A simulation approach for start-up without secondary neutron sources of Hualong One: A Monte-Carlo-deterministic framework

Since secondary neutron sources in Pressurized Water Reactors (PWRs) continuously produce tritium, the technology of replacing these sources with spent fuel assemblies has been proposed to reduce such emissions. To this end, this study introduces a Monte-Carlo-Deterministic coupling simulation approach for the Hualong One start-up without secondary neutron sources, utilizing NECP-MCX and Bamboo-C. Firstly, the Monte Carlo model was refined by criticality calculation and the thermal neutron sensitivity coefficient of the detectors was then calibrated. The approach was subsequently validated through analysis of the calibration experiments utilizing secondary neutron sources during Cycle 2 fuel loading process. Finally, the count rate of ex-core source-range detectors with spent fuel assembly neutron sources was predicted. The results indicate that the maximum relative error of the source-range detector count rate during the Cycle 2 calibration experiments is 11.11 %. The results further predict that placing a spent fuel assembly with a burnup of 29.39 GWd/tU at position R06 or R08 within the reactor core will satisfy the requirements for the Hualong One start-up. In summary, the simulation approach presented in this paper provides theoretical support for the Hualong One start-up in the absence of secondary neutron sources and contributes to reducing tritium emissions.