Functional reliability analysis of a molten salt natural circulation system

The functional reliability evaluation of a molten salt natural circulation system, the nitrate natural circulation loop, was performed. Improved procedures based on the RMPS were applied, considering all the uncertainties to avoid a mass of epistemic uncertainties for an innovative system and introducing a systematic sensitivity analysis process. The system was modeled using Relap5-MS. An uncertainty analysis package of molten salt fluid, named NCUAPackage, was developed to deal with the source correlation parameters and model uncertainties inside the code. 229 samples of 43 input uncertainty parameters were propagated through Relap5-MS. The result functional failure probability of is 0.039 including two failure modes. Sensitivity analysis screened out the most important parameters and revealed that the observables and input parameters follow good linear relationships. An important finding is that the model uncertainty of the heat coefficient of NDHX shell side contributes a lot to the failure probability. It is necessary to consider the model uncertainty for the design and reliability analysis.