Browsing by Author "Rainbow, MT"

Now showing 1 - 8 of 8
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    Application of the Monte Carlo transport code MORSE to the calculation of pulsed neutron experiments
    (Australian Atomic Energy Commission, 1978-03) Rainbow, MT
    An accurate calculation tool is essential for the assessment of nuclear data by the pulsed neutron technique. The Monte Carlo transport code MORSE is such a tool and its application to the calculation of pulsed neutron experiments is presented. Modifications to the code and a set of ancillary programs to enable the direct comparison of calculation with experiment are described. The time profile of the pulsed neutron source is treated in a manner which allows more efficient use of the code. However, as a consequence some parameters, such as detector responses at different times, are no longer uncorrelated. Error analysis which takes proper account of these correlations is presented.
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    Application of the pulsed neutron technique to fast metal systems
    (Australian Atomic Energy Commission, 1973-01) Moo, SP; Rainbow, MT; Ritchie, AIM
    The experimental apparatus and techniques which have been developed up to the end of 1971 at the AAEC Research Establishment at Lucas Heights to allow pulsed experiments to be performed in fast metal systems are described. The details of a metallic thorium assembly, the pulsed neutron source, timing systems and shielding and room return problems are discussed.
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    The calculation of angular neutron spectra from the thick target Li(p,n) source
    (Australian Atomic Energy Commission, 1977-10) Rainbow, MT; Ritchie, AIM; Sullivan, L
    Neutron energy spectrum of the thick target Li(p,n) source is well suited to neutronics experiments on fast reactors. In such applications the angular distribution of the source energy spectrum is required in a form suitable for reactor calculations. A method is described of using various experimental and theoretical estimates of the angular cross section of the Li(p,n) reaction to estimate the angular yield from a thick target in a form suitable for reactor calculations. The problem is discussed of determining the integration limits for angle integrated quantities appropriate to particular values of incident proton energy and target thickness. The resulting calculational techniques have been incorporated in a computer code LIPNA written for an IBM360/65. An ancillary, interactive program, written for a NOVA computer, prepares the input data for LIPNA, obviating the need for the occasional user to remember details of the code input requirements.
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    An improved thermal model for the computer code NAIAD.
    (Australian Atomic Energy Commission, 1982-12) Rainbow, MT
    An improved thermal model based on the concept of heat slabs has been incorporated as an option into the thermal hydraulic computer code NAIAD. The heat slabs are one-dimensional thermal conduction models with temperature independent thermal properties which may be internal and/or external to the fluid. Thermal energy may be added to or removed from the fluid via heat slabs and passed across the external boundary of external heat slabs at a rate which is a linear function of the external surface temperatures. The code input for the new option has been restructured to simplify data preparation. A full description of current input requirements is presented.
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    Measurement of the slowing down time to 0.3 eV in beryllium oxide.
    (Australian Atomic Energy Commission, 1970-07) Rainbow, MT; Ritchie, AIM
    The reaction rates of plutonium-239 and boron (1/v) were measured as a function of space and time in a large block of beryllium oxide following the injection of a pulse of fast neutrons. The time-dependent reaction rates associated with the various Fourier spatial modes were derived from the experimental results. The experimental value of the peaking time of the plutonium-239 reaction rate associated with the fundamental spatial mode was found to be 19.85 + 1.1 μ sec. A theoretical value of 16.5 μ sec was obtained using a time-dependent zero-dimensional diffusion code and a crystal scattering kernel for beryllium oxide. It is in marked disagreement with the experimental value. Measurements made of the time to peak in the plutonium-239 reaction rate as a function of distance from the source showed a total variation of a 4 μ sec in peaking time over a distance of 53 cm. Theoretical calculations of the peaking time as a function of distance showed a similar variation and the general trends were in good agreement with the experimental result. There was, however, a constant discrepancy between the theoretical and experimental results of the order of that noted for the fundamental mode.
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    Measurements in pulsed BeO assemblies with decay constants in the region of Corngold's limit.
    (Australian Atomic Energy Commission, 1968-05) Rainbow, MT; Ritchie, AIM
    Decay curves have been measured in BeO assemblies with bucklings in the range 1.93 x 10 -2 cm-2 to 5.34 x 10 -2 cm-2 at times from immediately after the initial pulse to at least 4.5 ms after the pulse. The decay curves for assemblies with B2 < 2.91 x 10 -2 cm-2 can be described by an exponential, from a minimum of 1.5 ms after the pulse to greater than 3.0 ms after the pulse. For bucklings greater than B2 = 3.3 x 10 -2 cm-2 the decay curves cannot be described by an exponential in this time region, and the departure from exponential increases with increased buckling. The results indicate a transition region at B2 ~ 3.0 x 10 -2 cm-2, (λ ~ 3.65 x 10 3 sec-1) which is consistent with the expression proposed by Kothari for the upper limit on discrete decay constants and well above Corngold's limit of λ* = (υΣinel) min ~ 2.5 x 10 3 sec-1. The transition point does not have any marked shape dependence. There is some shape dependence in the behaviour of decay curves for assemblies with B2 > 3.3 x 10 -2 cm-2 but little dependence of pulse length, or counter shape and position.
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    Time dependent 237Np, 235U and 239Pu fission rates in a thorium assembly during the interval 0 to 200 ns using a pulsed 9Be(d,n) source part I - experiment
    (Australian Atomic Energy Commission, 1973-03) Moo, SP; Rainbow, MT; Ritchie, AIM
    This paper describes a series of integral pulsed neutron experiments performed in a 0.4 x 0.4 x 0.4 m3 metallic thorium assembly in such a way as to allow direct comparison of space independent reaction rates with calculated reaction rates derived from a code which uses the asymptotic reactor theory approximation to describe leakage. The technique relies on the Fourier decomposition of measured space-time dependent reaction rates and the extraction from these of the reaction rate corresponding to the fundamental three-dimensional Fourier spatial mode. The reaction rates measured were the fission rates of 235U, 239Pu and 237Np following a short (~ 10 ns) burst of neutrons with a mean energy of ~ 2.7 MeV.
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    Time dependent 237Np, 235U and 239Pu fission rates in a thorium assembly during the interval 0 to 200 ns using a pulsed 9Be(d,n) source part II - theory
    (Australian Atomic Energy Commission, 1974-02) Moo, SP; Rainbow, MT; Ritchie, AIM
    Calculations are presented of the 237Np, 235U and 239Pu fundamental mode fission rates in a thorium assembly based on a diffusion theory code with a DB2 leakage term. Three different thorium cross section sets derived from the ABBN set, the UKNDL68 file and the ENDF/B-II file were used in the calculations and the results compared with each other and with experimental results reported previously. The sensitivity of the instantaneous decay constant of the fundamental mode to changes in partial cross sections is investigated.