Selected examples of the Canadian contribution to the development of understanding of the behavior of hydrogen in zirconium alloys are reviewed. To solve the technical problems faced by the nuclear industry, it was necessary to have values for the solubility and diffusivity of hydrogen in the alloys, the diffusivity needed for the three gradients of concentration, temperature, and stress. With these quantities known, sensible models for the accumulation of hydrogen at points in the reactor components and the morphology of the resultant hydride phase were developed.

Selected examples of the Canadian contribution to the development of under standing of the behavior of hydrogen in zirconium alloys are reviewed. To solve the technical problems faced by the nuclear industry, it was necessary to have values for the solubility and diffusivity of hydrogen in the alloys, the diffusivity needed for the three gradients of concentration, temperature, and stress. With these quantities known, sensible models for the accumulation of hydrogen at points in the reactor components and the molphology of the resultant hydride phase were developed.

Time-of-flight neutron diffraction has been used to measure the dilation of h.c.p. Zr by interstitial deuterium at 727 and 777 K. The dilation per atom of D is 2.78 Å3, and the partial molal volume is 1.67 cm3/mol. The lattice strain in the 〈c〉-direction is 1.65 times greater than in the 〈a〉-direction, and assuming tetragonal symmetry, the components of the λ-tensor are found to be λ1 = 0.032 and λ3 = 0.052.

Delayed failures at welds in components of Zi-2.5 wt % Nb are attributed to zirconium hydride forming at the root of a notch adjacent to the welds. Residual tensile stresses provide the driving force for growth of the hydride. The observed rate of growth is considerably higher than the rate calculated by techniques which give good quantitative agreement with experiments at about 575 K. Failures of the type studied here are inhibited by stress relief of the component in question.

Metals have been irradiated in the M.I.T. cyclotron at controlled temperatures up to 750° C. The construction of the specimen holder and its performance is briefly described.

Helium has been introduced into specimens of Brush Q.M.V. beryllium by irradiation with alpha particles in the M.I.T. cyclotron. During irradiation differert specimens have been held at a number of different temperatares from ambient to 740 deg C, respectively. The effect of the helium on the structure of the berylliuin has been studied by metallographic techniques. Helium concentrations as low as 0.05 vided the specimen received a sufficiently severe annealing treatment. Irradiation for 3.5 hr at 6OS deg C to a helium concentration of approx equal O.5 c/sup 3//cm/sup 3/ gave no structural effect, whereas irradiation at 740 deg C gave a marked effect. A helium concentration of approx equal 0.3 cm/sup 3//cm/sup 3/, giving no effect after irradiation at ambient temperatures, nor after an annealing treatment of 118 hours at 6OO deg C, gave an effect after 520 hr at this temperatare. Specimens irradiated at ambient temperatares have been annealed at the same elevated temperatare at which other specimens were irradiated with both time at temperature and gas concentrations kept to similar values. For each temperatare at which these comparisons were made no marked differenre in number or size of gas bubbles was detected. There was however an increasedmore » effect at grain boundaries in the case of irradiation at temperature. The results are discussed in terms of second phase particles acting as preferred points of gas bubble nucleation. The results suggest that the neutroninduced gas in the sheaths of beryllium-sheathed fuel elements will not cause catastrophic swelling at an operating temperatare of 600 deg C or lower. (auth)« less