Neutron Detector Technical Requirements for IAEA Safeguards Applications

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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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Whats 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

COL Julie A Bentz, PhD Director, Nuclear Defense
Policy National Security Staff
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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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EfficiencyIssues
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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
  non-hydrogenous 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
• 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

Centronics BF3 tubes
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Gas Proportional Counters versus Liquid and
Plastic Scintillation Detectors

• Scintillator Detectors with Phototubes

• 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

• 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

good - bad
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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
GE Reuter-Stokes 10B
Proportional Technologies, Inc.
Many technologies are being developed and assessed
PDT 10B Plate Detector
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Commercial 10B Layer Tubes
Centronics GE-RS LND Others
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Stability Requirements
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He-3 versus B-10 Pulse Height Distributions
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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
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Scalability
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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 (gt 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
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

structure
3He tubes In walls of Glove boxes
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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 RejectionforHigh BU MOXSpent Fuel
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Spent Fuel Applications - 3He Tubes in the
Advanced Experimental Fuel Counter (AEFC)
water
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Gamma Sensitivity for 3He Tubes (4 atm, 25 cm)
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Maintenance3He Tube MTBF 1000years(good luck
checking this) IAEA Support Electronics
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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 MCA (0.3 1) thus, the stability
  requirement (lt0.05 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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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

• optimization of die-away time and efficiency
  needed in order to minimize multiplicity
  uncertainty

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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 2x 12x 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
  6x 5x 26
• internal signal processing electronics included

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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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The experimental set-up
Source holder with set of cylinders
3He benchmark system
Work bench
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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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GE R-S preliminary tests
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GE R-S initial check-up HV plateau
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GE R-S comparison with vendor specifications
pulse height spectrum

• 2 µs shaping time used in LANL electronics

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GE R-S comparison with 3He 1 tube - deadtime
3He counter
10B counter
counts
time interval 0.1 us

• GE R-S system exhibits less deadtime than
  typical 1 3He counter

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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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Thank youQuestions?