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Advanced Variance Reduction for Global k-Eigenvalue Simulations in MCNP

Description: The "criticality" or k-eigenvalue of a nuclear system determines whether the system is critical (k=1), or the extent to which it is subcritical (k<1) or supercritical (k>1). Calculations of k are frequently performed at nuclear facilities to determine the criticality of nuclear reactor cores, spent nuclear fuel storage casks, and other fissile systems. These calculations can be expensive, and current Monte Carlo methods have certain well-known deficiencies. In this project, we have developed and tested a new "functional Monte Carlo" (FMC) method that overcomes several of these deficiencies. The current state-of-the-art Monte Carlo k-eigenvalue method estimates the fission source for a sequence of fission generations (cycles), during each of which M particles per cycle are processed. After a series of "inactive" cycles during which the fission source "converges," a series of "active" cycles are performed. For each active cycle, the eigenvalue and eigenfunction are estimated; after N >> 1 active cycles are performed, the results are averaged to obtain estimates of the eigenvalue and eigenfunction and their standard deviations. This method has several disadvantages: (i) the estimate of k depends on the number M of particles per cycle, (iii) for optically thick systems, the eigenfunction estimate may not converge due to undersampling of the fission source, and (iii) since the fission source in any cycle depends on the estimated fission source from the previous cycle (the fission sources in different cycles are correlated), the estimated variance in k is smaller than the real variance. For an acceptably large number M of particles per cycle, the estimate of k is nearly independent of M; this essentially takes care of item (i). Item (ii) can be addressed by taking M sufficiently large, but for optically thick systems a sufficiently large M can easily be unrealistic. Item (iii) cannot be accounted for by ...
Date: June 1, 2008
Creator: Larsen, Edward W.
Partner: UNT Libraries Government Documents Department

Computer simulation of laser-driven implosion of DT-filled glass microballoons

Description: The results of some experimental measurements of laser implosions are analyzed. Calculations are made of specific target irradiations and compared with experiments. A general description is given of exploding pushers and the physical processes involved are described. (MOW)
Date: October 17, 1975
Creator: Larsen, J.T.
Partner: UNT Libraries Government Documents Department

NON-SYMMETRICAL MAIN COOLANT SYSTEM ANALYSIS (NOMACS). PART I

Description: Non-symmetrical main coolant system analysis is an IBM-704 digital program for calculating the reactor generation, primary coolant temperature distribution, and steam temperature, pressure, and flow to the main and auxiliary turbines during a transient period. The program represents a system composed of a two-pass high pressure water cooled reactor ivith tivo main primary coolant loops each having its own steam generator, separator, and drum. The generated steam from each loop is piped into a common header which is then piped to the main and auxiliary turbines and other steam loads in the system. The mathematical representation for solution is described. (M.H.R.)
Date: September 11, 1957
Creator: Larsen, R.C.
Partner: UNT Libraries Government Documents Department

In situ conversion of coal. Final report, June 1, 1975--November 30, 1977. [Tulupov, muetherties and other catalysts]

Description: One of the factors which encouraged us to search for very mild liquefaction conditions was the reported existence of a variety of catalysts capable of causing the hydrogenation of aromatics at room temperature or slightly above and at hydrogen pressures of one or two atm. A number of such systems are described in James book. (Homogeneous Hydrogentation by B. R. James). Each promising system was tested with coal; nothing worked. Intermolecular hydride transfer from a variety of compounds to carbonium ions is a well known, well studied reaction and has been reviewed. The reaction developed uses BF/sub 3/.H/sub 2/O as the acid and Et/sub 3/SiH as the hydride donor. The organic compound to be reduced is protonated by the BF/sub 3/.H/sub 2/O to give a carbonium ion which then hydride abstracts from the Et/sub 3/SiH. Thus, half of the hydrogen introduced comes from water and the other half from the hydride donor. Two features of this reaction exist. One, it is a very mild reduction of aromatics which should find synthetic utility. Second, some sulfur is removed from coals under very mild conditions together with some conversion of bituminous coals.
Date: October 1, 1977
Creator: Larsen, J.W.
Partner: UNT Libraries Government Documents Department

Characterization of low density rigid urethane foam

Description: The chemical and mechanical properties of a low density, rigid polyurethane foam material taken from a Joint Test Assembly (JTA) after 13 years of storage were measured. Chemical analyses confirmed the composition to be Bendix Rigifoam 6003-1.5, a pentaerythritol/epsilon-caprolactone/tolyene diisocyanate polyurethane foam. Comparison of data from testing thermal and mechanical characteristics with data from a currently manufactured foam of identical composition indicates no degradation of properties had occurred. This information gives added confidence to the stockpile lifetime integrity of the Rigifoam 6003-2 foam system designated for use in other programs.
Date: October 1, 1978
Creator: Larsen, F.N.
Partner: UNT Libraries Government Documents Department

Engineering tradeoffs in miniaturization of electronics for very large detectors

Description: The trend toward Application-Specific Integrated Circuits and similar systems-on-a-chip-technologies is fueling a new wave of innovation in detector electronics, just in time to address some of the problems being introduced by detectors which will approach a million channels of electronics. The cost-effectiveness of these technologies can be easily demonstrated, and the trend of the past twenty years of achieving more powerful electronics at a lower per-channel cost should receive a major impetus. The investment required in the new technologies will reshape the work force of most laboratories, by providing more and better tools, and by requiring training or retraining of significant numbers of personnel. The need for new instrumentation standards will arise at new levels in the detectors of the future. The laboratories must also invest heavily in integrating various computer aided engineering and computer aided design tools into a smoothly functioning system. They must also establish a new and different kind of working relationship with vendors and suppliers of both basic devices as well as standard packaged products. This paper discusses three concepts.
Date: October 1, 1987
Creator: Larsen, R.S.
Partner: UNT Libraries Government Documents Department

Overview of the data acquisition electronics system design for the SLAC Linear Collider Detector (SLD)

Description: The SLD Detector will contain five major electronics subsystems: Vertex, Drift, Liquid Argon Calorimeter, Cerenkov Ring Imaging, and Warm Iron Calorimeter. To implement the approximately 170,000 channels of electronics, extensive miniaturization and heavy use of multiplexing techniques are required. Design criteria for each subsystem, overall system architecture, and the R and D program are described.
Date: September 1, 1985
Creator: Larsen, R.S.
Partner: UNT Libraries Government Documents Department

Status of the FASTBUS standard data bus

Description: FASTBUS is a new laboratory standard data bus intended for use in experimental data acquisition and control. The development of FASTBUS began with a feasibility study in 1976, and is presently at the development prototyping stage. The principal aims of the standard are to provide a factor of ten or more improvement in speed of data transfers over present systems, as well as to provide an architecture for systems containing multiple processors. Developmental prototypes now in progress include crates, backplanes, cooling devices, power supplies, test and diagnostic modules, and user modules. A sizeable software development effort is also underway. Several experiments have made commitments to use FASTBUS. A review of current work and potential applications is given. 10 figures.
Date: November 1, 1980
Creator: Larsen, R.S.
Partner: UNT Libraries Government Documents Department

Survey of literature relating to energy development in Utah's Colorado Plateau

Description: This study examines various energy resources in Utah including oil impregnated rocks (oil shale and oil sand deposits), geothermal, coal, uranium, oil and natural gas in terms of the following dimensions: resurce potential and location; resource technology, development and production status; resource development requirements; potential environmental and socio-economic impacts; and transportation tradeoffs. The advantages of minemouth power plants in comparison to combined cycle or hybrid power plants are also examined. Annotative bibliographies of the energy resources are presented in the appendices. Specific topics summarized in these annotative bibliographies include: economics, environmental impacts, water requirements, production technology, and siting requirements.
Date: June 1, 1980
Creator: Larsen, A.
Partner: UNT Libraries Government Documents Department

X-ray backlighting requirements for the double-shell target

Description: We have analyzed one specific NOVA double-shell target design and have determined the x-ray energies required for probing the performance of the implosion. It is virtually impossible to study the compression of the fuel or the motion of the inner pusher. An x-ray energy of about 9 keV appears to be ideal for measuring the behavior of the outer TaCOH shell for the majority of its travel. However, it would be advantageous to have an x-ray source of about 25 keV to measure the contact between the two shells. Development of narrowband x-ray line sources are more desirable than broadband continuum sources since the intensity per keV is many times greater in the line. Intensities of the probes are determined by the self-emission levels of the target capsule. For the 9 keV line source, an intensity of upwards to 10/sup 15/ keV/keV/sh/cm/sup 2//sr is required with a source area of about 0.01 cm/sup 2/.
Date: August 26, 1980
Creator: Larsen, J.T.
Partner: UNT Libraries Government Documents Department

Projected discrete ordinates methods for numerical transport problems

Description: A class of Projected Discrete-Ordinates (PDO) methods is described for obtaining iterative solutions of discrete-ordinates problems with convergence rates comparable to those observed using Diffusion Synthetic Acceleration (DSA). The spatially discretized PDO solutions are generally not equal to the DSA solutions, but unlike DSA, which requires great care in the use of spatial discretizations to preserve stability, the PDO solutions remain stable and rapidly convergent with essentially arbitrary spatial discretizations. Numerical results are presented which illustrate the rapid convergence and the accuracy of solutions obtained using PDO methods with commonplace differencing methods.
Date: January 1, 1985
Creator: Larsen, E.W.
Partner: UNT Libraries Government Documents Department

Unconditionally stable diffusion-acceleration of the transport equation

Description: The standard iterative procedure for solving fixed-source discrete-ordinates problems converges very slowly for problems in optically large regions with scattering ratios c near unity. The diffusion-synthetic acceleration method has been proposed to make use of the fact that for this class of problems the diffusion equation is often an accurate approximation to the transport equation. However, stability difficulties have historically hampered the implementation of this method for general transport differencing schemes. In this article we discuss a recently developed procedure for obtaining unconditionally stable diffusion-synthetic acceleration methods for various transport differencing schemes. We motivate the analysis by first discussing the exact transport equation; then we illustrate the procedure by deriving a new stable acceleration method for the linear discontinuous transport differencing scheme. We also provide some numerical results.
Date: January 1, 1982
Creator: Larsen, E.W.
Partner: UNT Libraries Government Documents Department

Core design and operating data for Cycles 1 and 2 of Peach Bottom 2

Description: The design and operating data needed to define the fuel characteristics, vessel internal components, nuclear steam supply system components, and reactor operation characteristics for Cycles 1 and 2 of the Peach Bottom 2 reactor are presented. The purpose is to provide reference quality data for use in the qualification of reactor core analysis methods and to provide the basis for the assessment of the irradiation environment during Cycles 1 and 2. The design data includes fuel assembly description, core component arrangements, control rod descriptions, core loading patterns, reactor internals description, and major piping arrangements. Hydraulic characteristics of the assemblies and the inlet orifices are also provided. Operating data is compiled for 24 steady-state points during Cycle 1 and 13 during Cycle 2. Each state point includes core average exposure, thermal power, pressure, flux, inlet subcooling, control configuration and axial in-core detector readings.
Date: June 1, 1978
Creator: Larsen, N.H.
Partner: UNT Libraries Government Documents Department

Diffusion-synthetic acceleration methods for the discrete-ordinates equations

Description: The diffusion-synthetic acceleration (DSA) method is an iterative procedure for obtaining numerical solutions of discrete-ordinates problems. The DSA method is operationally more complicated than the standard source-iteration (SI) method, but if encoded properly it converges much more rapidly, especially for problems with diffusion-like regions. In this article we describe the basic ideas beind the DSA method and give a (roughly chronological) review of its long development. We conclude with a discussion which covers additional topics, including some remaining open problems and the status of current efforts aimed at solving these problems.
Date: January 1, 1983
Creator: Larsen, E.W.
Partner: UNT Libraries Government Documents Department

Absorption and profile modification on spherical targets for. 25 < lambda < 2 microns

Description: LASNEX calculations for focused laser beams on spherical targets have been performed for laser wavelengths of 0.25, 0.5, 1.0 and 2.0 microns. One-dimensional calculations, including the ponderomotive force, show a profile steepening that determines the fractional absorption by anomalous mechanism. However, increased absorption occurs at the shorter wavelengths because of more efficient inverse bremsstrahlung absorption at the higher critical densities. In general, the absorption efficiency increases with shorter laser wavelength and decreases with increasing f-number of the illuminating optics for sufficiently long plasma scale lengths. The effect of the absorption and laser wavelength on the thermal and superthermal electron physics will be discussed along with the combined effects on the implosion performance. Certain aspects of two-dimensional LASNEX calculations are presented.
Date: April 4, 1978
Creator: Larsen, J.T.
Partner: UNT Libraries Government Documents Department

Fractal geometry of two-dimensional fracture networks at Yucca Mountain, southwestern Nevada: proceedings

Description: Fracture traces exposed on three 214- to 260-m{sup 2} pavements in the same Miocene ash-flow tuff at Yucca Mountain, southwestern Nevada, have been mapped at a scale of 1:50. The maps are two-dimensional sections through the three-dimensional network of strata-bound fractures. All fractures with trace lengths greater than 0.20 m were mapped. The distribution of fracture-trace lengths is log-normal. The fractures do not exhibit well-defined sets based on orientation. Since fractal characterization of such complex fracture-trace networks may prove useful for modeling fracture flow and mechanical responses of fractured rock, an analysis of each of the three maps was done to test whether such networks are fractal. These networks proved to be fractal and the fractal dimensions (D) are tightly clustered (1.12, 1.14, 1.16) for three laterally separated pavements, even though visually the fracture networks appear quite different. The fractal analysis also indicates that the network patterns are scale independent over two orders of magnitude for trace lengths ranging from 0.20 to 25 m. 7 refs., 7 figs.
Date: December 31, 1985
Creator: Barton, C.C. & Larsen, E.
Partner: UNT Libraries Government Documents Department