Patent Number: 061817619
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Now, the embodiment of a reactor start-up monitoring apparatus according to the present invention will be described with reference to drawings. A reactor start-up monitoring apparatus shown in FIG. 1 consists of an SRNM detector 1 (radiation sensor) measuring reactor power, i.e., a neutron flux in a reactor, an analog amplifier 2 (analog filter means) limiting and rectifying the output frequency band of an output pulse from the SRNM detector 1 and functioning as an antialiasing filter, an A/D converter (digital conversion means) 3 sampling an analog signal from the analog amplifier 2 at preset fixed sampling intervals and converting the signal to the first digital data SI, two signal processing systems, i.e., a pulse measurement system (pulse measuring means) 4 and a Campbell measurement system (sum operating means and pulse measuring means) 5, connected to the output side of the A/D converter 3 in parallel and reactor power monitoring means 6, such as a monitor, for continuously monitoring information on reactor power based on the measurement data from the both measurement systems 4 and 5. Among them, the pulse measurement system 4 consists of pulse counting means 7 for counting the output pulses of the SRNM detector 1 from the first digital data S1 of the A/D converter 3 and pulse measurement evaluating means 8 for evaluabng reactor power from the count value of the pulse counting means 7. The pulse counting means 7 consists of an operating unit executing processing along a detector output pulse selection algorithm preset in accordance with, for example, the sampling intervals of the N/D converter 3. Now, the algorithms executed by this operating unit will be described with reference to FIG. 2. FIG. 2 is a view for describing the relationship between the waveform of an SRNM detector output pulse and a sampling interval. Here, reference symbol S(k) in FIG. 2 denotes k-th sampling value out of a plurality of sampling values forming the first sampling data, and S(k+1) denotes the next sampling value. In this case, if the sampling interval is shorter, more waveform information can be extracted, thereby making it possible to accurately count only the detector output pulses with other error signals such as external noise removed. To carry out the processing in a real-time manner, it is desirable that they can be realized with a minimum sampling number. The inventor of the present invention conducted studies in view of the above respects and obtained the concept that if a sampling interval is 1/n (where n is a positive number), preferably a half to one-fourth of the pulse width (about 80 nsec) of a detector output pulse (the sampling interval of about 25 nsec), then it is possible to accurately discriminate (select) only the detector output pulses from among those including other noise signals of different pulse widths. This concept will be described for each sampling interval of the A/D converter 3 hereinafter. 1): First, if the sampling interval of the NVD converter is about one-third of the pulse width, that is, the sampling interval of 25 nsec shown in FIG. 2, the following operation is conducted to obtain k-th Out(k) for each sampling interval using the k-th sampling value S(k), three sampling values S(k-3), S(k-2) and S(k-1) before the k-th sampling value and positive constants a, b, c and d: EQU Out(k)=-a.times.S(k-3)+b.times.S(k-2)+c.times.S(k-1)-d.times.S(k) PA0 2): Likewise, if the sampling interval of the ND converter 3 is an integral multiple j of about one-third of the pulse width, the following operation is conducted to obtain k-th Out(k) at the intervals of about one-third of the pulse width: EQU Out(k)=-a.times.S(k-3.times.j)+b.times.S(k-2.times.j)+c.times.S(k-j)-d.time s.S(k) PA0 3): Likewise, if the sampling interval of the AND converter 3 is one-third to one-fourth of the pulse width, the positive constants of a, b, c and d are adjusted to values other than 1, whereby the same selection and counting are possible. PA0 4): Likewise, if the sampling interval of the A/D converter 3 is a half to one-third of the pulse width, the previous two sampling values are used for the first sampling data and the following operation is conducted: EQU Out(k)=-a.times.S(k-2.times.j)+2.times.b.times.S(k-1.times.j)-c.times.S(k) PA0 5): In addition, if the sampling interval is about one-third of the pulse width, that is, the sampling interval of 25 nsec shown in FIG. 2, as a method of counting the number of pulses more accurately than a case of 1) above, a detector pulse selection algorithm was contrived. Namely, the following operation is conducted to individually obtain two operation values Out1(k) and Out2(k) using the previous sampling values S(k-3), S(k-2) and S(k-1) and positive constants a, b, c and d: EQU Out1(k)=-a.times.S(k-3)+b.times.S(k-2) EQU Out2(k)=+c.times.S(k-1)+d.times.S(k) And the number of Out(k) higher than a preset value is counted, whereby it was confirmed that only the detector output pulses can be selected and counted. And the number of the operation values higher than a preset value is counted, whereby it was confirmed that only the detector output pulses can be selected and counted. As a result, it was found that the same selection and counting are possible. Then, if the two operation values fall within a range of the predetermined set value, it is determined that the pulse is a detector pulse. In this case, Out1(k) reflects the feature of pulse rise characteristics. In case of the detector output pulse shown in FIG. 2, a negative value of Out1(k) is lower than a pulse wave height value. Out2(k) reflects the feature of pulse fall characteristics. A negative value of Out2(k) is lower than a pulse wave height value. Then, determination values of negative values higher than the noise level are set for the two operation values Out1(k) and Out2(k), respectively. If each of the operation values indicates a value lower than the corresponding determination value, the pulse is determined as a detector output pulse. In this way, if waveform selection algorithms, in which a plurality of arithmetic formulas for pulse selection are set based on the characteristics of the pulse waveforms in the respective stages and a pulse is determined as a detector output pulse if the respective operation values satisfy the conditions as a pulse, are adopted, then more accurate pulse measurement can be conducted. Furthermore, since the method of digitally measuring the pulse is used and a logic for discriminating a noise component is conversely provided, it is possible to make more accurate pulse measurement by comparing the measurement result of the conventional analog measurement means with the digital measurement logic result of the present invention. It is noted that if the sampling interval of the N/D converter 3 is about one-fourth of the output pulse width of 80 nsec, the output frequency band of the analog amplifier 2 may be limited to about 20 MH.sub.Z or less. If the pulse width of the detector output pulse is 80 nsec, an amplifier having a frequency band of up to about 10 MH.sub.Z is normally used to amplify this output pulse. It was found that the above conditions can be satisfied by the operation values without adding any special filter. The pulse counting means 7 counts the number of pulses through waveform processing based on at least one of the waveform selection algorithms 1) to 5) above, and outputs the result to the pulse measurement evaluating means 8. The pulse measurement evaluating means 8 converts counting data from the pulse counting means 7 to a reactor power value, sequentially operates a set value to be compared with the magnitude of the operation value out(k) by the pulse counting means 7 as data for monitoring information on reactor power if necessary, counts counting frequency with respect to the set value and thereby monitors the occurrence frequency distribution of the operation value out(k), i.e., wave height distribution. The wave height distribution in this case does not indicate the wave heights of output pulses in a strict sense; however, it can be treated correspondingly and used to determine whether or not the output pulse of the SRNM detector 1 is normal. The Campbell measurement system 5 consists of sum operating means 9 for adding a plurality of sampling values serving as the first digital data from the A/D converter 3 shown in FIG. 1 to obtain a sum value and outputting the value at predetermined intervals, power operating means 10 for operating a mean square value in a predetermined frequency band from the output of the sum operating means 9, i.e., operating power and Campbell measurement evaluating means 11 for converting the operation result of the power operating means 10 to a reactor power and evaluate it. As the AND conversion performance required by the earlier stage of the Campbell measurement 5, an A/D converter having a bit accuracy higher than that of a low-bit A/D converter (about eight to twelve bits for currently commercially available converters) used for the above-stated pulse measurement system 4 is desired to broaden the measurement range as stated above. The inventor of the present invention contrived a method of generating high accuracy data even with the Campbell measurement while using the first digital data from the A/D converter 3 with lower bit accuracy for use in the pulse measurement, i.e., contrived use of the above-stated sum operating means 9. This sum operating means 9 can enhance measurement accuracy by changing (adjusting) conditions of the number of added values so that the sum of, for example, two eight-bit data has accuracy of nine bits. By utilizing these characteristics, an A/D converter 3 common to the pulse measurement system 4 and the Campbell measurement system 5 can be employed. Further, in case of the conventional analog type apparatus (see FIG. 4), a plurality of Campbell measurement gain amplifiers are required in the front stage of the RMS operators. According to the present invention, these amplifiers are not needed since the processing for adjusting the number of added values by the above-stated sum operating means 9 can take the part of the amplifiers. This is because if three values having different number of added values are set by means of software in advance, the same operation of the Campbell measurement as that in the analog type apparatus can be conducted. It is preferable that the analog amplifier 2 to be used has low noise characteristics so that signal components are higher than the noise level. The sum operating means 9 conducts sum operation a plurality of sampling values forming the first digital data S1 from the AND converter 3 under at least one of the two selection and operation conditions (sum operating conditions), i.e., a condition for adding previous sampled data at 25 nsec (40 MH.sub.Z intervals by the number equal to the sum number and a condition for thinning out sampling data within a certain distance to change the number of added values and then adding them. Then, the means 9 acquires the second digital data S2 having higher bit accuracy than that of the first digital data S1 and outputs the data S2 to the power operating means 10 on a certain output cycle. As for the two selection and operation conditions stated above, the former is characterized in that easy algorithms are provided and the latter is characterized in that time response in Campbell measurement is not affected by the number of added values. The output cycle of this sum operating means 9 is determined by the band for power (mean square value) operation in Campbell measurement. Normally, a cycle of 1 MH.sub.Z suffices. Since power operation is normally conducted in a low frequency band of several tens of hertz or a high frequency band of several hundreds of hertz, e.g., in a high frequency band of 100 kH.sub.Z to 400 kH.sub.Z for the present reactor start-up monitoring monitor, sampling having a cycle of about twice (about 1 MH.sub.Z cycle in this example) as long as the maximum frequency (400 kH.sub.Z in this example) as a band-pass filter is required. The power operating means 10 conducts band limitation, that is, band pass filter processing to the second digital data S2 from the sum operating means 9 to thereby obtain mean square values and operates the power in a preset frequency band. Here, the sampling cycle is, as stated above, decreased at the sum operating means 6. Due to this, as for an aliasing analog filter, it is enough to prepare only a filter for band limitabon to 10 MH.sub.Z or less for the above-stated analog amplifier 2. Although an antaliasing filter is used to limit the frequency band to 500 kH.sub.Z or less for normal sampling of 1 MH.sub.Z or less, the sum operating means 9 provided in the earlier stage already takes this part, the antaliasing filter is not needed. FIG. 3 is a view for describing the response characteristics of an input signal while comparing those of an analog filter with those of a digital filter. In case of an input signal shown in FIG. 3(a), the signal reaches a true value within a limited period of time if a digital filter is used (constitution without a feedback loop) as shown in FIG. 3(c), it takes a while for the signal to reach a true value if an analog filter is used as shown in FIG. 3(b). Thus, if a digital filter without feedback is employed for the sum operating means 9, it is possible to improve response characteristics compared with a conventional case where an analog filter is used. The power operating means 10 conducts integral processing after square operation. A band for the integral processing is determined to be about 50 Hz or less based on the time response characteristics in Campbell measurement. It is noted that as a result of studying a method of minimizing operation time, it was confirmed that it is enough to conduct band limitation and square operation in a cycle twice as long as a required frequency, i.e., a cycle of 100 HZ. Thus, it is possible to reduce operation quantity in the Campbell measurement system 5 (power operating means and Campbell measurement evaluating means 11) and to realize real-time processing by using high-speed operation elements. Accordingly, in this embodiment, by providing the Campbell measurement system 5 with the sum operating means 9, it is possible to use an A/D converter 3 common to pulse measurement and Campbell measurement. Also, by changing and adjusting the number of added values of the sum operating means, it is possible to reduce the number of a plurality of amplifiers used in the conventional Campbell measurement, with the result that the apparatus constitution can be greatly simplified compared with the conventional digital type apparatus. In addition, since the sum operating means 9 is provided, it is enough to prepare a filter having a high cutoff frequency suffices as an antialiasing analog filter. Due to this, it is possible to provide time response characteristics in Campbell measurement capable of following up a true value within a digitally limited period of time. Furthermore, the power operating means 10 and the Campbell measurement evaluating means 11 may conduct band pass filter processing and mean square processing according to their output cycles, so that operational load can be further reduced and real-time processing is thereby possible. As for the pulse measurement system 4, since simple algorithms for digitally sampling pulse waveforms and selecting detector pulses from the obtained sampling values have been developed, it is possible to select digitally sample pulses while those having different pulse widths are not counted and to realize pulse measurement with less erroneous counting. By doing so, it is possible to provide a reactor start-up monitoring apparatus in which simple algorithms capable of making full use of the characteristics of the digital filter and capable of conducting waveform selection and the digital operation for Campbell measurement in a real-time manner are installed, with simple apparatus constitution. As an applied example in which the characteristics of the digital filter as well as the advantage of increasing the range of the software design is used, the apparatus may be provided with means for operating mean square values in a plurality of frequency bands and selecting normal ones therefrom. For example, the apparatus may be additionally provided with a Campbell signal discriminating unit in which the frequency band for Campbell measurement is divided into a plurality of bands in advance, the amount of signals in a certain frequency band is compared with those in other bands, thereby determining that the certain band is abnormal using information (determining conditions) such as information indicating that the amount of signals in a certain band is larger than that in any other band because of the existence of external noise other than detector output pulses, an appropriate band for Campbell measurement is selected from a plurality of frequency bands based on the determination result or the amount of signals for every frequency and signals in the band are selected as normal data. In that case, it is possible to conduct measurement without little influence of noise and to provide a more reliable measurement apparatus. Moreover, as a method for reducing the influence of noise on Campbell measurement, it is useful to remove the noise component of time series data before converted into frequency band data. FIG. 4 shows an example of time series data of the noise induced from the inverter. Namely, in many cases, the surge type noise is induced at several milliseconds ' intervals. If the noise is removed while separating frequency bands, the noise cannot be removed for all of the bands since this surge pulse per se includes wide frequency components and all of the frequency bands are influenced by the noise. Obviously, however, the surge components can be discriminated from the time series data. Thus, it is useful to automatically determine the frequency and timing of the surge noise component and remove the surge noise component from the waveform thereof using the first digital data or the second digital data indicating time series data. In addition, as a determination method, when the detector data is sampled, it is possible that data of not less than or not more than a certain value is set as noise data, that the noise information is added to a digital value and that the noise data is removed in a later operation. The cycle of the inverter noise is several milliseconds and data using sampling data corresponding to the width of the surge pulse (several micron seconds) is recorded on digital data as noise data. It is also useful to adopt a method for monitoring not the measured signal data but other earth wire or the like and obtaining the cycle/timing of the noise data in the digital data based on the cycle and timing of the noise induced thereto. As stated above, even if data of a certain cycle is removed from the time series data, signal values in frequency bands higher than the frequency of the data of that cycle are corrected by an adjustment coefficient determined by the ratio of the removed data, whereby it is confirmed that the same result is obtained as that of the data which is not removed without any problem. In case of the inverter noise, in particular, its cycle is several milliseconds. While the data used for Campbell measurement is in bands of several hundreds hertz, it is possible to obtain a Campbell measurement value free from the influence of noise by this method and to realize a measurement apparatus free from the influence of noise further. According to the invention, the cycle/timing of the noise is obtained from the time series data and the result is added to the digital data. Thus, the added data is not used for the operation of the Campbell measurement and measurement without malfunction due to external noise can be made. According to the invention, the conventional analog measurement means is also provided, whereby the measurement result of the digital type pulse measurement means is compared with that of the analog type measurement means and, therefore, more accurate pulse measurement can be made.