Analysis of the Causes of Irregular ³⁶Cl Radionuclide Distribution in Irradiated Nuclear Graphite

Abstract—: The article is dedicated to analyzing the concentration processes of the long-lived ³⁶Cl radionuclide in irradiated graphite of uranium-graphite nuclear reactors. The ³⁶Cl radionuclide is one of the most important isotopes for assessing the safety of radioactive-waste disposal. An analysis of the so-called Nugget effect due to the substantial heterogeneity of the ³⁶Cl content in samples of irradiated graphite of nuclear reactors is carried out. In the same graphite elements, the difference in the ³⁶Cl concentration reaches 100 times regardless of operational factors, such as the neutron flux and temperature. The article discusses the main processes that can affect ³⁶Cl contamination in irradiated graphite. Particular attention is paid to determining the form of ³⁶Cl in graphite, taking into account the features of its manufacturing and thermodynamic modeling of the equilibrium compositions of reaction products during the purification of unirradiated graphite in a gaseous medium.