Challenges And Progress Of Uncertainty Analysis For The Pebble-Bed High-Temperature Gas-Cooled Reactor

There has been increasing demand for uncertainty quantification (UQ) in the nuclear engineering community. Thus far, most uncertainty analyses have focused on light water reactor (LWR). As an innovative reactor, the pebble-bed high-temperature gas-cooled reactor (PB-HTGR) features a continuous-fuel-cycling operation strategy and a movable core, which means the uncertainty analysis methods used for LWRs cannot be directly applied to the PB-HTGR. In this work, we summarize recent progress in the uncertainty analysis of the PB-HTGR at the Institute of Nuclear and New Energy Technology, Tsinghua University. We propose a framework for uncertainty analysis based on the well-developed, practical design of the PB-HTGR program system. In this framework, the uncertainty sources are divided into different components and steps, and the maximum fuel temperature in a depressurized loss of forced cooling accident is chosen as the final uncertainty output parameter. However, not all the issues are resolved as this system involves a complex combination of many physical and thermal factors. To date, within this framework, several milestones have been achieved in the PB-HTR uncertainty analysis. (1) We have developed the uncertainty analysis tool VSOP-UAM (very superior old program-uncertainty analysis in modeling), which uses a statistical sampling method. Using VSOP-UAM, we have achieved the uncertainty analysis of the equilibrium state, which is the typical state of the PB-HTGR, for the first time. (2) Using the VSOPUAM analysis tool, we have determined the uncertainty propagation of the nuclear cross-section data, fission product yields, and key structural parameters. (3) To determine the UQ of the fission product yields, we developed an advanced sampling method that prevents the sampling of non-physical negative samples. (4) To facilitate a benchmark definition and UQ for the PB-HTGR, studies have also been conducted under the auspices of the Coordinated Research Project on High-Temperature Gas-Cooled Reactor Uncertainty Analysis in Modeling, launched by the International Atomic Energy Agency.