CoverSheet - Los Alamos National Laboratory · Photon Spectrum (1/MeV) 252Cf(sf) Energy (MeV) CGMF only CGMF-MCNP FREYA only FREYA-MCNP. Operated by Los Alamos National Security,

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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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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


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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


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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


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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 )


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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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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


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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


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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)


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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


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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!


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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



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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


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



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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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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


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



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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


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


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


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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


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


CGMF onlyCGMF-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


CGMF onlyCGMF-MCNP



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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

Documents

CoverSheet - Los Alamos National Laboratory · Photon Spectrum (1/MeV) 252Cf(sf) Energy (MeV) CGMF only CGMF-MCNP FREYA only FREYA-MCNP. Operated by Los Alamos National Security,