A diffusion kinetic model of radiation-chemical transformations of oxalic acid in aqueous solutions was developed as applied to LRW management. The model describes the experimental results on oxalic acid decomposition to gaseous products in a wide pH range, in the presence and in the absence of oxygen and in solutions saturated with nitrous oxide. Liquid single-and two-phase (liquid3gas) systems formed in disposal of LRW in deep reservoir beds can be calculated using this model. Liquid radioactive wastes (LRWs) containing various organic and inorganic compounds are formed and accumulated in the course of processing spent nuclear fuel (SNF). These wastes are stored in open surface constructions and metal tanks or are disposed of in geological formations. Radiation-chemical reactions occurring during storage of LRW change the speciation of radionuclides contained in the wastes and result in formation and accumulation of gaseous products. To ensure the safety of LRW management, these processes should be comprehensively studied.The aim of this study was to develop a mathematical model of decomposition of oxalic acid and oxalate ions in acidic, neutral, and weakly basic aqueous solutions. Since oxalic acid is widely used in processing of SNF, large volumes of LRW containing oxalic acid are accumulated. The choice of this acid was determined by the fact that the mathematical model of its radiolysis can be used to describe real radiochemical and thermal transformations involving this acid. A great body of experimental data on radiolysis of solutions of H 2 C 2 O 4 and oxalate solutions favors successful development of this model. These data can be used to substantiate this model and check its main parameters as well as to develop the required software. In addition, development of a model adequately describing radiolysis of aqueous solutions of a simple compound such as H 2 C 2 O 4 can be a first step in developing general approach to simulation of radiationchemical transformations of more complex compounds such as CH 3 COOH and acetate ions, HNO 3 and nitrate ions, etc. It should be noted also that H 2 C 2 O 4 is formed in the course of radiolytic oxidative decomposition of CH 3 COOH. Hence, the main parts of the model under development can be used to create a new model of radiation-chemical transformations of LRW containing CH 3 COOH and HNO 3 . This general model can predict changes in the chemical compositions of LRW and gas evolution in formations and hence can determine safe operation conditions of underground disposal sites.
DEVELOPMENT OF THE MODEL, COMPARISON OF EXPERIMENTAL DATA, AND DISCUSSIONFirst, we developed a model of radiolysis of pure water and checked how this model describes available experimental data. The next step was to develop a model of radiolysis of aqueous solutions of H 2 C 2 O 4 . Finally, to assess practical applicability of the model, we checked how it describes the available experimental data.Model of water radiolysis. The model of radiation-chemical transformations of aqueous solutions o...