The behavior of radioactive sludge-based and simulated nuclear waste glasses has been compared by long-term testing of radioactive and simulated compositions of Savannah River Laboratory 165, 131, and 200 glasses. Static tests at glass surface area-to-solution volume (SA/V) ratios of 340 and 2000 m-1 up to 720 days show little difference in reactivity between radioactive and simulated waste glasses. The same leach trends are observed for both glass types. The differences in reactivity 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 reasonably be explained if the controlling reaction process and leachate pH values are accounted for. However, at an SA/V of 20000 m-1, the simulated nuclear waste glass, 200S, leaches faster than the corresponding radioactive glass by a factor of 40 within 1 yr. The accelerated reaction with the simulated glass 200S is associated with the formation of crystalline phases such as clinoptilolite (or K-feldspar), and a pH excursion. The radiation field generated by the fully radioactive glass reduces the solution pH, which, in turn, may retard the onset of the increased reaction rate. This result suggests that the fully radioactive nuclear waste glass 200R may be substantially more durable than the simulated 200S glass if the lower pH in the 200R leachate can be sustained. Meaningful comparison tests between radioactive and simulated nuclear waste glasses should include long-term and high SA/V tests.