Nuclear safety relies heavily on the quality of the results of numerical simulation codes. Among the various components of the simulation of the installation are the pellet-cladding mechanical interaction (PCMI), and the peak cladding temperature (PCT). Although the correlations describing the physical, mechanical, chemical, and thermal phenomena that occur in nuclear installations have reached a high level of quality, there remain uncertainties on the final results due to uncertainties in the input parameters which cannot be eliminated. A realistic estimate of these uncertainties is necessary to evaluate the reliability of the simulation results.
When the best-estimate approach plus uncertainty (BEPU) is employed in the design of a nuclear installation, design-basis accidents are studied more realistically. This method must be used even in the design of research reactors because they are at the origin of any development of nuclear technology. We propose through this study an uncertainty and sensitivity analysis of PCMI and PCT of a heavy water nuclear research reactor fuel rod.
To determine the input parameters that influence PCMI and PCT, we utilize the FEMAXI-6 code. The thermodynamic table of the FEMAXI-6 code is adapted to the case of heavy water. Two system codes are used for uncertainty and sensitivity analysis: RELAP5 and PARET. The study confirmed that in the event of a shortage of heavy water, light water can be injected in its place to remove decay heat from the core and shut down the reactor safely. The safety margin between the PCT and the saturation temperature is reduced from about 10°C in the conservative approach to less than 1°C by the BEPU approach.