Metal carbonyl decomposition and carbon deposition in the advanced gas-cooled nuclear reactor

Abstract

Carbon deposition in advanced gas-cooled nuclear reactors has been found to occur preferentially in those regions of the reactor core which receive gas directly from the coolant reprocessing plant. This discovery has led to the hypothesis that such deposition may be catalysed by iron or nickel carbonyls being transported into the reactor core. This article describes experiments involving the decomposition of metal carbonyls in simulated AGR gas mixtures under conditions of temperature and pressure similar to those found within the reactor cores. Nickel carbonyl has been shown to promote significant carbon deposition from the simulated AGR, gas mixtures. The carbons deposited in the laboratory have been compared and contrasted with those found within the AGR. Those gases present which are most susceptible to decomposition under the influence of the decomposition products of nickel carbonyl have been identified, and the influence of AGR fuel cladding material examined. Taken together the results provide a mechanism accounting for the nature and distribution of the carbon deposits occurring in these areas of AGR cores.