Ion Implantation Studies of Nuclear Waste Forms
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ION IMPLANTATION STUDIES OF NUCLEAR WASTE FORMS*
CLYDE J. M. NORTHRUP, JR., GEORGE W. ARNOLD, Sandia National Laboratories,** Albuquerque,
AND THOMAS J. HEADLEY New Mexico, USA
ABSTRACT The first observations of physical and chemical changes induced by lead implantation damage and leaching are reported for two proposed U.S. nuclear waste forms (PNL 76-68 borosilicate glass and Sandia titanate ceramics) for commercial wastes. To simulate the effects of recoil nucleii due to alpha decay, the materials were implanted with lead ions at equivalent doses up to approximately 3 1 x 1019 a decays/cm . In the titanate waste form, the zirconolite, perovskite, hollandite, and rutile phases all exhibited a mottled appearance in the transmission electron microscope (TEM) typical of defect clusters in radiation damaged, crystalline solids. One titanate phase containing uranium was found by TEM to be amorphous after implantation at the highest dose. No enhanced leaching (deionized water, room temperature, 24 hours) of the irradiated titanate waste form, including the amorphous phase, was detected by TEM, but Rutherford backscattering (RBS) suggested a loss of cesium and calcium after 21 hours of leaching. The RBS spectra also indicated enhanced leaching from the PNL 76-68 borosilicate glass after implantation with lead ions, in general agreement with the observations of Dran, et al. [6,7] on other irradiated materials. Elastic recoil detection spectroscopy (ERD), used to profile hydrogen after leaching, showed penetration of the hydrogen to several thousand angstroms for both the implanted and unimplanted materials. These basic studies identified techniques to follow the changes that occur on implantation and leaching of complex amorphous and crystalline waste forms. These studies were not designed to produce comparisons between waste forms of gross leach rates. INTRODUCTION Providing evidence for long-term stability and survivability of nuclear waste forms requires an understanding of the basic chemical and physical processes associated with waste form degradation and the need for such information has motivated the search for possible mineral analogues which have undergone natural degrading processes for long time periods. Although developers of waste forms have long been concerned about possible radiation effects, out of necessity, the early experiments were confined to screening tests using conditions foreign to actual repositories. These studies focused on determining the survivability of waste forms in short-term tests [1,2]. For example, numerous leaching studies have been performed on borosilicate glasses, some loaded with short lived isotopes, with the * **
This work was supported by the U. S. Department of Energy under contract DE-AC04-76-DP00789. Sandia National Laboratories is a U. S. Department of Energy facility.
668 principal diagnostic technique being analyses of solutions that were probably close to saturation in silica [3,4]. These simulated waste forms have not clearly shown enhanced lea
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