JPS6014318B2 - Neutron source area monitor count rate prediction device - Google Patents

Description

Detailed Description of the Invention The present invention provides an SRM that predicts the count rate of a neutron source region monitor (hereinafter abbreviated as SRM) at the time of restarting a nuclear reactor.
This invention relates to a counting rate prediction device.

A nuclear reactor is usually equipped with a number of neutron sources (for example, Sb-tech) in proportion to the size of the reactor core to supply the neutrons necessary for starting the reactor.

In addition, the reactor is equipped with an SRM and an intermediate region monitor (hereinafter referred to as IRM) to individually measure neutron east according to the output level.
(hereinafter abbreviated as LPRM) and a local power range monitor (hereinafter abbreviated as LPRM). In order to start up a nuclear reactor with such a configuration, control lever withdrawal is required, but this control lever withdrawal is performed when the count rate of the SRM is *whistle (countpe).
rsec) or higher. Normally, if a neutron source with a predetermined strength or higher is installed, the *PS standard value described above is satisfied, but when restarting the reactor after a long-term shutdown due to periodic inspections, the strength of the startup neutron source is lower than the predetermined strength. It may be attenuated below the value. Therefore, in order to start the reactor reliably, it is necessary to calculate the SRM count rate in advance and start the reactor only when the predicted value is equal to or higher than the father PS. In particular, after a nuclear reactor is shut down for a long period of time, the intensity of the neutron source decreases significantly, so a new neutron source irradiated outside the reactor may be required. Since this judgment needs to be made correctly and early in accordance with the external irradiation plan based on the predicted value of the SRM count rate, it is necessary that highly accurate predicted values of the SRM count rate be supplied and resupplied quickly. In addition, neutrons generated from transuranic elements accumulated in irradiated fuel can also be used as a neutron source, so the neutron force from these transuranic elements $R
It is necessary to calculate the above-mentioned predicted value taking into consideration the degree of contribution to the M count rate. However, in the past, these calculations were performed offline, which required time and effort to collect and input data necessary for predictive calculations, making it difficult to quickly perform highly accurate predictive calculations.

The present invention has been made in order to eliminate the above-mentioned difficulties, and an object of the present invention is to provide an SRM count rate prediction device that can perform predictive calculations of the SRM count rate quickly and with high accuracy.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing the configuration of a general reactor core. As shown in the figure, a large number of fuel assemblies 1 having a rectangular cross section are arranged in a well-regulated matrix. [Above fuel assembly] A number of cross gaps are formed between each other, and as shown in the figure, there are a neutron source 2 indicated by the symbol △ and an SRM detector 3 indicated by the symbol ×. , the LPRM detector 4 indicated by the symbol ○, and the control beam 5 indicated by the symbol +.
and is provided. FIG. 2 is a side view simply showing the positional relationship among the fuel assembly 1, SRM detector 3, and neutron source 2 in FIG. 1.

FIG. 3a is a perspective view schematically showing the positional relationship between the neutron source 2 and four fuel assemblies 1 arranged around the neutron source 2.

The positional relationship between the SRM detector 3 and the fuel assembly 1 is also substantially the same as that of the neutron source 2 described above, so illustration thereof is omitted. In a boiling water reactor, as shown in Figure 3a, the fuel assembly 1 is divided into several virtual segments (hereinafter referred to as segments), for example, la, lb, ~, in the direction of the core, and the output characteristics of each segment are determined. The characteristics of the entire reactor core are obtained based on this information. FIG. 3b is a perspective view showing the segment lc in FIG. 3a as an example. Neutron source 2 corresponding to segment lc
Four segments lc are arranged around c. FIG. 4 is a block diagram showing the overall configuration of an embodiment of the present invention. SRM detector 3 installed in the core of nuclear reactor 6
, IRM detector, LPRM detector 4, etc., are sent to the process calculation device 7. This process calculation device 7 calculates the output of the segments of the four fuel assemblies arranged around the neutron moat 2 and sends the results to the neutron east calculation Hishitaka 8 and the neutron emission rate calculation device 9. do.
Further, the process calculation device 7 obtains the burnup and void rate history of the four segments arranged around the SRM detector 3 and sends it to the neutron emission rate calculation device 9. Please note that the above. The process calculation device 7 sends control signals such as sampling signals to the nuclear reactor 6 in order to timely input detection signals from various detectors provided in the reactor core. The neutron east calculation device 8 obtains the neutron east at the position of the neutron source 2 based on the outputs of four segments arranged around the neutron source 2. The neutron source intensity calculation device 10 calculates the balance between the production and decay of isotopes 24Sb and 123Sb of an element forming the neutron source 2, such as antimony Sb, based on the neutron east at the position of the neutron source 2. The time rate of change in the number of atoms of the isotope is obtained, and the intensity of the neutron source 2 is obtained from this rate of change. Fifth
The figure shows the characteristics when an Sb-neutron source is irradiated with constant neutron energy, with the horizontal axis representing the irradiation time and the vertical axis representing the neutron source intensity (Curie C). The neutron emission rate calculation device 9 is located around the SRM detector 3.
The neutron emission rate of the fuel assembly 1 is obtained by tracking and calculating the production of heavy nuclides accompanying fuel combustion based on the output history, burnup, and void history of each segment. Furthermore, many of the heavy nuclides that accumulate as the fuel burns mentioned above emit strong a-rays, and the (a, n) reaction between these a-rays and 180 contained in the fuel generates neutrons. Also, some of the heavy nuclear weapons mentioned above undergo spontaneous nuclear fission and emit neutrons.Therefore, the neutron emission rate mentioned above is a value that takes into account the neutrons generated in the two paths mentioned above. FIG. 6 shows the neutron emission rate characteristics of the fuel assembly 1, with the burnup plotted on the machine axis and the neutron emission rate plotted on the vertical axis of the logarithmic scale. The neutron east at the position of the SRM detector 3 is obtained based on the intensity of the neutron and the neutron emission rate from the fuel assembly 1, and the SRM count rate is obtained based on the result. Taking the Sb-Be neutron source as an example, the stage (
r, n) can be obtained by calculating the reaction. In addition, the SRM count rate calculation device 11 calculates that when the reactor is shut down and the reactor output becomes zero, the neutron source strength and the accumulated amount of heavy nuclides are attenuated over time. The time at which the SRM count rate predicted value was calculated immediately before the reactor shutdown is stored, and the SRM count rate predicted value after the reactor shutdown is obtained by correction calculation as a function of the time elapsed from the reactor shutdown time. Further, the SRM count rate calculation device 11 includes:
When the arrangement of the fuel assemblies 1 is changed during a periodic inspection, the arrangement of the fuel assemblies 1 located around the SRM detector 3 will naturally also change. By inputting the necessary data regarding fuel assembly 1, you can create an SR that takes into account the contribution of neutrons emitted by fuel assembly 1 to the SRM count rate at startup after periodic inspection.
Perform correction calculation of M count rate predicted value. The operation of this embodiment configured as described above during operation of the nuclear reactor will be explained.

SR of the neutron east of reactor 6 in operation according to the output level
The M detector 3, the IRM detector, and the LPRM detector 4 detect these signals, and these detection signals are sampled by sending out a sampling signal from the process calculation device 6. Then, the output values of the four segments located around the neutron source 2 calculated by the process calculation device 7 are sent to the neutron east calculation device 8, and the neutron flux calculation device 8 calculates the output values of the neutron source 2. The neutron east at the position is calculated. The four segment output values are also sent to the neutron emission rate calculation device 9. On the other hand, the history of the burnup and void fraction of the four segments located around the SRM detector 3 calculated by the process calculation device 7 is sent to the neutron emission rate calculation device 9. 9, the neutron emission rate of the fuel assembly 1 is calculated. The value of neutron east at the position of the neutron source 2 calculated by the neutron east calculation device 8 is sent to the neutron source intensity calculation device 10, and the intensity of the neutron source 2 is calculated in this neutron source intensity calculation device 10. It is sent to the counting rate calculation device 11. This SRM count rate calculation device 11 inputs the neutron emission rate of the fuel assembly 1 sent out from the neutron emission rate calculation device 9 and the intensity of the neutron source 2, and predictably calculates the SRM count rate. The above process is executed every time the detection signal of the reactor 6 is sampled, so by sampling at time intervals according to the request, the neutron source strength and neutron emission rate necessary to obtain the SRM count rate are tracked and calculated. As a result, the SRM count rate can also be obtained for each sampling. Therefore, the SRM count rate is always available. In addition, SR from sampling of the detection signal of the nuclear reactor
Since everything is done online and automatically until the M counting rate is obtained, the time difference is shortened and at the same time errors due to human error can be removed, making it possible to obtain a highly accurate SRM counting rate. -Also, when the reactor 6 is stopped, the S
Since the RM count rate calculation device 11 stores the reactor shutdown time and calculates the SRM count rate as a function of the time after the reactor shutdown, it is possible to quickly know the highly accurate SRM count rate when restarting the reactor 6. Can be done. Therefore, when restarting the reactor, an important judgment regarding whether or not control lever withdrawal is possible can be made quickly and reliably. Note that the present invention is not limited to the one embodiment described above.

For example, in the embodiment described above, the neutron east calculation device 8, the neutron source intensity calculation device 10, the neutron emission rate calculation device 9, and the SRM count rate calculation device 11 were provided, but the process calculation device 7 is It may have the functions of all computing devices. Of course, various other modifications can be made without departing from the gist of the invention. As explained above,
According to the present invention, by sending timely sampling signals from the process calculation device to each detector in the reactor, necessary detection signals indicating the output status in the reactor can be automatically obtained in a timely manner. The SRM count rate predicted value is obtained by tracking and calculating data necessary for obtaining the SRM count rate predicted value in each calculation device based on the detected signal.

Therefore, when the reactor is shut down, the above predicted values can be corrected according to the reactor stop time, and when the arrangement of fuel assemblies is changed, correction calculations can be made according to the above changes. Therefore, when restarting a nuclear reactor after a long-term shutdown such as during a periodic inspection, a predicted value of the SRM count rate can be calculated quickly and with high accuracy, and the reactor can be restarted based on this highly accurate predicted value of the SRM count rate. S who can do
An RM count rate prediction device can be provided. Brief Description of the Drawings Figure 1 is a plan view showing the configuration of a general reactor D, Figure 2 is a schematic side view showing the positional relationship between the fuel assembly, SRM detector, and neutron source, and Figure 3 a. is a schematic perspective view showing the positional relationship between a neutron source and a fuel assembly arranged around it, FIG. 3b is a schematic perspective view showing a part of the virtual segment shown in FIG. 3a, Fig. 4 is a block diagram showing the overall configuration of an embodiment of the present invention, Fig. 5 is a neutron source intensity characteristic diagram of an Sb-Be neutron source, and Fig. 6 is a neutron emission rate characteristic diagram of a fuel assembly. .

DESCRIPTION OF SYMBOLS 1... Fuel assembly, 2... Neutron source, 3... SRM detector, 61... Nuclear reactor, 7... Process calculation device, 8
...Neutron East calculation device, 9...Neutron emission rate calculation device,
Wing 0...Neutron source intensity calculation device, 11...SRM count rate calculation device.

Figure 1 Figure 2 Figure 4 Figure 3 Figure 5 Figure 6

Claims (1)

[Claims] 1. A plurality of neutron sources that supply neutrons necessary for starting up a nuclear reactor, a plurality of neutron source area monitor detectors that detect neutrons from the neutron sources, and a system that monitors the output of the nuclear reactor for each level. a plurality of neutron detectors for detecting neutrons, and a plurality of fuel assemblies located around the neutron source by sending sampling signals to these neutron detectors, inputting detection signals from each detector, and based on those signals. a process calculation device that calculates the output for each segment of the body, and calculates the burnup and poid history for each segment of a plurality of fuel assemblies located around the neutron source region monitor detector;
a neutron flux calculation device that calculates the neutron flux at the position of the neutron source based on the calculated output value for each segment; and a neutron source strength that calculates the intensity of the neutron source based on the neutron flux at the position of the neutron source. a calculation device; a neutron emission calculation device that calculates a neutron emission rate from the fuel assembly based on the burnup and void history of the segment; and a neutron source area monitor based on the intensity of the neutron source and the neutron emission rate. A neutron source region monitor calculation rate comprising a neutron source region monitor count rate calculation device that calculates a predicted value of the calculation rate and also corrects and calculates the predicted value according to the reactor shutdown time when the reactor is shut down. Prediction device. 2. The neutron source region monitor count rate prediction device according to claim 1, wherein the neutron detector is formed of an intermediate region monitor detector and a local output region monitor detector.