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The initial processing in nuclear fuel reprocessing is a key preliminary step that involves preparing spent fuel into a suitable solution for solvent extraction. Its main task is to separate the nuclear fuel core from the cladding material, thereby preventing impurities from entering subsequent separation processes and improving the overall efficiency of the process. 1. Core processing step: Mechanical shearing – This is carried out at a distance, within a shielded heat chamber, to cut the spent fuel assemblies into segments of about 5 cm in length, thereby exposing the fuel core. At the same time, the released fission gases are collected; it is essential to prevent spontaneous combustion of zirconium debris and the spread of aerosols, as noted in international academic research. Chemical dissolution: The sheared component segments are immersed in nitric acid, where the uranium dioxide core is selectively dissolved at a temperature near the boiling point; the zirconium alloy/stainless steel cladding does not dissolve. After rinsing and testing for residual fuel content, it is disposed of as solid waste. Feed solution pretreatment: Insoluble particles in the feed solution are removed through filtration or centrifugation; thereafter, the uranium concentration and acidity are adjusted, and sodium nitrite is used to stabilize plutonium in its easily extractable +4 valence state, resulting in a feed solution that meets the requirements for extraction. 2. Key technical requirements: Nuclear criticality safety controls must be strictly implemented throughout the entire process. Geometrically confined dissolution equipment should be used, along with remote operation and radiation shielding measures for the whole process, to ensure operational safety in highly radioactive environments.