Leach Rates of High Activity Waste from Borosilicate Glass

Abstract

A paper prepared for presentation to the American Nuclear Soc iety Topical Meeting on the Back End of the LWR Fuel Cycle at Savannah, Georgia, on March 19~22, 1978. This paper was prepar~d in connection with work under Contract No . AT(07-2)-l with the U. S. Department of Energy. By acceptance of this paper, the publisher and/or recipient acknowledges the U. S. Government's right to retain a nonexclusive, royalt yfree license in and to any copyright covering this paper, along with the right to reproduce and to authorize others to reproduce all or part of the _copyrighted paper. would remain in its container out· of contact with water. ·In the unlikely event the container were breeched, the glass could come into contact with water. The low leach rate of glass would allow time for remedial action befm·e a significant fraction of radioactivity was released.Leach rates are usually expressed as the rate of glass disso-.. lution in units of g/(cm 2 -day). (Slide 1) This expression is chosen because radionuclides are asst~ed to be uniformly distributed through the glass and to enter solution as the glass dissolves.* The information contained in this article was developed during the course of work under Contract No. AT(07-2)-l with the U. S. Department of Energy.-1 -During the first few days of leaching,these assumptions are not strictly true,because measured leach rates decrease rapidly and sometimes depend on the radionuclide being leached. However, after several weeks, leach rates usually.become independent of the time and the radionuclide being leached, so the assumptions are valid for these longer periods.Borosilicate glass buttons were prepared from actual, fullyradioactive sludges obtained from six high-level waste storage tanks at Savannah River Plant (SRP). SRP waste spans a much wider range of compositions than is expected for light water reactor (LWR) waste.· LWR waste, however, will contain a much greater amount of fission products (!)· Typical LWR and SRP glass-forming frit compositions are compared on Slide 2. Slide 3 compares LWR and SRP wastes to be added to the frits. PROCEDURERadioactive SRP wastes were mixed with two types of borosilicate glass frit. Both frits had a higher Na/Si ratio (~0.38) than most commercial borosilicate glasses (0.05-0.07). This higher ratio allowed the radioactive glass to melt at a lower temperature than commercial glass, thus volatility of fission products was minimized. One frit contained 4 wt % LizO to reduce viscosity of the melt; the other was Li-free. Frit-sludge' mixtures were hea.ted at ll50"C for three hours, poured into graphite molds, and annealed at 500°C for one hour. In all three plots, glass made with combined sludges from Tanks 4 and 6 had the lowest leachability. On the average, Tank 13 sludge-glasses had the highest leachabilities. The combined Tank 4 and 6 sludge had the highest iron concentration of all the sludges; however, Tank 13 also contained predominately iron.Leachability of glass made with Tank 15 sludge (which contained the largest amount of al...

Synthesis of apatite phosphates containing Cs+, Sr2+ and RE3+ ions and chemical durability studies

“…[44]. Compared to borosilicate glass [45], it is significant to note the negligible leachability of Cs of the apatite structure waste forms studied in the current work. The mass loss of Sr is also noted to be fairly small.…”

Nuclear waste-form risk assessment for US defense waste at Savannah River Plant. Annual report FY, 1982

“…Table 4 shows the various release parameters computed for the progressive leaching of such a composite. We have given the major component the nominal leach rate, mass, and geometry of a cylinder of SRP 21-35-15 borosilicate glass, 22 reacting with brine at 363 K (90°C). The resulting cumulative fractional releases are shown in Fig.…”

“…29, the Laplace transform theory is ap plied to show that for a series sequence of paths, n=l, 2,..., N, the transform of J(or,T;t) is a product of transforms, e.g.. We are interested in the final mass transfer function J(ff,r;t) at the end of a series of paths that is either the inverse Laplace transform of Eq. (22) or a convolution integral in time, e.g., for two paths.…”

Interaction of La3+ and Ce4+ with polyethylene and polypropylene polymeric matrices

“…Leaching behavior is known to be the most important factor in the assessment of waste forms, which can be examined through the different leaching tests 16. Experimental leaching data can be analyzed with a variety of parameters, including the diffusion coefficient and dissolution rate constant, to predict the long‐term leaching behaviors 17, 18. According to some authors,19, 20 the leaching could be classified into two different stages during the leaching period.…”