Evaluation of Zircaloy-2 cladding corrosion characteristics by simulated BWR corrosion loop test

The effects of irradiation heat flux and void fraction on the corrosion behaviour of Zircaloy-2 cladding tubes were studied in an in-pile loop in Halden. The loop was designated to operate under typical coolant chemistry and thermohydraulic BWR conditions. Local radiation effects (shadow corrosion) on the cladding corrosion were evaluated by use of rings of platinum and hafnium, which served as β- and γ-emitters, respectively. Test materials were of an early BWR 8x8-type and a new more corrosion resistant BWR 9x9-type cladding. The first tests were performed with pellets of UO2 and Al2O3 in the tubes of the test materials during 180 days irradiation. The second test was performed with only Al2O3 pellets in the tubes. The corrosion behaviour of the test materials were characterised by destructive and nondestructive PIE, SEM and metallography. Nodular corrosion appeared on the 8x8 RJ-type, while a uniform oxide layer was formed on the 9x9 type. The β-emitters enhanced uniform oxide formation on the 9x9-type tubes, while nodular corrosion was enhanced on the 8x8-type. However, a second test showed a high γ-ray peak also enhanced uniform corrosion on the 9x9-type tube. The corrosion behaviour was more affected by the β-emitters than γ-emitters, heat flux and void fraction. Neutron flux, γ and β rays were computer analysed and the effect of the irradiation on the corrosion behaviour was discussed. A question was raised whether the Pt and Hf rings were insulated from the water, but they were in direct contact with water. Another question concerned the size relationship between ring and its effect - it was the same size as the ring