Accelerated Leach Test for Low-level Radioactive Waste Forms in the Hungarian NPP Paks

Abstract

IntroductionFor a number of years increasing attention has been given in Hungary to the management of the low and medium level radioactive wastes (LLW, MLW) being produced in Paks nuclear power plant.Some of these wastes, for example, evaporator bottom concentrates, pond sludge and spent ion exchange media are produced in relatively large volumes. In addition to national programs on the development of immobilization processes, the European Community commissioned programs on the immobilization of LLW and MLW. These wastes are immobilized by incorporating them into cement. In order to optimize these immobilization processes, for example with respect to waste loading, it was necessary to characterize the products with respect to such properties as density, strength, dimensional stability, leach resistance and so on. In this article we report about an accelerated leach test and the developed computer program. Experimental Accelerated leach testsAn accelerated leach test method was used for low-level radioactive waste forms in the Hungarian NPP Paks. The leach test method was designed to minimize experimental artifacts that could be misinterpreted as release mechanisms such as effects of increased ionic concentrations in the leachate. This is particularly important when the data is used for mechanistic interpretations and long-term extrapolations.The test method we used was a semi-dynamic leach test that is the leachant is changed at predefined intervals. The test requires a volume of distilled water that is 10 times the surface area of the sample. The leachant was changed twice on the first day and then daily for 11 more days.These experiments were performed using cylinders of 2.93 cm diameter and 4.96 cm height, prepared form Hungarian cement type CEM I 32,5-LH and CEM III/B 32, N LH/SR. Each cylinder was AbstractAn accelerated leach test method was used for low-level radioactive waste forms in the Hungarian NPP Paks. These experiments were performed using cylinders prepared form Hungarian cement type CEM I 32,5 LH and CEM III/B 32, N-LH/SR. Each cylinder was made using cement or cement plus additive using radioactive waste water. The cemented radioactive material was evaporator bottom residue or sludge as well as evaporator cleaning acid solution, spent ion exchange resin, decontamination solution from NPP Paks, containing 134 C s , 137 C s and 60 C o as main radioactive components. Leach tests were performed according to ASTM C 1308-08 standard. A computer program (ILT15) associated with the accelerated leach test was developed based on the ASTM C 1308-08 standard. Literature test and measured leaching data were analyzed to assess whether the model for diffusion from a finite cylinder describes leaching from cement based waste forms. In this paper some of the experimental and modeling work used to validate the test method are presented.