WO2017063615A1

WO2017063615A1 - Passively actuated cross-flow valve for a coaxial tubing

Info

Publication number: WO2017063615A1
Application number: PCT/CZ2016/000053
Authority: WO
Inventors: Otakar FRÝBORT; Karel GREGOR; Petr HÁJEK
Original assignee: Centrum výzkumu Rež s.r.o.
Priority date: 2015-10-12
Filing date: 2016-05-09
Publication date: 2017-04-20
Also published as: SK32018A3; SK288675B6; CZ306907B6; CZ2015723A3

Abstract

A passively actuated cross-flow valve suitable to be used in a double tubing in coaxial arrangement, said coaxial tubing comprising an inner branch and an outer branch, the cross-flow valve comprising two discs, namely a movable disc (1) and a fixed-mounted disc (2), the discs having the same shape and comprising six annular sectors, the diameter of said discs being adapted so that in use they are larger than the diameter of the outer tube of the coaxial tubing, and as such the discs extend up to the flow cross-sections of both branches of the coaxial tubing. The discs have slant drilled holes (6) in the annular sectors of the valve body (3), enabling crossing of the flows. Changing the valve position from closed to open is actuated by a lever (7), which is controlled by a piston (8). The piston is placed in a cylinder (9) and jointed with the valve body and is interconnectable via a signal pipe (10) with both the suction and delivery sides of a main circulation compressor in a circuit. The force of a spring (11) is adapted to act on the piston to, in use, overcome gas overpressure that is equal to the pressure difference between the suction side and the delivery side of the circulation compressor. If any change in pressure occurs, the proportion of forces acting on the piston will change and this will initiate movement of the lever and turning of the valve disc.

Description

PASSIVELY ACTUATED CROSS-FLOW VALVE FOR A COAXIAL TUBING

Field of the Invention

The invention generally relates to a passively actuated cross-flow valve for the coaxial tubing. This valve is primarily intended to ensure proper conditions for a safe final cooling of the gas-cooled fast nuclear reactor and extraction of decay heat from the active zone of the reactor. This valve, however, can be used for all tubing systems in a coaxial arrangement, which require crossing of the flow in the coaxial branches, closing of one branch and crossing of the another one, or closing of both tubing branches at the same time.

Known State of the Art

Coaxial valves had been developed even earlier but the valves were always located directly in the centreline of the tube, and moreover, the existing valves for the coaxial tubing were designed to close fully, enabling stopping of the flow in both coaxially arranged branches, or partially, enabling stopping of the flow in the outer branch and transferring of the flow into the inner branch. A valve for the coaxial tubing that would allow both flows to cross over each other and change the flow direction between each of the branches has not been constructed yet.

This type of valve is usable mainly in the GFR type reactor {Gas-cooled Fast Reactor) being prepared now. GFR represents one of 6 basic concepts being developed for the Generation IV nuclear energy reactor systems.

This reactor system uses gas (for example, carbon dioxide or helium) as coolant. Heated gas from the nuclear reactor flows through the hot branch into a heat exchanger, and then having been cooled there, it flows back to the reactor through the cold branch. The circulation circuits composed of the hot branch and the cold branch are connected to the reactor vessel and designed as coaxial circuits. These circulation branches have a coaxial arrangement pattern, i.e. two coaxially arranged tubes. The inner tube represents the hot branch while the cold branch is a space between the outer and inner tubes.

The properties of gaseous coolant also bring specific requirements for the safety of these reactors. Decay heat from the active zone of the nuclear reactor after its shutdown shall be extracted by forced or natural circulation of the coolant in the circuit specifically designated for this purpose. It is called accordingly "DHR circuit" {Decay Heat Removal) or "DHR loop". Under the anticipated normal operation of the nuclear reactor, this loop should not be used and should remain closed, or a defined minimum flow rate to keep the DHR system at required temperatures should be provided. At the same time, conditions suitable for the quick establishment of natural circulation in case of need (electricity failure) should be set up. This should be provided in accordance with requirements for the Generation IV reactors by a passively actuated system. Essentials of the Technical Invention

The invention relates to the construction of a valve that causes crossing of the flows in coaxial tubing while it is closed, and maintains the original flow direction while it is open, and to a passive control of the valve depending on a change in pressure in the primary circuit of the reactor system.

Essentials of the invention consist in the fact that the present system is composed of two main parts, namely a movable disc [1] and a fixed-mounted disc [2], diameter of which is larger than the diameter of the outer tube of the coaxial tubing, and as such they extend up to the flow cross-sections of both branches of the coaxial tubing. The discs have the same shape and they include six annular sectors with common central circle area, axes of which form an angle of 60°. Generally, discs have the same shape when viewed axially and include annular sectors with common central circle area. If the valve is open, sectors of both discs overlap, and if the valve is closed, sectors of both discs fill up the entire cross- section of the tubing. The fixed-mounted disc [2] is built into the valve body [3]. There is a roller bearing [4] with rolling elements [5] that are made of ceramics for high-temperature applications and enable rotary movement of the movable disc [1] against the fixed-mounted disc. Both discs have slant drilled holes [6] in their annular sectors to allow crossing of the flows when the valve is in "closed" position. Direction of the slant drilles holes is always identical at the respective disc. Holes in one disc body are oriented so as to enable crossing of the flow from the inner branch of the coaxial tubing into the outer branch, while the other disc has its slant drilled holes oriented so as to enable crossing of the flow from the outer branch of the coaxial tubing into the inner branch.

When the valve is open, discs are turned in relation to each other so that they overlap. The valve enables flow passage in both branches and the slant drilled holes in the disc bodies are closed under these circumstances, thus disabling the flows to cross each other. Flows in the outer and inner branch of the coaxial tubing pass through the valve while it is open so that they do not change their direction.

When the valve is closed, discs are turned in relation to each other so that they do not overlap and jointly fill up and close the flow cross-sections of both branches. Any direct flow passage through the outer and inner branches of the coaxial tubing is thus avoided. The slant drilled holes in the valve disc bodies are passable under these circumstances and enable cross passage of the flow through the valve in closed position. Some portion of the flow that passes through the slant drilled holes changes its direction and is transferred from the outer branch to the inner branch in one direction and from the inner branch to the outer branch in the other direction. Thus the main function of the cross-flow valve for the coaxial tubing is achieved.

A passive control of the valve shall mean a method that initiates change in the valve status from closed to open. This is not achieved by an active intervention of a human operator or by sending a signal from the control system to the motor that would actuate positioning of the valve. Positioning of the valve is achieved by a change in physical conditions (pressure level), which is initiated by a start-up (closing) or cut-off (opening) of the main circulation compressor in the reactor circuit. Changing the valve position from closed to open is actuated by a lever [7], which is controlled by a piston [8]. The piston [8] is placed in a cylinder [9], which is mechanically jointed with the body of the cross-flow valve [3] and is connected via a signal pipe [10] with both the suction and delivery sides of the main circulation compressor in the primary cooling circuit. Force of a spring [11] acts on the piston from one side while gas pushes against it from the other side with overpressure that is equal to the pressure difference between the suction side and the delivery side of the main circulation compressor. If any change in pressure in the primary circuit occurs, the proportion of forces acting on the piston will change and this will initiate movement of the lever and turning of the valve disc. Proper limits for slight turning of the disc, or more precisely, setting of the valve to open or closed position will be established by the length of the piston and by delimiting the stop position of the lever.

Considering the use of the valve in a helium environment at temperatures up to as high as 1000°C, movable disc may not get in direct contact with the fixed-mounted disc or the valve body because a diffusion welding of the parts is highly probable. This is why the valve is not 100% tight even when closed. Sealing between the inner and outer tubing is based on the principle of a labyrinth seal.

For applications in tubing with lower operating temperatures at which there is no risk of welding of the valve parts together, valves can be made in fully tight version without seals, using conventional packing materials such as Teflon or graphite.

Alternative design of the valve according to the presented technical invention has several annular sectors, depending on the model of the actuator and requirements for the pressure loss of the valve when it is open. Based on the admissible valve pressure loss, diameter of both the fixed-mounted and the movable disc may be identical with the diameter of the tube.

Another possible design of the valve according to the presented invention enables passive method of control via an electric actuator that will maintain the valve, while in operation, in the required position, and if a power supply failure (accident) occurs, the valve will be automatically set to the opposite position using a spring. For specific applications, passive control of the valve can be replaced with any manual actuator or an actively controlled pneumatic or electric actuator.

Depending on the application and environment, for which the valve is intended, valve bearing can be alternatively constructed as a roller bearing with either steel or metallic rolling elements, or as a plain bearing made from metallic or non-metallic sliding materials that are suitable for the use in the specific environment. Explanations to the Drawings

The figures in the attached drawings show a cross-flow valve for the coaxial tubing. Fig. 1 gives an overall view of the cross-flow valve for the coaxial tubing. Fig. 2 shows a sectional view of the valve. Fig. 3 and Fig. 4 show the cross-flow valve for the coaxial tubing under two limit conditions. Fig. 3 shows the valve in closed position during which the flows are crossing each other and the valve function is being fulfilled. Fig. 4 shows the valve in open position, in which no crossing of the flows occurs and the direction of the flow passage through the outer and inner branches of the coaxial tubing remains unchanged. Fig. 5 clearly shows how the slant drilled holes that enable crossing of the flows are arranged on the valve.

Examples of the Embodiment of the Invention

The passively actuated cross-flow valve for the coaxial tubing is a device that can be used as a principal safety component in the GFR reactor concept. This type of reactor system consists of a reactor vessel, a primary circuit, a secondary circuit and a DHR circuit. Gas, usually helium, is used in the GFR system as coolant. The active zone of the reactor that is located in the bottom part of the reactor vessel is used as heat source.

Heated gas from the nuclear reactor passes through the hot branch into the heat exchanger, and after being cooled there, it flows back into the reactor through the cold branch. The primary circulation circuit is composed of a hot branch and a cold branch (designed as coaxial tubes), a reactor vessel, main heat exchanger and a circulator. The circulation branches have a coaxial arrangement pattern, i.e. two coaxially arranged tubes. The inner tube represents the hot branch while the cold branch is an annular space between the outer and inner tubes.

Extraction of decay heat from the active zone of the nuclear reactor after its shutdown is one of crucial safety situations, which requires a passive control system. Cooling of the active zone of the reactor should be provided by natural circulation of the coolant in the circuit specifically designated for this purpose.

A special circuit is specifically dedicated to the extraction of decay heat from the nuclear reactor. It is called accordingly "DHR circuit" {Decay Heat Removal) or "DHR loop". The passively actuated cross-flow valve for the coaxial tubing is a key element and a component part of the DHR circuit, providing for its proper function.

Under the anticipated normal operation of the nuclear reactor, this loop should not be used and should remain closed. At the same time, conditions suitable for the quick establishment of natural circulation in case of need should be set up. This should be provided by a passively actuated valve. The valve when closed (Fig. 1 and Fig. 3) disables flow passage in the respective branch through the corresponding flow cross- sections, and by using the slant drilled holes, it enables change in the flow direction from the inner tube to the outer annular space and from the outer annular space to the inner tube for the opposite flow direction. Consequently, conditions for the quick establishment of natural circulation in DHR branch are set up in that way in case of need.

If circumstances occur, under which decay heat from the active zone of the reactor needs to be extracted, DHR loop should be made passable. The cross-flow valve is to be set into open position (Fig. 2) to allow flow passage through both branches in the respective direction without crossing of the flows. Opening of the valve and its setting into open position is provided by a lever system that moves the valve body into new position based on the change in pressure in the primary circuit. It is achieved passively without involvement of any active actuating elements; it is based solely on the change in pressure level in the primary circuit.

The mechanism of flow crossing is based on the slant drilled holes in the valve body. This principle has been verified in a HTHL channel (High-Temperature Helium Loop), which is a test plant operated by the Rez Research Centre, which was built to simulate chemical and physical conditions of the coolant for the future models of gas-cooled nuclear reactors. Detail taken from the set of drawings is shown in Fig.4.

The operation of the active channel was used to check the functionality of slant drilled holes in the coaxial tubing, which provide for transferring of the flow from the inner tube to the outer tube and vice versa. The same principle will be used for the crossing of flows in the valve when closed.

Industrial Applicability

A passively actuated cross-flow valve for the coaxial tubing is intended to be integrated into the decay heat extraction system in GFR systems. The valve, if having a purely closing function without slant drilled holes, can be used for the main loop of the GFR reactor to close the inner and outer tubing branches at the same time.

The valve in a cross-flow version or a purely closing version is also usable for non-nuclear systems, which are used as a GFR reactor model plant for conducting testing in the field of thermohydraulics.

Technically speaking, cross-flow valves for the coaxial tubing can be used for all tubing systems arranged in a coaxial pattern, which require a change in the flow direction, closing of the flows at the same time or crossing of the flows. Motivation for such crossing can be a change in the concentration of liquids, a change in temperature of the flowing media or a requirement for making a mixture from the flowing media. Other potential fields of application of these valves include chemical and heat industries or cryogenic systems. List of Reference Marks

[I] Movable disc

[2] Fixed-mounted disc

[3] Valve body

[4] Bearing

[5] Rolling elements

[6] Slant drilled holes

[7] Lever

[8] Piston

[9] Piston cylinder

[10] Signal pipe

[I I] Spring

Claims

Patent Claims Claimed Scope of Protection

1. A passively actuated cross-flow valve for the tubing in coaxial arrangement, specifically designated for the crossing of flows in the coaxial tubing when the valve is closed, and for maintaining the original flow direction when the valve is open, and its passive control based on change in pressure in the tubing system; this system is characterized by two component parts, namely two discs, diameter of which is larger than the diameter of the outer tube of the coaxial tubing, and as such they extend up to the flow cross-sections of both branches of the coaxial tubing. Both discs have the same six annular sectors with common central circle area, axes of which form an angle of 60°, (generally, discs have the same shape of annular sectors with common centre when viewed axially), with one disc fixed-mounted [2] and built into the valve body [3], and a bearing [4] that is mounted in the axis of the central circle area and fitted with rolling elements [5] enabling rotary movement of the movable disc [1] in relation to the fixed-mounted disc; at the same time, both discs have slant drilled holes [6] in their annular sectors, which enable crossing of the flows, and the direction of the slant drilled holes at the respective disc is always identical with the other disc and the holes in one disc body are oriented so as to enable crossing of the flow from the inner branch of the coaxial tubing into the outer branch, while the other disc has its slant drilled holes oriented so as to enable crossing of the flow from the outer branch of the coaxial tubing into the inner branch; setting the valve from open to close position and vice versa is achieved by a change in physical conditions (pressure level), which is initiated by a start-up (closing) or cut-off (opening) of the main circulation compressor in the reactor circuit; changing the valve position from closed to open is actuated by a lever [7], which is controlled by a piston [8]; the piston [8] is placed in a cylinder [9], which is mechanically jointed with the body of the cross-flow valve [3] and is connected via a signal pipe [10] with both the suction and delivery sides of the main circulation compressor in the primary cooling circuit, where force of a spring [11] acts on the piston from one side while gas pushes against it from the other side with overpressure that is equal to the pressure difference between the suction side and the delivery side of the main circulation compressor; if any change in pressure in the primary circuit occurs, the proportion of forces acting on the piston will change and this will initiate movement of the lever and turning of the valve disc.

2. Device according to Claim 1, where, with the valve open, discs are turned in relation to each other so as to mutually overlap and the slant drilled holes in the disc bodies cannot fulfil their function under these conditions and the flows in the outer and inner branch of the coaxial tubing passing through the valve while it is open do not change their direction.

3. Device according to Claim 1 , where, with the valve closed, discs are turned in relation to each other so as not to mutually overlap, but jointly fill up and close the flow cross-sections of both branches, thus avoiding the flow passage in the outer and inner branches of the coaxial tubing; however this happens not to a full extent, and the slant drilled holes in the disc bodies of the valve enable passage of the flow through the valve in closed position, and therefore some portion of the flow, which passes through the slant drilled holes, changes its direction and is transferred from the outer branch into the inner branch in one direction and from the inner branch into the outer branch in the other direction.

4. Device according to Claim 1, which is characterized by two component parts, namely two discs, diameter of which is larger than the diameter of the outer tube of the coaxial tubing, and as such they extend up to the flow cross-sections of both branches of the coaxial tubing; both discs of the device have the same shape of at least two annular sectors with common central circle area; and generally, discs have the same shape of annular sectors with common centre when viewed axially.

5. Device according to Claims 1 to 4, at which the diameter of the fixed-mounted disc and movable disc can be identical with the diameter of the tube, if reduced flow cross-section of the device is not a problem.

6. Device according to Claims 1 to 4, at which sealing between the inner and outer tubing is based on the principle of a labyrinth seal, considering the fact that the valve is not 100% tight even when closed because of alternative use of the valve in environments with temperatures up to as high as 1000°C, where it should be guaranteed that the movable disc may not get in direct contact with the fixed-mounted disc or the valve body because a diffusion welding of the parts is highly probable.

7. Device according to Claims 1 to 4, at which for applications in tubing with lower operating temperatures at which there is no risk of welding of the valve parts together, valves can be made in fully tight version without seals, using conventional packing materials such as Teflon or graphite.

8. Device according to Claims 1 to 4 and 5 or 6, where a bearing with rolling elements made from ceramics is used for high-temperature applications to enable rotary movement of the movable disc in relation to the fixed-mounted disc, or depending on the application and environment for which the valve is intended, the valve bearing can be alternatively a rolling bearing with steel or metallic rolling elements, or a plain bearing made from metallic or non-metallic sliding materials.

9. Device according to Claims 1 to 4, 7 and 5 or 6, where the passive control can be achieved via an electric actuator that will maintain the valve, while in operation, in the required position, and if a power supply failure (or accident of the system) occurs, the valve will be automatically set to the opposite position using a spring, or an actively controlled pneumatic, electric or manual actuator.

10. Device according to Claims 1 and 4 to 9, where discs do not include slant drilled holes and if the valve is set to closed position, during which the fixed-mounted disc and the movable disc do not overlap each other, flows in both directions are closed.