Fan switching method without purification exhaust system for nuclear island of VVER nuclear power plant

Abstract

The invention belongs to the technical field of nuclear power, and particularly relates to a fan switching method for a VVER nuclear power plant nuclear island without a purification exhaust system. According to the invention, the configuration of the main ventilation system of the nuclear island of the VVER nuclear power plant is fully utilized, and a new fan switching method without a purification exhaust system is adopted, so that the time that the exhaust air rate of the annular space of the double-layer containment is less than a normal value is shortened from 2 minutes to 10 seconds; the pressure rise of the annular space of the double-layer containment during fan switching can be prevented from exceeding a regulation limit value, so that radioactive substances are effectively prevented from being released to the environment when a design basis accident occurs.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear power, and particularly relates to a method for switching fans of a non-purified exhaust air system in the nuclear island of a VVER nuclear power plant. Background Art

[0002] The non-purified exhaust air system in the nuclear island of a VVER nuclear power plant is equipped with two exhaust fans, and the regular switching of these fans is carried out once a month. The existing fan switching process is as follows: the frequency converter of the operating fan unloads → the operating fan is shut down → the standby fan is started → the frequency converter of the standby fan loads. The problems existing in the existing method are as follows: the entire switching process takes about 2 minutes. During these 2 minutes, the air supply volume in the annular space of the double-layer containment remains normal, while the exhaust air volume is much less than the normal value. Therefore, each time the fan is switched, the pressure in the annular space of the double-layer containment will increase, exceeding the regulation limit value (the regulation stipulates that the pressure limit value in the annular space of the double-layer containment is -100 Pa to -400 Pa), and there is a high risk of radioactive substance leakage. Therefore, during the fan switching period, it is urgent to reduce the duration of the pressure in the annular space of the double-layer containment exceeding the regulation limit value. Summary of the Invention

[0003] To overcome the problems existing in the related art, a method for switching fans of a non-purified exhaust air system in the nuclear island of a VVER nuclear power plant is provided. The method includes:

[0004] Step 1: Close the first valve V1, open the second valve V2, and start one of the fans of the exhaust air system B with purification, so as to convert the exhaust air of the nuclear service building F1 to be carried by the exhaust air system B with purification;

[0005] Step 2: Put into use the second filter device GB2 reserved for the exhaust air system B with purification;

[0006] Step 3: After closing the third valve V3, monitor that the valve V4 automatically opens, thereby converting the exhaust air of the nuclear safety building and the annular space of the double-layer containment F2 to be carried by the exhaust air system B with purification;

[0007] Step 4: Control the frequency converter of the operating fan in the non-purified exhaust air system C to unload. After the unloading is completed, the operating fan is shut down. For example, control the frequency converter of the fifth fan C1 in the non-purified exhaust air system C to unload and complete the shutdown;

[0008] Step 5: Start the standby fan in the non-purified exhaust air system C and complete the loading of the frequency converter of this standby fan. For example, start the sixth fan C2 in the non-purified exhaust air system C and complete the loading of the frequency converter of this fan;

[0009] Step 6: Close the fourth valve V4, monitor that the third valve V3 automatically opens, and convert the exhaust air of the nuclear safety building and the annular space of the double-layer containment F2 to be carried by the non-purified exhaust air system C;

[0010] Step 7: Close the ninth valve V9 and the tenth valve V10, and exit the second filtration device GB2;

[0011] Step 8: Stop one of the fans with the purification exhaust system B, and start the other fan to conduct the regular test of this fan. For example, stop the third fan B1 and start the fourth fan B2 to conduct the regular test of the fourth fan B2;

[0012] Step 9: Stop the other fan with the purification exhaust system B to complete the regular test of all the fans with the purification exhaust system B;

[0013] Step 10: Close the second valve V2, open the first valve V1, and convert the exhaust of the nuclear service building F1 to be loaded with the non-purification exhaust system C.

[0014] In a possible implementation manner, in Step 1, after starting one of the fans with the purification exhaust system B, conduct the regular test of this fan.

[0015] In a possible implementation manner, in Step 8, after starting the other fan with the purification exhaust system B, conduct the regular test of this fan.

[0016] In a possible implementation manner, the main ventilation system of the nuclear island of the VVER nuclear power plant further includes module K;

[0017] When module K is put into operation, after the third valve V3 is closed, the instrument control device of the main ventilation system is triggered by module K to send a signal to open the fourth valve V4, and thus trigger the instrument control system to control the opening of the fourth valve V4; when module K is put into operation, after the fourth valve V4 is closed, the instrument control system of the main ventilation system is triggered by module K to send a signal to open the third valve V3, and thus trigger the instrument control system to control the opening of the third valve V3.

[0018] In a possible implementation manner, in Step 3, put module K into operation, close the third valve V3, and then monitor the automatic opening of valve V4 through module K.

[0019] In a possible implementation manner, in Step 6, close the fourth valve V4, and monitor the automatic opening of the third valve V3 through module K.

[0020] In a possible implementation manner, Step 7 further includes: exiting module K.

[0021] In a possible implementation manner, the signals for opening the fourth valve V4 and the third valve V3 are 1-second pulse signals.

[0022] The beneficial effects of the present disclosure are as follows: By making full use of the configuration of the nuclear island main ventilation system of a VVER nuclear power plant, a new method for switching the fans of the purification exhaust system is adopted, which shortens the time when the exhaust air volume in the annular space between the double containment vessels is less than the normal value from 2 minutes to 10 seconds. This can prevent the pressure in the annular space between the double containment vessels from rising beyond the regulatory limit during fan switching (in actual operation using this method, the maximum pressure in the annular space between the double containment vessels rises to -139 Pa, which does not exceed the limit), thereby effectively preventing the release of radioactive substances into the environment in the event of a design basis accident. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of the nuclear island main ventilation system of a VVER nuclear power plant shown in an embodiment of the present disclosure.

[0024] Figure 2 is a schematic diagram of the K module shown in an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Unless otherwise defined, the technical and scientific terms used in the present disclosure have the same meanings as those commonly understood by those skilled in the technical field to which the present disclosure belongs; the terms used in the present disclosure are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure; the term "including" and any variations thereof in the text of the present disclosure are intended to cover non-exclusive inclusion. Obviously, the embodiments described in the present disclosure are only a part of the embodiments of the present disclosure, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without creative efforts belong to the scope of protection of the present disclosure.

[0027] Referring to "embodiments" in the present disclosure means that specific features, structures, or characteristics described in connection with the embodiments may be included in at least one embodiment of the present disclosure. The phrase appears at various positions in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0028] Figure 1 is a schematic diagram of the nuclear island main ventilation system of a VVER nuclear power plant shown in an embodiment of the present disclosure, as Figure 1As shown in the figure, the main ventilation system of the nuclear island of a VVER nuclear power plant includes the main air supply system A of the nuclear island, the exhaust air system B with purification of the nuclear island, the exhaust air system C without purification of the nuclear island, and the exhaust air system D of the reactor building. Among them, the main air supply system A of the nuclear island is equipped with a first fan A1 and a second fan A2, which are used to supply air to five major branches, namely, the nuclear service building F1, the nuclear safety building, the annular space F2 between the double-layer containment, the upper layer of the nuclear auxiliary building F3, the upper layer of the nuclear auxiliary building F4, and the reactor building F5, after purifying the outdoor air O; the exhaust air system D of the reactor building is used to exhaust air from the reactor building F5; the exhaust air system C without purification of the nuclear island is used to exhaust air from four branches, namely, the nuclear service building F1, the nuclear safety building, the annular space F2 between the double-layer containment, the upper layer of the nuclear auxiliary building F3, and the upper layer of the nuclear auxiliary building F4 during normal operation; the exhaust air system B with purification of the nuclear island is used to exhaust air from the branches with radiation pollution after radiation pollution occurs in four branches, namely, the nuclear service building F1, the nuclear safety building, the annular space F2 between the double-layer containment, the upper layer of the nuclear auxiliary building F3, and the upper layer of the nuclear auxiliary building F4.

[0029] The nuclear reactor of the VVER nuclear power plant is located in the reactor building F5. To improve safety performance, the reactor building F5 is equipped with a double-layer containment, namely an inner containment and an outer containment. There is an annular space with a width of 1.8 m between them. This annular space is connected to the nuclear safety building and together they form the nuclear safety building and the annular space F2 between the double-layer containment. In related technologies, the nuclear safety building and the annular space F2 between the double-layer containment maintain a preset negative pressure (-100 Pa to -400 Pa) to prevent the release of radioactive substances to the environment under accident conditions. Since other buildings are not directly connected to the reactor building F5, there are no pressure requirements for other buildings (nuclear service building F1, upper layer of the nuclear auxiliary building F3, upper layer of the nuclear auxiliary building F4).

[0030] During normal operation, one of the first fan A1 and the second fan A2 of the main air supply system A of the nuclear island is in use and the other is in standby, one of the fifth fan C1 and the sixth fan C2 of the exhaust air system C without purification of the nuclear island is in use and the other is in standby, and one of the seventh fan D1 and the eighth fan D2 of the exhaust air system D of the reactor building is in use and the other is in standby; after radiation pollution occurs in four branches, namely, the nuclear service building F1, the nuclear safety building, the annular space F2 between the double-layer containment, the upper layer of the nuclear auxiliary building F3, and the upper layer of the nuclear auxiliary building F4, one of the third fan B1 and the fourth fan B2 of the exhaust air system B with purification of the nuclear island is started, and the branches with radiation pollution are transferred from the exhaust air system C without purification of the nuclear island to the exhaust air system B with purification of the nuclear island for load-bearing.

[0031] The designed air supply volume of the main air supply system A is 102500 m 3 / h, the designed exhaust air volume of the exhaust air system C without purification is 100000 m 3 / h, the designed exhaust air volume of the exhaust air system B with purification is 50000 m 3 / h, and the designed exhaust air volume of the exhaust air system D of the reactor building is 2500 m3 / h; It should be noted that the designed exhaust air volume of the purification exhaust air system B is 50,000 m 3 / h means that each of the third fan B1 and the fourth fan B2 has the ability to exhaust air with a flow rate of 50,000 m 3 / h, but the designed air volume of the first filter device GB1 of the purification exhaust air system B is 25,000 m 3 / h. If radioactive contamination occurs in both branches, it is also necessary to put into use the second filter device GB2 (with the same designed air volume of 25,000 m 3 / h) reserved for the purification exhaust air system B. And in the design, the purification exhaust air system B only considers the situation of radioactive contamination in two branches. Since the probability of radioactive contamination occurring in 3 to 4 branches simultaneously is extremely low, it is not considered.

[0032] The first valve V1 is the exhaust valve between the nuclear service building F1 and the non-purification exhaust air system C. The third valve V3 is the exhaust valve between the nuclear safety building and the annular space of the double-layer containment F2 and the non-purification exhaust air system C. The fifth valve V5 is the exhaust valve between the upper layer of the nuclear auxiliary building F3 and the non-purification exhaust air system C. The seventh valve V7 is the exhaust valve between the upper layer of the nuclear auxiliary building F4 and the non-purification exhaust air system C. The second valve V2 is the exhaust valve between the nuclear service building F1 and the purification exhaust air system B. The fourth valve V4 is the exhaust valve between the nuclear safety building and the annular space of the double-layer containment F2 and the purification exhaust air system B. The sixth valve V6 is the exhaust valve between the upper layer of the nuclear auxiliary building F3 and the purification exhaust air system B. The eighth valve V8 is the exhaust valve between the upper layer of the nuclear auxiliary building F4 and the purification exhaust air system B. The ninth valve V9 and the tenth valve V10 are the inlet and exhaust valves of the second filter device GB2 of the purification exhaust air system B.

[0033] Both the first fan A1 and the second fan A2 are centrifugal fans without frequency converters. The third fan B1, the fourth fan B2, the fifth fan C1, the sixth fan C2, the seventh fan D1, and the eighth fan D2 are all centrifugal fans with frequency converters. The switching of the above fans all adopts the method of first stopping the operating fan and then starting the standby fan. This is because if the standby fan is directly started (without stopping the operating fan), the total flow rate after the two fans are in parallel will increase significantly, resulting in a sharp rise in the pipe network resistance curve, causing the working point of the fan to quickly shift to the left, entering the surge zone with too low flow rate and too high pressure, triggering violent vibration and noise, and even damaging the equipment. Stopping first and then starting can ensure the gradual release of the system pressure and avoid the sudden change of the working point due to the flow rate superposition during parallel connection, thus maintaining the system stability.

[0034] If the switching methods of the fifth fan C1 and the sixth fan C2 adopt the switching methods of related technologies, it will cause the space pressure in the nuclear safety building and the annular space F2 of the double-layer containment to exceed the limit. The reasons are as follows: First, to ensure the ventilation of other buildings, the main nuclear island air supply system A cannot be shut down, and there is no valve to cut off the air supply; Second, the switching between the fifth fan C1 and the sixth fan C2 can only adopt the method of shutting down the operating fan first and then starting the standby fan; Third, there is a process for the frequency converter of the fifth fan C1 and the sixth fan C2 to load and unload during the switching process, which takes about 2 minutes. The above three points together result in the exhaust air volume in the annular space F2 of the double-layer containment being much smaller than the normal value within 2 minutes, so the pressure rises beyond the limit.

[0035] Based on the existing problems, the fan switching method for the nuclear island of a VVER nuclear power plant without a purification exhaust air system provided by the present disclosure provides a new fan switching method without a purification exhaust air system C. The method includes the following steps.

[0036] Step 1: Close the first valve V1, open the second valve V2, start one of the fans with the purification exhaust air system B, and conduct regular tests on this fan, and convert the exhaust air of the nuclear service building F1 to be carried by the purification exhaust air system B. For example, start the third fan B1 and conduct regular tests on the third fan B1.

[0037] Step 2: Open the ninth valve V9 and the tenth valve V10, and put into use the second filter device GB2 reserved for the purification exhaust air system B.

[0038] Step 3: Put into use the module K. After closing the third valve V3, monitor the automatic opening of the valve V4 through the module K, thereby converting the exhaust air of the nuclear safety building and the annular space F2 of the double-layer containment to be carried by the purification exhaust air system B.

[0039] Step 4: Control the frequency converter of the operating fan without the purification exhaust air system C to unload. After the unloading is completed, stop the operating fan. For example, control the frequency converter of the fifth fan C1 without the purification exhaust air system C to unload and complete the shutdown.

[0040] Step 5: Start the standby fan without the purification exhaust air system C and complete the frequency converter loading of this standby fan. For example, start the sixth fan C2 without the purification exhaust air system C and complete the frequency converter loading of this fan.

[0041] Step 6: Close the fourth valve V4, monitor the automatic opening of the third valve V3 through the module K, and convert the exhaust air of the nuclear safety building and the annular space F2 of the double-layer containment to be carried by the purification exhaust air system C without the purification exhaust air system C.

[0042] Step 7: Exit the module K; close the ninth valve V9 and the tenth valve V10, and exit the second filter device GB2.

[0043] Step 8: Stop one of the fans of the purification exhaust system B and start the other fan to conduct the regular test of this fan, thereby completing the regular tests of all the fans of the purification exhaust system B. For example, stop the third fan B1 and start the fourth fan B2 to conduct the regular test of the fourth fan B2.

[0044] Step 9: Stop the other fan of the purification exhaust system B;

[0045] Step 10: Close the second valve V2 and open the first valve V1 to switch the exhaust of the nuclear service building F1 to be loaded without the purification exhaust system C.

[0046] In this way, before switching the in-service fan and the standby fan of the purification exhaust system C without the purification function, the exhaust of the nuclear safety building and the annular space F2 of the double-layer containment is switched to be loaded by the purification exhaust system B, so that the switching of the in-service fan and the standby fan of the purification exhaust system C without the purification function will not affect the pressure of the nuclear safety building and the annular space F2 of the double-layer containment.

[0047] Since the two fans (the third fan B1 and the fourth fan B2) of the purification exhaust system B are in the stopped state during normal operation, and the two fans of the purification exhaust system B are also fans with frequency converters, before switching the in-service fan and the standby fan of the purification exhaust system C without the purification function, it is necessary to start the two fans of the purification exhaust system B first, load the nuclear service building F1 without the requirement of plant pressure, and then perform subsequent operations after the frequency converters of the two fans of the purification exhaust system B are loaded. Since the two fans of the purification exhaust system B need to be regularly tested once a month, according to the method of the present disclosure, the regular tests of the fans of the purification exhaust system B can be completed by the way during the fan switching of the purification exhaust system C without the purification function. Further, the time cost and related human and material resources consumed by the regular tests are saved.

[0048] Since the designed air volume of the first filter device GB1 of the purification exhaust system B is 25000m 3 / h and it can only operate with one branch, and at this time the purification exhaust system B is already operating with the nuclear service building F1, in order to also connect the nuclear safety building and the annular space F2 of the double-layer containment to the purification exhaust system B, it is also necessary to put into use the standby second filter device GB2.

[0049] To avoid air leakage between the purification exhaust system B and the non-purification exhaust system C, a logic interlock is set in the system, that is, the third valve V3 and the fourth valve V4 cannot be opened simultaneously (in addition, the first valve V1 and the second valve V2, the fifth valve V5 and the sixth valve V6, and the seventh valve V7 and the eighth valve V8 are also interlocked by this). Therefore, when the exhaust of the nuclear safety plant and the annular space F2 of the double-layer containment is switched to the purification exhaust system B, the valve V4 can be opened only after the valve V3 is closed. The full stroke time of both the valve V3 and the valve V4 is 5 seconds. During the 10 seconds when the valve V3 is closed and the valve V4 is opened, although the exhaust volume of the annular space F2 of the double-layer containment is less than the normal exhaust volume, the actual operation data shows that the pressure in the annular space F2 of the double-layer containment will not exceed the regulatory limit value.

[0050] The switching scheme of the present disclosure requires that the valve V4 be opened immediately after the valve V3 is closed, and similarly, the valve V3 be opened immediately after the valve V4 is closed. If the two valves are closed simultaneously for too long, the pressure in the annular space of the double-layer containment will still rise and may exceed the normal limit value. Therefore, an instrument control logic module K is added (refer to Figure 2 , the module K can be, for example, a switch or a trigger). When the module K is put into operation, after the third valve V3 is closed, the instrument control device of the main ventilation system is triggered by the module K to send a signal (such as a 1-second pulse) to open the fourth valve V4, and thus the instrument control system is triggered to control the opening of the fourth valve V4; when the module K is put into operation, after the fourth valve V4 is closed, the instrument control system of the main ventilation system is triggered by the module K to send a signal to open the third valve V3, and thus the instrument control system is triggered to control the opening of the third valve V3. The module K is set so that when the third valve V3 and the fourth valve V4 are closed simultaneously, the logic can clearly determine which valve needs to be opened.

[0051] After adopting the technical scheme of the present disclosure, while switching the in-service fan and the standby fan of the non-purification exhaust system C, the monthly regular test of the fan of the purification exhaust system B is also carried out, and the time when the exhaust volume of the nuclear safety plant and the annular space F2 of the double-layer containment is significantly less than the normal value is only 10 seconds, which can ensure that the pressure in the nuclear safety plant and the annular space F2 of the double-layer containment meets the regulatory limit values (-100 Pa to -400 Pa).

[0052] The embodiments of the present disclosure have been described above. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, the practical application, or the improvement of the technology in the market, or to enable other ordinary technical personnel in the technical field to understand the embodiments disclosed herein.

Claims

1. A method for switching the fan of the purification exhaust system in the nuclear island of a VVER nuclear power plant, characterized in that, The method includes: Step 1: Close the first valve V1, open the second valve V2, start one of the fans of the purification exhaust system B, and convert the exhaust of the nuclear service building F1 to the load of the purification exhaust system B. Step 2: Put into use the second filter device GB2 reserved in the purification exhaust system B. Step 3: After closing the third valve V3, the monitoring valve V4 automatically opens, thereby converting the exhaust of the nuclear safety building and the annular space F2 of the double-layer containment to the load of the purification exhaust system B. Step 4: Control the frequency converter of the operating fan without the purification exhaust system C to unload. After the unloading is completed, the operating fan stops. For example, control the frequency converter of the fifth fan C1 without the purification exhaust system C to unload and complete the shutdown. Step 5: Start the standby fan without the purification exhaust system C and complete the frequency converter loading of this standby fan. For example, start the sixth fan C2 without the purification exhaust system C and complete the frequency converter loading of this fan. Step 6: Close the fourth valve V4, and monitor that the third valve V3 automatically opens, converting the exhaust of the nuclear safety building and the annular space F2 of the double-layer containment to the load without the purification exhaust system C. Step 7: Close the ninth valve V9 and the tenth valve V10, and withdraw the second filter device GB2. Step 8: Stop one of the fans of the purification exhaust system B and start another fan for the regular test of this fan. For example, stop the third fan B1 and start the fourth fan B2 for the regular test of the fourth fan B2. Step 9: Stop the other fan of the purification exhaust system B to complete the regular test of all the fans of the purification exhaust system B. Step 10: Close the second valve V2, open the first valve V1, and convert the exhaust of the nuclear service building F1 to the load without the purification exhaust system C.

2. The method according to claim 1, characterized in that, In Step 1, after starting one of the fans of the purification exhaust system B, conduct a regular test on this fan.

3. The method according to claim 2, characterized in that, In Step 8, after starting the other fan of the purification exhaust system B, conduct a regular test on this fan.

4. The method according to claim 1, characterized in that, The main ventilation system of the nuclear island of the VVER nuclear power plant also includes module K. When module K is put into use, after the third valve V3 is closed, the instrument control device of the main ventilation system is triggered by module K to send a signal to open the fourth valve V4, and thereby trigger the instrument control system to control the opening of the fourth valve V4; when module K is put into use, after the fourth valve V4 is closed, the instrument control system of the main ventilation system is triggered by module K to send a signal to open the third valve V3, and thereby trigger the instrument control system to control the opening of the third valve V3.

5. The method according to claim 4, characterized in that, In Step 3, put into use module K. After closing the third valve V3, monitor that the valve V4 automatically opens through module K.

6. The method according to claim 4, characterized in that, In Step 6, close the fourth valve V4, and monitor that the third valve V3 automatically opens through module K.

7. The method according to claim 4, characterized in that, Step 7 also includes: withdrawing module K.

8. The method according to claim 4, characterized in that The signals for opening the fourth valve V4 and the third valve V3 are 1-second pulse signals.

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