Location and chemical bond of radionuclides in neutron-irradiated nuclear graphite

The locations and the chemical forms (chemical bonds) of radionuclides in neutron-irradiated nuclear graphite have been determined in order to develop principal strategies for the management of graphitic nuclear waste. Due to the relatively low concentration of radionuclides in neutron-irradiated nuclear graphite (<1 ppm) direct spectroscopic methods are not applicable to investigate chemical structures. Therefore, methods by analogy have been applied. Such methods are investigations of the chemically detectable precursors of radionuclides in neutron-irradiated nuclear graphite and subjection of irradiated graphite to different chemical reactions followed by measurements of the radionuclide-containing reaction products by sensitive radiochemical methods. The paper discusses the applicability of these methods. The radionuclides investigated in this study can be divided into three parts: tritium, radiocarbon and metallic activation and fission products. Tritium can be bound in neutron-irradiated nuclear graphite as strongly adsorbed tritiated water (HTO), in oxygen-containing functional groups (e.g. C–OT) and as hydrocarbons (C–T). Radiocarbon is covalently bound with the graphite structure. The activity can be described by a homogeneously distributed part and a heterogeneously distributed part (enriched on surfaces or in hotspots). Metallic radionuclides can be bound as ions or covalent metal–carbon compounds. The distribution of all these radionuclides is mainly dependent on the distribution of their inactive precursors

Das SUWOX-Verfahren zur Zersetzung waessriger Schadstoffe in ueberkritischem Wasser Entwicklung und Ergebnisse

Starting from the state achieved in the technical application of the Supercritical Water Oxidation (SCWO) process for the destruction of hazardous organic waste, the development of the SUWOX-process realized in FZK/IKET is reported. The SCWO-process offers the advantages of efficient and complete destruction of waste material in a fully contained system, but it has also the drawbacks of high material corrosion and restricted solubility of salts. For the treatment of aqueous waste the SUWOX process resolves these problems. The material corrosion is eliminated by the use of a double wall reactor, in which alumina is applied in case of acid formation. The precipitation of salts is prevented by the suitable adjustment of the operating conditions. The augmentation of the density causes the salts to remain in solution and to pass through the process. In special cases the preseparation of minor portions of low soluble salts may be required. (orig.)Ausgehend vom Stand der Technik des ueberkritischen Wasseroxidations-Prozesses (SCWO-Prozess) zur Zersetzung toxischer organischer Schadstoffe werden die Entwicklungsschritte beschrieben, die zu dem SUWOX-Verfahren des IKET fuehrten. Das SCWO-Verfahren bietet die Vorteile effizienter, vollstaendiger Schadstoffzersetzung innerhalb eines geschlossenen Prozesses, es hat jedoch die Nachteile hoher Werkstoffkorrosion und schlechter Salzloeslichkeit. Fuer die Behandlung waessriger Schadstoffe bietet das SUWOX-Verfahren eine Loesung fuer die beiden Probleme an. Die Materialkorrosion wird durch den Einsatz eines Doppelwand-Reaktors ausgeschaltet, beispielsweise durch die Anwendung von Oxidkeramik im Falle von Saeurebildung. Das Ausfallen von Salzen wird durch die geeignete Wahl der Betriebsbedingungen verhindert. Durch Steigerung der Dichte werden die Salze in Loesung gehalten und durchlaufen den Prozess. In besonderen Anwendungsfaellen kann fuer einen geringen Teil schwerloeslicher Salze eine Vorabscheidung erforderlich werden. (orig.)SIGLEAvailable from TIB Hannover: ZA 5141(6289) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman