Fuel Pellet-Cladding Interaction:

Fuel pellet-cladding interaction (PCI) might lead to cladding failure and following release of fission products into the reactor coolant. Pellet-cladding interaction PCI appears to be a complex phenomenon which tends to occur under power ramping conditions. The expansion of the fuel pellets due to high internal temperatures, cracking because of thermal stresses, and irradiation-induced swelling might lead to contact of the fuel along with the cladding. Chemical, Thermal, and mechanical interactions might then occur that, if not around accounted for in the design, might lead to cladding failure. Design features to counteract PCI involve the following.

a.  an increase in the cladding thickness
b.  an increase within the cladding-pellet gap along with pressurization to avoid cladding collapse
c. the introduction of a layer of graphite or other lubricant among the fuel and the cladding Operational limitations like as rate of power increase and power for a provides power ramp rate are imposed to lessen the effect of pellet-cladding interaction. Pellet-cladding interaction appears to be more likely to occur during initial power increase and could be extremely costly if cladding failure occurs.