Device and method for the lithium balancing of an ion exchange resin by continuous injection

Abstract

The invention relates to a method for the lithium balancing of an ion exchange resin (3a, 3b) connected to a primary circuit (1) of a nuclear power plant, the method comprising: obtaining (20) a measurement representative of a lithium concentration in the primary circuit; and continuously injecting (21) lithium hydroxide intended for the primary circuit, in which method: an injection flow rate of the lithium hydroxide is adjusted on the basis of the measurement obtained, so as to maintain a lithium balance in the primary circuit. The invention also relates to an injection device suitable for implementing this method.

Description

Description Device and method for lithium balancing of an ion exchange resin by continuous injection Technical field

[0001] This disclosure relates to the field of nuclear chemistry. More specifically, it relates to a process for balancing lithium in an ion exchange resin, as well as an injection device. Prior art

[0002] To protect the equipment present in the primary circuit of a nuclear power plant (circuit with radioactive fluids), it is necessary to control the pH of the water circulating in the primary circuit. Boron, present to control fission in a pressurized water reactor, is neutron-absorbing and acidic. The addition of a strong base helps to counterbalance this acidity. In pressurized water reactors (PWRs), the strong base added is lithium hydroxide (Li-OH): this is called "Boron / Lithium coordination". Failure to comply with the parameters of this coordination can lead to the shutdown of energy production.

[0003] The primary circuit water chemistry is balanced using demineralizers containing resins specifically designed to control the concentrations of different chemical compounds. To function optimally, these resins must have a precise lithium balance.

[0004] This balancing has been achieved so far by means of punctual injections. To carry out these injections, it is necessary to carry out valve closing and opening maneuvers, wait to see the results through chemical analyses, analyze the results, and then start again until the resins are properly balanced.

[0005] These current processes are long and costly, involve significant human resources and analysis times, as well as risks of dilution of the primary circuit by over-injection of water devoid of boric acid with an impact on fission control. In addition, they temporarily render unavailable a demineralizer, the doubling of which is a safety criterion. Summary

[0006] This disclosure improves the situation.

[0007] A method is proposed for balancing the lithium content of an ion exchange resin connected to a primary circuit of a nuclear power plant, the method comprising: obtaining a representative measurement of a lithium concentration in the primary circuit, and a continuous injection of lithium hydroxide into the primary circuit, in which method: a lithium injection rate is adjusted according to the measurement obtained so as to maintain a lithium balance in the primary circuit.

[0008] The features set out in the following paragraphs may, optionally, be implemented, independently of each other or in combination with each other:

[0009] In one example, the injection of lithium is carried out in a sampling circuit connected to the primary circuit.

[0010] In one example, the representative measurement of lithium concentration in the primary circuit is a measurement of primary circuit conductivity.

[0011] In one example, the lithium injection is carried out in synchronization with the operation of a primary circuit purification system.

[0012] In one example, lithium hydroxide is co-injected with at least one compound selected from boric acid and zinc acetate.

[0013] In one example, co-injection is performed using a single injection device.

[0014] In one example, the ion exchange resin is maintained in operation in a lithium unsaturated state without disturbing the lithium balance in the primary circuit.

[0015] According to another aspect, an injection device is proposed comprising: a reservoir comprising lithium hydroxide, and a pumping system for adjusting an injection flow rate of lithium hydroxide to a primary circuit of a nuclear power plant, and a control module for the pumping system.

[0016] In one example, the device includes an agitator. In one example, the pumping system control module is further configured to control the agitator.

[0017] In one example, the tank has a volume greater than or equal to 10L, preferably greater than or equal to 50L, more preferably greater than or equal to 100L.

[0018] In one example, the device is removably connected to the primary circuit.

[0019] In one example, the device is mobile.

[0020] According to another aspect, a computer program is provided comprising instructions for implementing all or part of a method as defined herein when this program is executed by a processor. Such a computer program may thus comprise an instruction for recording a measurement representative of the lithium concentration in the primary circuit, the execution of the recording instruction being able, for example, to be repeated over time so as to make it possible to obtain a series of time-stamped measurements. Alternatively, such a computer program may comprise an instruction for applying a control instruction for the pumping system, the control instruction being able, for example, to be set by an operator based on a measurement or a series of measurements available. According to another aspect, it is proposed a non-transitory, computer-readable recording medium on which such a program is recorded. Brief description of the drawings

[0021] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which: Fig. 1

[0022] [Fig. 1] is a simplified diagram of an example of a volumetric and chemical control (VCC) circuit interfacing with a primary circuit of a nuclear installation of the Pressurized Water Reactor (PWR) type. Fig. 2

[0023] [Fig. 2] is a schematic diagram of a continuous injection of lithium hydroxide into the primary circuit of a nuclear installation according to one embodiment. Fig. 3

[0024] [Fig. 3] shows an injection device according to one embodiment. Fig. 3

[0025] [Fig. 4] is a flowchart representing the general principle of a lithium balancing process according to the proposed technique. Description of the embodiments

[0026] In the following description, like reference numerals designate identical elements or elements having similar functions.

[0027] The present disclosure relates to a technique for balancing lithium in an ion exchange resin connected to a primary circuit of a nuclear power plant. This innovative technique is distinguished by its efficiency and operational simplicity.

[0028] Reference is made to Figure 1.

[0029] The water in the primary circuit 1 (RCP) of a nuclear reactor must be completely free of harmful pollutants for the lifetime of the materials constituting the circuit. To achieve this, on Pressurized Water Reactors, the water in the primary circuit is continuously extracted by a volumetric and chemical control circuit 2 or RCV circuit at the interface with the reactor. The water thus extracted is purified by a purification system formed by demineralizers 3a, 3b containing ion exchange resins. The function of these purification devices is to retain all the ions or species dissolved in the water in the primary circuit. The RCV circuit also includes an effluent discharge line 4, a water makeup line 5, a boron makeup line 6 and a line 7 allowing the injection of reagents via a small injection tank 8.

[0030] In addition to this requirement, the pH of the water in the primary circuit must be maintained at precise values ​​in order to control the risks of corrosion in the primary circuit. Maintaining the pH is obtained by injecting a base. In pressurized water reactors (PWR), it is lithium ion with the chemical formula Li-OH and enriched in Li-7. The lithium ion concentration reflects the pH and is a chemical parameter monitored for nuclear safety purposes with the objective of preserving the materials constituting the primary circuit. This preservation objective aims to guarantee the non-alteration of these materials in order to ensure the liquid containment of fluids with safety and environmental issues.

[0031] In current nuclear power plants, demineralizers contain ion exchange resins that are saturated with lithium ions before the demineralizers are put into service. This saturation is intended to prevent the resins from retaining lithium ions contained in the water in the primary circuit and thus destabilizing its pH. Presaturated ion exchange resins are more than 10 times more expensive than so-called "conventional" or "H-OH" resins, which retain all ions, including lithium. In addition, it often happens during operation that a resin, although presaturated, loses some of the lithium ions it initially contained. When it is put back into service, it then retains the lithium ions from the water it purifies until it regains saturation. Without action, this would lead to an unacceptable drop in the pH of the water in the primary circuit.

[0032] To avoid unacceptable downward drifts in lithium content, it is then necessary to carry out manual and punctual injections of lithium ion to compensate for the retention of lithium ions by the demineralizer during its resaturation phase.

[0033] Manual lithium injections have several constraints.

[0034] Operating protocols require that at least one demineralizer be in operation at all times to ensure the safety and efficiency of the process. However, implementing a manual lithium hydride injection process requires specific valve manipulations to isolate the demineralizer in question until it is effectively saturated and put back into operation, while ensuring that at least one other demineralizer remains in operation throughout the injection process.

[0035] Each lithium injection carries significant nuclear safety risks. The injected lithium consists of lithium-enriched water but without boric acid. Excessive injection could therefore reduce the boric acid concentration in the primary circuit, an essential element for controlling the reactivity of the reactor core. For this reason, each manual lithium injection into the nuclear reactor must be meticulously controlled. For each lithium preparation, the injection requires a volume of water of 200 to 1000L. After injecting this solution, a chemical analysis is carried out to assess the lithium ion concentration in the primary circuit water. If this first injection does not achieve the desired level, the process is repeated: a new lithium preparation is carried out, followed by a new injection and a new analysis.This continuous cycle of preparation, injection, and analysis to maintain the required chemical balance involves numerous human operations, inherently impacting the human resources assigned to reactor management and carrying risks of errors.

[0036] Current lithium balancing practices in nuclear power plants vary depending on the reactor type.

[0037] In the French fleet, with the exception of EPRs, injections are carried out manually via the small injection tank 8 provided in the RCV circuit. These methods induce the constraints previously mentioned, such as the complexity of manual handling and the associated risks.

[0038] At the Tricastin NPP, an innovation was implemented with the connection of a 3L injection tank connected to the return lines of the sampling system. This method reduces the risks of dilution of the primary circuit because the addition of lithium hydroxide is directly integrated into the sample flow, without the need for additional water. However, this approach remains limited because complete saturation of a resin would require a maximum volume of 650 L with a lithium hydroxide concentration of 100 g / L. Balancing a demineralizer in this way therefore has the same impacts as using the conventional method used in the French fleet.

[0039] For Konvoi-type reactors and EPRs, lithium balancing management is different. These reactors have two redundant demineralizers, one of which is in operation while the other is prepared with a resin unsaturated with lithium ions. The latter is saturated with lithium via a connection to a primary effluent discharge line loaded with lithium. However, this process is very slow, taking between two and six months, or even longer, thus limiting the availability of the demineralizer for purification operations. During this time, it is not fully available for purification because it cannot be put into operation.

[0040] These different methods, although functional, have limitations in terms of operational efficiency, risks related to manual interventions, and duration of the lithium saturation process. The need for a more efficient and automated process, such as that described above, is therefore clearly established in the current context of nuclear reactor management.

[0041] The proposed technique is based, as illustrated in Figure 4, on obtaining 20 a measurement of a quantity representative of the lithium concentration in the primary circuit and on the continuous injection 21 of lithium hydride into this same circuit.

[0042] As illustrated in Figure 2, the proposed technique can be implemented for example at the RCV circuit level, by providing a device 9 for measuring a quantity representative of a lithium ion concentration, for example a conductivity meter, which can be connected to the RCV circuit either upstream or downstream of the demineralizers 3a, 3b, as well as by providing a line 10 for continuous injection of lithium ion, again either upstream or downstream of the demineralizers. The lithium ion injection flow rate is adjusted dynamically according to the measurement obtained, thus making it possible to maintain an optimal lithium balance in the primary circuit.

[0043] The proposed technique offers many advantages.

[0044] In particular, it allows an ion exchange resin to be resaturated effectively without disturbing the chemical balance of the primary circuit.

[0045] Furthermore, the proposed technique is distinguished by its speed, requiring from one to ten days maximum for complete saturation, depending on the state of the reactor and the demineralizer. It is significantly faster than known methods, such as resaturation by recovery of primary effluents.

[0046] In terms of equipment safety, although the primary circuit includes two redundant demineralizers, the proposed technique allows a demineralizer to be kept in service even if partially or completely delithiated, thus maximizing the availability of the purification means and ensuring better protection against fission products or other contaminants. This represents a significant advantage in securing the purification means of the primary circuit.

[0047] Compared to manual injection methods, the proposed technique minimizes the risk of heterogeneous dilution of the primary circuit. Indeed, current manual injections require the addition of a large volume of clear water to push the reagent, while the proposed technique reduces this volume to less than 200L per day. Studies have also shown that the impact of extremely low injection rates, of the order of a few liters per hour, on the reactivity of the reactor core is not significant. Finally, the possible addition of boric acid in the solution injected with the proposed technique completely eliminates the risk of dilution, thus contributing to better control of the reactivity of the reactor core.

[0048] The proposed technique simplifies operations by eliminating the need for multiple lineage manipulations and long and complex administrative procedures associated with manual methods. The targeted demineralizer can be kept in operation without lineage modification until it is completely resaturation, thus reducing the human factor and the risk of operational errors.

[0049] The proposed technique ensures better stability of the pH of the primary circuit within the prescribed value ranges, thus limiting the risks associated with reaching concentrations for which the reactor must be shut down for safety reasons and minimizing dosimetry on maintenance activities.

[0050] The proposed technique allows the use of non-lithiated ion exchange resins, which represents a significant economic gain compared to methods requiring lithium pre-saturated resins.

[0051] Finally, the proposed technique applies to different reactor configurations using lithium hydroxide for pH regulation in the primary circuit and can be transposed to the injection of potash in VVER type reactors.

[0052] In a particular example of implementation of the proposed technique, it is possible to use, for the continuous injection of lithium hydroxide, an injection device with similarities to those dedicated to the continuous injection of zinc acetate and already implemented in the French nuclear fleet. However, notable differences exist, particularly in terms of desirable injection flow rates and desirable volume. For example, desirable flow rate values ​​for injection of lithium ion to balance or re-saturate a resin with lithium ions can vary between 2 and 8 L / h for a 1300 MWe reactor, while zinc acetate injection devices have a flow rate range of 0 to 1.5 L / h and a 60L tank, which is unsuitable for both lithium ion injection and co-injection of zinc acetate and lithium ion. It should be noted that zinc acetate is intended for the passivation of materials and the improvement of radiation protection but does not affect the pH management of the water in the primary circuit.

[0053] In a specific implementation example, it is envisaged to combine an injection device mounted on a mobile cart, which can be connected to the existing lines of the primary sampling system, with a continuous measuring device, such as a conductivity meter, to allow direct and continuous injection of lithium into the primary circuit, downstream of the demineralizer. This approach makes it possible to detect saturation of the demineralizer or to identify any anomaly during the injection.

[0054] It is also planned to automatically transmit data relating to the operation of the injection device and measurements from the measuring device to the reactor control room. This continuous monitoring of lithium injection is essential for controlling the evolution of the lithium ion content of the water in the primary circuit. The transmitted data may include, for example, an injection pump operation indicator, a set or measured injection flow rate value and conductivity measurements.

[0055] To illustrate, imagine that at a given moment, a resin in a demineralizer in operation is not saturated with lithium, thus capturing a portion of the lithium ions present in the primary circuit water. In this scenario, a lithium injection rate is carefully selected to precisely compensate for this retention, thus maintaining a stable lithium ion concentration in the primary circuit water.

[0056] In the event of an unexpected interruption in lithium injection, for example due to a malfunction of an injection pump, the lithium ion concentration in the water in the primary circuit begins to decrease. This decrease is due to the fact that the continuous retention of lithium ions by the unsaturated resin is no longer balanced by the lithium injection.

[0057] Conversely, if lithium injection continues after the demineralizer saturation has been reached, the lithium ion concentration in the primary circuit water increases. This occurs because the additional lithium injection is no longer balanced by the retention in the saturated demineralizer.

[0058] The automatic transmission of operational data from the injection device and continuous measurements to the control room allows operators to quickly detect both of the above-mentioned situations: an accidental injection stoppage or saturation of the resin with lithium ions. This facilitates rapid and precise adjustment of the lithium injection rate in response.

[0059] Alarm thresholds can be set to automatically signal when lithium concentrations approach prescribed operational limits. Preliminary studies highlight the importance of this continuous monitoring, revealing that prescribed limits can be reached quickly - the lower limits in 5 hours in case of interruption of the injection and the upper limits in 30 minutes in case of saturation. For example, the SWAN brand conductivity meter, model AMI INSPECTOR, suitable for covering a relevant measurement range from 0 to approximately 50 pS / cm, proves to be a suitable tool for the continuous monitoring of lithium injection, thus ensuring reactive and effective management.

[0060] The proposed technique is adaptable to all reactor configurations provided that volumetric, chemical and sampling control systems are available. This method remains applicable even when the reactor is operating at full power, thus providing essential flexibility and adaptability for optimal management of the primary circuit.

[0061] An example of an injection device suitable for implementing the proposed technique is now described with reference to FIG. 3. It comprises at least one reservoir 11, a pumping system 12, a module 14 for connection to the injection point and a control module (not shown).

[0062] The tank is capable of containing a sufficient quantity of lithium hydroxide to allow the resaturation of a demineralizer. Its capacity may, for example, be greater than or equal to 10 L, preferably greater than or equal to 50 L, more preferably greater than or equal to 100 L. A cylindrical polyethylene tank with an internal diameter of 600 mm and a height of 750 mm, for a total capacity of 200 L, has proven practical to use. The tank may be equipped with a lockable hatch at the top to ensure the safety and purity of the contents. The tank may also be equipped with an agitator 16 to ensure a homogeneous concentration of the lithium hydroxide. For example, a motorized agitator of the MIXEL brand, model Agipro 125, is suitable for this use. For precise monitoring of the liquid level, the tank can be equipped with a level reader (for example by means of graduations every 10L) and / or a counterweight measuring system on a float.Level sensors can also be provided to ensure safety by automatically stopping the pump when a critical high 17 or low 18 level is reached and / or by triggering an alarm on the control box. For example, the tank with a capacity of 200L has been equipped with sensors activated by magnetic balance for a low level set at 21.5L and for a high level set at 189.5L.

[0063] The pumping system coupled to the connection module is capable of allowing the continuous injection of the contents of the tank at an injection point to the primary circuit, according to a controlled flow rate. The connection module comprises a set of hoses and fittings suitable for connection at the injection point. As already indicated, the injection point can be chosen at a sampling line connected to the primary circuit. The pumping system is managed by the control module, which is configured to adjust a command of the pumping system according to the representative measurements of the lithium concentration in the primary circuit, thus ensuring a dynamic and precise adjustment of the injection flow rate.

[0064] The device thus described is capable of allowing the injection not only of lithium hydroxide, but also the injection or co-injection of any other chemical product compatible with the reference system. operating range of the reactor concerned. For example, the operating range of the injection device covers that of the flow rates for the injection of zinc acetate.

[0065] For example, the pumping system may include a peristaltic pump allowing a variable lithium injection flow rate in a range of 0 to 30 L / h. For increased safety, the pumping system may be coupled to an integrating meter for injected volume with an accuracy at least equal to one liter, such a meter making it possible to estimate, by projection, the reaching of saturation and / or to a password system for locking programmed flow rates. Connecting the pumping system to the conductivity meter in order to allow automatic regulation of the injection flow rate according to the conductivity measurements represents a perspective for the development of the proposed technique.

[0066] The injection device may also include a relief valve to protect the circuit to which it is connected against overpressure. This valve has a function of maintaining the safety and integrity of the circuit by regulating the internal pressure. For example, a Stübbe brand relief valve, model DVH 712-R set at 10 bars, is perfectly suited for this purpose.

[0067] Additionally, the device can be equipped with a set of valves for injection or recirculation lineage at zero flow. These valves allow the flow of lithium hydroxide to be controlled and directed, thus providing operational flexibility and the ability to adapt the injection process to specific needs.

[0068] A control box can also be integrated into the device, centralizing the start-up controls for the agitator and the pump and can also include alarm indicators linked to the high or low level of the tank, or to a pump fault. This box not only simplifies the operation of the device but also facilitates responsiveness in the event of anomalies.

[0069] The device can also be mounted on a mobile trolley of suitable dimensions to pass through the doors of the different premises and can be equipped with a removable connector for easy connection with the primary circuit. This configuration allows the same injection device to be made available to several reactors at the same nuclear site to resaturate the demineralizers when necessary, thus maximizing efficiency and reducing the need for multiple pieces of equipment.

[0070] A particular example of a mobile cart suitable for accommodating the injection device is now described.

[0071] The trolley is constructed of high-density polyethylene and reinforced with a steel frame, combining lightness and strength. This specific configuration makes it easy to move the device from one room to another while ensuring its durability. The trolley's dimensions are adapted to allow easy passage through standard doors, optimizing its mobility in various locations within the facility.

[0072] The trolley incorporates a steel tiller that improves maneuverability. This feature facilitates precise positioning and efficient movement of the device when transferring it between different points of use.

[0073] The trolley wheels are conveniently lockable to ensure the stability of the device and prevent any accidental movement during injection operations, thus increasing safety during operation.

[0074] Finally, the device may include a retention tank 15 formed of rising edges which are, for example, integrated into the trolley. Such a retention system, with a volume greater than that of the tank, makes it possible to effectively collect any leaks, in accordance with the regulations on the storage of chemical products. The retention tank may include a drain nozzle as well as a line connected to the tank of the device to drain it.

[0075] This disclosure is not limited to the examples described above, only as an example, but it encompasses all the variations that the person skilled in the art may envisage within the framework of the protection sought.

Claims

Claims

1. Method for balancing the lithium content of an ion exchange resin connected to a primary circuit (1) of a nuclear power plant, the method comprising: obtaining (20) a measurement representative of a lithium concentration in the primary circuit, and a continuous injection (21) of lithium hydride into the primary circuit, method in which: a lithium hydride injection rate is adjusted as a function of the measurement obtained so as to maintain a lithium balance in the primary circuit.

2. Method according to claim 1, in which the injection of lithium hydroxide is carried out in a sampling circuit (2) connected to the primary circuit.

3. Method according to one of the preceding claims, in which the measurement representative of the lithium concentration in the primary circuit is a measurement of the conductivity of the primary circuit.

4. Method according to one of the preceding claims, where the injection of lithium is carried out in synchronization with an operation of a purification system (3a, 3b) of the primary circuit.

5. Method according to one of the preceding claims, where the lithium hydroxide is co-injected with at least one compound chosen from boric acid and zinc acetate.

6. The method of claim 5, wherein the co-injection is performed using a single injection device.

7. A method according to any preceding claim, wherein the ion exchange resin is maintained in operation in a state of lithium unsaturation without disturbing the lithium balance in the primary circuit.

8. Injection device comprising: a reservoir (11) comprising lithium hydroxide, a pumping system (12) for adjusting an injection flow rate of lithium hydroxide to a primary circuit of a nuclear power plant, and a control module for the pumping system.

9. Device according to claim 8, in which the reservoir has a volume greater than or equal to 10L, preferably greater than or equal to 50L, more preferably greater than or equal to 100L. Device according to claim 8 or 9, wherein the device is connected to the primary circuit in a removably manner and / or wherein the device is movable.

Images