Abstract: The 2# cold trap replacement scheme in the primary loop of China Experimental Fast Reactor (CEFR) was introduced, including the design, construct and commissioning of the filling loop, the protective methods for safety in the filling procedure and the disposal of NaK waste. Filling of 447.4 kg NaK into the backup cold trap of CEFR and disposal of the waste NaK were completed successfully and safely. The results show that the method of filling NaK, the freezing and disassembling technique of the NaK loop connector, the cutting and sodium removing technology for the sodium pipes and the treatment for NaK waste are reliable and safe. Additionally, the protective measures for the safety of operators are suitable. Moreover, the technology introduced in the paper is applicable for the replacement of the 1# cold trap in the primary loop of CEFR.