A Method and Code Approximating Macroconstants for VVER Reactors in Parameters Range Corresponding to Normal Operation

The paper presents a method and code approximating macroconstants for computation of VVER reactors when reactor parameters vary in the range corresponding to normal operation. Macroconstants are represented in the expansion series formally coinciding with the Taylor expansion of 7 variables. The number of expansion members is chosen to correctly describe the K-inf value of cell and its derivatives with respect to water density, water and fuel temperature, and concentration of dissolved boron. The interface of approximation module with the cell code WIMS-D4 is realized. Precision verification of this approximation is performed by the example of the VVER-1000 reactor cell. This test showed that the maximum approximation error in K-inf in two Xe-135 states (stationary and free of Xe-135) at the beginning of campaign did not exceed 0.05