Induced nuclear reactions: processes – systems – and elements – Testing – sensing – measuring – or detecting a fission reactor... – Flux monitoring
Reexamination Certificate
1999-09-20
2001-01-30
Jordan, Charles T. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Testing, sensing, measuring, or detecting a fission reactor...
Flux monitoring
C376S259000
Reexamination Certificate
active
06181761
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nuclear reactor start-up monitoring apparatus installed in, for example, a boiling-water reactor, particularly relates to the contrivance of the constitution of a digital apparatus for signal-processing of an output pulse from a radiation sensor disposed inside or outside of a reactor pressure vessel as data for measuring and monitoring reactor power.
2. Description of the Related Art
In a recent boiling-water reactor, there are provided with radiation sensors such as six to ten SRNM (Start up Ranged Neutron Monitor) detectors and 100 to 200 LPRM (Local Power Ranged Monitor) sensors installed in a reactor pressure vessel of the reactor, and a reactor power monitoring apparatus such as, for example, a start-up ranged monitor and power ranged monitor, for measuring and monitoring reactor power based on the detected signals by these radiation sensors.
Among them, the start up ranged neutron monitor (to be referred to as “reactor start-up monitoring apparatus ” hereinafter) monitors reactor power at the time of reactor start-up or the like based on output pulses in accordance with neutron fluxes detected by the SRNM detectors. This apparatus performs processing for counting the number of output pulses of the SRNM detectors (to be referred to as “pulse measurement” hereinafter) in low reactor power ranges (10
−9
% to 10
−4
%) and performs processing for measuring the power of a fluctuabon component generated by the overlapping output pulses of the SRNM detectors, i.e., processing based on the principle of Campbell Law (to be referred to as “Campbell measurement” hereinafter) in high reactor power ranges (10
−5
% to 10%).
An example of a reactor start-up monitoring apparatus conducting the pulse measurement and Campbell measurement as stated above will be described based on
FIGS. 5 and 6
.
A reactor start-up monitoring apparatus shown in
FIG. 5
consists of an SRNM detector
100
detecting, as data for measuring reactor power, neutron fluxes in the reactor, an analog amplifier
101
amplifying and rectifying the detector output pulses, two signal processing systems connected in parallel to the signal output side, i.e., a pulse measurement system
102
and a Campbell measurement system
103
, and reactor power evaluating (monitoring) means
104
for continuously monitoring/evaluating reactor power at least at time of starting up the reactor based on the processing results of the measurement systems
102
and
103
.
Among those elements, the pulse measurement system
102
consists of a pulse wave height comparator
105
comparing the wave height value of the detector output pulse amplified by the analog amplifier
101
with a preset wave height value and counting the number of the detector output pulses having wave heights higher than the preset wave height value, and pulse measurement evaluating means
106
evaluating reactor power at the time of low power output by converting the counted pulse number to the output level of the reactor power.
Also, the Campbell measurement system
103
consists of a plurality of amplifiers (a small gain amplifier
107
, a medium gain amplifier
108
and a large gain amplifier
109
) amplifying and attenuating the detector output pulses amplified by the analog amplifier
101
under different conditions of a plurality of amplification factors and thereby limiting frequency bands to a specified band, a plurality of MS (Mean Square) operators
110
,
111
,
112
calculating mean square roots of the outputs of the amplifiers
107
to
109
and Campbell output evaluating means
113
for selecting an optimum value from the outputs of the operators
110
to
112
and for evaluating reactor power at the time of high power output.
In the reactor start-up monitoring apparatus stated above, if reactor power is low, pulse measurement is executed to adjust an output pulse to a signal level optimal to the pulse wave height comparator
105
and to accurately count the number of output pulses of the SRNM detector
100
by the analog amplifier
101
. If reactor power is high, Campbell measurement is executed. When the Campbell measurement is executed, about five figures which is the measurement range thereof, cannot be covered by a single MS (Mean Square) arithmetic element
110
,
111
or
112
. Due to this, as shown in this example, a plurality of amplifiers
107
to
109
amplify the output of the SRNM detector
100
at different amplification factors to thereby cover the overall measurement range. In that case, an amplifier can be formed of a single logarithmic amplifier. Recently, however, there are many cases where divided amplifiers are employed as described above in light of temperature characteristics and the like, which constitution makes it possible to continuously monitor the wide measurement range of the reactor.
Nevertheless, since the above-stated reactor start-up monitoring apparatus is constituted to signal-process detector output pulses with an analog circuit, there is a possibility that counting only based on the magnitude of pulses may cause error measurement by the influence of discharge pulses generated as a result of discharge within the SRNM detector and noise erroneously generated by electromagnetic induction in the vicinity of the monitoring apparatus. As a result, this apparatus has a disadvantage in that information contained in the waveforms of the detector output pulses cannot be always utilized efficiently.
To deal with the above disadvantage, it is necessary to sufficiently shield signal cables and the like to prevent the induction of external noise at the time of execution. Additonally, as measures to prevent erroneous measurement due to the external noise during execution, there is a method of using not only pulse wave heights but also other waveform information since the waveforms of the erroneous pulses are, in most cases, different from those of signal pulses. Further, since a detector output pulse is changed by the leakage of gas sealed in the detector or by the abnormal distance between electrodes, it is possible to detect these abnormal states during measurement by monitoring waveforms. In the present system, however, it is necessary to, for example, diagnose the detector while precluding the system from monitoring targets. According to the present system, it is necessary to provide circuits dedicated to Campbell measurement and pulse measurement, respectively to simultaneously conduct the measurements, which results in larger-sized and complicated circuits. Due to this, the measurements are conducted by different hardware and, therefore, the apparatus shown in
FIG. 5
has a problem that maintenance and inspection operations are carried out for the measurements, respectively. To solve this problem, it is desired that hardware parts are integrated, particularly, signal processing parts are integrated.
Considering the above, as means for solving the erroneous measurement problems with the analog circuit of that type, there is proposed a digital type reactor start-up monitoring apparatus for converting a detector output pulse to a digital signal and for conducting signal processing (e.g., in Japanese Patent Application Laid-Open No. 9-274095). Description will now be given to an example of this apparatus based on FIG.
6
.
A digital type reactor start-up monitoring apparatus shown in
FIG. 6
consists of an SRNM detector
100
, an analog amplifier
101
, as in the case of the above apparatus, a pulse measurement system
102
and a Campbell measurement system
103
connected to the signal output side in parallel, and reactor power evaluating (monitoring) means
104
, such as a monitor, for continuously monitoring reactor power at the time of reactor start-up based on the measurement results of the measurement systems
102
and
103
.
Among the elements, the pulse measurement system
102
consists of the first A/D converter
120
sampling the detector output pulse amplified by the analog amplifier
101
at intervals shorter
Izumi Mikio
Tarumi Teruji
Yunoki Akira
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Jordan Charles T.
Kabushiki Kaisha Toshiba
Mun Kyongtaek K.
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