A solution containing kilogram quantities of highly radioactive isotopes of
amerícium and curium (Am/Cm) and lanthanide fission products is currently
stored in a process tank at the Department of Energy's Savannah River Site
(SRS). This tank and its vital support systems are old, subject to
deterioration, and prone to possible leakage. For this reason, a program has
been initiated to stabilize this material as a lanthanide borosilicate (LBS)
glass.1 The Am/Cm has commercial value and is desired for use
by the heavy isotope programs at the Oak Ridge National Laboratory
(ORNL).
A recovery flowsheet was demonstrated using a curium-containing glass to
extract the Am/Cm from the glass matrix. The procedure involved grinding the
glass to less than 200 mesh and dissolving in concentrated nitric acid at
110°C. Under these conditions, the dissolution was essentially 100% after 2
hours except for the insoluble silicon. Using a nonradioactive surrogate,
the expected glass dissolution rate during Am/Cm recovery was bracketed by
using both static and agitated conditions. The measured rates, 0.0082 and
0.040 g/hrcm2, were used to develop a predictive model for the
time required to dissolve a spherical glass particle in terms of the glass
density, particle size, and measured rate. The calculated dissolution time
was in agreement with the experimental observation that the curium glass
dissolution was complete in less than 2 hr.