KR830001184B1 - Deceleration buffer for hydraulic linea motion drive - Google Patents

Abstract

This appts. is especially useful in inserting fuel elements into a pressurized vessel. This consists of a fixed main cylinder, a reciprocating drive piston(17), & a buffer(28) breaking a drive piston at the end of one's stroke. The stationary buffing cylinder(39) contains shock-absorbing water of which the path member places on the same axis of a main cylinder has many holes(54) detached each other and capable of fluid flow from a buffing cylinder. This is characterized by increase in breaking power over a drive piston caused by the increase of the resistance of the fluid moved from a buffing cylinder, as a buffing piston(41) is moving into one a closing holes one after another.

Description

Reduction Shock Absorber for Hydraulic Linear Motion Drive

1 is a longitudinal sectional view of a simplified drive device.

2 is a longitudinal sectional view of a driving shock absorber or braking device according to the present invention;

* Explanation of symbols for main parts of the drawings

11 drive device 12 drive cylinder

13 lower flange 14 housing tube

17: drive piston 18: piston ring seal

21: display tube 23: stop piston

26: stop piston tube 27: plug

28: shock absorber 29: shock absorbing shaft

32: crossing opening 31: hole

39: shock absorber cylinder 41: annular shock absorbing piston

43: lower flange 51: shoulder

The present invention relates to a hydraulic or fluid drive system which is particularly useful for inserting fuel elements into a pressure vessel, such as operating a control rod of a reactor.

In well-known reactors such as those used in the Dresten nuclear power plant near Chicago and Illinois, the reactor core contains a number of fuel assemblies arranged in an array that undergoes fission reactions on their own.

The core is embedded in a pressure vessel and submerged in a fluid, such as hard water, that acts as a coolant and neutron moderator. Each fuel assembly has a tubular flow passage that includes a fuel material such as uranium oxide or plutonium and extends vertically and has a substantially square cross section surrounded by an array of fuel elements or rods supported between the upper and lower joint plates. Within the pressure vessel the fuel assemblies are supported in an array spaced from each other between the upper core grid and the lower core support plate. The lower joint plate of each fuel assembly has a nose portion fitted to a socket formed in the core support plate so as to communicate with the pressurized coolant supply chamber. The nose portion is formed with an opening through which the pressurized coolant upstream through the fuel assembly flow channel to move heat from the fuel element. Representative fuel assemblies of this type are D. a. Invention by Veneer et al., Published in US Patent No. 3,654,077. Fuel elements or rods are disclosed in US Pat. No. 3,378,458.

Multiple control rods containing neutron absorbing material are selectively inserted into the spaces or gaps between the nuclear fuel assemblies to control the core reactivity. In a known core arrangement as disclosed in US Pat. No. 3,020,887, the vane of each control rod tip is inserted into the space between four adjacent fuel assemblies so that the control rod tip has a sparse cross section.

As disclosed in the above-mentioned patent publication 3,020,887, a neutron absorbing material in the control rod can control the neutron density and core output level, thereby providing a control rod drive for selectively driving the control rod in and out of the core. Suitable neutron absorbers, in which boron is usually used, are disclosed in the mentioned patent publication 3,020,887. Many of the control rods, for example 1/2 or more, are removed from the core during normal operation. Residual control rods are inserted into the reactor core in various dimensions to control reactor power level and shape.

In the event of a rapid shutdown of the reactor, the control rod drive must be operated to insert all control rods rapidly into the core depth (usually called an emergency stop). This emergency stop operation involves rapid acceleration of the drive and control rods, high speed insertion and sudden deceleration of the moving object at the end of the insertion stroke.

By way of example, such an emergency stop speed is about 152 cm / sec (5 ft / sec) in conventional devices. Therefore, the control rod drive is conventionally equipped with a braking or deceleration device such as a hydraulic shock absorber to prevent excessive mechanical shock to the drive. Such decelerators are disclosed in US Pat. Nos. 3,020,887 and 3,020,888, both of which are cited herein.

As shown in FIG. 4 of U. S. Patent No. 3,020, 887, the control rod drive has a drive piston that carries the hollow indicator tube and is fitted to linearly move within the cylinder. In the driving piston and the display tube, a stop piston tube provided with a stop piston at the upper end is disposed. A sealing ring is arranged between the drive piston and the stop piston tube and between the drive piston and the cylinder.

The braking device has a flow opening arranged in series at regular intervals in the stop piston just below the stop piston at the end of the drive piston stroke. The opening is gradually closed by the sealing ring passing through the opening as the drive piston approaches the end of the stroke. This gradually increases the fluid flow resistance from the hollow display tube, thereby gradually increasing the deceleration force on the drive piston.

However, in such a device, the deceleration force has the disadvantage of generating a relatively high pressure differential across the sealing ring. In recent years, more rapid accelerations and even faster insertion speeds (eg (305 cm / sec)) are required during faster emergency stop times, resulting in very high deceleration forces and increased pressure differential across the sealing ring. There is a risk of premature failure of the seal ring.

In the present invention, the drive braking device is provided with a buffer chamber or a buffer cylinder which is installed in the stop piston and filled with a fluid which is normally sealed. The shock absorbing cylinder is normally closed by an annular shock absorbing piston surrounding the shock absorbing shaft connecting the piston tube upper end to the stop piston. The spring in the shock absorbing cylinder causes the shock absorbing piston to exit the shock absorbing cylinder and engage with the shoulder of the shock absorbing shaft so that the shock absorbing cylinder is sealed to prevent the fluid in the cylinder from leaking out.

At the end of the insertion stroke of the piston, the drive piston engages the flange of the lower end of the shock absorbing piston and moves the shock absorbing piston into the shock absorbing cylinder. This operation opens the buffer cylinder so that the fluid in the cylinder flows out through a series of radial openings and axial holes disposed on the buffer shaft stage. As the shock absorber piston is further moved into the shock absorber cylinder, the piston gradually closes the opening, thereby preventing fluid from escaping from the shock absorber cylinder, thereby increasing the braking action.

When the drive piston stops, the shock absorber spring pushes the piston out of the cylinder, allowing fluid to flow in and the piston seated on the shock absorber shoulder to seal the cylinder again.

1 is a simplified diagram of a control rod drive with a shock absorbing or braking device of the present invention. As shown, the drive device 11 has a drive cylinder 12 supported in a housing tube 14 secured through the bottom 16 hole of a pressure vessel or the like and having a lower flange 13. do. A piston ring seal 18 is provided in the drive cylinder 12 and a drive piston 17 is provided that moves in the cylinder. The drive piston 17 and the control rod drive engagement spud 19 are connected by an indicator tube. In order to indicate the raised position of the display tube, the display tube 21 includes a latch groove 22 formed in series at regular intervals in engagement with a latch (not shown in this figure and shown in US Patent No. 3,020,887). have. In the display tube 21, a stop piston 23 including a piston ring seal 24 is provided. The stop piston 23 is held in a fixed position because it is connected to the stop piston tube 26 which is fixed to the lower end of the cylinder and sealed with a plug 27 in the lower region of the drive cylinder 12. The piston ring 35 provides a fluid seal between the stop piston tube 26 and the drive piston 17. The stop piston 23 is connected to the upper end of the stop piston tube 26 via a shock absorber or brake 28, which will be described in FIG. 2. For the purposes of the present invention, the shock absorber 28 has a cross opening 32 and a hole providing a flow passage between the stop piston tube 26 and the annular space 33 between the piston tube and the indicator tube 21. 31 is provided with a shock absorbing shaft 29.

A brief description of the operation of the drive unit 11 is as follows. In order to move the drive upward, a pressurized flow, such as water, is supplied through the updrive passage 34 to the bottom of the drive piston 17. At the same time, the downward drive passage 36 is opened at low pressure. Therefore, when the pressurized water drives the driving piston 17 upwards, the water in the annular space 33 passes down the stop piston tube 26 via the cross opening 32 and the hole 31 to open the passage 36. Is emitted through.

In order to move the drive down, the upward drive passage 34 is opened at a low pressure and pressurized water flows into the downward drive passage 36 to stop the stop seastone tube 26, the hole 31, and the cross opening 32. It flows into the annular space 33 via, and the water in the annular space 33 is pressurized to drive a drive piston downward.

Conventionally, the downward movement of the drive (removal of control rods) is carried out gradually (by one groove) at a relatively low speed. On the other hand, the upward movement of the drive device (control rod insertion) is sometimes performed continuously (such as inactive stop conditioning) at high speed. During this rapid insertion, the drive piston 17 is driven to the stop piston 23 at the end of the drive piston stroke. When approaching, it is necessary to restrain the drive piston movement and disperse a significant amount of kinetic energy of the moving part so as not to exert excessive mechanical impact on the drive.

A shock absorber 28 is provided for this purpose, and its function and structure will be described in detail with reference to FIG. 2 as follows.

The above-described shock absorbing shaft 29 is fixed to the stop piston tube 26 by the pin 37 such as the lower end and the stop piston 23 by the pin 38 to the upper end, respectively. The buffer shaft 29 is formed with a stepped hole 31 over most of the length of the buffer shaft from an open end formed at the bottom of the shaft to a closed end adjacent to the shaft top.

Under the stop piston 23 is formed a buffer cylinder 39 with an open end. The annular buffer piston 41 has an outer hole which can slide in close contact with the cylinder 39 and a piston ring seal 42 is provided adjacent to the upper end. The lower end of the piston 41 is formed with a lower flange portion 43 extending in and out while having an inner diameter that can slide in close contact with the large diameter portion 44 of the shaft 29. An upper flange portion 46 is formed at the upper end of the buffer piston, which extends in and out while having an inner diameter that can slide in close contact with the small diameter portion 47 of the shaft 29. The inner diameter of the body of the piston 41 is determined such that an annular fluid flow space 48 is provided.

The spring 49 in the cylinder 39 pushes the piston 41 out of the cylinder so that the upper flange 46 engages with the shoulder 51 where the buffer shaft 29 is formed near the aperture change. Water is retained in the buffer cylinder 39 due to the engagement of the upper flange 46 and the shoulder.

Near the aperture of the shaft 29, an annular recess 52 is formed which connects the fluid flow to the hole 31 via the cross opening 53. To obtain the required braking action. The small-diameter portion of the buffer shaft 29 located in the cylinder 39 is formed with holes or openings 54 (1) to 54 (9) arranged in series at intervals from each other. The opening is a fluid flow passage between the cylinder 39 and the top of the shaft 29 hole 31.

Plug 56 secured to something like pin 57 prevents fluid from flowing directly from top to bottom of hole 31. Engagement of the shoulder 51 and the piston flange 46 and the plug 56 retains the water necessary for the braking action in the cylinder 39. By retaining water in the cylinder 39, it is possible to prevent the loss of water, which turns water into steam under certain temperature and pressure conditions. In FIG. 1, the drive insertion is carried out by pressurized water flowing through the updrive passage while the downward drive passage is opened at low pressure, the low pressure being passed through the hole 31 of the shaft 29 through the piston tube 46. Can be extended.

Thus, if there is no plug 56, the pressure of the water in the cylinder 39 is, for example, about 3.447 x 10 ⁶ pascals (about 5000 psig). If the water temperature is at or above 121 ° C. (250 ° F.) or higher, the water in the cylinder will turn into steam, resulting in a loss of buffer water. As mentioned above, this problem can be avoided by retaining water in the cylinder.

The shock absorber and its operation will be described in detail as follows. As described above, when the drive piston 17 approaches the end of the stroke when the drive is inserted, the upper annular surface (marked 58 in FIG. 2) of the drive piston engages with the lower flange 43 of the buffer piston 41. The shock absorbing piston 41 is driven into the shock absorbing cylinder. This disengages the cushioning piston upper flange 46 from the shoulder 51 and releases water from the cylinder through the recesses 52 and the openings 54 (1) to 54 (9). The flow path of water is described as follows. That is, after passing through the opening 31 (54) through the opening (54) (1) to 54 (9), after passing through the crossing opening 53 into the annular space 48, through the crossing opening 59 (31) flows down into the stop piston tube (26). The damping piston 41 is further moved into the cylinder 39 and the upper flange 46 of the piston successively closes the openings 54 (1) to 54 (8). This gradually increases the resistance to fluid flow from the cylinder to disperse the kinetic energy of the moving part and provide the required braking action.

Claims (1)

A linear motion generator having a fixed main cylinder and a drive piston arranged to reciprocate and a shock absorber for braking the drive piston in a given direction at the end of the stroke of the drive piston, wherein the fixed buffer cylinder is disposed coaxially within the main cylinder. And a fixed buffer fluid passage member having a plurality of holes disposed coaxially within the buffer cylinder and spaced apart from each other to allow the buffer water to flow from the buffer cylinder, and elastic means for the buffer piston to drive the piston. Pushing the buffer piston in a given direction, the piston stop means normally restricts the buffer piston movement and seals the sac buffer cylinder normally so that the buffer water does not flow out. The cushioning piston by engaging As the buffer cylinder stops from the buffer piston stop means and moves along the buffer cylinder, the buffer cylinder is opened and the buffer water flows out of the cylinder through a spaced opening disposed in the buffer fluid passage member. It is mounted on the fluid passage member and disposed to reciprocate in the buffer cylinder, and the spaced openings are closed in sequence as the buffer piston is further moved into the buffer cylinder, thereby gradually increasing the fluid flow resistance from the buffer cylinder. Decelerating shock absorber for the hydraulic linear motion drive device, characterized in that to increase the braking force for the drive piston.

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