The Uncertainty Analysis Of Nuclear Cross Section By Considering The Correlation Effects Among Nuclides

The uncertainty sources in nuclear physics are simplified theory models,the input parameters and the engineering parameters uncertainty ect..Nuclear data is the foundamental input parameter of nuclear physics,and its' uncertainty has already been one of the important uncertainty source in the nuclear physics calculation.The safety assessment methods based on the Best Estimate model is significant to improve the economic benefit of the nuclear plant.As an important part in Best Estimate,the uncertainty and sensitivity analysis has becoming an indispensable part of the research in new nuclear reactors and facilities.Therefore,the research on uncertainty analysisi of nuclear data is greatly significance for currently pressurized water reactor and the future reactor.Based on the sampling methods,taken the nonlinear problem in the effective resonance integral sampling process into account,the code SUACL has been developed to analyze the nuclear data uncertainty.The covariance data used in uncertainty analysis process is produced by NJOY,which is based on the ENDF/B-VII.1.Plenty of perturbation samples are generated through the perturbation on WIMS-69 multi-group cross section produced by IAEA.The transport calculation is completed by the DRAGON to analyze the uncertainty of nuclear data in the lattice calculation of pressurized water reactor.On account of the different covariance data in each Evaluated Nuclear Data Files(ENDFs),the influence of the covariance matrix based on the different ENDFs on the uncertainty of infinite multiplication factor Kinf in lattice calculation is analyzed.It is found that obvious difference occurred to Kinf uncertainty in condition of based on different ENDFs.Such as the capture cross section of 238U,compared with result of ENDF/B-?.1,the results deviation of JENDL-4.0 and JEFF-3.2 are 5.6%and 44.4%respectively.So it is essential to choose an appropriate ENDF in the uncertainty analysis procedure.Secondly,research of the nuclide correlation problem in the nuclear data uncertainty analysis has been implemented.There exist significant differences between uncertainty of multi-nuclide perturbation model and the independent parameter Synthesis Formula when nuclide pair(1H-235U;1H-238U)is peturbed,but closer to the results of the Synthesis Formula of relative parameter.This phenomenon can be attributed to the correlation between nuclides.The uncertainty deviation between the model and the Synthesis Formula of independent parameter decrease rapidly in the condition of multi-nuclides are perturbed simultaneously,Which indicates the existence of two opposite correlation(positive correlation and negative correlation)in the nuclides.The establishment of multi-nuclide perturbation model effectively reduces the sample size of total uncertainty analysis and greatly improves the efficiency of total uncertainty analysis.Finally,the code SCAC based on the reverse sampling method has been developed to analyze the sensitivity coefficients.The feasibility study of this method is carried out through the self-set example.Input the files generated from SUACL and to perform the sensitivity analysis of nuclear datas using sampling method.In conclusion,in the process of uncertainty analysis of nuclear data,it is necessary to select the cross section library accorded with produced cross section and the nuclide correlation.What's more,it has proved that the sampling method has the capability of analyzing the sensitivity coefficient through the feasibility test of reverse sampling method.