The Influence of Chemical Composition of Liquid Radioactive Waste on the Evaporation Process
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The Influence of Chemical Composition of Liquid Radioactive Waste on the Evaporation Process P.P. Poluektov, L.P. Soukhanov and M.I. Zhicharev SSC RF VNIINM 123060, Russia, Moscow, P.O. Box 369 VNIINM Email: [email protected] ABSTRACT A method is suggested to assess the tolerable salt content of the evaporator bottoms from the data on solubility in salt systems taken as simplified models of liquid radioactive waste (LRW) arising from nuclear power plants (NPP) with boiling reactors. It has been demonstrated that the degree of evaporation may be substantially increased by implementing the process in nitric acid. Equations have been derived that allow the calculation of the minimum needed acidity of the solution to allow maximum evaporation. INTRODUCTION Under evaporation of LRW the salts for which the concentration exceeds their solubility limit, under the given conditions, crystallize and precipitate. Depending on the type of salt and some other factors the salt crystallization in the solution may be accompanied by the formation of deposits in heating pipes of an evaporator. The deposits reduce the heat transfer and, hence, the effective operation of evaporators. Upon massive precipitation from a solution being evaporated, the evaporator heating pipes or evaporator bottoms pipelines are likely to be fully encrusted. Salt deposition in an evaporator bottoms storage tank is also undesirable since it complicates the full emptying of the tank. Thus, the main requirements for the process conditions of LRW evaporation are: • •
Maximal reduction of LRW volume by evaporation; Prevention of evaporator bottoms salts arising from crystallization.
Hence, the final salt content of the evaporator bottoms has to approach the concentration of a solution saturated with salts of limited solubility. However, to put this apparent condition into practice, one needs an adequately simple procedure that shall promote the calculation or experimental determination of the concentration of the saturated solution and, hence, the final concentration of the evaporator bottoms.
METHODOLOGY AND RESULTS 1.
Procedure used to determine ultimately tolerable salt content of evaporator bottoms
This work suggests a simpler and universal route of determining the ultimately tolerable salt content of evaporator bottoms under evaporation of LRW arising from NPP with boiling reactors (RBMK-type). The method consists of constructing and applying the salt system simplified models of LRW. The practical implementation of the method comprises the following stages: • • • •
Analysis of the LRW chemical composition and its likely variations with time; Developing a salt system assumed to be a simplified model of LRW; Accumulate a salt system data base and other properties from literature sources and by experimental efforts; Use the salt system data base to predict the evaporation behavior of actual LRW.
When forming salt systems assumed to be simplified models of LRW we are guided by the following propositions: a. b.
Salts constituting the composition of a si
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