Patent Number: 048030406
Section: description

DETAILED DESCRIPTION OF THE INVENTION Reference will now be made to the present preferred embodiments of the invention, an example of which is illustrated in FIGS. 1 and 2. FIG. 1 illustrates the architecture of the failed fuel surveillance and diagnosis apparatus of the present invention. An artificial intelligence based "inference engine" 10 along with a factual knowledge base 12 comprise a knowledge system which is interfaced to the reactor's data acquisition system and control room instrumentation. The artificial intelligence based inference engine 10 will hereinafter be referred to as a judgmental knowledge base. The judgmental knowledge base, along with the factual knowledge base, comprise a knowledge system which may be used to emulate a reasoning task to interpert encoded knowledge of human experts stored therein. The reactor parameters which are used as input into the judgmental knowledge base 10 include readings from the primary coolant flow rate with a flow meter 14 and readings of the reactor power with a reactor power level detector 16. Preferably, these readings include two independent readings of the primary coolant flow rate through a first flow channel 17 and a second flow channel 18 and two independent readings of the reactor power through a first power channel 19 and a second power channel 20. The remaining input parameters originate within the DN monitoring station (DNMS). The DNMS 22 generates output signal 24, indicating the age of the delayed neutrons, and signal 26, indicating the ERA of a breached fuel element, to judgmental knowledge base 10. Preferably, the DNMS 22 is a multiple detector DN monitoring system, as the one disclosed in U.S. Pat. No. 4,415,524 issued to Kenny C. Gross et al. This system includes at least three DN activity detectors 28 and an ERA meter 30. In the prefered embodiment, which utilizes the ERA meter disclosed by the above-referenced patent, the DN age signal 24 and ERA signal 26 are generated by means of the three DN detectors in combination with a loop flow circuit 32 and pump 34. The pump 32 conveys coolant from reactor core through the loop 32 and back into the core. The three DN activity detectors 28 are placed proximate to the loop flow circuit 32. The DN activity detectors generate output signals to computer system 36, which communicates with factual knowledge base 12. The computer system 36 generates the DN age signal 24 and the ERA signal 26 by means of the equations disclosed in the above-reference patent. Factual knowledge base 12 contains factual data, which is available to the judgmental knowledge base 10 in the decision making process. Factual knowledge base 12 contains data relating to: the radioactive decay constants for the DN emitting fission products; isotopic fission yields; recoil correction factors; probabilities of neutron emmission; known flow delay times between successive DN detectors in the DNMS 22; equations for variations in transit times as a function of coolant flow rate; DN detector efficiencies and calibration factors; and any other relevant nuclear and system data. An operability validaton system 38 detects any malfunction in the components of DNMS system 22 and interfaces signals indicating a malfunction to the judgmental knowledge base 10. In the exemplary embodiment wherein the multiple detector DN monitoring system is utilized, detecting system 38 is comprised of a system which detects the flow in flow circuit 32, the status of the pump 34 and the temperature of the flow through the loop 32. The system includes a flow metering device 44 which measures the flow rate through loop 32 and thermocouples 46 which measure the temperature of the flow in the circuit. The system also includes a voltage meter 40 and a current meter 42 which measure the voltage and current of pump 34 respectively. Although the apparatus of the present invention has been described with reference to a multiple detector DN monitoring system, it will b readily apparent to those skilled in the art that other systems which measure the ERA may also be used along with the appropriate operatibilty validation system. The judgmental knowledge base 10 receives, as inputs, signals indicating the primary flow rate, the reactor power level, the delayed neutron age, the ERA, and the signals indicating the operability of the components in the DNMS from operability validation detector 38. Judgmental knowledge base 10 then implements an operability logic algorithm, which is illustrated in FIG. 2. Output from the judgmental knowledge base 10 is integrated with a display monitor 48 in control room 50 and then multiplexed back to data acquisition system 100 for archive backup storage. During operation with a breached element that gives a DN signal, the total age (i.e. sum of T.sub.tr and T.sub.h) that is output from the ERA meter 30 will be continuously monitored. If the age is increasing, a check will first be made to determine if T.sub.h is increasing. If so, the ERA value will be compared against a predetermined shutdown limit. That limit will replace the current administrative limit on DN-signal magnitude, and is expected to be far more conservative in limiting events that might challenge safety or radiological performance guidelines, while minimizing the possibilities of unnecessary reactor trips caused by events having no safety significance. If the computed ERA value exceeds the limit, an audible alarm 54 will be sounded and the operator will initiate a manual shutdown of the reactor. If T.sub.h is not increasing, then the sodium transport time is increasing. In this event, a check is first made with the two independent primary flow sigaals from flow channels 17 and 18. If it is determined that the flow through the core is not being changed, an alarm status is set and the check is made for a malfunction affecting flow control within the DNMS loop 22 itself. Signals employed for this comparison are the DNMS electromagnetic pump voltage and current from voltage meter 40 and current meter 42 respectively, the DNMS flow from flow meter 44 and the loop flow temperature from thermocouples 46. If it is determined that the indicated change in the T.sub.tr is attributed to a malfuction in the DNMS loop 22, then an attempt can be made to correct the problem during the time period provided for in the technical specifications, or the operator can initiate a manual shutdown. Finally, in the unlikely event that Ttr would be increasing while all primary and DNMS-loop signals indicate nominal readings, then this would be an indication of a possible formation of an assembly flow blockage. The reactor would then be scrammed. In the preferred embodiment of the present invention, an interactive terminal 62 is interfaced with display monitor 48 and judgmental knowledge base 10. The reactor operator is then provided with an interactive capability to manually query the status of any component of the system for operability validation. Thus, in this embodiment of the present invention, the system may be operated in a passive surveillance mode. Use of the present invention will reduce complexity and mitigate confusion in the reactor control room 50. It will minimize the possibility of human error or oversight, by providing automatic annunciation of discrepant signals or the incipiences of initiating faults. It also provides the reactor operator with a passive surveillance mode. This combination of automatic and manual systems reduces challenges to plant availability while allowing incorporation of the role of the operator in a manner of which most effectively augments the achievement of overall plant operability goals. In summary, diagnostic information made available from the present invention will be processed, compared against derived information from independent physical sensors, and presented to the reactor operator with the aid of the artificial intelligence-based surveillance and diagnosis system of the present invention. This apparatus, will be multiplexed to output devices in the reactor control room 50, will provide the operator with rapid identification (as much as ten minutes in advance of signals from the cover-gas monitoring system) of conditions that could lead to plant operational degradation, enabling him or her to terminate or avoid events which might challenge safety or radiological performance guidelines. The foregoing description of the preferred embodiments of the invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The embodiments were choosen and described in order to best explain the principles of the invention and its practical applications to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.