Mathematical Simulation of the Behavior of Spent Organic Extracting Agent in the Near-Well Region in the Case of Deep Burial

Abstract

A mathematical model of the physicochemical processes occurring in a reservoir bed with simultaneous disposal of organic and aqueous radioactive wastes in deep-lying porous geological formations is presented. The model includes a description of filtration, convective-dispersive mass transfer, sorption and desorption of radionuclides by the surrounding rock, radioactive decay, decomposition of organic components, and convective heat transfer and heat transmission. The numerical implementation of the method is used as a basis for developing computer software that makes it possible to perform predictive calculations of the change in the state of a reservoir bed of radioactive wastes. The results of the simulation of the dynamics of the thermal fields and the behavior of the components of the spent organic extracting agent and aqueous radioactive wastes in the reservoir bed in the deep-disposal test area are presented.In the course of reprocessing fissioning materials, the organic extracting agent, consisting of a solution of tributylphosphate (TBP) in a hydrocarbon diluent, undergoes radiation-chemical decomposition, as a result of which it loses its operational properties and is removed from operation. The spent extracting agent contains fission products, uranium and plutonium, and for this reason is classified as a radioactive waste. One method of isolating such wastes is deep burial in porous geological formations [1]. This served as a prerequisite for examining the burial of spent extracting agent together with aqueous radioactive wastes. Laboratory investigations and experimental-commercial tests showed that burial of spent extracting agent in underground reservoir beds is reliable, and have made it possible to determine the injection conditions. It was established that the organic impurities which are part of the liquid water wastes effectively decompose in reservoir bed [2]. In connection with the higher safety requirements for underground burial and the need for optimizing safety, it is important to give a quantitative description of the behavior of organic wastes taking account of their migration, which is considered to be transport and redistribution of chemical elements accompanying geochemical processes, and predict the change in the state of the underground stratum.Spent organic extracting agent is injected into an underground reservoir bed through wells, used for storing alkaline water wastes, specifically, from the Siberian Integrated Chemical Plant. The combined filtration of water wastes and spent extracting agent in the porous medium of a reservoir bed is accompanied by a large number of intercoupled nonequilibrium physicochemical processes. The data from observation of the state of the reservoir bed in the deep burial area shows that the