A QUALITATIVE APPROACH TO UNCERTAINTY ANALYSIS FOR THE PWR ROD EJECTION ACCIDENT

In order to understand best-estimate calculations of the peak local fuel enthalpy during a rod ejection accident, an assessment of the uncertainty has been completed. The analysis took into account point kinetics parameters which would be available from a three-dimensional core model and engineering judgment as to the uncertainty in those parameters. Sensitivity studies to those parameters were carried out using the best-estimate code PARCS. The results showed that the uncertainty (corresponding to one standard deviation) in local fuel enthalpy would be determined primarily by the uncertainty in ejected rod worth and delayed neutron fraction. For an uncertainty in the former of 8% and the latter of 5%, the uncertainty in fuel enthalpy varied from 51% to 69% for control rod worth varying from $1.2 to $1.0. Also considered in the uncertainty were the errors introduced by uncertainties in the Doppler reactivity coefficient, the fuel pellet specific heat, and assembly and fuel pin peaking factors