Jesson D. Hutchinson

Uncertainties of the Yn Parameters of the Hage-Cifarelli Formalism

One method for determining the physical parameters of a multiplying system is summarized by Cifarelli [1]. In this methodology the single, double and triple rates are determined from what is commonly referred to as Feynman histograms. This paper will examine two methods for estimating the uncertainty in the parameters used in inferring these rates. These methods will be compared with simulated data in order to determine which one best approximates the sample uncertainty.

Subcritical Measurements of a Plutonium Sphere Reflected by Polyethylene and Acrylic

Abstract Subcritical measurements were conducted with an alpha-phase plutonium sphere using the 252Cf source-driven noise analysis method. Measurements were performed with both polyethylene and acrylic reflectors. For each reflector type, five different reflector thicknesses were investigated: 0 (bare), 1.27, 2.54, 3.81, and 7.62 cm. A certain ratio of spectral quantities that depends on the fluctuations in the fission chain multiplication process was measured for each configuration. In addition, two types of Monte Carlo calculations were employed to estimate the keff and spectral ratio values of each configuration. From the measured and computed quantities, the multiplication and uncertainty of the system can be inferred. The polyethylene measurements compared well to previous measurements conducted with the same plutonium sphere and polyethylene reflector thicknesses. The acrylic measurements provide benchmark data of an alpha-phase plutonium sphere reflected by acrylic.

Lead Void Reactivity Worth in Two Critical Assembly Cores with Differing Uranium Enrichments

Abstract To validate lead (Pb) nuclear cross sections, a series of integral experiments to measure lead void reactivity worths was conducted in a high-enriched uranium (HEU)/Pb system and a low-enriched uranium (LEU)/Pb system using the Comet Critical Assembly at the National Criticality Experiments Research Center. There is a follow-on experiment to measure the lead void reactivity worths in a plutonium/Pb system that is currently under investigation. The critical experiments in the two uranium systems were designed to provide complementary data sets having different sensitivities to scattering cross sections of lead. The larger amount of the 238U present in the LEU/Pb core increases the neutron importance above 1 MeV compared with the HEU/Pb core. Since removal of lead from the core shifts the neutron spectrum to the higher energy region, positive lead void reactivity worths were observed in the LEU/Pb core while negative values were observed in the HEU/Pb core. This technical note is a preliminarily report of the experimental analysis results for the lead void reactivity worths with the Monte Carlo calculation code MCNP® version 6.1 together with nuclear data libraries JENDL-4.0 and ENDF/B-VII.1. The calculation values were found to overestimate the negative reactivity worths for the HEU/Pb core while being consistent for the LEU/Pb core.

Measurement of the thermal absorption cross section in lucite using fermi age theory

The diffusion processes of neutrons in Lucite have been investigated. The mechanisms of these processes have been described as having two steps. In the first step, the fast neutrons collide with the nuclei of Lucite, losing energy until they reach thermal energies, In the second step of the diffusion process, the thermal neutrons continue to diffuse through the Lucite without any significant loss of energy until they are finally absorbed or leak out of the system. Experiments were performed to study these two processes and to estimate the absorption cross section in Lucite. The experiments yielded an average range of 6.3 cm for fast neutrons slowing down to thermal energies and a thermal absorption cross section in Lucite of 0.52 b.

Subcritical Noise Measurements with a Nickel-Reflected Plutonium Sphere

Abstract Subcritical measurements were conducted with an α-phase plutonium sphere reflected by nickel hemishells using the 252Cf source-driven noise analysis method to provide criticality safety benchmark data. Measured configurations included a bare plutonium sphere as well as the plutonium sphere reflected by the following nickel thicknesses: 1.27, 2.54, 3.81, 5.08, and 7.62 cm. A certain ratio of spectral quantities was measured for each configuration, which varies linearly with the keff of the system under small perturbations. In addition, two types of Monte Carlo calculations were employed: a modified version of MCNP to calculate the ratio of spectral quantities and a KCODE calculation. From the measured and computed quantities, the effective multiplication factor of each configuration can be approximated. The inferred keff for all six configurations compared well with computed values. A comprehensive uncertainty analysis was then performed that includes uncertainties in the geometry and materials present in the system in addition to the uncertainties in the method and nuclear data.

Uncertainties in the Standard Moments, the Derivation of the Y1 to Y8 parameters, and the Derivation of w1 to w8 for Feynman Histograms

Momentum is a neutron multiplicity analysis software package that calculates a variety of parameters associated with Feynman histograms. While most of these parameters are documented in Cifarelli and Smith-Nelson, there are some parameters which are not. Most prominent of these are the uncertainties in the standard moments, and this paper will explicitly document these parameters. This paper will also document the higher-order Yn parameters and their associated ωn functions because they may be useful for future applications. The generation of what is referred to as Feynman histograms is not explained here.

Pictures from VIP Tour During CNEC and CVT Measurements 2016

Below are pictures from the VIP tour on July 13, 2016 at the DAF and Sedan Crater. The tour occurred during the CNEC and CVT Year Two measurements.

Pictures from Year Two CNEC and CVT Measurements

Below are all of the pictures for the CNEC and CVT measurements performed at the DAF in July 2016. In total there are 165 pictures. The photos on pages 2-105 were taken during the first week of measurements and the photos on pages 106-165 were taken during the second week of measurements. Many photos are applicable to both sets, which is why it is best to keep the entire set together. For most configurations, a description of the configuration was written on a white board; photos of the measurement setup were taken, then a photo of the white board was taken. For example, the pictures on pages 6-19 (which precede a white board picture on page 20) are of the configuration with Rocky Flats Shells 1-2 surrounded by 4 AmLi sources, which is listed on the white board picture on page 20. In some cases, the white board picture precedes the configuration pictures.

Kilowatt Reactor Using Stirling TechnologY (KRUSTY) Demonstration. CEDT Phase 1 Preliminary Design Documentation

The intent of the integral experiment request IER 299 (called KiloPower by NASA) is to assemble and evaluate the operational performance of a compact reactor configuration that closely resembles the flight unit to be used by NASA to execute a deep space exploration mission. The reactor design will include heat pipes coupled to Stirling engines to demonstrate how one can generate electricity when extracting energy from a “nuclear generated” heat source. This series of experiments is a larger scale follow up to the DUFF series of experiments1,2 that were performed using the Flat-Top assembly.

Characterization of the NPOD3 Detectors in MCNP5 and MCNP6

Researchers performed a series of measurements in May 2012 to characterize the NPOD3 detector systems. The detectors were placed in varying states of disassembly to determine the effect of individual components on detection efficiency. A 4.5 kg α-phase Pu sphere known as the Los Alamos BeRP Ball was used as the SNM source in both a bare configuration and reflected by varying thicknesses of polyethylene. A set of simulations matching the experimental setups were run and the data were compared to the measured data. The total and leakage multiplication and the inferred k values were determined for both the simulations and the measurements. Table 3 shows a comparison of the results from MCNP6 and MCNP5 with the list-mode patch to the measured results. The count rates for the calculated results were obtained by dividing the total line count in the list-mode file (equivalent to the total number of absorptions in the NPOD detectors) by the total run time. The count rates are identical for both codes, and they both produce the same multiplicity and inferred k values regardless of measurement time as expected.