UNCERTAINTY ANALYSIS FOR HOT CHANNEL

The fulfillment of the safety analysis acceptance criteria is usually evaluated by separate hot channel calculations using the results of neutronic or/and thermo-hydraulic system calculations. Traditionally, the evaluation is based on several conservative assumptions taking into account the uncertainty of input parameters and the large number of fuel rods in the core. In order to get more realistic results, an uncertainty analysis methodology was elaborated in the KFKI Atomic Energy Institute combining the response surface method with the one sided tolerance limits method of Wilks. In case of an ATWS event (inadvertent withdrawal of control assemblies), according to the conservative analysis, a number of fuel rods are experiencing DNB for a longer time and must be regarded as failed. Their number must be determined for a further evaluation of the radiological consequences. The results of conservative and uncertainty hot channel calculations are compared regarding to the number of failed fuel rods, the maximum clad surface temperature and the maximum fuel temperature