Transcript Document 7397717

LA-UR 11-01668
Neutron Detector Technical Requirements for IAEA
Safeguards Applications
H.O. Menlove and Daniela Henzlova
Safeguards Science and Technology Group , N-Division
Los Alamos National Laboratory
IAEA Neutron Detection Workshop
March 22-24, 2011
Vienna, Austria
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What’s the problem?
 3He
•
supplies are diminishing while demands are increasing
3He
—
—
—
Characteristics
Large cross section absorbs thermal neutrons (provides an energy signal that alerts the
presence of neutrons)
Very efficient material for neutron detection and gamma rejection
Inert and non-radioactive gas
120000
100000
80000
Other USG
Liters
COL Julie A Bentz, PhD
Director, Nuclear Defense Policy
National Security Staff
Space
Non-nuclear
60000
Science
Detection
Supply
40000
20000
0
FY'09
FY'10
FY'11
FY'12
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FY'13
FY'14
FY'15
FY'16
FY'17
FY'18
IAEA Neutron Detector Evaluation Criteria
1.
Efficiency
2.
Gamma Rejection (or neutron-gamma separation)
3.
Robustness & maintenance
4.
IAEA support electronics requirements
5.
Stability
6.
Dead-Time (count rate capability)
7.
Scalability
8.
Safety (probably number 1)
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Efficiency
Issues
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Slide 4
Thermal-Neutron Cross Sections
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Thermal-Neutron Cross Sections (0.025 eV)
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Thermal-Neutron Detectors
•
Benefit from very high capture cross sections (1000-5000 barns)
•
Benefit from high Q values (energy released in capture) to provide the
ionization signal
•
Benefit from being relatively independent of neutron scattering
reactions
•
Energy independence means that the measured signal is relatively
independent of sample configuration, container material, and nonhydrogenous matrices
•
These properties of energy independence are needed to make
quantitative calibration practical and not require a specific standard for
every assay sample
•
Multiplicity counting is used to make corrections related to the
variables such as multiplication and alpha reaction neutrons
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What about BF3?

The Good news
• Several commercial sources (LND, Centronics, etc.)
• Good safety record (40 years)
• Good gamma rejection
• Good stability

The Bad News
• Lower efficiency (~ ½ of a 3He tube)
• Lower gas pressure means low efficiency density
Centronics BF3 tubes
• Higher HV requirements
• Hazardous BF3 gas safety issue (mitigation methods underway)
•
Low efficiency density and safety issues make BF3 an unlikely candidate for
safeguards applications
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Gas Proportional Counters versus Liquid and Plastic
Scintillation Detectors
Gas
Proportional Counters
•Intrinsically
gamma resistance
(up to ~10 R/h)
•Stable under temperature change
•Efficiency relatively independent of
sample and moderation changes
•Large scale systems possible (4pi)
•Counting rate limitations
•Long neutron die-away times (long
gates)
•3He shortage, BF3 safety, 10B low
efficiency
+ good
- bad
Scintillator
Phototubes
•Fast
data collection
•High counting rate capability
•Neutron energy information
•Short die-away time for neutron
correlation counting
•Gamma sensitivity issues
•Temperature stability problems
•Efficiency is energy dependent
(calibrations change with each
sample)
•Limited scalability to 4 pi sample
geometry
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Detectors with
LASL Neutron Detector using Plastic Scintillators
and Active Assay (~1975)
5-cm
Pb
Plastic
Scintillator
AmLi Neutron
Interrogation
The “Random Driver”
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A Few He-3 Alternatives
Many technologies
are being developed
and assessed
Proportional Technologies, Inc.
GE Reuter-Stokes 10B
Scintillator Panel
HDPE Moderator
Boron-Coated
Straw Detectors
(4 mm dia.)
ORNL - Saint-Gobain
BC-523A
PDT 10B Plate Detector
LLNL - Liquid Scintillator Multiplicity Counter
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Commercial 10B Layer Tubes
Centronics
GE-RS
LND
Others
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Stability Requirements
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Slide 13
He-3 versus B-10 Pulse Height Distributions
3He
10B (very thin layer)
0.76 meV
neutrons
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3He Tube HV Plateau Curves
UWCC at 4 atm (500 ns)
ENMC at 10 atm (180 ns)
measured precision = 0.015%
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HV Plateaus for 3He – Singles, Doubles, and
Triples for Multiplicity counting
All 27 Channels Compared With One Channel
JNC ENMC High Voltage Plateau
80000
70000
4500
60000
4000
50000
All 27 Channels
40000
Channel 2
30000
20000
Counts per Second
Counts (cps)
5000
3000
Singles
2500
Doubles
2000
Triples
1500
1000
500
10000
0
1400
3500
0
1600
1800
1500
2000
High Voltage (V)
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1700
1900
High Voltage (V)
2100
Scalability
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Slide 17
Scalability
•
Large installed neutron detector systems and high efficiency portable
detectors represent ~ 95% of IAEA 3He requirements; thus, small
portable replacements will not impact the supply/demand problem
•
The large detectors are in slab geometry such as the AMGB or in 4-pi
geometry such as the AWCC, ENMC, UNCL, etc.
•
The active neutron volume should be a large fraction (> 80%) of the total
detector volume including the local electronics
•
The large detector systems should have the gamma rejection capability
of the 3He systems; however, the efficiency increases proportional to the
volume; whereas, the gamma pileup increases as the square of the
volume
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LANL 6Li-scintillator (~ 1996)
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Scalability of 3He Detector Systems
6LiF/ZnS
HLNC
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Epi-thermal Neutron Multiplicity Counter (ENMC)
Efficiency 64%
Die-away time 19 micro s
Cd
Liner
121 He-3 Tubes
Graphite End Plugs
Sample Cavity
200mm diameter
430mm tall
Impure Pu and MOX Assay
0.3-0.5% accuracy for
inventory samples
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iPCAS
Installed NDA
MOX
powder
36 kg
Ge detectors
3He tubes (30)
coincidence
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Unattended Glove Box Assay System
•
GUAM: Glovebox Unattended Assay and
Monitoring
•
Prototype system was installed in 2006
•
Innovation: Real-time, continuous
measurement of Pu “hold-up” in facility
•
Uses LIST Mode and neutron
coincidence counting
•
Results independent of Pu location
Detectors
Shielding panel
structure
3He tubes
In walls of
U N C L A S S I F I E D Glove boxes
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Glove box
High Precision Assay to Supplement DA
Installed at RRP
• ENMC-PS is high accuracy
substitute for DA
•Pu-240 accuracy 0.2-0.3%
•Pu nitrates, MOX solutions, MOX
powders
• Integrated HPGE
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Gamma Rejection
for
High BU MOX
Spent Fuel
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Slide 25
Spent Fuel Applications - 3He Tubes in the
Advanced Experimental Fuel Counter (AEFC)
HDPE
Pb
water
water
water
He-3 Tubes
(6 for coinc.)
He-3 Tubes
Floor
water
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Gamma Sensitivity for 3He Tubes (4 atm, 25 cm)
10000
7000
1000 R/hr Singles
Rate
500 R/hr Singles Rate
6000
200 R/hr Singles Rate
8000
1000
5000
100
100R/hr Singles Rate
4000
50 R/hr Singles Rate
3000
10
2000
1
1300
1500
1700
50R/hr 2 Singles
1000
20 R/hr 2 Singles Rate
0
20 R/hr Singles Rate
1900
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10R/hr Singles Rate
Maintenance
3He Tube MTBF ~ 1000years
(good luck checking this)
IAEA Support Electronics
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Slide 28
IAEA Neutron Detector Coincidence Electronics
(Shift Register History)
JSR-15
UNAP
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Summary – technical requirements
• Many safeguards applications of 3He includes neutron
coincidence (multiplicity) counting with 4pi geometry that
requires high efficiency and large volume.
• High accuracy and long term stability are required for MC&A (0.3
– 1%); thus, the stability requirement (<0.05% for 3He tubes)
• In-plant footprint space is restricted and insensitivity to high
gamma dose (~ 1R/h) is required
• IAEA will need replacement detectors that make use of
electronics and software that is in use for 3He based systems
• Commercial detectors for safeguards applications based on 10B
proportional detectors are under test at LANL (Henzlova to
present some preliminary results)
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Neutron Detector - Safeguards Test Objectives
 develop an integrated test program focused on the parameter space
important in nuclear safeguards applications
 evaluate neutron detectors for potential replacement of 3He tubes
 consider the detector properties that would allow commercial production
to safeguards scale assay systems
test program components:
Experimental – cover parameters of interest for safeguards
Monte Carlo modeling – use MCNPX to build reference 3He
system for each 10B system tested
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Slide 31
Figure Of Merit evaluation
 determine Figure Of Merit for each system to characterize multiplicity
counting capabilities
 maximize precision of counting of signal multiplets … efficiency
… die-away



FOM ~

2
 optimization of die-away time and efficiency needed in order to minimize
multiplicity uncertainty
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Slide 32
Tested 10B detection systems
GE/Reuter-Stokes system
• multiple individual 10B-lined tubes embedded in polyethylene,
housed in 16” long tube with 12” active length and 2” diameter
• testing will be performed with LANL external electronics and/or
custom made PDT preamplifier
Proportional Technologies Inc. system
• multiple individual 10B-lined straws embedded in
polyethylene in a detector pod of ~2”x 12”x 20”
• internal signal processing electronics included
Precision Data Technology Inc. system
• 10B multi-cell parallel plate architecture surrounded
by ½” of polyethylene with outer dimensions of 6”x 5”x 26”
• internal signal processing electronics included
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Slide 33
Benchmark 3He system – MCNP modeling
Monte Carlo modeling:
10B systems - variety of shapes and sizes determined by the vendors’ technology
 the measurement results need to be compared with a reference 3He system in
Monte Carlo space
 polyethylene slab containing 3He tubes of 1” diameter filled at 4 atm separated by
2” pitch; outer dimensions similar to tested detector pods
 a benchmark 3He system was selected to match a typical 3He detector slab used
in safeguards
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Slide 34
The experimental set-up
Source
holder with
set of
cylinders
3He
benchmark
system
Work
bench
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Slide 35
Flexibility of analysis – list mode

data recorded using standard shift register (JSR15)

where appropriate the List Mode data acquisition adopted

List Mode - arrival time of every
pulse recorded
 data available for re-analysis
 use of different gate widths
possible … dieaway time
 Time interval analysis to asses
system deadtime
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Slide 36
GE R-S preliminary tests
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Slide 37
GE R-S initial check-up – HV plateau
… FAST amplifier output
10B
2500
count rate [cps]
count rate [cps]
10B
2000
1500
1000
500
… shaping time 2 μs
2500
2000
1500
1000
500
0
200
400
0
600
200
count rate [cps]
HV [V]
5000
400
600
HV [V]
3He
(Ar+CH4) with AMPTEK
4000
3000
2000
1000
0
1500
1700
1900
HV [V]
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Slide 38
GE R-S comparison with vendor
specifications – pulse height spectrum
LANL
1400
shaping time: 2 μs
HV: 550V
1200
counts
1000
800
600
400
200
0
0
500
1000
channel number
 2 μs shaping time used in LANL electronics
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Slide 39
GE R-S comparison with 3He 1” tube deadtime
10B
counter
s
counter
count
3He
time interval [0.1 us]
 GE R-S system exhibits less deadtime than typical 1” 3He counter
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Slide 40
Summary / Future Plans
 integrated test program addressing safeguards relevant aspects
developed
• relevant for broad range of novel safeguards related techniques
 GE R-S system available, initial check and comparison with vendor
specified parameters underway
• long shaping time needed to reproduce vendor specifications
• short shaping time – favorable deadtime
 PTI system to be delivered in March
 PDT system expected May
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Slide 41
Thank you
Questions?
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Slide 42