JPH01250097A - Surveillance equipment for reactor core at fuel exchange time - Google Patents

Abstract

PURPOSE:To display predicted read values of an in-reactor neutron measuring instrument before and after a operation procedure by inputting the operation contents of fuel replacement and calculating a neutron flux distribution by a two-dimensional output distribution calculation model. CONSTITUTION:When operation in one optional step of the fuel replacement procedure is indicated to a input indicating mechanism 1, the input indicating mechanism 1 uses information in a fuel exchanging operation data base 2 to send fuel arrangements 101 and 102 before and after the indicated operation to a two-dimensional neutron flux distribution calculating mechanism 4. The calculating mechanism 4 performs calculation by referring to a fuel core constant data base 3 and sends the neutron level 103 of neutron measuring instrument positions before and after the operation to a neutron measuring instrument read converting mechanism 5. The converting mechanism 5 multiplies the neutron level 103 by a set neutron measuring instrument read conversion coefficient 104 to calculate a neutron read predicted value 105, which is sent to and displayed on an output display mechanism 106. The behavior of the in-reactor neutron measuring instrument can be grasped previously, so the reactor surveillance of high quality is performed.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is aimed at monitoring the reactor core during the fuel exchange process during periodic reactor inspections, by monitoring the readings of the in-core neutron measuring instrument during the fuel exchange operation. This invention relates to a reactor core monitoring device during fuel exchange that predicts and presents changes.

(Prior art) In general, during fuel exchange operations during periodic nuclear reactor inspections,
In order to avoid a reactivity accident in which the reactor becomes supercritical and the output suddenly increases, changes in the readings of the in-reactor neutron measuring instrument are monitored when loading and unloading fuel or when withdrawing control rods to ensure that the reactor is not subcritical at all times. It is necessary to confirm.

When the neutron measuring device is subcritical, the reading will be at a certain level depending on the subcriticality level (reactivity margin before reaching criticality), but the subcriticality may change due to the removal and removal of fuel and control rods during refueling work. Because of the change, the reading changes transiently and falls to a different level. When fuel is loaded or a control rod is withdrawn, positive reactivity is added, and the readings of the neutron measuring instrument are transient, as shown by curves a, b, and c in the graph of Figure 4. rise to and settle down at a higher level. If the degree of subcriticality is small and close to criticality, the rising period will be longer;
The level at which it becomes constant also becomes higher.

At supercriticality, the neutron level does not remain constant and increases exponentially.

On the other hand, when fuel is removed or control rods are inserted, negative reactivity is added, and the readings of the neutron meter are A transitional decline, falling to a lower level.

Those who monitor the reactor core during refueling must monitor that the refueling procedure is being carried out correctly, understand the behavior of this neutron level well, and constantly confirm that the reactor is subcritical. There is.

(Question 8 to be solved by the invention) During fuel exchange, control rods are fully inserted into the parts of the reactor core where fuel is loaded, and the parts where control rods need to be taken out for inspection or replacement work are All the fuel around the control rods has been removed, and based on safety regulations, there is enough margin to shut down the reactor so that even if one control rod is accidentally pulled out, the reactor remains subcritical. Therefore, if the refueling procedure is planned correctly, the reading of the in-reactor neutron measuring instrument will drop to a certain level within a few minutes, but if there is a mistake in the procedure, fuel may be loaded into a part of the reactor core that does not have control rods. If control rods are pulled out of the core where fuel is located, the margin for reactor shutdown will be reduced and neutron levels may increase rapidly. The probability of errors in procedure execution can be sufficiently reduced by automating the fuel exchange work, but if there is inappropriate data in the fuel exchange procedure itself, the margin for reactor shutdown may be reduced. obtain.

Apart from the need for monitoring from a safety perspective when neutron levels become high, when neutron flux levels become low and neutron meter readings become low, there are operational issues such as: occurs.

Neutron source region neutron measuring instrument (SRM: Source
The reading of eRange Monitor) is the setting lower limit value (
3 cps), an interlock prevents the control rod from being withdrawn. In order to replace the control rod itself, replace the in-core detector, or inspect the control rod drive mechanism, it is necessary to remove the surrounding fuel and then pull out the control rod. As refueling progresses and the amount of fuel removed from the core increases, the degree of subcriticality generally increases.
As neutron levels drop, the SRM readings will drop sharply, especially if defueling is performed around the SRM. Also, S.R.
When $4 of fuel around M is extracted, the degree of subcriticality locally becomes larger than the core average, and the actual reactor shutdown margin is smaller than judged from the readings, resulting in unexpected output due to careless operation. There is a possibility that an upper bound will occur.

For the above reasons, when monitoring the reactor core during refueling work, it is necessary to pay attention to changes in the readings of neutron measuring instruments after each work, and to ensure that there is sufficient margin for reactor shutdown and that neutron measurement values do not reach the lower limit. If changes in the readings of the neutron meter A-1 could be known in advance before refueling operations, core monitoring would be more reliable, but such a prediction function is not possible with conventional process computers. It had not been realized.

For this reason, conventionally, procedures such as adjusting procedures to avoid situations where the neutron level is too high or too low at the stage of planning fuel exchange work procedures have been done based on the experience and intuition of the work procedure planners. There is.

Furthermore, since there are no simulators or the like to train core monitoring operations during fuel exchange operations, the personnel involved in core monitoring operations had no choice but to gain experience through actual refueling operations.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a reactor core monitoring device during refueling that uses the details of the refueling work as input and presents to the user predicted values of the readings of the in-core neutron measuring instrument before and after the refueling work. be.

[Structure of the Invention] (Means for Solving the Problem) That is, a manual instruction means for manually inputting the content of fuel exchange work, and a fuel nuclear determination corresponding to fuel exchange work data and in-reactor fuel arrangement instructed by the input instruction means. a neutron flux distribution calculation means that calculates the neutron flux distribution before and after refueling work using a two-dimensional power distribution calculation model that takes into account a fixed neutron source from numerical data, and calculates the neutron level at the in-reactor neutron measuring instrument position; neutron meter reading conversion means for converting the neutron level obtained by the neutron flux distribution calculation means into a neutron meter reading; and output display means for outputting the neutron meter reading obtained by the neutron meter reading conversion means. It is characterized by having the following.

(Function) In the reactor core monitoring device during refueling of the present invention having the above configuration, in order to predict the core behavior during refueling, neutron flux distribution is calculated by two-dimensional diffusion calculation, and the neutron flux distribution is calculated using a neutron measuring instrument. Convert to reading.

In core neutron flux distribution calculations, eigenvalue calculations are often adopted for the purpose of subcriticality evaluation for safety evaluation.
In the core state during the refueling process, there are cases where fuel is removed and the core contains many water regions, which poses problems in terms of calculation convergence stability and time cost. Therefore, we adopt a neutron flux distribution calculation based on a fixed neutron source, which does not require an iterative solution method.

Then, from the fuel exchange work data based on the fuel exchange procedure manually performed by the manual instruction means and the fuel nuclear constant data, 2
The neutron flux distribution calculation means calculates the neutron flux distribution in the reactor in two cases, before and after the refueling procedure is executed, and from this neutron flux distribution, the neutron level at the neutron measuring instrument position is determined. Thereafter, this neutron level is converted into a neutron meter reading by the neutron meter reading conversion means, and the neutron meter readings before and after execution of the fuel exchange procedure are displayed on the output display means.

This makes it possible to predict changes in neutron meter readings without actually performing refueling operations.

In addition, the current neutron needle 4Pj device output signal is taken into the distribution deviation evaluation means, and by comparing it with the predicted value of the neutron measuring device reading predicted for the current core state, the size of the deviation and the distribution depending on the measuring device position are fixed. If the configuration is such that the fixed neutron source is sent to the source evaluation means, and the fixed neutron source is recalculated to reduce the deviation based on this deviation information, and then sent to the two-dimensional neutron flux distribution calculation means, the neutron measurement instrument reading before the refueling procedure is Since the predicted value and the actual neutron meter output signal are adjusted to match, the accuracy of the predicted neutron meter reading after the refueling procedure is performed is improved.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a reactor core monitoring device during refueling according to an embodiment of the present invention. The reactor core monitoring device during refueling according to this embodiment includes an input instruction mechanism 1, a refueling work database 2,
It is composed of a fuel nuclear constant database 3, a two-dimensional neutron flux distribution calculation mechanism 4, a neutron meter reading conversion mechanism 5, and an output display mechanism 6.

Furthermore, the fuel nuclear constant database 3 stores the nuclear constants of all fuels involved in refueling operations, making it possible to calculate the neutron flux distribution for any fuel arrangement. . Further, the fuel exchange work database 2 stores the fuel arrangement of the target reactor core, the fuel exchange procedure, and the position of the in-core neutron detector.

Next, the operation of the reactor core monitoring device during refueling having the above configuration will be explained.

When an input instruction is given to the input instruction mechanism 1 for a fuel exchange operation corresponding to one step in a preset fuel exchange procedure, or an arbitrary one-step fuel exchange operation for a specified fuel arrangement, the input instruction is Mechanism 1 includes fuel arrangement 101 before fuel exchange work and fuel arrangement 1 after fuel exchange work.
02 to the two-dimensional neutron flux distribution calculation mechanism 4.

The human power instruction mechanism 1 is configured as shown in FIG. Fuel arrangement 1 before fuel exchange work
01 is displayed. Further, the fuel arrangement 106 in the fuel pool is also displayed, and by using the mouse 11 to move the mouse cursor 107 on the fuel arrangement display mechanism 10, it is possible to specify the fuel to be replaced by operating the mouse 11. can. When the mouse 11 is operated in a place where there is no fuel after specifying the fuel, the movement of the fuel is specified. For example, after specifying fuel in the reactor core, specifying an empty position in the fuel pool will result in fuel removal, specifying fuel in the fuel pool and then specifying an empty position in the core will result in fuel loading, and after specifying fuel in the reactor core, Specifying an empty position in the core will result in fuel shuffling. In this way, one step in the refueling operation can be designated.

The two-dimensional neutron flux distribution calculation mechanism 4 refers to the fuel nuclear constant database 3 based on the fuel arrangement 101 and 102 before and after the fuel exchange operation, and imports the nuclear constant data necessary for calculation.
Perform two-dimensional neutron flux distribution calculations. A fixed neutron source is also set as nuclear constant data in the fuel nuclear constant database 3, and used for neutron flux distribution calculation. In addition, when predicting each work step sequentially according to the fuel exchange procedure,
Since the neutron flux distribution in the step can be adopted as the neutron flux distribution before the refueling operation in the next step, only the neutron flux distribution after the refueling operation is calculated in the next step. Then, data on the position of the in-reactor neutron detector is imported from the refueling work database 2, the neutron level at this position is calculated from the neutron flux distribution, and the neutron level 103 at the neutron measuring instrument position before and after the refueling work is calculated from the neutron meter. It is sent to the 1fFJ device reading conversion mechanism 5.

Since the neutron meter reading 4p1 and the neutron level are in a proportional relationship, the neutron meter reading conversion mechanism 5 multiplies the neutron meter reading conversion coefficient 104 set to the neutron level 103 to calculate the predicted neutron meter reading value 105. Then, it is sent to the output display mechanism 6 for display.

The two-dimensional neutron flux distribution calculation based on a fixed neutron source is
Since the calculation is completed within one second using a process computer or the like without requiring an iterative solution method, changes in neutron meter readings can be predicted by Δ-1 in real time in response to instructions for refueling work. Regarding the fixed neutron source and neutron measuring instrument reading conversion coefficient 104,
Appropriate predicted values can be obtained by making adjustments to match actual readings under representative core conditions.

According to the reactor core monitoring device at the time of refueling of this embodiment having the above configuration, the person in charge of core monitoring at the time of refueling can grasp the behavior of the in-core neutron measuring instrument in advance regarding the scheduled refueling plan, High-quality core monitoring is possible by identifying potentially problematic areas during the refueling procedure where neutron levels are too high or too low. Furthermore, when used at the stage of creating a fuel exchange plan, it is possible to improve procedures where neutron levels are likely to be a problem, so it is also effective in creating a fuel exchange plan.

It is also effective as a training simulator, as it allows you to experience monitoring the in-core neutron measuring instruments, which are important for core monitoring, without actually performing refueling work.

In this case, you can experience a simulated reactivity accident such as a control rod fall accident, which is important for training in core monitoring work.

In the above embodiment, the neutron measuring instrument reading was predicted for the refueling work step for one case, but it is also possible to simultaneously make predictions for multiple cases of work implementation candidates and use it as a guide for selecting the refueling work. In this case, instead of inputting the fuel exchange work individually using the input instruction mechanism 1,
Candidates for refueling work may be automatically determined and predicted.

Next, another embodiment of the present invention will be described with reference to FIG.

The core monitoring device during refueling of this embodiment includes a fixed neutron source evaluation mechanism 7 and a distribution deviation evaluation mechanism 8 in addition to the configuration of the core monitoring device during refueling of the previous embodiment.

In addition, an input instruction mechanism 1, a fuel exchange work database 2,
The operations of the fuel nuclear constant database 3, the two-dimensional neutron flux distribution calculation mechanism 4, the neutron measuring instrument reading conversion mechanism, etc. are the same as those in the previous embodiments, so a redundant explanation will be omitted.

In this embodiment, the distribution deviation evaluation mechanism 8 uses the output signal 108 of the in-core neutron measuring instrument 20 as a reference signal and compares it with the predicted value 105 read by the neutron measuring instrument before the fuel exchange operation. Usually, a plurality of in-core neutron measuring instruments 20 are installed (for example, SRM-4 channel), and a single neutron measuring instrument reading conversion coefficient 104 cannot correct the instrument reading deviation because it has a distribution. In-core neutron measuring device 20 for each channel
Although it is conceivable to set the neutron needle n1 instrument reading conversion coefficient 104 for each time, it would not correctly reflect the original physical phenomenon that the neutron level is proportional to the neutron measuring instrument reading. Therefore, the deviation distribution 109 is sent from the distribution deviation evaluation mechanism 8 to the fixed neutron source evaluation mechanism 7, and based on this, it is used for two-dimensional neutron flux distribution calculation so that the deviation distribution 109 is uniform and minimized. Fixed neutron source distribution 1
Correct 10. Based on the corrected fixed neutron source distribution 110, the neutron flux distribution before and after the refueling operation is recalculated, and the deviation between the predicted value 105 read by the neutron measuring instrument before the refueling operation and the output signal 108 is made sufficiently small. The neutron meter readings 105 before and after the fuel exchange work are sent to the output display mechanism 6 and displayed.

According to the reactor core monitoring device during refueling of this embodiment, the accuracy of neutron flux distribution calculation is improved based on the actual neutron measuring device output, so the behavior of the neutron needles 11 can be predicted with even higher accuracy.

In this example, the predicted result is displayed only on the output display mechanism 6, but by comparing the predicted value read by the neutron measuring instrument with the set reading upper and lower limits, the fuel exchange automation system and fuel exchange work monitoring system can be used. It can also be used as a WW signal or an interlock signal. In this case, regarding the in-core neutron measuring instrument, a channel whose predicted reading value is likely to deviate from the upper and lower limits may be identified and an alarm signal or the like may be issued.

Further, in the description of these embodiments, prediction for control rod operation was not explained, but it is naturally possible to predict it in the same way as fuel movement.

[Effects of the Invention] As explained above, according to the present invention, it is possible to predict the behavior of neutron measuring instrument readings during fuel exchange, reducing the workload of core monitoring work and improving the quality of core monitoring. can be achieved. In addition, by using this as a reference when creating a fuel exchange plan, it is possible to create a fuel exchange procedure that will bring the neutron level to an appropriate level.

Further, the present invention can be implemented as a function of a process computer. Therefore, for conventional core monitoring operations during fuel exchange,
Applying the invention is easy.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a reactor core monitoring device during refueling according to an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of the manual instruction mechanism shown in FIG. 1, and FIG. 3 is a diagram showing another embodiment of the present invention. FIGS. 4 and 5, which show the configuration of the example core monitoring device during refueling, are graphs showing changes in the neutron level as the degree of subcriticality changes. 1......Human power instruction mechanism 2......Fuel exchange work database 3...
・・・・・・Fuel nuclear constant database 4・・・・・・
...Two-dimensional neutron flux distribution calculation mechanism 5...
・Neutron meter reading conversion mechanism 6・・・・・・・・・Output display mechanism Applicant Japan Atomic Energy Corporation Applicant
Toshiba Corporation Representative Patent Attorney Sasa Suyama - Figure 3

Claims (1)

[Claims] (1) An input instruction means for inputting the details of the fuel exchange work, and a two-dimensional output considering a fixed neutron source from the fuel exchange work data instructed by this input instruction means and fuel nuclear constant data corresponding to the fuel arrangement in the reactor. A neutron flux distribution calculation means that calculates the neutron flux distribution before and after the fuel exchange operation using a distribution calculation model and calculates the neutron level at the position of the in-reactor neutron measuring device; A reactor core at the time of refueling, characterized by comprising a neutron meter reading conversion means for converting into a neutron meter reading, and an output display means for outputting the neutron meter reading obtained by the neutron meter reading conversion means. monitoring equipment.