BR112017011934B1 - PASSIVE INTERNAL HEAT REMOVAL SYSTEM FROM CONFINEMENT - Google Patents

Abstract

PASSIVE INTERNAL HEAT REMOVAL SYSTEM FROM CONFINEMENT. The present invention relates generally to the field of nuclear energy and more particularly to pressurized water reactor confinement internal heat removal systems (CPHRS), and is designed for circulation reactor confinement cooling. of the cooling liquid (water) in the system circuit. The technical result of the invention is the increase in heat removal efficiency, flow stability in the circuit and, consequently, the reliability of system operation. The system has at least one cooling water circulation circuit comprising a heat exchanger located within the containment and including an upper head and a lower head interconnected by heat exchange tubes, an ascending duct and a lowering duct connected to the heat exchanger, a cooling water supply tank located above the heat exchanger outside the containment and connected to the down duct, a vapor relief valve connected to the up duct and located in the water supply tank and connected hydraulically to the last. The upper head and the lower head of the heat exchanger (...).

Description

DESCRIPTIVE REPORT

[0001] The present invention relates generally to the field of nuclear energy and, more particularly, to pressurized water reactor confinement internal heat removal systems (C PHRS), and is designed for cooling of Reactor confinement by natural circulation of the cooling liquid (water) in the system circuit.

[0002] According to the background of the invention, there are numerous designs of reactor confinement heat removal systems based on circulating heat removal systems.

[0003] The Patent in the R.U.S. RU2125744, G21C15/18 dated 27/1/1999 discloses a system for passive heat removal from the internal volume of a nuclear reactor confinement structure which includes the first heat exchanger located on the exterior of the confinement structure, the second heat exchanger on the inside the reactor confinement structure. The first heat exchanger and the second heat exchanger are hydraulically connected in a closed circuit via pipes with the refrigerant passing through the confining structure and the above exhaust pipe open to the atmosphere. The system also includes a tank filled with water at a defined level that is connected to the confinement structure and located close to its upper wall. The first heat exchanger is immersed in the water in the tank and extended vertically from the base plate joining the bottom of the tank to the upper section dividing the tank into two hydraulically connected volumes. The tank is equipped with a cover that forms the first channel and the second channel, one of which covers the corresponding area formed by the vertical heat exchanger, and is connected to the corresponding area only. One of the channels is connected to the external air intake, the other is connected to the exhaust pipe, and the water in the tank blocks the connection between the channels when the tank is filled to the set level.

[0004] The Patent in the R.U.S. RU2302674, G21C9/00 date 10/7/2007 discloses a containment heat removal system comprising a heat exchanger installed under the containment, the inlet and outlet thereof passing through the containment and being connected to the closed circulation circuit of low boiling point refrigerant, including a turbine with an electrical generator, a power unit with a steam generator located below the containment, and power unit safety systems, one of which has a hydraulic unit and a water turbine of steam. The heat exchanger is installed under the containment dome and is designed as two stacked circular tubes connected by C-shaped finned tubes, with the ends of the tubes facing the containment wall and confining the hydraulic unit to ensure the safety of power unit.

[0005] The closest analogue of the claimed invention is the PHRS system disclosed in Utility Model Patent in the U.S. RU85029, G21C15/18 dated 20/7/2009 and comprising a refrigerant circulation circuit, including at least one heat exchanger located inside the confinement and a tank with refrigerant supply installed above the heat exchanger outside the confinement interconnected by the inlet and outlet ducts. The system is also equipped with a vapor receiver installed in the refrigerant supply tank and hydraulically connected to the latter and connected to the outlet duct.

[0006] The disadvantage of said devices is a potential water hammer in the system.

[0007] The purpose of the invention is to provide a system for efficient heat removal from reactor confinement.

[0008] The technical result of the invention is the increase in heat removal efficiency, flow stability in the circuit and (without water hammer), consequently, the reliability of system operation.

[0009] Said technical result is achieved due to the fact that the internal passive heat removal system of pressurized water reactor confinement with at least one cooling water circulation circuit comprises a heat exchanger located inside the confinement and which includes an upper head and a lower head interconnected by heat exchange tubes, a rising duct and a down duct connected to the heat exchanger, a cooling water supply tank located above the heat exchanger on the exterior of the containment and connected to the down duct, a vapor relief valve connected to the up duct and located in the water supply tank and hydraulically connected to the latter. The upper head and lower head of the heat exchanger are divided into heat exchange tube sections under the presumption that:

[0010] L/D ≤ 20,

[0011] where L is the head section length,

[0012] D is the head hole,

[0013] the rising duct design provides the minimum rising section height hrs to satisfy the following criteria:

[0014] ΔPcres=Δprsghrs + Δphθghhe,

[0015] hrs= (ΔPcres-Δpheghhe) Mp^g,

[0016] where ΔPcres is the total hydraulic resistance of the circuit,

[0017] hhe is the heat exchanger height,

[0018] g is the gravity factor,

[0019] ΔprS=pcw-(p'( 1-x)+p ” x), Δphe= pcw-phw,

[0020] Where pcw is the lower duct water density,

[0021] phw is the rising duct water density within the heat exchanger height range,

[0022] p', p” are the water and vapor saturation density,

[0023] x is the average mass vapor quality of the two-phase mixture in the rising section.

[0024] The above technical result is also achieved in specific options of the invention due to the fact that:

[0025] - the system includes four channels, each comprising four cooling water circulation circuits,

[0026] - at least a part of the rising duct from the upper heads of the heat exchanger sections to the vapor relief valve has an upward slope at an angle of at least 10° with respect to the horizontal line,

[0027] - the ascending duct includes sections with an angle of inclination less than 10° in relation to the horizontal line, with the length of such sections being Lsec1 and the hole being Dsec1 and satisfying the following criteria: Lseci/Dseci - 10,

[0028] - at least one part of the lowering duct has a downward slope at an angle of at least 10° with respect to the horizontal line,

[0029] - the lowering duct includes sections with an angle of inclination less than 10° in relation to the horizontal line, the length of such sections being Lsec2 and the hole being Dsec2 and satisfying the following criterion: Lsec2/Dsec2 < 10,

[0030] - the height of the heat exchange tube ensures that the criterion of turbulent convection on the outer surface of the heat exchanger is satisfied, namely:

[0031] Ra>4 1012,

[0032] in which

[0033] Ra is the Rayleigh criterion,

[0034] g is the gravity factor,

[0035] l is the typical structure size — heat exchanger tube height,

[0036] v is the vapor-air kinematic viscosity coefficient,

[0037] pw is the density of vapor-air medium in the outer wall of the heat exchanger piping,

[0038] pc is the density of vapor-water medium in confinement,

[0039] SC is the Schmidt number,

[0040] Ddif is the vapor diffusion factor.

[0041] - the heat exchanger is located under the confinement dome,

[0042] - the heat exchanger section has a single-row vertical beam,

[0043] - the spacing between any adjacent tubes in the heat exchanger section satisfies the equivalent plane wall criterion.

[0044] For the purposes of the present application, the rising section means the portion of the rising duct in which the refrigerant is a vapor-water mixture (two phases) with the quality of vapor of medium mass x. This section is called “ascending” since it makes a great contribution to the development of natural circulation in the circuit and determines its intensity.

[0045] The experiments conducted show that the above system parameter correlations provide the most efficient heat removal without disturbance by coolant mass flow rate or water hammering due to the selection of the best system geometry: the correlation between the length and bore of the head heat exchanger sections, length of the circulating circuit rising section, height of the heat exchange tubes and optimized arrangement of the system heat exchangers in the containment.

[0046] The correlation of the section length and the bore of the heat exchanger heads is selected in order to minimize the non-uniformity of refrigerant flow distribution among the heat exchanger tubes, that is, to reduce the so-called "effect header". Uniform distribution of flow in piping is the key conditions for improved energy efficiency and performance of heat exchangers. One of the methods used to improve refrigerant distribution within the head heat exchanger channels is to reduce the pressure loss of the medium flow in the head. This is achieved by reducing the head length and increasing the head bore within the capabilities of the device manufacturing process and other design features. For heads that satisfy the L/D < 20 criterion, the pressure loss along the length of the head is minimal, and the distribution of refrigerant flows among the heat exchanger tubes is the most uniform. When said criterion is exceeded, the uniformity of media distribution among the heat exchanger channels is degraded, which results in instability and disturbance by refrigerant mass flow and, subsequently, in reduced heat emission from the heat exchanger.

[0047] The design of the invention is illustrated by the drawings in which:

[0048] Figure 1 shows the cooling water circulation circuit design,

[0049] Figure 2 shows the experimental dependence of the emission of C PHRS cooling circuits on the pressure of the vapor-gas fluid in the tank,

[0050] Figure 3 shows the calculated dependence of pressure and temperature on time over the course of an accident.

[0051] The claimed system is a combination of cooling water circulation circuits. In the preferred embodiment of the invention, the claimed system consists of four completely independent channels, each comprising four circulation circuits.

[0052] The circulation circuit (Figure 1) comprises a heat exchanger (1) located inside the confinement (under the dome) and which includes an upper head (2) and a lower head (3) interconnected by exchange tubes heat exchangers (4) that form a single-row vertical heat exchange beam. An up duct (5) and a down duct (6) are connected to the heat exchanger (1). A cooling water supply tank (emergency heat removal tank (EHRT)) (7) connected to the downduct (6) is located above the heat exchanger on the exterior of the containment. A vapor relief valve (8) connected to the rising duct (5) is located in the cooling water supply tank (7) and connected thereto hydraulically. The vapor relief valve (8) is designed to eliminate condensate-induced water hammer and increased level of vibration in the rising duct system (5). The rising pipe of the steam relief valve (8) has a connection hole that allows it to perform these functions.

[0053] The upper head (2) and the lower head of the heat exchanger (3) are divided into heat exchange tube sections under the presumption that:

[0054] L/D ≤ 20,

[0055] where L is the head section length,

[0056] D is the head hole,

[0057] the rising duct design provides the minimum rising section height hrs to satisfy the following criteria:

[0058] ΔP res Δprsghrs + Δpheghhe,

[0059] hrs= (ΔPcres-Δpheghhe) /Δprsg,

[0060] where ΔPcres is the total hydraulic resistance of the circuit,

[0061] hhe is the heat exchanger height,

[0062] g is the gravity factor,

[0063] ∆ρrs=ρcw-(ρ´(1-x)+ρ”x),

[0064] ∆ρhe= ρcw-ρhw,

[0065] ρcw is the lower duct water density,

[0066] phw is the rising duct water density within the heat exchanger height range,

[0067] p, p” are the water and vapor saturation density

[0068]x is the average mass vapor quality of the two-phase mixture in the rising section.

[0069] The heat exchanger section has a single-row vertical beam. It is preferred that the spacing between any adjacent section tubes meets the wall of equivalent plane criterion.

[0070] In the preferred embodiment of the invention, the height of the heat exchange tube ensures that the criterion of turbulent convection on the outer surface of the heat exchanger is satisfied, namely:

[0071] Ra>4 -1012,

[0072] in which

[0073] Ra is the Rayleigh criterion,

[0074] g is the gravity factor,

[0075] l is the typical structure size — heat exchanger tube height,

[0076] v is the vapor-air kinematic viscosity coefficient,

[0077] pw is the density of vapor-air medium in the outer wall of the heat exchanger piping,

[0078] pc is the density of the vapor-water medium in confinement, v

[0079] SC is the Schmidt number,

[0080] Ddif is the vapor diffusion factor.

[0081] The rising duct from the heat exchanger section upper heads to the vapor relief valve has an upward slope to the angle of at least 10° with respect to the horizontal line, except for certain sections with a slope less than 10°, which has the length Lsec1 and the hole Dsec1, which satisfies the following criterion: Lsec1/Dsec1≤10.

[0082] The lowering duct has an inclination downwards to an angle of at least 10° with respect to the horizontal line, with the exception of certain sections with an inclination of less than 10°, length Lsec2 and hole Dsec2, which satisfies the following criterion : Lsec2/Dsec2 ≤ 10.

[0083] In the specific embodiment of the invention for the Leningrad-2 NPP reactor plant, the heat exchangers (1) of the circuits are located along the perimeter on the inner confining wall above the elevation of 49.3 m. Each heat exchanger has a heat exchange area of 75 m2. The heat exchange beam height is 5 m and is formed by 38x3 mm vertical tubes. The total heat exchange area of each channel is equivalent to 300 m2. The length (L) of the upper and lower sections of the heat exchanger heads is equal to 2.755 mm. The outer/inner diameter (D) of the upper head is 219/195 mm, the one among the lower heads is 194/174 mm.

[0084] System heat emission is selected to reduce and maintain confinement pressure at internal pressure within design limits during accidents based on reactor design, including those involving serious damage to the core.

[0085] The isolation valves (9) and (10) designed to isolate the heat exchanger (1) in the event of a leak, are mounted on the rising duct (5) and the lowering duct (6). In order to prevent excessive pressurization of the C PHRS circuits in the event of an emergency closure of the isolation valves, safety valves (not shown) are installed to discharge fluid flow below the tank level (7).

[0086] Isolation and safety valves are located in the annular reactor building envelope compartments at elevation +54.45 m.

[0087] The operation of the claimed system is based on natural refrigerant circulation and does not require starting actions. Heat energy is removed from confinement by condensation of vapor from the vapor mixture on the outer surface of the heat exchanger (1) from where it is transferred to the water supply tank (7) through natural circulation. Heat is ultimately removed from the water supply tank to the final heat sink by evaporation of the water in the tank. The cooling water supply tank (7) is supplied with refrigerant from the vapor relief valve (8), followed by the return of cooled refrigerant (water) to the heat exchanger (1) through the step-down duct (6). In this way, heat energy is transferred from the internal confinement volume to the final heat sink, the environment, through evaporation of the water in the tank (7) using the circulation circuit.

[0088] For experimental justification of the proposed system design efficiency, a significant amount of experimental work was carried out in various configurations.

[0089] The research was carried out on a full-scale model of the C PHRS cooling circuit installed on the JSC “Afrikantov OKBM” test stand. The PHRS model C circuit included a model condenser-heat exchanger, operating ducts located in the confinement model tank, and an operating vapor relief valve located in the water supply tank.

[0090] The heat removal capacity of the tested cooling circuit and the parameters of the vapor-gas medium in the tank are approximated to the actual reactor accident conditions of the operating system to the maximum point. Therefore, with the geometry and parameters of the C PHRS cooling circuit practically comparable to the full-scale cooling circuit design, the research results obtained for the C PHRS cooling circuit model are representative and can be applied to the circuit C PHRS cooling system operational.

[0091] Tests performed on the full-scale C PHRS cooling loop cycle show that at the maximum cooling water temperature of 100°C in the cooling water tank and the specified design capacity per cooling loop cycle, the pressure in the tank will not exceed the design limit pressure of 500 kPa.

[0092] Figure 2 shows the experimental dependence of the emission of C PHRS cooling circuits on the pressure of the vapor-gas fluid in the tank.

[0093] Figure 3 shows how the operation of the C PHRS influences the parameters inside the confinement in the event of an accident based on the project that involves depressurization of the reactor plant primary circuit (high peak) and safety system failure (line I shows parameters without PHRS operation, and line II shows parameters with PHRS operation).

[0094] The C PHRS cooling circuit model tests performed show that the circuit design parameters are satisfied in terms of both heat removal efficiency and circuit flow stability. Within the entire cooling circuit operating range (power operation from the initial state to water boiling), no hammering by water in the tank or vibration of the elements and structures of the tested circuit that could affect its operability were observed.

[0095] Therefore, the claimed system allows maintaining pressure under confinement below the design level without operator intervention for a long period of time and within the entire range of beyond-design based accidents involving mass and energy release. under confinement.

Claims (9)

1. Internal passive heat removal system of pressurized water reactor confinement with at least one cooling water circulation circuit comprising: - a heat exchanger (1) located inside the confinement and comprising an upper head (2 ) and a lower head (3) interconnected by heat exchange tubes (4), - an ascending duct (5) and a descending duct (6) connected to the heat exchanger (1), - a water supply tank cooling unit (7) located above the heat exchanger (1) outside the containment and connected to the descending duct (6), - a vapor relief valve (8) connected to the ascending duct (5), located in the steam supply tank water (7) and hydraulically connected to it, characterized in that the upper (2) and lower heads (3) are divided into heat exchange tube sections (4) under the presumption that: L/D ≤ 20, in which L is the head section length (2, 3), D is the head internal diameter (2, 3), the rising duct design (5) provides the minimum rising section height hrs to satisfy the following criteria: ΔP cres =Δprsgh rs +Δpheghhe, hrs=(ΔPcres — Δpheghhe) /Δprsg, where ΔPcres is the total hydraulic resistance of the circuit, hhe is the heat exchanger height, g is the gravity acceleration factor, Δprs=pcw- (p'(1-x)+p ” x), Δphe= pcw—phw, pcw is the down duct water density (6), phw is the up duct water density (5) within the height range of heat exchanger (1), p', p” are the water density and vapor saturation, x is the average mass vapor quality of the two-phase mixture in the rising section, and the heat exchange tubes ( 4) have a height that allows satisfying the turbulent convection criteria on the outer surface of the heat exchanger (1), when: Ra >4-1012, in Ra is the Rayleigh number, g is the gravity acceleration factor, l is the typical structure size — height of heat exchanger tubes (4) (1), v is the kinematic viscosity of the vapor-air medium, pw is the density of the vapor-air medium in the outer wall of the heat exchanger piping (1), pcont is the density of the vapor-water medium in the confinement, v Sc = is the Schmidt number, Ddif is the vapor diffusion factor. 2. System, according to claim 1, characterized by comprising four channels, each channel having four cooling water circulation circuits. 3. System according to claim 1, characterized in that at least a part of the rising duct (5) of the upper heads (2) of the heat exchanger sections (1) for the steam discharge device (8) is inclined upwards at an angle of at least 10° to the horizontal line. 4. System, according to claim 3, characterized in that the ascending duct (5) comprises portions made with an inclination of less than 10° in relation to the horizontal line, while said portions have length Lsec1 and diameter is Dsec1 that satisfy the relation Lsecl/Dsecl ≤ 10. 5. System, according to claim 1, characterized in that at least a part of the descending duct (6) has a downward inclination of at least 10° in relation to the horizontal line. 6. System, according to claim 5, characterized in that the descending duct (6) includes portions made with an inclination of less than 10° in relation to the horizontal line, while said portions have a length Lsec2 and diameter Dsec2 that satisfy the relation Lsec2 /Dsec2 ≤ 10. 7. System, according to claim 1, characterized in that the heat exchanger (1) is located under the confinement dome. 8. System according to claim 1, characterized in that the heat exchanger section (1) has a single-row vertical beam. 9. System according to claim 1, characterized in that the spacing between any adjacent tubes (4) in the heat exchanger section (1) meets the equivalent plane wall criterion.