Irradiation of Sintered Beryllium Oxide to High Fast-Neutron Doses at 110, 650, and 1100 Deg. C PDF Download
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Category :
Languages : en
Pages : 29
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Author:
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Category :
Languages : en
Pages : 29
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Author: R. P. Shields
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ISBN:
Category : Beryllium oxide
Languages : en
Pages : 96
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Languages : en
Pages :
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Specimens of 0.428 to 1.18 in. dia. BeO were irradiated at 1.4 x 10/sup 20/ to 2.8 x 10/sup 21/ fast neutrons/cm/ (>1 Mev), with irradiation times of 2.03 x 105 to 5.60 x 106 sec, at 110 to 1025 C, and gamma heat generation rates of 18 to 25 w/g. The greatest damage appeared in bodies irradiated for high neutron doses at low temperatures. Greater doses could be tolerated at higher temperatures. Specimens irradiated at 110 deg C powdered at an accumulated dose of 1.5 x 10/sup 21/ 1.1 x 10/sup 21/ neutrons/cm/sup 2/ and at 737 deg C at a dose of 1.6 x 10 /sup 21/ neutrons/cm/sup 2/ remained intact. Specimens irradiated at 827 to 950 deg C at a dose of 2.1 to 2.6 x 10/sup 21/ neutrons/cm/sup 2/ fractured. Changes in linear dimensions up to 4% were observed. X-ray diffraction measurements revealed changes in the c lattice parameter up to 7 x 10-3 DELTA c/c0 for material irradiated at 110 deg C but only 1 to 2 x 10-3 DELTA c/co at 444 to 1025 deg C. The DELTA c/c0 value appeared to saturate at a dose of 3 x 10/sup 20/ neutrons/cm/sup 2/ in the latter temperature range. All temperatures above 444 deg C were equally effective in suppressing the DELTA c/c0 values. Changes in the a parameter were smaller by a factor of 7. He was retained even at irradiation temperatures of 1025 deg C. Gases could be removed only by dissolving the BeO in fused salt. The He content of the BeO varied linearly with fast-neutron dose up to 1.6 x 10/sup 21/ neutrons/ cm/sup 2/, with a slope of 205 standard mu l per g of BeO per 10 neutrons/cm/sup 2/. The tritium content of BeO irradiated at 110 deg C followed a (neutrons/cm) curve up to 6.4 ppm at 2.1 x 10 neutrons/cm/sup 2/. Specimens irradiated above 444 deg C contained much less tritium. Voids 0.1 to 0.3 mu in diameter which were not in the original material were found by electron microscopy in the interior of grains and at grain boundaries. No evdence of chemical decomposition was observed. Radial temperature differences during irradiation increased by 50 to 100%, indicating a decrease in thermal conductivity. It was concluded that the observed changes could be caused either by gas generation or atomic displacements. The hypothesis that thermal stress alone produced failure was rejected. Results indicate that great caution must be exercised in designing BeO moderators for nuclear reactors. Under some conditions physical deterioration occurs to such a degree as to render the material unsuitable for use. For greatest life the moderator should be kept above 400 deg C, and probably 800 to 1000 deg C is more desirable. The design of the irradiation assembly is described. Temperatures were controlled by varying the composition of a helium- argon mixture in an annulus. Sixtythree specimens were irradiated in six assemblies. (auth).
Author:
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ISBN:
Category : Nuclear energy
Languages : en
Pages : 894
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Author: A. J. Rothman
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Category : Beryllium oxide
Languages : en
Pages : 62
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Author: G. L. Hanna
Publisher:
ISBN: 9780642995681
Category : Nuclear fuel elements
Languages : en
Pages : 16
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Author: International Atomic Energy Agency
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ISBN:
Category : Nuclear energy
Languages : en
Pages : 1178
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Category :
Languages : en
Pages :
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Neutron and gamma penetrations through and behind BeO were measured. Neutron spectra measurements by threshold foil techniques indicated practically no change in the fast-neutron spectrum above 2.5 Mev in BeO. Thus, beryllium appears to lie in the transition region between the very light elements that harden a fission spectrum and the heavier elements that soften it. The ratio of fast-neutron fluxes below and above 2.5 Mev increased rapidly with distance through the BeO. Information indicated that the flux peaked at around 1.5 to 2.5 Mev. In this energy range the scattering cross section of beryllium goes through a minimum. Fast neutron dose measurements through BeO were compared with those calculated by the moments method. The removal cross section for BeO was determined from fast-neutron dose rates measured in the water behind the slabs. Gamma dose rates were measured through and be hind the BeO slabs with a carbon chamber. The gamma dose rate decreased with a relaxation length of about 11 cm near the source. The relaxation length increased with distance through BeO, indicating spectrum hardening. Gamma spectra were measured at intervals behind BeO slabs with a collimated sodium icdide crystal. The 6.8 and 3.41 Mev beryllium capture gamma rays became dominant as the distance through the BeO increased. Thermal flux was measured through and behind the BeO with both a fission chamber and gold foils. Thermal flux distributions for these tests were calculated by a multilevel diffusion code. The calculations differ from the experiment at large penetration distances through BeO. (auth).
Author: American Nuclear Society
Publisher:
ISBN:
Category : Nuclear engineering
Languages : en
Pages : 836
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Author:
Publisher:
ISBN:
Category : Nuclear energy
Languages : en
Pages : 660
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