Hydride embrittlement and irradiation effects on the hoop mechanical properties of pressurized water reactor (PWR) and b
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DUCTION
ZIRCALOYS*
are used as cladding material in the
*ZIRCALOY is a trademark of INCO Alloys International, Huntington, WV.
nuclear industry for fuel elements. Their mechanical properties can be drastically affected by the presence of hydrides, which form when hydrogen content exceeds the terminal solid solubility.[1–7] It has been found, at room temperature, that ZIRCALOYs undergo a ductile-to-brittle transition when the hydrogen content (hydride volume fraction) in the specimen is higher than some critical value.[1–6] Final heat treatment of the material can shift this transition considerably.[1,3] It can be stated that, based on the previous investigations, there is a direct correlation between this transition and the microstructure and the hydride morphology. The investigations have been limited to low and medium hydrogen content and on the ZIRCALOYs with a relatively gross microstructure up to now. It would be very interesting to examine the hydride embrittlement sensitivity in materials issued from different thermomechanical treatments. The understanding of the damage and fracture mechanisms would contribute to the research and development in order to improve the properties of ZIRCALOYs through advanced compositions and thermomechanical processing, and to optimize the microstructure within the corresponding specifications. On the other hand, it was reported that hydrides in
irradiated material may reduce ductility below the values induced by irradiation alone, particularly if the hydride distribution is nonuniform.[8] Siemens data, according to Reference 9, indicate that even up to 2000 ppm, hydride does not decrease the ductility of irradiated ZIRCALOY. The difficulty in drawing conclusions from the data reported, however, arises from the fact that the reported ductility of irradiated materials is very sensitive to the sample geometry and the testing method.[9,13] In this series of articles, Part I is concerned with the general influence of hydride on the mechanical properties of ZIRCALOYs at two temperature (20 ⬚C and 300 ⬚C) and for hydrogen content up to 4500 ppm. A novel ring tensile test will be used to obtain a gauge length in which the hoop strain and stress are almost uniform.[10,11] The damage and fracture mechanisms will be investigated by scanning electron microscopy (SEM) fracture surface and profile observations with special attention given to the ductile-to-brittle transition as a function of the hydrogen content at two temperatures. The macroscopic behavior of the hydrided ZIRCALOYs is then correlated to the damage and fracture mechanisms by appropriate mechanical modeling. The results reported in Part II[12] and Part III[13] of this series of papers will be used to provide some insight into the understanding of the influence of hydrides on mechanical properties of ZIRCALOYs. II. EXPERIMENTAL PROCEDURE
S. ARSENE, formerly Ph.D. Student with Lab. MSS/MAT, Ecole Centrale Paris, is Research Engineer, Pechiney CRV SNMT, 38341 Vorepee, Cedex, France. J.B. BAI, CNRS Researcher, and P. BOMPARD
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