Abstract: To provide intrinsic reactor safety, the fuel sub-assemblies of a nuclear reactor core are provided with reactivity control mechanisms operable, in response to temperature rises above desired limits, to interact with adjacent fuel sub-assemblies and effect radial dilation of the core in order to reduce reactivity. Various embodiments are disclosed in which differential thermal expansion of an operating device or devices (34; 40; 42, 44, 46; 50) is translated into radially outward displacement of a lever or levers (28) for contact with neighbouring sub-assemblies.

Abstract: In a known design of liquid metal cooled fast fission nuclear reactor, the primary pumps (22) plug into the outboard ends of the high pressure pipes (28), leading to the development of a vertical load which has to be supported by substantial additional structure to avoid subjecting the reactor diagrid (18) to significant bending moments. The invention resides in connecting the inboard ends of the high pressure pipes (28) to the diagrid (18) via spigot and socket joints (40) so that the pipes are not rigidly connected at either end. With this arrangement loads are developed at each end of the pipes which combine to produce radial reaction loads acting on smaller moment arms whereby the total moments imposed on the diagrid are reduced.

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: An inspection system for detecting leakage from for example the primary vessel (11) of a nuclear reactor includes a camera (29) carried by an umbilical cable (28) which can be fed through a duct assembly (22) comprising a series of tubular sections (23) connected endwise by flexible bellow (24). A guide track (18) extends around the top of the vessel (11) and each duct section (23) is provided with wheels (25) which engage the track (18). A curved guide tube (17) feeds the duct sections (23) from a vertical entry position (15) in the roof (13) into a horizontal track-engaging disposition. The track (18) includes spaced flanges (20b, 21b) through which the umbilical cable can extend and depend downwardly into the annular space between the primary vessel (11) and a surrounding guard vessel (12).

Abstract: A signal synthesizer is provided for producing pulses simulating characteristics of echo pulses generated during ultrasonic scanning so that the simulated pulses can be used in the calibration of equipment for processing the outputs of ultrasonic transducers. The synthesizer produces an envelope signal of selectively variable amplitude and rise and fall time and multiplies this envelope respectively with a high frequency pulse train and a substantially zero amplitude signal in a dual matched multiplier so that the subtractively combined outputs of the multiplier are free of unwanted feedthrough components introduced by the mulitplier.

Abstract: In a method of determining the rate of heat transfer from a surface due to liquid convection, a coating of a material capable of dissolving in the convecting liquid and whose optical properties on irradiation are proportional to the thickness of the coating, is applied to the surface and is then exposed to radiation and to the convecting liquid, the change in the amount of radiation transmitted or reflected from the coating giving an indication of the rate of heat transfer.

Abstract: A facility for posting irradiated fuel from a preparation chamber of a dry storage complex into storage canisters within a clean chamber and for posting contaminated canisters from a closed bucket in the clean chamber into the preparation chamber. The facility comprises two coaxial tubular port members extending from the preparation chamber into the clean chamber, the port members having masking means for the canister and bucket closures and means for withdrawing them into the preparation chamber.

Abstract: A scanning device, particularly for viewing above the core of a nuclear reactor, has links 29 pivoted together at 33 with means 35, 35a limiting relative movement in one sense. At least one link carries a transducer 36, preferably ultrasonic, for viewing. There may be two transducers arranged to view in different directions. The transducers may be mounted in a removable module.A deployment arrangement may have a vertical hollow mast 20 down which the links can be pushed to engage a deflect element 31 to reach an arm 23 from which the links can extend as a cantilever.

Abstract: A roof shield for a nuclear reactor comprises a normally fixed radially outer portion, a radially inner portion rotatable about a vertical axis, and a connection between the inner and outer portions which permits relative angular movement between the portions without loss of containment, the connection comprising a radially inner wall of the outer portion, an upper portion of the inner wall being so arranged that on upward movement of the inner portion the upper wall portion receives substantially no angular movement, the lower end of the upper portion being at a position below the level of the upper surface of the outer portion.

Abstract: In a nuclear reactor of the type in which the vault has a roof in which inner and outer rotatable shields are mounted, coolant is supplied to the roof and shields via duct penetrations which extend in the plane of rotation and can be brought into alignment and connected together by slidable connectors when relative rotation between the shields and roof is not required. When such rotation is to be effected, the connectors can each be retracted into a respective duct so that rotation is not obstructed thereby.

Abstract: A vessel for the long term storage and monitoring of nuclear fuel materials incorporates a device (12) within its interior for providing an externally detectable signal indicating whether any pressure loss has occurred. The device (12) comprises a magnet (32) attracted towards a boundary wall (11) of the vessel and urged in that direction by the internal pressure within the vessel acting on a diaphragm (26). The magnet (32) is subjected to oppositely directed forces by pressurized fluid in chamber (40) bounded by diaphragm (26) and a spring (30), the arrangement being such that these latter forces collectively or individually are effective to drive the magent (32) away from the wall (11) in the event of a pressure loss within the vessel thereby producing an externally detectable change in magnetic flux.

Abstract: A vessel for the storage and monitoring of nuclear fuel materials incorporates a device (12) within its interior for providing an externally detectable signal indicating whether any temperature rise has occurred. The device (12) comprises a magnet (32) attracted towards a boundary wall (11) of the vessel and maintained in that position by a temperature-sensitive element such as a thermal link (38). The magnet (32) is subjected to an oppositely directed force by a spring (30), which is effective to drive the magnet (32) away from the wall (11) in the event of a substantial temperature rise within the vessel thereby producing an externally detectable change in magnetic flux.

Abstract: In the detection of failed fuel in liquid metal cooled nuclear reactors, a helical annular linear induction pump (5,6) electromagnetically pumps coolant in sampling pipes (4) from fuel sub-assemblies of the reactor core to a selector mechanism (9,10) which collects, in turn, the discharge from each sampling pipe (4) for supply to equipment for monitoring for the presence in the coolant of products indicative of fuel failure. The selector mechanism collects the discharge without contacting the sampling pipes (4) and the same pump (5,6) is employed to pump the selected samples via pipe 11 to the monitoring equipment. This pump may also serve to pump a proportion of the bulked sample from the non-selected sampling pipes after discharge into a vessel (7), the bulked sample being conducted through the pump via pipes (13).

Abstract: In a liquid metal cooled nuclear reactor with a nuclear fuel assembly in a coolant-containing primary vessel housed within a concrete containment vault, there is thermal insulation to protect the concrete, the insulation being disposed between vessel and concrete and being hung from metal structure secured to and projecting from the concrete, the insulation consisting of a plurality of adjoining units each unit incorporating a pack of thermal insulating material and defining a contained void co-extensive with said pack and situated between pack and concrete, the void of each unit being connected to the voids of adjoining units so as to form continuous ducting for a fluid coolant.

Abstract: The combination in a nuclear reactor of a concrete containment and thermal insulation for the roof of the containment, the thermal insulation being secured to the roof by hangers each of which has a linkage connector at its upper end by means of which it is secured to the roof, the linkage connector permitting movement of the hanger in two dimensions, and means at the lower end of each hanger serving to support the thermal insulation from beneath and permitting lateral movement of the insulation in two dimensions.

Abstract: A pipework junction (10, 11) has internal insulation to limit the effect of thermal shock in the form of a two part (14, 15) internal sleeve in which the parts of the sleeve are joined (34) and are, for the most part of their external surfaces, spaced from the junction by a small clearance (20) adequate to ensure that they do not lock to the junction when subjected to thermal shock. Piston rings (62) may be provided to restrain flow along the small clearance and the sleeve may be stabilized in the junction by having an expanded part (63) engaging a recess (64), which also serves to restrain flow along the small clearance.

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: A liquid metal cooled nuclear reactor of the kind in which the reactor core is disposed in a pool of liquid metal contained in the inner vessel of a double-walled steel tank supported in a vault having a roof the reactor has the roof supported by a conical support skirt carried by the wall of the vault, a single annular weld securing a main roof member to the skirt, and the conical skirt including a forked part providing inner and outer annular skirt portions from which the inner and outer vessels of the tank are carried respectively.

Abstract: Apparatus for sampling fluid flow in a plurality of passages comprises a conduit connected to the passages. A device is movable along the conduit to connect a selected passage to the conduit and allow flow from the passage through the device and conduit to test equipment which may be external to a vessel containing the passages. In one arrangement normally-closed valves are associated respectively with the passages and the movable device opens the valve of the selected passage. In an alternative arrangement which obviates the need for valves, a flexible pipe in the conduit may be used to pull the device, the flow being along the pipe.

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.