Engineering Papers⌕ Search

Engineering topics

Grove, Travis

Publications and source records attributed to Grove, Travis.

27 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A New Era of Nuclear Criticality Experiments: The First 10 Years of Comet Operations at NCERC

Comet is a general-purpose, heavy-duty, vertical-lift assembly designed for flexibility in conducting a variety of critical experiments. It is currently located at the National Criticality Experiments Research Center (NCERC) in Nevada. In the past, Comet resided at Technical Area-18 in Los Alamos, New Mexico, as part of the Los Alamos Critical Experiments Facility (LACEF). The Comet assembly was relocated to NCERC in 2008 and became fully operational in June of 2011. The first critical experiment performed on Comet at NCERC was a verification of one of the previous configurations of the Zeus experiment series. Over the next 10 years, many additional experiments followed including other Zeus configurations as well as completely new designs. This paper discusses the Comet vertical-lift assembly, the transition from LACEF to NCERC, and a selection of experiments that have been performed on Comet during its first 10 years of operation at NCERC.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

A New Era of Nuclear Criticality Experiments: The First 10 Years of Planet Operations at NCERC

Planet is a vertical-lift assembly machine currently located at the National Criticality Experiments Research Center (NCERC) at the Nevada National Security Site. In the past, Planet resided at Technical Area-18 in Los Alamos, New Mexico, as part of the Los Alamos Critical Experiments Facility (LACEF). Following the de-inventorying of LACEF, the Planet assembly was relocated to NCERC in 2008 and became fully operational in June of 2011. The Class Foils experiment, which involves stacking highly enriched uranium foils to obtain a critical configuration, was the first critical experiment performed on Planet. As a major component of the Nuclear Criticality Safety Class taught for the U.S. Department of Energy (DOE) Nuclear Criticality Safety Program, the Class Foils experiment allows personnel from all over the DOE complex to handle nuclear material and to complete the approach to critical safely and successfully. This paper describes the Planet vertical assembly and recent engineering upgrade and a selection of the experiments that have been performed on Planet since its transition to NCERC 10 years ago.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Using Prompt Neutron Decay Constant Measurements to Obtain Additional Kinetics Information

Prompt neutron decay constant measurements are typically used to infer the prompt neutron lifetime in a chain-reacting system, but these measurements include much more information about the kinetics of the system. This work focuses specifically on the Rossi-α method of measuring the prompt neutron decay constant. The Rossi-α system of equations consists of five unknown parameters. With five unknowns and three equations, the system of equations solved by the Rossi-α measurement is under-determined. It has been postulated that a well posed problem can be formulated using independent measurement configurations on a single system. The external source strength, the effective delayed neutron fractions, and Diven’s parameter do not typically change for different configurations of a single experiment. If good detector geometry is chosen, the detector efficiency does not change for multiple measurements of a single experiment using Rossi-α measurements. By making these assumptions, there are only two unique variables. This knowledge can be used to solve for most of the unique parameters using two independent, unique Rossi-α measurements.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Prompt Neutron Decay Constant Measurements on a Copper Reflected Intermediate Enrichment Uranium System with Lead Intersitial

This work examines a set of prompt neutron decay constant measurements performed on the Zeus critical experiment. The Zeus experiment was designed to measure the lead void reactivity coefficient associated with an intermediate enrichment uranium system. The initial goal was to perform the measurements on a low enriched uranium system, but weight limitations on the Comet critical assembly only allowed for a system with 21%-22% effective uranium enrichment to be built. The Zeus critical experiment was performed on the Comet critical assembly machine located at the National Criticality Experiments Research Center (NCERC). The Comet critical assembly machine is a vertical lift assembly capable of supporting general large size critical experiments. This critical experiment consists of a copper reflector set most notably used in other configurations of the Zeus experiment series. The fuel used during the Zeus experiments consists of cylindrical highly enriched uranium (HEU) plates with a nominal 1/8-in. (0.318-cm) thickness. These plates were collocated with natural uranium plates to reduce the effective enrichment of the system to 21%-22%. Lead plates are interleaved between each fuel set.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Designing Critical Experiments Using Gaussian Process Optimization

New nuclear applications may lack similarity between the application and existing ICSBEP benchmarks. Without accurate benchmark data, predictive simulations will have high uncertainty in the estimate of a parameter of interest (such as k eff ). The design of critical experiments tuned for specific applications of interest is one solution to reducing uncertainty in the necessarily nuclear data. We propose an optimization technique to design critical experiments that match the cross-section sensitivities of an application model while minimizing the number of simulation runs in the optimization. The optimization of a critical experiment is slow because the potential design space covers many qualitative variables (types of material and geometries) and corresponding quantitative variables (e.g., material dimensions) and the evaluation of any specific design requires running an expensive code like MCNP1 and Whisper. The optimization of expensive black-box computer codes with quantitative variables has been extensively explored in the literature of design of computer experiments. We propose a modified version of standard Gaussian process (GP) optimization that optimizes over multiple discrete configurations of qualitative variables in parallel which reduces the computational cost of the entire optimization. The goal of this work is to minimize the number of MCNP evaluations while still exploring many different design configurations in parallel.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Characterization of a Polyethylene Moderated Highly Enriched Uranium System

The polyethylene interstitial materials for the Class Foils experiment are one of the teaching tools used to teach criticality safety at the National Criticality Experiments Research Center (NCERC). This set of polyethylene plates is designed to provide the optimal H/{sup 235}U ratio on the critical mass curve allowing the experiment to have the minimum amount of {sup 235}U. This makes a great teaching tool to show that either additional {sup 235}U or additional moderator would increase the critical mass. The optimal H/{sup 235}U ratio and increased hydrogen density compared to the previously used Lucite plates has reduced the critical mass by 34%, to 997.9 ± 0.65 g. The robustness of this experiment makes it ideal for hands on training. The fuel foils consist of thin highly enriched uranium (93 wt% {sup 235}U) metal foils laminated in plastic; each foil weighs approximately 68 grams. The fuel is interleaved between interstitial plates to attain a critical configuration. The critical configuration requires 14.5 fuel foils. Rossi-α experiments have been proposed as a method of benchmarking kinetics properties given by neutronics codes such as MCNP. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

Prompt Neutron Decay Constants in a Highly Enriched Uranium-Lead Copper Reflected System

Rossi-{alpha} measurements were performed on highly enriched uranium (HEU)-lead copper reflected systems to determine the prompt neutron decay constants. These constants represent an eigenvalue characteristic of these particular critical configurations, which can be experimentally measured by the Rossi-a or pulse neutron source techniques and calculated by a deterministic or Monte Carlo method. In the measurements presented in this summary, highly enriched uranium interleaved with lead plates and reflected with copper were assembled to a high multiplication and the prompt neutron decay constants were determined by the Rossi-{alpha} technique. This research intended to benchmark the lead neutron cross sections; it was a collaboration between the Japanese Atomic Energy Agency (JAEA) Fast Critical Assembly Facility (FCA) in Tokai, Japan and the Los Alamos National Laboratory (LANL) in the U.S. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

A new critical experiment in support of the nuclear criticality safety class - 14488

A new critical experiment has been performed on the Planet vertical assembly machine at the National Criticality Experiments Research Center (NCERC). The purpose of the experiment was to compare the moderator properties of polyethylene versus Lucite and to use the experiment as an instructional tool for criticality safety engineers. The Lucite version of this experiment has been performed many times since the mid-1970's. Similar to the Lucite critical experiment, the polyethylene experiment was designed to emphasize the factors that affect criticality; namely, enrichment, reflection, interaction, moderation, mass, shape, volume, density, concentration, and poisons. The critical mass obtained with the moderating high density polyethylene plates was 997.0 ± 0.65 grams of highly enriched uranium, which is approximately 34% lower than the critical mass obtained using the Lucite moderating plates. This 34% decrease is mostly attributable to the higher hydrogen and carbon atom densities of polyethylene versus Lucite. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗