Estimation of uncertainties for subcritical benchmark measurements - 14387

Conference · Tue Sep 15 04:00:00 EDT 2015

OSTI ID:23100857

Hutchinson, J.; Smith-Nelson, M.; Cutler, T.; Grove, T. ^[1]; Richard, Benoit ^[1]

---

1. Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM (United States)

Subcritical measurements are used for many applications including nonproliferation, treaty verification, in-situ monitoring for criticality, and reactor subcriticality monitoring. Most analysis methods involve correlated neutron detection, based upon the property that fission events can create multiple neutrons that are born at nearly the same time (on a scale of 10{sup -13} or 10{sup -14} seconds). Many different time-correlated methods have been used since the 1950's and are still widely utilized today. This particular work describes an uncertainty analysis of measured data using the Hage-Cifarelli formalism of the Feynman Variance-to-Mean method. The Feynman Variance-to-Mean method was introduced by Feynman et al. in 1956 and is based upon the differences between the detector count data and the data that would be expected from measurements taken from a Poissonian source. The Hage-Cifarelli formalism relates moments of the Feynman histograms to several parameters of a system: leakage multiplication (M{sub L}), spontaneous fission rate (F{sub S}), (α,n) neutron emission rate (S{sub α}), detector efficiency (ε), and the moments of the number of neutrons emitted per fission (ν). The first part of the uncertainty method described in this work will show how to determine uncertainties of the first (R{sub 1}) and second (R{sub 2}) reduced factorial moments of the Feynman histograms. The second part of the method will describe how to determine the uncertainties in the other parameters given uncertainties in the reduced factorial moments; in particular, this work will focus on determining the uncertainties in M{sub L} and F{sub S}. This work will utilize measured data from a recent benchmark evaluation with a 4.5 kg sphere of α-phase plutonium to validate the uncertainty analysis. (authors)

• Research Organization: American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
• OSTI ID: 23100857
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
42 ENGINEERING
BENCHMARKS
CRITICALITY
EFFICIENCY
MONITORING
NEUTRON DETECTION
NEUTRON EMISSION
NON-PROLIFERATION TREATY
PLUTONIUM
SPONTANEOUS FISSION
VERIFICATION