On the mechanism of aluminum ignition in steam explosions

An available theory [Epstein, M., Fauske, H.K., 1994. A crystallization theory of underwater aluminum ignition. Nucl. Eng. Des. 146, 147–164] of the ignition of aluminum melt drops under water, which is based on the assumption that the aluminum oxide (Al₂O₃) drop-surface skin first appears in a metastable molten state, is compared with existing experimental data on the ignition of aluminum drops behind shock waves in water [Theofanous, T.G., Chen, X., DiPiazza, P., Epstein, M., Fauske, H.K., 1994. Ignition of aluminum droplets behind shock waves in water, Phys. Fluids 6, 3513–3515]. The predicted and measured ignition temperature of about 1770 K coincides approximately with the spontaneous nucleation temperature of supercooled liquid Al₂O₃ (1760 K). This suggests that the crystallization of the oxide layer represents a strong ‘barrier’ to aluminum drop ignition under water. Apparently a similar interpretation is applicable to aluminum drop ignition in gaseous oxidizing atmospheres. We conclude from the theory that the low-temperature aluminum ignitions (in the range 1100–1600 K) that have been observed during steam explosions are a consequence of the short aluminum drop oxidation times in this environment relative to the characteristic time for Al₂O₃ crystallization. Several aspects of the aluminum drop/shock interaction experiments besides ignition are discussed in the paper. In particular, the experiments provide strong evidence that during the course of a vapor explosion metal fragmentation occurs via a thermal mechanism at low pressure and precedes the development of a high-pressure shock.     

Experimental Investigations of the Hydrodynamics of the Flow Part of Models of a Water-Based Liquid-Metal Target

The hydrodynamics of the flow part of variants of a water-based design of a liquid-metal target is investigated from the standpoint of its meeting the requirements. Investigations of the measurement of the velocity fields in the region of heat release of the liquid-metal target and also of the effect of variations of certain geometric characteristics of the target on the hydrodynamics in this region are performed. The optimal values of the individual geometric parameters of the target were determined from the results of this work and conclusions are drawn concerning whether or not the target structure meets the requirements as a whole. 5 figures.     

Models of Ceramic Tritium Breeding Zones in the Blanket of a Thermonuclear Reactor

The development, performed in the 1980s–1990s, of models of tritium breeding zones for blankets of thermonuclear reactors, based on the use of ceramic lithium-containing materials, is described. 5 figures, 1 table.     

Russia's Strategy in Reactor Safety Investigations

The views of the author on the content of programs for future scientific research on the safety of domestic reactors are presented. The classification of the scientific-research work is based on the principle of deep stacking of protection. The fields of interest to those who order the scientific-research work are examined: the Ministry of Atomic Energy, Rosénergoatom, State Atomic Inspectorate, and international organizations. It is suggested that the center of gravity of Russian research on the safety of nuclear power plants be transferred from analysis of accidents to the study of measures for preventing them. Special importance is attached to investigations on increasing the level of the safety culture of the personnel, specifically, studying the effect of the human factor on safety. It is suggested that the efforts of specialists in various fields of science be concentrated in this direction.     

Accuracy aspects in multiphase flow metering using X-raytransmission

The composition of a mixture of several components flowing through a pipe can be determined by means of an X-ray transmission technique/analysis. We present some aspects of the theory relating to an application in which the component volume fractions of an oil, water, and gas mixture are determined. It will be shown that on fundamental grounds, this technique has its limits regarding the number of components that can be distinguished in relation to the achieved accuracy of the measured attenuation     

Corium spreading and coolability: CSC Project

In the context of severe accidents, large R&D efforts throughout the world are currently directed towards ex-vessel corium behaviour. Among the mitigation means which can be envisaged, the European industries and utilities are considering the implementation of a core-catcher outside the reactor pressure vessel in order to prevent basemat erosion and to stabilize and control the corium within the containment. The CSC project focused on two key phenomena for external core-catcher efficiency, reliability and safety: spreading and coolability. An experimental programme, covering different scenarios and including both simulant and real materials provided a lot of results which now constitute a large database and which enabled the qualification of computer codes.