JPH0774835B2 - Forced circulation reactor with fluid diode for natural circulation - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to energy generation systems and, more particularly, to forced circulation two-phase nuclear reactors.
The main object of the present invention is to provide a forced circulation boiling water reactor (FCBW).
R) is to increase the core neutron power stability when the pump is stopped.

[0002]

BACKGROUND OF THE INVENTION Nuclear reactors generate heat as a by-product of nuclear fission in the core and typically use a liquid transfer medium to remove this heat from the core. In a two-phase reactor, the heat of the core vaporizes the liquid transfer medium. This energy in the form of steam pressure is easy to transfer from the reactor for use elsewhere. The predominant type of two-phase reactor is the boiling water reactor (BW
R). Accordingly, much of the following discussion of BWRs can be readily applied to other two phase reactors.

In BWRs, the heat generated by nuclear fission of the core causes water to boil and can be used to generate steam. Water that has passed through the core without being vaporized is recirculated within the reactor vessel to form a continuous flow of water through the core. The steam generated is separated from the water and removed from the reactor vessel to generate energy. For example, steam is used to drive turbines, which are also used to drive generators to generate electricity. In the process, the vapor condenses and is returned to the container as feed water. The condensate is combined with water, which is recirculated internally to continue to assist heat transfer.

BWRs are identified by the means used to recirculate water within the reactor vessel. A forced circulation boiling water reactor (FCBWBR) relies mainly on a pump to drive water along a recirculation path. Natural circulating boiling water reactors (NCBWRs) rely primarily on the driving force generated by the density difference between the downcomer and the vapor column above the core. NCBWBR has the advantage of being simple. However, their inherent low pumping capacity limits reactor power. Therefore, the largest capacity BWRs are all FCBWRs. FCBWR and N
Despite the distinction between CBWRs, FCBWRs are preferably designed to utilize natural circulation so that decay heat can be removed from the core if the pump is stopped.

In NCBWR, the water rising from the core is guided vertically, promoting steam-water separation and supporting a relatively low density steam / water head on the core. Water recirculates down the reactor vessel and the ring downcomer between the chimney and the core. The water in the downcomer is denser than the steam and water mixture in the core and chimney region.
Differences in density force upward circulation through the core and chimney and downward circulation through the downcomer.

Natural circulation partially limits power output because of the limited circulation speed which causes the water to flow through the core for longer than the optimal time to be converted to steam. . Excessive boiling results in a large amount of steam in the core. This large amount of steam has an adverse effect on the stability of the core, which is due to the stability-deca
y ratio) depends on the ratio of the two-phase pressure drop to the single-phase pressure drop. In NCBWR, this problem is addressed by limiting the amount of heat generated by the core and thus the power output of the reactor.

FCBWRs, on the other hand, are typically designed to exceed the power available using only natural circulation. Excessive boiling and core instability occurs when full pump power failure occurs in an FCBWR operating at maximum capacity. Several independent pumps are provided to minimize the potential for total pump output failure.

Despite the level of safety provided by redundant pump operation, it is still worthwhile to increase the throughput or flow rate through natural circulation in FCBWRs. Natural circulation is particularly attractive as a stability backup because it does not depend on active components. Therefore, improvements in natural circulation are highly desirable in FCBWRs.

Conventionally, some bypass valves are used to increase the natural circulation in FCBWRs. This valve is designed to open automatically when the pump stops pumping, thereby increasing the cross-section of running water and enhancing natural circulation. The valve automatically closes while the pump is operating, preventing backflow through the valve. This bypass valve has moving parts that cause reliability problems.

[0010]

OBJECTS OF THE INVENTION It is an object of the present invention to provide the advantages that a bypass valve has to an FCBWR without the need for moving parts.

[0011]

SUMMARY OF THE INVENTION The present invention is used in FCBWRs to promote natural circulation when the pump is not operating.
To this end, the FCBWR has a chimney that supports the buoyancy head above the reactor core. The pump creates a pressure differential across the boundaries of the fluid circuit. The present invention has an opening through the boundary to enhance the natural circulation caused by the buoyancy head supported by the chimney. According to the invention, these openings consist of fluidic diodes that suppress backflow across the boundary when the pump is operating. In a typical implementation of the invention, the chimney function is achieved by a suitably designed vapor separator and the circuit boundary is the pump deck.

Fluidic diodes function similarly to check valves, except that they have no moving parts and do not completely seal. Fluidic diodes typically have openings that are relatively unobtrusive to "downstream" flow. However, the "upstream" flow diverts across the opening, creating turbulence with another upstream flow. This turbulence suppresses the upstream flow through the openings.

One type of fluidic diode has a set of nested cylinders. Each cylinder has a redirector extending radially inward and downstream. The redirector directs the downstream flow to the central opening without causing substantial turbulence.
Upstream flow is trapped between the cylinders and redirected radially inward across the openings. The cross flow into this opening mixes with another upstream flow, causing turbulence and restricting the upstream flow.

In the present invention, the flow in the downstream direction generated with a relatively small resistance is a natural circulation flow. The backflow caused during pumping is the upstream flow that meets the greater resistance. The fluidic diode allows flow in the downstream direction, but resembles a check valve that prevents flow in the upstream direction. Since the fluidic diode is not completely encapsulated, its effectiveness is not 100%. However, the basic advantage is achieved if the resistance to upstream backflow is at least twice the resistance in the downstream flow during natural circulation.

The main advantages of the invention are: 1) the valve sticking in the closed position when the valve has to be opened in response to a pump trip and stuck as intended, or 2) damaged by fatigue. In some cases, the neutron stability of the core is enhanced when the pump is stopped, without the drawbacks of moving parts that could adversely affect other parts of the reactor. Stability is improved because the enhanced natural circulation reduces the ratio of two-phase pressure drop to single-phase pressure drop in the core. It also improves the fission rate stability collapse ratio and improves core neutron power stability.

Since the fluid diode has no moving parts, reliability can be increased. The present invention is compatible with existing FCBWRs and does not require major redesign. The present invention can automatically respond to pump power failure without relying on an active feedback system. Thus, the present invention can reliably and effectively respond to reduced forced recirculation. These and other features and advantages of the invention will be apparent from the following description with reference to the accompanying drawings.

[0017]

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, an FCBWR system 100 includes a reactor pressure vessel 102 and its internal components as shown in FIG. Heat is FCBWR100
Of a fissionable material, which has a fuel bundle 106 of fissile material. Water circulating up through the core 104 is at least partially converted to steam. The steam separation assembly 108 separates steam from water, which is recirculated through the fluid return path. Steam separation assembly 10
Reference numeral 8 serves as a chimney that supports the drive head and promotes natural circulation of water in the container 102. The remaining water is removed from the steam by the steam dryer 110. The steam then exits the reactor through a steam outlet 112 near the vessel head 114.

The amount of heat generated in the core 104 is adjusted by inserting and retracting the control blades 116 and by changing the core flow. The degree to which the control blade 116 is inserted into the core 104 absorbs neutrons that can be used to promote chain reactions that generate heat within the core 104. A control rod guide tube 118 below the core 104 maintains vertical motion during the insertion and withdrawal of the control blades 116. The hydraulic control rod drive 120 performs the inserting and retracting operations of the control blade 116. A control rod drive housing 122 extends through the bottom head 124 of the container 102, where the housing is welded to a stub tube 126, which is also welded to the bottom head 124 of the container. The fuel bundle 106 is supported from below by a fuel support casting 128 mounted on a core support plate 130 provided at the base of the core 104. The top guide 132 assists in aligning the fuel bundles 106 when the fuel bundles 106 descend within the core 104.
The container 102 is mounted on a concrete pedestal 134.

The recirculation path in vessel 102 rises through core 104 and up through upstanding tube 136 of separator assembly 108 to vapor separator 137 of separator assembly 108.
Through upwards, outwards, and downwards through the downcomer 13
8 going radially outward, down through the downcomer 138, radially inward through the core inlet plenum 140, and back to the core 104.

A shroud 142 surrounds the core 104 so as to define the radially inner wall of the downcomer 138, and the downcomer 1 from the steam / water mixture rising through the core 104.
The fluid flowing downward through 38 is separated. The shroud 142 extends to the lower side of the core 104, and
8 and the core inlet plenum 140 form a boundary. The shroud 142 has ten electric pumps 146 (1
Only 10 are shown, but 6 to 10 are common) extending downward to a pump deck 144 to which are mounted. During forced circulation, the main flow path from downcomer 138 to core inlet plenum 140 passes through the annular inlet of pump 146. The shroud 142 is supported by the shroud support portion 148.

In accordance with the present invention, the flow cross-sectional area between the downcomer 138 and the core inlet plenum 140 is natural through the fluidic diode 202 (one shown in FIG. 2) when forced circulation is stopped. Increased by circulation. Each fluid diode 202 includes (cylinders 204a, 204b and 20
4c) (shown as 4c) has a radially nested cylinder 204 which extends inwardly into a bosh and redirects as shown in FIGS. 2, 3 and 4. 206 (direction changers 206a, 206b and 206c
Including). Each redirector 206 has an elliptical radius of curvature that increases from the circumference of the cylinder toward the center of the cylinder as shown in FIG. Rib support 208
As shown in FIG. 2, the cylindrical bodies 204 are supported with a certain space provided between them. Ten fluid diodes 202 are provided between each pair of adjacent pumps 146 (as shown in FIG. 3) and are attached to the pump deck 144 by welds 210.

If pump 146 is not operating,
The coolant is pump 1 as indicated by arrow 402 in FIG.
Flows downstream through 46. This natural circulation flow is downcomer 1
Driven by the differential pressure between the chimney action of 38 and the vapor separation assembly 108. However, the pump 146
Due to the limited flow cross-section of the pump, the pump can only provide limited natural circulation. The overall flow cross section of the natural circulation through the pump deck 144 is increased by the fluid diodes 202, each of which is shown in FIGS.
And each has a central opening 212 as shown in FIG. In each fluid diode 202, the redirector 206 concentrates natural circulation at each opening 212, as indicated by the flow arrow 404. The redirector 206 is configured to minimize turbulence to the natural circulation flow to minimize resistance to the natural circulation flow.

In operation, the pump forces water through the pump deck 144 as indicated by flow arrow 406. This forced flow creates a positive pressure differential across the pump deck 144. That is, the fluid pressure downstream of the deck 144 becomes higher than the fluid pressure upstream of the deck 144. This positive pressure difference causes a reverse flow 408 toward the fluid diode opening 212 as shown in FIG.
cause. This backflow 408 undesirably reduces the net efficiency of forced circulation when not restricted. However, most of this backflow is due to flow arrow 41.
They are trapped between the cylinders 204 as indicated by 0 and then redirected radially inwardly and downstream by the redirector 206 as indicated by the flow arrows 412. This redirected backflow produces a vortex flow 414 and a transverse flow 416 across the opening 214. The vortex flow 414 and the cross flow 416 mix,
A turbulent flow that interferes with the backflow 408 and blocks the backflow 408 is generated. Therefore, a net backflow 4 through the fluidic diode 202
18 is substantially reduced as compared to through aperture 212 in the absence of the asymmetric effect of fluidic diode 202.

The distance between the container wall 102 and the shroud 142 is 26 inches. The redirector 206 extends such that the central opening 212 has a constant diameter of 6 inches and the ten fluid diodes 202 pass the desired amount of increased natural circulation flow. As shown in FIG. 5, when looking at the fluid diode 202 from above the pump deck 144, the top redirector 206 of the outer cylinder 204a.
Only a can be seen. When viewed from below, the concentric circular structure of the cylindrical body 204 is clearly visible as shown in FIG. The rib support portion 208 is also shown in FIG.

As shown in FIG. 7, the method 700 of the present invention.
Has a conditional branch step 701 depending on whether the pump 146 is operating. If the pump is not running, then in step 711 fluid can flow downstream with minimal resistance through the fluidic diode 202, increasing natural circulation. If the pump 146 is operating, then in step 721 the fluid diode 2
The backflow through 02 is redirected radially and downstream, producing a crossflow 416. In step 722, vortex flow 414 and cross flow 416 mix with backflow 408 to create turbulence and concomitant resistance to backflow.

Those skilled in the art will understand that other embodiments are possible. Different fluid diode diameters can be used depending on the flow requirements and the number of fluid diodes actually used. The diameter of the central passageway or opening 212 need not be constant. Another fluid diode has a diverter configured to gradually narrow the backflow passage. Fluidic diodes of other designs can also be used. In particular, cascading diodes, Tesla diodes, scroll diodes, momentum fluid diodes, spiral diodes and spiral amplifiers are considered. For example, B.I. E. A. Jacobs and P.M.
J. Baker's paper `` The cascade connection diode (The
Cascade Diode ", Proceedings of The Third Cranfield Fluidics C
onference), Document No. K5, British Fluid Dynamics Research Association,
Cranfield, Bedford, UK (British Hyd
rromechanics Research Association, Cranfield, Bedf
ord, United Kingdom), 1968, pp. 63-8
2; also E. Sher's paper, "A Logical and Experimental Study of the Characteristics of Scroll Diodes in the Stable State.
(Theoretical and Experimental Study of the Scroll
Diode Characteristics and Steady Conditions) '', The Journal of Fluid Control,
Vol. 12, No. 4. Debridge Publisher
Publishing Co., Capertino, CA (Cuper
tino, California), December 1980, pp. 57-
70; Syled and J.I.
R. In a paper by Tippetts, `` A High Gain Active Diode
e--the Reserve Flow Vortex Amplifier) ", Proceedings of the Sixt
hCranfield Fluidics Conference), Ref. J4,
British Hydromechanics Resear
ch Association), Cranfield, Bedford, United Kingdom (197)
4 years, pp. 55-67; and Frank W. H .; Pole
(Frank W. Paul) Paper `` Fluid Mechanics of the Momentum Fluelic
Diode) ", IFAC on Fluids, November 1968
Proceedings of the November, 196
8, IFAC Symposium on Fluidics), Reference A1, Peter
Peter Pregrinus Ltd, London, 1
969, pp. See 1-15. Generally has a low impedance (resistance) in one direction and a high impedance (resistance) in the other direction.
Means for allowing asymmetrical flow with can be used to enhance natural circulation in accordance with the present invention.

Although the boiling water reactor shown has an internal electric pump, the invention is equally applicable to a reactor using a jet pump. Although the embodiments described have been carried out with boiling water reactors, the present invention is also applicable to other forced circulation reactors where natural circulation limited recirculation is possible. Two-phase reactors other than boiling water reactors have a vapor phase that can act as a buoyancy head for natural circulation, so such reactors can also be considered.
These and other changes and modifications to the embodiments described above are also contemplated by the present invention, the scope of which is limited by the claims.

[Brief description of drawings]

FIG. 1 is a partial cutaway perspective view of a forced circulation boiling water reactor according to the present invention.

2 is a cross-sectional view of a portion of the reactor of FIG. 1 showing one type of fluid diode structure according to the present invention.

3 is a perspective view of a portion of the reactor of FIG. 1 using an internal pump and fluidic diode according to the present invention.

4 is a cross-sectional view showing the flow of fluid through the pump and fluidic diode of the reactor of FIG. 1, with the flow arrows indicated by dotted lines representing natural circulation and the flow arrows indicated by solid lines representing forced circulation. It shows the flow between.

5 is a top plan view of the pump and fluidic diode of FIG. 3. FIG.

FIG. 6 is a bottom plan view of the pump and fluidic diode of FIG. 5, particularly showing rib supports between the cylindrical portions of the diode.

FIG. 7 is a flow chart of a method implemented by the present invention.

[Explanation of symbols]

 100 FCBWR system 102 Pressure vessel 104 Core 106 Fuel bundle 108 Steam separator 110 Steam dryer 138 Downcomer 140 Core inlet plenum 142 Shroud 144 Pump deck 146 Pump 202 Fluid diode 204 Cylindrical body 206 Turner 212 Opening

Continuation of the front page (56) Reference JP-A-5-188173 (JP, A) JP-A-5-188172 (JP, A) JP-A-59-52791 (JP, A) JP-A-1-197696 (JP , A) JP-A-58-193490 (JP, A)

Claims (9)

[Claims] 1. A reactor vessel (102) and a reactor core (104) disposed within the vessel, the reactor core defining a reactor core inlet plenum (140) below the reactor core. A core (104); chimney means (108) disposed on the core for guiding fluid upwardly out of the core along a substantially vertical path to support a steam / water column therein; A fluid return path for recirculating fluid exiting the chimney means to the core inlet plenum and defining upstream and downstream directions; and the fluid return path for driving the fluid in the downstream direction along the fluid return path. Means (146) that can be controlled to increase the pressure difference across the boundary (144) of the fluid, and that asymmetrically inhibits the flow of fluid across the boundary and allows fluid to traverse the boundary in the downstream direction. Relatively free A fluid diode means (202) for passing and restraining fluid flow across the boundary in the upstream direction, the fluid diode means crossing the boundary when the pump means is inactive. Flow of natural circulation (40
4) Unforced forced circulation two-phase reactor in which the fluid diode means suppresses backflow (408) across the boundary when the pump means is operating. 2. A nuclear reactor according to claim 1, wherein the flow resistance in the upstream direction by the fluid diode means (202) is at least twice the flow resistance in the downstream direction by the fluid diode means. 3. Reactor according to claim 1, wherein said fluid diode means (202) has no moving parts. 4. The atom of claim 1, wherein said fluid diode means is configured to suppress said backflow (408) by creating a turbulent flow when said pump means (146) is operating. Furnace. 5. A nuclear reactor pressure vessel (102) having a cylindrical vessel wall and a radiative core (104) for producing heat, the nuclear reactor core being disposed within the nuclear reactor pressure vessel, A radioactive core (104) defining a core inlet plenum (140) within the vessel and below the core; a chimney means (108) for supporting a steam / water column; and vertically and at least partially of the core. A cylindrical shroud (142) extending vertically to a lower level of the core, the shroud comprising a downcomer (1
38) defining a radially inner boundary, the vessel wall defining a radially outer boundary of the downcomer, and a cylindrical shroud (142) and internal parts disposed within the vessel. Recirculation pump means (146) having a pumping means for forming a pressure differential from the downcomer pipe to the core inlet plenum, the pressure differential being positive when the pump means is operating. Means (146) and a pump deck (14) provided at the base of the downcomer.
4) wherein pump internal components are mounted on the deck, the deck and the shroud defining a downcomer / plenum boundary between the core inlet plenum and the downcomer (144) Fluid diode means (202) attached to the pump deck for asymmetrically restricting fluid flow, the fluid being relatively free to pass through the pump deck in the downstream direction; Fluid diode means (2) for restricting fluid flow in the upstream direction through the
02), and the fluid diode means (4) when the pump means is not operating, a natural circulation flow (4) through the pump deck.
04) unsuppressed and the fluid diode means restricts backflow (408) through the pump deck when the pump means is operating. 6. The fluid diode means (202) comprises a plurality of radially nested cylinders (204) that redirect fluid in a downstream direction and a radially inward direction. When the fluid flows in the downstream direction, each of the diverting means (206) does not suppress the flow (404) in the downstream direction because the diverting means does not generate turbulence relatively, and the fluid flows in the upstream direction. In the case of flow in a direction, the diversion means causes a relatively large amount of turbulence to cause a reverse flow (40
The nuclear reactor according to claim 5, which acts to suppress 8). 7. A method for improving the stability of a core in a forced circulation two-phase nuclear reactor, wherein a natural circulation flow causes the pumping means to operate when the pumping means of the forced circulation reactor is not operating. By-passing through the opening (202) (711) and limiting (721, 722) backflow (408) through the opening when the pump means is operating. . 8. The method of claim 7, wherein the step of limiting the backflow comprises generating a turbulent flow (722) across the opening. 9. A method for improving core stability in a forced circulation two-phase nuclear reactor having a pump (146) forcing a cooling liquid downstream across a pressure differential boundary along a recirculation path, comprising: When the pump of the forced circulation reactor is not operating, the natural circulation flow is made to flow downstream through the opening (202) at the boundary of the recirculation path so that the resistance to the natural circulation flow becomes relatively small ( 711), if the pump operates to forcibly drive the coolant in a downstream direction across the boundary, resulting in a backflow (408) at the opening, a portion of the backflow. To form a cross flow (416) across the opening (712) and mix the cross flow with the back flow to create a turbulence that creates a relatively high resistance to the back flow. Existence The method is.