Experimental evaluation of primary water chemistry for prevention of axial offset anomaly

A test loop was designed to simulate the operating conditions affecting the axial offset anomaly on the fuel cladding in nuclear power plants. In this study, accelerated simulation tests for deposit formation on the Zirlo cladding surface were performed in a solution containing varying amounts of Li and B with different concentrations of Ni and Fe. The amounts of formed deposit were relatively low in the non-boiling condition, while the amounts of formed deposit were increased in the zone in which the boiling occurred. The external surface showed numerous pores, and the thickness of deposits on the cut surface was approximately 20 μm. In addition, the commercial code, FLUENT 6, was applied to calculate the thermal-hydraulic analysis of nucleated boiling on the simulated AOA water chemistry. SEM, EDX and SIMS were used for surface analysis of the deposit, and the separated deposits were analyzed by ICP-AES and AAS. In conclusion, the water chemistry with operation conditions of 5.0 ppm Li and pH 7.4 was found to produce the least deposit formation on the fuel cladding surface. The current simulated tests may be applied for developing methods for preventing AOA in nuclear power plants.

This figure shows the summarized results of simulated experimental tests, A4–A11, with varying concentrations of H3BO3 and LiOH. When the initial concentration of Li was increased from 2.2 ppm to 5.0 ppm, the deposited amounts of Fe and Ni were dramatically decreased from 2.8 μm/cm2 to 0.5 μm/cm2. The deposited amounts of Ni and Fe were also higher in the test specimen that was operated at pH 6.9 rather than pH 7.4.Figure optionsDownload as PowerPoint slideHighlights
► A test loop was designed to simulate the effects on AOA with varying water chemistry.
► The amounts of formed deposit were increased in the boiling region.
► The water chemistry with operation conditions of 5.0 ppm Li and pH 7.4 was found to produce the least deposit formation on the fuel cladding surface.