Study Of The Uncertainty Propagation Method In Control Rod Worth Calculation

Control rods worth is an important reactor parameter,which directly influences reactivity control and reactor safety during operation.There exist many uncertainty factors when calculating control rod worth,such as nuclear data library,control rod manufacturing tolerance,calculating method,and reactor state changes.To optimize the nuclear reactor core design,an efficient calculation method for identifying and quantifying control rod worth uncertainty is urgently demanded.However,uncertainty analysis on control rod worth hasn’t been systematically developed successfully as other important parameters,e.g.,effective neutron multiplication factor,power distribution.So,it is extremely essential to probe into the propagation of uncertainty using a rational,efficient method in control rod worth calculation,so as to improve the credibility of control rod worth calculation.This paper identified the uncertain inputs during control rod worth calculation,and according to control rod worth calculating process,the uncertainty propagation method in control rod worth calculation was came up with based on high-order perturbation theory coupled with sampling method and statistical method.The relations between uncertainty sources and control rod worth can be presented visually when calculating the control rod worth using perturbation theory,which provide great basis to analyze control rod calculating uncertainty systematically.But when dealing with strong absorption,perturbation theory will introduce some error unacceptable.If we want gain more precise results of control rod worth,high-order perturbation theory should be applied to reduce the error to an acceptable level.In this work,control rod worth calculation method has been derived based on high-order perturbation theory,and then a control rod worth calculating code was developed.To verify the feasibility of this propagation method as well as the correctness of this control rod worth calculating method based on high-order perturbation theory,this paper established a simplified mini-core model according to CASL benchmark,and calculated control rod worth at different rod position using the self-developed code.The results shows,compared with traditional twice critical calculations,this calculating method can provide control rod worth with required accuracy according to different control rod step size.At the same time,with regard to macroscopic cross section,uncertainty of control rod differential worth has been quantified by employing sampling method and statistical method,verifying this uncertainty propagation method to be practicable initially.