Containment Internal Passive Heat Removal System

Abstract

The invention relates to the nuclear energy field, including pressurized water reactor containment internal passive heat removal systems. The invention increases heat removal efficiency, flow stability in the circuit, and system reliability. The system has at least one cooling water circulation circuit comprising a heat exchanger inside the containment and including an upper and lower header interconnected by heat-exchange tubes, a riser pipeline and a downtake pipeline connected to the heat exchanger, a cooling water supply tank above the heat exchanger outside the containment and connected to the downtake pipeline, a steam relief valve connected to the riser pipeline and located in the water supply tank and hydraulically connected to the latter. The upper and lower header of the heat exchanger are divided into heat exchange tube sections on the assumption that: L/D≦20, L being the header section length, D being the header bore.

Claims

1. A pressurized water reactor containment internal passive heat removal system with at least one cooling water circulation circuit, comprising: a heat exchanger located inside the containment and comprising an upper header and a lower header interconnected by heat-exchange tubes, a riser pipeline and a downtake pipeline connected to the heat exchanger, a cooling water supply tank located above the heat exchanger outside the containment and connected to the downtake pipeline, a steam relief valve connected to the riser pipeline, located in the water supply tank and connected to the same hydraulically, wherein the upper and the lower headers are divided into heat-exchange tube sections on the assumption that:
L/D≦20, where L is the header section length, D is the header bore, the riser pipeline design provides the minimum riser section height h.sub.rs to meet the following criterion:
ΔP.sup.c.sub.res=Δρ.sub.rsgh.sub.rs+Δρ.sub.hegh.sub.he,
h.sub.rs=(ΔP.sup.c.sub.res−Δρ.sub.hegh.sub.he)/Δρ.sub.rsg, where ΔP.sup.c.sub.res is the circuit total hydraulic resistance, h.sub.he is the heat exchanger height, g is the gravity factor,
Δρ.sub.rs=ρ.sub.cw−(ρ′(1−x)+ρ″x),
Δρ.sub.he=ρ.sub.cw−ρ.sub.hw, ρ.sub.cw is the downtake pipeline water density, ρ.sub.hw is the riser pipeline water density in the within the heat exchanger height range, ρ′, ρ″ are the water and steam saturation density, x is the mean mass steam quality of the two-phase mixture in the riser section.

2. A system according to claim 1, wherein the system includes four channels, each comprising four cooling water circulation circuits.

3. A system according to claim 1, wherein at least a part of the riser pipeline from the upper headers of the heat exchanger sections to the steam relief valve has an upward inclination to an angle of at least 10° in relation to the horizontal line.

4. A system according to claim 3, wherein the riser pipeline includes sections with an inclination angle of less than 10° in relation to the horizontal line, the length of such sections is L.sub.sec1 and the bore is D.sub.sec1 meeting the following criterion: L.sub.sec1/D.sub.sec1≦10.

5. A system according to claim 1, wherein at least a part of the downtake pipeline has a downward inclination to an angle of at least 10° in relation to the horizontal line.

6. A system according to claim 5, wherein the downtake pipeline includes sections with an inclination angle of less than 10° in relation to the horizontal line, the length of such sections is L.sub.sec2 and the bore is D.sub.sec2 meeting the following criterion: L.sub.sec2/D.sub.sec2≦10.

7. A system according to claim 1, wherein the heat-exchange tubes have a height allowing to meet the criteria of turbulent convection on the heat exchanger outer surface, namely:
R.sub.a>4.Math.10.sup.12, where $R_a=\frac{{\mathrm{gl}}^3.Math.S_c}{{\nu }^2}.Math.\frac{{\rho }_w-{\rho }_{30}}{{\rho }_{30}}.Math.\text{:}$ R.sub.a is the Rayleigh criterion, g is the gravity factor, l is the typical structure size—heat exchanger tube height, ν is the steam-air kinematic viscosity coefficient, ρ.sub.w is the steam-air medium density on the outer wall of the heat exchanger tubing, ρ.sub.c is the steal-water medium density in the containment, $S_c.Math.\frac{\nu }{D_{\partial u.Math..Math.\phi }}$ is the Schmidt number, D.sub.dif is the steam diffusion factor.

8. A system according to claim 1, wherein the heat exchanger is located under the containment dome.

9. A system according to claim 1, wherein the heat exchanger section has a single-row vertical bundle.

10. A system according to claim 1, wherein the spacing between any adjacent tubes in the heat exchanger section meets the equivalent plane wall criterion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The design of the invention is illustrated by drawings, where:

[0043] FIG. 1 shows the cooling water circulation circuit design,

[0044] FIG. 2 shows the experimental dependence of the C PHRS cooling circuit output on the pressure of the steam-gas fluid in the tank,

[0045] FIG. 3 shows the calculated dependency of pressure and temperature on time in the course of an accident.

DETAILED DESCRIPTION

[0046] The claimed system is a combination of cooling water circulation circuits. In the preferable embodiment of the invention, the claimed system consists of four completely independent channels, each comprising four such circulation circuits.

[0047] The circulation circuit (FIG. 1) comprises a heat exchanger (1) located inside the containment (under the dome) and including an upper header (2) and a lower header (3) interconnected by heat-exchange tubes (4) forming a single-row vertical heat-exchange bundle. A riser pipeline (5) and a downtake pipeline (6) are connected to the heat exchanger (1). A cooling water supply tank (emergency heat removal tank (EHRT)) (7) connected to the downtake pipeline (6) is located above the heat exchanger outside the containment. A steam relief valve (8) connected to the riser pipeline (5) is located in the cooling water supply tank (7) and connected to the same hydraulically. The steam relief valve (8) is designed for elimination of condensate-induced water hammer and increased vibration level in the system riser pipeline (5). The riser pipe of the steam relief valve (8) has a connection hole enabling it to fulfill these functions.

[0048] The upper header (2) and the lower header (3) of the heat exchanger are divided into heat-exchange tube sections on the assumption that:

L/D≦20,

[0049] where L is the header section length,

[0050] D is the header bore,

[0051] the riser pipeline design provides the minimum riser section height h.sub.rs to meet the following criterion:

ΔP.sup.c.sub.res=Δρ.sub.rsgh.sub.rs+Δρ.sub.hegh.sub.he,

h.sub.rs=(ΔP.sup.c.sub.res−Δρ.sub.hegh.sub.he)/Δρ.sub.rsg,

[0052] where ΔP.sup.c.sub.res is the circuit total hydraulic resistance,

[0053] h.sub.he is the heat exchanger height,

[0054] g is the gravity factor,

Δρ.sub.rs=ρ.sub.cw−(ρ′(1−x)+ρ″x),

Δρ.sub.he=ρ.sub.cw−ρ.sub.hw,

[0055] ρ.sub.cw is the downtake pipeline water density,

[0056] ρ.sub.hw is the riser pipeline water density in the within the heat exchanger height range,

[0057] ρ′, ρ″ are the water and steam saturation density,

[0058] x is the mean mass steam quality of the two-phase mixture in the riser section.

[0059] The heat exchanger section has a single-row vertical bundle. It is preferable that the spacing between any adjacent section tubes meets the equivalent plane wall criterion.

[0060] In the preferable embodiment of the invention, the heat-exchange tube height ensures that the criterion of the turbulent convection on the heat exchanger outer surface is met, namely:

R.sub.a>4.Math.10.sup.12,

[0061] where

[00003]$R_a=\frac{{\mathrm{gl}}^3.Math.S_c}{{\nu }^2}.Math.\frac{{\rho }_w-{\rho }_{30}}{{\rho }_{30}}.Math.\text{:}$

[0062] R.sub.a is the Rayleigh criterion,

[0063] g is the gravity factor,

[0064] l is the typical structure size—heat exchanger tube height,

[0065] ν is the steam-air kinematic viscosity coefficient,

[0066] ρ.sub.w is the steam-air medium density on the outer wall of the heat exchanger tubing,

[0067] ρ.sub.c is the steal-water medium density in the containment,

[00004]$S_c.Math.\frac{\nu }{D_{\partial u.Math..Math.\phi }}$

is the Schmidt number,

[0068] D.sub.dif is the steam diffusion factor.

[0069] The riser pipeline from the upper heat exchanger section headers to the steam relief valve has an upward inclination to the angle of a least 10° in relation to the horizontal line, except for certain sections with an inclination less than 10°, having length L.sub.sec1 and bore D.sub.sec1, meeting the following criterion: L.sub.sec1/D.sub.sec1≦10.

[0070] The downtake pipeline has a downward inclination to the angle of a least 10° in relation to the horizontal line, with the exception of certain sections with an inclination less than 10°, length L.sub.sec2 and bore D.sub.sec2, meeting the following criterion: L.sub.sec2/D.sub.sec2≦10.

[0071] 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 containment inner wall above elevation 49.3 m. Each heat exchanger has a heat-exchange area of 75 m.sup.2. The heat-exchange bundle height is 5 m and is built up by 38×3 mm vertical tubes. The total heat-exchange area of each channel amounts to 300 m.sup.2. The length (L) of the upper and lower sections of the heat exchanger headers equals 2,755 mm. The outer/inner diameter (D) of the upper header is 219/195 mm, the one of the lower header is 194/174 mm.

[0072] The system heat output is selected so as to reduce and maintain pressure in the containment inside pressure within the design limits during beyond design basis accidents of reactors, including those involving severe core damage.

[0073] Isolating valves (9) and (10) designed for isolation of the heat exchanger (1) in the event of its leakage are mounted on the riser pipeline (5) and downtake pipeline (6). To prevent overpressurization of the C PHRS circuits in case of emergency closing of the isolating valves, safety valves (not shown) are installed to discharge fluid below the tank (7) level.

[0074] The isolating and safety valves are located in the reactor building envelope annulus compartments at elevation+54.45 m.

[0075] The claimed system operation is based on coolant natural circulation and requires no startup actions. Heat energy is removed from the containment by steam condensation from the steam-air mixture on the outer surface of the heat exchanger (1) from where it is transferred to the water supply tank (7) by means of natural circulation. Heat is ultimately removed from the water supply tank to the ultimate heat sink by evaporation of the water in the tank. The coolant is supplied from the steam relief valve (8) to the cooling water supply tank (7), followed by the cooled coolant (water) return to the heat exchanger (1) through the downtake pipeline (6). Thus, heat energy is transferred from the containment internal volume to the ultimate heat sink, the environment, by means of evaporation of the water in the tank (7) using the circulation circuit.

[0076] For experimental justification of the proposed system design efficiency, a significant amount of experimental work has been performed on several experimental setups.

[0077] Research has been performed on a full-scale model of the C PHRS cooling circuit installed on the JSC “Afrikantov OKBM” test stand. The C PHRS circuit model included a heat-exchanger-condenser model, operational pipelines located in the containment model tank, and a operational steam relief valve located in the water supply tank.

[0078] The heat removal capacity of the tested cooling circuit and parameters of the steam-gas medium in the tank are approximated to the actual reactor accident conditions of the operational system to the maximum extent. 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 may be applied to the operational C PHRS cooling circuit.

[0079] The tests performed on the full-scale C PHRS cooling circuit loop shows that at the maximum cooling water temperature of 100° C. in the cooling water tank, and the specified design capacity per cooling circuit loop, the pressure in the tank will not exceed the design limit pressure of 500 kPa.

[0080] FIG. 2 shows the experimental dependence of the C PHRS cooling circuit output on the pressure of the steam-gas fluid in the tank.

[0081] FIG. 3 shows how the functioning of the C PHRS influences parameters inside the containment in case of a beyond design basis accident involving depressurization of the reactor plant primary circuit (large leak) and safety system failure (line I shows parameters without PHRS operation, and line II shows parameters with PHRS operation).

[0082] The full-scale C PHRS cooling circuit model tests performed show that the circuit design parameters are met both in terms of heat removal efficiency and circuit flow stability. Within the whole range of cooling circuit operation (power operation from the initial state to water boiling), no water hammering in the tank or vibration of the elements and structures of the tested circuit were observed that could affect its operability.

[0083] Therefore, the claimed system allows to maintain the pressure under the containment below the design level without operator's intervention for a long period of time and within the whole range of beyond design basis accidents involving release of mass and energy under the containment.