Abstract: A fluid flow control device includes a thermally conductive conduit section having both interior and exterior heat exchange surfaces, with the interior surface being adapted to contact fluid flowing thereover. A controllable heat transfer means coupled to the conduit section has a first operative state for removing heat from the exterior heat exchange surface to reduce the temperature of the conduit section sufficiently to freeze liquid adjacent the interior heat exchange surface and thereby at least partially restrict the flow of fluid thereover. In a second operative state, the heat transfer means supplies heat to the interior heat exchange surface to melt at least a portion of any frozen liquid adjacent the interior heat exchange surface and thereby permit the flow of fluid thereover.

Abstract: A fluid flow control device includes a thermally conductive conduit section having both interior and exterior heat exchange surfaces, with the interior surface being adapted to contact fluid flowing thereover. A controllable heat transfer means coupled to the conduit section has a first operative state for removing heat from the exterior heat exchange surface to reduce the temperature of the conduit section sufficiently to freeze liquid adjacent the interior heat exchange surface and thereby at least partially restrict the flow of fluid thereover. In a second operative state, the heat transfer means supplies heat to the interior heat exchange surface to melt at least a portion of any frozen liquid adjacent the interior heat exchange surface and thereby permit the flow of fluid thereover.

Abstract: A system for combusting materials containing radioactive nuclides to permit recovery of the radioactive nuclides includes a combustion zone for combusting a sample material containing at least one radioactive nuclide. The combustion products are continuously exhausted from one end of the combustion zone, and a continuous pressurized stream of oxygen-containing gas is introduced into the combustion zone between the exhaust end of the zone and the sample during the combustion thereof. At least a portion of the pressurized oxygen-containing gas stream is directed through the combustion zone in a spiral path toward the sample to circulate at least a portion of the combustion products around the combustion zone as they flow toward the exhaust end of the zone counter to the flow of the spiraling stream of oxygen-containing gas, thereby intimately mixing the combustion products with the oxygen-containing gas in the combustion zone.