Interaction of Nitric Acid with Organic Compounds
Research of Characteristics and Dynamics of Exothermic Reaction Runaway of Nitric Acid with Organic Compounds in Heterogeneous Systems
Tech Area / Field
- FIR-FUC/Fuel Cycle/Fission Reactors
- ENV-RWT/Radioactive Waste Treatment/Environment
3 Approved without Funding
Institute of Problems of Chemical Physics, Russia, Moscow reg., Chernogolovka
- All-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar, Russia, Moscow\nInstitute of Physical Chemistry and Electrochemistry, Russia, Moscow
- British Nuclear Fuels Ltd (BNFL) / Waste Disposal Research Group Sellafield R&D, UK, Cumbria, Seascale\nLos Alamos National Laboratory, USA, NM, Los-Alamos\nFlorida State University / Department of Chemistry and Biochemistry, USA, FL, Tallahassee
Project summaryThe objective of the Project is to perform theoretical and experimental studies of kinetic regularities of a chemical interaction of nitric acid (HNO3) and hydrocarbon mixtures with different additives and to develop a scientific background for prediction of a reaction runaway and control it to avoid industrial accidents. Such a study is necessary to determine conditions of the reaction runaway, the development of an accident and its consequences.
At processing of spent fissile fuels and radioactive wastes a two-phase extraction system is used. Its organic phase contains a solution of tri-n-butyl phosphate (TBP) in a hydrocarbon diluent, and the mineral one contains a solution of nitrates in HNO3. Since heat release rates at oxidation of hydrocarbons by nitric acid are rather high and heat removal methods (e.g., cooling jacket) can be insufficiently effective, a sharp increase of temperature of a reaction mass can result in a process self-acceleration leading to a reaction runaway,. a sharp increase of pressure and a possible apparatus failure. As a result a release of fissile products in environment, development of secondary oxidative processes (ignition of hydrogen and organic component vapours in air) and initiation and development of detonation and shock waves will take place.
Analysis of accidents took place at a number of radiochemical installations in USA and Russia shows that the main cause of accidents is the chemical reaction runaway which is determined by exothermal oxidative processes in the aqueous HNO3 solution / organic substance solution two-phase system.
Available information on the chemical mechanism of interaction of hydrocarbon mixtures with aqueous HNO3 solutions, the kinetic regularities of the heat release in oxidative processes, the critical conditions and dynamics of the process runaway, parameters and characteristics of secondary phenomena is insufficient for a correct determination of safe conditions of a process carrying out. This does not allow one to perform a mathematical simulation of behavior of the aqueous HNO3 solution / organic substance solution system in extreme conditions.
The proposed project represents a complex of theoretical and experimental studies. The scientific tasks defined for the research can be listed as follows:
- to investigate the chemical mechanism of interaction of HNO3 solutions with hydrocarbon / TBP mixtures, to determine the kinetic parameters and the heat effects of the main stages;
- to develop mathematical model and software for calculation of the critical conditions and dynamics of the hydrocarbon / TBP / nitric acid reaction runaway;
- to investigate experimentally the regularity of the hydrocarbon / TBP / nitric acid reaction runaway;
- to perform mathematical simulation of initiation and development of the secondary phenomena – an apparatus failure, formation of explosive mixtures in environment, initiation and development of detonation, propagation and interaction of shock waves.
The anticipated results and their application. The results of the research to be carried out are the following:
- to determine the chemical mechanism and the kinetic parameters of the interaction of HNO3 with hydrocarbon / TBP mixtures;
- to determine the kinetic regularities of the heat release in the interaction HNO3 with hydrocarbon/TBP mixtures in both the organic and the aqueous phase;
- to determine a vapour equilibrium pressure, a vaporization heat of components of the aqueous HNO3 solution / organic substance solution system and to carry out calculation of kinetics of a heat absorption at vaporization;
- to determine the kinetic regularities and the mechanism of accumulation of gaseous and liquid-phase products in the interaction HNO3 with hydrocarbon / TBP mixtures;
- to develop mathematical models and to provide software for calculation of critical conditions and dynamics of the organic components/nitric acid reaction runaway;
- to obtain the experimental data on the critical conditions and dynamics of process runaway;
- to develop the mathematical models for calculation of a character of failure of the model apparatus after the hydrocarbon / TBP / nitric acid reaction runaway and estimation of consequences of such a failure;
- to determine the regularities of the release of reaction products from the apparatus broken down, the formation of explosion-dangerous mixtures in air, the development of detonation in environmental with chemically reactive gases, propagation of shock waves and their interaction with surroundings objects.
Scope of activities. The Project supposes carrying out the following tasks:
1. Analysis of available data on thermochemistry of transformation in the aqueous HNO3 solution / organic compound solution systems and on industrial accidents.
2. Experimental study of the mechanism and the kinetic regularities of the heat release in the interaction of HNO3 solutions with hydrocarbon / TBP mixtures.
3. Experimental study of the kinetics of the formation of gaseous and liquid-phase products of thermolysis and radiolysis in the system: an aqueous HNO3 solution – a TBP solution in hydrocarbon mixtures.
4. Mathematical simulation and experimental study of the regularities of the organic compounds / nitric acid exothermic reaction runaway in heterogeneous systems.
5. Mathematical simulation of initiation and development of secondary phenomena after the apparatus failure.
The scientific significance of the project consists in that the chemical mechanism of oxidation of TBP / hydrocarbons mixtures by nitric acid and nitrogen dioxide will be determined; the main stages of the process will be revealed and their kinetic constants and thermal effects will be determined; the regularities of the chemical exothermal reactions runaway in two-phase systems will be explored; influence of hydrodynamic flows in a reaction medium on the regularities of the reaction runaway will be investigated; the factors influencing on character of the apparatus failure under the action of internal pressure will be determined; the processes defining initiation, propagation and interaction of shock and detonation waves will be explored.
The practical significance of the project relates to its ultimate objective, that is, to provide the experimental and theoretical methods for a preliminary estimation of the safe conditions of carrying out of the reaction in the aqueous HNO3 solution / organic compound solution system. The results obtained in the course of implementation of the project can be used for analysis of the kinetic regularities and the optimal conditions of carrying out of a number of industrial nitration and oxidation processes, for example, in pharmaceutical and dye industry, in reprocessing of solid rocket propellants.
The team of researchers formed and successfully co-operated earlier in the activity connected with development of solid rocket propellants and explosives is supposed to participate in the project performing. The employees of the Institute of Problems of Chemical Physics of the Russian Academy of Sciences, Institute of Electrochemistry of the Russian Academy of Sciences and All-Russian A.A.Bochvar Scientific Research Institute of Inorganic Materials – potential participants of the project – are the highly qualified researchers with the wide experience of the activity in the field of combustion, thermal stability, development of technologies for processing of spent fissile materials and radioactive wastes.