Kinetics of Chronic Oxidation of NBG-17 Nuclear Graphite by Water Vapor

Contescu, Cristian I¹  Burchell, Timothy D¹  Mee, Robert² 

[1] Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States);Univ. of Tennessee, Knoxville, TN (United States)

关键词: Graphite;    moisture;    oxidation;    kinetics;    HTGR;    VHTR;   

DOI  :  10.2172/1185975
RP-ID  :  ORNL/TM--2015/142
PID  :  OSTI ID: 1185975

美国|英语

来源: SciTech Connect

【 摘 要 】

This report presents the results of kinetic measurements during accelerated oxidation tests of NBG-17 nuclear graphite by low concentration of water vapor and hydrogen in ultra-high purity helium. The objective is to determine the parameters in the Langmuir-Hinshelwood (L-H) equation describing the oxidation kinetics of nuclear graphite in the helium coolant of high temperature gas-cooled reactors (HTGR). Although the helium coolant chemistry is strictly controlled during normal operating conditions, trace amounts of moisture (predictably < 0.2 ppm) cannot be avoided. Prolonged exposure of graphite components to water vapor at high temperature will cause very slow (chronic) oxidation over the lifetime of graphite components. This behavior must be understood and predicted for the design and safe operation of gas-cooled nuclear reactors. The results reported here show that, in general, oxidation by water of graphite NBG-17 obeys the L-H mechanism, previously documented for other graphite grades. However, the characteristic kinetic parameters that best describe oxidation rates measured for graphite NBG-17 are different than those reported previously for grades H-451 (General Atomics, 1978) and PCEA (ORNL, 2013). In some specific conditions, certain deviations from the generally accepted L-H model were observed for graphite NBG-17. This graphite is manufactured in Germany by SGL Carbon Group and is a possible candidate for the fuel elements and reflector blocks of HTGR.