The Study Of The Sensitivity Calculation Of The Theoretical Model Parameters And The Covariance Evaluation For The Fast Neutron Reaction Cross Sections Of Zirconium

Recently, with the development of nuclear power, great amounts and various kinds of nuclear data are comprehensively required in the current nuclear study. Among these data, covariance of the evaluated neutron cross sections are directly related to the economy and security of nuclear device, especially, it’s one of the most important items in the present study of the fourth generation nuclear reactor. Correct covariance of nuclear reaction cross section is very helpful to adjust the microscopic nuclear reaction cross sections within a reasonable range so as to reduce the uncertainties of the integral parameters. However, because the covariance evaluation involves a lot of theoretical and experimental knowledge, the relevant evaluation methodology has become one of the most difficult and hottest issues in the field of nuclear data since1970s.Zirconium (Zr) alloy is an ideal structural materials in the nuclear reactor design, while the covariance data of Zr is still absent in Chinese evaluated nuclear data library (CENDL). Therefore, the main purpose of this thesis is to evaluate thecovariance of n+Zr cross sections for CENDL. The work is based onthe theoretical model parameters utilized in the latest CENDL3.1(released in2009) and the analysis of the new experimental dataand the deterministic least squares covariance calculation method.At first, the program-SEMAW was applied in this work tocalculate the sensitivities of the theoretical model parameters forn+90,91,92,93,94,95,96Zr, all parameters were adopted from CENDL3.1. It isdeserved to mention here that SEMAW is the newly developed codein China Nuclear Data Center (CNDC) to calculate the modelparameter sensitivities to the nuclear reactions cross sections forstructure nuclei. In this work,11reaction cross sections of n+Zrand36key parameters concerned in optical model, compoundnucleus model and direct reaction model were discussed at thesame time. Then, some important items such as the steps in thenumerical derivatives and the selections of sensitive parameterswere obtained after discussion. This calculation is mainly aimed toprovide the necessary sensitivity matrix (F) to the covariancecalculation using least square approach.Next, we focused on the covariance evaluation of two chiefneutron emitted reactions (n,2n) and (n,inl) for the most abundantstable isotope90Zr whose abundance is51.45%. Because a lot ofexperimental data of90Zr(n,2n)89Zr are available in the ExperimentalNuclear Reaction Data library—EXFOR, we collected all thosereported measurements in EXFOR and performed a systematicresearch to their error information, including the statistical errorsand various systematic errors sourced from neutron flux, sample, monitor cross sections, detector and activation data of residualnucleus, etc. in activation measurement, and the correlation ofthese errors. Finally, we achieved the covariance (Vn,2n) fromexperimental data based on the analysis above and the owncharacters of90Zr(n,2n)89Zr.Due to the absence of measurement, the deterministic leastsquare method was employed in this work to generate thecovariance of90Zr(n,inl)90Zr. This calculation was performed basedon the sensitivities Fn,2nand covariance Vn,2nobtained in ourprevious work. After derived the covariance of model parameters(Vc), we got the expected covariance of the inelastic scatteringcross sections (Vn,inl) using Vcand sensitivities Fn,inl. This covarianceevaluation incorporated the information from the model parametersuncertainties and the experimental errors of (n,2n) at the same time,that was because the cross sections of90Zr(n,inl)90Zr in CENDL3.1was just originated from the theoretical calculation with theguidance of the existing experimental data.In conclusion, different approaches were utilized to evaluatethe covariance data according to the different types of reactions.The applied methods in this thesis are also suitable to thecovariance evaluation of other nuclei and reactions. Covariancedata of90Zr will be included in CENDL and applied to the design ofChinese fourth generation nuclear reactor and the comparison withother international covariance work.