[en] A new mathematical method was developed for the evaluation of data of thermocouples used for temperature monitoring in the primary coolant system of WWER-type nuclear reactors. The processes of in-core calibration of the thermocouples and the measurement of mixing factors of different primary cooling loops are combined. The numerical solution of the derived equations makes possible the determination of thermohydraulical mixings, the improvement of estimations concerning water and heat flow and the calibration of thermocouples based on the same measured data. The development of a FORTRAN program for the computerized solution of the equations is going on. (D.Gy.)