JPS59188591A - Method of operating 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] [Field of Application of the Invention] The present invention relates to a method of operating a nuclear reactor equipped with a control rod for output adjustment and a device for controlling the concentration of liquid poison in a moderator. The present invention relates to a method of operating a nuclear reactor that changes the insertion position of control rods for output adjustment according to the output level during daily load follow-up operation.

[Background of the invention]

In general, in nuclear reactors with relatively small power reactivity coefficients, such as heavy water-moderated reactors, as the core becomes larger, the power distribution of the core varies spatially due to changes in xenon concentration, resulting in so-called xenon spatial oscillations. do. This xenon spatial oscillation is caused by the direct production of xenon absorbing neutrons through nuclear fission of fuel, indirect production through the decay of iodine, direct annihilation in which xenon absorbs neutrons and annihilation, and natural decay of xenon, resulting in spatially varying xenon concentrations. Occasionally this occurs.

FIG. 1 shows an example of power distribution fluctuation due to xenon spatial vibration in the radial direction of the core in a heavy water-moderated nuclear reactor. The core power distribution fluctuation shown in FIG. 1 shows how it changes over time, with Ohr being the time when xenon spatial imaging occurs. Localized increases in output due to such fluctuations in output distribution are unfavorable for the health of the fuel and the operation of the reactor, so xenon spatial vibrations are controlled.

As a method of controlling this xenon spatial vibration, the reactor core is divided into multiple regions, and 4! ri5j [A method of controlling the output independently of the recording is generally used. FIG. 2 shows an example in which the core is divided into multiple regions, and in this example, it is divided into five regions. In FIG. 2, a large number of fuel assemblies 12 are loaded in a core tank 10. The periphery 5 of the fuel assembly 12 is filled with heavy water moderator 14, and a neutron detector 16 and a power adjustment control rod 18 are arranged at appropriate positions in the core tank 10. . The divided regions of the reactor core are divided into five regions, which are the central part of the core and its surroundings divided into four equal parts, and the output adjustment control rods 18tl belonging to each region are driven independently to keep the output of each region constant. Operation is controlled to maintain The output adjustment control rod 18 is normally operated with the nominal position (center position) as the half-insertion position, which is the most suitable position for vertical driving. However, as a result of the power adjustment control rod being always placed in the manually inserted position, combustion of the upper half of the fuel is suppressed and combustion of the lower half is promoted, causing inconvenience at the end of the reactor operating cycle. That is, the third
As shown in the figure, at the beginning of the operation cycle, the power adjustment control rod 18 is in the half-inserted position, so the power of the core is low in the upper half in the axial direction of the core and high in the lower half, and the lower half of the fuel is burned. is promoted. Then, when the output adjustment control rod 18 is pulled out at the end of the cycle, the output of the upper half of the fuel whose combustion has been suppressed becomes extremely large, and the axial peaking approaches the allowable limit value, resulting in extremely thermal hardship. state. Therefore, when xenon spatial vibration occurs at the end of the cycle, the output adjustment control rod 18
It is no longer possible to move the reactor up and down significantly, which poses a problem in the operation of the reactor.

As a result, when xenon spatial oscillations occur at the end of the cycle, the entire output of the reactor must be reduced, reducing the operating rate of the reactor and causing economic problems.

Moreover, non-uniform combustion of the fuel lowers the fuel extraction burnup, which is undesirable from the viewpoint of fuel economy.

[Purpose of the invention]

The present invention has been made in order to eliminate the drawbacks of the prior art, and an object of the present invention is to provide a method of operating a nuclear reactor that can completely improve the fuel extraction burnup.

[Summary of the invention]

The present invention provides a method for operating a nuclear reactor in which the output of the reactor is changed in accordance with fluctuations in the full load of the reactor. By changing the concentration of poison in the moderator depending on the insertion position of the moderator), combustion in the upper part of the fuel is promoted at low power, and combustion in the axial direction of the fuel is made uniform, thereby improving the extraction burnup. It is configured so that it can be done.

[Embodiments of the invention]

FIG. 4 shows the relationship between the thermal output of the nuclear reactor and the xenon oscillation. In general, the relationship between the thermal output of a nuclear reactor and xenon imaging differs depending on the size of the reactor, etc. In a nuclear reactor with an electrical output of about 600,000 kW, the thermal output of the reactor is as shown in Figure 4. When it becomes about 70% or less, the neutron flux in the reactor core decreases, and the amount of xenon produced, which is proportional to the magnitude of the neutron flux, decreases, so that xenon spatial vibrations no longer occur. Therefore, when the thermal output is 70% or less, there is no need to drive the output adjustment control rod up and down at the nominal position of the half-inserted position to control the xenon spatial vibration. At a sufficiently low output level where the thermal output is 70% or less, even if all the control rods for output adjustment are pulled out, the output distribution will remain within the output distribution envelope formed at the rated output (
If the fuel enters the fuel envelope), it will not cause any problems regarding the integrity of the fuel. The present invention has been made based on the above-mentioned fact, and in an operating method in which the output follows load fluctuations, the control rod for output adjustment is placed in the shallow insertion position or the fully withdrawn position during operation at a low output level, and the rated output is Sometimes, the power adjustment control rod is inserted in a semi-inserted position.

FIG. 5 shows an example of an output change pattern that follows the load. The output change pattern shown by the solid line in Figure 5 is to operate at the rated output, that is, 100% output, for 14 hours during the day, reduce the output to 50% in one hour, and output 50% output for 8 hours at night. This figure shows the so-called daily load follow-up slow shift turn, where the output is increased to 100% of the rated output in one hour after operation. The broken line indicates the insertion position of the power adjustment control rod in the axial direction of the reactor core.

That is, at rated output, the power adjustment control rods are inserted to the axial node 7.5, which is the half-insertion position (nominal position), and when the electrical output is at a low output value of 50%, the control rods are inserted into the core, which is the shallow insertion position. It is inserted up to the axial node 14 (pulled out to the core axial node 13) and operated. In addition, when the core axial direction node is 00, it indicates the full insertion position, and 15
indicates the fully withdrawn position.

FIG. 6 shows an example of a control device for carrying out the operating method shown in FIG. 5. In FIG. 6, a large number of pressure pipes 20 are arranged in the core tank 10, and fuel assemblies 12 are housed in the pressure pipes 20. The heat generated by the combustion of the fuel assembly 12 is carried to a heat exchanger (not shown) by the light water coolant (H2O) 22 flowing through the pressure pipe 20. Also, inside the core tank 10, there is a heavy water guide pipe 2 that guides a heavy water moderator (DzO) 14.
4 and a neutron detector 16 are installed,
A control rod 18 for output adjustment can be inserted.

The heavy water moderator 14 in the core tank 10 is guided to the heavy water guide pipe 24 via a heavy water circulation path 28 by a heavy water circulation pump 26. The heavy water circulation path 28 is provided with a heavy water purification tower 30 for purifying the heavy water moderator, and a poison removal cylinder 32 for removing poison from the heavy water moderator 14 is attached.

The neutron detector 16 is connected to an output change rate determiner 36 and an output distribution calculator 38 via a neutron flux-to-output converter 34. The signal from the output conversion rate determiner 36 is sent to an adjustment rod withdrawal output determiner 40 or an adjustment rod insertion output determiner 42, and is compared with the signal from the output setting device 44. The adjustment rod withdrawal determination device 40 sends a signal to the adjustment rod shallow insertion position indicator 45. This adjustment rod shallow insertion position indicator 45 receives a detection signal from a control rod position detector 48 connected to a control rod drive device 46 that drives the output adjustment control rod 18, and a control rod shallow insertion position setting device 50. It is set to receive a signal from the 1-poison injection indicator 60 and sends an output signal to the 1-poison injection indicator 60. Further, the signal from the adjustment rod insertion output determiner 42 is transmitted to the control rod insertion position detector 48 and the adjustment rod nominal position setter 52.
It is input to the adjustment rod nominal position indicator 54 which is connected to.

The output distribution calculator 38 described above inputs the output distribution at each time to the envelope storage device 56 and also to the output distribution determiner 58. Envelope storage device 5
6 calculates an envelope based on the input output distribution and inputs it to the output distribution determiner 58. Output distribution determiner 58
determines whether the output distribution inputted from the output distribution calculator 38 falls within the envelope, and sends a signal to the poison injection indicator 60 and the poison removal indicator 62.

The poison injection indicator 60 is the adjustment rod shallow insertion position indicator 4
5 and the output distribution determiner 58, the heavy water circulation path 2
The poison injection regulating valve 66t of the poison dissolving tank 64, which has been added to 8 to 9, is controlled.

(9) Further, the poison removal indicator 62 controls the poison removal adjustment valve 68 of the poison removal tower 32 based on the signals from the adjustment rod nominal position indicator 54 and the output distribution determiner 58.

Daily load tracking in the control device configured as described above is carried out as follows.

When the reactor is operated at the rated output, the output adjustment control rod 18 is at the nominal position (in the core axis direction)+1. is inserted to the center of the card.

When the output of the nuclear reactor is to be reduced from the rated output to 50% output as shown in A in FIG. 5, it is done as follows. An output change pattern is input to an output control device (not shown), and based on this output change pattern, changes in xenon concentration and samarium concentration are predicted and calculated as shown in FIG. 7, and reactivity changes are determined. and,
The output control device determines the poison injection rate to compensate for the change in reactivity, controls the poison injection regulating valve 66 of the poison dissolving tank 64, and starts output control for load following. On the other hand, the output setting device 44 is set to (10) select whether to place the output adjustment control rod 18 in the shallow insertion position where it is pulled out by more than 70% or to push it in to the nominal position.For example, the reactor output is 75% of the rated output. Output is input.

The power of the nuclear reactor is detected as a neutron flux by a plurality of neutron detectors 16 installed in the reactor core tank 10, and after being converted into reactor power by a neutron flux-output converter 34,
The signal is input to the output control device, output change rate determiner 36, and output distribution calculator 38 (not shown). A power control device (not shown) injects poison from the poison dissolution tank 64 into the core tank 10 according to a predetermined injection rate, and outputs minute fluctuations in the reactor power detected by the neutron detector 16 via the control rod drive device 46. The output is decreased while being adjusted by the adjustment control rod 18.

The output change rate determiner 36 determines whether the change in the reactor output detected by the neutron detector 16 via the neutron flux-output converter 34 is positive or negative, and the output of the reactor increases. Determine whether it is in the middle or descending. Then, when the reactor power is decreasing as shown in FIG.

The adjustment rod withdrawal power determiner 40 uses the reactor power sent from the output change rate determiner 36 and the reactor power instructed by the power setting device 44 (75% of the rated power in this embodiment).
Compare with. By comparing these outputs, the output change determiner 3
When the reactor output from 6 is greater than the output instructed by the output setter 44, the injection of shivozen is continued by the above-mentioned output control device. Then, when the output from the output change rate determiner 36 becomes smaller than the -fc power as instructed by the output setter 44, it indicates that the output from the output change rate determiner 36 is 75% or less of the rating. When the adjustment rod is inserted, the output signal of the adjustment rod withdrawal output determiner 40 is sent to the adjustment rod shallow insertion position indicator 45. The adjustment rod shallow insertion position indicator 45 indicates the insertion position of the output adjustment control rod 18 transmitted via the control rod position detector 48 and the control rod insertion position instructed from the adjustment rod shallow insertion position setting device 50. The insertion position of the output adjustment control rod 18 is adjusted (1
2) When the rod is deeper than the position indicated by the shallow rod insertion position setter 50, send an output signal tube to the poison injection indicator 60.

On the other hand, the output distribution calculator 38 uses the neutron flux-to-output converter 3
4, the power distribution within the reactor including the power distribution of the fuel adjacent to the power adjustment control rod 18 is calculated. This calculated output distribution is sequentially input to the envelope storage device 56, and the temporal envelope of the output distribution is stored therein. Further, the current output distribution calculated by the output distribution calculator 38 and the envelope stored in the envelope storage device 56 are input to the output distribution determiner 58. When the power distribution determiner 58 determines that the current power distribution is within the power/perope range with sufficient margin, it transmits a signal indicating that there is no problem with the health of the fuel to the poison injection indicator 60. When the poison injection indicator 60 receives the signals from the adjustment rod shallow insertion position indicator 45 and the output distribution judger 58, it further opens the poison injection adjustment valve 66 and removes the total weight of the poison in the poison dissolution tank 64 (13). The water is injected into the core tank 10 via the water circulation path 28 and the heavy water guide pipe 24. When voids are injected into the core tank 10, the reactivity of the core decreases, so a power control device (not shown) compensates for this decrease in reactivity and controls the control rods to maintain the full predetermined output according to the output change pattern. The output adjustment control rod 18 is pulled out via the drive device 46. When the output adjustment control rod 18 is pulled out to the position indicated by the adjustment rod shallow insertion position setting device 500, the adjustment rod shallow insertion position indicator 45 sends a poison injection stop signal to the poison injection instruction device 60.

When the output of the reactor drops to 50% of the rated power in this way, the output control device (not shown) switches to fc as shown in FIG. 5B.
In order to maintain 50% output, the poison concentration in the core tank 10 is adjusted. That is, as shown in FIG. 7, the reactivity of the nuclear reactor changes as the xenon concentration in the fuel changes, so the poison removal adjustment valve 68 is opened to compensate for this change in reactivity, and the poison removal tower is closed. Poison of heavy water moderator 14 in 32? Remove 7 and also dissolve poison (
14) Poison is injected into the heavy water moderator from tank 64.

During this time, the power adjustment control rods 18 are almost maintained at the shallow insertion position instructed by the adjustment rod shallow insertion position setting device 50 as shown in FIG. be moved and adjusted.

When the power of the nuclear reactor is increased from 50% to 100% of the rated power as shown in FIG. That is, the output control device (not shown) removes poison from the heavy water at a predetermined poison removal rate, as shown from the 9th hour to the 10th hour in FIG. 8, in accordance with the output change pattern, thereby increasing the output. When the output of the reactor starts to rise, the output change rate determiner 36 determines that the output of the reactor is increasing, and sends the signal of the reactor output to the adjustment rod insertion output determiner 42.
to communicate. When the output becomes larger than the adjustment rod insertion output determiner, a signal is sent to the adjustment rod nominal position indicator 54 (15). The adjustment rod nominal position indicator 54 transmits a signal to the poison removal indicator 62 when the insertion position of the output adjustment control rod 18 is shallower than the position indicated by the adjustment rod nominal position setting device 52.

The poison removal indicator 62 receives a signal from the power distribution determiner 58 indicating that the reactor output is within the envelope with sufficient margin, and the poison removal adjustment valve 6
8 is further opened, and the core tank 1 is passed through the heavy water circulation path 28.
The heavy water moderator 14 in 0 flows into the poison removal tower 32 to remove poison. Therefore, the reactivity of the core increases to a predetermined value, and the output control device (not shown) inserts the output adjustment control rod toward the nominal position. When the output adjustment control rod 18 is inserted to the nominal position in this way, the adjustment rod nominal position indicator 54 determines that the output adjustment control rod 18 has been inserted to the nominal position, and the poison removal indicator 54 determines that the output adjustment control rod 18 has been inserted to the nominal position. 62 to stop poison removal.

Thereafter, the reactor power is maintained at the power control device's rated power. That is, as shown in FIG. 7, the removal or injection of poison is performed so as to ensure the reactivity which varies according to the change in the concentration of fluorine (16). Then, minute fluctuations in the output of the nuclear reactor are adjusted by moving an output adjustment control rod inserted at the nominal position up and down in the vicinity of the nominal position.

FIG. 7 shows output fluctuations controlled based on the daily load follow-up output change pattern shown in FIG. 5, and it can be seen that the electrical output is controlled according to plan. Furthermore, as shown by the broken line in Fig. 8, the concentration of poison in the heavy water in this example is higher than that in the conventional case because more poison is injected at the low output level when the electrical output is 75% or less. It can be seen that the poison concentration is increasing.

In this way, when the power adjustment control rod 18 is pulled out to the shallow insertion position, that is, to the position μ゛14 in the core axial direction during 50% power operation of the reactor, the power adjustment control is performed at the end of the reactor operation cycle. Even when the rod is in the fully withdrawn position, the output at the upper part of the reactor core (in the axial direction) does not become very large.

By pulling out the force adjustment control rod 18 to the fully shallow insertion position when the output is low, combustion in the upper part of the fuel is promoted and the burnup distribution in the axial direction of the reactor is relatively uniform. be done.

Therefore, even if the power adjustment control rods 18 are completely withdrawn at the end of the operation cycle, the reactor power in the core axial direction is normalized, and the thermal limit value of the axial power (9th
The relative output shown in the figure does not exceed about 1.4 v), and the safety of the nuclear reactor can be improved. Therefore, even if an unstable phenomenon such as xenon spatial oscillation occurs at the end of the cycle, the output adjustment control rods can be sufficiently driven to control the xenon spatial oscillation, improving reactor controllability and The operating rate of the furnace can be increased. In addition, as a result of fully promoting the burnup of fuel near the power adjustment control rods and the upper half of the core, the burnup of fuel taken out increases and fuel economy can be improved.

In the above embodiment, a heavy water-moderated nuclear reactor is described, but the present invention can also be applied to a nuclear reactor in which poison is completely dissolved in light water, such as a pressurized water reactor (18). Further, although the case has been described in which the signal from the in-core neutron detector 16 is used as the output signal of the nuclear reactor, the output signal may be replaced with an electrical output signal of the generator.

〔Effect of the invention〕

As explained above, according to the present invention, in the operation of a nuclear reactor with power fluctuations, by withdrawing the power adjustment control rod to the shallow insertion position at low power, combustion of fuel in the upper part of the core is promoted, and as a result, The fuel extraction burnup can be improved.

[Brief explanation of the drawing]

Figure 1 shows an example of xenon spatial vibration in a heavy water-moderated reactor, Figure 2 shows an example of a heavy water-moderated reactor core divided into multiple regions, and Figure 3 shows the reactor operating cycle. A diagram showing the conventional relative power in the core axis direction at the initial stage and at the end of the operation cycle, Figure 4 is a diagram showing the relationship between the reactor thermal output and the xenon vibration attenuation ratio, and Figure 5 is the power output of the reactor of the present invention. FIG. 6 is a diagram showing the relationship between the electrical output and the insertion position of the output adjustment control rod in the embodiment related to the operation method, and FIG.
) A diagram showing an example of a control device for implementing such a nuclear reactor operating method, FIG. 7 is a diagram showing changes in xenon concentration and samarium concentration with respect to changes in electrical output, and FIG. A diagram showing changes in the conventional poison concentration in the heavy water moderator and the poison concentration in the embodiment according to the present invention, and FIG. 9 shows a cycle in the conventional nuclear reactor operating method and the operating method according to the embodiment according to the present invention. FIG. 3 is a diagram showing a comparison of relative power in the axial direction of the core at the final stage. 10... Core tank, 14... Heavy water moderator, 16
...Neutron detector, 18...Output adjustment control rod, 3
2... Poison removal tower, 36... Output change rate determiner, 38... Output distribution calculator, 40... Adjustment rod extraction output determiner, 42... Adjustment rod insertion output determiner, 45・・・
- Adjustment rod shallow insertion position indicator, 54... Adjustment rod nominal position indicator, 58... Output distribution judger, 6o... Poison injection indicator, 62... Poison removal indicator, 6
4... Poison dissolution tank. Agent Patent Attorney Tatsuyuki Unuma (20) No. 1, All Rights Reserved, No. 20, No. 1, Deba $ 4 Figure θ 5θ l
θθ thickness J is the claw upper blade (7S) No. T closed $ ω

Claims (1)

[Claims] 1. In a method of operating a nuclear reactor in which the poison concentration in the moderator and the insertion position of a control rod for output adjustment are changed to make the output follow load fluctuations, the control rod is placed in a shallow insertion position during low output operation of the reactor. A method for operating a nuclear reactor, characterized in that the control rod is withdrawn by the above amount, and the concentration of poison in the moderator is changed in accordance with the insertion position of the control rod.