289 Matching Results

Search Results

Advanced search parameters have been applied.

ENDF/B-VII.0 Data Testing for Three Fast Critical Assemblies

Description: In this report we consider three fast critical assemblies, each assembly is dominated by a different nuclear fuel: Godiva (U235), Jezebel (Pu239) and Jezebel23 (U233) [1]. We first show the improvement in results when using the new ENDF/B-VII.0 data [2], rather than the older, now frozen, ENDF/B-VI.8 data [3]. We do this using what we call a one code/ multiple library approach, where results from one code (MCNP) are compared using two different data libraries (ENDF/B-VII.0 and VI.8). Next we show that MCNP results are not specific to this one code by using what we call a one data library/multiple code approach; for this purpose we invited many codes to submit results using the ENDF/B-VII.0 data; the most detailed results presented in this report compare MCNP and TART. The bottom line is that we have shown that using the new ENDF/B-VII.0 data library with a variety of transport codes, for the first time we are able to reproduce the expected K-eff values for all three assemblies to within the quoted accuracy of the models, namely 1.0 +/- 0.001. This is a BIG improvement compared to the results obtained using the older ENDF/B-VI.8 data library. Another important result of this study is that we have demonstrated that currently there are many computer codes that can accurately use the new ENDF/B-VII.0 data.
Date: July 27, 2007
Creator: Cullen, D E; Blomquist, R N; Brown, P N; Dean, C J; Dunn, M E; Lee, Y et al.
Partner: UNT Libraries Government Documents Department

Engineering study for closure of 209E facility

Description: This document is an engineering study for evaluating alternatives to determine the most cost effective closure plan for the 209E Facility, Critical Mass Laboratory. This laboratory is located in the 200 East Area of the Hanford Site and contains a Critical Assembly Room and a Mix room were criticality experiments were once performed.
Date: July 7, 1997
Creator: Brevick, C.H.; Heys, W.H. & Johnson, E.D.
Partner: UNT Libraries Government Documents Department

Monthly progress report for November 1954: Critical assembly research

Description: This report very briefly describes the status of a critical assembly project. Three items are reported. A study of counter response and spatial distribution of the flux from the assembly indicated a greater efficiency for 100 KeV neutrons than for 1-3 MeV neutrons for Hansen counters. An improved counter significantly increased the counting rate for the measurements of neutron emission from oralloy and tuballoy. Coding was begun for a one-group multiregion adjoint flux problem.
Date: November 1, 1954
Creator: Carothers, J.
Partner: UNT Libraries Government Documents Department

Solution High-Energy Burst Assembly (SHEBA) results from subprompt critical experiments with uranyl fluoride fuel

Description: The Solution High-Energy Burst Assembly (SHEBA) was originally constructed during 1980 and was designed to be a clean free-field geometry, right-circular, cylindrically symmetric critical assembly employing U(5%)O{sub 2}F{sub 2} solution as fuel. A second version of SHEBA, employing the same fuel but equipped with a fuel pump and shielding pit, was commissioned in 1993. This report includes data and operating experience for the 1993 SHEBA only. Solution-fueled benchmark work focused on the development of experimental measurements of the characterization of SHEBA; a summary of the results are given. A description of the system and the experimental results are given in some detail in the report. Experiments were designed to: (1) study the behavior of nuclear excursions in a low-enrichment solution, (2) evaluate accidental criticality alarm detectors for fuel-processing facilities, (3) provide radiation spectra and dose measurements to benchmark radiation transport calculations on a low-enrichment solution system similar to centrifuge enrichment plants, and (4) provide radiation fields to calibrate personnel dosimetry. 15 refs., 37 figs., 10 tabs.
Date: October 1, 1997
Creator: Cappiello, C.C.; Butterfield, K.B. & Sanchez, R.G.
Partner: UNT Libraries Government Documents Department

Derivation of criticality safety benchmarks from ZPR fast critical assemblies

Description: Scores of critical assemblies were constructed, over a period of about three decades, at the Argonne National Laboratory ZPR-3, ZPR-6, ZPR-9, and ZPPR fast critical assembly facilities. Most of the assemblies were mockups of various liquid-metal fast breeder reactor designs. These tended to be complex, containing, for example, mockups of control rods and control rod positions. Some assemblies, however, were `physics benchmarks`. These relatively `clean` assemblies had uniform compositions and simple geometry and were designed to test fast reactor physics data and methods. Assemblies in this last category are well suited to form the basis for new criticality safety benchmarks. The purpose of this paper is to present an overview of some of these benchmark candidates and to describe the strategy being used to create the benchmarks.
Date: September 1, 1997
Creator: Schaefer, R.W. & McKnight, R.D.
Partner: UNT Libraries Government Documents Department

On the Use of Rossi Alpha Critical Assembly Measurements for Validating and Constraining Nuclear Data

Description: Critical assemblies are exquisitely sensitive to details of the microscopic nuclear reactions that govern neutron multiplication. For this reason experimental studies of critical assemblies represent a cornerstone in the process of validating nuclear data. Several different characteristics of a critical system can be measured. The most commonly considered is the so-called effective k eigenvalue, k{sub eff}. Another well-measured property of these systems is {alpha}{sub 0}, the inverse e-folding time of the neutron population in the absence of {beta}-delayed neutrons. Through Monte Carlo calculations and appear to perturbation theory they show that for fast critical systems {alpha}{sub 0} and k{sub eff} can be viewed as lying on a single straight line for any reasonable assumptions about the underlying nuclear data. This means that the two quantities provide the same constraint on nuclear data. In principle, {alpha}{sub 0} could be associated with a very small uncertainty, and this would make the measurements for neutron multiplication rates more useful than k{sub eff} for constraining nuclear data. In practice, though, uncertainties in k{sub eff} and {alpha}{sub 0} are dominated by uncertainties in the representation of the critical system, and not by pure measurement errors for these quantities. This, together with the linear relation between {alpha}{sub 0} and k{sub eff}, implies that the two measured quantities provide exactly the same constraint on nuclear data. They do not consider other measured or inferred characteristics of critical assemblies, such as neutron generation times or spectral indices, that may be valuable in the validation process.
Date: March 7, 2007
Creator: Pruet, J & Sleaford, B
Partner: UNT Libraries Government Documents Department


Description: The Lawrence Livermore National Laboratory (LLNL) Physics Division has produced the next iteration of LLNL's evaluated nuclear database, ENDL2009. ENDL2009 is the second in a series of major ENDL library releases designed to support LLNL's current and future nuclear data needs. This library includes 585 distinct transport-ready evaluations in the neutron sub-library and many physics improvements for stockpile stewardship, attribution signatures, key radiochemical diagnostics and performance of conventional and hybrid fission/fusion reactors. In building this library, we adopted the best of the world's nuclear data efforts: 46% of the library is from the ENDF/B-VII.0 library, 10% is from the JENDL libraries and 8% from other libraries. The remaining 36% of the neutron sub-library and all of the charged-particle sub-libraries consist of new evaluations developed at LLNL for the ENDL2009 library. In addition, ENDL2009 supports new features such as energy-dependent Q values from fission, support for unresolved resonances and average momentum deposition. Finally, this release is our most highly tested release as we have strengthened our already rigorous testing regime by adding tests against LANL Activation Ratio Measurements and more than 1200 new critical assemblies. Our testing is now being incorporated into our development process and is serving to guide database improvements.
Date: April 25, 2010
Creator: Brown, D A; Beck, B; Descalle, M; Hoffman, R; Ormand, E; Navratil, P et al.
Partner: UNT Libraries Government Documents Department

Physics verification program Part III, Task 9. Quarterly technical report, April--June 1973

Description: An experimental program is in progress to measure the fission rate in UO/ sub 2/ fuel at selected positions within a critical assembly and to compare it with the neutron absorption rate in the boron of a simulated lumped burnable poison material. (11 references) (auth)
Date: December 1, 1973
Creator: Baldwin, M.N. & Webb, H.W.
Partner: UNT Libraries Government Documents Department

710 reactor program, progress report No. 12

Description: Declassified 4 Sep 1973. Information on the development of the 710 Reactor is presented concerning the performance testing of refractory-metal fuel elements, critical experiment mockup of 710 Reactor, reactor component design and development, and test facilities and pilot loop design. (DCC)
Date: January 28, 1965
Partner: UNT Libraries Government Documents Department

710 reactor program, progress report No. 13

Description: Declassified 4 Sep 1973. Information on the development of the 710 Reactor is presented concerning the performance testing of refractory-metal fuel elements, critical experiment mockup of 710 Reactor, reactor component design and development, and test facilities and pilot loop design, (DCC)
Date: March 31, 1965
Partner: UNT Libraries Government Documents Department

Naval reactors physics handbook. Volume 3: The physics of intermediate spectrum reactors

Description: The present volume has been prepared for persons with some knowledge of the physics of nuclear reactors. It is intended to make available the accumulated physics experience of the Knolls Atomic Power Laboratory in its work on intermediate spectrum reactors. Only those portions have been selected which were deemed to be most useful and significant to other physicists concerned with the problems of reactor design. The volume is divided into four parts which are more or less independent of one another. Part 1 (Chaps. 2--9), Investigation of Reactor Characteristics by Critical Assemblies, reflects the importance of the properties of critical assemblies and of the techniques for obtaining experimental information about such assemblies. Part 2 (Chaps. 10--20), Reactivity Effects Associated with Reactor Operation, details the use of both critical assemblies and reactor theory to make and test predictions of the manner in which the reactivity of an intermediate power reactor will vary during operation. Part 3 (Chaps. 21--26), Heat Generation and Nuclear Materials Problems, considers how reactor heat generation is spread out in space and time, and what nuclear effects result from the presence of beryllium or sodium in the reactor. Part 4 (Chaps. 27--38), Reactor Kinetics and Temperature Coefficients, relates to the transient or near-transient behavior of intermediate reactors.
Date: September 1, 1958
Creator: Stehn, J.R.
Partner: UNT Libraries Government Documents Department

Criticality measurements for control and accountability of fissile materials on critical assemblies

Description: Operational critical assemblies are subject to the same standards of materials control and accountability (MC and A) as other fissile materials. Typically these assemblies are not easily dismantled and the fuel components cannot be inventoried by traditional methods of destructive or non-destructive materials assay. Because of the large mass or unusual geometry of the fuel components these parts are often categorized as difficult-to-measure (DTM) items. The use of criticality to infer fissile inventory, in conjunction with physical security and two-person control procedures, provides accurate and cost-effective MC and A for these large critical assembly components. This method is being implemented at the Los Alamos Critical Experiments Facility (LACEF) and at several national nuclear research centers in Russia.
Date: May 1, 1997
Creator: Paternoster, R.; Kompaniets, G. & Polyakov, D.
Partner: UNT Libraries Government Documents Department

SHEBA operating experience

Description: The Solution High Energy Burst Assembly (SHEBA) is a critical assembly fueled with a solution of 5% enriched Uranyl Fluoride, U(5%)O{sub 2}F{sub 2}. The fuel is stored in critically safe storage containers and then pumped into the ``Critical Assembly Vessel`` where the solution becomes critical. The system was designed to achieve criticality in a cylindrically symmetric configuration. The SHEBA facility also incorporates a shielding pit into which the entire assembly can be lowered to provide shielding for elevated power runs. The major goals of the SHEBA assembly project are to study the behavior of nuclear excursions in a low-enrichment solution, to evaluate accidental criticality alarm detectors for fuel-processing facilities, to provide radiation spectra and dose measurements to benchmark calculations on a low-enrichment solution system, and to provide radiation fields to calibrate personnel dosimetry. SHEBA is also being used to provide a neutron flux test bed to benchmark calculations. Rather than providing the details of these particular projects, this paper summarizes the free-run operating experience obtained as a result of the projects.
Date: May 1, 1997
Creator: Cappiello, C.C. & Butterfield, K.B.
Partner: UNT Libraries Government Documents Department

Safety analysis of the Los Alamos critical experiments facility: burst operation of Skua

Description: A detailed consideration of the Skua burst assembly is presented, thereby supplementing the facility safety analysis report covering the operation of other critical assemblies at Los Alamos. As with these assemblies the small fission-product inventory, ambient pressure, and moderate temperatures in Skua are amenable to straightforward measures to ensure the protection of the public.
Date: May 1, 1979
Creator: Orndoff, J.D.; Paxton, H.C. & Wimett, T.F.
Partner: UNT Libraries Government Documents Department

ENDF/B-VII.0 Data Testing Using 1,172 Critical Assemblies

Description: In order to test the ENDF/B-VII.0 neutron data library [1], 1,172 critical assemblies from [2] have been calculated using the Monte Carlo transport code TART [3]. TART's 'best' physics was used for all of these calculations; this included continuous energy cross sections, delayed neutrons in their spectrum that is slower than prompt neutrons, unresolved resonance region self-shielding, the thermal scattering (free atom for all materials plus thermal scattering law data S({alpha},{beta}) when available). In this first pass through the assemblies the objective was to 'quickly' test the validity of the ENDF/B-VII.0 data [1], the assembly models as defined in [2] and coded for use with TART, and TART's physics treatment [3] of these assemblies. With TART we have the option of running criticality problems until K-eff has been calculated to an acceptable input accuracy. In order to 'quickly' calculate all of these assemblies K-eff was calculated in each case to +/- 0.002. For these calculations the assemblies were divided into ten types based on fuel (mixed, Pu239, U233, U235) and median fission energy (Fast, Midi, Slow). A table is provided that shows a summary of these results. This is followed be details for every assembly, and statistical information about the distribution of K-eff for each type of assembly. After a review of these results to eliminate any obvious errors in ENDF/B data, assembly models, or TART physics, all assemblies will be run again to a higher precision. Only after this second run is finished will we have highly precise results. Until then the results presently here should only be interpreted as approximate values of K-eff with a standard deviation of +/- 0.002; for such a large number of assemblies we expected the results to be approximately normal, with a spread out to several times the standard deviation; see the calculated ...
Date: October 1, 2007
Creator: Plechaty, E F & Cullen, D E
Partner: UNT Libraries Government Documents Department

Test Suite for Nuclear Data I: Deterministic Calculations for Critical Assemblies and Replacement Coefficients

Description: The authors describe tools developed by the Computational Nuclear Physics group for testing the quality of internally developed nuclear data and the fidelity of translations from ENDF formatted data to ENDL formatted data used by Livermore. These tests include S{sub n} calculations for the effective k value characterizing critical assemblies and for replacement coefficients of different materials embedded in the Godiva and Jezebel critical assemblies. For those assemblies and replacement materials for which reliable experimental information is available, these calculations provide an integral check on the quality of data. Because members of the ENDF and reactor communities use calculations for these same assemblies in their validation process, a comparison between their results with ENDF formatted data and their results with data translated into the ENDL format provides a strong check on the accuracy of translations. As a first application of the test suite they present a study comparing ENDL 99 and ENDF/B-V. They also consider the quality of the ENDF/B-V translation previously done by the Computational Nuclear Physics group. No significant errors are found.
Date: May 22, 2006
Creator: Pruet, J; Brown, D A & Descalle, M
Partner: UNT Libraries Government Documents Department

Risk management for operations of the Los Alamos critical experiments facility

Description: The Los Alamos Critical Experiments Facility (LACEF) currently operates two burst reactors (Godiva-IV and Skua), one solution assembly (SHEBA 2--Solution high-Energy Burst Assembly), two fast-spectrum benchmark assemblies (Flattop and Big Ten), and five general-purpose remote assembly machines which may be configured with nuclear materials and assembled by remote control. SNM storage vaults support these and other operations at the site. With this diverse set of operations, several approaches are possible in the analysis and management of risk. The most conservative approach would be to write a safety analysis report (SAR) for each assembly and experiment. A more cost-effective approach is to analyze the probability and consequences of several classes of operations representative of operations on each critical assembly machine and envelope the bounding case accidents. Although the neutron physics of these machines varies widely, the operations performed at LACEF fall into four operational modes: steady-state mode, approach-to-critical mode, prompt burst mode, and nuclear material operations which can include critical assembly fuel loading. The operational sequences of each mode are very nearly the same, whether operated on one assembly machine or another. The use of an envelope approach to accident analysis is facilitated by the use of classes of operations and the use of bounding case consequence analysis. A simple fault tree analysis of operational modes helps resolve which operations are sensitive to human error and which are initiated by hardware of software failures. Where possible, these errors and failures are blocked by TSR LCOs.
Date: December 31, 1998
Creator: Paternoster, R. & Butterfield, K.
Partner: UNT Libraries Government Documents Department

Monte Carlo testing of unresolved resonance treatment for fast and intermediate critical assemblies

Description: The purpose of this study is to investigate the eigenvalue sensitivity to changes in unresolved resonance treatment by comparing RACER Monte Carlo calculations for several fast and intermediate spectrum critical experiments. Calculations performed using smooth, dilute-average, tabulated cross sections were compared with calculations using the probability table method to produce stochastically generated resonance cross sections in the unresolved resonance region. The use of the probability table method is superior to the dilute-average cross section method for representing the unresolved resonance region because the table method properly accounts for resonance self shielding; thereby, reducing the effectiveness of the cross sections in the region. The unresolved resonance region is typically found in the intermediate and fast energy range. Eleven benchmark critical assemblies that span a range of {sup 235}U enrichments (93.8 to 10.2%) and four highly enriched {sup 239}Pu and {sup 233}U assemblies were analyzed. These benchmarks were chosen to accentuate the reactivity importance of the unresolved resonance range.
Date: October 1, 1998
Creator: Weinman, J. P.
Partner: UNT Libraries Government Documents Department

Prompt neutron decay constants and subcritical measurements for material control and accountability in SHEBA

Description: Rossi-Alpha measurements were performed on the SHEBA assembly to determine the prompt neutron decay constants. These prompt neutron decay constants represent an eigenvalue characteristic of this particular assembly, which can be used to infer the amount of fissile material in the assembly. In addition, subcritical measurements using Rossi-Alpha and the source-jerk techniques were also performed on the SHEBA assembly. These measurements were compared against TWODANT calculations and agreed quite well. The subcritical measurements were also used to obtain a unique signature that represented the amount of material associated with the degree of subcriticality of the SHEBA assembly. Finally, the Feynman variance-to-mean technique in conjunction with TWODANT, were used to determine the effective delayed neutron fraction for the SHEBA assembly.
Date: August 1, 1998
Creator: Sanchez, R. & Jaegers, P.
Partner: UNT Libraries Government Documents Department

SHEBA prompt burst dynamics

Description: The Solution High-Energy Burst Assembly (SHEBA), located at the Los Alamos Critical Experiments Facility, is a homogeneous liquid-fueled reactor that is being prepared for prompt burst operation. As part of the preparations, a reactor safety study was performed in support of the new SHEBA experiment plan. This study looked at the maximum power, total energy yield, and maximum transient pressures that may occur in the reactor during prompt burst operation. The goal of this study is to analyze the neutronic and hydrodynamic behavior of the reactor during burst operation, and to ensure that prompt burst operation does not damage the reactor or exceed the safety envelope of the facility`s Safety Analysis Report (SAR).
Date: December 31, 1997
Creator: Kimpland, R.
Partner: UNT Libraries Government Documents Department

Solution High-Energy Burst Assembly (SHEBA) results from subprompt critical experiments with uranyl fluoride fuel

Description: Experiments were performed to measure a variety of parameters for SHEBA: behavior of the facility during transient and steady-state operation; characteristics of the SHEBA fuel; delayed-critical solution height vs solution temperature; initial reactor period and reactivity vs solution height; calibration of power level vs reactor power instrumentation readings; flux profile in SHEBA; radiation levels and neutron spectra outside the assembly for code verification and criticality alarm and dosimetry purposes; and effect on reactivity of voids in the fuel.
Date: August 1, 1997
Creator: Cappiello, C.C.; Butterfield, K.B.; Sanchez, R.G.; Bounds, J.A.; Kimpland, R.H.; Damjanovich, R.P. et al.
Partner: UNT Libraries Government Documents Department

Brief summary of unreflected and unmoderated cylindrical critical experiments with oralloy at Oak Ridge

Description: This report lists and briefly describes {approximately}50 critical and {approximately}20 subcritical experiments with unreflected and unmoderated uranium (93.2 wt% {sup 235}U) metal that could easily be incorporated into the International Handbook of Evaluated Criticality Safety Benchmark Experiments. Photographs of several assemblies are included.
Date: November 1, 1999
Creator: Mihalczo, J.T.
Partner: UNT Libraries Government Documents Department