An Experimental Study on the Influence of Gamma Radiation on Spent Fuel Dissolution in the Presence of a H2 Atmosphere

Javier Quiñones, Jose Manuel Cobo, Ángel González de la Huebra, Aurora Martínez Esparza

Any environmental performance assessment of spent fuel disposal requires a prediction of the spent fuel matrix alteration rate when contact with groundwater is established. Taking into account the disposal design the groundwaters at the expected depth of the vault are generally reducing. These reducing redox conditions near the spent fuel surface may be changed to oxidising ones by the radiolysis of water, due to radiation associated with the waste.

This study is focussed on the determination of the influence of the g radiation on the spent fuel matrix alteration rate. So a set of sequential leaching experiments under fixed conditions have been done.

The experiments simulate the repository environmental conditions when engineering barriers are degraded and groundwater arrives at the surface of the spent fuel. In these experiments SIMFUEL was used as analogue of the spent fuel. Two types of leachant,

  1. i.e., granitic water and
  2. bentonic-granitic water
were used in the sequential leaching experiments. The initial reducing conditions were simulated using three types of controlled atmospheres:
  1. 1 bar Ar,
  2. 2 mbar Ar and
  3. 1 bar H2.
SIMFUEL powder was the specimen used with a distribution size of 50 – 32 mm.

These experiments were irradiated in the gamma industrial irradiation facility (emplaced in Ciemat, labelled Nayade). The g dose rate (of a 60Co source) applied to the set of experiments was 14.2 mGy/s-1. This value simulates to the g dose date of the spent fuel with a burnup of 40 MWd/kg-1 U and around 50 years of cooling time.

The results obtained show a different behaviour as a function both of

In any case, [U] in leachates achieves values higher than those expected for reducing conditions. More specifically,

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Paper #: CC9.6