PPT

Expectation to Nuclear Emulsion
Technique for New Application in
Nuclear Engineering
T. Iguchi, K. Morishima, T. Naka, J.
Kawarabayashi, K. Watanabe
Nagoya Univ.
Neutron Measurement in Nuclear Engineering
• New type of neutron detectors are required in nuclear
engineering.
For instance,
– High resolution neutron imager
J-PARC neutron diffraction spectrometer
– Standard neutron detectors for a few tens of keV
Standardization of a neutron field
– Neutron distributions or absolute total flux from spent fuel rods
sub-criticality measurement
Neutron detectors appropriate for these applications
have not yet developed !!
Standardization of 24 keV neutron field
ISO8529-1: “Reference neutron radiations
-Characteristics and methods of production-”
24 keV neutron: One of the reference radiations for the response of neutronmeasuring devices as a function of neutron energy.
IMPORTANT: from the viewpoint of radiation protection.
@ NMIJ (National Metrology Institute of Japan) in AIST
Neutron
Energy
Neutron
Production
0.01 eV
1 keV
RI source
+Graphite pile
Unestablished
region
10 keV
100 keV
1 MeV
10 MeV
45Sc(p,n)
Reactor+Fe filter 7Li（p,n）7Be
D(d,n)3He T(d,n)4He
several 10 keV
Established
Energy points
Thermal
neutrons
144 keV
2.5 MeV
565 keV
5.0 MeV
14.8 MeV
Measurements of 24 keV neutrons
Measurement Method
Spectrometry
Flux Determination
Neutron Monitor
Problem
proportional counter
Recoil-proton proportional counter
BF3 or 3He proportional counter ≦ 24 keV
Recoil-proton counter > 24 keV
BF3 or 3He proportional counter
10B(n,a)
reaction)
Difficulty in separating
from thermal peak
Recoil-proton counter
Organic Scintillator:
n-g discrimination
Gas-filled type: Low sensitivity
Counts/sec
カウント/時間(1/sec)
0.3
Neutron induced reaction
base counter
(3He(n,p),
3He
Neutron Flux: ~500 n/cm2/s
(Reactor “YAYOI”&Fe filter)
~5 n/cm2/s (45Sc(p,n)@AIST)
24 keV
Thermal peak
due to 3He(n,p)T
0.25
0.2
Fe/Al
Fe/Al/Ti
0.15
0.1
0.05
0
0
200
400
600
800
1000
エネルギー(keV)
Deposited
Energy (keV)
1200
Spectra obtained from He-3 covered by Cd
Control of Nuclear Criticality
http://www.tepco.co.jp/~fukushima1-np/b42307b.html
For (safety and) effective store of fuel
assemblies in nuclear power plants
（spent fuel rod pit)
Accident example；
Two unused fuel assembles (PWR)
causes a nuclear criticality in a
water (non-boric) pool.
To avoid nuclear criticality outside reactor cores,
1.The fuel rods should be distributed at a distance.
Closed packed
2.Appropriate absorber will be placed around the fuel rods.
3.Experimental measurement of burn-up of the fuel rods, not calculation.
Sub-criticality should be estimated based on
experimental measurement.
Sub-criticality Measurement
Sub-criticality of fuel rod depends on
a spacial distribution of nuclides composition (U,Pu,TRU,FP)
inside of the fuel rod.
However, non-destructive measurement of the spacial
distribution of nuclides composition is impossible.
Conventional methods for Sub-criticality Measurement
are based on total amount and fluctuation of neutrons.
ex. γ/ｎ method、neutron source multiplication method, noise analysis method
Problems on neutron measurement
for fuel assembly
• Criticality is not uniform along axial direction fuel assembly
Spacial distribution of neutron flux is estimated by an
operating history of a nuclear reactor.
4 x fission chamber
(for n detection)
According to IAEA, the operating histry is NOT admissible
as “experimental data”.
2 x high purity Ge detector
(for g detection)
• Neutron measurement under the condition of
high g-ray background
（g/n=105～106）
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2 x 20 x ionization chamber
(for g detection)
Idea of Neutron Detection by
Nuclear Emulsion Technique
• Nuclear emulsion has not widely applied to nuclear
engineering excepting personal dosimeter
• Complex readout of nuclear tracks is bottle neck for
application.
Automatic readout system for nuclear emulsion developed by Prof. Niwa
is key technique for application of nuclear emulsion.
Track of recoil proton should have information about neutron energy,
orientation of neutron and spacial distribution of neutron source.
We propose a novel neutron detector
by nuclear emulsion.
Characterization of keV Neutron Field using
Multilayer Nuclear Emulsions
Requirements for keV Neutron determination
High sensitivity & n-gamma discrimination
Multilayer nuclear emulsions
Tracks of recoil-protons
Reconstruction
・Neutron Spectrum
・Directional Distribution
・Neutron Yield
Good discrimination between neutrons and gamma-rays
& High Sensitivity (large volume & solid state)
Neutron Characterization from a Fuel
Assembly by Nuclear Emulsions
Raping the fuel assembly by the emulsion films
After several hours, track information is read out
and neutron energy and absolute total flux are
reconstructed.
Gamma and neutron discrimination by track
darkness (dE/dx deference)
4.2m
⇒Applicable for high gamma-ray field
21cm
Requirements for Nuclear Emulsions
To apply the nuclear emulsion for these
applications, we need to evaluate
• sensitivity for ~10 keV neutron
(range of 10keV proton is order of 10-7m)
• neutron/gamma discrimination characteristics
(n/g ratio is more than 106).
Neutron Irradiation Test of OPERA film
at Yayoi Reactor
stacked emulsion films (5 OPERA) were irradiated
by fission neutrons at Yayoi reactor (Univ. of TOKYO)
Fast neutron reactor : max output 2kW
Stacked OPERA film
Cut into 25x25mm square
Light shielded
Vacuum packing
100 mm
125 mm
Neutron Irradiated Direction and Recorded Tracks
１．perpendicular
２．horizontal
Tracks of Recoil Proton in OPERA Film
Date:20071213 reactor power:2000 W
Distance form column: 3840mm hour：~２
BR04 pl02 perpendicular
BR09 pl02 horizontal
(Details see poster “Test of neutron monitoring” by Mr. Morishima)
Summary
• We expect that the nuclear emulsion may show
good characteristics as a neutron detector and
be applicable for
– ~10keV neutron detector
– sub-criticality monitor of fuel assembly.
by turning the software of automatic readout
system and use of NIT to select the neutron
tracks.
• Study of emulsion as a neutron detector is now
launched…
超高速自動飛跡読み取り装置（S－UTS）
・1972年より世界に先駆けて開発： TS （ Track Selector ）
・現在の世界最高速システム＝毎時50平方センチ
飛跡認識
画像処理専用
プロセッサ
原子核乾板
・高空間分解能で、全ての荷電粒子飛跡を１本１本記録（最小電離粒子）
乾板断面図
（電顕写真）
乾板断面図
（電顕写真）
乳剤の機械塗布
Ｆｕｊｉフィルム社製「OPERA film」
均質、取り扱い容易
表面保護層：１ミクロン
乳剤：４４ミクロン
10ミクロン
支持体：２０５ミクロン
（TAC）
乳剤
原子核乾板で捕らえた反跳原子核の飛跡
BR04 pl02
垂直照射
20071213
2000 W
射出口から3840mm
約２時間
原子核乾板で捕らえた反跳原子核の飛跡
BR09 pl02
水平照射
20071213
2000 W
射出口から3840mm
約２時間
Tracks Penetrating Two Films
Distribution of PH +VPH
MIP
Recoil Proton（？）
Pulse Height ： number of penetrated film
Volume Pulse Height ： sum of scattered light

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