Study on the monitoring technology of radioactivity in primary sodium of fast reactor

Primary sodium in fast reactor has a high radioactivity. The radioactive nuclide can't be detected by gamma spectrometer directly. An on-line radioactive monitoring technology was introduced in this paper. A series of collimators that could be disassembled and assembled were designed. Collimators were disassembled to increase detection efficiency while assembled to decrease dead time effects. Point source simulation method was used to calibrate the efficiency of gamma spectrometer. The energy range of the 6 standard point sources had covered the energies of all the interest nuclides. The monitoring results of primary sodium in China Experimental Fast Reactor adopted by this technology showed that the first three radioactive nuclides at the present stage were ²⁴Na, ²²Na and ¹²⁴Sb, respectively. By the efficiency calibration in this study, the radioactivity of ¹²⁴Sb was in the order of 10⁴ Bq/g. (authors)