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Title: Validation of the two-region Rossi-alpha model for reflected assemblies

Journal Article · · Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment
ORCiD logo [1];  [2];  [3];  [3];  [2];  [2]
  1. Univ. of Michigan, Ann Arbor, MI (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Univ. of Michigan, Ann Arbor, MI (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
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Nuclear criticality safety, nonproliferation and safeguards, emergency response, and stockpile stewardship utilize estimates of the keff multiplication factor. The value of keff cannot be directly measured, but it can be inferred from the prompt neutron period. One modality of measuring the prompt neutron period is the Rossi-alpha method, which is predicated on fitting a histogram of detection time differences due to the nonrandom temporal distribution of same-fission-chain neutrons. Recent works have developed the motivation and theory to expand traditional one-region point kinetic models resulting in one-exponential histogram fits to two-region models that result in two-exponential fits. This paper validates the new two-region model using organic scintillator measurements of copper-reflected weapons-grade plutonium (0:83 ≤ keff ≤ 0:94) and high-density- polyethylene-reflected highly enriched uranium (0:73 ≤ keff ≤ 0:95). Furthermore, the results show that more thermal systems have shorter prompt neutron periods in the core region due to increased induced-fission probabilities for moderated neutrons. Here, a new parameter introduced by the two- region model is also shown to be correlated to the amount of reflection, and may be used to infer assembly properties such as type and amount of reflector.

Research Organization:
Univ. of Michigan, Ann Arbor, MI (United States); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP); National Science Foundation (NSF); USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
NA0003920; DGE-1256260; NA0002534
OSTI ID:
1696779
Alternate ID(s):
OSTI ID: 1648376
Journal Information:
Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 981; ISSN 0168-9002
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

References (19)

Scintillation properties of solution-grown trans-stilbene single crystals
  • Zaitseva, Natalia; Glenn, Andrew; Carman, Leslie
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 789 https://doi.org/10.1016/j.nima.2015.03.090
journal July 2015
Measurement uncertainty of rossi-alpha neutron experiments journal November 2020
Coupled Fast-Thermal Power Breeder journal February 1958
Prompt Neutron Decay and Reactivity Measurements in Subcritical Uranium Metal Cylinders journal June 1968
Neutron detection in a high-gamma field using solution-grown stilbene
  • Bourne, M. M.; Clarke, S. D.; Adamowicz, N.
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 806 https://doi.org/10.1016/j.nima.2015.10.025
journal January 2016
Reflected-Reactor Kinetics journal May 1962
Rossi-alpha measurements of fast plutonium metal assemblies using organic scintillators
  • Hua, Michael Y.; Bravo, Caiser A.; MacDonald, Aaron T.
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 959 https://doi.org/10.1016/j.nima.2020.163507
journal April 2020
MCNP-PoliMi: a Monte-Carlo code for correlation measurements
  • Pozzi, Sara A.; Padovani, Enrico; Marseguerra, Marzio
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 513, Issue 3 https://doi.org/10.1016/j.nima.2003.06.012
journal November 2003
Dispersion of the neutron emission in U-235 fission journal August 1956
Digital pulse shape discrimination journal May 2007
Prompt Neutron Periods of Metal Critical Assemblies journal July 1957
Rossi-alpha experiment in the IPEN/MB-01 research reactor journal January 2005
A scintillation counter with neutron and gamma-ray discriminators journal April 1959
Results of Three Neutron Diagnosed Subcritical Experiments journal December 2018
An algorithm for charge-integration, pulse-shape discrimination and estimation of neutron/photon misclassification in organic scintillators
  • Polack, J. K.; Flaska, M.; Enqvist, A.
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 795 https://doi.org/10.1016/j.nima.2015.05.048
journal September 2015
Derivation of the Two-Exponential Probability Density Function for Rossi-Alpha Measurements of Reflected Assemblies and Validation for the Special Case of Shielded Measurements journal September 2019
Simulation of polyethylene-moderated plutonium neutron multiplicity measurements
  • Miller, E. C.; Dennis, B.; Clarke, S. D.
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 652, Issue 1 https://doi.org/10.1016/j.nima.2011.01.042
journal October 2011
MCNP Version 6.2 Release Notes report February 2018
Extrapolated experimental critical parameters of unreflected and steel-reflected massive enriched uranium metal spherical and hemispherical assemblies report December 1997

Figures / Tables (15)

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