Cause investigation of a fire and explosion at the nuclear fuel waste reprocessing plant indicated that self-heating ignition of an asphalt-salt-waste, bituminized, mixture (AS) caused the disaster. A 2201 drum was filled with the AS at a temperature of about 180 degreesC. About 20 h later the drum ignited and burned as it was being cooled. It is estimated that the AS contained approximately 55 wt,% blown asphalt, 25 wt,% NaNO3, 5 wt.% NaNO2 8 wt.% Na2CO3, 2 wt;% NaH2PO4, 1 wt.% Ba (OH)(2), 1 wt.% K-4[Fe(CN)(6)] and possibly 3 wt.% of other materials. To determine the reaction promoting factors and pertinent chemical reaction rates, self-reaction of the AS has been investigated by the use of a C80D heat flux reaction calorimeter. The oxidizing reactions with asphalt are ruled by NaNO2 rather than by NaNO3, in spite of a lower concentration of NaNO2. The kinetic rates of the interfacial reaction between salt particles and asphalt for the reaction controlled and diffusion controlled steps have been formulated as a function of salt particle size for both NaNO2 and NaNO3. Numerical solution of the heat balance equations formulating the heterogeneous reaction scheme indicates that a runaway reaction occurs when the AS-filling temperature is 208 degreesC for a drum filled with an AS mixture produced under standard operating conditions. Molecules containing intramolecular hydrogen, such as Na2HPO4 and NaHCO3, do not oxidize asphalt directly, however, their presence chemically promotes the oxidizing reaction of NaNO2. Moreover, NaHCO3 decomposition which produces gases creates many micro holes in the interior of the salt particles. This in turn promotes the oxidizing reactions that are diffusion controlled. Finally the consequence of a runaway reaction at 180 degreesC or lower is qualitatively explained by taking into account the chemical effect of intramolecular hydrogen and the physical effect of the NaHCO3 decomposition gases.