Alpha-Decay Damage of Cm-Doped Perovskite
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ALPHA-DECAY DAMAGE OF CM-DOPED PEROVSKITE H. MITAMURA*, S. MATSUMOTO*, T. TSUBOI*, E. R. VANCE**, B. D. BEGG** AND K. P. HART**
*Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken, 319-11, Japan **Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW, Australia
ABSTRACT Curium-doped perovskite slurry, which had the nominal composition of Cao.98919(Cm, Pu)0.01081AI0.O1081Tio.9891903, was calcined at 750'C for 2 h and then hot-pressed at 1250'C and 29MPa for 2 h. The hot-pressed cylinder samples had the specific 24 4 Cm activity of 22.3 GBq.g-1 on 31 March 1993. Their average density was 4.083 g.cm- 3 after the samples got a cumulative dose of 0.7x101 7 oxdecays.g-1. Change in density of Cmdoped perovskite reached 0.8% at a dose of 5x10 1 7 a decaysog-1. The rate of density change was slightly larger in the present perovskite material than in Cm-doped Synroc reported previously. Half-disk perovskite specimens, which had accumulated doses of 1.6x10r7 and 4.Ox101 7 cc decays.g-l, were MCC-1 leach tested in pH-2 solution at 90 0 C for two months. The leach rates of these specimens derived from weight losses were 1.7 and 2.3 g.m- 2 .day-1, respectively. These high leach rates caused a significant increase in pH in the later stage of the leaching runs. As-leached surfaces of Cm-doped perovskite showed the formation of anatase (TiO2). For the first 28 days, the Ca and Cm leach rates at the two different doses increased with leach time. More damaged specimens tended to give higher leach rates. In the final 28-day leaching run, both leach rates at the two different doses converged on each lower values although the Cm leach rate was lower than the Ca leach rate by a factor of >20. Nonradioactive perovskite material showed similar changes in Ca leach rate and pH to the Cm-doped one although the as-leached surfaces of the former material showed much higher degree of alteration of perovskite to anatase. INTRODUCTION In the titanate ceramic waste form, Synroc, actinide nuclides would be incorporated in perovskite and zirconolite phases [1]. In2 4our previous studies [2,3], alpha-decay damage effects on the titanate ceramic doped with 4 Cm (half-life, 18.1 years) were measured. How-
ever, microencapsulation by more durable phases could mask the effects of the deterioration of less durable ones, in particular perovskite. Single phase material is useful for getting direct information on this point. At present, we can utilize only limited data about the alphadecay damage of perovskite [4,5]. In the present study, perovskite samples doped with 244 Cm were prepared, and alpha-decay damage effects on their density and leaching behavior were investigated. The actinide nuclides have high pH sensitivity on their leaching behavior. As the Cm leach rate in pure water was not sensitive to accumulation of alphadecay damage, an acidic buffer solution was used in the present study to prevent adsorption of the curium on specimen surfaces and/or leach container wall as much as poss
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