Compendium of Indian NPP material properties generated by RSD, BARC. Volume VII- Version 1: Zirconium alloys

Zirconium alloys are used for fabrication of core components of nuclear reactors due to their excellent strength, corrosion resistance in high temperature water environment and most importantly, the favorable neutronic properties such as very low cross-section for absorption of thermal neutrons. There are various types of alloys that have been developed over the last several decades in order to make them suitable for specific applications. For example, Zr2.5Nb alloy was developed for the pressure tubes of CANDU type PHWR by adding 2.4-2.6% of Nb into the Zirconium matrix in order to increase strength as well as reduce hydrogen pickup during the residence time of the material in the reactor. Similarly, Ziraloy2 and Zircaloy-4 contain Sn and other alloying element such as Fe and Cr in order to obtain better strength and corrosion resistance in high temperature reactor water environment. The content of Ni in Zircaloy-4 is almost eliminated in order to reduce the extent of hydrogen pickup by the fuel clad of PHWRs. In this work, three different types of alloys, namely, Zr2.5Nb, Zircaloy-2 and Zircaloy-4 have been used for evaluation of their mechanical, creep and fracture properties. For Zr2.5Nb, materials from both quadruple melted extruded-pilgered 540 MWe PHWR pressure tubes (Section 3) and forged 700 MWe PHWR pressure tubes (Section 4) have been used in the tests in temperature range of RT to 800°C. While the literature data for this class of material are available for longitudinal and transverse direction (flattened specimens), the novelty of the present work has been innovative design of un-flattened transverse, radial and shear specimens. Similarly, Zircaloy-2 from calandria tubes of earlier 220 MWe Indian PHWRs (Section 5) and fuel clad of BWR (Section 6) have been used in the present work. For Zircaloy-4, materials from fuel clad (section 7) as well as bearing pad plates (Section 8) have been used to evaluate mechanical and fracture properties at RT and service temperature of 300°C. It has been observed that the mechanical and fracture properties of Zirconium alloys are dependent upon orientation of either pressure tube or rolled-plate from which specimens have been manufactured. The orientation-dependent properties have been evaluated for different types of materials and the reason for the difference in the properties has been provided based on the texture and microstructure information of the alloys. A long-term research project has been undertaken in RSD, BARC to systematically study and quantify the mechanical, creep and fracture properties of different types of Zirconium alloys depending upon their specific application and this volume shall be updated once more and more data are available. (author)