Dimensional changes of the fuel and the resulting cladding integrity problems under irradiation

This paper describes two experiments, one dealing with clad overstraining failures and the other with fuel densification. The two series of experiments (IFA-229 overpower experiment on high burn-up fuel rods, and IFA-401 fuel densification experiment) have demonstrated the existence of two different fuel performance problems. When viewed individually, it appears rather simple to avoid both. However, they are associated with two opposite effects, the overstraining failures to fuel expansion and the fuel cladding collapses to fuel contraction. It is natural therefore that design changes introduced to avoid one of the problems will result in an adverse effect relative to the other