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

Abstract

A method for balancing the lithium content of an ion exchange resin connected to a primary circuit of a nuclear power plant is proposed, the method comprising: obtaining a measurement representative of a lithium concentration in the primary circuit, and a continuous injection of lithium hydroxide into the primary circuit, in which method: a lithium hydroxide injection rate is adjusted as a function of the measurement obtained so as to maintain a lithium balance in the primary circuit. An injection device suitable for implementing this method is also proposed. Abstract figure: Figure 2

Description

Title of the invention: Device and method for lithium balancing of an ion exchange resin by continuous injection Technical field

[0001] The present disclosure relates to the field of nuclear chemistry. It relates more specifically to a method 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 (PWR), 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 stopping energy production.

[0003] The balancing of the water chemistry in the primary circuit is done using demineralizers comprising 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 operations, to wait to see the results by chemical analyses, to analyse the results, then to start again until the resins are correctly 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 make a demineralizer unavailable, the doubling of which is a safety criterion. Summary

[0006] The present disclosure improves the situation.

[0007] A method for balancing the lithium content of an ion exchange resin connected to a primary circuit of a nuclear power plant is proposed, 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, process in which: 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 one another or in combination with one another:

[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 measurement representative of the lithium concentration in the primary circuit is a measurement of the conductivity of the primary circuit.

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

[0013] In one example, the 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, there is provided an injection device comprising: a reservoir comprising lithium hydroxide, and a pumping system for adjusting a lithium injection flow rate to a primary circuit of a nuclear power plant, and a pumping system control module.

[0016] In one example, the device comprises an agitator. In one example, the control module of the pumping system 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 The computer program may include an instruction for applying a control instruction to 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, a non-transitory recording medium, readable by a computer, on which such a program is recorded is provided. Brief description of the drawings

[0021] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which: Fig.l

[0022] [Fig.l] is a simplified diagram of an example of a volumetric and chemical control circuit (RCV) 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 to 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 process lithium balancing according to the proposed technique. Description of the embodiments

[0026] In the following description, identical 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 [Fig.l].

[0029] The water in the primary circuit 1 (RCP) of a nuclear reactor must be completely free of pollutants harmful to the lifetime of the materials constituting the circuit. To achieve this, in 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 there by a purification system formed of demineralizers 3a, 3b containing ion exchange resins. These purification devices have the function of retaining all the ions or species dissolved in the water in the primary circuit. The RCV circuit further comprises 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 balloon 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 of the primary circuit. The pH is maintained by injecting a base. In pressurized water reactors (PWR), this is lithium ion with the chemical formula Li-OH and enriched in Li-7. The concentration of lithium ions reflects the pH and is a chemical parameter monitored for nuclear safety purposes with the objective of preserving the constituent materials of the primary circuit. This preservation objective aims to guarantee that these materials are not altered in order to ensure the liquid containment of fluids with safety and environmental issues.

[0031] In current nuclear power plants, the 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 the lithium ions contained in the water in the primary circuit and thus destabilizing its pH. Pre-saturated ion exchange resins have a cost more than 10 times higher than that of so-called "conventional" or "H-OH" resins retaining all ions including lithium. In addition, it frequently 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 its 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 the 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 injections of lithium present several constraints.

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

[0035] Each injection of lithium hydroxide carries significant risks in terms of nuclear safety. The injected lithium hydroxide consists of water enriched with lithium but without boric acid. Excessive injection could therefore reduce the concentration of boric acid in the primary circuit, an essential element for controlling the reactivity of the reactor core. For this reason, each manual injection of lithium hydroxide into the nuclear reactor must be meticulously controlled. For each lithium hydroxide preparation, The injection requires a volume of water of 200 to 1000L. After the injection of this solution, a chemical analysis is carried out to evaluate the concentration of lithium ions in the water of the primary circuit. If this first injection does not allow the desired level to be reached, the process is repeated: a new preparation of lithium ion is carried out, followed by a new injection and a new analysis. This continuous cycle of preparation, injection, and analysis allows to maintain the required chemical balance involves many human operations, inherently presenting an impact on the human resources allocated to the management of the reactor 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 risks associated with it.

[0038] At the Tricastin CNPE, 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 additional water addition. However, this approach remains limited because the complete saturation of a resin would require a maximum volume of 650 L with a lithium hydroxide concentration of 100g / L. Balancing a demineralizer in this way therefore induces the same impacts as using the conventional method implemented 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. This process is, however, 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 [Fig.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 to this same circuit.

[0042] As illustrated in [Fig. 2], the proposed technique can be implemented for example at the level of the RCV circuit, 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 injection flow rate of lithium ion 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 numerous advantages.

[0044] In particular, it makes it possible to resaturate an ion exchange resin 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 makes it possible to keep a demineralizer in service even if partially or totally delithiated, thus maximizing the availability of the purification means and guaranteeing 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, whereas 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 cancels 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 risks of operational errors.

[0049] The proposed technique guarantees better stability of the pH of the primary circuit in 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 configurations of reactors using lithium hydroxide for pH regulation in the primary circuit and can be transposed to the injection of potash into 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 ion, an injection device having similarities with those dedicated to the continuous injection of zinc acetate and already implemented in the French nuclear fleet. However, notable differences exist, in particular in terms of desirable injection flow rates and desirable volume. For example, desirable flow rate values ​​for the 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, whereas zinc acetate injection devices have a flow rate range of 0 to 1.5 L / h and a 60L reservoir, which is unsuitable for both the injection of lithium ion and the co-injection of zinc acetate and lithium ion.It should be noted that zinc acetate aims at the passivation of materials and the improvement of radiation protection but does not affect the management of the pH 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 the 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 indicator of operation of an injection pump, a setpoint or measured value of the injection flow rate and conductivity measurements.

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

[0056] In the event of an unexpected interruption of the lithium injection, for example due to a malfunction of an injection pump, the concentration of lithium ions in the water of 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 injection of lithium.

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

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

[0059] Alarm thresholds can be set to automatically signal when the lithium concentration approaches the prescribed operational limits. Preliminary studies highlight the importance of this continuous monitoring, revealing that the prescribed limits can be reached quickly - the low limits within 5 hours in the event of interruption of the injection and the high limits within 30 minutes in the event of saturation. As an 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 having an internal diameter of 600 mm and a height of 750 mm, for a total capacity of 200L has proven practical to use. The tank can be equipped with a lockable hatch at the top to ensure the safety and purity of the contents. The tank can 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 purpose. 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 was 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 connecting 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 control of the pumping system according to the measurements representative 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 operating reference of the reactor concerned. For example, the range of use of the injection device covers that of the flow rates for the injection of zinc acetate.

[0065] By way of example, the pumping system may comprise a peristaltic pump allowing a variable lithium injection flow rate in a range of 0 to 30 L / h. For increased security, 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. The connection of the pumping system to the conductivity meter in order to allow automatic regulation of the injection flow rate as a function of the conductivity measurements represents a perspective for the development of the proposed technique.

[0066] The injection device may further comprise a relief valve for ensure the protection of 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 to this use.

[0067] In addition, the device can be equipped with a set of valves intended for injection or recirculation lineage at zero flow. These valves make it possible to control and direct the flow of lithium hydroxide, thus providing operational flexibility and the possibility of adapting the injection process according 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 further 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 carriage suitable for accommodating the injection device is now described.

[0071] The trolley is constructed of high-density polyethylene and reinforced by a steel frame, thus combining lightness and robustness. This specific configuration facilitates the movement of the device from one room to another while ensuring its durability. The dimensions of the trolley are adapted to allow easy passage through standard doors, optimizing its mobility in various locations of the installation.

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

[0073] The wheels of the trolley are advantageously lockable in order to ensure the stability of the device and prevent any accidental movement during injection operations, thus reinforcing safety during its operation.

[0074] Finally, the device may comprise 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 comprise a drain nozzle as well as a line connected to the tank of the device to drain it.

[0075] The present disclosure is not limited to the examples described above, only by way of example, but it encompasses all the variants 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, wherein 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.

10. A device according to claim 8 or 9, wherein the device is removably connected to the primary circuit and / or wherein the device is movable.

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