Studies on deposition of corrosion products on zircaloy heat transfer surface with emphasis of high-temperature chemical behavior of dissolved hydrogen

Abstract

The present work aims at investigating the deposition behaviour of metal oxides on Zircaloy heat transfer surface in an attempt to reduce the deposition of corrosion products on fuel cladding in the nuclear reactor coolant system. In addition, high temperature chemical behaviour of dissolved hydrogen was examined. Chapter III looks at the deposition behaviour of corrosion products on the Zircaloy heat transfer surface under four different kinds of experimental factors: the oxidation state of Zircaloy, dissolved hydrogen, the pre-deposited iron oxide, and ferrous ions. First, the effects of the oxidation state of Zircaloy and dissolved hydrogen were evaluated by measuring the amount of the iron oxide deposited on two kinds of Zircaloy surfaces. Second, the effects of pre-deposited iron oxides were also investigated by determining the amount of nickel oxide deposited on two Zircaloy surfaces with dense and porous iron oxide layers. Finally, the effects of ferrous ions on the deposition of iron oxide micro-particles were examined in a suspended hematite solution and a mixed solution containing ferrous ions and suspended hematite. From the results, it was found that a heat treatment of the Zircaloy surface was effective for reducing the amount of the deposited iron oxide. The deposition of the iron oxides was promoted in the presence of dissolved hydrogen and ferrous ion. Furthermore, the deposition of nickel oxide increased only on the pre-deposited iron oxide with porous layer. In chapter IV, the formation of nickel ferrite was investigated as a function of temperature. It is generally known that nickel ferrite is formed on heat transfer surface in the presence of water vapor at high temperature and high pressure. Hence, the high temperature and high pressure loop should be used for studying the formation of nickel ferrite. However, in the present work, a new simple method was proposed to simulate the heat transfer surface on which nickel ferrite for...