Abstract: The TRPO process, an independently developed high-level liquid waste (HLLW) treatment process in China, is primarily designed to address the treatment of the HLLW generated from the Purex process. Solvent extraction is used in the TRPO process to remove long-lived alpha nuclides from HLLW, thereby significantly reducing the technical difficulty of long-term deep geological disposal of HLLW vitrified waste forms. To align with the feed conditions of the TRPO process and reduce the process load, the HLLW requires adjustment in terms of volume, acidity, and metal ion concentration through evaporation concentration and denitration operations. However, this process is accompanied by three significant operational challenges: boilover, droplet entrainment, and precipitate accumulation. Boilover can cause equipment vibration, and in severe cases, it may lead to equipment damage and the risk of radioactive leakage. Droplet entrainment can result in excessive radioactive emissions in the exhaust gas, endangering environmental safety. Excessive accumulation of precipitates can cause equipment clogging and scarring on the reactor wall. This paper proposes a novel external circulation kettle for the evaporation and denitration of HLLW. The design of the kettle strategically separates the heating zone, evaporation zone, and denitration reaction zone through lengthening the external circulation pipe and optimizing the feeding position of the denitration agent (formic acid). Here the heater is arranged at the lower part of the external circulation pipe, and heat is transferred into the reactor through convection. Additionally, improvements such as the elimination of the reaction induction period, the incorporation of a built-in cyclone separator, and the implementation of a precipitate control structure effectively address the aforementioned operational challenges. Demonstration tests indicate that the kettle, with an inner diameter of 70 cm, achieves a processing capacity of 56 L/h, maintains an acidity fluctuation range of less than 0.1 mol/L, and demonstrates a decontamination factor of 8.6×10⁶ when cesium (Cs) is utilized as a tracer element. By promoting the precipitation of molybdenum ions with zirconium (Zr) ions, the Zr concentration can be reduced from 435.8 ppm in the feed solution to 85.5 ppm in the concentrated solution, with a Zr removal efficiency of 84.9%. Furthermore, when the concentrated solution is continuously subjected to heat preservation operation under total reflux mode (80-90 ℃ for 8 h; 96-98 ℃ for 7 h), the Zr concentration can ultimately be decreased to 11.8 ppm, achieving an overall Zr removal efficiency of 97.3%. These further confirm that the proposed novel external circulation kettle can satisfactorily meet the interfacing requirements with both the TRPO process and the Purex process, and it is also applicable to other similar operational units.