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Preliminary results of GODIVA-IV prompt burst modeling

Description: The dynamic computer model developed to simulate GODIVA-IV prompt bursts adequately predicts the magnitude of power bursts. Also, it demonstrates the characteristic features of prompt bursts in metal assemblies, such as the change in shape of power pulses and the ringing of fuel surfaces at the onset of inertial effects. The model will be used to test more sophisticated reactivity feedback coefficients and neutronic-hydrodynamic coupling schemes. It will also be used for a more detailed analysis of inertial effects.
Date: June 1, 1996
Creator: Kimpland, R.
Partner: UNT Libraries Government Documents Department

Analysis of Godiva-IV delayed-critical and static super-prompt-critical conditions

Description: Super-prompt-critical burst experiments were conducted on the Godiva-IV assembly at Los Alamos National Laboratory from the 1960s through 2005. Detailed and simplified benchmark models have been constructed for four delayed-critical experiments and for the static phase of a super-prompt-critical burst experiment. In addition, a two-dimensional cylindrical model has been developed for the super-prompt-critical condition. Criticality calculations have been performed for all of those models with four modern nuclear data libraries: ENDFIB-VI, ENDF/8-VII.0, JEFF-3.1 , and JENDL-3.3. Overall, JENDL-3.3 produces the best agreement with the reference values for k{sub eff}.
Date: January 1, 2009
Creator: Mosteller, Russell D & Goda, Joetta M
Partner: UNT Libraries Government Documents Department

Criticality measurements for SNM accountability

Description: Based on extensive operating experience with the Godiva IV fast metal burst assembly at Los Alamos National Laboratory, the authors were able to create data plots for reactivity worths of standard configurations at various temperatures and room return locations. These plots show that the material uncertainties in criticality measurements are within {+-} 20 grams out of the 65.4 kilogram HEU Godiva core. This is superior to active neutron well coincidence counter (AWCC) measurements. The criticality measurements have the additional advantage of not requiring disassembly of the reactor. No disassembly means the measurement takes less time--it can be done during each operation--and there is less dose to measurement personnel.
Date: March 1, 1998
Creator: Bohman, J.; Martin, E.R.; Butterfield, K. & Paternoster, R.
Partner: UNT Libraries Government Documents Department

Impact of MCNP unresolved resonance probability-table treatment on uranium and plutonium benchmarks

Description: Versions of MCNP up through and including 4B have not accurately modeled neutron self-shielding effects in the unresolved resonance energy region. Recently, a probability-table treatment has been incorporated into a developmental version of MCNP. This paper presents MCNP results for a variety of uranium and plutonium critical benchmarks, calculated with and without the probability-table treatment.
Date: December 31, 1998
Creator: Mosteller, R.D. & Little, R.C.
Partner: UNT Libraries Government Documents Department

Measurements of delayed neutron parameters for U-235 and Np-237

Description: Delayed neutrons are emitted by excited nuclei formed in beta decay of fission products called delayed neutron precursors. About 1% of the total neutrons released in fission are delayed neutrons; however, this small fraction plays an important role in nuclear reactor control. The delayed neutrons determine the time-dependent behavior of reactors, and knowledge of parameters used to predict neutron emission rate is essential for establishing reactivity worths. The delayed neutron yields, decay constants, and the absolute yield for the six-group delayed neutrons have been measured for U-235 and Np-237. This experiment has been called for in the forecast of experiments needed to support operations in the US. The bare U-235 metal assembly Godiva IV at the Los Alamos Critical Experiment Facility (LACEF) provided the source of neutrons. Godiva IV generated about 10{sup 7} total fissions in the samples for the infinite and instantaneous irradiation needed to accentuate the shorter and longer-lived groups of delayed neutrons. The detection system used in the experiment consisted of 20 He-3 tubes embedded in a polyethylene cylinder. The delayed neutron activity resulting from the fast neutron-induced fission has been measured. The measured absolute yield for U-235 was determined to be 0.0163 {+-} 0.009 neutrons/fission. This value compares very well with the well-established Keepin absolute yield of 0.0165 {+-} 0.0005. The newly measured absolute yield value for Np-237 was 0.0126 {+-} 0.0007, which compares well to the recently reported value of 0.0129 {+-} 0.0004 by Saleh and Parish. The measured values for U-235 are corroborated with period (e-folding time) versus reactivity calculations.
Date: July 1997
Creator: Loaiza, D.
Partner: UNT Libraries Government Documents Department

The central void reactivity in the Oak Ridge enriched uranium (93.2) metal sphere

Description: The central reactivity void worth was measured in the Oak Ridge unmoderated and unreflected uranium (93.20 wt% {sup 235}U) metal sphere by replacement measurements in a small (0.460-cm-diam) central spherical region in an 8.7427-cm-radius sphere. The central void worth was 9.165 {+-} 0.023 cents using the delayed neutron relative abundances and decay constants of Keepin, Wimett, and Zeigler to obtain the reactivity in cents from the stable reactor period measurements using the Inhour equation. This value is slightly larger than measurements with GODIVA 1 with larger cylindrical samples of uranium (93.70 wt% {sup 235}U) in the center: 135.50 {+-} 0.12 cents/mole for GODIVA 1 and 138.05 {+-} 0.34 cents/mole for the Oak Ridge sphere measurements, and the difference could be due to sample size effect. The central worth in {Delta}k units was calculated by neutron transport theory methods to be 6.02 {+-} 0.01 x 10{sup {minus}4} {Delta}k. The measured and calculated values are related by the effective delayed neutron fraction. The value of the effective delayed neutron fraction obtained in this way from the Oak Ridge sphere is 0.00657 {+-} 0.00002, which is in excellent agreement with that obtained from GODIVA 1 measurements, where the effective delayed neutron fraction was determined as the increment between delayed and prompt criticality and was 0.0066. From these Oak Ridge measurements, using the delayed neutron parameters of ENDF-B/VI to obtain the reactivity from the stable reactor period measurements, the central void worth is 7.984 {+-} 0.021 cents, and the inferred effective delayed neutron fraction is 0.00754. This central void worth and effective delayed neutron fractions are 14.2% higher than those obtained from use of the Keepin et al. delayed neutron data and produce a value of delayed neutron fraction in disagreement with GODIVA 1 measurements, thus questioning the usefulness of the relative abundances and ...
Date: March 1, 1997
Creator: Milhalczo, J.T.; Lynn, J.J. & Taylor, J.R.
Partner: UNT Libraries Government Documents Department

Los Alamos Critical Experiments Facility. Quarterly progress report, January 1--March 31, 1993

Description: The Los Alamos Critical Experiments Facility (LACEF) is now operating after a lengthy period of shutdown that lasted from November 1989 until June 1991. Since June 1991, the efforts of the staff have concentrated on bringing the assemblies back to operational status. The facility is fully operational and performing experiments. This progress report nominally covers the second quarter of FY93 (first quarter of calendar year 1993). It has sections on nuclear criticality safety classes, SHEBA II Project, Godiva IV activities, Skua activities, basic neutron physics measurements, etc.
Date: December 31, 1993
Creator: Anderson, R. E.; Paternoster, R. R.; Robba, A. A.; Sanchez, R. G.; Butterfield, K. B.; Partain, B. Q. et al.
Partner: UNT Libraries Government Documents Department

Test Plan for Godiva Move from LANL TA-18 to Nevada Test Site Device Assembly Facility

Description: Godiva is an unshielded, pulsed nuclear reactor, used to produce bursts of neutrons and gamma rays for irradiating test samples. The Godiva reactor is part of the TA-18 Facility at Los Alamos National Laboratory. The Godiva reactor is to be moved to the Device Assembly Facility (DAF) at the Nevada Test Site, northwest of Las Vegas, Nevada. Bursts of ionizing radiation from Godiva have been found to produce radio waves and electrical interference in circuits and electrical equipment (e.g., alarm systems, interlocks, recording devices) near Godiva. Safety and security concerns regarding Godiva at the DAF are: (1) Can Godiva pulses induce detonators elsewhere in the DAF to explode?, (2) What is the expected strength of the electrical signal from Godiva elsewhere in the DAF? (3) Will Godiva pulses trigger security alarms, requiring additional administrative controls? This report addresses these issues, and describes a brief set of electrical measurements intended to verify that electromagnetic emissions from Godiva are unchanged by its relocation, and below a threshold of safety for detonators that are outside the actual room Godiva resides in. The following points will be described: the nature of Godiva electrical emissions, predicted electric field at a given distance, electromagnetic frequency, safety threshold for detonators, recommended ''stay out'' zone around Godiva for detonators, and recommended measurements to be made once Godiva has been installed at DAF.
Date: August 1, 2005
Creator: Garcia, M
Partner: UNT Libraries Government Documents Department

Calculated in-air leakage spectra and power levels for the ANSI standard minimum accident of concern. Final report

Description: This document represents Phase I of a two-phase project. The entire project consists of determining a series of minimum accidents of concern and their associated neutron and photon leakage spectra that may be used to determine Criticality Accident Alarm compliance with ANSI/ANS-8.3. The inadvertent assembly of a critical mass of material presents a multitude of unknown quantities. Depending on the particular process, one can make an educated guess as to fissile material. In a gaseous diffusion cascade, this material is assumed to be uranyl fluoride. However, educated assumptions cannot be readily made for the other variables. Phase I of this project is determining a bounding minimum accident of concern and its associated neutron and photon leakage spectra. To determine the composition of the bounding minimum accident of concern, work was done to determine the effects of geometry, moderation level, and enrichment on the leakage spectra of a critical assembly. The minimum accident of concern is defined as the accident that may be assumed to deliver the equivalent of an absorbed dose in free air of 20 rad at a distance of 2 meters from the reacting material within 60 seconds. To determine this dose, an analyst makes an assumption and choose an appropriate flux to dose response function. The power level required of a critical assembly to constitute a minimum accident of concern depends heavily on the response function chosen. The first step in determining the leakage spectra was to attempt to isolate the effects of geometry, after which all calculations were conducted on critical spheres. The moderation level and enrichment of the spheres were varied and their leakage spectra calculated. These spectra were then multiplied by three different response functions: the Henderson Flux to Dose conversion factors, the ICRU 44 Kerma in Air, and the MCNP Heating Detector. The ...
Date: July 1, 1995
Creator: Lee, B.L. Jr.; Dobelbower, M.C. & Tayloe, R.W. Jr.
Partner: UNT Libraries Government Documents Department

Coupled hydro-neutronic calculations for fast burst reactor accidents

Description: Methods are described for determining the fully coupled neutronic/hydrodynamic response of fast burst reactors (FBR) under disruptive accident conditions. Two code systems, PAD (1 -D Lagrangian) and NIKE-PAGOSA (3-D Eulerian) were used to accomplish this. This is in contrast to the typical methodology that computes these responses by either single point kinetics or in a decoupled manner. This methodology is enabled by the use of modem supercomputers (CM-200). Two examples of this capability are presented: an unreflected metal fast burst assembly, and a reflected fast burst assembly typical of the Skua or SPR-III class of fast burst reactor.
Date: January 1, 1994
Creator: Paternoster, R.; Kimpland, R.; Jaegers, P. & McGhee, J.
Partner: UNT Libraries Government Documents Department

Los Alamos benchmarks: calculations based on ENDF/B-V data

Description: The new and revised benchmark specifications for nine Los Alamos National Laboratory critical assemblies are used to compute the entire set of parameters that were measured in the experiments. A comparison between the computed and experimental values provides a measure of the adequacy of the specifications, cross sections, and physics codes used in the calculations.
Date: November 1, 1981
Creator: Kidman, R.B.
Partner: UNT Libraries Government Documents Department

Benchmark assemblies of the Los Alamos Critical Assemblies Facility

Description: Several critical assemblies of precisely known materials composition and easily calculated and reproducible geometries have been constructed at the Los Alamos National Laboratory. Some of these machines, notably Jezebel, Flattop, Big Ten, and Godiva, have been used as benchmark assemblies for the comparison of the results of experimental measurements and computation of certain nuclear reaction parameters. These experiments are used to validate both the input nuclear data and the computational methods. The machines and the applications of these machines for integral nuclear data checks are described.
Date: January 1, 1985
Creator: Dowdy, E.J.
Partner: UNT Libraries Government Documents Department

JEZEBEL and GODIVA. Informal report

Description: Various code options and input data are tested in the calculation of the fast reactor benchmarks, JEZEBEL and GODIVA. Their effects on the eigenvalue and /sup 238/U to /sup 235/U central fission rate ratio are documented. Although the results can be used to improve past or future calculations, it appears that no reasonable choice of data or options can bring the calculated central fission ratio into agreement with the experimental value.
Date: February 1, 1979
Creator: Kidman, R.B.
Partner: UNT Libraries Government Documents Department

Technical specifications for the Pajarito Site Critical Experiments Facility

Description: This document is to satisfy the requirement for technical specifications spelled out in ERDA Manual Chapter 0540, ''Safety of ERDA-Owned Reactors.'' Technical specifications are defined in Sec. 0540-048, and the requirement for them appears in Sec. 0540-015. The following technical specifications replace the document, ''Operating Limits for the Los Alamos Critical Assembly Facility,'' revised May 27, 1971. (auth)
Date: June 1, 1975
Creator: Paxton, H.C.
Partner: UNT Libraries Government Documents Department

Los Alamos Critical Assemblies Facility

Description: The Critical Assemblies Facility of the Los Alamos National Laboratory has been in existence for thirty-five years. In that period, many thousands of measurements have been made on assemblies of /sup 235/U, /sup 233/U, and /sup 239/Pu in various configurations, including the nitrate, sulfate, fluoride, carbide, and oxide chemical compositions and the solid, liquid, and gaseous states. The present complex of eleven operating machines is described, and typical applications are presented.
Date: June 1, 1981
Creator: Malenfant, R.E.
Partner: UNT Libraries Government Documents Department

ENDF/B-V, LIB-V, and the CSEWG benchmarks

Description: A 70-group library, LIB-V, generated with the NJOY processing code from ENDF/B-V, is tested on most of the Cross Section Evaluation Working Group (CSEWG) fast reactor benchmarks. Every experimental measurement reported in the benchmark specifications is compared to both diffusion theory and transport theory calculations. Several comparisons with prior benchmark calculations attempt to assess the effects of data and code improvements.
Date: August 1, 1981
Creator: Kidman, R.B.
Partner: UNT Libraries Government Documents Department

Analysis of central worths and other integral data from the Los Alamos benchmark assemblies

Description: We have compared theoretical calculations, based on ENDF/B-V and recent revisions, with integral data measured on the Los Alamos unmoderated critical assemblies Godiva, Jezebel, Flattop-25, and Flattop-Pu. The experimental data included in this analysis are multiplication factors k/sub eff/ and (in most cases) both fission rates and central-worth ratios for /sup 235/U, /sup 238/U, /sup 237/Np, and /sup 239/Pu. Based on this comparison, we conclude that there is a need for a new /sup 235/U evaluation, and increased accuracy is needed in certain integral measurements.
Date: October 1, 1984
Creator: Muir, D.W.
Partner: UNT Libraries Government Documents Department

Safety analysis of the Los Alamos Critical Experiments Facility. Volume II

Description: The Los Alamos critical assembly layout is designed to facilitate personnel protection by means of remote operation and stringent procedural controls during nonoperating periods. Public protection is straightforward because of the small fission-product inventory, essentially ambient pressures, and moderate temperatures.
Date: April 1, 1976
Creator: Paxton, H. C.
Partner: UNT Libraries Government Documents Department

Thirty-five years at Pajarito Canyon Site

Description: A history of the research activities performed at the Pajarito Canyon Site from 1946 to 1981 is presented. Critical assemblies described include: the Topsy assembly; Lady Godiva; Godiva 2; Jezebel; Flattop; the Honeycomb assembly for Rover studies; Kiwi-TNT; PARKA reactor; Big Ten; and Plasma Cavity Assembly.
Date: May 1, 1981
Creator: Paxton, H.C.
Partner: UNT Libraries Government Documents Department