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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 Article · · Nuclear Science and Engineering
 [1];  [2];  [2];  [3];  [3];  [3]
  1. Univ. of Michigan, Ann Arbor, MI (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States); University of Michigan
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Univ. of Michigan, Ann Arbor, MI (United States)
+ Show Author Affiliations
Rossi-alpha measurements of fissionable assemblies are used to estimate the prompt neutron decay constant, α, of a system, which can be used to infer reactivity. Previous works have demonstrated that two-exponential fits for Rossi-alpha measurements of reflected assemblies are better than one exponential fits; however, the two-exponential probability density function that is needed to obtain α from the fit parameters has not been derived. This paper derives the two-region point kinetics model (two-exponential fit) for Rossi-alpha measurements, a generalization of the current, one region model (one-exponential fit). The new model is validated with measurements of reflected, fissionable assemblies (highly enriched uranium with keff ≈ 0.95 and weapons-grade plutonium with keff > 0.77) with α held constant. Here, the results show that the twoexponential model can (i) predict the constant α, and (ii) deconvolve α and the time a neutron spends in the reflector, neither of which is possible with the one-exponential model.
Research Organization:
Univ. of Michigan, Ann Arbor, MI (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP); USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation; USDOE National Nuclear Security Administration (NNSA), Office of Nonproliferation and Verification Research and Development
Grant/Contract Number:
NA0002534; NA0003920
OSTI ID:
1698021
Alternate ID(s):
OSTI ID: 1798686
Journal Information:
Nuclear Science and Engineering, Journal Name: Nuclear Science and Engineering Journal Issue: 1 Vol. 194; ISSN 0029-5639
Publisher:
Taylor & FrancisCopyright Statement
Country of Publication:
United States
Language:
English

References (9)

Validation of statistical uncertainties in subcritical benchmark measurements: Part II – Measured data journal March 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
Feynman variance-to-mean in the context of passive neutron coincidence counting
  • Croft, S.; Favalli, A.; Hauck, D. K.
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 686 https://doi.org/10.1016/j.nima.2012.05.042
journal September 2012
Characterizing subcritical assemblies with time of flight fixed by energy estimation distributions
  • Monterial, Mateusz; Marleau, Peter; Pozzi, Sara
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 888 https://doi.org/10.1016/j.nima.2018.01.080
journal April 2018
A Note on the Nomenclature in Neutron Multiplicity Mathematics journal January 2019
Prompt Neutron Periods of Metal Critical Assemblies journal July 1957
Reflected-Reactor Kinetics journal May 1962
Polyethylene-reflected plutonium metal sphere : subcritical neutron and gamma measurements. report November 2009
Characterizing Subcritical Assemblies with Time of Flight Fixed by Energy Estimation Distributions text January 2018

Figures / Tables (12)

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TABLE I(p. 19)table TABLE I
TABLE II(p. 19)table TABLE II
Fig. 9(p. 20)figure Fig. 9
Fig. 10(p. 21)figure Fig. 10

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Related Subjects

42 ENGINEERING
Integral Experiments
Nuclear Criticality Safety Program (NCSP)
Rossi-alpha
neutron noise
prompt neutron decay constant
subcritical measurements