Redox chemistry of plutonium and plutonium surrogates in vitrified nuclear wastes

Lanthanide borosilicate glasses containing Pu and the nonradioactive analog element Ce were subjects of an x-ray absorption spectroscopy investigation to quantify the +3/+4 ratio of these redox-sensitive elements. The data show that the dominant oxidation states are +4 for Pu and +3 for Ce. The data also indicate that the reductive potential of glasses can be quantified from a solution chemistry method adapted to glass chemistry, although allowances must be made for glass composition. These data can therefore be used to formulate glass compositions and processing schedules that lead to a controlled oxidation state of Pu in melts. Furthermore, the data show that Ce is a poor analog for Pu behavior in melts and that the suitability of surrogates can be assessed by the evaluation approach presented here. The method demonstrated in this paper can be used to estimate the oxidation states of a range of multi-valent elements as functions of temperature and composition with data from only a single redox couple.