Abstract: In a nuclear reactor of the safety type, density locks constitute an important safety function. Two liquid systems can be kept apart by means of density locks. During normal operating conditions, the density locks prevent the warmer water from a primary cooling system from being mixed with the colder water from a secondary cooling system. At an increased temperature level, the density locks permit water to flow through so that the warmer water is mixed with the colder water to reduce the increased temperature level. To prevent an undesired transport through the density locks, for example boric acid leaking in from the secondary cooling system during normal operating conditions, the density locks are provided with a honeycomb consisting of tube pieces assembled in parallel. The honeycomb tube must be much longer than four times the tube diameter. To prevent the occurrence of a resonant interaction between internal waves in the honeycomb tube, the Brunt-Vaisala frequency ##EQU1## must vary through the tubes.

Abstract: Lining wear in an arc heated ladle containing a bath of melt and slag is reduced by rotating the melt in a horizontal direction to provide a concave bath surface in which the slag accumulates towards the center, thus preventing the slag attacking the ladle lining. In addition to heating the charge, the arc or arcs melt(s) the slag whereas the lining is partly protected from the radiation by the concave surface. A flow perturbing means is arranged at the ladle to attain an increased homogenization and the possibility of intensified sulfur removal.