Radiochemical stability of imidazolium-based ionic liquids constituted of the BuMeIm(+) cation and associated with four commonly used anions (X(-): Tf(2)N(-), TfO(-), PF(6)(-) and BF(4)(-)) has been investigated under gamma irradiation for high irradiation doses (up to 2.0 MGy). The anion effect has been examined by quantifying the radiolytic yields of disappearance for cation and anions and by identifying corresponding radiolysis products with several analytical techniques. On the one hand, a large number of radiolysis products are formed throughout the irradiation in ionic liquid solutions, resulting from reactions of primary generated species of cation and anion by indirect radiolysis. Primary generated species can react together throughout the irradiation by indirect radiolysis to form numerous radiolysis products in small quantities, indicating that several complex degradation pathways are involved for these radiation doses. This degradation pattern has been confirmed by identification of numerous gaseous radiolytic products. On the other hand, quantitative studies show that radiochemical stabilities of ionic liquids are in the same range of values as systems envisioned in nuclear fuel reprocessing with relatively low hydrogen yields. Indeed, this present work emphasizes the suitability of ionic liquids for applications in the nuclear fuel cycle.

The stability of the ionic liquid [MeBu3N][Tf2N], dry or after contact with water (where [MeBu3N]+ is the methyltributylammonium cation and [Tf2N](-) is the bistriflimide anion), was studied under 137Cs gamma irradiation in argon and in air. In a quantitative study with an absorbed dose of 2 MGy this ionic liquid was highly stable regardless of the radiolysis conditions. The radiolytic disappearance yields determined by ESI-MS were -0.38 and -0.25 micromol J(-1) for the cation and anion, respectively. ESI-MS, NMR, and liquid chromatography coupled with ESI-MS identified a large number of degradation products in very small quantities for the same dose. The cation radicals were formed by the loss of a Bu group, the Me group, or two H atoms to form a double bond with the butyl chain. Radiolysis of the anion produced mainly F and CF3 radicals. The anion radicals recombined with the cation to form a wide range of secondary degradation products regardless of the radiolysis conditions.