JPS6337914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a neutron flux monitoring device for a nuclear reactor that monitors the reactivity of a nuclear reactor in a boiling water nuclear power generation facility.

In general, a nuclear reactor constantly detects neutron flux and monitors the reactivity of the reactor in all conditions, such as when it is in power operation, when it is in a stopped state, and when it is loaded with fuel forming a partial core system. At the same time, if there is an abnormal increase in reactivity, control rods are inserted into the reactor core to perform a protective function.

Conventionally, three types of detectors with different sensitivities were installed at appropriate locations in the reactor core to detect neutron flux. That is, a low-sensitivity power range detector for measuring neutron flux during power operation, a high-sensitivity neutron source range detector for measuring neutron flux during reactor shutdown, and a reactor start-up or shutdown detector. An intermediate range detector having an intermediate sensitivity of each of the detectors used during operation was used.

However, the conventional monitoring device described above has the following disadvantages.

For example, a partial core system is formed during fuel loading and removal, but if the detector for neutron flux monitoring is located outside the system,
The neutron flux could not be detected effectively.

In addition, since these detectors are fixed at fixed positions within the core, it is not possible to measure the neutron flux in response to positional shifts in the partial core system. There were disadvantages in that the reactivity monitoring and protection functions of the fuel tank were deteriorated, and the methods for loading and unloading fuel were also limited.

For this reason, conventionally, when new fuel was first loaded, a fuel loading neutron detector that could be moved by a fuel exchanger was temporarily installed to monitor the reactivity of the partial cores and provide additional protection functions. However, since a new neutron detector for fuel loading is installed, it takes a long time to load the fuel, and the cost increases, creating a heavy economic burden. Furthermore, since a detector equivalent to the fuel loading neutron detector is not used during loading and unloading of replacement fuel, monitoring and protection functions against increased reactivity that may occur when withdrawing control rods are degraded. There was this inconvenience.

The present invention has been made in view of these points, and allows two or more types of detectors having different sensitivities to be selectively inserted into a detector guide tube provided in the reactor core depending on the operating state of the reactor. With this configuration, even in a partial core system, the same reactivity monitoring and protection functions as in the case of a full core loaded with fuel can be provided without using a conventional neutron detector for fuel loading. An object of the present invention is to provide a neutron flux monitoring device for a nuclear reactor that can safely and quickly load and unload neutrons.

The present invention will be described below with reference to embodiments shown in FIGS. 1 to 7.

FIG. 1 shows a cross section of a reactor core 1, in which five neutron sources 3 and twelve detector guide tubes 4 are arranged at the intersections of grid plates 2. To explain further, inside the core 1, as shown in FIG. 2, four fuel rods 6, 6 are respectively loaded in a plurality of fuel insertion holes 5 surrounded by a grid plate 2. A control rod 7 having a cross-shaped cross section is inserted between 6 and 6 so as to be movable up and down for reactivity adjustment, and a control rod 7 is inserted between the grid plates 2
A neutron source 3 or a detector guide tube 4 is inserted at the intersection of the two. Five neutron sources 3 are provided, one at the center and four at the outer periphery, so that they are substantially uniformly arranged within the reactor core. Further, the detector guide tubes 4 are provided at positions surrounding the neutron source 3 at the center, and four detector guide tubes are arranged at each of the center, intermediate, and outer circumferential portions.
Further, each detector guide tube 4 is installed within the reactor core 1 as shown in FIG. That is, the long detector guide tube 4 is inserted from below the reactor pressure vessel 8 so as to pass through the guide tube housing 9 fixed to the reactor pressure vessel 8, the lower grid plate 10, and the reactor core 1. , its upper end is fixed to the upper lattice plate 11, and its lower end is fixed to the lower end flange portion 12 of the guide tube housing 9. Further, a scanning tube 13 is provided at the lower end of this detector guide tube 4.
are butt-coupled by a connector 14. The detector 16 attached to the tip of the signal cable 15 is inserted into the detector guide tube 4 by extending the signal cable 15 from the lower end opening of the scanning tube 13.

Furthermore, in this embodiment, as shown in FIG.
The detector guide tube 4 is a combination of one each of detector guide tubes 4 in the central part, middle part, and outer peripheral part.
monitoring blocks 17a, 17b, 17c, 17
It is said to be d. A scanning tube 1 connected to a detector guide tube 4 provided in the middle of each monitoring block.
At the rear end of 3 is a neutron source area detector (not shown).
A detector drive device 18 is connected to each of the detectors for moving the neutron source area detector forward and backward into the detector guide tube 4. Further, an intermediate area detector (not shown) is provided at the rear end of the scanning tube 13 connected to the detector guide tube 4 provided in the center, and the intermediate area detector is inserted into the detector guide tube 4. A detector drive device 19 for moving the detector forward and backward is connected to each of the detectors.
Similarly, an intermediate area detector (not shown) is provided at the rear end of the scanning tube 13 connected to the detector guide tube 4 provided on the outer periphery, and the intermediate area detector is connected to the detector guide tube 4. Detector drive devices 20 for advancing and retracting the detectors are respectively connected thereto. In addition, in the middle of the scanning tube 13 connected to the detector guide tube 4 provided in the middle part, a neutron source region detector sent from the drive device 18 is connected to a branch scanning tube depending on the operating state of the reactor. A position selection device 23 that switches the insertion path of the detector in order to insert the detector through either one of the detector guide tubes 21 and 22 into the scanning tube 13 connected to either the central or outer detector guide tube 4.
is provided. Each of the above branch scanning tubes 21, 22
is connected to each scanning tube 13 through a merging portion 24.

Next, the monitoring of the neutron flux according to this example will be carried out in the fifth to
This will be explained with reference to FIG.

In the figure, the black rectangular part indicates the neutron source position, the white square part shows the position of the detector guide tube into which the intermediate region detector is inserted, and the white triangular part shows the detector into which the neutron source region detector is inserted. The position of the guide tube is shown, the white circular part shows the position of the detector guide pipe in which no detector is inserted, and the shaded part shows the fuel system.

FIG. 5 shows the arrangement of the monitoring system detectors in the entire core when all fuel is loaded. At this time, the position selection devices 23 of the respective monitoring blocks 17a, 17b, 17c, and 17d are not activated, and the determined detectors are moved from the respective detector drive devices 18, 19, and 20 to the determined detector guide tubes 4, This is what was inserted into 4. That is, high-sensitivity neutron source region detectors are inserted into the detector guide tubes at the middle of the reactor core 1, and intermediate region detectors are inserted into the detector guide tubes at the center and the outer periphery, respectively, to ensure a good neutron source. Bulk monitoring is performed.

When all the control rods are fully inserted in this state, the neutron flux is measured by the neutron source region detector, and the reactivity of the reactor is monitored. In this case, the intermediate region detector cannot detect the neutron flux and is simply used as a back-up device for the neutron source region detector.
Connected to protection system.

FIG. 6 shows a partial core system in which fuel is loaded only in the center of the core 1.

At this time, each monitoring block 17a, 17b, 17
The position selection device 23 of c and 17d operates, and the neutron source area detector sent from the detector drive device 18 is moved through the scanning tube 21 and the confluence point 24 to the detector guide tube provided in the center of the reactor core 1. and into its detector guide tube, respectively. On the other hand, an intermediate region detector is inserted into the detector guide tube at the outer periphery of the core 1 from the detector drive device 20 . At this time, no detector is inserted into the detector guide tube located in the middle of the core 1.

In this way, even in the partial core system, the neutron flux is measured by the highly sensitive neutron source area detector and good monitoring is continued. In this case, even when the control rod is inserted, the neutron source and neutron source area detector are in the system, so the neutron flux can be detected within the measurement range of the detector.
Reactivity can be monitored with multiple detectors at any given time.

FIG. 7 shows a case where fuel is loaded only on the outer periphery of the core 1.

At this time, each monitoring block 17a, 17b,
The position selection devices 23 of 17c and 17d operate in the same manner as described above to insert the neutron source area detector through the scanning tube 22 and the confluence point 24 into the detector guide tube at the outer periphery. Furthermore, an intermediate region detector is inserted into the detector guide tube at the center of the core 1, and no detector is inserted into the detector guide tube at the intermediate portion.

In this way, the neutron flux coming out of the fuel at the outer periphery can be well measured.

As described above, the neutron flux monitoring device of the present invention has the following effects.

(1) The highly sensitive neutron source region detector is configured so that it can be inserted into the detector guide tube located in any region of the reactor core depending on the operating status of the reactor.
Numerous detectors can monitor neutron flux from multiple directions even during the partial core state that is formed during fuel loading and removal, making it possible to appropriately respond to increases in reactor reactivity and prevent accidents. can do.

(2) Improved ability to monitor reactivity increases flexibility in fuel loading and unloading procedures.
Efficient and quick fuel loading and unloading becomes possible.

(3) Since the detector guide tube is configured to allow insertion of multiple types of detectors, the number of reactor internal structures can be reduced, and the fuel loading neutron detector that was conventionally used when loading new fuel can be omitted. It is possible,
The device can be simplified and loading new fuel becomes extremely easy. Further, since the neutron source region detector or the intermediate region detector is individually inserted into each detector guide tube, there is no need to adjust the arrangement positions of multiple types of detectors within the detector guide tube. In the above embodiments, the detectors have two types of sensitivities, but three or more types may be used.

[Brief explanation of the drawing]

The drawings show an embodiment of the neutron flux monitoring device for a nuclear reactor according to the present invention, in which Fig. 1 is a cross-sectional view of the reactor core, Fig. 2 is a partially enlarged plan view of the reactor core, and Fig. 3 is a vertical sectional side view of the reactor core. Figure 4 is a configuration diagram showing the connection state of the detector guide tube, scanning tube, and drive device. Figure 5 is a layout diagram of each detector etc. when full fuel is loaded. Figure 6 is each detection diagram when a partial core system is used. FIG. 7 is a layout diagram of each detector, etc. when fuel is loaded on the outer periphery. 1... Core, 4... Detector guide tube, 16... Detector, 18, 19, 20... Detector drive device, 2
3...Position selection device.

Claims (1)

[Claims] 1. A plurality of detector guide tubes arranged in the center, middle and outer periphery of the reactor core, and a highly sensitive neutron source region detector and intermediate region detection that are inserted individually into the detector guide tubes. and a detector drive device that is provided in correspondence with each of the detector guide tubes and inserts the detector into the detector guide tube, the detector guide tubes and the detector drive device being connected to each other. A neutron flux monitoring device for a nuclear reactor, characterized in that a position selection device is interposed in one of the scan tubes connected to the other detector guide tube to switch the insertion path of the detector.