Measurement and control methods for oxidation operation during nuclear power plant overhaul

Abstract

This disclosure belongs to the field of nuclear power technology, specifically to a method for measuring and controlling oxidation operations during nuclear power plant overhauls. This disclosure provides a complete chemical control and analysis method for nuclear power plant overhaul oxidation operations, encompassing preparation for overhaul oxidation operations, dosing, control and measurement of the oxidation operation platform, and purification. This method clarifies the parameters and control and analysis methods at each stage, improving oxidation operation performance and measurement capabilities. Furthermore, this method is simple to operate, significantly reduces costs, and is highly safe, making it suitable for widespread adoption.

Description

Technical Field

[0001] The present disclosure belongs to the field of nuclear power technology, and in particular relates to a method for measuring and controlling oxidation operation during overhaul of a nuclear power plant. Background Art

[0002] During the operation of pressurized water reactor (PWR) nuclear power plants, corrosion products generated by corrosion or wear on the surfaces of primary circuit piping and other equipment often form surface oxide films. These products can also dissolve or suspend in the primary circuit water, traveling with the flow of the primary coolant and depositing on metal surfaces, particularly in corners and narrow gaps between equipment and piping. These products are highly susceptible to generating corrosion activation products under neutron irradiation. During nuclear power plant unit shutdown, the reactor coolant system transitions from a slightly alkaline, reducing environment to an acidic, oxidizing one due to factors such as reactor cooling and pressure reduction, a rapid increase in boron concentration, a decrease in dissolved hydrogen, and the influx of air. This significantly increases the solubility of corrosion products in the coolant. If not effectively removed and controlled, this can significantly increase the dose levels of maintenance workers. Long-term accumulation of corrosion products can also cause localized blockages and reduced heat transfer efficiency. Therefore, during the specific cooling and pressure reduction phases of the unit, performing an oxidation process in the primary circuit not only removes released oxidation activation products but also forms an oxide film on the inner surfaces of the piping, further slowing or preventing the formation of activation products. However, in the current oxidation operation process, there are problems such as unsatisfactory oxidation operation effect; the measurement method of oxidation operation radionuclide is cumbersome and low in accuracy, and there is no method control and detection method for the oxidation operation process. Summary of the Invention

[0003] In order to overcome the problems existing in the related technologies, a measurement and control method for oxidation operation during overhaul of a nuclear power plant is provided.

[0004] According to one aspect of an embodiment of the present disclosure, a method for measuring and controlling oxidation operation during overhaul of a nuclear power plant is provided, the method comprising:

[0005] Step 101, pre-overhaul control: Before the overhaul, the first demineralizer is put into operation to purify the first refueling water tank. Under the action of the cooling circulation pump, the refueling water tank purification circuit flows through the first filter, the first demineralizer, and the second filter at a preset flow rate for a preset time period.

[0006] Step 102, control of the second desalter operation during the overhaul down phase: The second desalter is put into operation after the reactor reaches subcriticality for a preset time. During the overhaul down phase, the second line is used as the downflow loop. The second line is a downflow loop consisting of the reactor pressure vessel, the reactor coolant pump, the third filter, the second desalter, and the fourth filter connected in series in this order.

[0007] Step 103, preparation and implementation of oxidation operation in the down-stream phase of overhaul: At the start of the overhaul oxidation operation, a preset volume and concentration of hydrogen peroxide solution is injected into the chemical mixing and dosing tank at one time, and when the hydrogen peroxide solution reaches a preset temperature, the hydrogen peroxide solution is injected into the primary circuit. Thereafter, samples are taken at 10, 20, 30, 45, 60 minutes, 2 hours, 3 hours, 4 hours, and 6 hours respectively to observe the change trends of Co-58, Co-60, Sb-122, Sb-124, Ag-110m, I-131, Xe-133, and total γ;

[0008] Step 104, measurement of oxidation operation during the down-stream phase of the overhaul: Measure and obtain a gamma nuclide spectrum of a preset volume standard mixed radioactive source, so that the area counts of each major peak reach a preset threshold, input the energy peak on the gamma nuclide spectrum into the activity, calibration date, and uncertainty information of the corresponding nuclide on the standard source certificate, fit the efficiency curve, and complete the efficiency calibration;

[0009] Step 105, operation control of the oxidation operation main pump during the overhaul down stage: the operation purification time of the overhaul oxidation operation main pump is controlled to be 18 hours.

[0010] In one possible implementation, the resin volume of the first desalter 4 is 1.5m 3 The maximum working pressure is 0.05MPa.g, the maximum working temperature is 60℃, and the maximum working flow rate is 65m 3 / h, at 60m 3 / h flow rate for purification.

[0011] In one possible implementation, before the overhaul unit is decoupled, the 0.1 μm filter element of the third filter is replaced with a 0.45 μm filter element, and the replacement pressure difference is adjusted to 0.25 MPa.

[0012] In a possible implementation, during the actual measurement process, 1 g of the main system sample is taken during the oxidation operation and diluted to 20 g with high-purity water for measurement, and the measurement time is 100 seconds.

[0013] In one possible implementation, before measurement, a high-purity germanium multi-channel gamma spectrometer and the aforementioned source of a mixed standard solution with a preset volume are used to measure radioactive nuclides, and a nuclide library dedicated to oxidation operation is established.

[0014] The beneficial effects of the present disclosure are:

[0015] The present disclosure provides a complete chemical control and analysis method for overhaul oxidation operation through preparation for overhaul oxidation operation, dosing, control and measurement of the oxidation operation platform, and purification, providing a complete solution for the current mainstream oxidation operation process of pressurized water reactor nuclear power plants.

[0016] The present disclosure implements a strategy for purifying the refueling water tank and replacing the third filter before overhaul, which not only reduces the source of radiation dose during oxidation operation, but also avoids the problem of frequent clogging of the third filter during water filling in the water tank, which affects the overhaul period and increases the workload of overhaul personnel.

[0017] The present invention purifies the main system by controlling the operation of the second desalter in the down-flow phase of overhaul, replacing the traditional third desalter or fourth desalter through the chemical and volume control system downflow loop, with excellent results, while greatly reducing the operating costs and the additional re-commissioning work of the fifth desalter for removing the lithium bed.

[0018] The present disclosure obtains a testing method with good peak shape and stable and reliable results by setting the testing conditions, controlling the sample sampling amount and selecting the measurement activity time.

[0019] In summary, the present disclosure provides a complete set of chemical control and analysis methods for nuclear power plant overhaul oxidation operation through preparation for overhaul oxidation operation, dosing, control and measurement of the oxidation operation platform, and purification. It clarifies the parameters and control and analysis methods of each stage, improves the oxidation operation effect and measurement level, and at the same time, the present disclosure is simple to operate, significantly reduces costs, and is highly safe, and can be widely promoted and used. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of a method for measuring and controlling oxidation operation during overhaul of a nuclear power plant, shown in an embodiment of the present disclosure.

[0021] Figure 2 A schematic diagram of the refueling tank purification system in one example.

[0022] Figure 3 A schematic diagram of an overhaul oxidation operation purification system in an example.

[0023] In the picture:

[0024] 1. Refueling water tank; 2. Cooling circulation pump; 3. Second filter; 4. First desalter;

[0025] 5. First filter; 6. Heat exchanger; 7. Reactor pressure vessel; 8. Reactor coolant pump;

[0026] 9. The third filter; 10. The isolation valve before the second desalter; 11. The isolation valve before the third desalter;

[0027] 12. Isolation valve before the fourth desalter; 13. Second desalter; 14. Third desalter;

[0028] 15. Fourth desalter; 16. Isolation valve before fifth desalter; 17. Fifth desalter;

[0029] 18. The fourth filter. DETAILED DESCRIPTION

[0030] The present disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Unless otherwise defined, the technical and scientific terms used in this disclosure have the same meanings as those generally understood by those skilled in the art to which this disclosure belongs; the terms used in this disclosure are only for the purpose of describing specific embodiments and are not intended to limit this disclosure; the term "including" and any variations thereof in this disclosure are intended to cover non-exclusive inclusions. Obviously, the embodiments described in this disclosure are only some of the embodiments of this disclosure, not all of them. Based on the embodiments in this disclosure, all other embodiments obtained by those of ordinary skill in the art without making any creative work are within the scope of protection of this disclosure.

[0032] References to "embodiments" in this disclosure mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the disclosure. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] Figure 1 This is a flow chart of a method for measuring and controlling oxidation operation during overhaul of a nuclear power plant according to an embodiment of the present disclosure. Figure 2 This is a schematic diagram of the refueling water tank purification system in an example. Figure 3 This is a schematic diagram of an overhaul oxidation operation purification system in an example, see Figure 1 and Figure 2 The refueling water tank 1 purification system includes a refueling water tank 1 (equipment number PTR001BA), a cooling circulation pump 2, a second filter 3 (equipment number PTR002FI, which is a resin retention filter downstream of the reactor refueling water pool and spent fuel pool cooling and treatment system 001DE), a first desalinator 4 (equipment number PTR001DE, which is a desalinator of the reactor refueling water pool and spent fuel pool cooling and treatment system 001DE), a first filter 5 (equipment number PTR001FI, which is an upstream filter of the reactor refueling water pool and spent fuel pool cooling and treatment system 001DE) and a heat exchanger 6; Figure 2 As shown, the cooling circulation pump 2, the first filter 5, the first desalter 4 and the second filter 3 are connected in series to form a refueling water tank 1 purification circuit, which is used to purify the medium output from the refueling water tank 1. The medium purified by the refueling water tank 1 purification circuit flows back to the refueling water tank 1 through the heat exchanger 6.

[0034] See also Figure 1 and Figure 3 The overhaul oxidation operation purification system includes: reactor pressure vessel 7, reactor coolant pump 8, third filter 9 (equipment number RCV001FI, chemical and volume control system downstream filter), fourth filter 18 (equipment number RCV002FI, chemical and volume control system resin retention filter), second desalter 13 (equipment number TEP006DE, boron recovery system mixed bed desalter), third desalter 14 (equipment number RCV001DE, chemical and volume control system No. 1 mixed bed desalter), fourth desalter 15 (equipment number RCV002DE, chemical and volume control system No. 2 mixed bed desalter), and fifth desalter 17 (equipment number RCV003DE, chemical and volume control system cation bed desalter).

[0035] See also Figures 1 to 3 The measurement and control method for the overhaul oxidation operation of a nuclear power plant disclosed herein includes:

[0036] Step 101, control before overhaul. Before overhaul, the first desalter 4 is put into operation to purify the first refueling water tank 1. Under the action of the cooling circulation pump 2, the refueling water tank 1 purification circuit is cooled to a preset flow rate (for example, 60m 3 / h), respectively, through the first filter 5, the first desalter 4, and the second filter 3. In an application example, after the purification preset time (the preset time can be, for example, 168 hours), the total gamma content measured after purification is 0.6MBq / m 3 , turbidity <0.11NTU is far below the target value (the target value is total γ content <15MBq / m 3 , turbidity <1.0 NTU), effectively reducing the activated corrosion products and particulate impurities in the water of the refueling water tank 1, thereby reducing the impurity content that may be introduced into the main system, reducing the deposition of corrosion products in the core, and reducing the source term. In a possible implementation, the resin volume of the first desalter 4 can be 1.5m 3 The maximum working pressure can be 0.05MPa.g, the maximum working temperature can be 60℃, and the maximum working flow can be 65m 3 / h, daily 60m 3 / h flow rate for purification, wherein the exchange capacity of anion exchange resin (strong base) and cation exchange resin (strong acid) is roughly equal. The first filter 5 and the second filter 3 are filters with a filtration capacity of 0.45μm.

[0037] Step 102: Operation control of the second desalter 13 during the downtime of overhaul. Figure 1 and Figure 3The second desalter 13 is put into operation 3 hours after the reactor reaches subcriticality (nuclear power is 0). During the downtime of the overhaul, the second line is used as the downflow circuit. The second line is a circuit composed of the reactor pressure vessel 7, the reactor coolant pump 8, the third filter 9, the second desalter 13 (a second desalter front isolation valve 10 can be set at the water inlet of the second desalter 13), and the fourth filter 18 connected in series in this order, replacing the first line used as the downflow circuit in the related art. Figure 3 The first line can be a loop composed of the reactor pressure vessel 7, the reactor coolant pump 8, the third filter 9, the third desalter 14 (a third desalter pre-isolating valve 11 can be provided at the water inlet of the third desalter 14), and the fourth filter 18 connected in series in this order, or the first line can be a downstream loop composed of the reactor pressure vessel 7, the reactor coolant pump 8, the third filter 9, the fourth desalter 15 (a fourth desalter pre-isolating valve 12 can be provided at the water inlet of the fourth desalter 15), and the fourth filter 18 connected in series in this order. Figure 3 As shown, the water inlet and the water outlet of the fifth demineralizer 17 are respectively connected to the main line to form a loop, and a fifth demineralizer front isolation valve 16 can be provided at the water inlet of the fifth demineralizer 17 .

[0038] Calculations of purification efficiency show that the purification efficiency of the second demineralizer 13 remains consistently greater than 95% throughout the entire process, significantly meeting the regulatory requirement of greater than 80%. Furthermore, since the second demineralizer 13 utilizes a hydroxyl-type cation-cation mixed resin, while the third demineralizer 14 or fourth demineralizer 15 utilizes a lithium-hydroxyl-type resin (currently replaced every two fuel cycles, at a cost of approximately 1 million yuan per cycle), the replacement cost of the second demineralizer 13 is only one-tenth of the latter, significantly saving costs. Furthermore, the second demineralizer 13 functions as a lithium removal bed, eliminating the need for a separate fifth demineralizer 17 for lithium removal. After commissioning, the measured lithium concentration was less than 0.02 mg / kg, demonstrating superior lithium removal performance compared to the fifth demineralizer 17, further satisfying the requirement for a minimal lithium concentration prior to oxidation operation (target value: lithium concentration less than 0.3 mg / kg).

[0039] See also Figure 3During the normal power period of the third filter 9, a 0.1μm filter element is used. Before the overhaul unit is decoupled, the 0.1μm filter element of the third filter 9 is replaced with a 0.45μm filter element, and the replacement pressure difference is adjusted to 0.25Mpa. During the upward phase of the unit, after the loading is completed and the refueling pool is drained, the filter element of the third filter 9 is replaced with a 0.1μm filter element. This can not only ensure that as many impurities as possible are filtered out, but also avoid frequent filter clogging and replacement caused by excessive impurity products during the overhaul oxidation operation, which delays the overhaul period. Using this method, during the entire oxidation operation phase of a certain overhaul, the third filter 9 did not become clogged and need to be replaced. During the entire oxidation operation phase of another overhaul, the filter element of the third filter 9 was replaced three times because the above-mentioned filter element replacement was not performed on the third filter 9. In comparison, the above-mentioned filter element replacement effectively improves the purification effect of corrosion products in particulate form.

[0040] Step 103: Preparation and implementation of oxidation operation during the down-going phase of overhaul.

[0041] At the start of the overhaul oxidation operation, a preset volume and preset concentration (e.g. 18L, 30% concentration) of hydrogen peroxide solution is injected into the chemical mixing and dosing tank at one time. When the hydrogen peroxide solution reaches a preset temperature (e.g. 80°C), the hydrogen peroxide solution is injected into the primary circuit, and the chemical and volume control system downstream flow rate is adjusted to the maximum (e.g. 27m 3 / h), the purification platform is maintained for 8h. After the hydrogen peroxide solution is injected into the main system, samples are taken at 10, 20, 30, 45, 60 minutes, 2h, 3h, 4h, and 6h to observe the change trends of Co-58, Co-60, Sb-122, Sb-124, Ag-110m, I-131, Xe-133 and total γ. Using the above-mentioned dosing method, when the oxidation operation reaches the peak ( 58 Co peak), the hydrogen peroxide concentration was measured at 5ppm, and the dissolved oxygen was >5ppm, which fully met the requirement of oxygen concentration >1ppm, proving that the main circuit was fully oxidized.

[0042] Step 104: Measurement of oxidation operation during the down-stream phase of the overhaul. The measurement phase may use a mixed standard solution source of 20 g / bottle as shown in Table 1.

[0043] Table 1

[0044]

[0045] Before measurement, a high-purity germanium multi-channel gamma spectrometer (model may be, for example, GEM30P4-76) and a mixed standard solution source of the above specifications are used to measure radioactive nuclides. The following nuclide library for oxidation operation was established: Kr-85M, Kr-87, Kr-88, Xe-133M, Xe-133, Xe-135, Xe-138, Ar-41, Na-24, I-131, I-132, I-133, I-134, I-135, Cs-134, Cs-137, Cs-138, Co-58, Co-60, Cr-51, Mn-54, Ag-110M, Sb-122, Sb-124, Sb-125, Te-131M, Zr-95, Nb-95, Mo-99, Be-7, Fe-59, Ba-140, Ru-103, La-140, Np-239.

[0046] Place the sample to be tested in the sample slot of the acrylic sample holder on the probe or directly in the center of the probe;

[0047] Measure and obtain the γ-nuclides spectrum of 20ml of standard mixed radioactive source, so that the counts of each major peak area reach the preset threshold (recommended 10,000 counts or more), ensure sufficient statistical accuracy, and complete energy calibration;

[0048] The energy peak on the γ nuclide spectrum is input into the activity, calibration date, uncertainty and other information of the corresponding nuclide on the standard source certificate, and the efficiency curve is fitted to complete the efficiency calibration.

[0049] Sample measurement: In actual measurements, if the sample has a low radionuclide content, a longer measurement time is required. However, if the sample has a high radionuclide content, dead time can easily occur, leading to large measurement errors. This method uses a 1g sample from the main system diluted to 20g with high-purity water during oxidation operation, with a live time of 100 seconds, to obtain good peak results with stable and reliable results.

[0050] Step 105 , controlling the operation of the main pump for oxidation operation during the overhaul down phase.

[0051] The purification time of the main pump in overhaul oxidation operation is controlled to 18 hours, during which the purification bed efficiency is regularly monitored to ensure the most complete purification possible.

[0052] In an application example, referring to Table 2, the measurement and control method for oxidation operation of a nuclear power plant overhaul provided by the present disclosure was used during the overhaul of unit 107. As a result, when the main pump was stopped during the down phase of the overhaul of unit 107, the total γ of the main system was measured to be 7976 MBq / t. 58 The Co content is 4381 MBq / t, the lowest in all previous overhauls of a certain unit, proving that the method disclosed in the present invention can effectively improve the oxidation operation effect.

[0053] Table 2

[0054]

[0055] While various embodiments of the present disclosure have been described above, the above descriptions are illustrative, non-exhaustive, and not intended to be limiting of the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to existing technologies, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for measuring and controlling oxidation operation during overhaul of a nuclear power plant, characterized in that: The method comprises: Step 101, pre-overhaul control: Before the overhaul, the first demineralizer is put into operation to purify the first refueling water tank. Under the action of the cooling circulation pump, the refueling water tank purification circuit flows through the first filter, the first demineralizer, and the second filter at a preset flow rate for a preset time period. Step 102, control of the second desalter operation during the overhaul down phase: The second desalter is put into operation after the reactor reaches subcriticality for a preset time. During the overhaul down phase, the second line is used as the downflow loop. The second line is a downflow loop consisting of the reactor pressure vessel, the reactor coolant pump, the third filter, the second desalter, and the fourth filter connected in series in this order. Step 103, preparation and implementation of oxidation operation in the down-stream phase of overhaul: At the start of the overhaul oxidation operation, a preset volume and concentration of hydrogen peroxide solution is injected into the chemical mixing and dosing tank at one time, and when the hydrogen peroxide solution reaches a preset temperature, the hydrogen peroxide solution is injected into the primary circuit. Thereafter, samples are taken at 10, 20, 30, 45, 60 minutes, 2 hours, 3 hours, 4 hours, and 6 hours respectively to observe the change trends of Co-58, Co-60, Sb-122, Sb-124, Ag-110m, I-131, Xe-133, and total γ; Step 104, measurement of oxidation operation during the down-stream phase of the overhaul: Measure and obtain a gamma nuclide spectrum of a preset volume standard mixed radioactive source, so that the area counts of each major peak reach a preset threshold, input the energy peak on the gamma nuclide spectrum into the activity, calibration date, and uncertainty information of the corresponding nuclide on the standard source certificate, fit the efficiency curve, and complete the efficiency calibration; Step 105, operation control of the oxidation operation main pump during the overhaul down stage: the operation purification time of the overhaul oxidation operation main pump is controlled to be 18 hours.

2. The method according to claim 1, characterized in that The resin volume of the first desalter is 1.5m 3 The maximum working pressure is 0.05MPa.g, the maximum working temperature is 60℃, and the maximum working flow rate is 65m 3 / h, at 60m 3 / h flow rate for purification.

3. The method according to claim 1, characterized in that Before the overhaul unit is decommissioned, the 0.1μm filter element of the third filter is replaced with a 0.45μm filter element, and the replacement pressure difference is adjusted to 0.25Mpa.

4. The method according to claim 1, wherein In the actual measurement process, 1g of main system sample was taken during the oxidation operation and diluted to 20g with high-purity water for measurement, and the measurement time was 100 seconds.

5. The method according to claim 1, wherein Before the measurement, a high-purity germanium multi-channel gamma spectrometer and a source of the above-mentioned preset volume of the standard mixed solution are used to measure the radioactive nuclides, and a special nuclide library for oxidation operation is established.

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