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LA-UR-16-27342Approved for public release; distribution is unlimited.
Title: Correlated Fission Multiplicity Model Verification Efforts in MCNP6
Author(s): Rising, Michael Evan
Intended for: Advances in Nuclear Nonproliferation Technology and Policy Conference(ANTPC), 2016-09-25/2016-09-30 (Santa Fe, New Mexico, United States)
Issued: 2016-09-26
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Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Correlated Fission Multiplicity Model Verification Efforts in MCNP6
2016 ANS ANTPC Conference
27 September 2016
Michael E. Rising XCP-3 Division, Los Alamos National Laboratory
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Outline
§ Introduction
§ Background – Multiplicity Options – CGM and CGMF – LLNL Fission Library and FREYA
§ Verification Strategy
§ Numerical Results – Averages – Distributions – Correlations – Secondary Photon Bug Fixed
§ Conclusions
Slide 2
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Introduction
§ Application of interest – Global security and nuclear nonproliferation – Detection of special nuclear material (SNM) – Warhead measurement campaign (WMC) – Passive and active interrogation techniques – Coincident neutron and photon leakage
§ Key issues – Average nuclear data quantities are insufficient – Cannot predict correlated signatures of shielded SNM
§ Approach to obtain predictive capability – Use transport code MCNP for modeling neutrons and photons – Need microscopic fission event information – Fission event generators are under development – Implement in MCNP and compare to experiments
Slide 3
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Background
§ In tabulated nuclear data libraries (i.e. ENDF/B-VII.1): – Average secondary neutron and photon information can be available
• Average multiplicity, • Average spectrum, • Average energy-angle spectrum,
– Generally, high-dimensional distributions of secondary particles are unavailable • Multiplicity distribution, • Multiplicity-dependent emission spectra, • Multiplicity-dependent energy-angle emission spectra, • Neutron-neutron, neutron-photon and photon-photon correlations • Too much data to measure, evaluate and tabulate!
§ Default MCNP uses average quantities – In some cases, consider this a nuclear data “variance reduction” technique – Good for integral quantities, like flux and effective multiplication – Bad for studying detailed particle emission physics
Slide 4
χ (E)ν
χ (ν,E)χ (ν,E,θ )
P(ν )
χ (E,θ )
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Multiplicity Options
§ MCNP6.1.1 contains two (low-energy) event generators:
§ LLNL Fission Library1
– Spontaneous, neutron-induced and photo-fission – Fission Reaction Event Yield Algorithm (FREYA)2 isotopes:
• Spontaneous: 238U, 240Pu, 244Cm and 252Cf • Neutron-induced: 233U, 235U and 239Pu
– When available, FREYA generates secondary neutrons and photons
§ Cascading Gamma-ray Multiplicity (CGM)3 - LANL
– Generates secondary particles from a variety of reactions – No fission! (CGMF under active development)
1J.M. Verbeke, C. Hagmann, and D. Wright, Lawrence Livermore National Laboratory, UCRL-AR-228518 (2014).
2R. Vogt and J. Randrup, Phys. Rev. C, vol. 84, pp. 044612-1-14 (2011).
3T. Kawano, P. Talou, M.B. Chadwick, and T. Watanabe, J. Nucl. Sci. Tech., 47 (5), 462-69 (2010).
Slide 5
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UNCLASSIFIED
CGM and CGMF
§ CGMF is a superset of CGM with an added fission reaction capability
§ Fission fragments are sampled from a joint probability distribution function of mass (A), charge (Z) and total kinetic energy (TKE)
§ Uses Hauser-Feshbach statistical theory of nuclear reactions
§ Neutron / photon competition is treated during evaporation from fission fragments
§ Monte Carlo is used to sample each step in the de-excitation process
4B. Becker, P. Talou, T. Kawano, Y. Danon, and I. Stetcu, Phys. Rev. C, 87, 014617 (2013).
Slide 6
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
LLNL Fission Library and FREYA
§ FREYA is LLNL’s fission event generator
§ In MCNP6, it is accessible through LLNL Fission Package
§ The LLNL Fission Package includes more tabulated and fitted data used for lesser known isotopes FREYA can’t presently handle
§ FREYA uses a Monte Carlo Weisskopf approach – Neutrons emitted by sampling from Weisskopf spectrum – After neutrons are done emitting, gamma rays are emitted from residual energy
§ Computationally more efficient than Monte Carlo Hauser-Feshbach
Slide 7
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Verification Strategy
§ Prove the models are implemented as intended – Assume models are verified against theory
§ Check secondary neutron and photon emission quantities – Averages
• Multiplicity: , • Energy: ,
– Distributions • Multiplicity: , • Energy: ,
– Correlations • Multiplicity: • Angular:
§ Standalone code versus MCNP integrated code results
Slide 8
νn νγχn χγ
P(νn ) P(νγ )χn (E) χγ (E)
P(νn ,νγ )
n(!Ω) ⋅n(
!Ω)
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Numerical Results
§ Compare standalone against MCNP6 integrated – CGMF and FREYA – Spontaneous and neutron-induced fission – Roughly 1E6 fission events
§ Simple test problem description – Force collision at source location – Secondary particles stream without collision – Use PTRAC to calculate results
§ Quantities for comparison – Averages – Distributions – Correlations
§ Secondary photons bug fixed
Slide 9
n n
n
γ
γ γ
γ
γ
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Averages
Slide 10
CGMF
252Cf(sf) n(1.0273 MeV)+
239Pu n(thermal)+
235U
Quantity Standalone MCNP Standalone MCNP Standalone MCNP
⌫̄N 3.7415(13) 3.7439(16) 3.0512(11) 3.0481(11) 2.4315(11) 2.4305(11)
�̄N 2.0927(8) 2.0920(10) 2.0322(9) 2.0329(9) 1.9726(9) 1.9740(9)
⌫̄� 8.2721(32) 8.2680(37) 7.9039(31) 7.9053(31) 7.4328(30) 7.4425(30)
�̄� 0.8561(3) 0.8558(3) 0.9287(3) 0.9293(3) 0.9139(3) 0.9131(3)
FREYA
252Cf(sf) n(1.0273 MeV)+
239Pu n(thermal)+
235U
Quantity Standalone MCNP Standalone MCNP Standalone MCNP
⌫̄N 3.7415(12) 3.7402(12) 2.7745(10) 2.7753(10) 2.2014(10) 2.2011(10)
�̄N 2.2491(10) 2.2483(10) 2.0272(10) 2.0276(10) 1.8692(10) 1.8689(10)
⌫̄� 8.0961(30) 8.1055(30) 7.1463(26) 7.1453(26) 6.7010(25) 6.7034(25)
�̄� 0.8929(3) 0.8924(3) 0.9922(3) 0.9918(3) 0.9770(3) 0.9774(3)
§ Standalone versus integrated results are in agreement within statistics!
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Distributions
§ Energy spectrum of neutrons and photons – Cf-252 (sf), Pu-239 (n,f) and U-235 (n,f)
Slide 11
10-5
10-4
10-3
10-2
10-1
100
101
10-2 10-1 100 101
252Cf(sf)Neu
tron
Spec
trum
(1/M
eV)
Energy (MeV)
CGMF onlyCGMF-MCNP
FREYA onlyFREYA-MCNP
10-5
10-4
10-3
10-2
10-1
100
101
10-1 100 101
252Cf(sf)Phot
on S
pect
rum
(1/M
eV)
Energy (MeV)
CGMF onlyCGMF-MCNP
FREYA onlyFREYA-MCNP
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Distributions
§ Multiplicity of neutrons and photons – Cf-252 (sf), Pu-239 (n,f) and U-235 (n,f)
Slide 12
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0 1 2 3 4 5 6 7 8 9 10
n(1.0273 MeV)+239Pu
Prob
abili
ty D
ensit
y, P
(in)
Neutron Multiplicity, in
CGMF onlyCGMF-MCNP
FREYA onlyFREYA-MCNP
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
n(1.0273 MeV)+239Pu
Prob
abili
ty D
ensit
y, P
(ia)
Photon Multiplicity, ia
CGMF onlyCGMF-MCNP
FREYA onlyFREYA-MCNP
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Distributions
Slide 13
CGMF only
0
2
4
6
8
10
0 5 10 15 20CGMF-MCNP
0
2
4
6
8
10
0 5 10 15 20
FREYA only
0
2
4
6
8
10
0 5 10 15 20
n(1.0273 MeV)+239Pu
Photon Multiplicity
Neu
tron
Mul
tiplic
ity
FREYA-MCNP
0
2
4
6
8
10
0 5 10 15 20
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UNCLASSIFIED
Correlations
§ Multiplicity correlations – Tagging on number of neutrons or photons observed
Slide 14
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
0 1 2 3 4 5 6 7 8
252Cf(sf)Ave
rage
Pho
ton
Mul
tiplic
ity
Neutron Multiplicity
CGMF onlyCGMF-MCNP
FREYA onlyFREYA-MCNP
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
0 5 10 15 20
252Cf(sf)
Ave
rage
Neu
tron
Mul
tiplic
ity
Photon Multiplicity
CGMF onlyCGMF-MCNP
FREYA onlyFREYA-MCNP
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Secondary Photon Bug Fixed
§ Previously when zero neutrons emitted è zero photons emitted
§ MCNP6.2 includes this bug fix
Slide 15
0.0e+005.0e-041.0e-031.5e-032.0e-032.5e-033.0e-033.5e-03
0 5 10 15 20 25 30Photon Multiplicity
0 2 4 6 8 100
5
10
15
20
25
30
Neutron Multiplicity
Photon Multiplicity
Neutron Multiplicity = 0
0.0e+00
5.0e-03
1.0e-02
1.5e-02
2.0e-02
2.5e-02
3.0e-02
3.5e-02
4.0e-02
0.0e+001.0e-042.0e-043.0e-044.0e-045.0e-046.0e-047.0e-048.0e-04
0 5 10 15 20 25 30Photon Multiplicity
0 2 4 6 8 100
5
10
15
20
25
30
Neutron Multiplicity
Photon Multiplicity
Neutron Multiplicity = 0
0.0e+00
1.0e-02
2.0e-02
3.0e-02
4.0e-02
5.0e-02
6.0e-02
CGMF FREYA
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Correlations
§ Angular neutron-neutron correlations – Cf-252 (sf), Pu-239 (n,f) and U-235 (n,f)
Slide 16
2.0e-02
2.2e-02
2.4e-02
2.6e-02
2.8e-02
3.0e-02
3.2e-02
3.4e-02
3.6e-02
3.8e-02
4.0e-02
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
252Cf(sf)
Neutron-Neutron Angle (cos(e))
CGMF onlyCGMF-MCNP
FREYA onlyFREYA-MCNP
1.5e-02
2.0e-02
2.5e-02
3.0e-02
3.5e-02
4.0e-02
4.5e-02
5.0e-02
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
n(1.0273 MeV)+239Pu
Neutron-Neutron Angle (cos(e))
CGMF onlyCGMF-MCNP
FREYA onlyFREYA-MCNP
1.5e-02
2.0e-02
2.5e-02
3.0e-02
3.5e-02
4.0e-02
4.5e-02
5.0e-02
5.5e-02
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
n(thermal)+235U
Neutron-Neutron Angle (cos(e))
CGMF onlyCGMF-MCNP
FREYA onlyFREYA-MCNP
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
UNCLASSIFIED
Conclusions
§ Integrated fission event generator models appear to be implemented correctly!
§ Next version of MCNP 6.2 will contain two new fission event generators – CGMF from LANL – FREYA from LLNL/LBNL
THANK YOU!
Slide 17
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