JP2015524569A - Confinement flame system for mitigation after loss of coolant accident - Google Patents

Abstract

A method for controlling hydrogen combustion in LOCA includes opening a valve to allow a first primary containment gas to flow. A second secondary containment gas is withdrawn through the flame arrester. The first and second containment gases are burned in the isolated deflagration zone. The combusted first and second containment gases are cooled with thermoelectric elements and the cooled non-flammable oxidant-enriched product gas mixture is exhausted through a second flame arrester. A confinement flame system for a water-cooled nuclear reactor includes an inlet flame prevention device and an exhaust disposed within a housing for confining a deflagration of a first primary containment gas and a second secondary containment gas within the housing. A mouth flame prevention device is provided.

Description

  The present disclosure relates generally to a nuclear reactor SCRAM (emergency shutdown) and confined flame system for a nuclear power plant after a concomitant outage.

  This disclosure claims priority to the disclosure of US Provisional Application No. 61 / 680,008, filed Aug. 6, 2012.

  Boiling water reactor (BWR) type nuclear power plants facilitate the generation of power for a number of power companies around the world. BWR reactors are typically designed using a radionuclide hazardous material containment method that relies on multiple walls to prevent the release of radionuclides by a “zero emission design target concept”.

  The usual means of the multi-wall method includes a first wall represented by the composition and design of the nuclear fuel pellet itself, a second wall typically represented by a hermetic enclosure called a “fuel pin”. A number of fuel pins are supported and arranged in a detachable structure called a fuel rod, and a number of adjacent fuel rods constitute the “core” of the reactor.

  The third wall is represented by a sealed primary coolant hydraulic loop that surrounds the nuclear fuel “core” and the primary coolant water of the filling, the primary coolant water being the primary coolant pump, one or more primary − Surrounded by the primary reactor structure in communication with the secondary coolant loop heat exchanger, and the remaining primary loop components such as the interconnect piping along the attached controller, instrumentation and other primary loop support devices. Liquid water in the core enclosure is a fundamental feature in the design strategy that removes excess heat from the core, thereby maintaining the core material of the structure below its operating limit.

  The term “LOCA” refers to a situation that exists in the core when the heat removal function provided by water is lost or substantially impaired. As a result of LOCA, the core material temperature rises and eventually leads to an overheating condition of the core to a temperature range above the design limit temperature. At some point, residual water vapor chemically reacts with the fuel cladding material zirconium to produce zirconium oxide and hydrogen gas. Hydrogen gas and water vapor pose a problem of pressurization to surrounding structures.

  The primary loop component is housed within the fourth wall to prevent the release of radionuclides. This fourth wall is called the “primary enclosure” and seals the entire primary loop component. Typically, the primary containment atmosphere is an inert gas to prevent hydrogen combustion when hydrogen is released into the area. Primary enclosures are usually reinforced concrete structures that are fairly strong but with limited capacity to withstand internal pressurization without leakage.

  The fifth wall is a sealed structure called a secondary containment. In many BWR reactor construction designs, this fifth wall is filled with an air atmosphere and is designed to withstand an internal pressure that is not as high as the ambient pressure of the external atmosphere. If the hydrogen gas produced by the reaction with the fuel clad primary coolant water vapor breaks the fourth wall or primary containment structure, the hydrogen gas concentration level in the secondary containment atmosphere is a mixture of air, hydrogen and water vapor. Will rise to the point where it can become flammable. In such a case, the final fifth wall between the radionuclide store in the reactor core and the external environment is the secondary containment atmosphere by some form of ignition source, such as power spark or electrostatic discharge. Can be damaged as a result of being over-pressurized as it ignites.

  That said, current water-cooled nuclear reactors are extremely safe and perform fail-safe operation with minimal dependence on power supply, water distribution, and operator behavior, and stop nuclear reactions in the reactor core. Or “SCRAM” to reduce the heat output level to a very small level compared to the nominal operating output level. The residual low thermal power level resulting from the radiation decay of fission product material still present in the reactor core after SCRAM is extremely high to overheat the reactor core if the primary coolant flow through the core is not maintained or restored. It is enough. If off-site power from the power grid is suspended for long periods of time, such as when a backup power source such as a battery or generator set is exhausted or otherwise becomes unavailable, Can experience.

  Reactors also use a variety of passive systems that mitigate slow hydrogen accumulation from non-LOCA effects. For example, by inactivating in advance, an atmosphere in which oxygen is reduced is generated in the primary enclosure before starting operation, during operation start, and during continuous power generation operation. When building a power plant for the first time or during a period of non-operation, an inert gas (usually nitrogen) is released into the primary containment to replace the air in that space. This method reduces the activity of oxygen in the inert space below the level required for hydrogen combustion. Yet another passive system is a catalytic hydrogen recombiner. The hydrogen recombiner combines hydrogen and oxygen at a mixing ratio below the combustion limit to produce water, reducing the hydrogen concentration in the containment.

  Hydrogen generation after LOCA is fairly fast and can overwhelm some passive hydrogen mitigation systems during extremely rare facility outage scenarios.

1 is a schematic diagram of a reactor building showing a multi-wall design method augmented with a confined flame system in the disclosed state. FIG. 1 is a schematic exploded view of a confined flame system according to a disclosed non-limiting example. FIG.

  Various features will be apparent to those skilled in the art from the following detailed description of the disclosed non-limiting examples. The drawings that accompany the detailed description can be briefly described as described above.

  FIG. 1 schematically illustrates a water-cooled nuclear reactor 10 in relation to the external environment. During and after power generation operation, the water-cooled nuclear reactor 10 uses primary loop coolant to transfer heat from the reactor core contained in the fuel cladding 12 to the heat exchanger, which heats the heat. Move into the secondary coolant water pump feed loop to drive the steam turbine that generates power and remove and discard excess heat. The greater the temperature difference between the internal heat source and the external environment from which excess heat is released, the more efficiently the mechanical work of the turbine, such as rotating the generator, is achieved. Therefore, it is desirable that the inside is high temperature and the external environment is low temperature. This makes it desirable to place the water-cooled nuclear reactor 10 adjacent to a water supply source or other low-temperature heat storage for efficient power generation.

  The water-cooled nuclear reactor 10 typically includes nuclear fuel pellets that are aggregated and sealed in a fuel cladding 12, and the structure of the surrounding primary coolant loop 14 is housed in a primary containment structure 16. A secondary containment structure 18 surrounds the primary containment structure 16 and includes, but is not limited to, a secondary coolant loop 20 that is in thermal communication with the primary coolant loop, turbine, generator, refueling Other machine spaces including compartments, steam generator compartments, pump rooms, and the like (not shown) are included.

  A loss-of-coolant accident ("LOCA") can result in exposure of the fuel cladding 12, resulting in an increase in fuel temperature, which can be caused by residual superheated steam and This can lead to oxidation of the fuel cladding 12, which is a reactive zirconium alloy. This reaction is exothermic and produces hydrogen, which can leak into the primary containment structure 16 with water vapor if the primary coolant loop 14 is compromised. The mass release rate of hydrogen can be on the order of kg / s. As the zirconium-water reaction proceeds, the contents of the primary coolant loop 14 experience an increase in temperature, with the result that the pressure in the primary coolant loop 14 increases and may exceed the design pressure of the loop components. Reach the level. The operator can reduce the pressure in the primary coolant loop by venting a portion of the contents of the primary coolant loop 14 into the surrounding primary containment structure 16, or the surrounding primary containment structure 16. The option is to wait until a portion of the primary coolant loop 14 is compromised to the point of failure due to pressure to the uncontrolled discharge point into. At this point, due to the introduction of mixed water vapor and hydrogen coming from the primary coolant loop 14, the pressure in the surrounding primary containment structure 16 increases.

  The resulting mixture of released water vapor and hydrogen and the inert atmosphere normally retained in the primary containment structure 16 is not at risk of ignition because there is no air in the space. However, as the pressure increases, the primary containment structure 16 experiences the same situation that existed in the primary coolant loop 14 some time ago. The result of excessive pressure in the primary containment structure 16 is different in nature from the discharge of pressurized water vapor, hydrogen and inert gas from the primary coolant loop 14 into the primary containment structure 16 and is more severe. is there. The reason is that the hydrogen content of the mixture released into the air atmosphere of the secondary containment structure 18 can produce a combustible mixture in the secondary containment atmosphere, and this combustible mixture is ignited. This is because rapid pressurization may occur and damage to the final fifth wall of the containment wall between the radionuclide load entrained from the reactor fuel and the external atmosphere may occur. . If a system that maintains the hydrogen activity in the secondary containment atmosphere below the ignition limit is not used, a highly ignitable gas mixture can occur in the secondary containment atmosphere.

  The containment flame system 30 includes an intake 32 in the primary containment structure 16, an intake 34 in the secondary containment structure 18, and an exhaust 36 that returns to the secondary containment structure 18. A valve system 38, such as a nuclear licensed solenoid valve that meets the demanding and high expectations of the nuclear industry, controls the flow from the primary containment structure 16 into the containment flame system 30. It has been understood that various fail-safe systems can additionally be provided. The confinement flame system 30 operates to obviate a post-LOCA hydrogen combustion scenario in the secondary containment structure 18.

  Referring to FIG. 2, in the context of FIG. 1, the confined flame system 30 typically includes a housing 40, an inlet flame prevention device 42 for incoming gas from the secondary containment structure 18, and an incoming gas from the primary containment structure 16. The intake flame prevention device 53, the inert gas injector 44, the flame supply source 46, the power supply 48, and the exhaust flame prevention device 50 are provided. It should be understood that various other components and subsystems may be provided alternatively or additionally.

  An inlet flame arrester 53 is disposed in the housing 40 downstream of the inlet 32 to transmit a hydrogen and water vapor mixture from the primary containment structure 16 through the valve system 38 and into the confinement flame system. Seal in and around 52. The intake-port flame prevention devices 42 and 53 and the exhaust-port flame prevention device 50 operate as a flame catcher that stops fuel combustion by passing a flame front through a flow path that is too narrow to allow flame progression. These channels can be regular, such as in a wire mesh or metal aperture plate, or irregular, such as in a random packing. That is, the inlet flame prevention devices 42, 53 and the exhaust flame prevention device 50 confine deflagration within the housing 40 to the isolated deflagration zone 54 and the hot product gas zone 56. These hot deflagration zones and product gas zones are used to treat the extracted secondary containment gas due to natural convection for the secondary containment gas that is typically cooler and bulky outside the containment flame housing 40. Improve the amount.

  As a result, the intake 32 operates as an eductor that draws air from the secondary containment structure 18 through the intake flame prevention device 42 and then through the exhaust flame prevention device 50 upstream of the exhaust port 36. This configuration confines the deflagration of the combustible gas mixture within the housing 40. The eductor utilizes hydrodynamics to generate a suction force for the non-combustible secondary containment gas by the kinetic energy provided by the fast, non-combustible primary containment gas jet emitted by the valve system 38. The gas jet emitted from the primary containment can cause pumping or mixing without moving parts and thus without maintenance. The intake-flame prevention devices 42 and 53 and the exhaust-flame flame prevention device 50 operate as safety devices that stop the flame and thereby prevent hydrogen deflagration from moving outside the housing 40. Further, the intake flame prevention devices 42, 53 and the exhaust flame prevention device 50 can be protected from damage.

  A flame source 46 such as an augmented spark igniter (ASI) operates continuously to ignite hydrogen from the primary containment structure 16 and air from the secondary containment structure 18. A flame source 46 is located adjacent to the outlet of the primary conduit 52 from the primary containment. This conduit 52 is also provided with a flame prevention device 53 to prevent the flame from moving away from the deflagration zone 54 and into the interior of the primary coolant structure 16.

  The containment flame system 30 operates in response to a control subsystem 54 that includes a control module 56 (shown schematically) and a set of multiple sensors 58 (shown schematically) along the containment flame system 30. obtain. The control subsystem 54 typically includes a processor, memory, and interface. The processor can be any type of known microprocessor having the desired performance characteristics. The memory can be any computer readable medium that also has control performance such as logic as described herein and the desired performance characteristics of storing and releasing data. The interface facilitates communication with other components such as valve system 38, flame source 46, and power supply 48. The control subsystem 54 executes control logic that controls the deflagration through selective injection of inert gas, such as nitrogen, from a liquid nitrogen source through the inert gas injector 44, for example.

  The power source 48 operates to provide independent self-sufficient power to, for example, the valve system 38, the flame source 46, and the control subsystem 54. It should be understood that the power supply 48 can alternatively or additionally power various other components and subsystems. In one disclosed, non-limiting example, a turbine 60 is disposed in fluid communication with the primary conduit 52 downstream of the valve system 38. The relatively high pressure and flow rate of the hydrogen water vapor and inert gas mixture through the primary conduit 52 powers the turbine 60 to drive the generator 62 of the power supply 48, thereby providing the flame source 46, the control sub Generate power to power the system 54 and associated confinement flame apparatus.

  Alternatively or additionally, a thermoelectric cuff 64 surrounds the deflagration zone 54 and provides power. The thermoelectric cuff 64 generates electric power by directly using the combustion heat released in the deflagration zone 54. Various additional or alternative power supply systems that utilize energy release from the LOCA scenario are feasible, and the power thus generated is used to operate the confined flame system device, eg, a mechanical fan Alternatively, it should be understood that it improves the function and efficiency of the flame system, such as supplying power to the air mover to supplement the flow rate drawn from the secondary enclosure into the confined flame system.

  The hot product gas zone 56 is embedded in the housing 40 for thermal coupling with the hot product gas and is surrounded by a secondary secondary enclosure for thermal coupling with a cold gas mixture in the surrounding secondary containment atmosphere. It can be surrounded by a set of thermal diodes 66 (sometimes called heat pipes or reflux boilers) that extend into the atmosphere. The thermal diode 66 is essentially a series of heat pipes that operate to dissipate heat from the housing 40 into the secondary containment atmosphere. Again, it should be understood that various other configurations and combinations can benefit from the present specification.

  The containment flame system 30 can utilize an inert gas flow injected into the housing 40 to adjust the incoming hydrogen concentration and improve the efficiency of protected combustion in the deflagration zone 54. The containment flame system 30 is self-contained and self-contained and utilizes controlled extraction, spent gas recirculation, chimney effects, and cold storage effects to operate even in extremely rare facility outage scenarios. This is accomplished when there is little or no external power requirement to facilitate.

  The use of the terms “a”, “its” and like references in the context of the description (especially in the context of the appended claims) is specifically contradicted by the context, unless otherwise specified in the specification. Should be construed as including both singular and plural unless specifically stated otherwise. The modifier “about” used in connection with a quantity includes the value presented and has the meaning defined by the context (eg, it includes a degree of error associated with the measurement of a particular quantity). All ranges disclosed in the specification include endpoints, and the endpoints can be independently coupled to each other. Relative position terms such as “front”, “rear”, “upper”, “lower”, “upper”, “lower” and the like are related to the normal operating posture of the device, otherwise It should be understood that this should not be considered as a limitation.

  Although different non-limiting examples have certain exemplary components, embodiments of the invention are not limited to those particular combinations. Some of the components or features from any of the non-limiting examples can be used in combination with the features or components from any of the other non-limiting examples. For example, based on this teaching, it was mounted in a safety conduit that connects the sealed volume of the primary coolant loop 14 having a high pressure fluid with the sealed volume of the primary containment structure 16 having a substantially low fluid pressure. It is envisioned that additional energy for power generation could be drawn from other energy stores present in this type of scenario, such as the use of a turbo generator set.

  It should be understood that like reference numerals identify corresponding or similar elements throughout the several views. Although the configuration of particular components is disclosed in the illustrated embodiment, it should be understood that other configurations may benefit from the present specification.

  Although a particular sequence of steps is shown, described, and claimed, the steps can be performed in any order, separately or in combination, unless otherwise specified, and still benefit from the present disclosure. I want you to understand.

  The above description is exemplary rather than defined by the limitations therein. While various non-limiting examples have been disclosed herein, those skilled in the art will recognize that various modifications and variations are within the scope of the appended claims in light of the above teachings. Let's go. It is therefore to be understood that within the scope of the appended claims, the present disclosure may be practiced other than as specifically described. For that reason, it is necessary to examine the appended claims to determine the true scope and content.

Claims (18)

Open the valve so that the first containment gas flows,
Withdrawing the second containment gas through the inlet flame prevention device,
Burning the first and second containment gases in an isolated deflagration zone;
Cooling the burned first and second containment gas with a thermoelectric element;
Exhausting the cooled and product gas mixture produced by the combustion of the mixture of the first and second containment gas through an outlet flame arrester;
A method for controlling the combustion of hydrogen in LOCA, comprising:   2. The control of hydrogen combustion in the LOCA of claim 1, further comprising burning the first and second containment gases in an isolated deflagration zone between the inlet and outlet flame arresters. Method.   The method for controlling hydrogen combustion in a LOCA according to claim 1, further comprising placing an isolated deflagration zone in the housing.   The method of controlling hydrogen combustion in a LOCA according to claim 1, further comprising generating electrical power from combustion heat released into the isolated deflagration zone. A housing;
An inlet flame prevention device and an exhaust flame prevention device for confining the deflagration of the first and second containment gases in the housing;
A confined flame system for a water-cooled nuclear reactor.   6. The flame source of claim 5, further comprising a flame source for detonating a first containment gas from the primary containment structure and a second containment gas from the secondary containment structure within the housing. system.   The system of claim 6, further comprising a primary conduit for transmitting the first containment gas from the primary containment structure into the housing.   The system of claim 7, further comprising a valve system for controlling the flow of the first containment gas through the primary conduit.   The system of claim 6, wherein the flame source is an enhanced spark igniter.   The system of claim 9, further comprising a power source for supplying power to the flame source.   The system of claim 10, wherein the power source is a turbine in communication with the first containment gas.   The system of claim 10, wherein the power source is a thermoelectric cuff.   The system of claim 5, further comprising a thermal diode embedded in the housing. A primary enclosure structure;
A secondary enclosure structure surrounding the primary enclosure structure;
A confined flame system for detonating a first containment gas from a primary containment structure with a second containment gas from a secondary containment structure during a loss of coolant accident (“LOCA”);
A water-cooled nuclear reactor comprising:   The water-cooled nuclear reactor according to claim 14, further comprising a primary conduit that communicates the first containment gas from the primary containment structure into the containment flame system.   The water-cooled nuclear reactor according to claim 15, further comprising a valve system for controlling the flow of the first containment gas through the primary conduit.   The water-cooled nuclear reactor according to claim 16, further comprising an enhanced spark igniter for initiating deflagration of a mixture of the first containment gas and the second containment gas.   The water-cooled nuclear reactor according to claim 17, further comprising a power source for supplying power to the valve system and the enhanced spark igniter.

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