Turbidity control method for refueling pool of nuclear power plant

Abstract

The invention belongs to the technical field of nuclear power plant hydrochemical control, and particularly relates to a nuclear power plant refueling pool turbidity control method. Comprising the following steps: step 1, source water control; step 2, corrosion product control; and step 3, purification operation optimization. The method has the beneficial effects that water quality control of the refueling pool before unloading and during loading and unloading can be effectively guided; no additional system facility is added, no additional chemical reagent is added to change water quality, and application is convenient. 17.5 h of the first overhaul of a certain nuclear power unit can be shortened to 9.5 h, and the third overhaul of a certain unit can shorten the purification time before loading and unloading from 54 h of the second overhaul to 0 h.

Description

Technical Field

[0001] The invention belongs to the technical field of water chemistry control in nuclear power plants, and in particular relates to a turbidity control method for a refueling pool in a nuclear power plant. Background Art

[0002] When refueling a nuclear power unit, the refueling pool needs to be filled to the full level, and water is used as a shielding material for ionizing radiation to reduce the exposure dose of fuel workers. During loading and unloading operations, fuel operators stand on the fuel operation cart and visually observe the fuel assemblies to operate the fuel assemblies. Existing nuclear power units have experienced varying degrees of turbidity in the refueling pool during overhaul, making it difficult for fuel operators to clearly observe the fuel assemblies more than 10 meters underwater, affecting loading and unloading operations. When the water turbidity is high, the only corrective measure is to purify the water through the purification system, and there are no other effective measures. Such operations will affect the entire overhaul cycle. According to statistics, the longest overhaul cycle affected is about 54 hours, which seriously affects economic benefits.

[0003] In order to shorten the main line time of overhaul, reduce the overhaul period, and improve the economy of the unit, in view of the problem that the turbidity of the refueling pool during loading and unloading affects the loading and unloading, it is necessary to study the main factors affecting the turbidity of the refueling pool during overhaul, so as to establish effective control measures and treatment methods to ensure that the water quality of the refueling pool during loading and unloading is clear and the turbidity is qualified. Summary of the invention

[0004] The purpose of the present invention is to provide a turbidity control method for a refueling pool in a nuclear power plant, which can optimize the water quality control of the refueling pool during loading and unloading, reduce the waiting time for unit loading and unloading operations due to poor visibility in the refueling pool, shorten the main line time of overhaul, reduce the radiation dose of personnel, and at the same time improve the unit capacity factor, improve the economic benefit and safety of the unit.

[0005] The technical solution of the present invention is as follows: A method for controlling turbidity of a nuclear power plant refueling pool comprises the following steps:

[0006] Step 1: Source water control;

[0007] Step 2: Corrosion product control;

[0008] Step 3: Purification run optimization.

[0009] The step 1 includes the following:

[0010] Step 11: Control the source water quality. Purify the source water refueling tank through the fourth purification unit two weeks before the overhaul;

[0011] Step 12: If the refueling water tank is under maintenance during the overhaul, flush the refueling water tank after the maintenance is completed, and refill it with water after the turbidity of the flushing water is qualified;

[0012] Step 13: After unloading and draining, control the turbidity of the source water, ensure that the refueling water tank has sufficient purification time during the low water level period, ensure the water quality before loading, and control the turbidity expectation value at 0.1NTU level;

[0013] Step 14: After the overhaul is completed, the reactor water pool and component pool are decontaminated and the residual water is drained;

[0014] Step 15: Before filling with water, check the reactor water pool and component pool to ensure cleanliness.

[0015] The expected turbidity value during the purification process in step 11 is controlled at a level of 0.1 NTU.

[0016] The step 2 includes the following:

[0017] Step 21: One month before the overhaul, adjust the flow rate of the first purification unit or the second purification unit to the maximum;

[0018] Step 22: During the oxidation operation, the first purification unit, the second purification unit or the third purification unit is continuously operated at a maximum flow rate;

[0019] Step 23: During the overhaul oxidation-purification operation phase, the pore size of the first filter element is changed to 0.45 μm to shorten the bypass time when the filter element is replaced.

[0020] The step 3 includes the following:

[0021] Step 31: During the overhaul period, the turbidity of the relevant purification unit of the primary circuit is measured before switching, and the unit is connected to the system for operation after the turbidity is less than 0.20 NTU;

[0022] Step 32: After the reactor water pool is filled with water to a liquid level that satisfies the filter pump start-up level before unloading, the filter pump is put into operation to purify the reactor water pool;

[0023] Step 33: After unloading, keep the filter pump running continuously to purify the component pool;

[0024] Step 34: before filling the reactor water pool and component pool with water before unloading, replace the first filter screen and the second filter screen with a new fine filter screen;

[0025] Step 35: After the reactor pool is full of water before loading, the fourth purification unit is put into operation in time to purify the reactor pool with a large flow rate;

[0026] Step 36: Replace the second filter and the third filter elements with smaller filter elements.

[0027] Step 37: Reduce the resin loading of the third purification unit, use the purification unit during oxidation operation, and replace it after each overhaul to reduce the failure of the purification unit resin to use the third purification unit to purify the main circuit.

[0028] The purification unit in step 31 includes a first purification unit, a second purification unit and a third purification unit.

[0029] In step 36, the filter diameters of the second filter and the third filter are 0.1 μm.

[0030] The beneficial effects of the present invention are: it can effectively guide the water quality control of the refueling pool before unloading and during loading and unloading; it does not add additional system facilities, does not add additional chemical reagents to change the water quality, and is easy to use. It can shorten the 17.5h of the first overhaul of a nuclear power unit to 9.5h, and the third overhaul of a unit can shorten the purification time before loading and unloading from 54h of the second overhaul to 0h. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the main circuit purification;

[0032] Figure 2 It is a schematic diagram of purification of the reactor water pool 10 and the component pool 11.

[0033] In the figure: 1 main circuit, 2 first filter, 3 first purification unit, 4 second purification unit, 5 third purification unit, 6 charging pump, 7 circulation pump, 8 fourth purification unit, 9 refueling water tank, 10 reactor water pool, 11 component pool, 12 first filter, 13 second filter, 14 filter pump, 15 second filter, 16 third filter. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Through chemical condition tests and on-site sampling and analysis, it was found that the main reasons for the high turbidity of the refueling pool before loading and unloading, which affected the loading and unloading operations, were the source water quality, corrosion product control, and purification method optimization. The above problems were solved one by one through relevant measures, such as 1. Purify the source water in advance before overhaul to ensure the source water quality; 2. For corrosion products, first ensure the purification time during oxidation operation to ensure the removal of corrosion products, and adopt a new purification method to use the fourth purification unit 8 instead of the original downstream purification (such as Figure 1 ) to increase the purification flow rate from the original 20t / h to 60t / h to ensure that the required purification time is as short as possible; 3. By optimizing the operation mode of the purification unit, the filter element filter diameter, etc., the purification efficiency is better improved; through the implementation of the above measures, the turbidity control of the material exchange pool was successfully achieved.

[0036] A method for controlling turbidity of a nuclear power plant refueling pool is carried out in the following manner:

[0037] 1. Main circuit purification method

[0038] 1) Downstream purification

[0039] The purification method of the primary water sample can only be carried out by purifying the downstream water sample. The downstream purification system consists of 3 purification units (the first purification unit 3, the second purification unit 4 and the third purification unit 5). The first purification unit 3 and the second purification unit 4 are filled with 930L nuclear grade mixed resin, and the third purification unit 5 is filled with 1500L nuclear grade mixed resin. The three purification units are operated in parallel, and only one train can be put into operation at a time. The purification flow rate is about 20t / h.

[0040] 2) Large flow purification method

[0041] The fourth purification unit 8 of the refueling water tank 9 is optimized to replace the existing purification method to purify the main circuit 1, which can increase the purification flow rate from about 20 t / h to about 60 t / h.

[0042] 2. Purification of reactor water pool 10 and component pool 11

[0043] The purification of the reactor pool 10 and the component pool 11 can be achieved by a filter pump, such as Figure 2 shown.

[0044] A method for controlling turbidity of a nuclear power plant refueling pool comprises the following steps:

[0045] Step 1: Source water control;

[0046] Step 11: Strictly control the source water quality. Two weeks before the overhaul, purify the source water replacement tank 9 through the fourth purification unit 8, and control the expected turbidity value at 0.1NTU level to ensure that the source water quality meets the requirements.

[0047] Step 12: If the refueling water tank 9 is undergoing maintenance during the overhaul, ensure that the refueling water tank 9 is thoroughly rinsed after using chemicals such as passivation paste, and then fill it with water after the turbidity of the rinse water (<0.2NTU) is qualified to avoid impurities introduced by the maintenance work affecting the water quality of the refueling water tank feed water.

[0048] Step 13: After unloading and draining, in order to control the turbidity of the source water, ensure that there is enough purification time window for the material exchange water tank 9 during the low water level period to ensure the water quality before loading, and the expected turbidity value is controlled at 0.1NTU level.

[0049] Step 14: After the overhaul is completed, the reactor water pool 10 and the component pool 11 are decontaminated and the residual water is drained.

[0050] Step 15: Before filling with water, the reactor water pool 10 and the component pool 11 are inspected to ensure cleanliness and decontamination is performed if necessary.

[0051] Step 2: Corrosion product control

[0052] Step 21: One month before the overhaul, adjust the flow rate of the first purification unit 3 or the second purification unit 4 to the maximum (about 27 t / h).

[0053] Step 22: During the oxidation operation, the first purification unit 3, the second purification unit 4 or the third purification unit 5 is continuously operated at a maximum flow rate (about 27 t / h).

[0054] Step 23: During the overhaul oxidation-purification operation phase, the pore size of the first filter 2 element is changed to 0.45 μm to shorten the bypass time when the filter element is replaced, thereby affecting the filtering effect.

[0055] Step 3: Purification run optimization

[0056] Step 31: During the overhaul, the turbidity of the relevant purification units of the primary circuit (the first purification unit 3, the second purification unit 4 and the third purification unit 5) is measured before switching. The units can be connected to the system for operation only when the turbidity is less than 0.20 NTU.

[0057] Step 32: before unloading, after the reactor water pool 10 is filled with water to a liquid level that satisfies the start-up level of the filter pump 14 (elevation of about 15.2 m), the filter pump 14 is put into operation in time to purify the reactor water pool 10 .

[0058] Step 33: After unloading, keep the filter pump 14 running continuously to purify the component pool 11.

[0059] Step 34: Before the reactor water pool 10 and the component pool 11 are filled with water before unloading, the first filter screen 12 and the second filter screen 13 are replaced with new fine filter screens.

[0060] Step 35: After the reactor water pool 10 is full of water before loading, the fourth purification unit 8 is put into operation in time to purify the reactor water pool 10 with a large flow rate.

[0061] Step 36: Replace the filter elements of the second filter 15 and the third filter 16 with filter elements of smaller diameter.

[0062] Such as 0.1μm.

[0063] Step 37: Reduce the resin loading of the third purification unit 5, use the purification bed during oxidation operation, and replace it after each overhaul to reduce the failure of the purification unit resin to use the third purification unit 5 to purify the main loop 1.

Claims

1. A method for controlling turbidity of a nuclear power plant refueling pool, characterized in that: The steps include: Step 1: Source water control; Step 2: Corrosion product control; Step 3: Purification run optimization.

2. A method for controlling turbidity of a nuclear power plant refueling pool as claimed in claim 1, characterized in that: The step 1 includes the following: Step 11: Control the source water quality. Purify the source water refueling tank through the fourth purification unit two weeks before the overhaul; Step 12: If the refueling water tank is overhauled during the overhaul, flush the refueling water tank and fill it with water after the turbidity of the flushing water is qualified; Step 13: After unloading and draining, control the turbidity of the source water, and purify the water tank during the low water level period to ensure the quality of the water before loading. The expected turbidity value is controlled at 0.1NTU level; Step 14: After the overhaul is completed, the reactor water pool and component pool are decontaminated and the residual water is drained; Step 15: Before filling with water, check the reactor water pool and component pool to ensure cleanliness.

3. A method for controlling turbidity of a nuclear power plant refueling pool as claimed in claim 2, characterized in that: The expected turbidity value during the purification process in step 11 is controlled at a level of 0.1 NTU.

4. A method for controlling turbidity of a nuclear power plant refueling pool as claimed in claim 1, characterized in that: The step 2 includes the following: Step 21: One month before the overhaul, adjust the flow rate of the first purification unit or the second purification unit to the maximum; Step 22: During the oxidation operation, the first purification unit, the second purification unit or the third purification unit is continuously operated at a maximum flow rate; Step 23: During the overhaul oxidation-purification operation phase, the pore size of the first filter element is changed to 0.45 μm to shorten the bypass time when the filter element is replaced.

5. A method for controlling turbidity of a nuclear power plant refueling pool as claimed in claim 1, characterized in that: The step 3 includes the following: Step 31: During the overhaul period, the turbidity of the relevant purification unit of the primary circuit is measured before switching, and the unit is connected to the system for operation after the turbidity is less than 0.20 NTU; Step 32: After the reactor water pool is filled with water to a liquid level that satisfies the filter pump start-up level before unloading, the filter pump is put into operation to purify the reactor water pool; Step 33: After unloading, keep the filter pump running continuously to purify the component pool; Step 34: before filling the reactor water pool and component pool with water before unloading, replace the first filter screen and the second filter screen with a new fine filter screen; Step 35: After the reactor pool is full of water before loading, the fourth purification unit is put into operation in time to purify the reactor pool with a large flow rate; Step 36: Replace the second filter and the third filter elements with smaller filter elements. Step 37: Reduce the resin loading of the third purification unit, use the purification bed during oxidation operation, and replace it after each overhaul to reduce the failure of the purification unit resin to use the third purification unit to purify the main circuit.

6. A method for controlling turbidity of a nuclear power plant refueling pool as claimed in claim 5, characterized in that: The purification unit in step 31 includes a first purification unit, a second purification unit and a third purification unit.

7. A method for controlling turbidity of a nuclear power plant refueling pool as claimed in claim 5, characterized in that: In step 36, the filter diameters of the second filter and the third filter are 0.1 μm.

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