Analysis of a hypothetical criticality excursion during misloading of a high-capacity spent-fuel cask

In recent years, a considerable amount of research has been devoted to the analyses of criticality excursions occurring in spent-fuel casks. Several analyses have been performed to determine the consequences associated with criticality excursions initiated as a result of fuel assembly movement during transport of spent fuel and water reflood of casks containing irradiated fuel pins. Recently, efforts to increase the capacity of casks by taking credit for fuel burnup in the design of new casks have been undertaken. Misloading a cask with fuel of higher reactivity than the cask is designed for (e.g., loading fresh fuel into a cask designed for burned fuel) can result in a criticality accident and a subsequent transient excursion. During the transient, the cask and fuel are cooled via natural convection by the water in the spent-fuel storage pool. This paper presents a simple analysis of the neutronic and thermal-hydraulic consequences associated with such a PWR accident scenario.