Browsing by Author "Hanna, GL"
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- ItemFission gas retention in spherical beryllium oxide based fuel elements for the conceptual aborigine reactor.(Australian Atomic Energy Commission, 1972-07) Hanna, GLFission gas release from spherical BeO-based fuel elements designed for the conceptual ABORIGINE reactor and from 200 micron diameter fuel particles of U02-Th02 solid solution has been measured by in-pile sweep capsule testing In the temperature range 600ºC to 1000ºC, Release parameters (R/B ratios) of 10-7 to 10 s were measured on several fuelled spheres, and 10-4 to 10-2 on bare fuel particles. Two spheres with bonded cladding maintained good gas retention at 1000ºC for fast neutron doses (6 x 1020 nvt) which were three times that required of the ABORIGINE fuel element; however, the fission burnup (1.1 percent U + Th) was a factor of nine below the design burnup. It has thus been shown that BeO coatings on fuelled BeO spheres can in principle retain fission gases to the high standard required for ABORIGINE. Further work would be needed, (a) to assess the reliability of the fabrication process, (b) to test to high burnups fuelled spheres designed so that the coating is subjected only to fast neutron damage and which therefore should not crack from burnup effects, (c) to eliminate other possible cracking mechanisms such as thermal stress, and (d) to measure the release from cracked spheres under a range of conditions and thus to determine the allowable cracking rate more accurately.
- ItemFission product retention of fuelled beryllium oxide spheres and urania-thoria fuel particles in post-irradiation annealing experiments.(Australian Atomic Energy Commission, 1969-12) Roman, D; Randall, CH; Hanna, GLThe post-activation diffusion technique has been used to measure the release of Xe-133 from beryllium oxide based, spherical fuel elements and the urania-thoria fuel particles from which they were prepared. Release rate parameters (apparent diffusion coefficients, D') for bare fuel particles were of the order 10-8 sec-1 to 10-10 sec-1 at 1400ºC, whereas most spheres tested gave parameters of 10-16 sec-1 or less, indicating that the beryllia matrix and cladding were having a marked effect in retaining fission gases. Mid-anneal changes in release rates from bare fuel particles were observed at 1200ºC and 1400ºC, This behaviour is tentatively attributed to slight pore growth and the release of trapped gas from pores which open to the surface during annealing.
- ItemFull-energy-peak efficiencies of three gamma-ray detectors(Australian Atomic Energy Commission, 1967-01) Hanna, GL; Walker, DG; Beach, PMTwo sodium iodide scintillators and a lithium-drifted germanium detector are used in the analysis by gamma-ray spectrometry of gaseous fission products obtained in sweep-capsule fission product release experiments. A description is given of the measurements of full-energy-peak efficiencies of the three detectors for the source geometries used in counting the fission product samples. Experimental efficiencies are compared with calculated efficiencies for one of the sodium iodide detectors. Measurements made of the resolutions obtained with each detector are also noted.
- ItemFurther examination of irradiated hot-pressed beryllium oxide based fuel specimens.(Australian Atomic Energy Commission, 1964-08) Hanna, GLThe work reported in AAEC/E106 on the metallographic examination of (U,Th)02 dispersed in BeO irradiated in a thermal neutron flux is extended. X—ray diffraction studies have demonstrated that strain developed in the matrixes of both coarse and fine dispersions during irradiation was more severe in the fine dispersion. It is thought that in the coarse dispersion it arose from the swelling of fuel particles and in the fine dispersion, from fission fragment damage. The strain was relieved by annealing in the range 1000 — 1350ºC and was partly relieved in the coarse dispersion by crushing. Fission gas bubbles were observed in the microstructure of specimens annealed at 1250ºC and 1500ºC after irradiation.
- ItemHigh burnup irradiation testing of spherical beryllium oxide based fuel elements for a conceptual high temperature air-cooled reactor(Australian Atomic Energy Commission, 1973-05) Hanna, GL; Reeve, KDFuelled beryllium oxide spheres, with a thin layer of porous BeO separating the fuelled core from the unfuelled shell, were irradiated at 500ºC, 750ºC and 1000ºC to burnups of 13.4 to 15.6 per cent (U + Th) and fast neutron doses of 1.4 x 10 20 to 1.9 x 1020 nvt. The four spheres irradiated at 1000ºC were apparently undamaged but the shell had fractured in all those irradiated at 500ºC and 750ºC. Failure is believed to have been caused by enhanced expansion of the inner regions of the unfuelled shell arising from exposure to both fast neutrons and energetic β-particles. Further work necessary to prove a fuel element design for the proposed application is briefly outlined.
- ItemThe irradiation behaviour of beryllium based dispersion fuels - a preliminary irradiation experiment.(Australian Atomic Energy Commission, 1962-09) Hanna, GL; Hickman, BS; Hilditch, RJThe effects of fission fragment damage on vacuum hot pressed fuel specimens of (U Th) Be13 dispersed in a beryllium matrix were examined by irradiation in a predominantly thermal neutron flux. Damage equivalent to that caused by 4 x 10 19 to 11 x 10 19 fissions per cm3 (depending on specimen composition) was achieved at temperatures between 435º and 530ºC. All specimens increased in volume on irradiation. The increases ranged from 0.1 per cent, to 5 per cent., depending on the volume fraction of fuel phase and the number of fissions per cm3. Some of the volume change — possibly up to 0.7 per cent. — was due to thermal effects alone. Release of fission gases was as high as 2 per cent, in some cases and was generally higher than would be expected from recoil in specimens having no open porosity. The fractional release was greater in specimens which experienced a high volume increase. Microstructures showed no significant change on irradiation. All specimens were slightly porous before irradiation and it is considered that the swelling of specimens was due to the growth of existing pores and that the release of fission gases was facilitated by an increase in open porosity.
- ItemThe irradiation behaviour of beryllium oxide dispersion fuels.(Australian Atomic Energy Commission, 1963-03) Hanna, GL; Hickman, BS; Hilditch, RJSpecimens of beryllium oxide based dispersion fuels containing between three and twenty-six volume per cent, of U02— Th02 solid solution were irradiated to fission densities of 2 to 14 x 1019 fissions/cm3 of total specimen (equivalent burn—ups of 80 to 230 per cent.) at temperatures of 600 - 850ºC. The experiment was primarily designed to investigate fission product damage although some fast neutron damage did occur in the matrix, the specimens showed excellent resistance to fission product damage; dimensional changes were small, fission product escape was generally only that expected by recoil and there was no sign of cracking due to thermal stresses although these reached estimated values of about 30,000 p.s.i. in some specimens, Metallographic examination showed that some weakening of the matrix grain boundaries had occurred and some preliminary x-ray results suggested that the matrix was in a state of strain. It is suggested that these effects could be due either to fast neutron damage in the matrix or swelling of the fuel particles. The experiment did not provide any conclusive evidence for the superiority of coarse fuel particles (100 - 180μ.) over fine fuel particles (< 10μ) although the dimensional changes and the degree of matrix strain were higher in the latter specimens.
- ItemThe irradiation behaviour of cold-pressed and sintered beryllium oxide dispersion fuels.(Australian Atomic Energy Commission, 1964-06) Hanna, GL; Hilditch, RJCoarse and fine dispersions of (U.Th)O2 in BeO, prepared by cold-pressing and sintering, were exposed to fission fragment damage by irradiation in a thermalised neutron flux. Irradiation temperatures were between 610ºC and 720ºC and fission densities of 3 x 1019 to 2 x 1020 fissions per cm3 of compact were achieved. The dimensional stability of all specimens was very good and the greatest volume expansion was one per cent. Estimated thermal stresses ranged up to 32,000 p.s.i. but no thermal stress failure occurred. The fine and the most dilute coarse dispersions released only 0.1 per cent, of the fission gases but the remaining coarse dispersions released from 0.6 to 4.9 per cent. Coarse fuel particles were generally cracked after irradiation and by microscopy, fission fragment damage to the fuel — BeO interfaces was observed in the high burn—up specimens. Fission gas bubbles developed in coarse fuel particles on post—irradiation annealing at 1250ºC and 1500ºC.
- ItemThe irradiation behaviour of hot-pressed dispersions of (U,Th)Be13 in beryllium - second irradiation experiment.(Australian Atomic Energy Commission, 1963-11) Hanna, GL; Hickman, BS; Hilditch, RJFuel specimens having uranium—thorium beryHides as the fissile bearing phase were irradiated at 400 to 700 ºC to burn—ups between 7 and lla/0 uranium in a predominantly thermal flux, two specimens of massive (U.;Th)Be 13 exhibited good dimensional stability and low fission gas release. Dispersion specimens containing 20, 35, and 50v/o (U,Th)Be13 swelled by 3 to 18 per cent0 and released up to 33 per cent, of the gaseous fission products. The results indicate that the mixed beryllide is an inherently good fuel material and lead to the conclusion that the poor irradiation stability of hot—pressed specimens may not be typical of (U,Th) Be 13— Be dispersions prepared by other techniques.
- ItemA method for measuring the densities of single crystals of beryllium oxide(Australian Atomic Energy Commission, 1963-09) Hemphill, RJ; Hanna, GLA method is described whereby the density of a single crystal of beryllium oxide can be measured by suspending it in a dense liquid. The method is being used to measure radiation-induced changes in density and is sensitive to 1 part in 105. The absolute accuracy has not been established owing the lack of a suitable standard.
- ItemPreparation of the beryllides of uranium and thorium.(Australian Atomic Energy Commission, 1963-01) Hanna, GL; Turner, DNUranium and thorium beryllides and their solid solutions were prepared by reaction-sintering, reaction—pressing and arc—melting of mixed metal powders. The major difficulties of preparation were the large swellings accompanying reaction without pressure and the loss of beryllium at temperatures above 1200 — 1300ºC, the reaction—pressing method suffered least from these difficulties and yielded the purest and most dense products.
- ItemThe relationship between microcracking and mechanical properties in neutron-irradiated beryllium oxide(Australian Atomic Energy Commission, 1964-08) Hanna, GL; Stevens, GT; Hickman, BSBeryllium oxide bend test specimens of two grain sizes, 1—2 microns and 8—35 microns, were irradiated to fast neutron doses of up to 5 .6 x 1020 nvt (above 1 MeV) at 75 — 100ºC. Specimens were examined by X—ray line breadth (30.0 reflection), modulus of rupture, elastic modulus, open porosity, and lattice parameter measurements. The results show that there is no significant change in mechanical properties up to the dose at which microcracking is first observed i.e. .5 x 1020 nvt in the case of the fine grain size material and 1.2 x 1020 nvt in the case of the coarse grain size material. Above these doses the modulus of rupture and the apparent elastic constants fall rapidly. Microcracking occurred at an earlier dose in both materials than would have been expected from earlier work.
- ItemThe strength of irradiated beryllium oxide fuelled with UO2-ThO2(Australian Atomic Energy Commission, 1965-07) Hanna, GL; Hilditch, RJThe mechanical strength of hot-pressed and cold-pressed and sintered dispersions of (U,Th)O2 in BeO was measured before and after irradiation using the diametral compression test. The addition of more than 5 volume per cent. (U,Th)02 lowered the unirradiated strength to about 60 per cent, of the strength of BeO. Irradiation resulted in a marked drop in strength of all coarse dispersions. Hot-pressed fine dispersions behaved similarly to coarse dispersions of the same composition but the cold-pressed fine dispersions exhibited an apparent increase of strength on irradiation. High temperatures favoured the retention of strength during irradiation,