JPH0226755B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear reactor scram prevention device, particularly in a nuclear power plant equipped with a full-capacity turbine bypass plant and a partial-capacity turbine bypass plant. The present invention relates to a nuclear reactor scram prevention device that prevents scram occurrence in a partial capacity turbine bypass plant by changing the output of a full capacity turbine bypass plant.

Figure 1 shows the schematic configuration of a conventional nuclear power plant. Steam generated in the nuclear reactor 1 is sent to a turbine 3 via a steam control valve 2, and as the turbine 3 rotates, a generator 4 generates electricity. The power generated by the generator 4 is controlled by adjusting the opening of the steam regulating valve 2, and the opening of the steam regulating valve 2 is controlled by the main steam pipe pressure detected by the pressure detector 5 and the speed detector 6. This is done by calculating the turbine speed and the output of the load setter 7 using the turbine controller 8.

Here, when the generator load decreases, the turbine speed increases because the generator load and generator output become unbalanced. This speed increase is detected by the speed detector 6, and when the speed increase exceeds a preset value, the control valve opening request signal 11 output from the turbine controller 8 decreases, causing the steam control valve 2 to open. The amount of steam flowing into the turbine 3 is reduced, the generator output is reduced, and the increase in turbine speed is therefore suppressed.

In a boiling water nuclear power plant, the ability to change the reactor output (amount of steam generated) is approximately 30%/min, so if the closing operation of the steam control valve 2 is faster than the ability to change the reactor output, Turbine controller 8
The turbine bypass valve 9 is opened by the bypass valve opening request signal 12, and the unbalance between the amount of steam generated in the reactor and the amount of steam flowing into the turbine is directly sent to the condenser to prevent the reactor pressure from rising.

By the way, in a full-capacity turbine bypass plant, the turbine bypass valve 9 has a large capacity and can handle the entire rated steam flow rate of the reactor.
Even if the load on the generator 4 suddenly changes, it is possible to continue operation. On the other hand, the capacity of the turbine bypass valve 9 in a partial capacity turbine bypass plant is often 25% of the reactor rated steam flow rate, and operation can continue even with relatively small generator load fluctuations. When a large load fluctuation occurs, the turbine bypass valve 9 cannot process excess steam, and the neutron flux increases due to the increase in reactor pressure, resulting in a high neutron flux scram. Therefore, when a relatively large load change occurs, it is impossible to continue operating the partial capacity turbine bypass plant.

Therefore, nuclear power plants generally consist of four to six power plants, with one to two full-capacity turbine bypass plants installed per power plant. In a power plant equipped with such a partial capacity turbine bypass plant and a full capacity turbine bypass plant and connected to a DC transmission system, if a part of the DC transmission system is stopped due to an accident and the power transmission capacity is significantly reduced, the full capacity The turbine bypass plant will continue to operate, but
Partial capacity turbine bypass plants have no choice but to shut down the plant due to a significant reduction in generator load. As a result, although a certain amount of power transmission capacity is secured in the DC transmission system other than the system where the accident occurred, power station measurements indicate that only the full capacity turbine bypass plant can continue to operate.
The problem is that it is not possible to secure the amount of power generated to match the power transmission capacity.

The above will be explained by taking as an example a nuclear power plant shown in FIG. 2, which is equipped with four DC power transmission systems and ten boiling water nuclear power plants connected to these. As shown in the figure, the electric power generated by the generators 4 of the 10 nuclear power plants is converted into DC by four AC/DC converters 13, and then sent to the power consumption area via the DC transmission line 14. Power is transmitted to the DC/AC converter 15. In addition, the DC transmission system of the four units has a capacity of 25% of the output of the 10 nuclear power plants.
It is assumed that each person shares the percentage.

Here, consider a case where a ground fault occurs in one unit of the DC power transmission system and restart fails. in this case,
The generator load will be reduced to the rated value due to the interruption of the DC transmission system.
It rapidly decreases to 75%, but in general, the DC transmission system is 133%
% overload transmission capacity, if the transmitted power is increased quickly in a healthy DC transmission system, the generator load dropout time in nuclear power plants will be small, and even in partial capacity turbine bypass plants, transient reactor It can sufficiently absorb excess steam volume due to unbalance between output and load. Therefore, all nuclear power plants can continue to operate, and the rated power generation capacity can be ensured even after a system accident.

On the other hand, if an accident occurs in two of the four DC power transmission systems and the restart of the faulty system fails, the transmitted power changes over time as shown in FIG. 3a. As shown in the figure, the power that can be transmitted by the DC transmission system indicated by code 17 is approximately 50% due to the occurrence of an accident.
%. After that, even if a healthy DC transmission system was overloaded by 133% of its capacity, the power transmission capacity after the accident would remain at about 67% of its rated capacity. At this time, the AC system 16 between the generator and the AC/DC converter occurs due to an imbalance between the generator output and the load.
Due to the frequency increase, the nuclear power plant turbine control system operates, and the steam control valve is throttled so that the amount of steam flowing into the turbine matches the generator load, suppressing the frequency increase in the turbine and AC system. on the other hand,
Nuclear reactors automatically reduce their output as the turbine frequency increases, but this is gradual, at around 30%/min compared to the generator load and steam control valve operation mentioned above, so the reactor output (amount of steam generated) The imbalance between the amount of steam flowing into the turbine and the amount of steam flowing into the turbine will continue for some time.
At this time, approximately 33% of surplus steam corresponding to the unbalance between reactor output and generator load is sent directly to the condenser via the bypass valve, but the bypass valve capacity of the partial capacity bypass plant is approximately 25%. %, it is not possible to process all of the excess steam and the reactor pressure increases. This increase in reactor pressure collapses the voids in the reactor core and increases the neutron flux, causing a scram due to the high neutron flux.

Figures 3b and 3c show an outline of the temporal changes in the reactor parameters described above. In FIGS. 3b and 3c, reference numeral 18 indicates the amount of reactor steam generation, reference numeral 19 indicates the amount of steam flowing into the turbine, reference numeral 20 indicates the flow rate of steam passing through the turbine bypass valve, reference numeral 21 indicates the neutron flux, and reference numeral 2 indicates the amount of steam flowing into the turbine.
2 indicates the reactor pressure, and 23 indicates the neutron flux high scram setting value.

As described above, if an accident occurs in two of the four DC transmission systems and restart fails, all the partial capacity turbine bypass plants of the nuclear reactor power plant will be scrammed, and the full capacity turbine Only the bypass plant will continue to operate. Therefore, in order to secure power generation equivalent to approximately 67% of the transmission capacity of the DC transmission system even in the event of an accident in the two systems mentioned above, it is necessary to convert 6 to 7 of the 10 plants into full-capacity turbine bypass plants. The problem arises that the cost of constructing a nuclear power plant increases.

The present invention has been made to solve the above-mentioned problems, and even if a relatively large generator load reduction occurs due to an accident in the DC transmission system, it prevents scram occurrence in the partial capacity turbine bypass plant and generates power that meets the power transmission capacity. The object of the present invention is to provide a nuclear reactor scram prevention device that secures electric power and reduces the required number of full-capacity turbine bypass plants to be installed, thereby reducing the cost of constructing a nuclear power plant.

In order to achieve the above object, the configuration of the present invention is to detect the number of systems that have been shut down based on the occurrence of an accident or restart failure in a DC power transmission system, and to prevent reactor scrams in conventional nuclear power plants. When the number of systems reaches a predetermined number or more, the output of the full capacity turbine bypass plant is rapidly reduced. In order to detect the number of stopped systems in the DC transmission system mentioned above, it is preferable to detect the stoppage and restart failure of AC/DC converters. Preferably, this is done by outputting a signal equivalent to the relay activation signal to the full capacity turbine bypass plant.

With this configuration, the full-capacity turbine bypass plant has the ability to absorb large load fluctuations and the ability to rapidly reduce output, so when the transmission capacity of the DC transmission system decreases, the output of the full-capacity turbine bypass plant can be rapidly reduced. By lowering it, it is possible to relatively reduce the amount of reduction in the generator load in the partial capacity turbine bypass plant, and it is possible to prevent scrams in the partial capacity turbine bypass plant.

Examples of the present invention will be described in detail below. FIG. 4 shows an embodiment of the present invention. In FIG. 4, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and their explanations will be omitted.

A plurality of AC/DC converters 13 are connected to the system stop determination device 26, and a converter stop signal 24 and a restart failure signal 25 are input thereto. This system stop determination device 26 is connected to a plurality of full capacity turbine bypass plants 31, and is connected to a converter stop signal 24.
By performing a logical operation on the restart failure signal 25 and restart failure signal 25, if two or more AC/DC converters have stopped and restart has failed, a rapid output drop command signal 27 is output to the full capacity turbine bypass plant 31.

The output rapid drop command signal 27 is input to the OR circuit 29 of the turbine control system 32 as a signal equivalent to the power load unbalance relay activation signal 28, and is output from the OR circuit 29 as a regulating valve quick closing signal 30.

The operation of this embodiment will be explained below. If it is detected that two or more AC/DC converters have stopped and failed to restart by the logical operation of the converter stop signal 24 and restart failure signal 25 in the system stop determination device 26, the system will be stopped. A rapid output drop command signal 27 is output from the determination device 26 . This rapid output drop command signal 27 is output as a control valve quick closing signal via the OR circuit 29 of the turbine control system 32, and is used to quickly close the steam control valve 2 (FIG. 1) of the full capacity turbine bypass plant 31. This causes the generator output of the full capacity turbine bypass plant 31 to drop rapidly. At this time, in the full-capacity turbine bypass plant 31, when the steam control valve suddenly closes, the turbine bypass valve with sufficient capacity suddenly closes and processes all the excess steam, and the reactor output suddenly decreases due to the effects of the recirculation pump trip, etc. is carried out,
After that, it is possible to operate the power plant with a single load or to continue operating the plant at low output.

By carrying out the above-described operation of suddenly reducing the generator output of the full capacity turbine bypass plant, it is possible to prevent the generator load of the partial capacity turbine bypass plant from suddenly decreasing, and it is possible to prevent the occurrence of a scram. Thereafter, after a certain period of time, the output rapid drop command signal is automatically reset, and the steam control valve of the full capacity turbine bypass plant is opened in proportion to the generator load, and the generator continues to operate at low output.

The above will be further explained using FIGS. 5a and 5b. FIG. 5a is a diagram showing the reactor steam generation amount 18, turbine inflow steam flow rate (generator output) 19, and turbine bypass valve passing flow rate 20 of a full capacity turbine bypass plant, and FIG. 5b is a diagram showing a partial Capacity turbine bypass plant reactor steam generation amount 18, turbine inflow steam flow rate (generator output)
19 is a diagram showing a turbine bypass valve passing flow rate 20 and a turbine bypass valve capacity 34. As shown in the figure, in a partial capacity turbine bypass plant, the flow rate passing through the turbine bypass valve during transient periods is suppressed to less than 25% of the turbine bypass valve capacity, and no scram occurs. In addition, since sufficient generated power is secured by continuing operation of the partial capacity turbine bypass plant, the number of full capacity turbine bypass plants installed among the 10 plants will reduce the generator load of the partial capacity turbine bypass plant by 25% (turbine bypass valve capacity 3 to 4 units are required to prevent a sudden decrease in the number of units (equivalent to 20%) or more, and construction costs can be reduced.

Furthermore, even if the number of nuclear power plants and the number of DC transmission systems is other than the above, it is possible to similarly prevent scrams and reduce the number of installed full-capacity turbine bypass plants by changing the arithmetic logic of the system fault determination device. It is something.

As explained above, according to the present invention, it is possible to prevent the occurrence of scrams in partial capacity turbine bypass plants, and the unique effects of reducing the required number of full capacity turbine bypass plants and reducing power plant construction costs are achieved. is obtained.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a nuclear power plant;
The figure is a schematic diagram showing the connection state of the nuclear power plant and the DC transmission system, Figures 3 a to c are diagrams showing the generator load and reactor status at the time of a system accident, and Figure 4 is a diagram showing the state of the reactor at the time of a system accident. An explanatory diagram showing an example of FIG. 5a,
b is a diagram showing changes in state over time of the system and reactor of the example. 4... Generator, 13... AC/DC converter, 15
...DC AC converter, 26...System shutdown determination device, 31...Full capacity turbine bypass plant.

Claims (1)

[Scope of Claims] 1. Connected to a plurality of DC power transmission systems in which the power generated by the generator is converted to DC by an AC/DC converter on the generator side, then transmitted, and then converted back to AC by the DC/AC converter on the power consumption area. In a scram prevention device for a reactor of a nuclear power plant having a plurality of boiling water nuclear power plants equipped with a plurality of full capacity turbine bypass plants and a plurality of partial capacity turbine bypass plans, A nuclear reactor scram prevention device, characterized in that the number of stopped systems is detected from restart failure, and when the number of stopped systems exceeds a predetermined number, the output of the full capacity turbine bypass plant is rapidly reduced. 2. The occurrence of an accident in the DC power transmission system that exceeds the permissible generator load reduction range determined by the number of installed full capacity turbine bypass plants is determined by detecting the stoppage and restart failure of the AC/DC converter, and the power load is determined when the accident occurs. The nuclear reactor scram prevention device according to claim 1, wherein a signal equivalent to an unbalance relay activation signal is output to the full capacity turbine bypass plant to rapidly reduce the output of the full capacity turbine bypass plant.