Method for reducing tritium emission of pressurized water reactor unit

Abstract

The invention provides a method for reducing tritium emission of a pressurized water reactor unit, which comprises the following steps of: discharging a primary loop coolant into a refueling water tank in a containment vessel for temporary storage for t time, reducing tritium concentration in the primary loop coolant by utilizing natural decay, and then discharging the primary loop coolant so as to reduce the tritium emission of the pressurized water reactor unit, the t time is a fuel circulation period of the pressurized water reactor unit. The method is reasonable in design and easy to operate, the primary loop coolant is temporarily stored through the refueling water tank in the existing containment, the tritium concentration in the primary loop coolant is reduced through tritium natural decay, tritium emission of the pressurized water reactor unit can be reduced, additional devices and equipment are not needed, and the tritium treatment cost of the pressurized water reactor unit cannot be increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tritium emission control of nuclear power plants, and particularly relates to a method for reducing tritium emission of a pressurized water reactor unit. BACKGROUND

[0002] In a pressurized water reactor nuclear power plant, the generation and emission of tritium is an inevitable part of the nuclear reaction process. The main generation pathways of tritium in the primary loop include: 1) the reaction of soluble boron in the primary coolant with neutrons; 2) tritium generated by fuel ternary fission diffusing through the fuel cladding or leaking into the primary coolant through fuel cladding breakage; 3) tritium generated by the secondary source rod diffusing through the fuel cladding or leaking into the primary coolant through fuel cladding breakage; 4) the reaction of soluble lithium in the primary coolant with neutrons; 5) the reaction of deuterium in the primary coolant with neutrons; and 6) tritium generated in the combustible neutron absorber diffusing or leaking into the primary coolant through cladding breakage.

[0003] During the operation of the nuclear power plant, most of the tritium exists in the form of tritiated water (HTO). At normal pressure, the separation coefficient of H2O and HTO is only 1.03, and the separation is difficult, and common water treatment technologies such as flocculation, filtration, reverse osmosis and the like cannot achieve separation. As an isotope of hydrogen, tritium is usually difficult to remove by conventional radionuclide separation means, and it is also difficult to reduce the generation of tritium by controlling the above generation pathways.

[0004] The existing research on tritium separation technology mainly includes water rectification, gas / liquid phase catalytic exchange, and combined electrolysis catalytic exchange. Among them, the water rectification technology is relatively mature and has been applied in engineering, but the separation coefficient is low, the energy consumption is high, and a large plant space and capital investment are required.

[0005] The reaction of boron with neutrons is the main source of tritium generation, which usually accounts for more than 60% of the total amount of tritium emission. Therefore, the most effective way to reduce the generation of tritium from the source term is to reduce the boron concentration in the primary loop. If the refueling period of the unit is changed from 18 months to 12 months, the average boron concentration in the primary loop can be reduced, thereby reducing the amount of tritium generated. However, this method will directly increase the cost of fuel procurement, transportation and handling, increase the number of overhauls, operation and maintenance costs and human error risks, reduce the continuous operation time of the unit, and reduce the power generation capacity factor.

[0006] The existing technology also adopts the method of inserting part of the gray rod into the reactor core before the end of the fuel cycle, which fully utilizes the neutron absorption property of the gray rod, thereby reducing the demand for soluble boron in the primary coolant, reducing the tritium generated by the soluble boron reaction path, and further reducing the emission amount. However, using this method, a feasibility analysis needs to be carried out on the burn-up shadow effect caused by the long-term insertion of the gray rod before the operation of the reactor, including power distribution peak factor, axial power distribution control, shutdown margin, one-rod withdrawal accident and rod ejection accident analysis, which is relatively complex and not easy to implement.

[0007] Therefore, it is of great significance to provide a method for reducing tritium discharge of a pressurized water reactor, which makes full use of existing equipment of the pressurized water reactor and is simple and reliable in operation. SUMMARY

[0008] In view of the problems in the prior art, the present application provides a method for reducing tritium discharge of a pressurized water reactor unit, which is based on existing equipment of the pressurized water reactor and utilizes the method of tritium natural decay, dynamic temporary storage and discharge to reduce tritium discharge. The method is simple in operation, does not require the use of additional devices and equipment, and has low processing cost.

[0009] To achieve the above object, the present application adopts the following technical solutions:

[0010] The present application provides a method for reducing tritium discharge of a pressurized water reactor unit, which comprises:

[0011] The primary coolant is discharged into the in-containment refueling water tank for temporary storage for a period of t, and then discharged after the tritium concentration in the primary coolant is reduced by natural decay, thereby reducing the tritium discharge of the pressurized water reactor unit;

[0012] The period of t is one fuel cycle period of the pressurized water reactor unit.

[0013] The method for reducing tritium discharge of a pressurized water reactor unit according to the present application utilizes the existing in-containment refueling water tank to temporarily store the primary coolant, so that the primary coolant is subjected to natural decay in the in-containment refueling water tank, thereby reducing the tritium discharge of the pressurized water reactor unit. The present application takes one fuel cycle period of the pressurized water reactor unit as the temporary storage time of the primary coolant in the in-containment refueling water tank, which can effectively reduce the tritium discharge of the pressurized water reactor unit and make the tritium discharge of the pressurized water reactor unit meet the standard, without the need to add more in-containment refueling water tanks and increase the processing cost.

[0014] Preferably, the period of t is 12-18 months, for example, it can be 12, 13, 14, 15, 16, 17 or 18 months, etc.

[0015] Preferably, the period of time t for which the primary coolant is discharged into the in-containment refueling water tank for temporary storage is 12-18 months. This is because the refueling period of the pressurized water reactor unit is generally 12-18 months, and the maximum tritium value of the current unit to the maximum tritium value of the next fuel cycle is about one refueling period, which has the advantage of being able to temporarily store as much tritium as possible for natural decay.

[0016] Preferably, the method comprises: when the tritium concentration of the primary coolant rises to c Bq / g, the reactor coolant system discharges mg of primary coolant into the in-containment refueling water tank, and after the in-containment refueling water tank discharges mg of primary coolant after temporary storage for a period of t for natural decay.

[0017] The reactor coolant system described in this invention refers to the existing coolant system of a pressurized water reactor unit in a nuclear power plant, including a main loop structure and auxiliary equipment. The main loop structure consists of two closed-loop circulation loops, each including a steam generator and a reactor coolant pump. The steam generator converts the heat energy in the coolant into steam, driving the turbine to generate electricity; the reactor coolant pump forces the coolant to circulate, ensuring effective heat transfer. The main loop structure also includes main pipes, hot pipe sections, cold pipe sections, and connecting components. The auxiliary equipment includes a pressurizer and an automatic pressure relief system. The pressurizer maintains stable system pressure and prevents overpressure; the automatic pressure relief system rapidly releases pressure in emergencies to ensure safety.

[0018] Preferably, the reactor coolant system discharges mg of primary coolant into the refueling tank inside the containment and discharges mg of primary coolant from the refueling tank inside the containment, repeating this operation according to one fuel cycle. This effectively reduces tritium emissions from the pressurized water reactor unit, ensures that the tritium concentration in the refueling tank inside the containment meets national emission standards, and eliminates the need for additional equipment, thus not increasing the tritium concentration control costs of the nuclear power plant.

[0019] The present invention does not impose a detailed limit on the mass m of the primary coolant discharged into the refueling tank inside the containment. It can be reasonably set according to the volume of the refueling tank inside the containment in the actual pressurized water reactor unit.

[0020] Preferably, the cBq / g is 60,000 Bq / g or higher, for example, it can be 60,000 Bq / g, 65,000 Bq / g, 70,000 Bq / g, 75,000 Bq / g, 80,000 Bq / g, 85,000 Bq / g, 90,000 Bq / g, etc.

[0021] Preferably, the total amount of tritium in the primary loop coolant discharged into the refueling tank inside the containment is mc.

[0022] Preferably, the formula for calculating the total amount Q of tritium in the refueling tank inside the containment is:

[0023]

[0024] Where W is the total amount of tritium in the refueling tank inside the containment after the primary coolant is discharged into the refueling tank inside the containment during the previous fuel cycle, and the unit is Bq.

[0025] m represents the mass of the primary coolant discharged from the reactor coolant system into the refueling tank inside the containment, in grams.

[0026] M represents the water volume in the refueling tank inside the containment, in grams.

[0027] λ is the decay constant of tritium, ln2 / 12.3≈0.0564;

[0028] t represents the temporary storage time, in years;

[0029] c represents the tritium concentration of the primary coolant, expressed in Bq / g.

[0030] Preferably, the tritium concentration in the refueling tank inside the containment is Q / M.

[0031] Preferably, the total amount of tritium in the water discharged from the refueling tank inside the containment is mQ / M.

[0032] Preferably, the net temporary tritium storage in the refueling tank inside the containment is mc-mQ / M.

[0033] As a preferred technical solution of the present invention, the method includes:

[0034] When the tritium concentration of the primary coolant rises to above 60,000 Bq / g, the reactor coolant system discharges mg of primary coolant into the refueling tank inside the containment. After being stored for 12 to 18 months for natural decay, mg of primary coolant is discharged from the refueling tank inside the containment.

[0035] The reactor coolant system discharges mg of primary coolant into the refueling tank inside the containment and discharges mg of primary coolant from the refueling tank inside the containment, repeating the operation according to one fuel cycle, thereby reducing tritium emissions from the pressurized water reactor unit.

[0036] The total amount of tritium in the primary loop coolant discharged into the refueling tank inside the containment is mc;

[0037] The formula for calculating the total amount of tritium Q in the refueling tank inside the containment is:

[0038]

[0039] Where W is the total amount of tritium in the refueling tank inside the containment after the primary coolant is discharged into the refueling tank inside the containment during the previous fuel cycle, and the unit is Bq.

[0040] m represents the mass of the primary coolant discharged from the reactor coolant system into the refueling tank inside the containment, in grams.

[0041] M represents the water volume in the refueling tank inside the containment, in grams.

[0042] λ is the decay constant of tritium, ln2 / 12.3≈0.0564;

[0043] t represents the temporary storage time, in years;

[0044] c represents the tritium concentration of the primary coolant, expressed in Bq / g.

[0045] The tritium concentration in the refueling tank inside the containment is Q / M;

[0046] The total amount of tritium in the water discharged from the refueling tank inside the containment is mQ / M;

[0047] The total net temporary tritium storage in the refueling tank inside the containment is mc-mQ / M.

[0048] Compared with the prior art, the present invention has at least the following beneficial effects:

[0049] The method for reducing tritium emissions from pressurized water reactor units provided by this invention is simple to operate and reasonably designed. By temporarily storing the primary coolant in the refueling tank inside the containment before discharging it, the tritium concentration in the primary coolant is reduced by natural decay, thereby reducing tritium emissions from pressurized water reactor units. The method does not require additional equipment and will not increase the tritium treatment costs of nuclear power plants. Attached Figure Description

[0050] Figure 1 This is a trend diagram of tritium concentration in the refueling tank inside the containment vessel of Embodiment 1 of the present invention.

[0051] Figure 2 This is a trend chart of the total net temporary tritium content in the refueling tank inside the containment vessel according to Embodiment 1 of the present invention.

[0052] Figure 3 This is a trend diagram of tritium concentration in the refueling tank inside the containment vessel of Embodiment 2 of the present invention.

[0053] Figure 4 This is a trend chart of the total net temporary tritium content in the refueling tank inside the containment vessel in Embodiment 2 of the present invention. Detailed Implementation

[0054] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0055] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0056] Example 1

[0057] In this embodiment, the tritium concentration in the refueling tank inside the containment is 2500 Bq / g, and the water capacity of the refueling tank inside the containment is 2000 tons.

[0058] This embodiment provides a method for reducing tritium emissions from a pressurized water reactor unit, the method comprising:

[0059] When the tritium level in the primary coolant rises to 80,000 Bq / g, the reactor coolant system discharges 50 tons of coolant into the refueling tank inside the containment for storage for one fuel cycle (18 months). After that, the refueling tank inside the containment discharges 50 tons of water.

[0060] In the next fuel cycle, the reactor coolant system discharges another 50 tons of primary coolant into the refueling tank inside the containment. The relationship between the total amount of tritium Q in the refueling tank at this time and the total amount of tritium W in the refueling tank after the primary coolant was discharged into the refueling tank in the previous fuel cycle is: Q = 0.896W + 4.00 × 10⁻⁶. 12 .

[0061] The data results for 40 fuel cycles performed according to the method provided in this embodiment, including the water volume M in the refueling tank inside the containment, the mass m of the primary coolant discharged into the refueling tank inside the containment by the reactor coolant system, the tritium concentration c of the primary coolant discharged into the refueling tank inside the containment, the total tritium amount mc of the primary coolant discharged into the refueling tank inside the containment, the total tritium amount Q in the refueling tank inside the containment, the tritium concentration Q / M in the refueling tank inside the containment, the total tritium amount mQ / M of the water discharged from the refueling tank inside the containment, and the net temporary tritium amount mc-mQ / M, are shown in Table 1.

[0062]

[0063]

[0064] The tritium concentration trend in the refueling tank inside the containment in this embodiment is shown below. Figure 1 The trend of the total net temporary tritium storage in the refueling tank inside the containment is shown in [the figure]. Figure 2 .

[0065] from Figure 1 and Figure 2 As can be seen, after approximately 30 fuel cycles, both the tritium concentration trend and the net temporary tritium amount in the refueling tank within the containment stabilized. The tritium concentration in the refueling tank within the containment was approximately 1.90 × 10⁻⁶. 4 Bq / g, meeting national emission standards (<3.0×10⁻⁶). 7 (Bq / L). In this embodiment, during one fuel cycle, when the tritium level in the primary coolant rises to 80,000 Bq / g, 50 tons of coolant are temporarily stored in the refueling tank inside the containment. Based on a nuclear power plant with eight pressurized water reactor units, the total amount of tritium that can be temporarily stored is 3.2 × 10⁻⁶ Bq / L. 13 Bq can provide a tritium emission margin of approximately 10.7%, with the total liquid tritium emissions at multiple reactor sites not exceeding 3.0 × 10⁻⁶. 14 Bq / year, meeting national emission standards.

[0066] Example 2

[0067] In this embodiment, the tritium concentration in the refueling tank inside the containment is 2500 Bq / g, and the water capacity of the refueling tank inside the containment is 2000 tons.

[0068] This embodiment provides a method for reducing tritium emissions from a pressurized water reactor unit, the method comprising:

[0069] When the tritium level in the primary coolant rises to 80,000 Bq / g, the reactor coolant system discharges 80 tons of coolant into the refueling tank inside the containment for storage for one fuel cycle (18 months). After that, the refueling tank inside the containment discharges 80 tons of water.

[0070] In the next fuel cycle, the reactor coolant system discharges another 80 tons of primary coolant into the refueling tank inside the containment. The relationship between the total amount of tritium Q in the refueling tank at this time and the total amount of tritium W in the refueling tank after the primary coolant was discharged into the refueling tank in the previous fuel cycle is: Q = 0.882W + 4.00 × 10⁻⁶. 12 .

[0071] The data results for 40 fuel cycles performed according to the method provided in this embodiment, including the water volume M in the refueling tank inside the containment, the mass m of the primary coolant discharged into the refueling tank inside the containment by the reactor coolant system, the tritium concentration c of the primary coolant discharged into the refueling tank inside the containment, the total tritium amount mc of the primary coolant discharged into the refueling tank inside the containment, the total tritium amount Q in the refueling tank inside the containment, the tritium concentration Q / M in the refueling tank inside the containment, the total tritium amount mQ / M of the water discharged from the refueling tank inside the containment, and the net temporary tritium amount mc-mQ / M, are shown in Table 2.

[0072]

[0073]

[0074] The tritium concentration trend in the refueling tank inside the containment in this embodiment is shown below. Figure 3 The trend of the total net temporary tritium storage in the refueling tank inside the containment is shown in [the figure]. Figure 4 .

[0075] from Figure 3 and 4 As can be seen, after approximately 30 fuel cycles, both the tritium concentration trend and the net temporary tritium amount in the refueling tank within the containment stabilized. The tritium concentration in the refueling tank within the containment was approximately 2.7 × 10⁻⁶. 4 Bq / g, meeting national emission standards (<3.0×10⁻⁶). 7 Bq / L).

[0076] In this embodiment, during one fuel cycle, when the tritium level in the primary coolant rises to 80,000 Bq / g, 80 tons of coolant are temporarily stored in the refueling tank inside the containment. Based on a nuclear power plant with eight pressurized water reactor units, the total amount of tritium that can be temporarily stored is 5.12 × 10⁻⁶. 13 Bq can provide approximately 17.1% of the tritium emission margin, ensuring that the total emissions from multiple liquid tritium reactor sites do not exceed 3.0 × 10⁻⁶. 14 Bq / year, meeting national emission standards.

[0077] In summary, the method for reducing tritium emissions from pressurized water reactor units provided by this invention is simple to operate and rationally designed. By temporarily storing the primary coolant in the refueling tank within the containment before discharging it, the tritium concentration in the primary coolant is reduced through natural decay, thereby achieving a reduction in tritium emissions from the pressurized water reactor unit. The tritium concentration in the refueling tank within the containment meets national emission standards. This method requires no additional equipment and will not increase the tritium concentration control costs of nuclear power plants, making it suitable for widespread application in nuclear power plants.

[0078] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method of reducing tritium discharge from a pressurized water reactor unit, characterized by, The method comprises: The method comprises: The t time is a fuel cycle period of the pressurized water reactor unit.

2. The method of claim 1, wherein, The t time is 12-18 months.

3. The method of claim 1, wherein, The method comprises: When the tritium concentration of the primary coolant rises to c Bq / g, the reactor coolant system discharges mg primary coolant into the in-containment refueling water tank, and the in-containment refueling water tank discharges mg primary coolant after t time of natural decay.

4. The method of claim 3, wherein, The reactor coolant system discharges mg primary coolant into the in-containment refueling water tank, and the in-containment refueling water tank discharges mg primary coolant, which is repeated according to a fuel cycle period.

5. The method of claim 3, wherein, The c Bq / g is greater than or equal to 60000 Bq / g.

6. The method of claim 3, wherein, The total amount of tritium in the primary coolant discharged into the in-containment refueling water tank is mc.

7. The method of claim 3, wherein, The calculation formula of the total amount of tritium Q in the in-containment refueling water tank is: W is the total amount of tritium in the in-containment refueling water tank after the primary coolant is discharged into the in-containment refueling water tank in the last fuel cycle period, and the unit is Bq; M is the water capacity of the in-containment refueling water tank, and the unit is g; λ is the decay constant of tritium, ln2 / 12.3≈0.0564; t is the storage time, and the unit is year; c is the tritium concentration of the primary coolant, and the unit is Bq / g. The tritium concentration in the in-containment refueling water tank is Q / M.

8. The method of claim 3, wherein, The total amount of tritium in the water discharged from the in-containment refueling water tank is mQ / M.

9. The method of claim 3, wherein, The total amount of tritium in the in-containment refueling water tank is mc-mQ / M.

10. The method of claim 3, wherein, ​

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