JPS6243596A - Method of monitoring critical access of nuclear reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (a) Purpose of the Invention [Field of Industrial Application] This invention is a nuclear reactor that changes the boron concentration in the primary coolant by adding dilution water like a pressurized water reactor. This invention relates to a method for monitoring the approach of a nuclear reactor to achieve criticality.

[Prior art] In order to maintain a nuclear reactor in a critical state, it is necessary to balance the generation and absorption of neutrons and maintain the nuclear fission reaction in a constant state. In other words, the control rods are withdrawn from the core, and the boron concentration in the primary coolant is changed (lowering the boron concentration in the primary coolant by adding diluent). Achieve a critical state by

In pressurized water reactors, a method is adopted in which the concentration of boron in the primary cooling UItJ is gradually diluted from 11 degrees when the reactor is shut down by adding dilution water to avoid the reactor approaching a critical state. has been done. In this case, in order to understand to what extent the reactor is in a subcritical state at each of the 15 points approaching the critical state, and how much dilution water must be added to make it critical, the radiation source i! Nuclear t1 measurement (detection of neutrons) is performed by detecting neutrons in the I region. The detection of neutrons by this source area neutron detector is carried out, for example, by the source area neutron detector (NE-31
and N[-32), and the approach of criticality is monitored by the signal from this detector.

That is, the total number of neutrons generated by the neutron source indicated by reference numeral 2 in FIG.
n/5ec), it is known that S, /<1-K)...(1) formula % formula %.

Here, KeH is the effective multiplication factor of the reactor, which is K in the critical state. , f=i, o, and in the subcritical state Ko, , <1.
It is 0.

Furthermore, the number of neutrons that can be measured by the source region neutron detector 1 is proportional to the equation (1), and therefore inversely proportional to 1-Kerr. Generally, when approaching criticality, the following data processing (1/M) is performed to monitor criticality.

However, (1/M) = (detection value of neutrons in the source area under standard conditions) /
(I! Il source region middle region neutron detection value at the time of measurement
...Formula (2) However, line 8r in the standard state! The regional neutron detection value refers to the number of 81 neutrons measured by the source region neutron detector in a stable state before the start of critical approach, and this value is (1/M)
The same numerical value is used in the pron l-1 continuation.

In this way, by measuring the (1/M) data over time, we monitor the value of '-Keft, and therefore, (1/M)
The criticality of the reactor is monitored by monitoring the data as it approaches zero.

However, since 1=Kor, tt is actually proportional to the amount of dilution water, (1/M) has a decreasing relationship with the amount of dilution water.

As mentioned above, in the original method (calculation formula), (1,'M
) The plot should be a straight line of decrease in application versus 1-Ke [or dilution water m, but this is not actually the case. The reason for this is that the neutron source 2 is located near the outer boundary of the reactor core 3, as shown in Figure 3, and is not located deep inside the reactor core. This is because the neutrons that are generated include not only neutrons generated by nuclear fission in the reactor core 3, but also neutrons that enter directly from the neutron beam 112. Therefore, the shape of the (1/M) plot is neutron I! The relationship differs depending on the two-source co-located core configuration, and the relationship <Q, does not necessarily result in a linear relationship.

An example of this is shown in FIG. 4 for an actual pressurized water reactor.

The fourth factor shows the critical proximity record diagram (vs. dilution water Q) based on the (1/M) plot, and is 1=, but the curve indicated by the reference numeral 6 in the same figure is based on the detector NE-31 (1/M). )
The curve shown at plot 7 is a (1/M) plot with detector NE-32. In this way, 1-Ke
It can be seen that 1/M) for the amount of dilution water proportional to rr does not form a simple straight line. In particular, it can be seen that at the point approaching the criticality, there is a deviation from the straight line (dotted chain line) indicated by reference numeral 9 in the figure.

For the purpose of actual criticality control, it is important to predict how much diluted water will reach criticality when approaching criticality. Therefore, in the conventional method shown in Figure 4, (1 /M) Deviation from the straight line of the plot caused a problem in that accuracy was lacking in terms of criticality prediction.

[Problems to be solved by the invention] This invention was developed in light of the above-mentioned circumstances, and is used for conventional criticality control when approaching criticality (1).
/M) Criticality approach monitoring of nuclear reactors that can overcome the difficulty of predicting the final critical point caused by the fact that (1/M) is not a straight line with respect to 1-Korr in the plot, and can accurately predict the critical point. The purpose is to provide a method.

(0) Structure of the Invention [Means for Solving the Problem] In response to this objective, the method for monitoring criticality approach of a nuclear reactor of the present invention changes control rod operation and boron concentration in the primary coolant. In the method of performing critical tube beating at the time of criticality approach using the (1/M) plot, the (1/M) plot is obtained at least three times over time, and +-K for (1/M) at each time point. (V, -V) However, Vl... Necessary dilution water output V up to the critical point...
・・・・・・1 for diluted water up to the relevant measurement point. It is characterized by giving a constant formula to reproduce the (1/M) blower i-, and predicting the approach of a nuclear reactor to criticality by vl derived from multiple simultaneous equations written in IYi. .

Hereinafter, the details of this invention will be explained with reference to one embodiment and the drawings.

Figure 1 shows (1/M) blower 1 using the one-dimensional diffusion calculation code.
Example 11/M) plot of ' ``c(
The change VII) due to f is shown.

The straight line indicated by numeral 812 in the figure is an example in which there is a proportional relationship with respect to 1-Kaff, and the dashed line indicated by numeral 11 is an example in which there is a line J≦; inside the core outer boundary J, about 35cII. Yes, the dotted line indicated by 10 is about 2 points from the core outer boundary.
This is an example in which the rQ source is inside the 0 ctn. A3 in Figure 1
The curve indicated by the symbol J10.11 has the same shape as the curve P26.7 in Figure 4 mentioned above, and it can be seen that the shape of the plot changes depending on the source position. The feature of the present invention is to reproduce the (1/M) plot from these revised Song Dynasty and actual (1/M) plots into the following precept c''5 equation. That's what I'm saying.

In other words, <1/M) = 1F7 1) (2(V, -v) + 3
(V, -V) However,■...The required dilution water rate until the point where it becomes critical (K8.'=1.0)■......The dilution water jK until the relevant measurement point, 2.
3...(1/M) blower 1- Add dilution water to the constant equation to reproduce the blower 1-, and add dilution water at least three times over time during the critical approach process of the reactor (1/M). Given to the equation (2), from these multiple sets (simultaneous equations), It! ! ! Find the mV of dilution water required to reach M. In this way, ■■ is obtained, and the dilution water In(V) up to the last measurement point (if the measurement is carried out three times at the relevant measurement point (shut)) is the already measured known FJIt direct. By subtracting V from the Vl, it is possible to know the dilution water required from the measurement point to criticality, and therefore it is possible to accurately predict the approach of criticality.

By the method of the present invention described above, (1/M
) The fact that the plot can be reproduced is shown by point X in Figure 4. In general, the (1/M) plot can be reproduced using equation (3), so when actually performing critical approach, put the measured data of (1/M) into equation (3) and set each constant to 2. ．． You can set the value to 3 and tell the value of Vl (diluted water).

In addition, the light low change in the (1/M) measurement data is automatically entered into the equation (3), and the TV and
't)l! ! 1 It just depends on the configuration size. Also, Vl
If uttered, K in the standard state. 7. By giving K in advance, K at the time of measurement. 7. Calculate using the following equation.

Ko', -1-(v/V,)

For example, FIG. 2 is a block diagram showing the configuration of a critical approach monitoring device for carrying out the method of the present invention, and the neutron detection value measured by the source region neutron detector 1 is marked 88.
When the indicated size (1/M) is input to the Ω operator and specified [j
(1/M) tears are performed at +J intervals. The (1/M) plot prediction device indicated by the symbol 9 is the (1/M) plot prediction device described above.
<1/M) data output from the calculator 8, the already added dilution water m(V), and the reference K. 7. 3) Input each constant yilK so that it is in the form of the equation 2. 3 to aQ O, that is, equation (3) has 1. 2.
Since there are four unknowns, 3 and Vl, the data for (1/M) and V are given at multiple points in time, for example,
By giving at least three sets of (1/M) Vy''-tameters up to the point of measurement, 1, 2, and 3 are assigned to each constant.

As a result, the dilution water aV up to criticality, K according to equation (4). "[and outputs the conventional (1/M) plot prediction.

J3, Figure 2 shows the future (1/M) plot prediction,
K at the time of the measurement. t'' and the required dilution water content are output, but since these are determined for each radiation source area neutron detector, two vessels (for example, number 6.7 in Figure 4) are output. J, sea urchin) of the curve is determined.

(c) Effect of the invention According to the invention, K at the relevant measurement time point is determined from the plot <1/M). 4. It is possible to determine the dilution water m up to the critical point, and therefore it is possible to perform criticality management with improved criticality prediction accuracy and provide a method for monitoring the approach of criticality of a Tsuru nuclear reactor. Furthermore, automatic processing Lu1l head attachment makes it possible to achieve greater automation than manual criticality control based on (1/M) plots.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the measurement of changes due to eff in the (1/M) plot, FIG. 2 is a block diagram showing the configuration of a critical approach monitoring method for implementing the method of the present invention, and FIG. The figure shows the hierarchical relationship between the neutron?!1laQ and the source region neutron detector and the reactor, and Figure 4 is an example of criticality approach recording using the (1/M) plot in a pressurized water reactor. 1... Source area neutron detector 2... Neutron source 3... Core 6... Detector NE31 (1/
M) Plot 7... (1/
M) Plot 8...(1/M) Operator 9...(
1/M) Plot predicted head wearing X...(1/M) Blower i reproduced by the method of the present invention, Figure 2

Claims (1)

[Claims] Control rod operation and changing the boron concentration in the primary coolant (
1/M) plot to perform criticality management when approaching criticality, the (1/M) plot is
(1/M)=K_1√(V_T-v)+K_2(V_T
-v)+K_3(V_T-v)^2 However, V_T...The amount of dilution water required to reach the critical point v.
...Dilution water amount K_1, K_2 up to the relevant measurement point
, K_3...(1/M) A method for monitoring near-criticality of a nuclear reactor, characterized in that a constant equation is given to reproduce the (1/M) plot, and the near-criticality of a nuclear reactor is predicted by V_T derived from the plurality of simultaneous equations. .