CO8-1

Research and Development of Diamond dose Rate Detector forRadiation Mapping System in Highly Active Environments

Y. Takahashi, L. Payne1, C. Hutton1, K. Takamiya,
T. Saito, J. Hori, H. Unesaki, T. Scott1
Research Reactor Institute, Kyoto University
Interface Analysis Centre, School of Physics, Universityof Bristol

1

INTRODUCTION: Measurements of radiation doserates in highly active environments, such as the Fukushima Daiichi Nuclear Power Plant or Sellafield in UK, ischallenging due to the extreme environments encounteredand restricted access. Therefore, novel radiation detectortechnology is required to address these challenges. One
such example of a radiation detection material is diamond,as it is able to withstand and measure high radiation intensities, is chemically inert and formable into extremely
small, sensitive detectors. These detectors generate small
currents when exposed to radiation, and if the radiationlevels are high enough this can be measured. Testing ofsuch detectors is not possible in routine laboratories dueto the requirement to have high active radiation sourcesin UK. However, through a new collaboration formed
through Kyoto University-the University of Bristol bilateral symposia, UK researchers are accessible to the highactive radiation source at Kyoto University Research Reactor Institute (KURRI). This report presents some preliminary results from radiation testing of diamond detectors developed by University of Bristol at Co-60 facility
in KURRI.

proportional to an increase in current measured. This response would allow the use of this detector in civil nuclear applications as a reliable calibration factor can bederived. Following testing using the Co-60 facility, any
detectors that show promise for use, such as S1, will betested further using the other facilities present at KURRI.
This will include exposure to different energy gamma
radiation such as Cs-137, to establish if the incident
gamma energy has any effect on detector response. Additionally, upon restart of the Kyoto University Research
Reactor (KUR) and Kyoto University Critical Assembly(KUCA) the detector response in highly active gamma
and neutron/gamma mixed fields can be investigated.

Fig. 1 Diamond detector (left: S1, right: C1,C2)

EXPERIMENTS: Three diamond detectors as shownin Fig. 1 (S1, C1 and C2) were exposed to varying doserates using a Co-60 irradiator irradiation facility at
KURRI. This facility has a strong Co-60 source in a large
irradiation room that allows exposure to a large range ofdose rates from approximately 0.1 Gray/hour up to >4000
Gray/hour by the change of the irradiation position. The
diamond detectors were located on the end of a 50 meter
cable and controlled using custom built software thatapplies a 300 V bias voltage and records current data
every 50 ms. For each dose rate a background was recorded for 30 seconds before and after the source was introduced, with 60 seconds of data collected while thediamond was exposed to the source. The mean andstandard deviation of the current recorded was calculated
for each dose rate and background measurement. A background subtraction, between the start background andmeasurement current, was performed to allow the current
generated by irradiation to be plotted.
RESULTS: The response of the S1 detector to various
dose rates from Co-60 are shown in Fig. 2 as an example,
where the data point is a mean of 60 seconds of data andthe error bars are one standard deviation to give an indication of detector stability. Detector S1 shows a stable
and linear response, with an increasing dose rate being28077

Fig. 2 Dose rate response of S1 detector

Development of Non-destructive Methods Adapted
for Integrity Test of Next Generation Nuclear Fuels

Y. Takahashi, J. Hori, T. Sano, D. Ito, H. Unesaki,K. Nakajima
Research Reactor Institute, Kyoto University

INTRODUCTION:
A fast reactor system withtrans-uranium fuels containing minor-actinide is expected
to be effective for the incineration of high-level radioactive wastes. In order to realize the fast reactor system,
integrity evaluation of the fuels with high activity is required for the safety operation. However, present techniques are considered to be difficult to apply the evaluation of the fuels with high radioactivity and high decay
heat. In order to develop the related methodology adapted
for the integrity evaluation, the N-DeMAIN (Development of Non-Destructive Methods Adapted for Integrity
test of Next generation nuclear fuels) project has been
started from October 2014. In the project, the neutron
resonance transmission analysis is adapted for the identification and quantification of nuclides in the fuels bytime-of-flight (TOF) measurement. In addition, the determination of temperature distribution in the fuels basedon Doppler-effect and neutron imaging are conducted by
the neutron resonance technique. To obtain accurate databy these methods, high quality neutron beam regarding
neutron flux, time resolution and spatial resolution isrequired. The 46 MeV electron accelerator in Kyoto
University Research Reactor Institute (KURRI-LINAC)
will be used for the project because KURRI-LINAC is
the only pulsed neutron facility where nuclear materials
can be utilized in Japan. In order to satisfy the neutron
beam quality required to successfully execute the experiments described above, the design of the neutron source,
especially the moderator, reflector and collimator, shouldbe improved and optimized. In this project, the neutron
source system including moderator and reflector wasnewly developed as shown in Fig. 1 and the collimator in
12 m beam line was also re-arranged. The characteristicof the system was investigated experimentally.

EXPERIMENTS: A water-cooled photo-neutron target was set at the center of the neutron source system
located in the target room. To enhance the neutron flux inthermal and epi-thermal regions, the size of the moderator of polyethylene was 5 cm thickness and 15 cm square.
The measuring station at 12 m from the target on the 135
degree beam line was selected in this project. A leadshadow bar, 5 cm in diameter and 20 cm long, was placedon the neutron beam axis in front of the neutron source
system to reduce intense gamma-flash from the target
effectively. The collimators of polyethylene with 10%
boron of 20 cm thickness were set at following positions;15, 10, 5 cm in inner diameter at 3, 9, 12 m from the target, respectively. Neutron spectrum measurements wereobtained from capture reaction rate of 10B (22 mm diameter, purity 96.98%) and dummy samples. A BGO scintillator (2 inch diameter and 2 inch long) was used formeasuring total energy absorption gamma-rays. The conditions of the accelerator were as follows: average beam
current was 14.5 A, frequency was 50 Hz and pulse
width was 100 ns.
RESULTS: Measured neutron spectrum is shown inFig. 2. The neutrons in a few keV energy regions could
be measured owing to the reduction of gamma-flash influence. The thermal neutron flux of 2.36  102[n/cm2/A/s] and the epi-thermal neutron flux of 5.72 102 [n/cm2/A/s] were obtained under this experimental
condition. It was found we can obtain the maximum
thermal neutron flux of 4.72  104 [n/cm2/s] and themaximum epi-thermal neutron flux of 1.14  105[n/cm2/s] under 6 kW operation of KURRI-LINAC.
100flux-1

Counts/10s/cm2/sec/A

CO8-2

10-210-310-4

1010-310-2-110010101210310410Neutron Energy ( eV )Fig. 2 Measured neutron spectrum
Present study includes the result of “Development ofNon-Destructive Methods Adapted for Integrity test of
Next generation nuclear fuels” entrusted to the Kyoto
University by the Ministry of Education, Culture, Sports,
Science and Technology of Japan (MEXT).
Fig. 1 Newly developed neutron source system

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