotron but also thesteel bar for ferroconcrete in the radiation shield. The fastneutron is converted to the thermal neutron when it is passing through the water in the cooling water pipe.
Before the identification of the radioisotope, it wasdisassembled and moved to a low background area. The
low background area was defined as the natural background room, where was providing a lift up instrument andUsing a
was proofed against a heavy weight instrument.
Nal scintillation survey meter, and a GM counter themeasurement of radioactive materials were carried out.
The surface of instrument was checked by the smear
method to identify the contamination of radioisotope waste.
The radioactive waste is defined as the radioactive material-423-The 13th Symposium on Accelerator Science and Technology, Suita, Osakn, Japan, October 2001

from hospital, industry, and university, which is divided byJapanese law.
The radiation worker who is given educational training of radiation protection contributed toseparate the radioactive waste. The education of safety
manual was ruled before the contribution. The radiation
exposure received under the decommissioning was limited
under 30 j..LSv/day.
There are so many beam instruments and vacuum
chambers in the SF cyclotron. The extracted beam wasswitched into the four courses.
Course 1 was used toproduce the unstable nuclear beam (Cavel). Course 2
was devoted to TARN2 beam line (Cave2B). Course 3
and course 4 are located in the experimental room named
Cave 2A. The course 4 was separated to the Cave 3A andCave 3B, respectively.
A beam stopper for RI production was located in the course 3.
The radiation map of
the SF cyclotron was made to identify theradioactive area.
The measured radiation map showed that the center ofcourse 4 was strongly activated.
After the disassemblingof the SF cyclotron, contamination of the building wasevaluated by the high-sensitive and wide area radiation
detector (CONTAMAT).
We measured the compositionand quantity of the radioactive nuclei in the ferroconcrete.

struments have been transported with a shield box.
4. Radioisotope in the ferroconcrete
The instruments in the experimental rooms were disassembled and moved to the KEK Tukuba. The surface of ferroconcrete wall, ceiling, and floor was surveyed by using
the Nal scintillation survey meter. The background levelof the experimental room was 0.06 j..tSv/h.
The clearance level of the radioactivity is recommended as 1110 of natural background such as the 40K, U,and Th. The radioisotope in the ferroconcrete was measured by using the Ge detectors. Figure 2 shows the example of radioisotope in the ferroconcrete. The activity
peak was found at the 1Ocm depth from the ferroconcretewall.
The measured radioisotope level was 0.25 Bq/g.
The background level was 0.45 Bq/g for~In case ofvegetable, for example [5], spinach includes 0.15Bq/g andradish includes 0.048Bq/g.
The cow milk includes
0.048Bq/cc. The ground (0-5cm) includes ~ of 0.32
Bq/g.
If only 40K of 0.45Bq/g is involved in the ferroconcrete, the natural background becomes 0.06 j..LSv/h,
which is calibrated by the Nal scintillation survey meter.
0.30

3. Separation of radioactive material
An identification of radioactive material was carried out
based on the rules of IAEA. The Nal scintillation survey
meter and GM counter have been used to measure the surface dose of the radioactive material.
Using the Ge detector and multichannel analyzer carried out the mass
analysis of radioisotope.
For convenient, portable radiation monitor has been used to measure the radiation level.
The measurement device was calibrated by 60Co. In orderto move the radioactive element to the KEK Tsukuba; surface dose of transported material should be controlled under the 5 j..tSv/h, named L-type transportation. The separation of radioactive elements was carried out by the following rules:
A Beam transport line was composed of the vacuum
chamber. The vacuum chamber has no flange systembecause of screw-nut structure. It means that half of outer
diameter of vacuum chamber was designed less than bore
radius of Q-magnet.
So, dismantling time of vacuum
chamber was shorter than flange type vacuum chamber.
On the other hand, the upstream of vacuum chamber in theH-type 120 degree analyzer magnet was higher radiationlevel compared with down stream of the vacuum chamber.
The higher radioactive element over the surface doseof 5 j..tSv/h should be moved to the JRIA.
The 50litter"yellow can" was used to pack the radioact\ve waste. An
oversized radioactive waste such as a long vacuum chamber was cut within the 50cm length.
The cutting machine was used in the green house to avoid spreading thedust of waste.
On the other hand, in case of the surface
dose exceeds 500 j..tSv/h the acceptation of radioactive
waste was refused by the JRIA.
In that case, Pb shield
was used to decrease the radiation level.
The radioisotope in the accelerator components comprises mainly 6°Co.
The energy of gamma ray from 60Co is 1 MeV.
The Pbwith thickness of lOcm decreases the gamma ray intensity
by the 1/100 of initial conditions. The radioactive in--·-----·-·-·--·-- 1111Zn65

0.25....._

J:!.l

0.20'·~0'e 0.15

E1Sc461111Na22--~--·

CIMn541- 1-- 1- 1--0">".;::l0Eul52

I 11Csl34(j~

1- 1- 1- 1-- 1--

0.10

11Co601-0.05

-0.00
040

10.

bl II n80 120 160 200 240 280 320 360 4tXJ 440

Depth from Surface (mm)Fig.2 Depth dependence of the radioactive isotope in theferroconcrete sampled at the wall near the deflector of SF
cyclotron. The natural background of ~ is excluded inthis figure.
We also measured the radioisotope by using the ionchamber.
The background level was 0.102 Bq/cm2 at thefloor of ferroconcrete.
The 40K was main activity in thenatural background. The 40K measured at ground surface(0-5cm) were 0.84Bq/cm2 •The 134Cs measured at groundsurface (0-5cm) was 0.25Bq/cm2• We investigate the relation between the surface level and radioactive isotope intensity.
It was found that linear curve was obtained.
A calibration constant (Bq/g vs. j..tSv/h) is of(58.56x-3.617)E-2 for 60Co, where x the measured surface
dose, j..tSv/h.
The steel-bar in the ferroconcrete was activated. The
y-ray spectrum of the steel-bar sampled at the surface offerroconcrete is tabulated in Table 1.
In case of steel-bar
in the ceiling where is 10 em thickness, the steel-bar wasactivated up to 0.45 j..tSv/h.
They are stressed to radioactive waste.

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The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

The photo of each instrument was taken to identify theradioactive instrument in the steel-box.

Table 1 yray spectrum of the steel bar. (Bq/g)
F1(3.5+/-0.4)E-l(7.2+/-0.4)E-1
F2(2.0+/-0.2)E-1 (5.8+/-1.7)E-2 (1.9+/-0.2)E-1
F3(1.4+/-0.3)E-l
BG
5.0E-2
5.6E-2
5.1E-2· BG=Back ground level of Ge detector.
5. Transportation of radioactive instruments
The radioactive instruments separated from the SF cyclotron were moved to KEK Tsukuba. The maximum weightof cyclotron magnet yoke is 48 ton, and side yoke is 13 ton.
The weight of rf resonator is 26 ton. The surface levels of
the magnet have been measured after the disassembling of
the rf resonator and beam deflector. The portable gamma
ray detectors have been used to measure the radioactive
level around the magnet yoke. The measurement resultshows that maximum level of gamma ray was l6J!Svlh.
It was so difficult to transport the heavy weight and partially activated magnet pieces because of limit of radiationlevel during the transportation [2].

Table 2 Amount of radioactive materials moved to KEK
Source of material
No. of material
Ratio(%)
Cyclotron room431
57.9
Cave 2A
185
24.8
Cave 3B
709.4Cave 3A
233.1
Power Sup. room
192.5
Ion source
15
2.0RFroom
20.3
Total
745 pieces
100%6. Conclusion
The SF cyclotron was disassembled and transported toKEK Tsukuba. The radioactive waste from the SF cyclotron was mainly vacuum chamber for the beam transport
line. The 57 % of the vacuum chamber was radioactive
waste.
The main part of SF cyclotron becomes radioactive.
The ferroconcrete irradiated by the neutron beam
was activated and their radiation level was investigated.
The 60Co, 134Cs, 152Eu are main components of the radioisotope in the ferroconcrete.
The RI concrete was packed
in the 200-litter drum can and total of 540 cans has beentransferred to JRIA. The packing factor of RI concrete in
the 200litter drum can was 57%.
Acknowledgements
The authors wish to express their thanks to the Radiation
Science Center of KEK-Tanashi for their support on radiation safety control of SF cyclotron. The authors indebted
to the member of CNS University of Tokyo for their support and helpful contribution. The radio chemical analysis of radioactive nuclei in the ferroconcrete was contracted
by Japan Environment Research Corporation.

Fig.3 Upper magnet yoke of SF cyclotron moved to theKEK storage house (left). A supporting base and alift-up hanger are also seen.
The radioactive instruments of the SF cyclotron havebeen settled in the building of KEK-Tsukuba. The
amount of radioactive materials is tabulated in the Table 2
while the total amount of separated materials is 2557
pieces. The storage area was proofed against the heavy
weight instruments.
In order to storage the magnet yokeof the SF cyclotron, the floor of storage building reinforced
with 25 mm thickness of the steel plate.
The vacuumpump was housed in the woody box.
The surface radiation level of the woody box was measured and confirmed
to keep the surface radiation level of 5J!Sv/h.
The
woody boxes are piled on the floor up to 2.5 m higher because of construction of semi-second floor to increase thestorage area.
The ferroconcrete blocks, which wereused to make the radiation shield, were radioactive materials with the surface dose of under 0.14 J!Svlh.
The
radioactive instruments, which were used in the beam
monitoring system, have been implemented in the steel-box.

References[1] Radioactive Material Transportation, ST-1, IAEA.
[2] Transport Safety Standard of the Radioactive Material,
the Ministry of Transport.1999. (In Japanese).
[3] Guidebook for the Safe Transport of Radioactive Material, the Ministry ofTransport.l999. (In Japanese).
[4] Text of Transport Safe Standard of Radioactive Material,
the Ministry of Transport, and the Science and Technology Agency, 1999. (In Japanese).
[5] Report on Field Research of Radioactive Material in the
Nagano Prefecture, edited by Nagano Prefecture Institute for Environment and Public Health, 1999. (InJapanese)-425-