Nuclear reactor protection device

Abstract

The invention relates to a low-power reactor with a high-temperature coolant for nuclear power engineering. The high-temperature coolant device for protecting a nuclear reactor comprises a power supply network, an absorption rod (4, 4a, 4b) which is made to be inserted into the core for emergency protection and is equipped with an actuator with a holding electromagnet for fixing the rod in a given position, an additional emergency protection absorption rod (5), and a universal electrical disconnector (11) for the power supply network current. The power supply network is designed so that the current flows through the windings of the holding electromagnets of all the absorption rods in sequence. In addition, the circuit of the current comprises at least one direct-acting thermal current disconnector (8) located in a jacket isolated from the coolant in the hot coolant flow or at the core outlet, and at least one electrical circuit breaker (11) installed in the jacket of the absorption rod (5), isolated from the coolant, and located above the absorption rod (5), which comprises a temperature-sensitive current disconnector (9) with a fusible lock. The technical result is to ensure that all absorption rods are triggered in an emergency.

Description

Technical Field

[0001] The present invention relates to nuclear power engineering, primarily to low-power reactors with high-temperature coolants (liquid metal, molten salt, helium, supercritical pressure water) having a sufficient margin for the operability of the fuel elements in terms of temperature compared to the maximum coolant temperature at the core outlet. Background Art

[0002] The most serious accidents in reactors (which may lead to fuel damage and radioactive release) are related to overheating of fuel elements (FE) beyond operational safety limits when the core outlet coolant temperature exceeds the permissible value. The cause of this temperature increase may be related to a reduction in coolant flow, or to an increase in reactor power output, or to a deterioration in the heat dissipation of the FE, coolant, or to a combination of the aforementioned causes.

[0003] In order to avoid such accidents in all reactors, an electrical signal is generated in the reactor control and protection system (CPS) that the coolant temperature is higher than the set value, which shuts down the nuclear reactor (NR) by triggering the emergency protection (EP) of the reactor. According to this signal, the electromagnet windings that fix the EP absorber rod (AR) outside the core are de-energized, and the emergency protection absorber rod (EP AR) is inserted into the core and stops the fission chain reaction in the reactor under the action of springs, gravity or Archimedean force (if the EP absorber rod is buoyant in the coolant and placed under the core in a charged state) (see I.Ya. Melyanov, AI Evanov and LV Konstantinov, "Scientific and Technical Foundations of Nuclear Reactor Control", Moscow, Energoizdat, 1981). This is a traditional CPS system.

[0004] In this conventional CPS system, despite the necessary redundancy, when the CPS fails multiple times or intentionally prevents malicious interference with the CPS circuit, there is still a possibility that the emergency protection absorption rod triggering failure may occur due to the failure of the control electrical signal. In addition, the EP AR efficiency in the conventional nuclear reactor control and protection system is usually less than the temperature and power effects of the burnup, reactivity, and the total reactivity margin of the power control, which is compensated by the AR that performs these functions (the AR includes the spacer rod and the control rod). Therefore, if the reactivity margin compensated by these ARs is released without authorization (multiple faults in the control system, intentional preventive malicious interference with the CPS circuit), the core temperature will inevitably rise above the allowable value, and the fuel will melt, resulting in a serious accident.

[0005] Passive EP systems are known which are triggered by an increase in coolant temperature and which eliminate the above mentioned disadvantages of conventional EP systems associated with possible failure of the electrical signal triggering the EP when the coolant temperature increases above a set value. This is a direct acting EP.

[0006] In a direct-acting passive EP system, a device that fixes the emergency protection absorber rods to the outside of the core (e.g., a fusible lock, a bimetallic lock, a device based on a shape memory alloy, an electromagnetic lock made of a material with a corresponding Curie temperature, etc.) is connected to the CPS through an electrical circuit and is directly triggered when the coolant temperature rises above a set value. Such devices are described in the IAEA document "Passive Shutdown Systems for Fast Neutron Reactors" (IAEA Nuclear Energy Series No. NR-T-1.16, Vienna, 2020). At the same time, as in the case of the conventional EP described above, the emergency protection absorber rods are inserted into the core under the influence of springs and / or gravity.

[0007] The disadvantage of the direct-acting passive EP system is that it can only be considered as an additional emergency protection (AEP) to the conventional AS system with electromagnetic AR holding, which is triggered not only by the electrical signal of temperature increase exceeding the set value, but also by other EP electrical signals (increase in NR power output, shortening of reactor cycle, other process signals such as pressure increase, pump shutdown, etc.), and when such direct-acting passive EP is triggered, not all ARs electromagnetically held in a given position will be triggered, including ARs that compensate for burnup, poisoning, temperature and power reaction effects, and reaction margins for power control. If these rods are withdrawn from the core without authorization and the entire reaction margin is released (multiple faults in the control system, intentional preventive malicious hidden interference with the EP circuit), the temperature in the core will inevitably rise above the allowed value, and the fuel will melt, resulting in serious consequences.

[0008] According to US Pat. No. 4,076,587 (G21C7 / 12, G21C9 / 00, G21C9 / 027; published on Aug. 22, 1972), a fusible device and its use in the design of an NR emergency shutdown system are known. This fusible device for an automatic emergency shutdown system of fast reactors keeps the neutron absorber above the core under normal operating conditions, but when the operating characteristics (e.g., temperature) reach a level above a specified threshold, the neutron absorber is released in the form of a free fall to the lower part of the casing at the level of the reactor core due to the melting of the fusible located below the neutron absorbing mass. In this case, the neutron absorber is located inside the casing, isolated from the coolant, and placed in a fuel tank.

[0009] The disadvantage of this technical solution is that when the coolant temperature rises above a certain value and triggers the fusible device, only the neutron absorber located in the casing jacket above the fusible device is inserted into the core, while all other ARs of the conventional CPS are held in a given position by electromagnetic locks. If the electrical signal triggered by the EP fails, it will not be inserted into the core, which may cause the fuel to melt.

[0010] According to Russian patent No. RU2539356 (G21C7 / 00; published on January 20, 2015), a NR protection device for fast-neutrons is known, in which, in at least one EP AR, when the coolant temperature increases to exceed a given value, the protection device ensures that all EP ARs are triggered in the event of a triggering electrical signal failure or a EP rod driver failure. This is achieved by using a thermal disconnector of the EP AR, which uses a material that loses its magnetic properties when the temperature of the sodium leaving the core rises above the Curie temperature. In this case, the EP absorption rod (or multiple absorption rods) are inserted into the core together with the armature of the holding electromagnet by the action of gravity and acceleration springs, and when the armature of the thermal disconnector falls together with the first EP rod (the temperature of the magnetic circuit exceeds the Curie point), due to the disconnection of the relay and due to the disconnection of the circuit of the winding (coil) of the holding electromagnet of the remaining EP rod, the remaining EP rods (the temperature of the coolant in the magnetic circuit has not yet reached the Curie point) are also inserted into the core.

[0011] This technical solution can be considered as the prior art closest to the present invention, and its disadvantages include the following points.

[0012] Firstly, this known fast neutron NR protection device can be used only in reactors using coolants with dielectric properties. In case of using conductive liquid metal coolants in fast reactors, the relay contacts will always be closed, since the magnetic circuit and the relay are installed in the reactor vessel filled with liquid metal coolant, as disclosed in the above-mentioned patent. Placing an EP AR with a thermoelectric isolating switch (relay) in the reactor using a sheath isolated from the coolant, as shown in patent RU2539356, and ensuring the possibility of partial refueling by lateral movement of the EP rod located on the rotating plug, is technically not feasible.

[0013] The electrical connection of the moving contacts of the relays to the windings (coils) of the electromagnets that hold the EP rods is ensured by flexible cables cleaned with liquid metal coolant. Ensuring their reliability under reactor conditions is a tricky problem.

[0014] Even if a coolant with dielectric properties is used in the reactor, the reliability of the electrical contacts in the relays is difficult to guarantee due to vibration, corrosion, radiation, and thermo-mechanical effects, since the relays are placed in a hot coolant flow with high neutron and gamma radiation fields, and sparks will be generated during multiple EP triggering.

[0015] Moreover, when the NR protection device claimed in patent No. RU2539356 is triggered by exceeding the Curie point, the AR of the conventional CPS, whose actuator is equipped with an electromagnetic lock, fixes it in a given position, intended to compensate for the reactivity margin of the burnup, poisoning, temperature and power reaction effects, and the power control as well as the EP AR are not inserted into the core. This leads to the possibility of a "drift" of the reactor if all the controlled ARs of the conventional CPS "self-move" upwards without authorization (multiple faults in the control system, deliberate preventive malicious covert interference with the CPS circuits). It is impossible to increase the number of EP absorption rods of the declared type to cover the burnup, temperature and power reactivity effects and the reactivity margin of the power control (compensated by the AR of the conventional CPS), since such an increase can only be achieved by reducing the number of ARs of the conventional CPS. Therefore, this known protection can only supplement the conventional CPS.

[0016] Placing the armature and magnetic circuit made of materials with appropriate Curie temperatures above the EP AR, away from the core coolant outlet, results in a temperature lag in EP triggering, which could cause fuel melting in a rapid emergency process.

[0017] Finally, a disadvantage of the closest prior art is the need to use additional power supplies, switchgear and other necessary components in the known emergency protection devices, which components have their own failure probability, thus reducing the reliability of the device. Summary of the invention

[0018] The problem to be solved by the present invention is to eliminate the above-mentioned disadvantages of the patents of the same family and improve the safety of the nuclear reactor.

[0019] The technical result of the proposed invention is to ensure that all absorber rods (AR) of the conventional EP system are triggered in the event that the coolant temperature rises above the set value, and in the event of a failure due to some reason, all ARs of the conventional EP system and all other ARs intended to compensate for burnup, temperature and power reactivity effects, poisoning effects and reaction margins for power control are triggered by electromagnetic holding of the ARs, whose drivers are equipped with electromagnets that can hold these ARs in a given position, because the circuits in the windings (coils) of the holding electromagnets of all ARs of the conventional CPS are open, regardless of the function they perform, using direct-acting thermal current disconnectors (TCD) and electrical current disconnectors (ECD), which are triggered when the ARs of the direct-acting AEP (excluding the drivers on the reactor cover) enter the core.

[0020] The use of the claimed NR protection device based on the increase of the coolant temperature above the set value will be particularly effective for achieving another technical result related to the above technical result, which aims to improve the safety of the reactor with a reaction margin significantly exceeding the effective fraction βeff of delayed neutrons, which is higher than the EP AR efficiency in the conventional CPS. In particular, the possibility of fast neutron reactor excursion is excluded when using the proposed NR protection device if the entire reaction margin is released without authorization due to multiple faults in the control system or intentional preventive malicious covert interference with the CPS circuit. This will be ensured by the negative feedback effect, the technical limitation of the rate of withdrawal of the absorber rods from the core, and the placement of the TCD, ECD and AEP rods inside the reactor, which makes them unable to be interfered with by humans.

[0021] Brief description of the invention

[0022] In order to solve the above problems and achieve the specified technical effects, it is proposed that current flows sequentially through the common electrical disconnector (CED) of the conventional CPS and an electrical signal is applied thereto for EP triggering. The holding electromagnet windings of all AR drives of the conventional EP system and the holding electromagnet windings of the remaining AR drives of the conventional CPS, regardless of their functions (automatic or manual power control, compensation of various reaction effects), are equipped with holding electromagnets and possibly springs, which are connected in series with the coolant (similar to a thermocouple measuring the coolant temperature) through a thermal current disconnector (TCD) installed in a sheath. The core outlet is connected to the heat exchanger inlet (steam boiler inlet) at any convenient place in the hot coolant flow, or for a direct cycle NR, to the NR outlet of the turbine, and when the coolant temperature exceeds a set value, a direct-acting AEP rod is inserted into the core through the current disconnector (ECD), thereby triggering the current disconnector (ECD).

[0023] To this end, the claimed protection device for a nuclear reactor with a high-temperature coolant comprises a current supply network, controllable absorber rods with actuators equipped with acceleration springs for release into the core and holding electromagnets for holding them in a given position, additional emergency protection absorber rods, and a common electrical isolation of the supply network through which the current flows continuously through the windings of the holding electromagnets of all controlled absorber rods. The controlled absorber rods are made in such a way that, in the case of normal operation of the nuclear reactor, they can be inserted into and withdrawn from the core of the nuclear reactor, and, in the case of de-energization of the emergency signal and the windings of the holding electromagnets, the rods can be inserted into the core by means of acceleration springs or by gravity. The current circuit of the electromagnet flowing through the winding of the holding electromagnet includes at least one direct-acting thermal current isolating switch, which is made to disconnect the current circuit when the coolant temperature rises above a set value, and at least one electrical isolating switch is installed in the jacket of the additional emergency protection absorption rod, isolated from the coolant, and above the additional emergency protection absorption rod, a temperature-sensitive current isolating switch with a fusible lock is provided. At least one of the direct-acting thermal current isolating switch is installed in the jacket isolated from the coolant, in the hot coolant flow, or at the core outlet.

[0024] Therefore, when the coolant temperature rises above the set value, the triggering of any TCD or any ECD of any AEP rod will result in the triggering of all ARs of the conventional CPS, whose actuators are equipped with holding electromagnets.

[0025] The claimed nuclear reactor protection device and possible embodiments thereof are explained in more detail below with reference to the accompanying drawings, but the invention is not limited thereto. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a reactor emergency protection device that is directly triggered by the coolant temperature rising above a set value is shown.

[0027] Figure 2 A possible embodiment of an insulating sheath with an AEP rod in standby mode is shown, wherein a fusible lock of a temperature-sensitive current disconnector (TSCD) is located below the AEP rod and an ECD is located above the AEP rod.

[0028] Figure 3 Shown according to Figure 2 Bottom view of a possible embodiment of an insulating sheath.

[0029] The following components are marked with their locations in the figure:

[0030] 1: Power supply;

[0031] 2: General electrical isolating switch;

[0032] 3: trigger the control signal of EP;

[0033] 4: Traditional EP absorption rod;

[0034] 4a: rods to compensate for burnup, poisoning and temperature effects;

[0035] 4b: control rod;

[0036] 5: AEP absorbent core;

[0037] 6: AEP absorption rod sheath;

[0038] 7: Holding electromagnet;

[0039] 8: Thermal current isolation switch;

[0040] 9: Thermal isolation switch with fusible lock;

[0041] 10: AEP absorption rod lower tail piece;

[0042] 11: Current isolating switch;

[0043] 12: Current isolating switch body;

[0044] 13: Current isolating switch cable;

[0045] 14: Fusible pin;

[0046] 15: Fusible pin spring;

[0047] 16: support ring;

[0048] 17: Acceleration spring. DETAILED DESCRIPTION

[0049] The nuclear reactor protection device claimed to be protected is shown as follows Figure 1 As shown, it includes a power supply network, specifically a power supply 1; a general electrical isolating switch 2 for specifying the current of the power supply network, whose operation is controlled by a control signal 3 for triggering a nuclear reactor EP; a conventional CPS and EP absorption rod (hereinafter also referred to as AR); and an AEP absorption rod 5 (hereinafter referred to as AEP AR 5), which is placed in a sheath 6 of the AEP absorption rod.

[0050] In this application, the AR of the conventional CPS and EP is the absorber rod 4 of the conventional EP, the rod 4a that compensates for burnup, poisoning and temperature effects, and the control rod 4b (see Figure 1 ). In other words, in this application, AR refers to all absorber rods except AEP AR 5, which are inserted into the core in an emergency (for emergency protection purposes), regardless of the specified insertion mechanism used therein, the insertion rate and the actuator that initiates the insertion. In this application, AEP AR 5 means absorber rod, which is different from AR, which is why in the figures, different reference numerals are used for absorber rods of conventional CPS and EP and AEP absorber rods.

[0051] The AR comprises an actuator with holding electromagnets 7 to hold the absorber rods in a given position. In addition, some or all ARs may comprise acceleration springs to accelerate the insertion of the absorber rods into the core.

[0052] If an emergency occurs and the electrical signal cannot trigger the EP due to the coolant temperature rising above the set value, the AR is triggered to be inserted into the core by the thermal current isolation switch 8 (hereinafter also referred to as TCD 8). In this case, the TCD 8 is installed in a sheath or pipe (not shown in the figure), isolated from the coolant, located in the hot coolant flow or at the core outlet. The actuator that causes the closing / opening of the contacts of the TCD 8 at the required temperature can be a bimetallic plate or a plate made of a shape memory alloy known to those skilled in the art. Bimetallic fuses that protect networks from overcurrents are widely used in electrical engineering, and reversible shape memory alloys are used in fire alarm detectors. Among the intermetallic copper and manganese compounds, compounds with a martensitic transformation temperature suitable for the purpose under consideration can be selected. In order to prevent oxidation of the electrical contacts, if they do not contain a precious metal coating, the inner cavity of the TCD 8 sheath is filled with an inert gas, or a mercury sealed switch can be used.

[0053] The AEP AR 5 is placed in a jacket 6, isolated from the coolant (without the actuator on the reactor cover), and is kept in the upper position by a thermal disconnect switch 9 (hereinafter also referred to as TSCD 9) with fusible locks, which mechanically disconnects the lower tail piece 10 of the AEP AR 5 from the wall of the insulating jacket when the coolant temperature rises above a set value. The TSCD 9 is installed in the jacket 6, at the level of the hot coolant outlet of the core below the AEP AR 5.

[0054] The length of the sheath 6 is selected to ensure insertion of the AEP AR 5 when the TSCD 9 is triggered to the bottom of the core.

[0055] All ARs equipped with electromagnetic locks that fix them in a given position are inserted into the core to prevent electrical signal failure that triggers EP through a current isolating switch 11 (hereinafter also referred to as ECD 11) in case of emergency. Meanwhile, the ECD 11 having contacts that reduce heat and radiation effects is installed in the upper part of the sheath 6, above the AEP AR 5. The ECD 11, which is triggered by the mechanical movement of the contact movement, is widely used in the engineering field (e.g., door open / close signal device).

[0056] Preferably, the ECD 11 is located in an ECD body 12 within the sheath 6, and an ECD cable 13 extends from the ECD body 12 to connect the ECD 11 to a power supply network.

[0057] The fusible lock of TSCD 9 may include a fusible pin 14 and a spring 15 for the fusible pin, wherein the fusible pin 14 abuts against a support ring 16 located in the lower tail piece 10 of the AEP AR 5 in an upper position in order to retain the AEP AR 5. The melting point of the fusible lock material is selected to exclude false triggering of the AEP, especially in the case of a triggering temperature exceeding the conventional EP due to an increase in coolant temperature. For example, PSr 65.690-710 silver solder can be used to make the fusible pin 14. In order to confirm the operability of the lock design with the fusible pin 14 and the spring 15 for the fusible pin, multiple tests were conducted with the specified material of the fusible lock to confirm the ability to retain the AEP AR 5 model under the influence of an earthquake and to determine the triggering time at different coolant heating rates. Based on the test results, a TSCD 9 fusible lock design embodiment was selected, which met the specified requirements for the triggering temperature (about 700°C) and provided an acceptable triggering time.

[0058] In order to accelerate the triggering of the AEP ARs 5, they may include an acceleration spring 17 which is fixed in a compressed position when in standby mode.

[0059] The core ends of the TCD 8 cable and the ECD 13 cable are connected to the corresponding terminal boxes. These cables leading out from the terminal boxes are connected in series in a closed circuit without any switching device, through which the power supply 1 of the conventional CPS passes through the universal electrical disconnector 2, which disconnects the entire circuit when it receives an electrical signal from the CPS to trigger the EP, and the current of the windings of the holding electromagnet 7 of all ARs, regardless of their functions, can perform the emergency protection function in the event of an emergency. Emergency flows.

[0060] Conversely, when any AEP AR 5 falls, the upper tail piece of the AEP AR 5 opens the contacts of the ECD 11 and the current flows sequentially through the TCD 8, the universal electrical disconnector 2 and the windings of the holding electromagnets 7 of all AR actuators, regardless of their function (automatic or manual power control, compensation of various reactive effects).

[0061] This NR protection device does not interfere with the operation of the conventional EP system and all other AR systems for any electrical signals for triggering the AR, these come from the CPS, according to the algorithm embedded therein, to the common electrical disconnect switch 2, connected in series to the closed circuit of the current flowing in series through the windings of the holding electromagnets 7 of all ARs. The emergency protection will also be triggered by the direct-acting TCD 8 or ECD 11 of the AEP, as a "secondary" protection, because when the coolant temperature rises above the set value, the TCD 8 or TSCD 9 fusible lock located below the AEP AR 5 will be triggered, mechanically disconnecting the AEP AR 5 and the sheath 6, while the ECD 11 located above the AEP AR 5 disconnects the common circuit. Since all TCD 8 cables and ECD cables 13 of all AEP ARS 5 from the junction box are connected in series with the windings of the holding electromagnets 7 of all ARs in a single circuit, without any switch device, when at least one TCD 8 or one TSCD 9 fusible lock in the sheath 6 of the AEP AR 5 is triggered, the windings of the holding electromagnets 7 of all ARs (including ARs of the conventional CPS system, ARs of the conventional EP system, and the complete set of ARs and AR 5) will perform the EP function and be flushed with the coolant at the highest temperature. The AEP system is the last line of protection, and even if the drivers of all ARs located on the reactor cover have a mechanical failure (for example, when a load falls on the cover or AR rods are deformed due to other reasons), the system will be triggered, which can prevent the ARs of the conventional CPS from falling freely into the core. After its triggering (which rarely happens), the AEP sheath 6 and AEP AR5 should be replaced.

[0062] Thus, if for some reason the electrical signal triggering the EP fails due to an increase in the coolant temperature above the set value, or the absorber rods are removed without authorization in the event of multiple failures in the CPS circuit or preventive concealment of malicious acts, the present invention provides significant advantages compared to known emergency protection systems, as a result of which the safety of the nuclear reactor is increased, including the exclusion of the possibility of fast neutron reactor excursions. In particular, these advantages are ensured by the following features of the claimed nuclear reactor protection device:

[0063] - triggering (insertion into the core) all the absorption rods when the current circuit in the winding of the holding electromagnet of the conventional CPS is broken by at least one direct-acting TCD or at least one ECD of the AEP AR equipped with a TSCD with fusible locks in a conventional CPS equipped with springs and electromagnets to hold all the absorption rods in a given position;

[0064] -TCD, TSCD fusible locks and ECD are installed inside the reactor to ensure they are not affected by external factors;

[0065] - There are no AEP AR drivers in the reactor cover, which excludes the possibility of AEP rods triggering failure under external influences.

[0066] At the same time, the protection level of the nuclear reactor is achieved against external influences (e.g. from a control panel) or in the event of a failure of a conventional CPS (where an error / transfer command is executed, e.g. the command “all rods up; no more control signals received”) since the final position of all CPS ARs will be their position at the lower limit switch, it is not possible to physically enter the entire reaction margin compensated by the absorption rods.

Claims

1. A protection device for a nuclear reactor with a high temperature coolant, wherein the protection device comprises: a power supply network, A plurality of absorbing rods can be inserted into the core for emergency protection, the plurality of absorbing rods having an actuator equipped with a holding electromagnet for holding the plurality of absorbing rods at a given position, wherein The plurality of absorption rods are made so that they can be inserted into and withdrawn from the core of the nuclear reactor when the nuclear reactor is operating normally, and can be inserted into the core if an emergency signal occurs and the windings of the holding electromagnets are de-energized; Additional emergency protection absorber rod, a universal electrical disconnector of the power supply network, wherein the power supply network is designed so that current flows sequentially through the windings of the holding electromagnets of all the plurality of absorption rods, Features: The circuit in which the current flows through the winding of the holding electromagnet comprises: at least one direct-acting thermal current isolating switch capable of disconnecting the current loop when the coolant temperature rises above a set value, wherein the direct-acting thermal current isolating switch is installed in a jacket isolated from the coolant in the hot coolant flow or at the core outlet, at least one electrical circuit breaker located within the jacket of the additional emergency protection absorber rod, isolated from the coolant, and located above the additional emergency protection absorber rod, and a temperature-sensitive current isolating switch with a fusible lock, located below the additional emergency protection absorption rod; In which, the cable of the direct-acting thermal current isolating switch and the cable of the electrical circuit breaker are connected in series with the windings of the holding electromagnets of the multiple absorption rods in a single circuit. When the fusible lock of the direct-acting thermal current isolating switch or the temperature-sensitive current isolating switch is triggered, the multiple absorption rods and the additional emergency protection absorption rods are inserted into the core for emergency protection.

2. The protection device according to claim 1, characterized in that: The high temperature coolant is a liquid metal coolant.

3. The protection device according to claim 1, characterized in that: The fusible lock includes a fusible pin and a spring of the fusible pin.

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