The present volume Uranium C5 covers the physical properties of U0 - the production 2 and preparation of U0 were already treated in Uranium C4, whereas the chemical proper 2 ties will be the subject of the forthcoming part C6. U0 is the most important chemical compound in all aspects of nuclear technology. 2 It is and will be for the foreseeable future the fuel for all light and heavy water reactors as well as (in the mixed crystal with Pu0 ) for the fast breeder reactors. Therefore, the 2 nuclear engineer has to understand the behavior of U0 under all conditions existing during 2 operational (and possibly failure) states of a nuclear reactor, e. g. , not only in the solid state but also to some extent in the liquid and gaseous states. Besides high scientific interest in the sometimes unique or unusual properties, e. g. , at low temperatures, a lot of data and physical properties which are critical for its use as a nuclear fuel have been determined more or less accurately. Creep, swelling, irradiation densification, and fission gas behavior in the fuel are properties which have been evaluated up to the high temperatu res (near the melting point) which may exist in U0 fuel due to its low thermal conductivity. 2 Besides these more technical data there have been accumulated a lot of important physical data, e. g.

This volume C 3, as a part of the Gmelin "Thorium" Handbook, Series C, describes the thorium-nitrogen compounds. Included are compounds both of technological importance like the nitrides and the nitrates and those of merely scientific interest, such as amides and related compounds. However, due to the decreasing technical importance of the nuclear thorium fuel cycle, especially with the advanced fuels like the nitride ThN, in recent years, the thorium compounds with nitrogen have been investigated much less extensively than the correspond ing uranium compounds. In order to have the data for the Th-N-X systems accumulated in one specific volume, the decision was made to publish this volume without incorporating other Th systems. ThN is the compound with the lowest N :Th ratio. In addition to its (former) nuclear interest due to its thermal and radiation stability, it has many very interesting physicochemical properties. Thorium nitrate, the other well-investigated compound, is of importance because it is (in the form of an adduct with tri-n-butylphosphate) the extracted compound when burnt-up thorium fuels are reprocessed. Despite the wealth of accumulated data on the chemical and physicochemical properties of the compounds discussed, the knowledge of the compounds and of the systems is far from satisfactory - it must be deepened and improved in further studies. I would like to thank the competent authors for their critical contributions as well as the Gmelin-Institute for the excellent cooperation provided, especially Prof. Dr. Fluck and Dr. Keim, the editor-in-chief of this volume.

The present volume describes the general properties of the thorium atom and ions, the thermodynamics of its compounds and solutions, the behavior of solutions and solid com pounds under the influence of its own radiation as well as an external radiation field, and spectroscopic data in great detail. The different chapters are of special interest to scientists who work in these fields, and also in the corresponding fields of other elements. In some special fields there exists a detailed knowledge of this radioelement whereas in other fields, such as M6Bbauer spectra, lower oxidation states, or radiation stability, there are large gaps. Due to the fact that the significance 23 of thorium as a breeder fuel ( 2"fh to be converted to fissile 233U after thermal neutron capture) has decreased within the last decade, the behavior of thorium is not as yet so thoroughly investigated as the heavier radioactive element uranium. Many of these data, however, are not only of academic interest, e.g., the knowledge of atomic spectra is needed for some analytical methods, especially in the trace concentration region. Due to the noble gaS-like electronic configuration of the tetravalent ion, there are no absorption bands in the visible region so that in general spectra and data are very scarce. This volume is a very detailed and critically reviewed compilation, written by experts from the Federal Republic of Germany, Belgium, and the United States.

Es ist eines der besonderen Ziele des Gmelin-lnstituts, den neuesten Kenntnisstand uber das gesamte Gebiet der Actinidenelemente zu vermitteln. Der erste Schritt in dieser Richtung war die Be arbeitung der Transurane, die jetzt komplett vorliegt. Die entsprechenden Bande uber die Elemente Protactinium und Uran sind in Bearbeitung und werden voraussichtlich 1977 bzw. 1978!1980 erscheinen. Der vorliegende Erganzungsband* "Thorium'" C 2 uber "Ternare und polynare Oxide'" ist der erste Band der Reihe, die dem Element Thorium gewidmet ist. Entsprechend der Unterteilung der Uran- und Transuranebande ist die Beschreibung des Thoriums in vier Teile gegliedert: Teil A "Das Element'" Teil C ,. Verbindungen'" Teil B "Metall und Legierungen"' Teil D "Chemie in Loesung'" Die vorgezogene Herausgabe dieses Bandes wird durch die Tatsache gefoerdert, dass Th0 und 2 ThOrUOrMischoxide speziell fur Hochtemperaturkernreaktoren als Brutstoffe fur die Erzeugung 233 von U von Bedeutung sind. Daher ist es auch von Interesse, nahere Einzelheiten uber die moeg lichen Wechselwirkungen von Spaltproduktoxiden mit Th02 zu erfahren. Der vorliegende Band gibt dazu die Moeglichkeit, als er die Literatur bis Ende 1975 umfasst. Daneben ist es sicher gut, Kenntnis zu erhalten von Lucken experimenteller Ergebnisse auf diesem Gebiet. Dies mag einen Anstoss zu neuen Arbeiten geben. Um einen vollstandigen UEberblick und eine geschlossene Darstellung uber das im Titel genannte Gebiet zu geben, wurden alle ternaren und polynaren Metalloxid-Systeme des Thoriums aufgenommen, fur die nicht ein neuer Gmelin-Band vorlag, ferner sind einige der im Thorium-Hauptband von 1954 aufgefuhrten Literaturzitate mit eingearbeitet.