LONG-TERM COMPARISON OF DISSOLUTION BEHAVIOR BETWEEN FULLY RADIOACTIVE AND SIMULATED NUCLEAR WASTE GLASSES

The behavior of radioactive sludge-based and simulated nuclear waste g lasses has been compared by long-term testing of radioactive and simul ated compositions of Savannah River Laboratory 165, 131, and 200 glass es. Static tests at glass surface area-to-solution volume (SA / V) rat ios of 340 and 2000 m-1 up to 720 days show little difference in react ivity between radioactive and simulated waste glasses. The same leach trends are observed for both glass types. The differences in reactivit y at an SA / V of 2000 m-1 or below are not large enough to alter the order of glass durability for the different compositions nor to change the controlling glass dissolution processes. The small differences in reactivity between fully radioactive and simulated glasses can reason ably be explained if the controlling reaction process and leachate pH values are accounted for. However, at an SA / V of 20 000 m-1, the sim ulated nuclear waste glass, 200S, leaches faster than the correspondin g radioactive glass by a factor of 40 within 1 yr. The accelerated rea ction with the simulated glass 200S is associated with the formation o f crystalline phases such as clinoptilolite (or K-feldspar), and a pH excursion. The radiation field generated by the fully radioactive glas s reduces the solution pH, which, in turn, may retard the onset of the increased reaction rate. This result suggests that the fully radioact ive nuclear waste glass 200R may be substantially more durable than th e simulated 200S glass if the lower pH in the 200R leachate can be sus tained. Meaningful comparison tests between radioactive and simulated nuclear waste glasses should include long-term and high SA / V tests.