The interaction of molecular hydrogen with α-radiolytic oxidants on a (U,Pu)O2 surface
Journal article, 2018

In order to assess the impact of α-radiolysis of water on the oxidative dissolution of spent fuel, an un-irradiated, annealed MOX fuel pellet with high content of Pu (∼24 wt%), and a specific α-activity of 4.96 GBq/g MOX , was leached in carbonate-containing solutions of low ionic strength. The high Pu content in the pellet stabilizes the (U,Pu)O 2 (s) matrix towards oxidative dissolution, whereas the α-decays emitted from the surface are expected to produce ∼3.6 × 10 −7 mol H 2 O 2 /day, contributing to the oxidative dissolution of the pellet. Two sets of leaching tests were conducted under different redox conditions: Ar gas atmosphere and deuterium gas atmosphere. A relatively slow increase of the U and Pu concentrations was observed in the Ar case, with U concentrations increasing from 1·10-6 M after 1 h to ∼7 × 10-5 M after 58 days. Leaching under an atmosphere starting at 1 MPa deuterium gas was undertaken in order to evaluate any effect of dissolved hydrogen on the radiolytic dissolution of the pellet, as well as to investigate any potential recombination of the α-radiolytic products with dissolved deuterium. For the latter purpose, isotopic analysis of the D/H content was carried out on solution samples taken during the leaching. Despite the continuous production of radiolytic oxidants, the concentrations of U and Pu remained quite constant at the level of ∼3 × 10-8 M during the first 30 days, i.e. as long as the deuterium pressure remained higher than 0.8 MPa. These data rule out any oxidative dissolution of the pellet during the first month. The un-irradiated MOX fuel does not contain metallic ε-particles, hence it is mainly the interaction of ra diolytic oxidants and dissolved deuterium with the surface of the mixed actinide oxide that causes the neutralization of the oxidants. This conclusion is supported by the steadily increasing levels of HDO measured in the leachate samples.

Author

Lovisa Bauhn

Chalmers, Chemistry and Chemical Engineering, Energy and Material, Nuclear Chemistry

Niklas Hansson

Chalmers, Chemistry and Chemical Engineering, Energy and Material, Nuclear Chemistry

Christian Ekberg

Chalmers, Chemistry and Chemical Engineering, Energy and Material, Nuclear Chemistry

Patrik Fors

Vattenfall

Rémi Delville

Belgian Nuclear Research Center

Kastriot Spahiu

Swedish Nuclear Fuel and Waste Management Company

Chalmers, Chemistry and Chemical Engineering, Energy and Material, Nuclear Chemistry

Journal of Nuclear Materials

0022-3115 (ISSN)

Vol. 505 54-61

Subject Categories

Other Chemical Engineering

Other Chemistry Topics

Bioenergy

DOI

10.1016/j.jnucmat.2018.04.006

More information

Latest update

5/9/2018 1