Thermal decomposition behaviour of irradiated tri n-butyl phosphate and mixture of di and mono n-butyl phosphate-nitric acid systems

Tri-n-butyl phosphate (TBP) is employed in nuclear reprocessing plants. During the evaporation process, formation of red oil, an unstable compound can cause runaway reaction. In this context, thermal decomposition of TBP-HNO3 and TBP-n-dodecane has been studied as a function of HNO3 concentration using adiabatic calorimeter. Effect of radiolysis on thermal decomposition of TBP has been investigated for the first time. Neat TBP is stable up to 527 +/- 1 K and the irradiated TBP is up to 513 +/- 1 K. Thermal decomposition of degradation products of TBP namely, dibutyl and monobutyl phosphates have also been investigated for the first time. Thermo-kinetic parameters e.g. enthalpy of decomposition, activation energy, pre-exponential factor and order of reaction were computed. Enthalpies of decomposition for TBP-4 M HNO3 vary from 64 to 495 kJ mol(-1) whereas that of TBP-8 M HNO3, 368-1187 kJ mol(-1). TBP-HNO3 on thermal decomposition produces CO, CO2, NOx, hydrocarbons and highly viscous black liquid.