METAL-CARBONYL DECOMPOSITION AND CARBON DEPOSITION IN THE ADVANCED GAS-COOLED NUCLEAR-REACTOR

Carbon deposition in advanced gas-cooled nuclear reactors has been fou nd to occur preferentially in those regions of the reactor core which receive gas directly from the coolant reprocessing plant. This discove ry 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 ca rbonyls in simulated AGR gas mixtures under conditions of temperature and pressure similar to those found within the reactor cores. Nickel c arbonyl has been shown to promote significant carbon deposition from t he simulated AGR, gas mixtures. The carbons deposited in the laborator y have been compared and contrasted with those found within the AGR. T hose gases present which are most susceptible to decomposition under t he influence of the decomposition products of nickel carbonyl have bee n identified, and the influence of AGR fuel cladding material examined . Taken together the results provide a mechanism accounting for the na ture and distribution of the carbon deposits occurring in these areas of AGR cores.