Patent Number: 044118589
Section: description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings in detail, FIG. 1 illustrates diametrically a local power monitoring system for the fuel assembly of a nuclear power reactor, the system being generally referred to by reference numeral 10. The raw data acquisition for the system is located in the reactor fuel core and consists of a plurality of local power rate sensors generally referred to by reference numeral 12 in FIG. 1. The signal outputs of the sensors are fed along two parallel paths through a direct analog signal processing line 14 and a precision computer line 16 in order to produce an averaged power readout 24 and a precision power readout 18, respectively. Data input to the precision computer is obtained from other sources, including for example, information calculated from sensor sensitivity models, power shock models, and various correction factors such as core condition and time domain corrections. In the processing path of computer 16, the sensor signal lines are individually biased by precalibration to obtain precision heat rate measurements from the sensor signals which are converted into local fuel power outputs corrected in accordance with various plant condition parameters from the data sources denoted by reference numeral 20 in FIG. 1. The precision power readout 18 so obtained may be fed to an analyzer 22 to provide fuel power failure forecasts and power distribution recommendations for failure avoidance purposes. The analyzer may alternatively receive its input from the averaged power readout 24 to which the signal processor 14 feeds its output in the form of local fuel power rate measurements. A calibrator 26 is connected to the signal processor 14 through which on-line correction of the processed signal output thereof may be effected by comparison of the readout 24 with the precision readout 18 while it is in operation. Thus the readout 24 may be operated continuously to provide the necessary information to the utility operator while computer 16 is non-functional in order to avoid power plant shut down because of interruptions in the supply of data to computer 16 for various reasons such as data updating. The type of sensor utilized in the power monitoring system of the present invention is very critical. As shown in FIG. 2, neutron flux sensors heretofore utilized for precision power monitoring purposes exhibited a significant change with time in signal level for a constant linear heat generation rate for a unit fuel rod length, as depicted by curve 28, assuming no emitter burn-out. With emitter burn-out compensation, the change in signal level for the neutron flux sensor is denoted by curve 30. In contrast thereto, the signal level change for a gamma sensor of the type disclosed in the aforementioned prior application is depicted by curve 32 in FIG. 2, requiring less drastic time domain correction. FIG. 5 illustrates one of the gamma sensors 34 extending through a guide tube 36 from a reactor installation to the seal flange connector 38 located at an instrument removal zone, of a pressure water reactor, for example. The sensor extends through the seal flange 40 and the thermocouple signal cables 42 thereof project through the seal plug 44 to the power monitoring hardware. Thus, gamma radiation produced by fission products in the reactor fuel assembly cause internal heating of the inner core 46 of the sensor to generate the signals in the thermocouple cables 42. While these signals provide for more accurate determination of linear heat generation rate because of its substantially direct relationship thereto, there is a signal response delay when a change in power occurs, as exhibited by the signal characteristic curve 48 shown in FIG. 3. In accordance with the present invention, the signal is modified to compensate for such slow signal response as indicated by deconvoluted heating rate signal curve 50. Referring now to FIG. 4, the signal cables from each of the sensors 34 are shown connected to a terminal box 52 through which signals of millivolt level are fed to a scanner or multiplexer 54. By way of example, eight sensors 34 are associated each fuel rod assembly of a reactor core and each sensor has two signal cables associated therewith to provide sixteen signal cables from each fuel rod assembly. In a light water reactor, between 350 to 450 of such signals are present to provide the local power rate measurements through the terminal box 52 to the scanner 54. The scanner may be a solid state multiplexer from which a signal sequence is fed to a first analog signal corrector 56 through which the signals are calibrated to provide a plurality of analog signals in signal path 58, representing local heat rates in the sensors. The signal path 58 represents a plurality of signal lines fed in parallel to the direct analog processing line in the precision signal processing line as aforementioned in connection with FIG. 1. In the precision processing line, the input analog signals enter a precision signal converter 60 through which the sensor signals are given in individual bias and corrected in accordance with a signal sensitivity model through calibrator 62 in order to obtain precision heat rate signals that are fed to a plant process computer 64 to which input data is also fed from model data storage 66 and plant condition data source 68. The signal output of the computer is then modified through a dynamic filter 70 to compensate for slow signal response as discussed with respect to FIG. 3. The signal output is then applied to the precision readout 24 in the form of a precision power display monitor furnishing local fuel power rate information for each fuel rod. Direct conversion of the signals in path 58 to local power rate information is effected through a second signal converter 72 to produce outputs reflecting the local fuel power rate for fuel rods adjacent to each of the sensors. The signal outputs are then modified by a dynamic filter 74 and passed through an extrapolator 76 to the continuous display monitor 24 as averaged power rate information. Signal correction may be effected through a calibrator 78. A substantially accurate readout is obtained by such direct signal processing only because of the more accurate signal information furnished by sensors 34 and the measures taken to compensate for slow signal response and on-line calibration through calibrator 28 from comparison with data obtained from the precision monitor 18. FIG. 6 illustrates a less complex version of the system insofar as the direct continuous signal processing path is concerned. The outputs of the sensors are fed through analog signal lines directly to calibrated voltmeters 82. The signals in these lines 80 are also fed to the contacts of a scanner 84 from which the signals are fed in sequence to the precision signal processing line 16 as hereinbefore described with respect to FIGS. 1 and 4.