Published: Jan 1979
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Under the condition postulated for a loss-of-coolant accident (LOCA), Zircaloy-4 fuel cladding may experience a temperature transient during which it absorbs an appreciable amount of oxygen from the coolant. Theoretical models for predicting cladding behavior during loss-of-coolant (LOC) are being developed, but until the failure mechanisms can be clearly established, an empirical criterion must be employed.
Since, under LOCA conditions, the fuel cladding would be predominantly exposed to tensile hoop stresses, the effects of oxygen on the tensile properties of Zircaloy-4 were investigated. It was found that, from room temperature to 800°C, the tensile properties were essentially independent of maximum cladding temperature and cooling rate, but were dependent on the oxygen distribution through the cladding wall.
On the basis of the present work, but also consistent with other published work, an interim oxygen embrittlement criterion is proposed, which states: “the oxygen concentration must be less than 0.7 weight percent over at least half the cladding thickness.”
Since the proposed criterion requires a prediction of the oxygen distribution for a given temperature transient, the available computer models are briefly described and compared with experiment. Preliminary results suggest that the prediction of OXWEX, SIMTRAN 1, and PRECIP 1 are in reasonable agreement with experiment.
oxidation, temperature transient, zirconium, ultimate tensile strength, embrittlement
Senior research officer, Materials and Component Development Branch, Whiteshell Nuclear Research Establishment, Pinawa, Manitoba