An experimental program to study solvent degradation in the New Separation Plant at Windscale is reported. To determine solvent life, TBP/odorless kerosene was recycled through an extraction, backwash, 1 and solvent process system having similar residence times to those proposed for the design. Radiation was provided in a single stage by a strontium 90 source. The experiment has been used to predict the effects of solvent degradation, as measured by Zr/Nb distribution, on the first cycle of purification and solvent washing. Examination of this degraded solvent from the recycle experiment by infrared analysis showed the presence of C=0, and N03 groupings, but no other groups were identified. Batches of solvent were degraded in a high γ-field at doses up to 125 watt-hr/liter in contact with nitric acid and uranyl nitrate, and were found to give high Zr/Nb retention in a standard Z2 test, whilst the retention of Ru was found to be small with irradiations up to 35 watt-hr/liter; at 60 watt-hr/liter significant retention of the Ru was noted. The G-values for production of compounds containing carbonyl, carboxylic acid, nitrate and nitrogroupings were determined in this series of irradiations. Synthetic long chain (C12) ketones, carboxylic acids, nitro compounds, nitrites, nitrates, olefines, hydroxamic acids, nitro alcohols, and short chain (C4) nitrolic acids have been examined as possible ligands. Of these, only the hydroxamic acids give powerful retention of activity, and the zirconium complexes were sufficiently stable to withstand the extraction and washing conditions. Comparison of the batch degraded trials and the recycle trials showed that the pattern of products detectable by infrared analysis differed. The removal of ligands by the normal alkali washes used in the New Separation Plant has been compared with that obtained with alkanolamines, alkaline permanganate, and fluoride solutions, and with purification by distillation techniques.