JPS6060593A - Nuclear reactor power distribution monitoring device - 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] [Field of Application of the Invention] The present invention monitors the power distribution using the measured values of power range monitors in the reactor core, and in particular, monitors the power distribution with a minimum number of monitors.
This invention relates to a method for obtaining necessary and sufficient output distribution monitoring accuracy.

[Background of the invention]

A plurality of power range monitors are installed in the core of a large nuclear reactor such as a power reactor. One of the purposes of this installation is to burn fuel more safely and economically by monitoring the power distribution within the reactor core.

Hereinafter, in this specification, a boiling water reactor (BWR, . . . ) will be explained in detail by taking an example.

FIG. 1 is a horizontal cross-sectional view of the core. Fuel is regularly distributed in the core in the form of fuel assemblies 1.The fuel assemblies 1 are arranged in a 2x2 mesh except for a part of the outermost periphery of the core (indicated by diagonal lines in the figure). (Thick lines in the figure).The square consisting of four fuel assemblies divided in this way is called cell 2.Figure 2 is an enlarged view of one of the cells.Cell Inside, as mentioned above, there are four fuel assemblies 1a to 1d, and around them there are four cross-shaped control rods 3a to 3d.

In the worst example, only one of the control rods 3d is partially inserted, and the other three are all pulled out. A string 4 for monitoring the in-furnace power range can be installed in the center of each cell. Inside the string 4 are two types of output area monitors. One is the local power range monitor (LPRM).
) 5a to 5d, and the neutron flux is constantly measured at four locations in the height direction of the reactor core.

The other is the mobile in-core instrumentation system (TIP).

The TIP is normally stored outside the core, and is only used when measuring the continuous neutron flux distribution in the core height direction.
Run inside.

Conventionally, the measured values of 'l' I P and LPRM have been used to monitor the output distribution in the following manner (FIG. 3).

(1) Travel through the TIP and measure the continuous NL neutron flux distribution Rot,k of each string in the core height direction.

Here, the subscript t is the string number, and k is the node position in the core height direction.

Normally, the reactor core is divided into 24 nodes in the height direction, and the bottom of the reactor is divided into 24 nodes.
l, the fireside is set to -24.

(2) When monitoring the output distribution, a value R7k corresponding to the TIP measurement value at that time is calculated using the following formula.

Rt, = FLt, b + ΔR4 + ΔRt, k...
・(]) Here, ΔRL is a correction for the influence of the movement of the control rods adjacent to the string after measuring R't, k, and is calculated by the amount of movement of the control rods and the amount of movement of the control rods at the nodes. Calculate using constants created in advance depending on the distance to the tip. On the other hand, ΔRz, I, PRM 11 constant value during output distribution monitoring, and (RL, 10ΔF)
It is calculated from the difference between the LPRM measurement value calculated from Lzk) and the corresponding value.

(3) From the T I P equivalent value Rtk calculated by equation (1), 4 free aggregates j (=1 to 4
) is subtracted using the following equation.

Pt, +, = Fj-Rt,k (2) Here, the conversion coefficient FJ is the fuel type, burnup, and moderator density of the fuel assembly, and the combination and control of fuel types around the string. It is a function of the rod insertion state, etc., and is calculated using constants created in advance.

(4) If the correction value of equation (1) - ΔR't, "k, ΔRn7 becomes large and f'c, then the vehicle runs on TIP and R
+4. Update k.

According to this method, if TIP running is carried out as follows (a), the output distribution monitoring error can be maintained at 4 to 5% or less.

■ When the control rod insertion button is changed.

■ Even if you click the picture frame insertion button or leave it as is, the previous TI
From P run, when the core average burnup advances IGW-d/ by the Japanese calendar.

The output distribution monitoring error σ is defined by the following equation.

Here, R, R: string t, node 4k t, k TIP measurement value of k, total Calculated value (Hiiragi value 1).

L, to: total number of strings, number of nodes.

With monitoring errors of this level, nuclear reactors can be operated safely. However, in order to calculate the output distribution using the above method, a string containing not only all cells but also an output area monitor is required. In the core shown in FIG. 1, the number of strings is 204. but,
In reality, only 52 strings are implemented as shown in FIG. 4 (marked with * in the figure). This takes advantage of the fact that, in principle, the core operates with quarter symmetry. 1/4 symmetry means that the fuel loading slam and the control rod slam are mirror symmetrical or rotationally symmetrical with respect to the 1-point line in the figure as the axis of symmetry. In this case, as shown in Figure 5, the implemented string L
The measurement value of the output area monitor at the symmetrical position of the other quadrant (
In the case of mirror symmetry, L1 to L39 In the case of rotational symmetry, L
1 to L3R) can be used as a virtual measurement value. Using this property, if we virtually move the strings implemented in the other three quadrants to the upper right quadrant of Figure 4, we can see that
It will be indicated by a mark. In other words, if the reactor core is operated with quarter symmetry, there will effectively be a string for every cell, and using the methods (1) to (4) above,
Output distribution can be monitored with high accuracy.

However, this method requires the number of strings to be equal to the total number of cells in the core, and as the core becomes larger, the following problems arise.

(1) The number of strings increases, increasing installation costs. Additionally, as the LPRM, which is permanently placed in the reactor core, gradually deteriorates, the strings must be replaced periodically, which also increases the cost.

(ft) RX, TIP running is necessary to measure k, but as the number of strings increases, the time required to run all the strings increases. During TIP driving,
Since the power distribution needs to be kept stable, operational flexibility is reduced during this time.

That is, it is not preferable to arrange a large number of strings as shown in FIG. 4 in order to improve economy and efficiency.

Therefore, in recent years, methods to reduce the number of strings have begun to be considered. FIG. 6 shows an example of this method, in which every other string is reduced from the conventional arrangement shown in FIG. As a result, the number of strings is reduced to 24, less than half of the 52 in FIG. 4.

However, with this placement method, if the core is operated with quarter symmetry, even if the strings are moved to one quadrant as shown by the circles in FIG. 6, cells with no strings will occur. ) For cells where there is no IJ song and the output area monitor cannot obtain a fixed value, use the conventional methods (1) to (4).
), the output distribution cannot be monitored, and therefore the output distribution monitoring error increases.

In order to solve this problem, a method has been proposed that uses Pro1) Durham, which has a built-in physical model of the reactor, to calculate the power distribution. A physical model of a nuclear reactor (hereinafter abbreviated as a reactor model) is a physical model that uses equations that describe the nuclear properties and thermal-hydraulic properties within the reactor core, and uses equations that describe the nuclear properties and thermal-hydraulic properties in the reactor core to determine the core thermal output, core coolant flow rate, control rod position, etc. The output distribution is calculated from 2). The node-coupled motel FLARE is one example.

Power distribution calculation using a reactor model does not originally require measured values from a power range monitor. However, the output distribution monitoring error in that case is about 6 to 7 inches. This can be calculated within minutes using an online process calculator.
, due to the need to terminate the nuclear reactor model.

That is, even when using a nuclear reactor model, it is necessary to use the measured values of the power range monitor in order to achieve the conventional power distribution monitoring accuracy.

[Purpose of the invention]

An object of the present invention is to provide a method for monitoring power distribution with conventional accuracy using a program incorporating a nuclear reactor model.

Furthermore, another object is to provide a method for optimally arranging strings containing power range monitors used in the above-mentioned monitoring method in a reactor core.

[Summary of the invention]

In a nuclear reactor, if a square consisting of four fuel assemblies is defined as one cell, a string containing a built-in power range monitor is placed in a checkered pattern every cell, and a physical model of the reactor is created. The output distribution calculated by the internal output distribution calculation program is calculated using the measured value of the output area monitor mentioned above.
In a method for monitoring the power distribution of a nuclear reactor and in a nuclear reactor whose main feature is to compensate for If all the strings in the area are virtually transferred using symmetry, the entire core will be arranged so that the virtual string arrangement in the flame expansion area will be in the checkered pattern every other cell of the flame. This is a method for arranging monitors for the power range in a nuclear reactor, characterized by arranging IJ songs, as shown in Figure 7. Use area monitor measurement values as an auxiliary aid.

(1) During TIP driving, calculate the output distribution using the reactor model and compare the value that is compatible with the TIP measurement value with the actual TIP measurement value, and minimize the difference between the two. Adjust the parameters of the motel.

(2) During power distribution monitoring, a value equivalent to the LPRM measurement value obtained by converting the power distribution calculated by the reactor model,
The actual LPR and M measurement values are compared, and the output distribution is corrected based on the difference between the two.

Here, the parameters to be adjusted in (1) above do not affect a local part of the reactor core, but around 5 to 6 parameters that affect the entire reactor core are avoided. In addition, the amount of correction of the output distribution using the LPRM measurement value is based on the observation error of 2
It is about a decrease of ~3 inches.

The reason why the number of strings can be reduced will be explained later, but one reason why the number of strings can be reduced is that the number of parameters is small and the amount of correction of the output distribution is small.

The basic procedure of the output distribution monitoring method has been explained above. Next, a method for arranging strings will be explained.

The strings are arranged in a checkerboard pattern as shown by the O marks in (a) and (b) of Figure 8, with the tags focusing on one-fourth of the core. In both cases, the following two rules are satisfied.

■ The density is one string for every two cells.

■ The spacing between the strings becomes equal.

These two rules are necessarily determined in response to physical phenomena for the following reasons.

Rule (2) regarding the arrangement of strings is determined by the principle that the influence from each fuel assembly should be reflected on the power range monitor in at least one string. In order to satisfy this principle, the average range for fast neutrons generated in a fuel assembly to be decelerated to thermal neutrons, absorbed, and used for the next nuclear fission must be the closest distance from that fuel assembly. The density of the IJ can be determined so that it is longer than the distance to the string. Based on diffusion theory, the following equation 8) approximately holds true in a thermal neutron reactor.

r2 = 68M2-(3), r2: average M2 of the square of the straight-line distance from the neutron birth point to the absorption point; moving area BWR is M2 = 10 o ~ 150 Cctrt), and this can be expressed as Substituting into (3), r2=600 to 900 [ci]. Therefore, the average range is j-25 to 30 [z+:]. On the other hand, in BWR, one side of the cell is 1r
t (approximately 30 cnr). In other words, (
(a) or (b)), all fuel assemblies must be within the average neutron relaxation distance from the nearest string (as shown in Figure 9, a partially enlarged view). (low line circle).

The string arrangement as explained above is sufficient because
As mentioned above, this is to improve the method of monitoring the power distribution of the ship. In other words, unlike the conventional method based on the measured value of the output %j range monitor, 1) the power distribution is directly calculated using the reactor model without using the defined value of the output range monitor, and this output In order to correct the distribution, a method is adopted in which the measured values of the output value range monitor are used as an auxiliary measure.

Therefore, if there is one string that reflects the influence of each fuel assembly, the output distribution of that fuel assembly can be correctly corrected.

Next, the reason for establishing the rule (2) regarding the arrangement of strings is to rationally correct the output distribution. That is, first of all, if the fuel assemblies are arranged evenly as shown in FIG. 8, the amount of correction of the output distribution of each fuel assembly will be the same.

This means that the total $I:h degree of power distribution for each fuel assembly is approximately the same. The absence of local unevenness in calculation accuracy not only facilitates monitoring but also improves safety. Second, by arranging them evenly, the output distribution can be corrected using the same procedure at all locations. Since the correction process is carried out by a program stored in a computer, the simplification of the program and the calculation time will be explained in detail based on the drawings of the embodiment of the present invention.

First, an embodiment of a method for monitoring output distribution will be described. Among the procedures shown in Fig. 7, for the example during TIP running, the method of Japanese Patent Publication No. 53-22639 ``Nuclear Reactor Power Distribution Monitoring Device'' can be used, so we will not discuss the details here)
Further explanation will be omitted. In this method, FLARE is used as a reactor model, and there are six Le-Li phase paranokes (two mixing parameters of the neutron transport nucleus and four albedos). When the power distribution is calculated using a reactor model with this parameter set to 'vJta Ml, the monitoring error is about 7 inches.

In order to reduce this visual error i, in the first method of monitoring the output distribution of the present invention, the output distribution is further corrected using the LPRM measurement value. An embodiment of this correction method is shown in FIG. 10. The procedure is as follows.

(1) The power distribution Pry,k calculated using the reactor model is T
IP equivalent value R4k and LPR, M equivalent value is suspected.

Convert to This transformation is the inverse transformation of equation (2).

(2) For each ring, LPRM position in (=1
In ~4), the difference ΔLL,* between the LPRM measurement value and the calculated value is calculated using the following equation.

ΔL t, s −L4 a Ltsu1. ...(4)
Here, LL. is the LPRM measurement value.

(3) For each string, there are 4 points Δ in the core height direction
Lt. is linearly interpolated to calculate the difference ΔB4k between the 24 nodes corresponding to T I P.

(4) Fuel assembly j (-1 to 4
), the output distribution is corrected using the following formula.

Pt, 1. to = Pt, I, k・(1+Ct, +, hl
...(5) ΔRt, PRM 0j''・0...'Rr,.

pt,... is the output distribution after correction.

(5) For cells where no string exists, the first
As shown in FIG. 1, '□C24+I+k is used as the correction coefficient czt +I+ for one surrounding string 2t to t4, and the virtual correction coefficient CleI J l k is calculated using the following formula.

1″4 Ct・l'1k--Σ Ct, r, k...(6)4
t, tt If the output distribution is corrected using the LPRM measurement value using the above procedure, the monitoring error of the output distribution will further improve by 2 to 3 centimeters and become below the target of 4 to 5 centimeters. In addition, in tooth 8 section, for cells located at the outermost periphery of the core and without strings,
The correction coefficient cannot be calculated using the method shown in FIG. 11 and equation (6). In such a case, the average value of the correction coefficients of two or three surrounding strings may be used.

Next, an example of a method of arranging the sh IJ will be described. An example in which the core is operated with quarter symmetry is shown in FIGS. 12 and 13. If the entire IJ ring is virtually transferred to the upper right quadrant using symmetry, FIG. 8(a) is obtained from FIG. 12, and FIG. 8(b) is obtained from FIG. 13. That is, both embodiments satisfy the rules (2) and (2) regarding the string arrangement described above.

Furthermore, in the embodiments shown in FIGS. 12 and 13, when looking at the arrangement of IJs in the entire core, there is no local deviation and they are distributed almost uniformly throughout the entire core. LPr%
In addition to monitoring the power distribution, the constant value of M is determined by monitoring the average power range monitor (APRM) or control rod withdrawal prevention monitor (R
It is used as an input to nuclear reactor protection systems such as BM). Therefore, uniform distribution throughout the entire core means that the reactor protection system can be activated immediately no matter where an abnormality occurs.

In addition to the embodiments described above, the following three practical examples can also be realized without changing the basic concept of the output distribution monitoring method and IJing force distribution method of the present invention.

(1) Output is low at the outer periphery of the core, and even if the monitoring accuracy of the output distribution deteriorates somewhat, there will be no major impact on safety or economy. It is also possible to delete strings that exist in a cell. In this way, (a) has 4 lines, Φ) has 6 lines,
The number of strings can be reduced.

(11) As a method of calculating the correction coefficient for a cell where no ring exists, instead of taking a simple average as in equation (6), smoothly interpolate the sliding coefficients of the surrounding strings. There is also a possible method.

(If the +rrt core is operated with one-eighth symmetry,
As shown in the example in FIG. 14, the strike song may be placed at the 9th mark of the priesthood. When gathered in one area, it forms a checkered pattern as shown by the circle.

〔Effect of the invention〕

As explained above, by adopting the string arrangement method and output distribution monitoring method according to the present invention, the number of strings can be reduced by half, economical efficiency can be improved, and output distribution can be monitored with less error. , which has the effect of measuring efficiency.

[Brief explanation of the drawing]

Figure 1 is a horizontal cross-sectional view of the reactor core, Figure 3 is a diagram showing the configuration of the No. 21\1Iri cell, Figure 3 is a diagram showing the conventional power distribution monitoring method, Figure 4 is a diagram showing the conventional IJ ring arrangement, Figure 5 is a diagram showing the symmetrical relationship between IJ and Figure 6 is
FIG. 7 is a diagram showing an example of reducing the number of IJ strings, FIG. 7 is a diagram showing the output distribution monitoring method of the present invention, FIG. 8 is a diagram showing the string arrangement method of the present invention, and FIG. 9 is a part of FIG. The enlarged drawings, FIGS. 10 and 11, are diagrams showing an embodiment of the output distribution monitoring method, and FIGS. 12, 13, 14 are diagrams showing an embodiment of the string arrangement method. l...Fuel assembly, 2...Cell, 3...8 control rods,
4...String% 5...LPRM, 6...T
IP conduit. ￥51 圀″fJ2rj3 3rd 30th 412] ￥S；f＠ fig. 6′￥JrII2Il fig. 8 (廄) (shi)

Claims (1)

[Scope of Claims] 1. In a nuclear reactor, strings with built-in power range monitors are arranged in a checkerboard pattern every other cell, with each square defined as one cell consisting of four fuel assemblies. A power distribution monitoring method for a nuclear reactor, characterized in that the power distribution calculated by a power distribution meter program having a built-in physical model of the nuclear reactor is corrected using the curve j constant value of the power range monitor. 2. In a nuclear reactor, when the core is operated with symmetry, all strings in other regions are placed in one of the smallest regions surrounded by the symmetry axis using symmetry. In a nuclear reactor, the strings are arranged throughout the reactor core so that the virtual string arrangement within the area becomes a checkerboard pattern every other cell of the frame in the preceding paragraph. Output area monitor placement method.