Feeder Pipe Oxidation in the Presence of Steam During a Nuclear Reactor Accident

Abstract

A Canada Deuterium Uranium (CANDU) reactor has hundreds of carbon steel feeder pipes that are connected at one end to the fuel channels at the reactor face and are connected at the other end to the reactor inlet and outlet headers above the reactor. The production of hydrogen gas from metal–water interaction at high temperatures is a major concern during a severe accident in a nuclear reactor. It is generally accepted that the main source of hydrogen gas during a severe accident is the chemical interaction of Zircaloy fuel cladding and the water coolant. However, it has recently been suggested that the amount of hydrogen produced by the oxidation of carbon steel located outside of a CANDU core could exceed that produced by zirconium oxidation. In this work, the linear and parabolic oxidation rate constants of CANDU feeder carbon steel, in the temperature range of 600–1,100°C, were measured to be W/t = 1.806 × 103 exp (− 126,337/RT) and W2/t = 1.879 × 105 exp (− 135,835/RT), respectively. For parabolic steam oxidation beginning at roughly 90 minutes after reaching steady-state heating temperatures, the latter equation should be used. These rates are about a factor of 5–10 greater than oxidation rates measured in 304L stainless steel and in zirconium specimens, meaning that the carbon steel oxidation can be significant in an accident.