Hydrogen Pick-Up in Zirconium Alloys

The effect of hydrogen on Zr alloys used for fuel cladding is a very important problem from the point of view of reactor safety. Three kinds of experiments were carried out, the results of which can be summarized as follows.(1) Corrosion test: This test was performed to clarify the relation between coolant water conditions and hydrogen pick-up. The factors considered were the composition of the alloys (Zircaloy-2 and -4), as well as the gas content (oxygen, hydrogen and flourine ion), pH, temperature and pressure of the water. Among these, the amount of flourine ion and temperature were found to be the only factors that have appreciable effect on hydrogen absorption.(2) Hydrogen distribution test: The effect of alloying elements (Be, V, Y and Nb) on hydrogen distribution in Zircaloy under temperature gradient was examined. The shift of the hydrogen peak was observed to be influenced in different ways according to the alloying element added.(3) Mechanical test: The effect of hydrogen content on the mechanical properties of the alloys was studied. In tensile test, no appreciable effect of hydrogen content up to 300ppm, was observed. In burst test also, little influence of absorbed hydrogen on the burst strength of Zircaloy-2 tubing was discerned, but severer cracking in the tubing as well as increasing tendency toward brittleness was apparent with increasing hydrogen content.