ANALYTICAL MODEL FOR TRANSIENT GAS FLOW IN NUCLEAR FUEL RODS.

The safety analysis of light water reactors considers creep deformation (Ballooning) of Zircaloy clad nuclear fuel rods. The driving force for clad ballooning is the internal pressure of the fuel rods relative to the coolant pressure. As ballooning occurs, the local internal driving pressure decreases unless there is gas flow to the region of deformation from a higher pressure region. If the gas flow is highly restricted then the cladding ballooning may be slowed by reduced local internal pressure. A realistic analysis of clad ballooning, presented in this paper, requires a space and time calculation of internal gas pressure.