| Burst tents of the commercial low tin Zircaloy-4 tubes are performed at room and high temperature(400℃) in order to evaluate the degradation of mechanical integrity of the hydrided tubes. Experimental results show that UHS (Ultimate Hoop Strength) decreases exponentially in both cases as the hydrogen content increases. It is also found that when the hydrogen concentration increases up to 1,000 ppm, UHS decreases to 50% of its initial strength in the room temperature test while it decreases only by 20% in the high temperature test even when the concentration exeeds 2,000 ppm. It is revealed that TCE (Total Circumferential Elongation) and UBE (Uniform Burst Elongation) decreases drastically with increasing hydrogen content. Fractographical analysis with SEM (Scanning Electron Microscope) confirms the ductile-brittle transition in the TCE and UBE measurements. It is concluded that Zircaloy-4 tubes may possibly lose its ductility when hydrogen content exceeds 700 ppm by hydrogen pick-up during normal operation, especially, in the high burn-up and extended cycle. |
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