The separation of trivalent lanthanides from actinides is one of the important steps in the selective partitioning of used nuclear fuel. However, these separations occur in the presence of a radiation field that degrades both ligands and solvents, potentially reducing the overall extraction efficiency. To quantitatively predict the impact of radiation under process scale extraction conditions, we have investigated the aqueous stability of one ligand that has shown promise for lanthanide/ actinide separations, 2,6-bis[(di(2-ethylhexyl) phosphino) methyl] pyridine N,P,P-trioxide (NOPOPO). In this study the stable products produced in radiolysis of NOPOPO, and two model analogues (2-methylphosphonic acid) pyridine N,P dioxide and 2,6-bis(methylphosphonic acid) pyridine N,P,P trioxide), have been determined. In addition the temperature-dependent reaction rate constants for the hydroxyl (.OH) radical reaction with these three species were also measured.