Fuel and cladding interaction, irradiation results. Analysis of SNR-typical fast flux experiments

In oxide fuel pins of SNR-typical irradiation experiments two types of clad inner corrosion were observed: matrix attack and intergranular attack. The experimental results show that the temperature of the fuel cladding interface has a significant influence on the depth of cladding attack. The temperature dependence of the cladding attack is characterized by a threshold temperature above which inner corrosion begins, a temperature range of rapid increase proportional with increasing temperature (resulting from- the described analysis) and by a temperature range up to 700 deg. C of saturation of the corrosion attack. Both threshold temperature and average as well as maximum values of corrosion depth also depend on initial fuel stoichiometry. The corrosion depth tends to diminish with lower fuel stoichiometry. For stoichiometric fuel the maximum corrosion depth does not exceed 120μm with a 2σ-confidence level. This statement is valid for burn up ≤10 % and clad inner temperature ≤700 deg. C. (increase of cladding attack above this experimental range is not excluded). No differences in resistivity against inner corrosion could be detected for the in-pile tested cladding materials. The burnup influence in the range of 5-10% is not significant