Objective To verify the feasibility of microwave drying technology for tritium removal from spent molecular sieve, aiming to resolve the industrial problems of the massive accumulation and high disposal costs of tritium-containing spent molecular sieve generated during the operation of heavy water reactor.

Methods Cold simulation and hot radioactive tests were performed on the basis of an independently developed test equipment for tritium removal by microwave drying, which had a processing capacity of 500 g/batch. Cold simulation test used new molecular sieve provided by Qinshan Nuclear Power Plant Phase 3 to verify the processing capacity of the test equipment for tritium removal by microwave drying; optimize operating parameters; and analyze the mass fraction reduction rate, bound water removal rate, and thermal behavior characteristics of the dried samples. Hot radioactive test used spent tritium-containing molecular sieve provided by Qinshan Nuclear Power Plant Phase 3. Under strict radiation protection conditions, the change law of tritium activity concentration before and after tritium removal were analyzed.

Results The results of cold simulation test showed that the independently developed test equipment for tritium removal by microwave drying had stable processing performance, and its processing capacity of 500 g/batch met standards. Moreover, the volume of the dried molecular sieve significantly reduced to 1/2 of their original volume, the mass fraction of the samples decreased by 16.26%, and the bound water removal rate reached 8.25%, indicating that microwave drying effectively removed adsorbed and bound water. The results of hot radioactive test demonstrated that after microwave drying, the tritium activity concentrations of spherical (initial tritium activity concentration of 9.03×10⁴ Bq/g) and strip (initial tritium activity concentration of 3.58×10⁵ Bq/g) spent molecular sieves decreased to 236.00 and 746.17 Bq/g, respectively. Both values met the landfill limit for extremely low-level radioactive waste (<1000 Bq/g). The radioactive downgrading of waste was therefore realized.

Conclusion Microwave drying technology can efficiently remove tritium-containing water from spent molecular sieve, providing a new approach for the safe and economical disposal of low-level radioactive spent molecular sieve.