Patent Number: 046559922
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGS. 1 and 2 of the drawings, the upper portions of a number of fuel or breeder sub-assembly wrappers or channels 10 are shown which each discharge liquid sodium coolant into a bulk volume 11. An interrogating ultrasonic transducer 12 immersed in liquid sodium in the bulk volume 11 emits a beam 13 of ultrasonic pulses which is narrow as viewed in FIG. 1 but wider as viewed in FIG. 2. This beam glances over the outlet ends of the channels 10 and returns echoes from diametrically-opposed edges 10A and 10B on each channel. The edges can be considered as locality point pairs. By measuring the time intervals t1, t2 and t3 and with knowledge of the diameter of the channels, it is possible to resolve the means temperature of sodium issuing from the outlets of the channels 10 non-invasively and before any significant cross-flow can take place. FIG. 3 shows a plan of a fast reactor core comprising a hexagonal array of fuel and breeder material sub-assemblies. The upper parts of the fuel or breeder sub-assemblies are of cylindrical shape, their lower ends terminate in spikes for engagement in a diagrid structure of the reactor and they are of hexagonal section over the remaining length. The inner sub-assemblies are assigned to reactor fuel and control devices, the outer three `rings` of sub-assemblies, i.e. those outside the phantom line 50, are assigned to breeder fuel. The construction of the reactor in this embodiment may be such that the temperatures of the inner sub-assemblies are measured by thermocouples, whereas the breeder sub-assembly temperatures are to be measured by ultrasonics. As shown, a device S is provided for emitting two ultrasonic beams, B1 and B2. It may comprise waveguides or immersed transducers suitable for sodium and operating in transmit-receive mode. The beams are made to sweep over the outer breeder sub-assemblies by oscillating the device S clockwise and anticlockwise alternately. A device similar to S may be placed at every vertex (or every alternate vertex) of the hexagonal array, so that the devices S may collectively scan all of the breeder sub-assemblies by means of beams B1 and B2. In order to understand the function of the electronics used to realise the measurement, the problem of examining the echoes from one sub-assembly will be described with reference to FIG. 4. The ultrasonic beam from the scanning source S gives rise to echoes as a result of reflection from the `high spots` on the sub-assembly top at D1 and D2. The echo times T1 and T2 are to be measured so that their difference can be computed for the temperature determination. By knowing the angle of direction .theta. of the beam from some known reference direction, and from the pulse-echo times, it is possible to calculate the location of the high spots D1 and D2 (i.e. points at which the reflecting surfaces are normal to the beam), and plot them as an ultrasonic image of the area. In practice, because of the divergence of the beam, the image obtained of the high spots would be two `streaks`, I1 and I2. It should be noted that whilst the image is streaked, the echoes always arise from the high spots, but these may reflect from edge rays of the actual sonic beam. The exact orientation of the high spots may be determined by examining the intensity I of the reflected signal. FIG. 5 shows how this would vary with the direction of the beam for one high spot, D1. The maximum signal is obtained when the central ray of the beam is pointing directly at the high spot, and so the orientation of the point D1 can be determined in terms of the angle .theta.. The time difference T1-T2 between the signals from both D1 and D2 provides an indication of the sonic velocity, and hence fluid temperature, whether the echoes arise from the central ray of the beam or not. In most cases this would be true, but when the beam is not pointing directly at the high spots, it may also be reflecting from an adjacent sub-assembly, and confusion between signals may occur. Consequently the need to identify when the echoes are coming from a correctly pointed beam. The electronic system to identify the echoes and report deduced temperatures is shown diagrammatically in FIG. 6. The scanner S is driven in its oscillatory motion by a motor 52 which may be a stepping motor. For this example, however, the motor is considered free-running. A position encoder 54 on the mechanical drive enables the direction (.theta.) of the scanning tranducer S to be determined at anytime. The controlling processor 56 (Intel 8086) loads a waveform generator 58 (Namlak type VHR 2195) with data for driving a selected one of the transducers with the optimum pulse shape for accurate timing of echoes. The waveform is then passed to the selected transducer through a multiplexer 60 to a transducer driver 62. The returned echo signals received by the transducer are passed through a pre-amplifier 64 via a multiplexer 66 to a logarithmic response amplifier 68. This has a dynamic range of typically 60-70 db, allowing the entire range of reflected echoes to be accommodated. The individual echoes from targets in the path of the ultrasonic beam are detected by the peak detector 70, which then interrogates a timing clock 72 to obtain a timing for each echo. The amplitude of the echo is digitised by an analogue to digital convertor 74. The entire data for each echo, viz its digitised amplitude, its time since pulsing of the respective transducer, and the position of the scanner S at the time of echo reception are all stored temporarily as a single data `word` in a First-In-First-Out store (FIFO) 76. Each succeeding echo has its data placed sequentially into the store. After about 2 milliseconds all echoes of interest from a particular transducer transmit pulse will have been received, but a further 5 milliseconds (say) will elapse before all spurious echoes will have died away, and the same, or an adjacent transducer may then be pulsed. During this period, the data in the FIFO 76 is extracted and interpreted. The approximate location of the wanted echoes will, of course, already be known. A data processor (Intel 8086) 78 recognises the wanted echoes, and stores the precise amplitude and timing data for each in an appropriate table in a random access memory 80. This memory, in effect, stores all the data for all the `streak` images described earlier in tabulated form. As the scanning device S moves, and the transducers are pulsed, these tables are updated with the latest information. When the FIFO 76 is empty, the controlling processor 56 prepares and fires the next transducer pulse. The random access memory 80 that stores the echo tables is of two-port form. An analysing processor 82 (Intel 8086) examines these tables, deduces the maximum signal for a particular echo (i.e. the peak of a `streak`, cf. FIG. 5), calculates time differences between appropriate echoes, and temperatures for specific fuel assemblies. The processor 82 may operate independently of the remainder of the system so that it can apportion its time to suit various purposes. For example, it can devote more time to examining the temperature variations (temperature noise) of a particular sub-assembly, or more time to the more critical breeder sub-assemblies. It may, of course, apply different significance to the temperatures deduced for different assemblies, e.g. apply a different threshold for instituting different types of output signal (e.g. alarm signals) for alerting operators and/or automatic control of the reactor. An output processor 84 (Intel 8087) via output lines 86 may drive alarm and possibly reactor shut-down facilities. In addition, various displays and hard-copy output for information and experimentation may be provided via the output lines 86. In FIG. 7 a fuel channel 30 is fitted internally with two reflectors 30A, 30B. These are interrogated by an ultrasonic beam 33 from a transducer 32 enabling temperature or temperature noise in the region of the channel between the reflectors to be measured. Reflector 30A has a horizontal face (so that some of the beam 33 is reflected back along its path of incidence) and an inclined face (so that some of the beam 33 is reflected to reflector 30B). Reflector 30B simply has an inclined face. FIG. 8 shows a general view of the top portion of a fast reactor sub-assembly 90, and identifies the top edge 91 (which forms the outlet of the sub-assembly and may be castellated), an orientation bar 92, a burst pin detection pipe 94, and a plate 96 which retains the breeder fuel. As shown in FIG. 9, a transmit-receive transducer 98 can be located (as indicated by arrows 100) from two or more of these features. Thus it is possible to obtain the time difference, and hence temperature information required since the separation distances between the targets 91, 92, 94 and 96 will be accurately known. Thus, a transducer can be placed to obtain echoes from all four targets simultaneously. In each of the embodiments described, it will be noted that the ultrasound source is physically discontiguous with the zone or zones at which temperature measurements are to be made, i.e. in the sense that the ultrasound is coupled from a remote location to the zone or zones through the fluid itself without relying on any intermediary structure which would otherwise interfere with fluid flow through such zones.