The Influence of Hydrogen on the Radiolytic Oxidation of UO2
Licentiate thesis, 2020

Spent nuclear fuel from the nuclear fuel cycle contains radiotoxic nuclides which must be safely stored for over 100 000 years. The Swedish final repository concept, KBS-3, is based on engineered and geological barriers that prevent the nuclear fuel from coming in contact with groundwater, which is the most credible vector to transport the radionuclides into the biosphere. In the safety assessment of a repository, the water intrusion scenario must therefore be investigated.

The UO2 matrix contains the majority of the long-lived radiotoxic elements. As the U(IV) form is highly insoluble, the release of the radiotoxic nuclides is largely governed by oxidation of the UO2 matrix into the much more soluble U(VI) form. Oxidation can occur due to the formation of radiolytic oxidants through the ionization or excitation of water molecules in contact with fuel.

Oxidation of UO2 pellets using external Am-241 sources was studied under conditions where the UO2 surface and the source were separated by 30 µm water. H2 was shown to suppress the surface oxidation as well as dissolution. This was shown by direct measurement of the surface oxidation state using XPS, as well as through concentration measurements in solution using mass spectrometry (ICP-MS).

Oxidative dissolution of 10 and 24 wt% Pu-doped MOX pellets was also studied under Ar and D2 atmospheres. The D2 atmosphere suppressed the uranium dissolution. However, corrosion of the stainless-steel materials present in the autoclave system was also observed. A calculation model was also developed for calculating dose-rates from α-doped UO2 based material.

Hydrogen Effect

Radiolytic Oxidation

Dose-Rate

XPS

UO2

MOX

HB4
Opponent: Dr. Olivia Roth

Author

Niklas Hansson

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

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

Journal of Nuclear Materials,; Vol. 505(2018)p. 54-61

Journal article

N.L. Hansson, P.L. Tam, C. Ekberg, K. Spahiu. XPS study of external α-radiolytic oxidation of UO2 in the presence of argon or hydrogen

N.L. Hansson, C. Ekberg, K. Spahiu. Alpha Dose Rate Calculations for UO2 Based Materials using Stopping Power Models

Subject Categories

Inorganic Chemistry

Materials Chemistry

Other Chemistry Topics

Areas of Advance

Energy

Materials Science

Licentiatuppsatser vid Institutionen för kemi och kemiteknik, Chalmers tekniska högskola: Ny Serie Nr 2020:01

Publisher

Chalmers University of Technology

HB4

Opponent: Dr. Olivia Roth

More information

Created

2/10/2020