JP2011053231A - High-temperature nuclear reactor system having opposed diffusion mechanism for preventing air from entering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent air from entering a high-temperature nuclear reactor at the time of accidental breakage in a primary pipe. <P>SOLUTION: A high-temperature nuclear reactor system includes a high-temperature nuclear reactor 8 and an opposed diffusion mechanism 9. The opposed diffusion mechanism 9 includes: a gas storage container 20, placed outside of the high-temperature nuclear reactor, which contains a gas lighter than air; a flow channel 21 through which the gas lighter than air is supplied from the gas storage container to the core top part of the high-temperature nuclear reactor; and a flow rate adjuster 22 for limiting the flow rate of the gas lighter than air. At the time of pipe breakage, the gas lighter than air is continuously supplied to the core top part so as to prevent air from entering the pipe. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  In the present invention, in order to prevent the natural circulation of the intruding air in the reactor in the event of a pipe breakage that constitutes the inflow channel and the outflow channel, a gas that is lighter than air is continuously supplied to the top of the core from the continuous counter diffusion mechanism. It is related with the high temperature reactor system which prevents the natural circulation flow of the air in a nuclear reactor by supplying in this way.

  The above-mentioned sustained counter air diffusion mechanism (SCAD mechanism) is a mechanism that continues to diffuse gas lighter than air from the upper part of the furnace in a form in which the flow direction opposes the air entering by molecular diffusion from the fracture opening. It is.

  In order to prevent the natural circulation of air to the nuclear reactor in the main pipe piping breakage accident, in the present invention, a high temperature nuclear reactor system using a continuous opposing diffusion mechanism has been clarified. Well-designed high-temperature reactors with regard to core structure, fuel type, etc., the SCAD mechanism provides a continuous supply of gas lighter than air to the top of the core, and counter-diffusion and convection are focused on reactor cooling without the occurrence of natural circulation It is supplied at a steady state flow rate that can be maintained in the material flow path.

  At present, research and development of high temperature reactor technology has a strong interest all over the world. This reactor could be an attractive nuclear option with the potential for high-efficiency energy production at high temperatures and high reactor safety.

  In reactor technology, it is a reactor system based on general design features in which a graphite moderation core is housed in a coated particle fuel and steel pressure vessel. A pressurized gas, usually helium gas, is used as the reactor coolant. The reactor pressure vessel has a coolant duct connected to the energy facility. The reactor system is usually housed in a vented containment structure located underground.

  The purpose of improving the safety of the nuclear reactor is to break the large-diameter coolant duct, which is a design standard event. In a coolant loss event, the nuclear fission reaction is terminated by an inherent negative temperature coefficient for reactivity, and the decay heat is removed by heat conduction and heat radiation to the reactor cooling system outside the reactor pressure vessel. . The fuel and core are maintained below the allowable safe design temperature for many months. However, as an important safety issue, there remains a problem of fuel and core graphite oxidation in the case of entering the reactor from a primary system pipe where a large amount of air is broken by natural circulation.

  Immediately after the pipe breaks, the reactor coolant gas is ejected through the break opening, and the reactor primary system is rapidly depressurized to the atmospheric pressure in the reactor containment building. Air intrusion into the reactor will be followed by two consecutive events.

  In the first stage, the air in the containment building slowly enters the reactor system by molecular diffusion and natural convection. In the second stage, the gas mixture forms a density imbalance through the reactor system flow path until the density difference, i.e., buoyancy increases so as to initiate the natural circulation of gas in the reactor system. Air enters the reactor with a severely oxidised graphite of the fuel and graphite core structure and, as a result, a natural circulation flow with a flow rate that is high enough to impair the integrity of the fuel. The latter has an important safety impact.

JP 2002-131460 A

Saito, S., Tanaka, T., et al., 1994.Design of High Temperature Engineering Test Reactor (HTTR), JAERI 1332, Japan Atomic Energy Research Institute. Katanishi, S. and Kunitomi, K., 2003. Safety Design Philosophy of Gas Turbine High Temperature Reactor (GTHTR300), Transaction of Atomic Energy Society of Japan, Vol. 2, No. 1, pp. 55-67. Takeda, T. and Hishida, M., 2000. Study on the passive safe technology for the prevention of air ingress during the primary-pipe rupture accident of HTGR, "J. of Nuclear Engineering and Design 200, pp. 251-259.

  To date, several techniques have been proposed to mitigate air ingress into high temperature reactors. One of the existing methods has been proposed as a substitute for a low-pressure confined building ventilated in a high-pressure reactor containment building without leakage (Non-patent Document 1). The amount of air that can enter through the reactor break is limited to the total amount of air present in the containment volume. The containment structure is expensive to construct and in high temperature reactors additional safety measures arise.

  As an alternative, ventilated containment buildings have been proposed that limit the amount of air leakage that can be tolerated. In order to limit the amount of air leakage, a double confinement structure concept has been proposed (Non-Patent Document 2). The outer structure is designed to confine most of the air that naturally circulates from the outer periphery, thereby limiting the amount of air that can enter the internal structure that houses the reactor.

  Furthermore, as another alternative method, helium gas injection into a low-temperature channel in the lower region of the reactor having the highest gas density has been proposed (Patent Document 1; Non-Patent Document 3). In order to prevent an increase in buoyancy, which is the driving force of the natural circulation flow, in the nuclear reactor, helium gas is injected to replace the heavy mixed gas in the low-temperature channel.

  The present invention solves the safety and practicality issues associated with preventing air ingress by providing a reactor system that encompasses a high temperature reactor and a sustained SCAD mechanism. The SCAD mechanism continuously supplies a gas lighter than air to the upper part of the core at a speed that allows stable convection without sustaining natural circulation flow in all the target reactor channels. This prevents the natural circulation of air in the nuclear reactor. That is, when the reactor piping is broken, air may enter from the breakage opening. At this time, a large amount of air enters due to the generation of a natural circulation flow that makes a round of the reactor. However, in the initial stage after the fracture, there is a period in which air enters mainly due to molecular diffusion. Therefore, if a gas (for example, helium) that is lighter than air entering from the opening through molecular breakage is supplied from the upper part of the core immediately after the breakage, a natural circulation flow in which a large amount of air enters is generated. Can be prevented.

  The SCAD mechanism provides an economical and reliable solution to prevent significant air ingress in a reactor main pipe failure. The present invention provides significant advancements and technological prospects for current and future utilization systems with respect to the state of the art in high temperature reactor technology in safety and economy.

  The reactor that is the heat source of the energy production facility is not limited in any core shape, power, or fuel design. Also, it is not limited to any choice for facility harmony to implement efficient heat utilization in energy production. Coolant, preferably helium gas, but may include other alternative gases or gas mixtures, heated to the appropriate high temperature by heat released from fission in the core and transported through a duct to a heat utilization facility . The reactor is housed in a steel pressure vessel.

  The nuclear reactor is equipped with a SCAD mechanism, and is mainly composed of a gas storage vessel, piping for releasing gas from the storage vessel into the reactor, and a flow control device. The gas storage vessel is preferably a compressed gas tank located outside the primary reactor system to simplify maintenance work. In this case, the piping is used to connect an external gas storage container inside the nuclear reactor. For effective counter-diffusion, gas is continuously released from the vessel to a region near the top of the core. The flow control device may be a fixed or variable size orifice, an active or passive adjustment valve, or a combination thereof.

  An alternative embodiment of the present invention is to apply various duct structural arrangements to the reactor for coolant transport between the reactor and the facility. Various duct configurations are required to facilitate design goals specifically focused on core, pressure vessel, and facility placement. In another alternative embodiment of the present invention, the SCAD mechanism is provided inside the reactor system to achieve shortened connection piping and a more compact installation in the installation and performance goals of other equipment.

  In the past, several original reactor system configurations have been clarified. As an example of an alternative system configuration that has been clarified, the present invention is that the SCAD mechanism is located either inside or outside the reactor pressure vessel. The inner installation achieves a compact installation, while the outer installation simplifies maintenance work on the SCAD mechanism. The disclosed design technology provides significant benefits in safety and economy to the latest high temperature reactor technology and enhances the technology prospects for current and future applications.

  In the above-mentioned Patent Document 1 filed before the present application by the inventor of the present application, a high-temperature reactor system for preventing a natural circulation flow of air in the reactor is disclosed. The purpose is to inject a helium gas to prevent a natural circulation flow in which the air makes a round in the reactor pressure vessel. On the other hand, in the present invention, helium gas is injected from the upper part of the vessel where a more stable stratification is formed by injection, and this is a high temperature nuclear reactor system provided with a continuous counter diffusion mechanism.

FIG. 2 shows a schematic diagram of a high temperature reactor system having a concentric duct located near the bottom of the reactor pressure vessel utilizing a sustained SCAD mechanism located outside the reactor in accordance with the present invention. FIG. 2 shows a schematic diagram of the high temperature reactor system of FIG. 1 with one or more concentric ducts located near the bottom of the reactor pressure vessel in accordance with an alternative embodiment of the present invention. FIG. 2 shows a schematic diagram of the high temperature reactor system of FIG. 1 with one or more non-concentric ducts located near the bottom of the reactor pressure vessel in accordance with another alternative embodiment of the present invention. FIG. 2 is a schematic diagram of the high temperature reactor system of FIG. 1 that is a combination of concentric and non-concentric ducts located near the bottom of the reactor pressure vessel in accordance with yet another alternative embodiment of the present invention. 1 shows a schematic diagram of a high temperature nuclear reactor system with a SCAD mechanism located inside the nuclear reactor.

  An outline of the high temperature reactor system of the present invention is shown in FIG. The system consists of a high temperature reactor 8 and a SCAD mechanism 9. Heat is generated by fission in the high temperature reactor 8 and is utilized to heat a predetermined coolant gas to an appropriate high temperature. Hot gas is transported through a duct to a practical heat utilization facility.

  More specifically, the high temperature reactor 8 comprises a reactor pressure vessel 14, a reactor internal structure 15, a core 16, and a concentric duct 17 at the bottom of the reactor. The coolant gas is heated in the core 16 to a suitable high temperature ranging from 700 ° C. to 1000 ° C. depending on the temperature capability of the nuclear fuel being used. The coolant gas is transported to the facility in the outflow channel 19 of the concentric duct 17 and returns to the reactor in the inflow channel 18 of the concentric duct 17.

  The SCAD mechanism 9 includes a gas storage container 20, a gas pipe 21, and a flow rate control element 22. A steady flow of gas can flow from the gas storage container 20 to the inside 8 of the reactor through the pipe 21. The flow of the pipe 21 is actively controlled actively or passively by the flow control element 22. In general, the gas flux in the reactor coolant channel can be inferred according to Fick's Law for diffusion below.

Here, N is the molar flux, x is the molar concentration, c is the molar density of the mixture, D is the diffusivity, and z is the directional coordinate. The subscript h indicates the gas supplied from the gas storage container 20, and the subscript a indicates air. Other gases or gas mixtures that may actually exist are not included to simplify the principle illustration. The first group on the right-hand side of equation (a) is the flux due to diffusion that occurs as a result of the concentration gradient, and the second group is the flux that results from the bulk flow of the gas mixture.

  The system of equation (a) is formed with all the major reactor coolant channels of interest and is solved simultaneously with appropriate operating and boundary conditions. The operating conditions are such that the minimum flow rate of gas supply to maintain counter diffusion is applied until the diffusion and convection of air entering the reactor are zero, and the flux of various gases or gas mixtures is constant in a steady state. The boundary condition is the assumed gas composition along the reactor coolant flow path.

The minimum flow calculated from equation (a) is used to determine the main system parameters of the SCAD mechanism 9. One of the parameters, the flow coefficient Cv of the flow control element 22, is determined so that the gas passing through the flow control element 22 matches or exceeds the required minimum flow calculated from the above equation (a). If the gas storage container 20 has a pressure more than twice the ambient pressure, the gas flowing through the flow rate control element 22 has a sonic velocity. Starts in such a case the container 20 the gas flowing from the pressure P _o, under conditions that ends at the pressure P _t after time t, the volume parameter V for gas storage vessel 20 is determined by the correlation of the following The

The above equation (b) assumes an isothermal state at a constant temperature T of the gas storage container 20. The gas constants R and r are physical properties of a specific working fluid in the gas storage container 20.
FIG. 2 is an overview of an alternative embodiment of the present invention, and parts similar to those in FIG. 1 are designated by the same reference numerals and will not be described in detail. As shown in FIG. 2, the reactor has two concentric ducts 25 at the lower height position of the reactor pressure vessel 14. The first concentric duct 25 has a coolant outflow channel 19, while the second concentric duct 26 has a coolant inflow channel 18. The outer annular channel of the concentric duct may be used for other coolant flows such as reactor vessel cooling flow. Alternative duct structures are used to achieve different design and performance goals such as construction material selection for the reactor pressure vessel 14.

  FIG. 3 is an overview of an alternative embodiment of the present invention in which one of the concentric ducts in the embodiment of FIG. 2, ie, duct 26 is replaced with a non-concentric duct. As shown in FIG. 3, the non-concentric duct 27 has a coolant inflow channel 18. Those parts of FIG. 3 previously identified in FIGS. 1 and 2 are given the same numbers and will not be described. Non-concentric duct designs are simpler and may be more economical than the concentric ducts previously described. However, the feasibility of non-concentric ducts depends on the performance and effectiveness of other design parameters as high temperature steel and insulation.

  FIG. 4 is a schematic view of another embodiment of the present invention in which the concentric duct 17 in the embodiment of FIG. 1 is replaced with a separate non-concentric duct. As shown in FIG. 4, the first non-concentric duct 28 has a coolant outflow channel 19, while the second non-concentric duct 29 has a coolant inflow channel 18. In FIG. 1, those parts of FIG. 4 previously identified are given the same numbers and will not be described. The use of all non-concentric ducts achieves design goals that are comparable to similar design regulations, as will be explained next.

  FIG. 5 is a schematic view of the SCAD mechanism 9 installed outside the nuclear reactor relocated inside the nuclear reactor. Parts previously identified in FIG. 1 are given the same numbers and will not be described. The internal SCAD mechanism can achieve the introduction of a more compact and generally less expensive system in other possible design benefits. However, maintenance work on the SCAD mechanism 9 may be more difficult.

  Specific embodiments of the invention are presented in the figures and description. These schemes have been described and described in terms of the principles and practical application of the invention in order to make use of the invention in various ways and to enable other technologies suitable for a particular use. It should not be construed as limiting the scope of the invention described in detail, and in fact many modifications and changes are possible from a learning standpoint. For example, many changes are possible in both the reactor and the SCAD mechanism, including the use of different numbers and duct configurations, to enhance the flow within the different reactors with respect to operating principles, ducts and SCAD designs. Includes adding additional elements to the mechanism. Similarly, changes also exist because of the deployment arrangements and arrangements related to the overall reactor system configuration, and the possibility of utilization systems extending from power generation and process heat utilization to its cogeneration. Thus, the scope of the invention should be determined by the following claims and their legal equivalents.

Claims (8)

Inflow for inducing and directing the flow of coolant gas, provided in the lower part of the high temperature reactor composed of a reactor core, an inner vessel structure for containing the reactor core, and a pressure vessel for enclosing the inner vessel structure Counter-diffusion to prevent the occurrence of a natural circulating flow of intrusion air in the high temperature reactor in the event of a break in the piping that comprises the flow channel and the outflow channel for inducing coolant gas flow from the high temperature reactor A high temperature nuclear reactor system having a mechanism,
The counter-diffusion mechanism is installed outside the high-temperature reactor and contains a gas storage vessel containing a gas lighter than air, and a flow path for supplying a gas lighter than air from the gas storage vessel to the top of the core of the high-temperature reactor. And a flow control device for limiting the flow rate of gas lighter than air,
In the event of a pipe rupture accident, a gas lighter than air is continuously supplied from the counter diffusion mechanism to the top of the core of the high temperature reactor, thereby causing molecular diffusion from the rupture site of the pipe provided in the lower part of the high temperature reactor A high-temperature reactor system that prevents the natural circulation of air in the high-temperature reactor by continuously diffusing a gas lighter than air in the flow direction opposite to the invading air.   The reactor system of claim 1 having an inflow channel comprised of one or more concentric channels for directing and directing from a high temperature reactor in response to a coolant gas.   The reactor system of any preceding claim, comprising the aforementioned outflow channel comprising one or more concentric channels for directing and directing from a high temperature reactor corresponding to the number of coolant gas channels. .   The reactor system of claim 1 having an internal vessel structure comprising one or more flow paths for directing and directing coolant gas.   The nuclear system of claim 1, wherein the gas storage container has one or more gas sources that are lighter than air.   The nuclear power system of claim 1, wherein the nuclear power system has one or more flow paths between the gas storage vessel and the high temperature reactor through which a gas lighter than air flows.   The reactor system of claim 1, wherein the flow regulator has one or more flow control elements to limit the flow rate of a gas that is lighter than air in the flow path.   The reactor system of claim 1, wherein the coolant gas and the gas lighter than air are the same.