[en] The dependence of in core self-powered detector (SPD) reading on local energy release in the WWER-440 reactor fuel assemblies is studied in a general form. The technique for determining relations between an assembly linear power and the signals of the detectors with rhodium emitters is suggested. The fuel assembly power is calculated on the base of the function determined as the ratio of energy release to the SPD signal, which depends on the fuel enrichment and burnup, coolant temperature and boron concentration in water. On the basis of preliminary computer calculations this function is represented in the analytical form with a few free parameters. The function parameters are found by the least square fit method on the basis of the data obtained during the reactor normal operation. It is concluded that determination of the parameters for the relation between the fuel element power and normalized detector signal is advisable to carry out periodically during NPP operation, particularly if new or modified neutron detector assemblies are installed