JP2008256681A - System for monitoring pressure fluctuations in nuclear power plant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a monitoring apparatus for measuring pressure fluctuation in reactor equipment, with high accuracy and high reliability. <P>SOLUTION: The apparatus is provided with an optical fiber 3, having a strain-measuring unit 4 adhered onto the surface of piping 2 connected to a reactor pressure vessel housed in a reactor containment 1 for measuring the strain applied to the pining 2 connected to the reactor pressure vessel; a strain converter 5, connected to the optical fiber 3 for converting a light signal into an electrical signal and a monitor 7 connected to the strain converter 6. Alternatively, the optical fiber 3 may be designed to directly pass through a through-hole 5 formed in the reactor containment 1 without converting the light signal to the electrical signal and the light signal may be converted to the electrical signal by a strain converter installed outside of the reactor containment 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a system for monitoring pressure fluctuations in a nuclear power plant such as a boiling water reactor.

  In boiling water reactors, if the heat output is increased with the current structure and the steam flow rate is increased, the pressure pulsation in the main steam system will increase in some plants and this will propagate to the reactor and be transferred to the reactor. It is also assumed that the steam dryer installed inside will be damaged.

  There are also known cases where pressure pulsations that occur according to the number of rotations of the pump and the number of blades damage the equipment in the furnace when the number of rotations of the pump is changed to increase the recirculation flow rate. Yes. In general, as means for suppressing pressure fluctuation, there are known a method of releasing pressure or a method of installing a Helmholtz resonator to absorb and suppress pulsation.

  As such a suppression means, for example, a means for discharging steam to the water pool when the pressure rises above a certain pressure, and a number of buffering holes are provided in the discharge pipe into the water in order to suppress water surface vibration at the time of discharge. In other examples, a method of installing a Helmholtz resonator adjacent to a pressure vessel of a pulsation generation source (see, for example, Patent Document 1) is performed.

In particular, in the latter method, it is necessary to grasp the frequency and magnitude of pressure pulsation. Therefore, for example, it is conceivable to install a pressure sensor with good time response in the pipe, but it is disadvantageous in terms of cost to newly provide a through-hole in the pipe which is a pressure vessel having a high internal pressure. For this reason, in recent years, a technique for detecting the pressure pulsation in the pipe or the reactor indirectly by detecting the strain on the pipe surface has been performed. In addition, in order to transmit the signal measured by such a method to the outside of the containment vessel, an instrumentation through hole containing a signal transmission line made of metal is usually used. Since there is a converter between the electrical and optical signals inside and outside the containment vessel, the metal signal transmission line is converted into an optical fiber signal transmission line and penetrates the containment vessel wall. Optical fiber instrumentation through holes have been developed.
JP-A-7-139738

  In the above-described method for monitoring the strain on the pipe surface, the main steam pipe and recirculation system pipe to be monitored are in the reactor containment vessel that is sealed during operation, and thus cannot enter the containment vessel. The strain amplifier or strain gauge cable installed inside cannot be adjusted. For this reason, the signal / noise ratio (S / N ratio) is adjusted to be high at the time of installation before operation, but cannot be readjusted when the measured stress value or electromagnetic field environment changes due to operation and the S / N ratio deteriorates. . Since the strain on the pipe surface due to pressure pulsation is very small, it may become impossible to monitor due to the deterioration of the S / N ratio. In addition, the number of measurement control lines that penetrate the inside and outside of the containment vessel is limited by the number of wire penetrating devices that penetrate the inside and outside of the containment vessel called instrumentation penetration, so the number of strain gauges installed is limited. There is also. Furthermore, it is desirable to install monitoring points at intervals of about one-tenth of the wavelength of the pulsation so that the shape of the standing wave formed by the pressure pulsation can be sufficiently captured in the pipe. If a strain gauge is installed at a position far away from each other, the distance from each strain gauge to the strain amplifier becomes longer. Strain gauges usually read minute changes in resistance values by converting them to voltages using a bridge balanced circuit, so the error increases as the length of the signal line to the amplifier increases in this way, and ambient electromagnetic noise is also reduced. It becomes easy to pick up.

  The present invention has been made to solve the above-described problems, and measures pressure pulsations in piping and pressure vessels in a reactor containment vessel at a number of points with a high S / N ratio. An object of the present invention is to obtain a pressure fluctuation monitoring device capable of providing a means for transmitting the signal to the outside.

  The present invention has been made to solve the above problems, and is attached to the surface of a reactor pressure vessel housed in a reactor containment vessel or a pipe connected to the reactor pressure vessel, and these reactors An optical fiber having a strain measuring unit for measuring strain of a pressure vessel or a pipe connected to the reactor pressure vessel, a strain transducer connected to the optical fiber to convert an optical signal into an electrical signal, and a strain transducer A pressure fluctuation monitoring system for a nuclear power plant, comprising a connected monitoring device.

  In the present invention configured as described above, since the pipe strain is transmitted in the form of light through the optical fiber, it is not affected by electromagnetic noise until it reaches the converter. For this reason, the S / N ratio is greatly improved. Moreover, since the existing instrumentation through-hole can be used, it can be easily added to the existing plant.

  Embodiments of a pressure fluctuation monitoring apparatus according to the present invention will be described below with reference to the drawings.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a perspective view showing a part of the structure of the first embodiment.

  A strain measuring unit 4 attached in the circumferential direction of a pipe 2 installed inside the reactor containment vessel 1, an optical fiber 3 for guiding an optical signal measured by the strain measuring unit 4, and a meter in the reactor containment vessel 1 An optical signal-voltage signal converter (strain converter) 6 installed near the loading / unloading port 5 and a monitoring device 7 for observing an output signal from the converter 6 are configured.

  In the present embodiment configured as described above, since the pipe strain is transmitted in the form of light in the optical fiber 3, electromagnetic noise is not picked up until the transducer 6 is reached. The S / N ratio is improved regardless of the distance between the strain measuring unit 4 and the transducer 6. Moreover, since the existing instrumentation wire through-hole can be used, a pressure fluctuation monitoring device having a high S / N ratio can be easily constructed in an existing plant.

  The position of the strain measurement unit 4 is a position where the pressure amplitude of the standing wave of the pressure pulsation in the pipe calculated by acoustic analysis based on the frequency of the pressure pulsation during the operation of the reactor and the speed of sound in the pipe 2 is maximized ( It is preferable to install it on the part of the vibration belly.

  Furthermore, the position of the strain measurement unit 4 is the structural vibration with the standing wave of the pressure pulsation in the pipe 2 calculated by acoustic analysis based on the frequency of the pressure pulsation during the operation of the reactor and the speed of sound in the pipe 2 as input. It is preferable to install at a position where the surface strain amplitude by analysis becomes a maximum. For example, when there are multiple positions where the pressure amplitude is maximized, the surface strain amplitude is usually higher in the portion where the pipe thickness is thinner. In this case, the pressure amplitude is maximized and the pipe wall thickness is increased. It is preferable to install the strain measurement unit 4 in a relatively thin portion.

(Second embodiment)
Next, a second embodiment of the pressure fluctuation monitoring apparatus for a nuclear power plant according to the present invention will be described with reference to FIG.

FIG. 2 is a perspective view showing the configuration of the second embodiment in partial cross section.

  The instrumentation through-hole 5 of the reactor containment vessel 1 in this embodiment is a physical through-hole that does not contain a metal wire. The optical fiber 3 is directly passed through the instrumentation through hole 5, and the optical signal / voltage signal converter 6 is installed outside the reactor containment vessel 1.

  In the present embodiment configured as described above, the optical fiber 3 is directly taken out of the reactor containment vessel 1. For this reason, it does not receive noise from the electromagnetic field environment in the nuclear reactor containment vessel 1 including the through-hole 5 which is easy to pick up electromagnetic noise. For this reason, even when the reactor is in operation, a high S / N ratio can be measured only by adjusting the outside of the containment vessel that can be entered by a person.

  In addition, the optical fiber strain gauge can transmit signals from the strain measuring units 4 at a plurality of points using only one optical fiber 3, but in the first embodiment, the signal is converted into an electrical signal in the reactor containment vessel 1. Instrumentation penetration 5 must be used. On the other hand, in this embodiment, the optical fiber 3 can transmit signals from the plurality of strain measurement units 4 to the outside of the reactor containment vessel only by using one through-hole. For this reason, it is possible to easily monitor a plurality of points by simply replacing one of the instrumentation through holes 5 including the existing metallic signal line with the instrumentation through hole 5 for the optical fiber 3. A fluctuation monitoring device can be built in an existing plant.

(Third embodiment)
Next, a third embodiment according to the present invention will be described with reference to FIG. FIG. 3 is a perspective view showing a part of the configuration of the third embodiment.

  In this embodiment, the through-hole 5 of the reactor containment vessel 1 is an optical fiber instrumentation through-hole, and the optical fiber 3 attached to the pipe 2 is coupled to the optical fiber 9 in the through-hole by an optical fiber coupler 8. The optical fiber coupler 8 again couples the transmission optical fiber outside the reactor containment vessel 1 to the optical signal-voltage signal converter 6 installed outside the reactor containment vessel 1.

  The distortion signal generated by the converter 6 is input to a fast Fourier transformer (frequency analyzer) 10 to output a frequency and a distortion amplitude value. With this frequency and strain amplitude value as input, a standing wave distribution of pressure pulsation including the reactor pressure vessel 13 connected to the pipe 2 is calculated by the acoustic analysis routine 12 in the computer 11.

  This calculation result is transferred to the structural vibration analysis routine 14 in the computer 11, and the pressure pulsation amplitude on the surface of the reactor internal structure 15 such as a steam dryer housed in the reactor pressure vessel is input to obtain the structural vibration. Perform analysis and output maximum strain amplitude value. This maximum strain amplitude value is passed to the comparison routine 17 and compared with the allowable strain amplitude calculated with the reactor temperature and the structure material as inputs. When the maximum strain amplitude value is larger than this value, A warning signal is displayed on the monitor 16.

  In the present embodiment configured as described above, the internal structure of the reactor structure can be easily and accurately applied from the outside of the pressure boundary without installing a resistance-type strain gauge that is weak against electromagnetic noise. A monitoring device for diagnosing soundness can be constructed.

Example 4
Next, a fourth embodiment of the pressure fluctuation monitoring apparatus for a nuclear power plant according to the present invention will be described with reference to FIG.

  FIG. 4 is a perspective view showing a part of the configuration of the fourth embodiment. This embodiment is a modification of the first embodiment, and is configured to measure strains of a plurality of strain measuring units 4 using a plurality (two in the illustrated example) of optical fibers 3. A signal multiplex transmission amplifier 20 is disposed in the reactor containment vessel 1, and a demodulation amplifier is disposed outside the reactor containment vessel 1. Each optical fiber 3 is connected to a respective converter 6, and the electrical signal converted here is sent to a signal multiplex transmission amplifier 20 and multiplexed. Then, it penetrates the through hole 5 with a single line, is separated into a plurality of voltage signals by the demodulation amplifier 21, and is sent to the monitoring device 7.

  According to this embodiment, the strains of the plurality of strain measuring units 4 can be measured, and the through hole 5 can be penetrated by one line.

(Other examples)
Each embodiment described above is merely an example, and the present invention is not limited to these. For example, the contents of the computer 11 of the third embodiment (FIG. 3) can be applied to other embodiments.

The perspective view which shows 1st Embodiment of this invention in a partial cross section. The perspective view which shows 2nd Embodiment of this invention in a partial cross section. The conceptual diagram which shows 3rd Embodiment of this invention. The perspective view which shows 4th Embodiment of this invention in a partial cross section.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Reactor containment vessel, 2 ... Piping, 3 ... Optical fiber, 4 ... Strain measuring part, 5 ... Through-hole, 6 ... Converter (strain converter), 7 ... Monitoring apparatus, 8 ... Optical fiber coupler, 9 ... Through Optical fiber in hole, 10 ... Fast Fourier transformer (frequency analyzer), 11 ... computer, 12 ... acoustic analysis routine, 13 ... reactor pressure vessel, 14 ... structural vibration analysis routine, 15 ... internal reactor structure, 16 ... Monitor, 17 ... comparison routine, 20 ... signal multiplex transmission amplifier, 21 ... demodulation amplifier.

Claims (8)

  Affixed to the surface of the reactor pressure vessel housed in the reactor containment vessel or piping connected to this reactor pressure vessel, the strain of these reactor pressure vessels or piping connected to this reactor pressure vessel is reduced. A nuclear power plant comprising: an optical fiber having a strain measuring unit for measuring; a strain converter connected to the optical fiber to convert an optical signal into an electrical signal; and a monitoring device connected to the strain converter. Pressure fluctuation monitoring system.   2. A pressure fluctuation monitoring system for a nuclear power plant according to claim 1, wherein the optical fiber is directly passed through a through hole provided in the containment vessel without being converted into an electrical signal, and an optical signal is transmitted by a strain transducer installed outside the reactor containment vessel. A pressure fluctuation monitoring system for a nuclear power plant, characterized by converting the power into an electric signal.   The pressure fluctuation monitoring system for a nuclear power plant according to claim 1, wherein the optical fiber is directly connected to an optical fiber for transmission of an optical fiber type instrumentation through hole provided in the containment vessel without being converted into an electric signal, and is connected to the outside of the containment vessel. A pressure fluctuation monitoring system for a nuclear power plant, wherein an optical signal is converted into an electric signal by an installed strain transducer.   The pressure fluctuation monitoring system for a nuclear power plant according to claim 1, wherein a plurality of voltage signals output from the converter are input to a signal multiplex transmission amplifier installed in the storage container, and an output signal of the signal multiplex transmission amplifier is input to the storage container. A pressure fluctuation monitoring system for a nuclear power plant, which is separated into a plurality of voltage signals by a demodulating amplifier installed outside the containment vessel through an instrumentation through-hole.   2. A pressure fluctuation monitoring system for a nuclear power plant according to claim 1, wherein the strain measurement unit uses a vibration wave pressure frequency in the reactor operation and a sound wave in the piping calculated by acoustic analysis based on the sound velocity in the piping. A pressure fluctuation monitoring system for a nuclear power plant that is installed at a position where the pressure amplitude of the nuclear power plant becomes maximum.   6. The pressure fluctuation monitoring system for a nuclear power plant according to claim 5, wherein the strain measurement section uses a pressure pulsation standing wave in a pipe calculated by acoustic analysis based on the frequency of pressure pulsation during reactor operation and the speed of sound in the pipe. A pressure fluctuation monitoring system for a nuclear power plant, which is installed at a position where the surface strain amplitude is maximized by structural vibration analysis. In the nuclear power plant pressure fluctuation monitoring apparatus according to claim 1,
A frequency analyzer that performs fast Fourier transform using the measured strain signal as input and identifies the frequency of the strain signal;
Based on the frequency of the strain signal identified by the frequency analyzer, the standing wave of pressure pulsation in the pipe and the reactor pressure vessel connected to this pipe is calculated by acoustic analysis, and the strain signal is calculated in the reactor pressure vessel. Conversion means for converting the pressure amplitude into
A pressure fluctuation monitoring system for a nuclear power plant characterized by comprising: In the nuclear power plant pressure fluctuation monitoring system according to claim 7,
The maximum strain amplitude generated in the reactor pressure vessel structure is calculated by structural vibration analysis of the reactor pressure vessel structure using the calculated standing wave of the pressure pulsation in the reactor pressure vessel as an input, and the piping surface Means for converting a strain signal into a maximum strain amplitude generated in a structure installed in a reactor pressure vessel connected to the pipe;
Compare the maximum strain amplitude calculated in the reactor pressure vessel structure calculated from the measurement results with the allowable strain amplitude calculated from the operating temperature during measurement and the fatigue limit of the materials that make up the structure. A visual or audible warning to the monitor or operator if the maximum strain amplitude calculated from exceeds the allowable strain amplitude;
A pressure fluctuation monitoring system for a nuclear power plant characterized by comprising:

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