The formation and chemical properties of the major degradation products of several diluents in contact with acidic nitrate solutions have been studied, together with (1) methods for purifying degraded solvent, (2) methods of pretreating the solvent to minimize degradation, and (3) the relative stability of several solvent systems. Emphasis was on Amsco 125-82, a specially treated naphtha used extensively at ORNL in radiochemical processing. Degradation of the diluent, usually containing 1M TBP, was induced by boiling with HNO3 or by irradiating (Co60γ) while agitating the solvent phase with HNO3. Nitroparaffins, RNO2, were the major degradation products and were formed at twice the rate when TBP was present during degradation. Under the conditions of degradation 100 watt-hr/ liter exposure was essentially equivalent to 11 hr boiling with 2M HNO3 as shown by Zr-Nb extraction, total organic nitrogen analysis, and spectrophotometric analysis. Extraction from acid solution of certain fission products, e.g., Zr-Nb but not Ru, increased markedly after the degraded solvent had been treated with alkaline reagents, and a test employing solid calcium hydroxide was developed to estimate the extent of diluent degradation. The alkaline treatment converted a significant fraction of the nitroparaffin to the enol form. There was synergistic extraction of Zr-Nb by the combination of TBP and degraded diluent. Cleanup of the degraded solvents can be attained by scrubbing with alkanolamines to remove nitroparaffin-amine salts or by contacting with activated alumina. Both methods have doubtful economy and the latter requires solids handling. Low pressure flash distillation is an effective, inexpensive method for partial or total repurification of degraded TBP-Amsco. With aliphatic diluents the configuration most stable against nitration is the simplest, e.g., n-dodecane. Pretreating Amsco 125-82 by scrubbing with concentrated sulfuric acid before degrading with hot nitric acid improved its stability. Aromatic diluents increase the radiation stability and extraction selectivity of TBP. The stabilities of the simple alkylbenzenes against nitration vary widely with the number of alkyl groups, their type, and their position, but a mixture of diethylbenzenes low in the para isomer and some of the polymethylbenzenes have not formed fission product extractants in routine tests. Nitration of the benzene ring does not produce Zr-Nb extractants.