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Results of Experiment 1: FCE Calibration With BORAX Core

Description: Summary: The justification of using polyethylene whose hydrogen density of 0.132 gm/cm³ with a distributed void of 15.9 percent as a mockup of water at 70°F and having a hydrogen density of 0.111 gm/cm³ was tested in the FCE. A mockup close to the BORAX core was built and its critical mass determined. Corrections were calculated for differences in the hydrogen desnity and self shielding of the fuel. The effective FCE critical mass agreed with that of the BORAX core to within one percent.
Date: October 1, 1956
Creator: Starr, E. & Toops, Edward Chassell
Partner: UNT Libraries Government Documents Department

Recalculation of Critical Masses of U and Pu Water Tamped Solutions

Description: A report discussing a method of computing the critical mass of U₂₃₅ contained in a water solution confined to a spherical core and surrounded by an infinite water tamper, a modification of said method in which the effect of the resonance fission and absorption is taken into account, and physical constants required to calculate the critical mass using these methods.
Date: September 1, 1949
Creator: Greuling, Eugene
Partner: UNT Libraries Government Documents Department

Summary report of session VI

Description: This report gives a brief review of the presentations in Session VI of the Ecloud'02 Workshop and summarizes the major points during the discussions. Some points (e.g., the critical mass phenomenon) are not conclusive and even controversial. But it has been agreed that further investigations are warranted. The topic of Session VI in the Ecloud'02 workshop is ''Discussions of future studies, collaborations and possible solutions.'' Half of the session is devoted to presentations, another half to discussions. This report will focus on the latter. There are six presentations: (1) R. Macek, Possible cures to the e-cloud problem; (2) G. Rumolo, Driving the electron-cloud instability by an electron cooler; (3) U. Iriso Ariz, RF test benches for electron-cloud studies; (4) F. Caspers, Stealth clearing electrodes; (5) F. Ruggiero, Future electron-cloud studies at CERN; and (6) E. Perevedentsev, Beam-beam and transverse impedance model.
Date: August 19, 2002
Creator: Chou, Weiren; Brüning, O.; Metral, E. & Giovannozzi, M.
Partner: UNT Libraries Government Documents Department

Relationship between k{sub eff} and the fraction of critical mass

Description: It is not universally understood that k{sub eff} and fractional critical mass are related in a non linear fashion. For example, a neutronic system with a k{sub eff} = 0. 95 is NOT at 95% of its critical mass. What is striking is just how non-linear the relationship between k{sub eff} and critical mass really is. This relationship is investigated and documented below for both unfavorable (i.e., very reactive) and favorable (less reactive) geometries. The implications of this non-linearity for criticality safety regulation will also be discussed.
Date: May 1, 1997
Creator: O`Dell, R.D. & Parsons, D.K.
Partner: UNT Libraries Government Documents Department

Fundamental-mode sources in approach-to-critical experiments

Description: The 1/M method is commonly used in approach-to-critical experiments to ensure criticality safety. Ideally, a plot of 1/M versus amount of nuclear material or separation distance will be linear. However, the result is usually a curve. If the curve is concave up it is said to be conservative, since the critical mass is underestimated. However, it is possible for the curve to be non-conservative and overestimate the critical mass. This paper discusses one of the factors contributing to the shape of the 1/M curve and how it can be predicted and measured. Two source distributions, producing the same number of spontaneous fission neutrons, will not necessarily contribute equally towards the multiplication of a given system. For this reason equally sized units added during an approach-to-critical will have different effects on the multiplication of the system. A method of denoting the relative importance of source distributions is needed. One method is to compare any given source distribution to its equivalent fundamental-mode source distribution. An equivalent fundamental-mode source is an imaginary source distributed identically in space, energy, and angle to the fundamental-mode fission source that would produce the same neutron multiplication as the given source distribution. A factor, denoted as g* and defined as the ratio of the fixed-source multiplication to the fundamental-mode multiplication, is used to relate a given source strength to its equivalent fundamental-mode source strength (Spriggs, et al., 1999).
Date: May 1, 2000
Creator: Goda, J. & Busch, R.
Partner: UNT Libraries Government Documents Department

Analytical review of minimum critical mass values for selected uranium and plutonium materials

Description: Current subcritical limits for a number of uranium and plutonium materials (metals and compounds) as given in the ANSI/ANS standards for criticality safety are based on evaluations performed in the late 1970s and early 1980s. This paper presents the results of an analytical study of the minimum critical mass values for a set of materials using current codes and standard cross section sets. This work is meant to produce a consistent set of minimum critical mass values that can form the basis for adding new materials to the single-parameter tables in ANSI/ANS-8.1. Minimum critical mass results are presented for bare and water reflected full-density spheres and for full density moist (1.5 wt-% water) as calculated with KENO-Va, MCNP4A and ONEDANT. Calculations were also performed for both dry and moist materials at one-half density. Some KENO calculations were repeated using several cross section sets to examine potential bias differences. The results of the calculations were compared to the currently accepted subcritical limits. The calculated minimum critical mass values are reasonably consistent for the three codes, and differences most likely reflect differences in the cross section sets. The results are also consistent with values given in ANSI/ANS-8.1. 3 refs., 2 tabs.
Date: September 1, 1997
Creator: Morman, J.A.; Henrikson, D.J. & Garcia, A.S.
Partner: UNT Libraries Government Documents Department

Critical mass study of 231 process tanks

Description: An estimated minimum critical mass for each of the process vessels in the 231 Building has been calculated on the basis of critical mass data given in the P-11 Project Document HW-24514. The calculations are made assuming the plutonium to be a homogeneous mixture of precipitate and water with some slight neutron poisoning due to other elements. The precipitate is further assumed to have partially settled making an effectively infinite water reflector above the plutonium and hence reducing the critical mass.
Date: August 19, 1952
Creator: Lanning, D.D.
Partner: UNT Libraries Government Documents Department

Recuplex nuclear safety equipment revisions

Description: A number of equipment revisions have been recommended by the Engineering Department for conversion of Recuplex to a manufacturing facility. These revisions include three items affecting the critical mass safety of the solvent extraction system: replacement of the bottom disengagement section of the H-3 stripping column with an always safe unit; replacement of the H-9 and H-10 intercolumn, organic phase surge tanks with always safe tanks; and replacement of the colorimetric plutonium monitors in the aqueous and organic raffinate streams with units insensitive to stream contaminants. This memorandum is intended to clarify the needs for these equipment revisions in achieving a safe and flexible operating system and to indicate the relative effects of revising each of the various equipment pieces separately. The general bases for the present criticality control measures in the solvent extraction system are reviewed briefly prior to discussion of the individual revisions.
Date: May 16, 1956
Creator: Judson, B.F.
Partner: UNT Libraries Government Documents Department

DOE EPSCoR Initiative in Structural and computational Biology/Bioinformatics

Description: The overall goal of the DOE EPSCoR Initiative in Structural and Computational Biology was to enhance the competiveness of Vermont research in these scientific areas. To develop self-sustaining infrastructure, we increased the critical mass of faculty, developed shared resources that made junior researchers more competitive for federal research grants, implemented programs to train graduate and undergraduate students who participated in these research areas and provided seed money for research projects. During the time period funded by this DOE initiative: (1) four new faculty were recruited to the University of Vermont using DOE resources, three in Computational Biology and one in Structural Biology; (2) technical support was provided for the Computational and Structural Biology facilities; (3) twenty-two graduate students were directly funded by fellowships; (4) fifteen undergraduate students were supported during the summer; and (5) twenty-eight pilot projects were supported. Taken together these dollars resulted in a plethora of published papers, many in high profile journals in the fields and directly impacted competitive extramural funding based on structural or computational biology resulting in 49 million dollars awarded in grants (Appendix I), a 600% return on investment by DOE, the State and University.
Date: February 21, 2008
Creator: Wallace, Susan S.
Partner: UNT Libraries Government Documents Department

Mass and Density, Criticality Relationship

Description: Here I present some well known relationships that allow the variation in critical mass versus density to be written in a simple analytical form; these relationships have appeared extensively in the open literature for over 50 years, but seem to be periodically forgotten. These relationships are exact for bare, homogeneous systems, and approximate [but reasonably accurate] for reflected systems. With these relationships anyone can quickly estimate the critical mass corresponding to any given density, using nothing more complicated than a hand calculator.
Date: April 10, 2001
Creator: Cullen, D E
Partner: UNT Libraries Government Documents Department

Mass and Density, Criticality Relationships, Generalized

Description: As it relates to neutron transport calculations, in an earlier report I defined scaling laws relating reactivity or criticality to the mass, density and dimensions of geometrically simple systems. Here I generalize these scaling laws to any geometry. These are well known relationships that allow the variation of critical mass versus density and/or dimensions to be written in a simple analytical form. With these relationships anyone can quickly estimate the critical mass corresponding to any given density, using nothing more complicated than a hand calculator. In addition I point out that these scaling laws can be used to easily predict the sensitivity of a system's K-eff to variations in density and/or dimensions. These relationships have appeared extensively in the literature for over 50 years, but seem to be periodically forgotten. As such, this report is not intended to present any new information, but rather it is intended merely to refresh our memories. The main idea is that you do not have to perform neutron transport calculations every time a parameter of a system is changed; instead you can use simple scaling laws to determine what will change. Here is a quick summary of results.
Date: June 28, 2004
Creator: Cullen, D E
Partner: UNT Libraries Government Documents Department

The Formation of First Generation Stars and Globular Clusters in Protogalactic Clouds

Description: Within collapsing protogalaxies, thermal instability leads to the formation of a population of cool fragments which are confined by the pressure of a residual hot background medium. The critical mass required for the cold clouds to become gravitationally unstable and to form stars is determined by both their internal temperature and external pressure. Massive first generation stars form in primordial clouds with sufficient column density to shield themselves from external UV photons emitted by nearby massive stars or AGNs. Less massive photoionized clouds gain mass due to ram pressure stripping by the residual halo gas. Collisions may also trigger thermal instability and fragmentation into cloudlets. While most cloudlets have substellar masses, the largest become self-gravitating and collapse to form protostellar cores without further fragmentation. The initial stellar mass function is established as these cores capture additional residual cloudlets. Energy dissipation from the mergers ensures that the cluster remains bound in the limit of low star formation efficiency. Dissipation also promotes the formation and retention of the most massive stars in the cluster center. On the scale of the protogalactic clouds, the formation of massive stars generates intense UV radiation which photoionizes gas and quenches star formation in nearby regions. As gas density accumulates in the center of the galactic potential, the self-regulated star formation rate increases. At the location where most of the residual gas can be converted into stars on its internal dynamical timescale, a galaxy attains its asymptotic kinematic structure such as exponential profiles, Tully-Fisher, and Faber-Jackson laws.
Date: July 7, 2003
Creator: Murray, S
Partner: UNT Libraries Government Documents Department

Critical mass studies of plutonium solutions

Description: The chain reacting conditions for plutonium nitrate in water solution have been examined experimentally for a variety of sizes of spheres and cylinders. The effects on the critical mass of the displacement of hydrogen and the addition of poisons to the fuel were measured in water tamped and bare reactors. In this report the data obtained in the investigation is presented graphically and in tables. Some preliminary analysis has been made yielding the results: (i) the absorption cross-section of Pu{sup 240} is 925 {plus_minus} 200 barns and (ii) the minimum critical mass of Pu{sup 239} in water is 510 grams at concentration of about 33 grams per liter.
Date: May 19, 1952
Creator: Kruesi, F.E.; Erkman, J.O. & Lanning, D.D.
Partner: UNT Libraries Government Documents Department

Critical mass information applied to purex and recuplex design

Description: Some time ago, a series of experiments (the P-11 project) were conducted to determine the critical mass of plutonium in variously sized and shaped vessels and with various solution concentrations. These experiments were rather general in nature, hence, it is necessary to interpret the data to the specific critical mass problems of interest in separation processes. The design of new continuous flow separation processes calls for even further extrapolations of these data to vessel geometries far from the range of present experimental knowledge. The purpose of this report is to review for reference the estimates used in the design of the critically safe portions of Purex and Recuplex. This report is compiled for engineering use in approximate design; however, any design of vessels involving criticality hazards will be reviewed by the Critical Mass Group.
Date: April 1, 1953
Creator: Lanning, D.D.
Partner: UNT Libraries Government Documents Department

Critical mass calculations for the recuplex installation

Description: The methods of an analysis of the critical safety of process tanks in the Recuplex installation are discussed and results of the analysis are tabulated in this report. A minimum critical condition for a thermal chain reaction is estimated for 0-200 MWD/T Pu and for 400 MWD/T Pu for each tank in the installation vhich normally contains, or could contain, plutonium. All estimates are based on experimental critical mass data from the P-11 project and from Oak Ridge critical mass experiments.
Date: May 20, 1954
Creator: Raftery, R. P.
Partner: UNT Libraries Government Documents Department

An updated nuclear criticality slide rule

Description: This Volume 2 contains the functional version of the updated nuclear criticality slide rule (more accurately, sliding graphs) that is referenced in An Updated Nuclear Criticality Slide Rule: Technical Basis, NUREG/CR-6504, Vol. 1 (ORNL/TM-13322/V1). This functional slide rule provides a readily usable {open_quotes}in-hand{close_quotes} method for estimating pertinent nuclear criticality accident information from sliding graphs, thereby permitting (1) the rapid estimation of pertinent criticality accident information without laborious or sophisticated calculations in a nuclear criticality emergency situation, (2) the appraisal of potential fission yields and external personnel radiation exposures for facility safety analyses, and (3) a technical basis for emergency preparedness and training programs at nonreactor nuclear facilities. The slide rule permits the estimation of neutron and gamma dose rates and integrated doses based upon estimated fission yields, distance from the fission source, and time-after criticality accidents for five different critical systems. Another sliding graph permits the estimation of critical solution fission yields based upon fissile material concentration, critical vessel geometry, and solution addition rate. Another graph provides neutron and gamma dose-reduction factors for water, steel, and concrete. Graphs from historic documents are provided as references for estimating critical parameters of various fissile material systems. Conversion factors for various English and metric units are provided for quick reference.
Date: April 1, 1998
Creator: Hopper, C. M. & Broadhead, B. L.
Partner: UNT Libraries Government Documents Department


Description: This Calculation Note performs and documents MCNP criticality calculations for plutonium (100% {sup 239}Pu) hydraulic fluid mixtures. Spherical geometry was used for these generalized criticality safety calculations and three geometries of neutron reflection are: {sm_bullet}bare, {sm_bullet}1 inch of hydraulic fluid, or {sm_bullet}12 inches of hydraulic fluid. This document shows the critical volume and critical mass for various concentrations of plutonium in hydraulic fluid. Between 1 and 2 gallons of hydraulic fluid were discovered in the bottom of HA-23S. This HA-23S hydraulic fluid was reported by engineering to be Fyrquel 220. The hydraulic fluid in GLovebox HA-23S is Fyrquel 220 which contains phosphorus. Critical spherical geometry in air is calculated with 0 in., 1 in., or 12 inches hydraulic fluid reflection.
Date: October 3, 2007
Partner: UNT Libraries Government Documents Department


Description: Five sets of benchmark experiments are reviewed herein that cover a diverse set of fissile system configurations. The review specifically focused on the change in critical mass of these systems at elevated temperatures and the temperature reactivity coefficient ({alpha}{sub T}) on the system. Because plutonium-based critical benchmark experiments at varying temperatures were not found at the time this review was prepared, only uranium-based systems are included, as follows: (1) HEU-SOL-THERM-010 - UO{sub 2}F{sub 2} solutions with high U{sup 235} enrichment; (2) HEU-COMP-THERM-016 - uranium-graphite blocks with low U concentration; (3) LEU-COMP-THERM-032 - water moderated lattices of UO{sub 2} with stainless steel cladding, and intermediate U{sup 235} enrichment; (4) IEU-COMP-THERM-002 - water moderated lattices of annular UO{sub 2} with/without absorbers, and intermediate U{sup 235} enrichment; and (5) LEU-COMP-THERM-026 - water moderated lattices of UO{sub 2} at different pitches, and low U{sup 235} enrichment. In three of the five benchmarks (1, 3 and 5), modeling of the critical system at room temperature is conservative compared to modeling the system at elevated temperatures, i.e., a greater fissile mass is required at elevated temperature. In one benchmark (4), there was no difference in the fissile mass between the room temperature system and the system at the examined elevated temperature. In benchmark (2), the system clearly had a negative temperature reactivity coefficient. Some of the high temperature benchmark experiments were treated with appropriate (and comprehensive) adjustments to the cross section sets and thermal expansion coefficients, while other experiments were treated with partial adjustments. Regardless of the temperature treatment, modeling the systems at room temperature was found to be conservative for the examined systems, i.e., a smaller critical mass was obtained. While the five benchmarks presented herein demonstrate that, for the conditions examined, modeling of the systems at room temperature is conservative as compared to modeling ...
Date: June 10, 2009
Creator: Yates, K.
Partner: UNT Libraries Government Documents Department