JPH07111473B2 - Control rod operation system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control rod operating system for operating a control rod to bring a subcritical reactor into a critical state, and particularly, to increase the reactor power stably. However, the present invention relates to a control rod operating system suitable for minimizing the start-up time to the critical level.

[Conventional technology]

At the time of starting the boiling water reactor, about 200 control rods inserted in the core are gradually pulled out,
The nuclear reactor is changed from a subcritical state to a critical state and further to a supercritical state. Conventionally, such control rod operation is performed by an operator. The operator operates the control rod while monitoring the neutron flux n, the reactor cycle T, and the like in order to prevent the reactor from having a sudden reactivity. Here, the relationship between T and n is expressed by the following equation. Here, 1 / T is called the neutron flux change rate.

As described above, the operation of the control rod is performed based on the accurate judgment of the operator, but recently, for the purpose of labor saving and shortening of start-up time, the control rod operation as described above is performed. Is required to be automated or to output an appropriate guide.

The known example closest to the present invention is the "automatic critical operating device for a nuclear reactor" disclosed in Japanese Patent Laid-Open No. 50-146796. This known example relates to an apparatus for automatically operating a control rod to bring a subcritical reactor into a critical state, and determines the operation timing of the control rod and the withdrawal amount based on the reactor cycle T. That is, the reactor cycle T is a predetermined value (eg 20
When it is 0 seconds or more, the operation timing command for pulling out the control rod is output, and the pulling amount at that time is determined according to the size of the furnace cycle T. In the embodiment, the pull-out amount is set to a value proportional to T.

Other known examples related to the operation of changing the reactor from subcritical to critical include "Reactor Critical Proximity Method" in JP-A-54-53792 and "Control rod" in JP-A-60-179689. "Automatic operation device". In these second and third known examples,
It is described that the withdrawal speed of the control rod is adjusted.
On the other hand, the present invention is directed to a system for adjusting the control rod operation timing and the withdrawal amount while the control rod withdrawal speed is not changed and is constant (for example, 30 mm / s).
Therefore, the present invention is essentially different from the second and third known examples.

[Problems to be solved by the invention]

In the above-mentioned first known example, since the pull-out amount of the control rod is determined based on one parameter called the furnace cycle, there are the following problems.

That is, as can be seen from FIG. 4 and FIG. 10 which will be described later, the reactor cycle T (the reciprocal of the neutron flux change rate) changes intricately after pulling out the control rod and, for example, its minimum value is the pulling out of the control rod. It was confirmed by experiments that the amount significantly changed depending on how close the reactor was to criticality. However, in the above-mentioned publicly known example, since such a state change of the reactor is not taken into consideration, it is difficult to make the extraction amount of the control rod accurate, and as a result, the reactor cycle becomes abnormally short or However, there is a problem that the startup time to the critical point becomes long.

It is an object of the present invention to provide a control rod operating system suitable for minimizing the start-up time to criticality while maintaining a stable furnace cycle.

[Means for solving problems]

In order to achieve the above object, the control rod operating system according to the invention as set forth in claim 1 is a control rod operating system for operating a control rod of a nuclear reactor to make a subcritical reactor critical. Pull out the control rod at a time, at least, the total amount of control rod withdrawal estimated to be necessary to be withdrawn from the present time to the critical point, and the withdrawal amount of the control rod at the previous operation, and its Of the control rod calculated by the first means and the first means, which is calculated based on the time when the furnace cycle lasts longer than a predetermined value or the time when the neutron flux change rate stays below the predetermined value. It is characterized in that a second means for displaying the amount of pull-out on the display device is provided.

In order to achieve the above object, the control rod operating system according to the invention as set forth in claim 2 is a control rod operating system for operating a control rod of a nuclear reactor to make a subcritical reactor critical. Pull out the control rod at a time, at least, the total amount of control rod withdrawal estimated to be necessary to be withdrawn from the present time to the critical point, and the withdrawal amount of the control rod at the previous operation, and its And a control rod calculated by the first means, which is calculated based on the time when the furnace cycle lasts longer than a predetermined value or the time when the neutron flux change rate stays below the first predetermined value. Second means for displaying the extraction amount on the display device, and a function for stopping the extraction operation of the control rod when the neutron flux change rate exceeds the second predetermined value at the time of extracting the control rod. It is characterized by having the means of That.

In order to achieve the above object, the control rod operating system of the invention described in claim 3 calculates the control rod by the first means in the invention described in claims 1 and 2. It is characterized in that a fourth means for automatically pulling out by the pulling amount is provided.

[Action]

When the state of the reactor becomes suitable for control rod extraction, the neutron flux n and the total extraction amount L of the control rods up to the present time L (control rod extraction amount lp extracted in the past lp) according to a known inverse multiplication factor method or the like. The total amount Lr of pulling out control rods from the present time to the critical point is estimated based on For the principle of the inverse multiplication factor method, see the reference (Koji Fushimi; Reactor, Kyoritsu Shuppan, 1972.
Year) and the above-mentioned second known example, JP-A-54-53792. Based on this Lr, the control rod withdrawal amount lp at the previous operation, and the dynamic behavior pattern of the furnace cycle at that time (for example, low level duration Δt ₁ and high level duration Δt ₂ described later), The withdrawal amount 1 for continuously withdrawing the control rod is calculated and displayed on the display device. When the control rods are automatically operated, a specific group of control rods is drawn by 1 according to the control rod drawing procedure. The dynamic behavior pattern (△ t ₁ , △ t ₂ ) of the reactor cycle at this time is measured, and when the reactor state becomes stable again and becomes suitable for control rod operation, the above-mentioned control is performed again. The rod is pulled out. Such operation is repeated until the reactor reaches a critical level (strictly, until a supercritical state in which the continuous reactor cycle is between 100 seconds and 400 seconds).

Therefore, in the present invention, since the pull-out amount l of the control rod is appropriately changed according to the change in the reactor state, it is possible to minimize the start-up time to the critical level while maintaining the reactor cycle within an appropriate range. it can.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings in the case of automatically operating a control rod.

In FIG. 1, 1 is a nuclear reactor, 2 is a core, 3 is a control rod,
4 is a control rod drive device, 5 is a control rod operation monitoring control device, 6
Is a neutron instrumentation device, 7 is a central monitoring and control panel for an operator to output an operation command while monitoring the plant state, 11 is a control rod automatic operation device having a central role in this embodiment, 11
1 is a control rod operation timing determining unit that determines the operation timing of the control rod in the automatic control rod operating device 11, and 112 is a control rod operating amount that also calculates the pull-out amount of the control rod in the automatic control rod operating device 11. It is the decision unit.

Next, the function of each of the above devices will be outlined. About 200 control rods 3 are inserted in the core 2 of the nuclear reactor 1. Before the reactor is started, these control rods 3 are all inserted in the core 2, and the reactor 1 is in a subcritical state. At this time, the level of the neutron flux indicating the reactor output is about 5 × 10 ^-9 % with respect to the rated 100%, and when the control rod 3 is gradually pulled out from the core 2, the neutron flux increases. That is, the output of the nuclear reactor 1 is adjusted by changing the pulling position of the control rod 3 in the core 2 up and down.

The central supervisory control panel 7 has a control rod operation command (command of operation timing and extraction amount) f, a withdrawal position e of the control rod 3 in the core 2, a measured value g of neutron flux n, reactor cycle T, etc. Is provided with a display device for easy monitoring, a switch for controlling the operation of each device, a push button, and the like. When starting the reactor, a command a with the content of "automatically operate the control rods to make the reactor critical"
Is output to the control rod automatic operation device 11.

The control rod automatic operation device 11 automatically determines the operation timing of the control rod 3 and the withdrawal amount 1 which were conventionally judged by humans,
Outputs operation commands b and f.

The control rod operation monitoring control device 5 has a built-in control rod withdrawal operation procedure, and when the operation command b is input, the control rods of a specific group among the control rods 3 according to the above operation procedure are transferred to the core 3. The control rod drive command d is output to the control rod drive device 4 while inputting the control rod pull-out position e so as to pull out the control rod with the pull-out amount l.

The control rod drive device 4 operates so as to pull out the designated control rod 3 from the core 2 at a constant speed (for example, 30 mm / s) based on the drive command d.

The neutron instrumentation device 6 measures the neutron flux n of the core 2, the reactor cycle T, and the like.

Next, the operation of this embodiment will be described. When the control rod 3 is fully inserted and a command a for starting the reactor is output from the central monitoring control panel 7, the control rod automatic operation device 11 causes the control rod 3 to have a predetermined initial withdrawal amount. For example, 24 m (corresponding to the case where 26 control rods are pulled out by 0.92 m at the same time), the command b, f for pulling out is output. Control rod operation monitoring controller 5
Operates to pull out the control rods of group 1 (26 rods) in accordance with the command b according to the control rod pulling operation procedure by a total of 24 m (each control rod is 0.92 m). When the pulling-out operation of the control rod is completed, the control rod operation end signal c is returned to the control rod automatic operating device 11. The control rod automatic operation device 11 automatically determines the timing for pulling out the next control rod and the pulling amount 1 according to the operating procedure, based on the signal c, the neutron flux n, and the measured value g of the reactor cycle T. . When it is determined that the control rod should be operated, the control rod operation command b is output again to the control rod operation monitoring control device 5, and the control rod withdrawing operation is automatically performed. At this time, the operation command f is simultaneously displayed on the central monitoring and control panel 7. The automatic operation of the control rod as described above is repeated until the criticality is reached.

Next, the operation of the control rod automatic operating device 11 which plays an important role in this embodiment will be described in detail.

FIG. 2 shows the configuration of the control rod automatic operating device 11. Pre-processing section
At 113, preprocessing of parameters used for determining the timing of control rod operation and the withdrawal operation amount 1 is performed. Pre-processing section
At 113, the elapsed time after the control rod operation is completed is calculated and used as one parameter when determining the operation timing. In, the neutron flux change rate that is the reciprocal of the reactor cycle T is calculated. Then, in this neutron flux change rate, the time Δt ₁ and the high level (1
/ 100 seconds) and the time duration Δt ₂ is calculated. Then, it is judged whether or not the reactor has reached criticality. Here, it is determined that the reactor has reached a critical level when the rate of change of neutron flux is kept at a low level (1/200 seconds) or more for 2 minutes or more after the control rod drawing is completed. Then, based on the inverse multiplication factor method,
Lr is estimated.

The control rod operation timing determination unit 111 determines whether to start the control rod withdrawal or to interrupt the control rod withdrawal based on the logic shown in FIG. FIG. 4 shows the characteristics when the operation timing of the control rod is determined based on such a logic. In FIG. 4, the neutron flux change rate temporarily rises when the control rod extraction is started, and gradually decreases when the control rod extraction is completed. In the case of 10 seconds), it will be below the low level.
When 15 seconds have passed after the control rod operation was completed and the state of the reactor became stable, the control rod was again pulled out based on the logic shown in FIG.

One of the points of the present embodiment is the method of determining the withdrawal amount l in such intermittent control rod operation.

A conventional method of previously determining the pull-out amount 1 of the control rod will be described below with reference to FIGS. 9 and 10.

FIG. 9 shows the control rod withdrawal operation procedure and the withdrawal amount 1 set at the time of creating the operation plan. A change of the pull-out position by 1 in FIG. 9 means that the control rod moves by 18.3 mm. The procedure for pulling out the control rods is to pull out the 26 control rods of group 1 from pulling positions 0 to 200, and then pull the control rods of group 2 from 0 to 195. In this case, the withdrawal amount l is also 24,12,4.8,
It is set in advance, such as 0.48m. FIG. 10 shows the characteristics when the method of setting the drawing amount l in advance is followed. Time 0 is a time point when the withdrawal of the control rods 3 in the fully inserted state is started, and in this example, the reactor reaches the critical level 11 minutes after the start of the startup. However, if the withdrawal amount l is kept constant, the maximum value of the neutron flux change rate becomes larger as the reactor criticality is approached. If the withdrawal amount l is relatively large immediately before the criticality is reached, the continuous reactor after the control rod withdrawal 70 cycles
It can be seen that the problem of becoming extremely short in seconds (the neutron flux rapidly increases) occurs. On the other hand, on the contrary, when the control rod withdrawal amount 1 is set to be sufficiently small, the neutron flux change rate is low and the continuous reactor cycle becomes appropriate as 100 seconds or more, but the startup time until the criticality is achieved is, for example, 50 minutes. It has been experimentally confirmed that the problem of becoming longer will occur.

A method of determining the control rod withdrawal amount 1 according to the present embodiment, which solves the above-mentioned problems concerning the furnace cycle and the starting time, will be described below.

FIG. 5 is a diagram for explaining parameters used for determining the control rod withdrawal amount l. The total amount of control rod withdrawal (remaining amount of withdrawal) Lr from the present time to criticality is the estimated value Lc of the total amount of control rod withdrawal at the critical time estimated based on the inverse multiplication factor method and the total amount of control rod withdrawal L to the present time (past Total amount of lp)
Is the difference. Lc is the total amount of extraction when the inverse multiplication factor no / n, which is the ratio of the neutron flux n to the initial value no, becomes approximately 0. The low level duration of the neutron flux rate of change Δt ₁ is the time when the rate of change remained above the low level after pulling out the control rod by lp, and the high level duration Δt ₂ was also above the high level. It's a continuous time.

Thus, based on many parameters, the extraction amount l
In this embodiment, fuzzy control is used as a method of determining This method will be described with reference to FIG.

Fuzzy control is a method in which some control rules expressing operating know-how are compared with a plant state and an operation amount is calculated by online calculation. One control rule is
"If Lr is medium (M), △ t ₁ is medium (M),
If t ₂ is large (B), the withdrawal amount 1 is made very small with respect to Lr (Z) or is smaller than the previous withdrawal amount lp (S) (the smaller value of both) is used. " Such a rule. Although this rule uses a qualitative expression that it is large or small, the degree to which the plant state belongs to the set is quantified using the membership function μ. FIGS. 7A and 7B show 20 control rules and membership function μ. The control rule in FIG. 6 corresponds to the rule # 9 in FIG. The procedure for calculating the drawing amount l corresponding to the plant state using these control rules is as follows.

(1) For each control rule, the degree of conformity with the current plant state (Lr, Δt ₁ , Δt ₂ ) μi (control rule #
i) the degree of conformity to the current plant state) and the extraction amount li according to the rule. μi is the minimum value of the degree μi ₁ , μi ₂ , μi ₃ that Lr, Δt ₁ and Δt ₂ belong to each set, and li is (Z · Lr) and (S · l) in control rule #i.
p) is the minimum value.

(2) Calculate the weighted average value of li of each control rule by μi, and set it as the withdrawal amount l of the control rod. However, rules where μi is less than or equal to a predetermined value μo (0.4 in this case) are excluded from the calculation.

By doing so, the group of control rods and the pull-out amount l at each operation step can be calculated by, for example, (group 1,24
m), (group 1,24m), (group 1,19.2m), (group 1,16.8m), (group 1,12m), (group 2,12)
m), (group 2,7.7 m), (group 2,7.2 m), (group 2,3.8 m), (group 2,2.4 m), etc., and the withdrawal amount l is appropriate according to the plant condition. It will be changed.

8 (a) and 8 (b) show the characteristics of the reactor critical proximity according to this example. As can be seen by comparison with the characteristics by the conventional method shown in FIG. 10, the neutron flux change rate is within an appropriate range in this example, the neutron flux is relative to the scrum set value corresponding to the reactor cycle of 10 seconds. It rises stably with a sufficient margin. At the same time, the startup time to reach criticality is 21
It will be short enough. After the criticality was reached, the continuous furnace cycle was also an appropriate value of 200 seconds.

According to the above-described embodiment of the present invention, the following effects can be obtained.

(A) Since the pull-out amount l of the control rod can be appropriately changed according to the reactor state, while maintaining a stable neutron flux change rate (reactor cycle) (while stably increasing the neutron flux). The start-up time to the critical can be minimized.

(B) Since the fuzzy control is used to determine the control rod withdrawal amount l, the same judgment as the operator can be realized relatively easily using a computer.

As another embodiment of the present invention, instead of taking Δt ₁ or Δt ₂ as the characteristic of the dynamic behavior pattern of the neutron flux change rate, for example, the maximum value of the neutron flux change rate can be taken. It is also possible to take only _one of Δt ₁ and Δt ₂ . In this case, the contents of FIGS. 5 to 7 are partially changed, but the effect is almost the same as that of the above embodiment.

As still another embodiment of the present invention, as the state quantity when calculating the control rod withdrawal amount 1, the control rod coordinates indicating whether the control rod to be withdrawn is the central portion or the peripheral portion of the core, or the withdrawal of the control rod. It is also possible to include the position and the like. At this time, although the calculation program for the withdrawal amount 1 becomes a little complicated, the withdrawal amount 1 can be set to a more appropriate value, which has the effect of further shortening the startup time.

As another embodiment of the present invention, there is also a method of calculating the control rod withdrawal amount 1 using a data table prepared in advance. That is, for various values of Lr, lp, Δt ₁ , Δt ₂ ,
This is a method in which the pull-out amount 1 is calculated in advance based on, for example, fuzzy control, and in online calculation, data corresponding to the actual state amount is extracted from the data table in which these calculation results are summarized. In this case, the storage area of the data table becomes large, but there is an effect that the online program becomes simple.

In the above embodiment, the calculation method of the withdrawal amount 1 when the number of control rods to be simultaneously withdrawn does not change, but the present invention can be applied even when the number of control rods changes in the middle. it can.

In still another embodiment of the present invention, the operator does not operate the control rods automatically, but the control rods are manually operated by the operator based on the pulling amount (or the pulling amount of each control rod) displayed on the display device. There is also a system to operate. Even in this case, since the pull-out amount of the control rod that may be pulled out continuously is displayed on the display device, labor saving of the operation can be achieved, and the start-up time to the critical level can be minimized while keeping the furnace cycle stable. The effect is that you can do it.

In the first embodiment of the present invention, the control rod withdrawal amount l
Was determined based on the fuzzy control utilizing the driving know-how, but it can be determined using a mathematical model. In this case, it is necessary to modify the mathematical model to adapt to the plant state by using the measured values such as the total amount of control rod withdrawal up to criticality and the relationship between control rod withdrawal amount and furnace cycle. It is possible to highly accurately predict and calculate the maximum value of the control rod withdrawal amount l. Therefore, there is an effect that the start-up time can be further shortened while keeping the furnace cycle stable.

〔The invention's effect〕

According to the present invention, the withdrawal amount of the control rod can be appropriately changed according to the change in the reactor state, so that the startup time to the reactor criticality can be minimized while maintaining the reactor cycle stable. There is an effect that can be done.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention, FIG. 2 is a diagram showing a functional configuration of an automatic control rod operating device, and FIGS. 3 and 4 are diagrams for explaining a method of determining control rod operating timing. FIG. 5, FIG. 6, FIG. 6, FIG. 7 (a), (b) are diagrams for explaining the method of determining the control rod withdrawal amount, and FIG. 8 (a), (b) are the figures. FIGS. 9 and 10 are diagrams for explaining the characteristics of an embodiment of the invention, and FIGS. 9 and 10 are diagrams for explaining the conventional method and its characteristics. 1 ... Reactor, 2 ... Core 3 ... Control rod, 4 ... Control rod drive device 5 ... Control rod operation monitoring control device, 6 ... Neutron instrumentation device 7 ... Central monitoring control panel, 11 ... … Automatic control rod operation device 111 …… Control rod operation timing determination unit 112 …… Control rod operation amount (withdrawal amount) determination unit g …… Measured values of neutron flux and reactor cycle b …… Control rod operation command (operation timing and Command of pull-out amount) f ... Control rod operation command.

Claims (3)

[Claims] 1. A control rod operating system for operating a control rod of a nuclear reactor to bring a subcritical reactor into a critical state, wherein a pull-out amount of a control rod for pulling out a predetermined control rod at a time is at least critical from the present moment. The total amount of control rod withdrawals estimated to have to be extracted before, the amount of control rod withdrawal at the previous operation, and the time at which the reactor cycle lasts for more than a predetermined value or the neutron flux change rate is predetermined. Time to stay below the value,
2. A control rod operating system, comprising: a first means for calculating the control rod and a second means for displaying the pull-out amount of the control rod calculated by the first means on a display device. 2. A control rod operating system for operating a control rod of a nuclear reactor to bring a subcritical reactor into a critical state, wherein a pull-out amount of a control rod for pulling out a predetermined control rod at a time is at least critical from the present moment. The total amount of control rod withdrawals estimated to have to be extracted before, the amount of control rod withdrawal at the time of the previous operation, and the time at which the reactor cycle lasts for more than a predetermined value or the neutron flux change rate is The first means for calculating the control rod based on the time for which the predetermined value of 1 or less is maintained, the second means for displaying the pull-out amount of the control rod calculated by the first means on the display device, and the control rod are pulled out. The control rod operating system is provided with a third means for performing a function of stopping the pulling-out operation of the control rod when the neutron flux change rate exceeds the second predetermined value. 3. The control rod operating system according to claim 1, further comprising a fourth means for automatically pulling out the control rod by the pulling amount calculated by the first means.