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1. Name of Experiment:
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FNS/JAERI Measurement of Radiation Skyshine with D-T Neutron Source
(March 2002 and March 2003)
2. Purpose and Phenomena Tested:
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The D-T neutron skyshine experiments [1] have been carried out at the Fusion
Neutronics Source (FNS) of JAERI. The radiation dose rate outside the target
room was measured at distances up to 550 m from the D-T target point.
3. Description of Source and Experimental Configuration:
----------------------------------------------------
FNS is an accelerator based intense D-T neutron source. It has two target
rooms: target room I has a fixed tritium target containing 3.7E+11 Bq
tritium and the target room II has a rotating tritium target containing
3.7E+13 Bq tritium. The target room I was used for the shyshine
experiments. Figure 1 shows the cross-sectional view of target room I
along a north-south cut. The target room is 15 x 15 m² wide and 9.1 m high.
The thickness of the concrete of the roof and the vertical walls is 1.15 m
and 2 m, respectively. The floor of the target room is an iron grating in
order to reduce the neutron scattering from the floor. The tritium target
is located 1.8 m above the floor, 5.5 m away from the south wall and 2.75 m
from the west wall. The target room has a port in the roof with a size of
0.9 x 0.9 m² for the shyshine experiments.
This port is usually closed with a concrete plug. In the skyshine experiment,
the concrete plug was removed and only 2 mm thick stainless steel plates
closed the port in order to keep the reduced air pressure in the target room.
The neutron attenuation by 2 mm stainless steel plates was negligible. FNS
was operated with an acceleration voltage of 360 kV and a target current of
1.4 mA in this experiment. The source neutron yield was ~1.7E+11 n/s, which
was monitored by the associated alpha particle measurement with a silicon
surface barrier diode installed in the beam line.
Figure 2 shows the measurement points in the environment. FNS is located
on a rather flat land only 150 m distance from the Pacific ocean. The north
and east sides are surrounded with a forest of pine trees which are about
10 m tall. The neutron dose rate was measured at the distance from 20 to
550 m in the pine forest along the north direction, at distances from 20
to 140 m on a road along the south direction and at 200, 230 and 300 m
along the south west direction.
4. Measurement System:
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Neutron dose rates were measured with the spherical rem-counters, He-3 and BF3
Fuji Electric NSN10002, just on the ground at all measurement points shown in
Figure 2.
The neutron spectra were evaluated with boner spheres with multi-moderators of
0.5, 1, 2, 3, 5 and 9 cm thickness along the north direction, and unfolded by
SAND-II code.
Secondary gamma-ray spectra were measured with a high purity Ge detector and
a NaI scintillation counter with a size of 125 cm in diameter by 125 cm long
at distances of 20, 50 and 100 m, and with a NaI scintillation counter with
a size of 200 cm in diameter by 200 cm long at distances of 200 and 300 m.
5. Description of Results and Analysis:
-----------------------------------
The measured neutron dose in the south and south west directions are shown
in Figure 3. The numerical data of the neutron dose are given in Table 1.
Neutron spectra measured at a distance of 50, 100 and 200 m and unfolded by
SAND-II code are shown in Figure 4. They are compared with the first MCNP-4B
calculations (forest was not included in the calculational model).
Figure 5 shows the pulse height spectra measured with the NaI scintillation
counter at the distances of 20, 50 and 100 m. Numerical data of Fig. 5 are
given in the file sky-NaI.txt. The information on the detector response
function and the detector efficiency, needed for the comparison with the
calculation, is not yet available.
Few characteristic gamma-ray lines can be observed in the spectra, like the
natural gamma-ray background from K-40 and Tl-208, the energy peaks from the
H-1(n,gamma) and Fe-56(n,gamma) reactions. A continuum spectrum in the energy
range of 3-7 MeV was enhanced by the shyshine, which is considered to be the
convolution of Compton spectra from some neutron capture reactions. The high
purity Ge detector observed additional peaks of the Si-28(n,gamma) reaction
at 3.539 and 4.934 MeV at the distance of 20 m only, which is considered to
arise from the FNS building.
Experiment Analysis:
Transport calculations with the MCNP-4B code are presented in [1]. The
calculations were performed using the JENDL-3.2 nuclear data library.
The corresponding sample input for the MCNP-4B code is given in the file
mcnp4b-sky.inp. The forest was not modeled in this calculation.
More recent analysis with the MCNP-4C code and JENDL-3.2 nuclear data are
described in [2]. The corresponding MCNP-4C input data are included in
mcnp4c-sky.inp and the comparison of the measured and calculated neutron
dose rate is presented in sky-mcnp4c.xls. In this model the FNS building
and the measurement field were modelled in a simplified cylidrical geometry,
and the pine forest was modelled by homogenised cell with a height of 10 m.
6. Special Features:
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None
7. Author/Organizer:
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Experiment and analysis:
T. Nishitani, K. Ochiai, J. Hori, S. Sato, M. Yamauchi,
M. Nakao, M. Wada, C. Kutukake, S. Tanaka
Japan Atomic Energy Research Institute
Tokai-mura, Naka-gun, Ibaraki-ken 319-1195, Japan
Phone: +81-29-282-6859 (for T.N)
FAX: +81-29-282-5709 (for T.N)
S. Yoshida, R. Tanaka, I. Murata, A. Takahashi
Osaka University
Yamadaoka 2-1, Suita, Osaka, 565-0871, Japan
J. Kaneko, M. Wakisaka, T. Sawamura
Hokkaido University
Kita 8 Nishi 5, Kita-ku, Sapporo 060-0808, Japan
Compiler of data for Sinbad:
S. Kitsos
OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France
Reviewer of compiled data:
I. Kodeli
OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France
The data were kindly contributed by Dr. Takeo Nishitani.
8. Availability:
------------
Unrestricted
9. References:
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[1] S. Yoshida, T. Nishitani, K. Ochiai, J. Kaneko, J. Hori, S. Sato,
M. Yamauchi, R. Tanaka, M. Nakao, M. Wada, M. Wakisaka, I. Murata,
C. Kutukake, S. Tanaka, T. Sawamura, and A. Takahashi:
Measurement of Radiation Skyshine with D-T Neutron Source,
Fus. Eng. Des. 69 (2003) 637-641
(22nd Symposium on Fusion Technology (SOFT-22), Helsinki, 9-13. Sept. 2002).
[2] T. Nishitani, K. Ochiai, S. Yoshida, R. Tanaka, M. Wakisaka, M. Nakao,
S. Sato, M. Yamauchi, J. Hori, M. Wada, A. Takahashi, J. Kaneko and
T. Sawamura, D-T Neutron Skyshine Experiments and the MCNP Analysis,
J. Nucl. Sci. & Technol., Sup. 4, p. 58-61 (March 2004)
10. Data and Format:
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DETAILED FILE DESCRIPTIONS
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Filename Size[bytes] Content
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1 fnssky-a.htm 10,175 This information file
2 fnssky-e.htm 3,527 Description of experiment
3 mcnp4b-sky.inp 8,342 Input data for MCNP-4B calculations
4 mcnp4c-sky.inp 8,565 MCNP-4C Input data (including pine forest)
5 sky-fig1.jpg 67,850 Fig. 1: Cross-sectional view of the target room
6 sky-fig2.jpg 73,941 Fig. 2: Measurement points in the environment
7 sky-fig3.jpg 35,348 Fig. 3: Neutron dose distribution
8 sky-fig4.pdf 14,901 Fig. 4: Neutron spectra at 50, 100 and 200 m
9 sky-fig5.jpg 44,498 Fig. 5: Secondary gamma-ray spectra
10 sky-NaI.txt 161,908 Secondary gamma-ray pulse height spectra (numerical data)
11 sky-mcnp4c.xls 22,528 Measured and MCNP-4C calculated neutron dose rates
12 sky-ref1.pdf 297,540 Reference 1
13 proc_147.pdf 867,745 Reference 2
File fnssky-e.htm contains the following table:
Table 1: Neutron dose rate distributions.
Figures are included in the JPG and PDF formats.
SINBAD Benchmark Generation Date: 02/2003
SINBAD Benchmark Last Update: 07/2006
