Variation with temperature and porosity, of the moduli rupture and elasticity of standard isostatically pressed and sintered beryllia.

Some properties of isostatically pressed and sintered UOX beryllia, fabricated at Lucas Heights to a grain size of ≤3μ were measured. The modulus of rupture of material of density 2.86 to 2.90 g cm-3 was measured in four-point bending over the temperature range 20ºC to 1000ºC. The data could be represented by the equation: σf = 33,000 - 7.46T p.s.i. The total variance was 19.5 x 10 6 p.s.i. made up of a "within" batch variance, of 15.8 x 10 6 p.s.i. and a "between" batch variance of 3.7 x 10 6 p.s.i. The modulus of rupture at 20ºC was measured on material with a total porosity range of 4 to 35 per cent; the data could be represented by the equation: σ = σ0 exp(-2.44P) p.s.i. The modulus of elasticity was measured in four-point bending on 97-5 per cent, dense material and the data could be represented by the equation: E = (51.45 x 10 6)+(l.264x10 2 T)-(1.442+10-1T2)-(2.595x10-3T3) p.s.i. The modulus of elasticity was measured as a function of porosity in the range 2 to 36.4 per cent. The data could be represented by the equations E = Eo (1-1.47P) x 10 6 p.s.i

Mechanical properties of BeO-(UTh)O2 dispersion fuels.

Dispersions of (UTh)02 in BeO were fabricated using (UTh)02 particles made from mixed powders of U02 and Th02 or by co-precipitation of U02 and Th02. The behaviour of the dispersions was studied by measuring the modulus of rupture and Young's modulus. Modulus of rupture measurements were made by four-point bending of cylindrical specimens, and Young's modulus was calculated from the deflection of rectangular beams. The out-of-pile control specimens for two irradiation experiments, X121 and X105, were also tested. Examination of matching fracture faces showed that cracks passed through (UTh)02 particles, indicating that they were bonded to the matrix. The results were compared with previous results on BeO-Th02 dispersions. The strength of dispersions of (UTh)02 in BeO decreased with increasing (UTh)02 particle size and increasing (UTh)02 concentration. For dispersions of 1.7 v/o (UTh)02 made from mixed oxides in BeO, the strength increased with increasing temperature while for dispersions of (UTh)02 made by co-precipitation, the strength remained unchanged with temperature up to 500ºC and decreased as the temperature was raised to 1000ºC, Young's modulus decreased with increasing (UTh)02 concentration. Young's modulus of 1.7 v/o (UTh)Oa dispersions remained unchanged up to about 600ºC} then decreased slightly as the temperature was raised to 1000ºC, Increasing the (UTnJOa concentration from 1.7 to 20 v/o displaced the curve to lower values. In general, the behaviour of dispersions of (UTh)02 in BeO was similar to that of ThOa in BeO. The differences in behaviour between dispersions of (UTh)Oa made from mixed oxides and by co-precipitation, observed in modulus of rupture tests, were attributed to variations in matrix grain size caused by iron cexamination of the co-precipitated (UThJOg. It was concluded that to obtain maximum strength, the particle size of the (UThJOg should not exceed 5jj., and the particles should contain no impurity which could cause grain growth in the beryllia matrix

Conditions applying to Australian uranium exports - safeguards obligations under NPT.

The Australian Government's expressed desire to inhibit the spread of nuclear weapons and its wish to prevent Australia's uranium exports being used for manufacture of nuclear explosives are underwritten by Australia's formal international obligations. Australia is not free to export its material without paying due regard to supra-national requirements. This paper defines two safeguards regimes, one applying to countries such as Australia which are party to the Treaty on Non-Proliferation of Nuclear Weapons (NPT), the other to those which are not parties. The application of safeguards and the role of the International Atomic Energy Agency (IAEA) are briefly explained. Australia's obligations under the NPT and those stemming from specific undertakings to the IAEA are stated. The latter require Australia to ensure that Non-Nuclear Weapons States not party to the NPT give assurances that Australian uranium will not be used for the manufacture of nuclear explosives and that they will permit verification by the IAEA. These obligations give rise to a set of minimum conditions applying to exports of Australian uranium which vary according to the NPT status of the importing countries

Effects of irradiation on beryllia-based fuels.

Dispersions of (UTh)O2 in beryliia, containing 1.7 per cent to 25 per cent (UTh)C>2 in three fuel particle sizes, coarse (150 —200μ)> medium (33 — 35μ and fine (<10 and <5º) were irradiated to burnups of 3—10 per cent of heavy metal atoms in the range 300-900ºC, in both fast and thermal fluxes. Changes in volume, lattice parameter, line breadth, and modulus of rupture were measured. Volume changes in the fine dispersions were ascribed wholly to fission fragment damage and were about 50 per cent greater than those caused by fast neutrons alone; they increased with increasing fission fragment flux, and decreased as irradiation temperature increased. Volume changes in medium and coarse dispersions were about 25 per cent greater than those caused by fast neutrons alone; the enhancement of the damage is attributed to the additional β flux. As fuel particle size increased, deterioration in strength under irradiation was more marked. This was attributed to more intense fission fragment damage in the recoil zone around larger particles causing volume increases which exceeded those of the remainder of the matrix. For maximum initial strength and retention of strength under irradiation the fuel particle size should not exceed 5μ, and the inter-particle spacing should not exceed 30