Since the 1969 BNES International Conference on the Physics of Fast Reactor Operation and Design in London, significant advances have been made in fast reactor physics. In October 1973 there was held an International Symposium on Physics of Fast Reactors, in Tokyo. Based principally on the papers presented at this Tokyo Symposium a review is presented on the progress of fast reactor physics in recent years, and the outstanding topics of importance.

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Chlorination of triuraniumoctaoxide (U₃O₈) with the organic chloride HCP (hexachloropropene, Cl₃CCCl=CCl₂) was studied in order to gain basic information useful for the reprocessing of nuclear spent fuels.
Hexachloropropene reacts with U₃O₈ at temperatures above 70°C. When mixtures of HCP/U₃O₈ molar ratio above 9 are heated at 100°C for 4 hr, there is seen formation of two kinds of intermediate chloride-UCl₅·TCAC (TCAC: trichloroacrylyl chloride, Cl₂C=CClCOCl)-and a new adduct compound of UCl₆ with HCP-UCl₆·nHCP.
The UCl₅·TCAC is mainly produced at HCP/U₃O₈ molar ratios from 9 to 18, while at higher molar ratios (HCP/U₃O₈) above 24 the UCl₆·nHCP is formed.
Also, UCl₅·TCAC is converted to UCl₆·nHCP with HCP at 100°C.
The UCl₅·TCAC is soluble in hot HCP, but the new adduct compound is insoluble.
Above 110°C, these intermediate chlorides decompose thermally into UCl₄.

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