One approach to demilitarize solid rocket propellants is treatment with ammonia. Ammonia extracts the oxidizers ammonium perchlorate and HMX, yielding a solid residue that is more suitable for incineration and less sensitive to impact and other modes of accidental initiation. Ammonia treatment of nitroglycerin-containing propellants is complicated by an exothermic reaction between ammonia an nitroglycerin. If not removed, the heat generated by this reaction can cause propellant ignition. To help design safe treatment processes, a model for the ammonia-propellant reaction was developed, which integrates transient energy and species conservation equations to simulate ammonia diffusion, heat generation, and heat flow in a propellant and in the solid residue resulting from ammonia treatment. It was calibrated using residue thickness and thermocouple data for one propellant. The calibrated model was used to predict conditions leading to ignition of thin propellant strips. The results agree well with experimental observations.