TALL-3D open and blind benchmark on natural circulation instability

Abstract Design and safety analysis of the currently developed pool type liquid metal cooled fast nuclear reactors is currently impaired by limited operational experience for such systems and insufficient confidence in the predictive capabilities of the applied modelling. Understanding of pool-reactor thermal-hydraulics is crucial for assessment of reactor performance and passive safety systems reliability. Credibility of the analysis tools can be established in the process of code validation, which includes open and blind benchmarks against integral experiments. TALL-3D is a lead-bismuth eutectic (LBE) loop built to provide experimental data for validation of standalone and coupled system thermal-hydraulics (STH) and computational fluid dynamics (CFD) codes. This paper summarizes the results of the open and blind benchmark exercise, performed using experimental data on natural circulation instability in liquid metal flows from the TALL-3D facility. An approach for selection of experimental data for benchmark and tests for model input calibration is presented. A list of parameters, initial and boundary conditions are defined based on modelling limitations and sources of experimental uncertainty. A set of requirements and assessment criteria for the blind calculations were specified. Results of simulations are compared to experimental data. Implications of the benchmark test results for the codes validity and lessons learned are reported.