Abstract: A method of cleaning a fuel assembly contaminated with a radioactive alkali metal in which the fuel assembly is subjected to heating with an inert gas followed by being placed under vacuum and finally cooled with an inert gas; the latter two steps being performed in repetitive cycles.

Abstract: A self-actuating, self-locking flow cutoff valve particularly suited for use in a nuclear reactor of the type which utilizes a plurality of fluid support neutron absorber elements to provide for the safe shutdown of the reactor. The valve comprises a substantially vertical elongated housing and an aperture plate located in the housing for the flow of fluid therethrough, a substantially vertical elongated nozzle member located in the housing and affixed to the housing with an opening in the bottom for receiving fluid and apertures adjacent a top end for discharging fluid. The nozzle further includes two sealing means, one located above and the other below the apertures.