A nuclear power plant radioactive anion Sb-124 nuclide purification system and method

Abstract

The present invention belongs to the technical field of controlling the source term of radioactive anions in a primary circuit during a refueling overhaul of a nuclear power plant, and specifically relates to a system and method for purifying radioactive anions Sb-124 in a nuclear power plant. The system comprises: a primary circuit main pipeline, a reactor special drainage system, a chemical and volume control system degasser, and a primary circuit coolant temporary storage system. The primary circuit main pipeline is connected to the chemical and volume control system degasser via the reactor special drainage system, the chemical and volume control system degasser is connected to the primary circuit coolant temporary storage system to purify the Sb-124 nuclide, and the primary circuit coolant temporary storage system is connected to the primary circuit main pipeline to achieve closed-loop purification of the Sb-124 nuclide. The present invention can reduce the primary circuit Sb-124 radiation source term, reduce the radiation level in the maintenance area, and reduce the radiation exposure dose to personnel.

Description

Technical Field

[0001] The invention belongs to the technical field of primary loop radioactive anion source item control during refueling overhaul of a nuclear power plant, and particularly relates to a system and method for purifying radioactive anion Sb-124 nuclides in a nuclear power plant. Background Art

[0002] Nuclear power plants have historically primarily reduced radiation fields by controlling nickel and cobalt source terms. However, data indicates that after controlling Co-58 and Co-60, the primary contributors to post-shutdown radiation fields at some nuclear power plants have shifted to anionic nuclides such as Sb-124, whose activity accounts for over 30% of the total gamma activity in the primary circuit. Analysis of the properties of Sb-124 revealed a half-life of 60.2 days, similar to that of Co-58. Furthermore, at the same radioactivity level, the gamma radiation level generated by Sb-124 at a distance of 1 meter is 1.6 times that of Co-58, posing significant challenges and difficulties for collective dose control at nuclear power plants.

[0003] Currently, radiation source control during refueling overhauls for VVER-type pressurized water reactor (PWR) nuclear power plants primarily involves removing cationic radionuclides from the primary circuit during the unit's downtime (a weakly alkaline, hydrogen environment) by operating a desalination bed cation resin. However, VVER purification systems lack mechanical filters, and the system operates primarily when the primary circuit is sealed. Consequently, this method is ineffective in removing Sb-124 radionuclides from VVER units, hindering the reduction of radiation doses for maintenance workers. Furthermore, prolonged use of the desalination bed cation resin to purify the primary circuit media can easily lead to elevated sulfate concentrations, complicating subsequent primary circuit water quality adjustments during the unit's startup phase.

[0004] Therefore, how to provide a method for purifying and removing the radioactive anion Sb-124 in the primary circuit during the unit refueling overhaul is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] The present invention aims to provide a system and method for purifying radioactive anions Sb-124 in a nuclear power plant. The method reduces the primary circuit Sb-124 radiation source term by utilizing a combination of multiple process systems during the Sb-124 release window and utilizing different time windows during primary circuit depressurization and shutdown, thereby reducing the radiation level in the maintenance area and the radiation exposure dose to personnel.

[0006] The technical solution for achieving the purpose of the present invention is as follows:

[0007] A nuclear power plant radioactive anion Sb-124 nuclide purification system comprises: a primary loop main pipeline, a reactor special drainage system, a chemical and volume control system degasser, and a primary loop coolant temporary storage system. The primary loop main pipeline is connected to the chemical and volume control system degasser via the reactor special drainage system, the chemical and volume control system degasser is connected to the primary loop coolant temporary storage system to purify the Sb-124 nuclide, and the primary loop coolant temporary storage system is connected to the primary loop main pipeline to achieve closed-loop purification of the Sb-124 nuclide.

[0008] The system also includes a chemical and volume control system charging valve, and the primary circuit coolant temporary storage system is connected to the primary circuit main pipeline via the chemical and volume control system charging valve.

[0009] The primary coolant temporary storage system includes: a primary coolant temporary storage system water pump, a primary coolant temporary storage system anion filter and a primary coolant temporary storage system resin trap. The chemical and volume control system degasser is connected to the primary coolant temporary storage system anion filter and the primary coolant temporary storage system resin trap in sequence via the primary coolant temporary storage system water pump.

[0010] The chemical and volume control system charging valve is installed downstream of the primary coolant temporary storage system resin trap, and the primary coolant temporary storage system resin trap is connected to the primary circuit main pipeline through the chemical and volume control system charging valve.

[0011] A method for purifying radioactive anions Sb-124 in a nuclear power plant, the method comprising:

[0012] Step 1: Confirm that the unit is in maintenance cold shutdown and the primary circuit is connected to the atmosphere;

[0013] Step 2: Install pulse control on the reactor special drainage system valves;

[0014] Step 3: Check the status of the devices involved in the system and perform operation verification to ensure that the devices are available;

[0015] Step 4: Evaluate filter resin purification capacity;

[0016] Step 5: Start the water delivery pump of the primary coolant temporary storage system;

[0017] Step 6: Pulse open the reactor special drainage system valve to control the discharge flow;

[0018] Step 7: Maintain a stable degasser liquid level in the chemical and volume control systems by regulating valves;

[0019] Step 8: Take a chemical sample from the primary circuit and analyze the current Sb-124 radioactivity A tAnd compare it with the set purification target A0, the comparison is as follows:

[0020] a) If A t >A0, then execute step 6 and increase the downstream flow rate;

[0021] b) If A t <A0, then execute step 9;

[0022] Step 9: Continuously purify the primary circuit medium, monitor the primary circuit liquid level, track the purification effect of Sb-124 and other corrosion activation products in the primary circuit, and evaluate the purification efficiency of the resin bed;

[0023] Step 10: Track the status of the unit, stop the purification before desealing the reactor and lifting the reactor top cover, shut down the pump group, restore the system valve status, restore the system equipment to a safe standby state, and complete the purification.

[0024] The calculation formula of the filter resin purification capacity in step 4 is: C 剩 =C0-C 用 ,

[0025] Where C 剩 Indicates the current purification capacity of the filter resin, C0 indicates the initial purification capacity of the filter resin, C 用 Indicates that the filter resin has used its purification capacity.

[0026] In step 6, the downstream flow rate is controlled to be 4 kg / s.

[0027] In step 8, if A t >A0, increase the downstream flow rate to 5kg / s.

[0028] The beneficial technical effects of the present invention are:

[0029] 1) The method of the present invention makes full use of existing system equipment, and through process combination, changes in system equipment status, a new primary circuit medium purification path is found, without the need for modification or additional equipment.

[0030] 2) The method of the present invention creates a process and method for removing the anionic Sb-124 nuclide during the refueling overhaul of a VVER unit.

[0031] 3) The method of the present invention does not need to occupy the overhaul critical path, does not affect the isolation of the main system, and has a good match with the overhaul work plan.

[0032] 4) In addition to having a high removal effect on the primary-loop radioactive anion Sb-124, the method of the present invention also has a good removal effect on other anions, such as I.

[0033] 5) The method of the present invention can effectively solve the problem of increased sulfate ions in a single circuit caused by traditional source term control technology, and can effectively remove sulfate ions.

[0034] 6) The method of the present invention does not lead to an increase in waste gas, waste liquid, concentrated liquid and distilled residual liquid, and has good environmental protection.

[0035] 7) The method of the present invention further reduces the radiation level of the primary radioactive source term and the working area. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a process flow chart of a nuclear power plant radioactive anion Sb-124 nuclide purification system provided by the present invention;

[0037] Figure 2 This is a flow chart of a method for purifying radioactive anions Sb-124 in nuclear power plants provided by the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0039] The existing technologies and methods for the purification and removal of radioactive source items in the primary circuit of nuclear power plants during refueling overhauls have the following shortcomings: during the reactor refueling outage, the water chemical conditions such as the oxygen content, heat flux and pressure in the primary circuit medium change, and a large amount of Sb-124 deposited on the surface of primary circuit related system equipment is released. However, the existing source item purification and removal technologies of nuclear power plants cannot effectively remove Sb-124.

[0040] The present invention is based on the existing primary coolant temporary storage system and chemical and volume control system of the power station. Through the combined operation of the above system equipment, the primary circuit radioactive anion Sb-124 is purified and removed within a specific time window.

[0041] like Figure 1 As shown, the present invention provides a nuclear power plant radioactive anion Sb-124 nuclide purification system, including: a primary circuit main pipeline, a reactor special water drainage system, a chemical and volume control system degasser, a primary circuit coolant temporary storage system and a chemical and volume control system charging valve; the primary circuit coolant temporary storage system includes: a primary circuit coolant temporary storage system water pump, a primary circuit coolant temporary storage system anion filter and a primary circuit coolant temporary storage system resin trap.

[0042] The primary loop main pipeline is connected to the degasser of the chemical and volume control system through the reactor special drainage system. The degasser of the chemical and volume control system is connected to the anion filter of the primary coolant temporary storage system and the resin trap of the primary coolant temporary storage system in sequence through the water pump of the primary coolant temporary storage system to purify the Sb-124 nuclide; the resin trap of the primary coolant temporary storage system is connected to the primary loop main pipeline through the charging valve of the chemical and volume control system to realize the closed-loop purification of the Sb-124 nuclide.

[0043] Specifically, after the first loop is connected to the atmosphere, the coolant gradually changes from an alkaline reducing environment to an acidic oxidizing environment, and the Sb-124 nuclides deposited on the first loop system equipment are quickly released into the first loop coolant in the form of anions. A feasible medium operation loop is found from the complex process system to achieve the purification of the radioactivity of the first loop coolant. The specific process is: the first loop coolant in the main pipeline is introduced into the degasser of the chemical and volume control system through the reactor special drainage system, and the associated equipment of the degasser and the coolant temporary storage system is utilized to introduce the first loop coolant into the anion resin desalination bed of the system through the temporary storage system pump group to achieve purification, and finally the purified first loop coolant is introduced into the first loop charging pipeline of the unit, thereby achieving closed-loop purification of Sb-124 nuclides in the form of anions. The purification path requires the combined operation of multiple systems and the isolation and online operation of the pipelines required for the purification loop through the system valves. The process flow of the system of the present invention is as follows Figure 1 shown.

[0044] The present invention provides a method for purifying radioactive anions Sb-124 in nuclear power plants, comprising:

[0045] Step 1: Confirm that the unit is in maintenance cold shutdown and the primary circuit is connected to the atmosphere;

[0046] Step 2: Install pulse control on the reactor special drainage system valves;

[0047] Step 3: Check the status of the devices involved in the system and perform operation verification to ensure that the devices are available;

[0048] Step 4: Evaluate the purification capacity of the filter resin. The capacity evaluation method is as follows: C 剩 =C0-C 用 , C 剩 Indicates the current purification capacity of the filter resin, C0 indicates the initial purification capacity of the filter resin, C 用 Indicates that the filter resin has used its purification capacity;

[0049] Step 5: Start the water delivery pump of the primary coolant temporary storage system;

[0050] Step 6: Pulse open the valve of the reactor special drainage system to control the discharge flow rate to 4 kg / s;

[0051] Step 7: Maintain a stable degasser liquid level in the chemical and volume control systems by regulating valves;

[0052] Step 8: Take a chemical sample from the primary circuit and analyze the current Sb-124 radioactivity A t And compare it with the set purification target A0, the comparison is as follows:

[0053] c) If A t >A0, then execute step 6 and increase the downstream flow rate to 5kg / s;

[0054] d) If A t <A0, then execute step 9;

[0055] Step 9: Continuously purify the primary circuit medium, monitor the primary circuit liquid level, track the purification effect of Sb-124 and other corrosion activation products in the primary circuit, and evaluate the purification efficiency of the resin bed;

[0056] Step 10: Track the status of the unit, stop the purification before desealing the reactor and lifting the reactor top cover, shut down the pump group, restore the system valve status, restore the system equipment to a safe standby state, and complete the purification.

[0057] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. However, the present invention is not limited to the above embodiments. Various modifications can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Any content not described in detail in the present invention may be adapted from existing technologies.

Claims

1. A nuclear power plant radioactive anion Sb-124 nuclide purification system, characterized in that: The system comprises: a primary circuit main pipeline, a reactor special drainage system, a chemical and volume control system degasser, and a primary circuit coolant temporary storage system. The primary circuit main pipeline is connected to the chemical and volume control system degasser via the reactor special drainage system, the chemical and volume control system degasser is connected to the primary circuit coolant temporary storage system to purify Sb-124 nuclides, and the primary circuit coolant temporary storage system is connected to the primary circuit main pipeline to achieve closed-loop purification of Sb-124 nuclides. The system also includes a chemical and volume control system charging valve, and the primary circuit coolant temporary storage system is connected to the primary circuit main pipeline via the chemical and volume control system charging valve; The primary coolant temporary storage system comprises: a primary coolant temporary storage system water pump, a primary coolant temporary storage system anion filter and a primary coolant temporary storage system resin trap, and the chemical and volume control system degasser is connected to the primary coolant temporary storage system anion filter and the primary coolant temporary storage system resin trap in sequence via the primary coolant temporary storage system water pump; The chemical and volume control system charging valve is installed downstream of the primary coolant temporary storage system resin trap, and the primary coolant temporary storage system resin trap is connected to the primary circuit main pipeline through the chemical and volume control system charging valve.

2. A method for purifying radioactive anions Sb-124 from a nuclear power plant, using the radioactive anion Sb-124 purification system for a nuclear power plant according to claim 1, characterized in that: The method comprises: Step 1: Confirm that the unit is in maintenance cold shutdown and the primary circuit is connected to the atmosphere; Step 2: Install pulse control on the reactor special drainage system valves; Step 3: Check the status of the devices involved in the system and perform operation verification to ensure that the devices are available; Step 4: Evaluate filter resin purification capacity; Step 5: Start the water delivery pump of the primary coolant temporary storage system; Step 6: Pulse open the reactor special drainage system valve to control the discharge flow; Step 7: Maintain a stable degasser liquid level in the chemical and volume control systems by regulating valves; Step 8: Take a chemical sample from the primary circuit and analyze the current Sb-124 radioactivity A t And compare it with the set purification target A0, the comparison is as follows: If A t >A 0， Then execute step 6 and increase the downstream flow rate; If A t <A 0， Then execute step 9; Step 9: Continuously purify the primary circuit medium, monitor the primary circuit liquid level, track the purification effect of Sb-124 and other corrosion activation products in the primary circuit, and evaluate the purification efficiency of the resin bed; Step 10: Track the status of the unit, stop the purification before desealing the reactor and lifting the reactor top cover, shut down the pump group, restore the system valve status, restore the system equipment to a safe standby state, and complete the purification.

3. A method for purifying radioactive anions Sb-124 in a nuclear power plant according to claim 2, characterized in that: The calculation formula of the filter resin purification capacity in step 4 is: C 剩 =C0-C 用 , Where C 剩 Indicates the current purification capacity of the filter resin, C0 indicates the initial purification capacity of the filter resin, C 用 Indicates that the filter resin has used its purification capacity.

4. A method for purifying radioactive anions Sb-124 in a nuclear power plant according to claim 3, characterized in that: In step 6, the downstream flow rate is controlled to be 4 kg / s.

5. A method for purifying radioactive anions Sb-124 in a nuclear power plant according to claim 4, characterized in that: In step 8, if A t >A0, increase the downstream flow rate to 5kg / s.

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