Uncertainty analysis on natural circulation characteristics under ocean conditions

Abstract

The stability of natural circulation is more susceptible to the uncertainties involved in the thermal-hydraulic process because the driving force is relatively small. Especially in the marine nuclear power plants, the complex ocean motions will introduce more uncertainties in the natural circulation operation. In this work, the joint probability distribution function of wave parameters was investigated, which provided a more realistic simulation of the ocean conditions. On that basis, it was applied to generate ocean motion parameters as uncertain input via the Metropolis-Hastings algorithm. A thermal-hydraulic code that is capable of simulating system behaviors under ocean conditions was developed to propagate the uncertainties. Additionally, the sensitivity analysis was carried out to identify the parameters that have a significant impact on natural circulation characteristics. Results show that the intense ocean motions will introduce large uncertainties in the natural circulation operation, especially at the startup stage. The rolling amplitude contributes the most on the natural circulation flow rate and the coolant temperature, while the heaving motions have less influence. Uncertainties introduced by the ocean motions will damage the natural circulation ability and stability, which need further considerations during the design optimization.