Oxidationskinetik innovativer Kohlenstoffmaterialien hinsichtlich schwerer Lufteinbruchstörfälle in HTR's und Graphitentsorgung oder Aufarbeitung

Abstract

Currently future nuclear reactor concepts of the Fourth Generation (Gen IV) are underdevelopment. To some extend they apply with new, innovative materials developed just for thispurpose.This thesis work aims at a concept of Generation IV Very High Temperature Reactors (VHTR) inthe framework of the European project RAPHAEL (ReActor for Process heat, Hydrogen AndELectricity generation). The concept named ANTARES (AREVA New Technology based onadvanced gas-cooled Reactors for Energy Supply) was developed by AREVA NP. It is a heliumcooled, graphite moderated modular reactor for electricity and hydrogen production, by providingthe necessary process heat due to its high working temperature.Particular attention is given here to oxidation kinetics of newly developed carbon materials (NBG-17) with still unknown but needed information in context of severe air ingress accident in VHTR’s.Special interest is paid to the Boudouard reaction, the oxidation of carbon by CO2. In case of anair ingress accident, carbon dioxide is produced in the primary reaction of atmospheric oxygenwith reflector graphite. From there CO2 could flow into the reactor core causing further damage byconversion into CO. The purpose of this thesis is to ascertain if and to what degree this couldhappen.First of all oxidation kinetic data of the Boudouard reaction with NBG-17 is determined byexperiments in a thermo gravimetric facility. The measurements are evaluated and converted intoa common formula and a Langmuir-Hinshelwood similar oxidation kinetic equation, as input forthe computer code REACT/THERMIX. This code is then applied to analyse severe air ingressaccidents for several air flow rates. The results are discussed for two accident situations, in whicha certain graphite burn off is achieved. All cases show much more damage to the graphite bottomreflector than to the reactor core. Thus the bottom reflector will lose its structural integrity muchearlier than the core itself will be damaged by oxidation