Research reactor’s fuel element integrity is essential for nuclear safety. In normal operations, radionuclides could be well contained in fuel element. Unfortunately, under severe conditions, the amount of radionuclides may increase, releasing to the primary coolant and, as a result, crack or damage the fuel element mechanically or chemically. Thus, it is imperative to help operators take measures effectively, locating damaged fuel assembly in reactor cores rapidly. In this paper, a quantitative fuel failure positioning method based on cesium (134Cs and 137Cs) detection was studied. An exact model to describe the relation between cesium radioactivity and fuel burnup based on nuclide conversion chain was put forward. Radioactivity measurement data has approved the validation of this method when it applied to HFETR. Moreover, based on the measurement of 24Na activity, we proposed an approach to identify fuel failures and cladding corrosion. The validation results further indicate the accuracy and good applicability of this method, that provides guarantee for the safe operation of HFETR.