An offline boron saturation system for nuclear power units

Abstract

The present invention relates to the technical field of resin bed purification in nuclear power units, and specifically discloses an offline boron saturation system for nuclear power units, which is divided into a high-concentration boron preparation circuit, a resin bed boron saturation circuit, and a resin bed filling and recovery circuit. The bottom outlet of the low-position water tank is connected to the top inlet of the resin bed through a pipeline, and a boric acid delivery pump is provided on the pipeline; the bottom outlet of the resin bed is connected to the inlet of the high-position water tank through a pipeline; an overflow pipeline is connected to the side wall of the high-position water tank and communicated with the low-position water tank; by starting the boric acid delivery pump, the boron-containing water in the low-position water tank is injected into the resin bed to saturate the resin in the resin bed, and the water flowing out of the resin bed enters the high-position water tank and flows into the low-position water tank through the overflow pipeline. The offline boron saturation system of the present invention has many advantages such as simple operation, low industrial risk, and high benefits, can improve the inherent safety of the unit, reduce the management cost, and improve the reactivity management level of the unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of resin bed purification of nuclear power units, and particularly relates to an offline boron saturation system for nuclear power units. Background Art

[0002] The resin beds (mixed beds) of the following several systems of the current M310 nuclear power unit will directly affect the boron concentration in the primary loop or the spent fuel pool: RCV Chemical and Volume Control System RCV001 / 002DE (mixed bed), PTR Reactor Refueling Pool and Spent Fuel Pool Cooling and Treatment System PTR001DE (mixed bed), TEP Boron Recovery System TEP006DE (mixed bed). Since the above resin beds are all mixed beds, the anion resin will absorb boron present as borate ions, resulting in a decrease in the boron concentration in the system. Before the above resin beds are put into use, boron saturation operations need to be carried out first, and they can only be put into the system after being completely boron saturated.

[0003] RCV001 / 002DE and TEP006DE perform boron saturation operations by absorbing the primary loop coolant. The desalination bed without boron saturation is connected to the process system, so that the primary loop coolant flows through the desalination bed, and the boron in the primary loop coolant is absorbed by the desalination bed to achieve boron saturation. Since the boron concentration of the primary loop coolant will decrease significantly after passing through the desalination bed, in order to avoid the unplanned increase in power caused by the dilution of the primary loop, it is necessary to bypass the boron-removed primary loop coolant to the boron recovery system through the valve RCV030VP downstream of the desalination bed, and then put the desalination bed into the system after it is boron saturated. If an operation error occurs and the desalination bed without boron saturation is mistakenly put into use, it will cause the primary loop to be mistakenly diluted. Since the reactivity change caused by the change in the boron concentration of the desalination bed is very large, it will have a non-negligible impact on the safety of the reactor. Data analysis shows that from 1999 to 2005, there were more than a dozen human factor-related reactivity control events in a nuclear power base. Among them, there were eight events that caused accidental dilution or boronization of the primary loop during related operations on the REA system, or there were other potential risks. Five of these eight events occurred during the large-flow replenishment of the primary loop.

[0004] PTR001DE adopts the method of directly putting it into the system for boron saturation, that is, the replaced resin bed does not perform boron saturation operation, and after being rinsed, it is directly put into the system, and the boron-saturated water in the spent pool is used to saturate it with boron. This boron saturation method will directly lead to a decrease in the boron concentration in the spent pool. In the case of power operation, the total volume of the PTR system is 1561t (1326m in the spent pool 3 , and 235m in pipelines, etc. 3)Calculations are carried out. For example, when the desalination bed is saturated with boron, the boron concentration in the spent fuel pool will decrease by 24.1 ppm, which will lead to a reduction in the subcriticality of the spent fuel pool and may cause the boron concentration to violate the requirements of the technical specifications. The technical specifications require the boron concentration in the spent fuel pool to be between 2300 - 2500 ppm to ensure sufficient subcritical margin.

[0005] When the unit enters the end of its service life, the boron concentration in the primary circuit is too low to saturate the newly replaced resin bed with boron. If the newly replaced resin bed is TEP006DE, generally, two units with relatively high boron concentrations are selected for boron saturation; if the newly replaced resin bed is RCV001 / 002DE, the newly replaced resin bed can only be isolated by means of temporary operation isolation, and boron saturation operation is carried out after the boron saturation conditions are met.

[0006] In addition, due to the different functions of the resin beds, there are anion exchange resin beds, cation exchange resin beds, mixed bed resins, etc. for nuclear-grade resins in the nuclear island. The current method for resin replacement in the unit is to directly load the new resin into the desalination bed, which cannot verify the types of resins in the desalination bed, and there are also potential safety hazards of misplacing resins during the replacement process.

[0007] In summary, the current commonly used method of online boron saturation for desalination beds has relatively high safety hazards and risks of human error. Therefore, it is urgent to design an offline boron saturation system for nuclear power units. Summary of the Invention

[0008] The purpose of the present invention is to provide an offline boron saturation system for nuclear power units, which avoids the influence of the existing boron saturation method on the reactivity of the primary circuit and realizes the offline boron saturation of the resin bed.

[0009] The technical solution of the present invention is as follows:

[0010] An offline boron saturation system for nuclear power units is arranged in a non-production building and is divided into three loops: a high-concentration boron preparation loop, a resin bed boron saturation loop, and a resin bed filling and recovery loop;

[0011] The high-concentration boron preparation loop includes a stirrer, an electric heater, a concentrated boron tank, a manual drain valve, a low-level water tank, a circulation pump, a recirculation valve, and connected pipeline valves;

[0012] The bottom outlet of the concentrated boron tank is connected to the low-level water tank through pipeline A, and a manual drain valve is provided on pipeline A. The bottom outlet a of the low-level water tank is connected to the top inlet of the concentrated boron tank through pipeline B, and a circulation pump and a recirculation valve are successively provided on pipeline B;

[0013] The resin bed boron saturation loop includes a low-level water tank, a resin bed, a boric acid transfer pump, a high-level water tank, an overflow pipeline, an emergency drain valve, a resin trap, and connected pipeline valves;

[0014] The resin bed is filled with resin that needs to be saturated with boron;

[0015] The bottom outlet b of the low-level water tank is connected to the top inlet of the resin bed through pipeline C, and a boric acid transfer pump is provided on pipeline C; the bottom outlet of the resin bed is connected to the inlet of the high-level water tank through pipeline D; an overflow pipeline is connected to the side wall of the high-level water tank and is connected to the low-level water tank;

[0016] The resin bed filling and recovery loop includes a resin transfer funnel and a resin discharge valve;

[0017] The resin transfer funnel is connected to the top end of the resin bed through pipeline F and is used to load the resin that needs to be saturated with boron into the resin bed;

[0018] A recovery pipe is connected to the bottom end of the resin bed, and a resin discharge valve is provided on the recovery pipe for discharging the resin saturated with boron in the resin bed for recovery.

[0019] A resin trap is provided on pipeline D for trapping broken resin in the loop.

[0020] The bottom of the high-level water tank is connected to the low-level water tank through pipeline E, and an emergency drain valve is provided on pipeline E;

[0021] If the overflow pipeline malfunctions and causes the water level in the high-level water tank to be too high, the water in the high-level water tank can be discharged to the low-level water tank by opening the emergency drain valve.

[0022] The position of the high-level water tank is higher than that of the resin bed, and the gravity effect ensures that the resin bed is full of water when there is temporary resin in it.

[0023] A make-up water pipeline and a drain pipeline are provided on the low-level water tank. When the low-level water tank is being repaired, it can be flushed through the make-up water pipeline and drained through the drain pipeline.

[0024] A branch pipe is provided on pipeline F and is connected to a normal washing inlet valve for introducing flushing sample water into the resin bed.

[0025] During the operation of the resin bed boron saturation loop, the high-concentration boron preparation loop can operate independently to achieve the purpose of online adjusting the boron concentration in the low-level water tank.

[0026] High-concentration boric acid is prepared in the concentrated boron tank through an electric heater and a stirrer;

[0027] The prepared boric acid is discharged to the low-level water tank by opening the manual discharge valve;

[0028] By continuous preparation, the boron concentration in the low-level water tank is increased until it meets the target boron concentration;

[0029] Circulate the high-concentration boron preparation loop through a circulating pump and a recirculation valve to ensure uniform and accurate boron concentration and prevent boron crystallization.

[0030] By starting the boric acid transfer pump, inject the boron-containing water in the low-level water tank into the resin bed to saturate the resin in the resin bed. The water flowing out of the resin bed enters the high-level water tank and flows into the low-level water tank through the overflow pipeline.

[0031] If an abnormality occurs in the overflow pipeline, causing the water level in the high-level water tank to be too high, the overflow of the high-level water tank can be avoided by stopping the boric acid transfer pump.

[0032] After the boron concentration sampling at the upstream and downstream of the resin bed is qualified, the flushing and draining operations of the resin bed can be carried out.

[0033] During the boron saturation process, the boron concentration in the loop can be gradually adjusted to be consistent with the boron concentration in the primary loop of the unit where the resin bed is about to be replaced, reducing the amount of boric acid absorption and release during the ion balance process after resin replacement, and minimizing the disturbance to the unit after resin replacement to the greatest extent.

[0034] The remarkable effects of the present invention are as follows:

[0035] The offline boron saturation system of the present invention has many advantages such as simple operation, low industrial risk, and high benefits. It can fundamentally solve the potential safety hazards existing in the demineralizer bed (mixed bed) of M310 nuclear power units under the current management mode, transform the risk management related to the demineralizer bed (mixed bed) from human defense to technical defense, improve the inherent safety of the unit, reduce the management cost, and improve the unit reactivity management level.

[0036] (1) Improved safety: The boron saturation operation of the resin bed is carried out offline, which can effectively reduce the risk of incorrect input of the demineralizer bed. With offline boron saturation, the most serious reactivity consequence is the risk of introducing clear water with the volume of the demineralizer bed (which will be less than the volume of the demineralizer bed after removing the resin volume) into the primary loop, and the situation of continuously diluting the primary loop will not occur, and the event of incorrect input of the demineralizer bed can be completely avoided.

[0037] (2) Reduced risk of human error. Operations such as interruption of cooling in the spent fuel pool, replenishment of boron-containing water in the spent fuel pool, makeup water to the refueling water tank, water filling and exhaust and flushing of the demineralizer bed are all high-risk operations that are not often carried out. If the offline boron saturation method is adopted, the risk of reactivity events caused by large-flow replenishment in the primary loop can be effectively avoided.

[0038] (3) Reduce radioactive waste and relieve the pressure of reprocessing. 1) There will be broken resin in the new resin. A special resin catcher is provided in the off-line boron saturation system, which can reduce the introduction of broken resin into the process system, reduce the replacement frequency of filters in the primary circuit, and reduce the generation of radioactive waste; 2) By adopting the off-line boron saturation method, only one flushing is required after the demineralized bed is installed, which can reduce the generation of radioactive waste liquid; 3) The unpacking work of the new resin will be carried out in the non-radioactive workshop, which can minimize the generation of packaging waste.

[0039] (4) Ensure the correct resin type. The type of the resin bed can be verified during the off-line boron saturation process to ensure that the type of the newly replaced resin bed is correct.

[0040] (5) Improve the availability of the resin bed. The new resin has been boron-saturated off-line. Only water filling and flushing operations are required for the newly replaced resin, and it can be used at any time after replacement, effectively improving the availability of the resin bed.

[0041] (6) Reduce the radiation dose of personnel. The environmental dose in the area where the boron saturation operation of the resin bed is carried out online is generally high. If the off-line boron saturation method of the resin is adopted, the operation time of personnel can be effectively reduced, so as to achieve the purpose of reducing the radiation dose of personnel.

[0042] (7) High economy. The off-line boron saturation system can be shared by multiple units. For power plants with group reactor management, only one set of resin bed off-line boron saturation system needs to be set up for the whole plant, which has high economy. Description of the Drawings

[0043] Figure 1 It is a schematic diagram of the off-line boron saturation system.

[0044] In the figure: 1. Agitator; 2. Electric heater; 3. Concentrated boron tank; 4. Manual drain valve; 5. Low-level water tank; 6. Circulation pump; 7. Recirculation valve; 8. Resin bed; 9. Boric acid transfer pump; 10. High-level water tank; 11. Overflow pipeline; 12. Emergency drain valve; 13. Resin catcher; 14. Resin transfer funnel; 15. Normal washing inlet valve; 16. Resin discharge valve. Detailed Embodiments

[0045] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0046] As Figure 1 shown, an off-line boron saturation system for a nuclear power unit is arranged in a non-production workshop and is divided into three loops: a high-concentration boron preparation loop, a resin bed boron saturation loop, and a resin bed filling and recovery loop.

[0047] The described high-concentration boron preparation loop is used to prepare high-concentration boric acid, and includes a stirrer 1, an electric heater 2, a concentrated boron tank 3, a manual drain valve 4, a low-level water tank 5, a circulation pump 6, a recirculation valve 7, and connected pipeline valves.

[0048] The bottom outlet of the concentrated boron tank 3 is connected to the low-level water tank 5 through pipeline A, and a manual drain valve 4 is provided on pipeline A. The bottom outlet a of the low-level water tank 5 is connected to the top inlet of the concentrated boron tank 3 through pipeline B, and a circulation pump 6 and a recirculation valve 7 are successively provided on pipeline B. The stirrer 1 is used to stir the boric acid in the concentrated boron tank 3, and the electric heater 2 is used to heat the boric acid in the concentrated boron tank 3.

[0049] High-concentration boric acid is prepared in the concentrated boron tank 3 through the electric heater 2 and the stirrer 1, and the target boron concentration is 7000 ppm (the boron concentration of the configured boric acid can be adjusted according to actual needs). The prepared boric acid is discharged into the low-level water tank 5 by opening the manual drain valve 4. By continuous preparation, the boron concentration in the low-level water tank 5 is increased until it meets the target boron concentration. The high-concentration boron preparation loop is circulated through the circulation pump 6 and the recirculation valve 7 to ensure uniform and accurate boron concentration and prevent boron crystallization.

[0050] During the operation of the resin bed boron saturation loop, the high-concentration boron preparation loop can operate independently to achieve the purpose of online adjusting the boron concentration in the low-level water tank 5.

[0051] The described resin bed boron saturation loop is used for resin boron saturation, and includes a low-level water tank 5, a resin bed 8, a boric acid transfer pump 9, a high-level water tank 10, an overflow pipeline 11, an emergency drain valve 12, a resin trap 13, and connected pipeline valves.

[0052] The resin bed 8 is filled with resin that needs to be boron-saturated.

[0053] The bottom outlet b of the low-level water tank 5 is connected to the top inlet of the resin bed 8 through pipeline C, and a boric acid transfer pump 9 is provided on pipeline C; the bottom outlet of the resin bed 8 is connected to the inlet of the high-level water tank 10 through pipeline D, and a resin trap 13 is provided on pipeline D; the bottom of the high-level water tank 10 is connected to the low-level water tank 5 through pipeline E, and an emergency drain valve 12 is provided on pipeline E; an overflow pipeline 11 is connected to the side wall of the high-level water tank 10 and is connected to the low-level water tank 5.

[0054] The position of the high-level water tank 10 is higher than that of the resin bed 8, and the gravity effect is used to ensure that the resin bed 8 is full of water when there is temporary resin in it.

[0055] A makeup water pipeline and a drain pipeline are also connected to the low-level water tank 5. When the low-level water tank 5 is under maintenance, it can be flushed through the makeup water pipeline and drained through the drain pipeline.

[0056] The resin trap 13 described above is used to trap broken resin in the loop.

[0057] By starting the boric acid transfer pump 9, the boron-containing water in the low-level water tank 5 is injected into the resin bed 8 to saturate the resin in the resin bed 8 with boron. The water flowing out of the resin bed 8 enters the high-level water tank 10 and flows into the low-level water tank 5 through the overflow pipeline 11. If the overflow pipeline 11 malfunctions and causes the water level in the high-level water tank 10 to be too high, the water in the high-level water tank 10 can be discharged into the low-level water tank 5 by opening the emergency drain valve 12 or the boric acid transfer pump 9 can be stopped to avoid overflow of the high-level water tank 10. After the boron concentrations sampled upstream and downstream of the resin bed 8 are qualified (refer to the online boron saturation qualification standard), the flushing and draining operations of the resin bed 8 can be carried out.

[0058] During the boron saturation process, the boron concentration in the loop can be gradually adjusted to be consistent with the boron concentration in the primary loop of the unit for which the resin bed is about to be replaced, reducing the amount of boric acid absorption and release during the ion balance process after resin replacement and minimizing the disturbance to the unit after resin replacement to the greatest extent.

[0059] The resin bed filling and recovery loop described above includes a resin transfer funnel 14, a normal flushing water inlet valve 15, and a resin discharge valve 16, which can achieve the filling, flushing, draining, and recovery of the resin bed 8. The boron-saturated resin is finally transported to the nuclear island in small barrels after being packaged.

[0060] The resin transfer funnel 14 described above is connected to the top of the resin bed 8 through a pipeline F and is used to load the resin that needs to be saturated with boron into the resin bed 8. A branch pipe is provided on the pipeline F to connect the normal flushing water inlet valve 15, which is used to introduce flushing sample water into the resin bed 8. A recovery pipe is connected to the bottom end of the resin bed 8, and a resin discharge valve 16 is provided on the recovery pipe, which is used to discharge and recover the boron-saturated resin in the resin bed 8.

[0061] The above shows and describes the basic principles, main features, and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0062] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An offline boron saturation system for a nuclear power unit, characterized in that: It is set in a non-production workshop and is divided into three loops: a high-concentration boron preparation loop, a resin bed boron saturation loop, and a resin bed filling and recovery loop; The high-concentration boron preparation loop includes a stirrer (1), an electric heater (2), a concentrated boron tank (3), a manual drain valve (4), a low-level water tank (5), a circulation pump (6), a recirculation valve (7), and connected pipeline valves; The bottom outlet of the concentrated boron tank (3) is connected to the low-level water tank (5) through pipeline A, and a manual drain valve (4) is provided on pipeline A. The bottom outlet a of the low-level water tank (5) is connected to the top inlet of the concentrated boron tank (3) through pipeline B, and a circulation pump (6) and a recirculation valve (7) are successively provided on pipeline B; The resin bed boron saturation loop includes a low-level water tank (5), a resin bed (8), a boric acid transfer pump (9), a high-level water tank (10), an overflow pipeline (11), an emergency drain valve (12), a resin trap (13), and connected pipeline valves; The resin that needs to be boron-saturated is installed in the resin bed (8); The bottom outlet b of the low-level water tank (5) is connected to the top inlet of the resin bed (8) through pipeline C, and a boric acid transfer pump (9) is provided on pipeline C; the bottom outlet of the resin bed (8) is connected to the inlet of the high-level water tank (10) through pipeline D; an overflow pipeline (11) is connected to the side wall of the high-level water tank (10) and is connected to the low-level water tank (5); The resin bed filling and recovery loop includes a resin transfer funnel (14) and a resin discharge valve (16); The resin transfer funnel (14) is connected to the top end of the resin bed (8) through pipeline F and is used to load the resin that needs to be boron-saturated into the resin bed (8); A recovery pipe is connected to the bottom end of the resin bed (8), and a resin discharge valve (16) is provided on the recovery pipe and is used to discharge and recover the boron-saturated resin in the resin bed (8).

2. An offline boron saturation system for a nuclear power unit as described in claim 1, characterized in that: A resin trap (13) is provided on pipeline D and is used to capture broken resin in the loop.

3. An offline boron saturation system for a nuclear power unit as described in claim 1, characterized in that: The bottom of the high-level water tank (10) is connected to the low-level water tank (5) through pipeline E, and an emergency drain valve (12) is provided on pipeline E; If an abnormality occurs in the overflow pipeline (11) resulting in too high a water level in the high-level water tank (10), the water in the high-level water tank (10) can be discharged to the low-level water tank (5) by opening the emergency drain valve (12).

4. An offline boron saturation system for a nuclear power unit as described in claim 1, characterized in that: The position of the high-level water tank (10) is higher than the position of the resin bed (8), and the gravity effect is used to ensure that the resin bed (8) can maintain a full water state when there is temporarily stored resin in it.

5. An offline boron saturation system for a nuclear power unit as described in claim 1, characterized in that: A makeup water pipeline and a drain pipeline are provided on the low-level water tank (5), and it can be flushed through the makeup water pipeline and drained through the drain pipeline during the maintenance of the low-level water tank (5).

6. A nuclear power unit offline boron saturation system as claimed in claim 1, characterized in that: A branch pipe is provided on the pipeline F to connect to the positive flushing inlet valve (15) for introducing flushing sample water into the resin bed (8).

7. A nuclear power unit offline boron saturation system as claimed in claim 1, characterized in that: During the operation of the resin bed boron saturation loop, the high-concentration boron preparation loop can operate independently to achieve the purpose of online adjusting the boron concentration in the low-level water tank (5).

8. A nuclear power unit offline boron saturation system as claimed in claim 1, characterized in that: High-concentration boric acid is prepared in the concentrated boron tank (3) through the electric heater (2) and the stirrer (1); The prepared boric acid is discharged into the low-level water tank (5) by opening the manual discharge valve (4); By continuously preparing, the boron concentration in the low-level water tank (5) is increased until it meets the target boron concentration; The high-concentration boron preparation loop is circulated through the circulation pump (6) and the recirculation valve (7) to ensure uniform and accurate boron concentration and prevent boron crystallization.

9. A nuclear power unit offline boron saturation system as claimed in claim 1, characterized in that: By opening the boric acid transfer pump (9), the boron-containing water in the low-level water tank (5) is injected into the resin bed (8) to saturate the resin in the resin bed (8). The water flowing out of the resin bed (8) enters the high-level water tank (10) and flows into the low-level water tank (5) through the overflow pipeline (11); If an abnormality occurs in the overflow pipeline (11) resulting in too high a water level in the high-level water tank (10), the overflow of the high-level water tank (10) can be avoided by stopping the boric acid transfer pump (9); After the boron concentration sampling of the upstream and downstream of the resin bed (8) is qualified, the flushing and draining operations of the resin bed (8) can be carried out.

10. A nuclear power unit offline boron saturation system as claimed in claim 9, characterized in that: During the boron saturation process, the boron concentration in the loop can be gradually adjusted to be consistent with the primary loop boron concentration of the unit whose resin bed is about to be replaced, reducing the amount of boric acid absorption and release during the ion balance process after resin replacement, and minimizing the disturbance to the unit after resin replacement to the greatest extent.

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