EFFECT OF HYDROGEN ON LOW-CYCLE FATIGUE RESISTANCE OF Zr-1%Nb CLADDING

When operated in aqueous coolant, zirconium fuel rod claddings absorb part of hydrogen formed during their oxidation. Hydrogen accumulated during the period of operation can affect the fatigue strength of zirconium claddings. This paper describes the low-cycle fatigue testing conducted on the samples 3 mm wide, cut out from Zr-1%Nb cladding tubes (circle divide 9.13 mm, wall thickness 0.68 mm), in as-received state (finish annealing at 580 degrees C, 3 hours, recrystallized condition), as well as on the samples cut out from the tube sections hydrogenated in gaseous hydrogen, formed during the TiH2 dissociation. Hydrogen concentration in the hydrogenated samples: 200 ppm and 500 ppm; temperature of the fatigue tests: 350 degrees C; oscillation frequency: 0.2 Hz; strain amplitude: 10(-3)...10(-2). Based on the results of the tests, fatigue curves were plotted for non-hydrogenated and hydrogenated Zr-1%Nb samples. It was established that at the temperature of 350 degrees C, the fatigue strength of hydrogenated samples is slightly higher. This may be due to the fact, that part of hydrogen that is in the solid solution increases the plasticity of zirconium and zirconium alloys.