Durability of Actinide Ceramic Waste Forms Under Conditons of Granitoid Rocks

摘要

Three samples of (sup 239)Pu-(sup 241)Am-doped ceramics obtained from previous research were used for alteration experiments simulating corrosion of waste forms in ion-saturated solutions. These were ceramics based on: pyrochlore, (Ca,Hf,Pu,U,Gd)(sub 2)Ti(sub 2)O(sub 7), containing 10 wt.% Pu and 0.1 wt.% Am$ zircon, (Zr,Pu)SiO(sub 4), containing 5-6 wt.% Pu and 0.05 wt.% Am$ cubic zirconia, (Zr,Gd,Pu)O(sub 2), containing 10 wt.% Pu and 0.1 wt.% Am. All these samples were milled in an agate mortar to obtain powder with particle sizes less than 30 micron. Sample of granite taken from the depth 500-503 m was studied and then used for preparing ion-saturated water solutions. A rock sample was ground, washed and classified. A fraction with particle size 0.10-0.25 mm was selected for alteration experiments. Powdered ceramic samples were separately placed into deionized water together with ground granite (approximately 1gram granite per 12-ml water) in special Teflon(trademark) vessels and set at 90 C in the oven for 3 months. After alteration experiments, the ceramic powders were studied by precise XRD analysis. Aqueous solutions and granite grains were analyzed for Am and Pu contents. The results show that alteration did not cause significant phase transformation in all ceramic samples. For all altered samples, the Am contents in aqueous solutions after experiments were similar (approximately n x 10(sup 2) Bq/ml) as well as Am amounts absorbed on granite grains (approximately n x 10(sup 5) Bq/g). Results on Pu contents were varied: for the solutions--from 60 Bq/ml for pyrochlore ceramic to 2.1 x 10(sup 3) Bq/ml for zircon ceramic$ and for the absorption on granite--from 2.6 x 10(sup 4) Bq/g for zirconia ceramic to 1.4-6.8 x 10(sup 5) Bq/g for pyrochlore and zircon ceramics.