Abstract: A proportion of the liquid metal flow passing through a fast reactor steam generator unit (SGU) is diverted past the outlet to a quiescent zone in the region of immersed tube-to-tubeplate welds at the water entry ends of the tubes, into which zone are given off any hydrogen bubbles which may result from a water leak into the liquid metal. The liquid metal in this zone is caused to flow through a weir system above which there is a gas space for collection of hydrogen, suitable means being provided for detection of hydrogen in this space. The hydrogen is entrained at the water inlet tube plate, the invention making use of the slow solution rate of hydrogen in sodium at lower temperatures prevailing in the quiescent zone at the water inlet end.

Abstract: A tube-in-shell heat exchanger has double sealing joints between the tubes and a tube plate of the heat exchanger constituted by the provision of a secondary tube plate spaced from the normal tube plate and through which each tube extends with sealing in addition to the normal tube to tube plate sealing joints, there being a bellows enveloping the tubes and sealed to both the normal and the secondary tube plates. The space between these tube plates can be monitored for leakage.

Abstract: In a method of repairing a defective tube in a tube-in-shell heat exchanger by inserting a tubular repair sleeve within the defective tube and sealingly bonding one end region of the sleeve to the tube and the other end region of the sleeve to the tube sheet in a manner such that the defect (for example a defective tube/tube sheet weld) is bridged, the improvement of providing a support against which the said one end of the sleeve can be explosively welded to the tube. The support comprises a mass of low melting point alloy cast around the tubes so as to provide support at the welding level for the defective tube as well as surrounding tubes. The support is removed after welding by remelting the alloy and causing the liquid alloy to run away. Inserts of high melting point metal can be included in the mass as reinforcement, and the casting can be effected in a removable box of which the tube sheet forms the base, the walls surrounding at least a part of the tube array which includes the defective tube.

Abstract: A method of repairing a defective tube in a tube-in-shell heat exchanger which entails inserting within the defective tube a tubular sleeve and sealingly bonding the end regions of the sleeve to the tube to bridge the defect, the tubular sleeve having axial flexibility (for example by being circumferentially corrugated). The sleeve may be mechanically keyed to the tube at positions adjacent to the bonding at the end regions of the sleeve.

Abstract: A tube-in-shell heat exchanger for effecting heat exchange between steam conducted by the heat exchange tubes and liquid metal conducted through the shell. The tubes penetrate the tube sheet by means of clearance apertures and are sealed thereto with thermal sleeves which are brazed to the tubes so that fusion welds are avoided in the sodium/water barrier.