fissile material experiments at the device assembly facility
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Consortium for Verification Technology
Fissile material experiments at the Device Assembly Facility
CVT Workshop – October 20, 2016
Michael Hamel1, Pete Chapman2, Michael Streicher1
1University of Michigan2North Carolina State University
Consortium for Verification Technology
Campaign objectives
• July 11-21, 2016, CVT and CNEC conducted experiments with Cat-I SNM at DAF for a second time
• Provided CVT and CNEC students, post-docs, and faculty with the opportunity to conduct hands-on experiments with Category I (weapons usable) special nuclear material (SNM)
• Included a neutron generator for active interrogation of HEU
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Device Assembly Facility
• Located within the Nevada National Security Site, 90 minutes northwest of Las Vegas
• Operated by NSTec for the NNSA
• Houses the National Criticality Experiments Research Center
• Supports critical and subcritical measurements of WGPu, HEU, and Np
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Las Vegas
DAF
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• North Carolina State University– Prof. John Mattingly, Jonathan Mueller, Pete Chapman
• Princeton University– Prof. Alex Glaser, Sebastien Phillipe, Benjamin Reimold
• University of Illinois– Prof. Clair Sullivan, Mark Kamuda
• University of Michigan– Prof. Igor Jovanovic, Michael Streicher, Bennett
Williams, Jason Nattress, Lazar Supic, Michael Hamel
• Oak Ridge National Laboratory– Jason Newby
• Los Alamos National Laboratory– Jesson Hutchinson, Donnette Lewis, et al.
CVT campaign participants
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Sources
• SNM sources– BeRP ball: 4.5-kg WGPu metal sphere
– Thor core: 4.1-kg WGPu metal disk
– Rocky Flats shells: 13.7-kg HEU metal shells
– Neptunium: 6.1-kg metal sphere
• Interrogating Sources– AmLi
– DD neutron generator
– DT neutron generator
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Rocky Flats shells with AmLi
Assembly of Rocky Flats shells
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• Neutron coded aperture imager (ORNL/SNL)
• Bubble detectors array (Princeton)
• NaI, CsI scintillators (Illinois)
• Dual particle imager (Michigan)
• One dimension transmission imager (Michigan)
• Polaris and Orion CZT imagers (Michigan)
Instruments
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Dual-particle imager• Combined Compton and neutron
scatter camera• Two-plane design
– Front Plane: EJ-309 liquid organic scintillators
– Back Plane: EJ-309 and NaI(Tl)
• Separate neutron and photon signals
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NaI(Tl)EJ-309
Back PlaneFront Plane
Neutron Image Photon Image
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AmLi experiment
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Top View6.25×104 n/s AmLi
in 1” lead pig
Aluminum table
Dual-Particle Imager
116 cm
13.7 kg HEU
Measurement time: 850 min
DPI
13.7-kg HEU
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AmLi experiment
• Most neutron emitted by AmLiare less than 1.5 MeV
• Threshold of DPI ensures measured neutrons are from induced fission
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Neutron Image Photon Image
Neutron Spectrum
Photon Spectrum
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DT experiments
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Top ViewTarget
Generator tube
Aluminum table
Dual-Particle Imager
155 cm28 cm
13.7 kg HEU
13.7-kg HEU
DT generatorDPI
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DT experiments
• Generator emitted 14.1 MeV neutrons
• Operated at 300 Hz with a 10% duty cycle
• 333 μs pulse length
• Digitized start of veto signal and vetoed based on pulse arrival times
• 335,700 ns after start of pulse
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Neutrons per Second
No Veto With Veto
698 0.0048
Neutron Image:No Veto
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DT experiments
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HEU
HEU with poly moderator
DT Generator position
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Identifying Fissile Assemblies in Fast Neutron Images
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Neutron Coded Aperture Imager (NCAI)
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2015 DAF Campaign Update• Passive measurements of
bare BeRP ball (WGPu)• Used Time-Correlated
Pulse-Height (TCPH) analysis to identify fissile assemblies
• Neutrons depositing more energy than predicted by their time-of-flight indicate fission chain reactions
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2015 DAF Campaign Update
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BeRP
252Cf
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2016 DAF Campaign
• Active measurements of Rocky Flats HEU shells
• AmLi, DD and DT generator drivers
• Used energy or time cuts to identify fissile assemblies
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AmLi Sources
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• 4x AmLi sources• ~ 105 n/s• Rocky Flats shells 1-24• 15 hour run time
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AmLi Sources
• No cuts needed
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D-D Generator
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• 300 Hz• 10% duty cycle• ~ 106 n/s• Rocky Flats shells 1-24• 100 minute run time
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D-D Generator
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D-D Generator Energy Cut (Edep > 2.75 MeV)
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D-T Generator
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• 300 Hz• 10% duty cycle• ~ 107 n/s• Rocky Flats shells 1-24• 1 hour run time
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D-T Generator
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D-T Generator Time Cut (t > 333 ns)
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Fast Neutron Images of Fissile Assemblies
• 2016 DAF Campaign Conclusions– AmLi drivers may be used without cuts– D-D generators may be used with energy cuts
• Best to operate in continuous mode• Some tritium still present
– D-T generators may be used with time cuts• Must be used in pulse mode with veto
• Future Work – Perform simulations of 2015 DAF Campaign scenario
to investigate lower bound of multiplication for which a TCPH-filtered image successfully identifies a multiplying assembly
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M
“Black Box” Complete Source Characterization
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Digital CZT array
γ,x-ray
nfast
nthermal
Z?
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• Orion Prototype Digital CZT Array System
• Objects:– Rocky Flats Shells– BeRP Ball– Thor Core (2015)– Np Sphere (2016)
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0 100 200 300 400 500 600 7000
1
2
3
4
5
6
7
8
9
10
11x 105
Energy (keV)
Coun
ts p
er 0
.25
keV
bin
0.63 %
Corrected Count Map57Co Coded Aperture Shadow
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Rich Spectral Information Comparable with HPGe
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Thor Core Measurement
*Compared with ORTEC Micro-Detective (5 cm x 3.3 cm)
n113Cd 114Cd
IC e-γ
γ
γ
500 550 600 650 700 7500
1
2
3
4
5
6
Energy (keV)
Cou
nts
per m
inut
e pe
r keV
BarePoly Sphere Steel + Poly
Unique Thermal Neutron Signature!
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Rich Spectral Information Comparable with HPGe
• Energy resolution sufficient to estimate 240Pu
• Use spectral data to identify shielding
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140 160 180 200 220 240
101
102
Energy (keV)
Cou
nts
per 0
.5 k
eV b
in p
er m
inut
e
Bare HEUIron shielded HEU
U
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Spectral-Based Shielding Identification
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Final Shielding Identification Results• Demonstrated on Pu, U, and Np sources
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0 5 10 15 20 250
20
40
60
80
100
Z N
umbe
r
Mass Thickness (g / cm2)
Peak AttenuationSmall Angle ComptonTrue Value
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SNM Orientation through Gamma-ray Imaging
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Fast Neutron Detection
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0 50 100 150 2000
20
40
60
80
100
120
Energy (keV)C
ount
s pe
r min
ute
per 0
.5 k
eV b
in
Module 1
0 50 100 150 2000
20
40
60
80
Energy (keV)
Cou
nts
per m
inut
e pe
r 0.5
keV
bin
Module 3
0 50 100 150 2000
20
40
60
80
100
Energy (keV)
Cou
nts
per m
inut
e pe
r 0.5
keV
bin
Module 2
0 50 100 150 2000
20
40
60
80
100
120
Energy (keV)
Cou
nts
per m
inut
e pe
r 0.5
keV
bin
Module 4
Cf-252Cs-137
• Nuclear recoil in high-Z materials generate very few electron-hole pairs
• Energy depositions less than 20 keVeeare candidates
• Many experiments have confirmed fast neutron detection– See upcoming IEEE
NSS conference
Consortium for Verification Technology
Fissile material experiments at the Device Assembly Facility
CVT Workshop – October 20, 2016
Michael Hamel1, Pete Chapman2, Michael Streicher1
1University of Michigan2North Carolina State University
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