[en] The various power-ramp tests have been conducting by using BOCA/OSF-1 facility installed in JMTR for the safety research of LWR fuels. In the power-ramp tests, it is important to evaluate the linear heat rate of the fuel rod accuratelly during the tests for obtaining the threshold of the fuel failure, etc. In this paper, the method and its accuracy for evaluating the linear heat rate of the fuel rod was examined. As the method for evaluating the linear heat rate, we used the method with evaluating only the outlet temperature of the OSF-1 coolant, instead of the ordinary calorimetric method, i.e. the method using the flow rate and the temperature difference between the inlet and the outlet of the OSF-1 coolant because the inlet temperature of the OSF-1 coolant is unstable. The accuracies in evaluating the linear heat rate of the fuel rod are +-6.5 % at 300 W/cm and +-4.5 % at 600 W/cm, respectively. (author)