Hydride Effect on the Burst Properties of HANA-4 and HANA-6 Cladding Tubes

Zirconium alloys have been used as nuclear fuel cladding material because they have satisfactory mechanical strength and corrosion resistance. As new alloys for high burn-up fuel in reactors is being required, KAERI has developed some Zr-based new alloys, called HANA alloys, for high burn-up fuel cladding material. The sample specimens of HANA-4 (Zr-1.5Nb-0.4Sn- 0.2Fe-0.1Cr) cladding tube material showed good performance in both corrosion and creep at the irradiation test up to 10GW/MtU in Halden test reactor. In addition to good creep performance, the other mechanical properties such as tensile, burst, fatigue are also required for the cladding to show the good performance in reactor. When a zirconium alloy is used in a nuclear reactor, hydrides form in it from not only external hydrogen sources such as waterside corrosion, dissolved hydrogen in coolant, water radiolysis but also internal sources such as hydrogen content in fuel pellets and moisture absorbed by the uranium dioxide fuel pellet. The terminal solubility of hydrogen in Zircaloy is about 150 ppm at 350 .deg. C which is near the coolant temperature of power reactor. But the local hydrogen content in the irradiated Zircaloy-4 cladding tube can be over 1000 ppm. Thus, hydrogen embrittlement of zirconium alloys has been extensively studied because hydrides may act as a sudden failure. The tensile strength of the HANA-4 cladding tube increased and tensile elongation decreased with the increase of hydrogen in it up to 500 ppm. To know the effect of hydrogen on the burst properties of HANA-4 and HANA-6(Zr-1.1Nb-0.05Cu) the cladding tubes at reactor operation temperature, the burst tests at 350±1 .deg. C were attempted on HANA-4 and HANA-6 as well as Zircaloy-4 (Zr-1.26Sn-0.23Fe-0.12Cr) and A (Zr- 1.0Nb-0.99Sn-0.11Fe) sample cladding tubes which have about 500 to 1200 ppm hydrogen