Research On The Rod Cusping Effect And The Stiffness-confinement Method For The Space-time Kinetic Equations

The measurement of the differential rod worth is one of the importantexperiments during the core star-up, the conventional measurementmethods include the boron dilution method and the relative scale method,another special measurement way is the dynamic measurement method ofWestinghouse Company. In conventional methods, in order to evaluatethe computer code and the loading pattern of the assemblies, thethree-dimensional core code will be used to monitor the experiment andcalculate the differential rod worth. While the dynamic scale methodneeds a fast calculation on the kinetic equations to get the relativeparameters. This essay consider two aspects, one is the rod cusping effectin the worth curve monitoring by the nodal core code, the other is thestiffness-confinement method on the kinetic equations.The essay begins with the nodal method and the analysis of thereasons of the rod cusping effect. The tool used for core calculation is thethree-dimensional analysis code PLUM, whose kernel theory isSemi-Analytical Nodal Method. The essay then describes some typicalmethods for the cuspping effect, and studies a new model, which gets thefine-mesh flux shape as well as the homogeneous cross sections and axialdiscontinue factors of the partially-rodded nodes from an extra onedimensional problem solving process. Numerical test is performed todiscuss the efficiency of the method based on the Qinshan-Yiqi core, therod movements both consider single group rod assembly moving andcoupled rod assemblies moving. Numerical result shows that the studiedmethod can effectively eliminate the rod cuspping effect, and is betterthan the approximate flux-volume weighted method.On the other hand, the dynamic measurement method developed byWestinghouse Company is very popular in industrial because its veracityand rapidness. This method requires a fast and exact way to solve the kinetic equations. Because of the intrinsic stiffness problem of theequations, the most widely used way to tackle the time variable is thetraditional backwards difference method. While the stiff-nessconfinement method is a special method compared to the traditional one.This essay will give a basic discussion on the main thought of thestiffness-confinement method, and use it to solve two one-dimensionaltest problems.