Abstract: A detect system was developed for the fuel elements with shutdown of more than 4 months and that can not be taken out from water and tested for the damage of fuel element cladding. The high temperature water is used by the system to heat the fuel element to release the radionuclide, and pressure changes are applied to accelerate the radionuclide release, and then the content of ¹³⁷Cs and ⁸⁵Kr is collected and detected to determine whether the fuel element is damaged. The results show that the system can conduct the damage detection of fuel element cladding without taking the fuel out from water, and has the characteristics of convenient, fast and accurate.