JP2009210546A - Method and device for determining lprm signal cable erroneous connection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To confirm whether there is an erroneous connection of signal cables from detectors of an LPRM during the operation of a nuclear reactor. <P>SOLUTION: This LPRM signal cable erroneous connection determining method for determining the erroneous connection of the signal cables from a plurality of detectors fixedly arranged to mutually different heights in a guide tube of the LPRM installed in a pressure vessel of a boiling water reactor, to detect thermal neutrons, is characterized by determining that there is no erroneous connection when the phase delay of signals indicating the variation of thermal neutron flux density based on the variation of cooling material density interlocked with the variation of a void amount has occurred to the upper detectors in sequence from the lower detector and determining that there is the erroneous connection when the phase delay has not occurred to the upper detectors in sequence from the lower detector. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and apparatus for determining an erroneous connection of a signal cable of an LPRM (local output region monitor) installed in a pressure vessel of a boiling water reactor.

  In a boiling water reactor, as shown in FIG. 5, in order to monitor the thermal neutron flux distribution in the reactor pressure vessel 10, a number of local output region monitors are provided between the fuels 11 in the reactor pressure vessel 10. (LPRM) 12 are installed in a distributed manner, and each LPRM 12 is installed in the reactor pressure vessel 10 through the bottom wall of the reactor pressure vessel 10 in order to detect thermal neutrons at a plurality of heights. Guide tube 13, a plurality of detectors 14 </ b> A to 14 </ b> D fixedly arranged at different heights in the guide tube 13, and a movable in-core reactor (not shown) that moves up and down electrically in the guide tube 13 In recent years, a signal cable from a plurality of detectors 14A to 14D in the guide tube 13 of the LPRM 12 has a connector below the lower end portion of the guide tube 13. In data section 15A-15D, erroneous connection for cable 16A~16D leading to the monitoring device of the thermal neutron flux distribution is scattered.

  This event can be detected by checking the difference between the LPRM output value and the TIP output value, or by checking the discrepancy between the control rod (CR) insertion / extraction position and the LPRM output value close to the CR. There is sex. However, in order to determine the final erroneous connection, it is necessary to stop the operation of the nuclear reactor and visually inspect the cable connector portion in the reactor containment vessel.

  As described above, the judgment of the event is conventionally made when the difference between the LPRM output value and the TIP output value is large during operation, or when the insertion / extraction position of the CR affects the erroneous connection LPRM signal. The possibility of being overlooked cannot be denied. Even if it seems that an erroneous connection has been detected, it cannot be determined whether it is an erroneous connection by itself or other factors such as signal drift of the LPRM detector. Moreover, since the said connection part exists in a nuclear reactor containment vessel, the visual inspection during operation | movement of a nuclear reactor is impossible. Therefore, even if the possibility of an incorrect connection is pointed out, it is necessary to consider factors other than the incorrect connection as a countermeasure, and therefore it is not always possible to prepare for efficient inspection and repair.

  Therefore, it should be possible to determine whether or not there is a misconnection during operation of the nuclear reactor and to determine the misconnection channel, and conversely, in terms of ensuring traceability for the construction of the relevant part, It is a problem to be able to confirm that no erroneous connection has occurred in order to lead to efficient plant operation and maintenance.

  An object of the present invention is to advantageously solve the above-described problems, and the LPRM signal cable misconnection determination method of the present invention is different from each other in a guide tube installed in a pressure vessel of a boiling water reactor. Shows fluctuations in thermal neutron flux density based on fluctuations in coolant density linked to fluctuations in void volume when determining misconnections in signal cables from multiple detectors that are each fixedly positioned at height and detect thermal neutrons When the phase lag of the signal occurs sequentially in the upper detector with respect to the lower detector, there is no erroneous connection, and when the phase lag does not occur sequentially in the upper detector with respect to the lower detector It is characterized by determining that there is an erroneous connection.

  In addition, the LPRM signal cable misconnection determination device of the present invention includes a plurality of detectors that are fixedly arranged at different heights in guide tubes installed in a pressure vessel of a boiling water reactor and detect thermal neutrons. In the device for determining the erroneous connection in the signal cable from, signals output from the signal cables from the plurality of detectors, each indicating a variation in the thermal neutron flux density based on a variation in the coolant density linked to the variation in the void amount Phase difference detection means for detecting a phase difference in the case of the above, and based on the phase difference detected by the phase difference detection means, there is no erroneous connection when the phase lag occurs sequentially in the upper detector with respect to the lower detector A connection state determination unit that determines that there is an erroneous connection when the phase delay is not sequentially generated in the upper detector with respect to the lower detector, and the connection state determination unit performs And judgment result output means for outputting the judgment result, and is characterized in that it comprises a.

  According to the LPRM signal cable misconnection determination method of the present invention, a plurality of detectors fixedly arranged at different heights in guide tubes installed in a pressure vessel of a boiling water reactor and detecting thermal neutrons When determining the misconnection in the signal cable from the core, the fluctuation of the thermal neutron flux density is also caused by the fact that the fluctuation of the coolant density linked to the fluctuation of the void amount propagates from the lower core to the upper core according to the coolant flow. Paying attention to the point of movement from the lower part to the upper part of the core, if the phase lag of fluctuations in the thermal neutron flux density detected by multiple detectors occurs sequentially in the upper detector relative to the lower detector, an incorrect connection will occur. Therefore, it is determined that there is a misconnection when the phase lag is not sequentially generated in the upper detector with respect to the lower detector. It can be confirmed during the operation.

  In addition, according to the LPRM signal cable misconnection determination device of the present invention, a plurality of thermal neutrons that are fixedly arranged at different heights in the guide tubes installed in the pressure vessel of the boiling water reactor are detected. In a device that determines misconnection in the signal cable from the detector, the fluctuation of the coolant density linked to the fluctuation of the void amount propagates from the lower core to the upper core according to the coolant flow. Focusing on the fact that the fluctuation also moves from the lower core to the upper core, the phase difference detection means is a signal from the plurality of detectors on the fluctuation of the thermal neutron flux density based on the fluctuation of the coolant density linked to the fluctuation of the void amount. The phase difference in each signal output from the cable is detected, and the connection state determination means is connected to the detector with the lower phase delay based on the phase difference detected by the phase difference detection means. It is determined that there is no erroneous connection when the upper detector is sequentially generated, and there is no erroneous connection when the phase lag is not sequentially generated in the upper detector with respect to the lower detector, and the determination result Since the output means outputs the determination result made by the connection state determination means, the presence or absence of erroneous connection in the signal cables from these detectors can be confirmed during operation of the nuclear reactor.

  In the method and apparatus of the present invention, it is preferable to determine the misconnection mode based on the phase lag reversal mode between the lower detector and the upper detector. In this way, it is possible to determine not only the presence / absence of erroneous connection, but also which detector among the plurality of detectors is causing the erroneous connection.

  In the method and apparatus of the present invention, preferably, the fluctuation of the thermal neutron flux density is determined by a signal having a dominant frequency of nuclear thermal hydraulic vibration of a boiling water reactor, that is, a signal in the vicinity of 0.5 Hz. In this way, the dominant frequency of nuclear thermal hydraulic vibration is closely related to the variation in coolant density that is linked to the variation in void volume, so the phase lag based on the variation in coolant density can be detected more accurately. Can do.

  Hereinafter, embodiments of the present invention will be described in detail based on examples shown in the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the LPRM signal cable erroneous connection determination device of the present invention for carrying out an embodiment of the LPRM signal cable erroneous connection determination method of the present invention. The LPRM signal cable misconnection determination device of this embodiment includes a phase difference detection unit 1 as a phase difference detection unit, a connection state determination unit 2 as a connection state determination unit, and a determination result output unit as a determination result output unit Specifically, it is composed of a personal computer that functions as the phase difference detection unit 1, the connection state determination unit 2, and the determination result output unit 3 based on a program given in advance. .

  By the way, in the pressure vessel 10 as shown on the right side of the boiling water reactor as shown in FIG. 5, a plurality of fuel assemblies 11A each including a plurality of fuels 11 are arranged side by side as shown in FIG. The cooling water W as a coolant flows from the bottom to the top through the vertical flow paths in the fuel assemblies 11A. In the cooling water W in the fuel assembly 11A, voids are generated due to the heat generated by the nuclear reaction of the fuel assembly 11A. As a result, the cooling water W in the flow path has a higher void ratio in the upper part between the gas phase and the liquid phase. Two-phase flow. In this two-phase flow, when the flow rate at the inlet of the channel fluctuates, the fluctuation propagates to the upper part of the channel with a time delay, and the fluctuation of the thermal neutron flux passing through the cooling water W is also accompanied by this from the lower part of the channel. Propagates to the upper part of the channel with time delay. The frequency of this fluctuation is the dominant frequency of nuclear thermal hydraulic vibration, and is usually around 0.5 Hz.

  As shown in FIG. 2, guide tubes 13 of the LPRM 12 are arranged between the fuel assemblies 11A so as to extend in the vertical direction along the cooling water flow path, and the guide tubes 13 have different heights. For example, four detectors 14 </ b> A to 14 </ b> D are fixedly arranged to detect the density of thermal neutron flux passing through the cooling water W.

  In the apparatus of this embodiment, the cables 16A to 16D connected to the connector portions 15A to 15D below the lower end portion of the guide tube 13 of the signal cables from the four detectors 14A to 14D are detected by the phase difference detection. The phase difference detection unit 1 is connected to the unit 1 and passes the output signals from the cables 16A to 16D through the band-pass filters, respectively, so that only the signal in the vicinity of 0.5 Hz which is the dominant frequency of the nuclear thermal hydraulic vibration is obtained. Taking out, for example, obtaining a cross-correlation function for each pair of four cables 16A to 16D, and evaluating the time delay or time advance from the positive / negative of the peak position of the cross-correlation function on the time axis The phase difference between these signals is detected.

  The phase difference detection result is sent from the phase difference detection unit 1 to the connection state determination unit 2. Here, the four detectors 14A to 14D have a time delay in the order of the detectors 14B, 14C, and 14D from the bottom to the top, that is, the detectors 14B, 14C, and 14D. Is output. Therefore, if the cables 16A to 16D are correctly connected to the connector portions 15A to 15D below the lower end portion of the guide tube 13, the output signals of those cables 16A to 16D are detected at the bottom as shown in FIG. From the bottom to the top of the cable 16A connected to the detector 14A, that is, the cables 16B, 16C, and 16D connected to the detectors 14B, 14C, and 14D, respectively, have a phase difference sequentially. Therefore, the connection state determination unit 2 determines whether or not the detection result of the phase difference has a phase difference sequentially with respect to the cable 16A in the order of the cables 16B, 16C, and 16D.

  Specifically, the connection state determination unit 2 investigates how the phase difference mode is set for each pair of the four cables 16A to 16D, and the phase difference mode illustrated in FIG. The presence / absence and mode of erroneous connection are determined based on the correspondence table with the mode of erroneous connection. In FIG. 4, A, B, C, and D indicate output signals of the cables 16A, 16B, 16C, and 16D, respectively, + sign indicates that the latter phase is advanced with respect to the former, and-sign indicates It shows that the latter phase is delayed with respect to the former. For example, as shown at the top of FIG. 4A, the signals of the cables 16B, 16C and 16D are delayed (−) with respect to the signal of the cable 16A, and the signals of the cables 16C and 16D are delayed with respect to the signal of the cable 16B ( -), If the signal of the cable 16D is delayed (-) with respect to the signal of the cable 16C, it is determined that there is no erroneous connection, and if not, depending on the position of the set where the signal has advanced (+), It is determined that the erroneous connection state shown at the left end of each of FIGS.

  Normally, since the gas phase velocity of the core is about 7 m / s and the core length is less than 4 m, the time for the above-mentioned fluctuation of the void amount to pass through the core is less than about 0.6 seconds. Since the cycle of nuclear thermal hydraulic vibration, which is the reciprocal of the dominant frequency of force vibration, is sufficiently short compared to about 2 seconds, one cycle is output to the output signal by the bottom detector 14A and the top detector 14D. Since there is no minute delay, there is no misjudgment between delay and advance.

  The determination result is sent from the connection state determination unit 2 to the determination result output unit 3, and the determination result output unit 3 displays the determination result sent from the connection state determination unit 2, that is, whether or not there is an erroneous connection, for example, on a screen display. Display on the device screen and output.

  Although the present invention has been described based on the illustrated examples, the present invention is not limited to the above-described examples, and can be appropriately changed within the scope of the claims. For example, in the method of the present invention, the inspector However, the apparatus corresponding to the phase difference detection unit 1 detects the phase difference for each pair of the four cables 16A to 16D, and the phase difference mode is mistaken for the phase difference mode shown in FIG. The presence / absence and mode of erroneous connection may be determined by comparison with a correspondence table with connection modes. Further, although the phase difference detection unit 1 uses a software digital filter in the above embodiment, an analog filter using hardware (electronic circuit) may be used instead.

  Thus, according to the LPRM signal cable erroneous connection determination method and apparatus of the present invention, it is possible to confirm during the operation of the nuclear reactor whether or not there is an erroneous connection in the signal cable from the LPRM detector.

It is a block diagram which shows the structure of one Example of the LPRM signal cable incorrect connection determination apparatus of this invention for enforcing one Example of the LPRM signal cable incorrect connection determination method of this invention. It is explanatory drawing which shows the fuel assembly in the pressure vessel of a boiling water reactor, the cooling water flow path between them, and the guide tube of LPRM. It is explanatory drawing which shows the phase difference of the output signal of four cables of LPRM. (A), (b) is explanatory drawing which shows the correspondence table with the aspect of the phase difference used with the method of the said Example, and the aspect of a misconnection. It is explanatory drawing which shows the fuel in the pressure vessel of a boiling water reactor, and the guide tube of LPRM.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Phase difference detection part 2 Connection state determination part 3 Determination result output part 10 Reactor pressure vessel 11 Fuel 11A Fuel assembly 12 LPRM
13 Guide tube 14A to D Detector 15A to D Connector 16A to D Cable

Claims (6)

In determining an erroneous connection in signal cables from a plurality of detectors that are fixedly arranged at different heights in LPRM guide tubes installed in a pressure vessel of a boiling water reactor and detect thermal neutrons,
When the phase lag of the signal indicating the fluctuation of the thermal neutron flux density based on the fluctuation of the coolant density linked to the fluctuation of the void amount is sequentially generated in the upper detector with respect to the lower detector, there is no erroneous connection, An LPRM signal cable misconnection determination method, wherein a determination is made that there is a misconnection when a phase lag is not sequentially generated in an upper detector with respect to a lower detector.   2. The LPRM signal cable misconnection determination method according to claim 1, wherein a misconnection mode is determined based on a phase delay reversal mode between the lower detector and the upper detector.   3. The LPRM signal cable misconnection determination method according to claim 1, wherein the fluctuation of the thermal neutron flux density is determined by a signal of a dominant frequency of nuclear thermal hydraulic vibration of a boiling water reactor. In an apparatus for judging erroneous connection in signal cables from a plurality of detectors fixedly arranged at different heights in a guide tube of LPRM installed in a pressure vessel of a boiling water reactor and detecting thermal neutrons ,
Phase difference detection means for detecting a phase difference in signals respectively output from signal cables from the plurality of detectors, showing a variation in thermal neutron flux density based on a variation in coolant density linked to a void amount variation;
Based on the phase difference detected by the phase difference detecting means, there is no erroneous connection when the phase lag is sequentially generated in the upper detector with respect to the lower detector, and the phase lag is higher than the lower detector. A connection state determining means for determining that there is an erroneous connection when the detectors of the two are not sequentially generated,
Determination result output means for outputting a determination result made by the connection state determination means;
An LPRM signal cable misconnection determination device comprising:   5. The LPRM signal cable error according to claim 4, wherein the connection state determination means determines an erroneous connection mode based on a reverse mode of the phase delay between the lower detector and the upper detector. Connection determination device.   The LPRM signal according to claim 4 or 5, wherein the phase difference detection means determines the fluctuation of the thermal neutron flux density based on a signal of a dominant frequency of nuclear thermal hydraulic vibration of a boiling water reactor. Cable misconnection determination device.

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