FRACTIONALIZATION OF GRAPHITIC REACTOR COMPONENTS

摘要

Some 900 t of graphitic reactor components (moderators, reflectors and thermal columnsfabricated from graphite or carbonstone) in Germany will sooner or later be subject todecommissioning and/or dismantling.To dismantle these graphitic components, comprehensive information about amount (volumes,masses, dimensions, ...) and radiological as well as thermal history is needed. Results of stocktakingof graphitic reactor components in Germany are presented.To fractionalize graphitic components, cutting techniques had to be developed and/or adapted tothe special recommendations in nuclear industry: A minimization of secondary waste emission isas well desired as the ability to be applied by remote handling and as necessary as a certainperformance in cutting thicker structures. Available experiences stemming from former cuttingoperations (1) are taken into account. Next milestone is the development of collecting techniquesregarding graphite dust occuring from cutting operations. First applications of this techniques willtake place in the final evaluation of preselected cutting techniques on irradiated graphite at thevery end of this project.Fractionalizing graphitic components will reduce the volume to be stored, minimize disposalcosts and reach a separation of activated/contaminated and non-radioactive parts. For example,the amount of MOSAIK type II containers needed for graphitic parts of the AVR-reactor wasestimated to a number of 2,511 and might be reduced down to some 50% (2).Results of the scientific works carried out so far are shown in examples. Mechanical properties ofgraphite from different nuclear installations vary greatly with respect to hardness, tensile andpressure strength, density and, obviously, source. German, british and russian graphite grades arecharacterized and compared (3-8). Part of stock taking of graphitic parts and their propertiesdescribe calculations of neutron density flux, represented by a set of results for the thermalcolumn of the RFR reactor from Rossendorf. Graphite, as an inflammable substance, has to beexamined regarding potential explosion hazards. Results of such experiments are shown.A great number of cutting techniques was applied and evaluated with respect to a futureapplication on nuclear graphite. Several techniques are documented and their performances arecompared. Evidence is shown for the favoured technique to be applied in the final evaluationworks on irradiated graphite.Future aspects comprise the testing of the filter technique, which is still under construction, thefinal evaluation to the end of this project and the presentation of the results in a concludingworkshop. A vision lies in the application of the selected techniques for cutting and filteringgraphitic parts in chemically contaminated installations from the chemical or pharmaceuticalindustry.