Abstract: A gastight seal for a rotating spindle or the like is made by tightly fitting an externally spirally ribbed element into a bore in another element and machining out that part of the element which projects inside the spiral rib so as to leave only the spiral rib flexed within the bore.

Abstract: A method is given for obtaining recesses in a surface by etching. The obtained surface with recesses can be used for example in bearings.According to the invention, an etching method is given, wherein the depth of the recesses is controlled by forcing an etching fluid along the surface to be etched by means of a flow guiding template in places defined by this template.The etching rate in the recesses to be etched is controlled by adjustment of the flow velocity of the etching liquid and the slit height in the flow-guiding template.The recesses to be etched are deeper when the flow velocity of the etching fluid and the slit height are both higher.

Abstract: The invention relates to a method for the preparation of aniondeficient actinide nitrate solutions. Anion deficient actinide nitrate solutions are used for the preparation of ceramic spherical ceramic nuclear fuel.According to the invention one or more actinide oxides selected from the group of PuO.sub.2, UO.sub.2, U.sub.3 O.sub.8, UO.sub.3 of oxides ranging between UO.sub.2 and UO.sub.3 are dissolved in one or more actinide nitrates which are molten in their water of crystallination. The obtained mixture is subsequently diluted with water.