Safety of Tri-n-butyl phosphate (TBP) and nitric acid solutions in two-phase systems at elevated temperatures
- Westinghouse Savannah River Company, Aiken, SC (United States)
This paper addresses the prevention of self-accelerating oxidation of nitric acid and tributyl phosphate (TBP). An accident of this type, which occurred at Tomsk-7, Russia, in 1993, resulted from a slow chemical reaction occurring initially at sub-boiling temperatures. The accumulating heat and vapors overpressurized and burst a process tank. Two safety issues are addressed in this summary of experimental data: circumstances under which convection or radiation cooling of vessels will exceed reaction heat, and measures which can prevent or mitigate such reactions. Heat generations rates have been found to range widely. Thermodynamic calculations confirm that heat generation is reduced by a large factor when nitrogen oxides are able to escape from the reaction mixure. Scoping calculations show that the evaporation of water is potentially the most effective mechanism for heat removal in a large vessel, and experiments have demonstrated that water evaporation is effective for preventing runaway reactions in a vented, two-phase system operated below about 120 C. These data indicate that venting is the key to controlling runaway reactions. However, other experiments have indicated that the self-heating reaction did not present a danger, even if reaction heating led to an accelerating reaction, in a sufficiently vented system. To determine how much venting was required, experiments were performed with pure organic phase and two-phase TBP-nitric acid mixtures. Data show a critical ratio of organic mass to vent area, above which the reacting system can reach potentially dangerous pressures. Experiments show runaway reactions occurring in vented systems only as the temperature approaches 130 C. These results clearly indicate that adequate venting of vessels containing heated TBP and nitrate is the key to controlling their reaction.
- OSTI ID:
- 210285
- Report Number(s):
- CONF-9509139--
- Country of Publication:
- United States
- Language:
- English
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