Radiological inventory of irradiated graphite samples

Abstract

In France, graphite is present as reflector, moderator or structural element in 9 gas cooled reactors which are now in the decommissioning phase The storage, whose characteristics have to be determined, dedicated to irradiated graphite is planned in France for 2010. Consequently, the radiological inventory of the graphite has to be done Measurement campaigns already organized on different graphite samples showed discrepancies for the computed “calculation/measurement” ratio and the necessity to acquire more experimental results was stressed. The ability to realize an experimental radiological inventory, with particular attention to 3H, 14C, 36Cl, and 63Ni, was studied. A new mineralization was developed based on an acid attack (iodic + sulfuric acid). This process causes a high gaseous emission and cannot be applied to analyses of volatile elements such as 14C, 3H, and 36Cl. The routine pyrolysis protocol used to measure these elements in other matrices was specially adapted to the graphite samples. After these mineralizations, radiochemical steps were conducted in order to separate the different requested radionuclides. The mean yield of the complete separation process was evaluated for each of them and the detection limits were determined.