Toward development of a low-temperature failure envelope of cases for high-burnup RIAs under PWR operational conditions

Abstract

A Reactivity-Initiated Accident (RIA) is a design-basis accident that occurs when the reactor loses one of its control rods. A reactivity insertion will follow such events, drastically increasing the fuel pellet’s temperature and volume due to thermal expansion. The fuel pellet and the cladding will interact mechanically, which could lead to cladding failure. This work presents the development of cases where low-temperature failures are more likely to happen for high-burnup fuels under PWR operational conditions. A coupled computational model between the nuclear fuel performance code BISON, MOOSE’s Thermal-Hydraulic Module (MOOSE-THM), and MOOSE’s Stochastic Tools Modules (MOOSE-STM) was created to study the thermal-hydraulic behavior of a high-burnup fuel rodlet during the first stages of an RIA transient, allowing us to identify three scenarios: the system reached CHF, leading to high-temperature failure, the system failed due to PCMI, or the system survived the whole transient without failing. To address these scenarios, we performed a sensitivity analysis with more than 140,000 model replicates through MOOSE-STM varying parameters such as the power pulse width, power pulse total energy deposition, hydride rim thickness, coolant inlet temperature, and coolant inlet mass flux. We also compared two PCMI failure criteria in our analysis. Our results suggest that the hydride rim thickness and the power pulse width will be the key parameters impacting the failure type our system would undergo during the power transient. Using the data from our simulations, we constructed two failure maps, one for each PCMI failure criterion, showing how the failure type is affected by each parameter considered in the sensitivity analysis. We also provided a closed-form expression for the boundary between the PCMI and CHF failure types as a function of the hydride rim thickness and power pulse width.