Dissolution Behavior of M5 Cladding in Hydrofluoric–Nitric Mixed Acid

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Abstract
M5 cladding has emerged as a prominent fuel cladding material due to its excellent corrosion resistance. The dissolution behavior of M5 cladding is critical in both the initial cleaning stage and the reprocessing of spent fuel cladding. This study investigated the dissolution of M5 cladding in hydrofluoric–nitric (HF-HNO3) mixed acid at varying concentrations. When the HF concentration exceeds 0.5 mol/L, the addition of strong oxidizing HNO3 significantly reduces the dissolution rate. Moreover, HNO3 effectively inhibits the HF-induced corrosion pitting, lowering surface roughness to 0.812 μm at a 1:5 ratio of HF:HNO3. In addition, a surface structural analysis reveals the dissolution mechanism of M5 cladding. The β-Nb precipitated in the mixed acid was oxidized to stable Nb2O5 by HNO3 while the M5 matrix surface was continuously oxidized to ZrO2. This passivation layer inhibits further dissolution, slowing the process and enhancing the uniformity of M5 cladding.
Funding Information
  • National Key Research and Development Program of China (2022YFB4603000)

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