Peculiarities of Application of the Gas Extraction Method for Determination of Hydrogen Content in Samples of Irradiated Zirconium Materials

Abstract

Results of multiyear research of zirconium materials from nuclear reactors show that the hydrogen content measured by a high-temperature extraction method does not always correlate with the number and size of zirconium hydrides measured by metallography. Additional examinations found that hydrogen is contained not only in the metal but also in the oxide film of samples under examination. This means that the level of hydrogenation of zirconium materials under irradiation should be estimated by the hydrogen content in metal only to allow for a correct comparison of the results of gas analysis and metallographic investigations. In this connection, the hydrogen content was measured separately in the metal and in the oxide film. A device to mechanically remove sediments and oxide film from samples was developed. However, when removing the oxide mechanically, a top layer of metal is also removed, as a rule, which leads to an uncontrolled increase in the measurement error because of a nonuniform distribution of hydrides in the metal. The assessment of the contribution of oxide hydrogen using a curve “total hydrogen content vs. oxide film thickness” showed no distinct dependence. Moreover, it was stated that the results of the total hydrogen content measurements by the high-temperature extraction method can be affected by the elementary composition of sediments and oxide films on the surfaces of spent items. The performed research resulted in the development of a technique to measure the hydrogen mass fraction by high-temperature extraction in an inert gas flow separately in the metal and oxide film without any preliminary mechanical removal of the oxide. This will allow examining the dependence between the hydrogen content in the oxide film and its thickness, as well as estimating a possible correlation between the hydrogen mass fraction in the metal and the quantitative characteristics of hydrides measured by a metallographic image.