Drip tests to measure radionuclide release from spent nuclear fuel are being performed at 90 °C at a drip rate of 0.75 ml every 3.5 days. The test conditions are designed to simulate the behavior of spent fuel under the unsaturated and oxidizing conditions expected in a potential repository at Yucca Mountain. The 238 U, 239 Pu, ,17 Cs, w Sr, "Tc, and l29 I content in the leachate after 581 days of testing is reported. These data provide valuable information for estimating the release of long-lived radionuclides. A comparison is made between our results and those of other researchers. The "Te release fractions are suggested to be representative of matrix dissolution.

A program has been established for DOE Environmental Restoration and Waste Management (EM) to evaluate factors that are likely to affect waste glass reaction ,during repository disposal, with emphasis on an unsaturated environment typical of what may be expected for the proposed Yucca Mountain repository site. This report covers progress in FY 1991 on the following tasks: 11 A critic_ review of those parameters that affect the reactivity of glass in an unsaturated environment is in progress. This effort involves a search of the literature to identify the important parameters. Temperature and glass compositions are the first parameters examined in detail. 2, An interface between waste producers and the repository program is being implemented. 3. A series of tests has been started to evaluate the reactivity of fully radioactive glasses in a high-level waste repository environment mad compare it to the reactivity of synthetic glasses of similar composition. 4. The effect of radiation upon the durability of waste glasses at a high glass surface. _ea-tc)-liquid volume fSA/V) _ttio m3d higl_ gas-to-liquid volume ratio will be assessed. These tesLsaddress both vapor m_d high SA/V liquid conditions. 5. A series of test:_ is being performed to compare the extent of reaction (_t" nuclear waste glasses at various SA/V ratios, Such differences in the SA/V ratio may significantly affect glass durability. 6. An_ytical electron microscopy (AEM), infrared spectroscopy, and nuclear : resonant profiling are being used to assess the glass/water reaction pathway by identil'ying intermediate phases that appear on the reacting glass. Additionally, colloids trom the leach solutions are being studied using AEM.

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Two well-characterized types of spent nuclear fuel (ATM-103 and ATM-106) were subjected to testing under potential unsaturated conditions with simulated groundwater at 90 °C. The actinides present in the leachate were determined at the end of two successive periods of ~60 days. A vessel acid strip was done at the end of the second period. Both colloidal and soluble actinide species were detected in the leachate which had pHs ranging from 4 to 7. The uranium phases identified in the colloids by transmission electron microscopy were schoepite and soddyite. The actinide release behavior of the two fuels appeared to vary. Both the total amount of material released and the relative amount of each isotope released was different for the two fuels.

Cobalt ferrite (CoFe2O4) nanoparticles were successfully synthesized by polymer matrix templated synthesis. Synthetic ion-exchange resins were used as hosts for the coprecipitation of cobalt ferrite where the nanopores of the resin acted as the constrained environment. The weight fraction of the particles within the resin was roughly 16%. X-ray diffraction analysis indicated that cobalt ferrite crystallites were about 1–7 nm in diameter. Magnetic properties measured using an alternating gradient magnetometer showed the particles (prepared using initial salt solution ratio of Fe3+:Co2+ of 1.5:1.0) were superparamagnetic with magnetization M (of the particle-resin system) in the range of 3.0 to 4.4 emu/g at 10 kOe of applied field. The least upper bound of the magnetic size was about 3 nm in diameter. Ratios of Fe3+ to Co2+ within the matrix of the resin before and after precipitation were investigated by x-ray fluorescence spectrometry and were found to be sensitive to the initial salt solution mixture. The ratio Fe3+:Co2+ of 1.5:1.0 was found to be a better mixture in terms of magnetization value. Spherical shape cobalt ferrite particles 2–8 nm in diameter were observed using transmission electron microscopy. The close agreement between the physical and crystallite size indicated that the particles are largely monocrystals.