Abstract: Based on the precise measurements of the activity and component of fission products in the primary helium of 10 MW High-Temperature Gas-Cooled Reactor (HTR-10), the feature of the fission product released from the fuel element was analyzed, meanwhile, the failure fraction of the fuel particle or the U-contamination was directly deduced, and the radiation safety of HTR-10 was proved. The activity of inert gas nuclides in sample was experimentally measured, and the primary radioactivity was deduced. In the experiment ^85mKr, ⁸⁷Kr, ⁸⁸Kr, ¹³³Xe, ¹³⁵Xe, ^135mXe, ¹³⁸Xe, ⁸⁸Rb, ¹³⁸Cs were detected and measured. Through the comparison between the experimental results and the calculated ones, the U-contamination of graphite ball was obtained to be less than 5.7×10^－7.