A new method for calculation of the rate of irradiated and unirradiated fuel oxidation by measuring the magnetic susceptibility is proposed. The specific magnetic susceptibility was measured by radio-frequency method. The rate of formation on was calculated from experimental data. Rate constants of reaction for temperatures 573 K and 623 K were obtained. The experimental results give an activation energy for formation . The rate constant of reaction for ordinary temperature (293 K) was found from obtained data. The results of this work indicate that oxidation process flows slower for irradiated fuel than for unirradiated one.