Uncertainty Analysis In Physical Calculation Of Pebble Bed HTR

The research on the uncertainty of physical calculation is popular and difficult in the physical analysis of the reactor.After continuous development and research,the uncertainty analysis of the light water reactor（LWR）has been mature.In terms of high-temperature gascooled reactors,the large amount of graphite,unique coated particle design,and higher operating temperature all make the uncertainty quantification method of the high-temperature gas-cooled reactor significantly different from that of the light water reactor.In order to provide guidance for subsequent optimization design,it is needed to find important sources that affect the calculation uncertainty of high-temperature gas-cooled reactors.As a result,it is necessary to research on the uncertainty of physical calculation of the pebble bed high temperature gascooled reactor.This paper focuses on the impact of the unique core design of the pebble bed high temperature gas cooled reactor on the calculation of eigenvalues and the uncertainty of nuclear data propagation.Based on the HTR-10 fuel pebble information,ten fuel pebble models were established.Based on the HTR-10 core information and three core states,six core models were established.Based on the PBR-250 fuel pebble information,five fuel pebble models and four body-centered cubic models representing the relationship between fuel pebbles at different positions in the reactor core are also established.At fuel pebble scale,the different fuel pebble models were used to study the eigenvalue calculation uncertainties introduced by TRISO particles filling rate and random dispersion of TRISO particles.And the influence of different fuel pebble models on eigenvalue calculation and neutron spectrum.The effects of different fuel pebble models,different temperatures,different materials,and different relative covariance libraries on the uncertainty of nuclear data propagation were also studied,and a mechanism analysis was performed.At reactor core scale,the effects of different body-centered cubic models on eigenvalue calculation,neutron energy spectrum,and uncertainty of nuclear data propagation were studied.And analyzed different temperature distribution,material composition,and different relative covariance databases for the mechanism of uncertainty differences in nuclear data propagation in depth based on the established HTR-10 reactor core model.The eigenvalue calculation results show that the uncertainty introduced by the random distribution of the TRISO particles in the fuel pebble model for the eigenvalue calculation is about 40 pcm,which is far less than the uncertainty propagated by the nuclear data.Fuel pebble high-fidelity models,regular lattice models,and RPT models have very close eigenvalue calculation results and neutron spectrum results,indicating that under certain circumstances,regular lattice models and RPT models can be used instead of high-fidelity models for physical calculations.The results of the uncertainty of nuclear data propagation indicate that an increase in temperature will lead to a decrease in eigenvalues and an increase in the uncertainty of nuclear data propagation,and the nuclear reaction that has the greatest effect on the uncertainty of nuclear data propagation is the average number of neutrons emitted per fission event of ²³⁵ U.