The release fractions of the five elements in the ε-phase (99Tc,
97Mo, Ru, Rh, and Pd) as well as that of 238U are
reported for the reaction of two oxide fuels (ATM-103 and ATM-106) in
unsaturated tests under oxidizing conditions. The 99Tc release
fractions provide a lower limit for the magnitude of the spent fuel
reaction. The 99Tc release fractions indicate that a surface
reaction might be the rate controlling mechanism for fuel reaction under
unsaturated conditions and the oxidant is possibly
H2O2, a product of alpha radiolysis of water.