Patent Number: 046719199
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates in general to power level monitors for nuclear reactors; and more particularly, to power level monitors which detect neutron emissions from a pressurized light water nuclear reactor. 2. Description of the Related Art Several types of radiation detectors are used in the monitoring of nuclear reactors. One type detects gamma radiation from, e.g., power generation/cooling loops. Other radiation detectors sense the emission of neutrons from, e.g., the core barrel which surrounds the reactor. The neutron sensors are typically one of two types, the first type is used to detect infrequent emissions during low level operation of the reactor, such as during the start-up of the reactor in what is termed the source range. The second type of neutron sensors, for example dual uncompensated ionization chambers, such as WL-24156, manufactured by Westinghouse Industrial & Government Tube Division, detect more frequent emissions of neutrons in intermediate and power ranges. The signals output by the second type of neutron sensors include flow induced perturbations or "nuclear noise", particularly in the power range, caused by vibration of the core barrel generated when water from the cooling loops enters the core barrel. A prior art circuit for monitoring the power level of a nuclear reactor by detection of neutron emissions is illustrated in FIG. 1. The neutron sensors 10 are of the second type, described above, and output a current which indicates the number of neutrons detected during a sampling period. A current-to-voltage amplifier 15, such as an NM310 summing and level amplifier (part no. 3378C21), manufactured by Westinghouse Electrical Systems Division, converts the current signal to a voltage signal which is supplied to a rate/lag circuit 20, such as an NM311 power range rate circuit (part no. 3378C20), manufactured by Westinghouse Electrical Systems Division. The rate/lag circuit 20 is represented by an amplifier 25 having one input directly receiving the voltage from the current-to-voltage amplifier 15 and another input receiving the voltage signal filtered by an RC circuit comprising a variable resistor 30 and capacitor 35; however, a typical rate/lag circuit will include additional elements. Proper adjustment or alignment of the prior art power level monitoring circuit illustrated in FIG. 1 requires the generation of known input signals, adjustment of the rate/lag circuit 20 by, e.g., changing the resistance of the variable resistor 30. Next, additional adjustments are made to circuits (not shown) which receive the output of the rate/lag circuit 20. In practice, the alignment of the rate/lag circuit 20 has been found to be quite difficult, sometimes requiring reiterative adjustment of the rate/lag circuit 20 and the following circuits. In addition, the noise filtering capability of prior art power level monitoring circuits has been limited to removing some high frequency signals. Also, the use of an RC network in the rate/lag circuit 20 results in relatively slow response for prior art power monitoring circuits, making quick detection of transients difficult. SUMMARY OF THE INVENTION An object of the present invention is to provide a power level monitor having noise reduction capability. Another object of the present invention is provide a power level monitor capable of quick detection of transients in the neutron flux of a nuclear power reactor. A further object of the present invention is to provide a power level monitor which is easily aligned. Yet another object of the present invention is to provide a power level monitor which generates a prediction of the power level of a nuclear reactor. The above objects are accomplished by a power level monitor including a neutron detector, a current-to-voltage amplifier, an analog/digital converter and a microprocessor. When neutrons are detected, the neutron detector outputs a signal which is amplified into an analog voltage by the current-to-voltage amplifier. The analog voltage is converted into a digital sample signal by the analog/digital converter that is supplied to the microprocessor which outputs signals indicating reactor power level, rate of change of the reactor power level and predicted reactor power level for a sampling period having a predetermined length. The signals output by the microprocessor are generated from the digital sample signal by converting the sample signal into a converted signal; multiplying the converted signal by a first constant to produce a first multiplied signal; multiplying the converted signal by a second constant divided by the length of the sampling period to produce a second multiplied signal; summing a prior rate of power level change signal produced during an immediately previous sampling period with the second multiplied signal to produce the current rate of power level change signal for the current sampling period; summing a prior power level signal produced during the immediately previous sampling period with the length of the sampling period multiplied by the prior rate of power level change signal produced during the immediately previous sampling period to produce a predicted power level signal; subtracting the predicted power level signal from the sample signal to produce the converted signal; and summing the converted and predicted power level signals to produce the current power level signal. These objects together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like reference numerals refer to like parts throughout.