expectation to nuclear emulsion technique for new application in nuclear engineering
DESCRIPTION
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, - PowerPoint PPT PresentationTRANSCRIPT
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 fieldISO8529-1: “Reference neutron radiations
-Characteristics and methods of production-”
Unestablished region
Established Energy points
Thermal neutrons
2.5 MeV144 keV
565 keV 5.0 MeV
14.8 MeV
NeutronProduction
0.01 eVNeutronEnergy
RI source +Graphite pile
7Li ( p,n )7Be
D(d,n)3He T(d,n)4He
1 keV 10 keV 100 keV 1 MeV 10 MeV
several 10 keV
45Sc(p,n)Reactor+Fe filter
24 keV neutron: One of the reference radiations for the response of neutron-measuring devices as a function of neutron energy.
@ NMIJ (National Metrology Institute of Japan) in AIST
IMPORTANT: from the viewpoint of radiation protection.
Measurements of 24 keV neutrons
3He proportional counterRecoil-proton proportional counter
Measurement Method
Spectrometry
Flux Determination
Neutron Monitor
BF3 or 3He proportional counter 24 keV≦Recoil-proton counter > 24 keVBF3 or 3He proportional counter
Characterization
0
0.05
0.1
0.15
0.2
0.25
0.3
0 200 400 600 800 1000 1200エネルギー(keV)
カウ
ント/時
間(1/
sec)
Fe/ AlFe/Al/ Ti
24 keV
Cou
nts/
sec
Deposited Energy (keV)
Thermal peak due to 3He(n,p)T
Neutron induced reaction base counter
(3He(n,p), 10B(n,) reaction)Difficulty in separating
from thermal peak
Recoil-proton counterOrganic Scintillator:
n- discriminationGas-filled type: Low sensitivity
Spectra obtained from He-3 covered by Cd
Problem
Neutron Flux: ~500 n/cm2/s (Reactor “YAYOI”&Fe filter)~5 n/cm2/s (45Sc(p,n)@AIST)
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.2.Appropriate absorber will be placed around the fuel rods.3.Experimental measurement of burn-up of the fuel rods, not calculatio
n.
http://www.tepco.co.jp/~fukushima1-np/b42307b.html
Control of Nuclear Criticality
Sub-criticality should be estimated based on experimental measurement.
Closed packed
Sub-criticality MeasurementSub-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
Spacial distribution of neutron flux is estimated by an operating history of a nuclear reactor.
According to IAEA, the operating histry is NOT admissible as “experimental data”.
• Neutron measurement under the condition of high -ray background
( /n=105 ~ 106 )
• Criticality is not uniform along axial direction4 x fission chamber (for n detection)
2 x high purity Ge detector (for g detection)
2 x 20 x ionization chamber (for g detection)
●●●●●●●●●●●●●●●●●●●
●●●●
●●●●●●●●●●●●●●●●●●●
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fuel assembly
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.
We propose a novel neutron detector by nuclear emulsion.
Track of recoil proton should have information about neutron energy, orientation of neutron and spacial distribution of neutron source.
Automatic readout system for nuclear emulsion developed by Prof. Niwa is key technique for application of nuclear emulsion.
Characterization of keV Neutron Field using Multilayer Nuclear Emulsions
Multilayer nuclear emulsions
Tracks of recoil-protons
・ Neutron Spectrum・ Directional Distribution・ Neutron Yield
Reconstruction
Good discrimination between neutrons and gamma-rays& High Sensitivity (large volume & solid state)
Requirements for keV Neutron determinationHigh sensitivity & n-gamma discrimination
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)
⇒Applicable for high gamma-ray field
4.2m
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
Tracks of Recoil Proton in OPERA FilmDate:20071213 reactor power:2000 WDistance 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)
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
支持体:205ミクロン( TAC )
乳剤
乾板断面図(電顕写真)10ミクロン
乾板断面図(電顕写真)