CH668850A5 - CORE REACTOR WITH A REACTOR CORE ADJUSTABLE BY CONTROL STAFF. - Google Patents

Description

DESCRIPTION

The invention relates to a nuclear reactor having a reactor core which can be regulated by control rods in a reactor pressure vessel which contains a liquid coolant, and a device for moving and positioning the control rods which comprises piston-cylinder units which are acted on by the coolant and in which step sections of pistons and face cylinders with narrower and wider gaps.

In control devices of the type mentioned above, the lines and valves which control the application of the piston-cylinder units are a weak point because leaks lead to the nuclear reactor being switched off because there is a risk of loss of coolant. The lines and valves mentioned are under full reactor pressure, so that repairs to improve the tightness in the operation of the nuclear reactor are hardly possible.

The invention is based on the object of improving the tightness of a nuclear reactor of the type mentioned at the outset in order to reduce the risk of undesired shutdowns and at the same time to optimally simplify the control members.

According to the invention, it is provided that several units are each connected to a valve block via a single control line, in which control valves for actuating the units are combined and connected to a common propellant pump for the coolant, and that the valve block with all control lines carrying the coolant are sealed metallic inclusion is housed with the reactor pressure vessel.

In the invention, the solution to the stated problem is tackled simultaneously in two ways. Firstly, the routing of the lines and the combination with a valve block reduce the risk of leaks. On the other hand, the tight metallic enclosure with the reactor pressure vessel ensures that leaks in the hydraulics do not lead to coolant leakage from the primary system of the reactor. Therefore, the operation of the reactor can continue because the hydraulic drive system of the control rods in the proposed embodiment is practically insensitive to leaks.

In principle, the invention can be implemented in such a way that all parts for hydraulic actuation are arranged within the reactor pressure vessel. The valve block is attached to the reactor pressure vessel and communicates with its interior through a special opening. The valve block itself can provide the required tightness

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the reactor pressure vessel by closing the special opening. In addition, it can also be provided that the valve block is surrounded by a hood covering the opening. For both embodiments, it is advantageous if the valve block is flanged directly to the reactor pressure vessel as an essentially cylindrical steel body and has parallel longitudinal bores, each associated with an assembly, into which mechanical parts of the control valves engage radially from the outside, while the magnetic drive elements of the valves on the outer circumference of the Valve block accessible and arranged in the drying.

The valve block can advantageously be assembled with the drive pump in order to avoid pressure-carrying intermediate lines. The drive pump can be arranged in such a way that the control rod is raised in relation to the primary pressure by a negative pressure generated by the pump, or by a corresponding positive pressure. Only the latter type is referred to here, since it is superior in terms of safety.

A particularly favorable embodiment, both in terms of space and in terms of reliability, is that the drive pump is a canned pump with a central suction channel placed directly on the valve block, in the pressure chamber of which the longitudinal bores on the circumference of the valve block leading to the units in an annular distribution flow out. The valve block then forms an element that contains all the essential lines in the form of internal bores, so that coolant losses to the outside are hardly possible. In addition, such a valve block can be exchanged as a compact component with a tolerable effort. In the event of a malfunction, remedial action can be taken quickly.

In the proposed arrangement, each unit is assigned two control valves located in parallel in the control line, which cooperate with the constriction and extension of the piston-cylinder unit. A single control valve is sufficient for bars that should not move to intermediate positions between the top and bottom position.

If both control valves are closed, only a minimal flushing flow determined by a small bypass or deliberate valve leaks flows through the line in question. This small flushing flow passes through the play between the stepped piston and the cylinder in the lifting unit without any appreciable drop in pressure, so that the control rod remains in the lowest position.

When the first of the two control valves (holding valve) is opened, the flow through the control line increases to such a value that the pressure required to raise the control rod builds up in the constrictions of the piston-cylinder unit. The staff keeps its position at the upper end of a constriction, but will not raise it beyond the next extension.

Opening the second control valve (lift valve) increases the flow through the control line to such an extent that the full lift pressure is also reached in the extension. The control rod moves up as long as this lift valve remains open.

The control rods are retracted from any position by the action of gravity when the lift and hold valve is closed, that is to say when the control line is shut off. The water in the lifting unit is squeezed through the piston gaps by the weight of the rod.

The lowering speed achieved in this way is not sufficient in many cases. The suction and pressure chamber of the drive pump can be short-circuited to increase it. As a result, the propellant pump pressure partially breaks down and the medium in the lifting unit can replenish

In addition, blow open the control valves through the control line.

This short circuit takes place via large, expediently hydraulically balanced solenoid valves in the valve block. These short-circuit valves can not only leak in the closed position, they should even let a defined bypass flow through.

It is also possible, at the same time as the short-circuit valves, which are kept closed by magnetic excitation, to de-energize the propellant pump itself and thus to ensure the propellant pressure collapse in a redundant manner.

As a diversified measure and in order to accelerate the shutdown process even more, the pressure chamber in the valve block can be temporarily connected to an initially pressure-free pressure vessel with limited content via solenoid valves. As a result, in addition to gravity, a corresponding proportion of the reactor system pressure in the shutdown direction also becomes effective for a period of time limited by the container size.

The control valves are expediently loaded by the drive pump pressure in the closing direction. This has among other things the advantage that the closing forces are applied by the pump pressure itself and that de-energized valves are always in the down position. On the other hand, the resulting hydraulic closing force must be overcome when the control valves are opened by correspondingly strong magnetic forces. It is therefore recommended that the control valves that are magnetically actuated during the opening stroke are preferably fed with reduced energy after leaving the closed position with the aid of a time control, since only a fraction of the opening force is needed to keep the control valves open.

In order to reduce the consumption of driving pump power and the thermally unfavorable feeding of cooler control medium into the reactor, the flow through the lifting units is drastically reduced in their uppermost position. This can be done by a correspondingly tight play between the piston and cylinder in this position or better by a support seat effective there between the piston and cylinder.

The pressure change in the control line when the top position is reached can be used to display the same. For example, a small piston or metal bellows can be arranged in the area of the holding valve, which is always open in this position, in such a way that it responds to line pressure changes. This movement can be transmitted electrically or magnetically to the outside.

A normal centrifugal pump delivers very different characteristics in cold and warm operating conditions. This complicates the design of such control rod drives, which have to work under all conditions and with great security.

Apart from electrical control processes, a safe method that cannot be influenced from the outside in order to keep the decisive motive pump pressure constant is that a corresponding bypass between the suction and pressure chamber of the pump is controlled by a throttle valve, the movement of which is connected in series Bimetal elements (e.g. alternative austenite-ferrite or zircon pipes) are made.

A comparable throttle control can also attack at another point (e.g. pump inlet swirl) and be controlled arbitrarily from the outside.

A pump pressure control (e.g. bypass throttle) which is arbitrarily effective from the outside within a certain design-related range can also be used, in particular when starting up the cold reactor

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to move individual control rods with great sensitivity. The prerequisite for this is that only one rod per valve block is moved between the top and bottom position.

An improvement in the production of hydraulic control rod drives is still possible in that the piston-cylinder units consist of a smooth cylinder and a piston grooved in the form of a labyrinth, and that the associated diameter clearance stages in the piston rod and one surrounding them at the cylinder end Bushing are incorporated, while the difficult to machine long cylinder remains smooth.

There are two basic arrangements for the control rod drives.

In the first one, which can be used for all control rod shapes, the lifting unit consisting of piston and cylinder lies above the core area in the reactor pressure vessel and at least one core height above it. In the extreme case, the units could also be housed in thimbles on the lid of the reactor pressure vessel.

The piston rod is connected to the control rod, which is movable in the core, via a detachable coupling. The pistons and cylinders are mutually interchangeable. In this version, lifting units and control lines must be dismantled when changing fuel assemblies.

In the second arrangement option, the lifting unit is located in the core area itself. The cylinder, as the lifting cylinder, forms the central part of the cross control rod, and the piston arranged at the upper core edge is supported on the lower core support plate by the approximately fuel element-long tube of a piston rod. They are connected to the piston rod via a simple plug-in or bayonet connection.

This version is predestined for boiling water reactors. The control line leads into the unit from above and then has to be removed when changing the fuel assembly, or it connects from below and leads along the pressure vessel wall to a valve block arranged on the pressure vessel (not on the cover).

In the case of an arrangement with a lifting unit that is separate from the control rod, it makes sense to release the releasable couplings of the units together if an expansion is necessary. This is done in particular in such a way that the clutches of all units are simultaneously released / released by a part supporting the actuating cylinder when it moves upwards, the actuating piston rod being rotated over a curve in the lowest part of its position relative to the actuating cylinder in such a way that it engages the rotary coupling connecting the control rod comes out of engagement. Here the pipelines can also be accommodated in the space above the core and designed to be detachable. In this way, the design is such that the control line comprises a tube leading from above into the cylinder of the assembly, which is provided with detachable connections for removal when the fuel element is changed.

To explain the invention in more detail, an exemplary embodiment is described with reference to the accompanying drawing. 1 shows a small boiling water reactor, which is used in particular as a heating reactor, in a vertical section. In Fig. 2 essential parts of the reactor for the invention are shown schematically on a larger scale. 3 is a schematic diagram of a drive variant. In Fig. 4, a device for displaying the position of a control rod is drawn. 5 shows an alternative embodiment for the valve block. Fig. 6 shows schematically an arrangement with a lifting unit lying above the core. FIG. 7 shows two arrangement diagrams with a lifting unit according to FIG. 1 lying in the core area

or 2. The right side shows a coolant tube 71 fed from above.

1 shows the cylindrical reactor pressure vessel 1 of a boiling water reactor for, for example, 200 MWui, which surrounds the reactor core 2. The fuel elements 3 of the reactor core 2 comprise control rods 4, the absorber material of which is arranged in a cross shape in a known manner, so that it can be moved in the cruciform gap between four fuel elements in each case.

A control rod guide frame 6 is arranged above the reactor core 2. The guides lie essentially in chimneys in the form of vertical sheet metal shafts, which lead the coolant (H2O) heated and partially evaporated in the reactor core 2 upwards to heat exchangers 7, which are distributed above the reactor core 2 on the circumference of the reactor pressure vessel 1.

The reactor pressure vessel is closed with a lid 8 which is screwed onto a flange 9. A central unit 10 for a hydraulic system for driving the control rods 4 is also arranged on the flange 9. Lines 11 indicated by dash-dotted lines lead from the central unit to the underside of the reactor core 2.

In Fig. 2 it can be seen that the cross-shaped control rod 4 is attached with its individual wings 12 to a hollow cylinder 13 which slides over a fixed piston 14. For the upward movement, which leads the control rod 4 from the position shown in FIG. 2 in the reactor core 2 upward into the control rod guide frame 6, the hydraulic drive 17 consisting of cylinder 13 and piston 14 is acted upon from below through line 11 with pressure fluid, which comes from above comes from the central unit 10.

The central unit 10 is covered with a stable, pressure-resistant hood 20, which is tightly connected to the flange 9 of the reactor pressure vessel 1. A canned motor 21, which drives a pump rotor 22, sits under the hood 20. The pump rotor 22 is mounted centrally in a control head (valve block) 23. This is a metal block with a plurality of channels, on which control valves 24 and 25 for actuating the drives 17 are accommodated. The metal block protrudes through an opening 26 in the flange 9 into the reactor pressure vessel 1.

In the middle of the control head 23, a channel 27 is provided, which serves to suck the reactor coolant through the pump 22 and is extended downward into the reactor pressure vessel 1 with a pipe 28. The pipe 28 leads at least into the area below the heat exchanger 7, so that the coolant cooled in the heat exchanger 7 can be sucked in by the pump rotor 22 via the filter 30 provided on its underside 29.

The coolant is pressurized by the pump rotor 22 and conveyed in the radial direction into an outer ring channel 32. From there it arrives via control valves 24 to inner channels 33 and 34, which continue in the control lines 36, 37, which are indicated by dash-dotted lines. They lead to the underside of the reactor core 2 and reach the one drive 17 shown via the line 11.

In Fig. 3 it can be seen that the pump 22 is provided with a bypass 40, via which the excess pressure of the hydraulic drive can be regulated. The shut-off valve 25 is located parallel to the bypass 40, and when it is opened the hydraulic system suffers a sharp drop in pressure. This leads to an accelerated retraction of the control rods 4.

The hydraulic fluid is supplied to the drives 17 in normal operation via a respective control valve 24, which is actuated magnetically, for example, via a coil 43. The valve disk 44 of the control valve 24 sits, for example, in the annular channel 32 shown in FIG. 2 at the beginning of the control line 11, which leads to the control rod drive 17 from below.

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The suction line 28 leads to the suction side of the pump 22, as has been explained with reference to FIG. 2. It can be provided with a cooler 45, the outer cooling circuit of which is denoted by 46 and indicated by dash-dotted lines. The cooling circuit can alternatively be arranged behind the pump 22 (46, 47). In addition, it is sketched in dash-dotted lines in FIG. 3 that the drives 17 ′ could also lie above the guide block 6.

FIG. 4 shows a constructively designed embodiment for the control valve 24, in fact divided, so that the closed position can be seen on one side of the center line and the open position on the other. It can be seen that the valve plate 44 is seated in an elongated cylindrical housing 50 which can be screwed into the central unit 10 with a threaded piece 49. A collar 51 on the housing 50 can be provided with a sealing weld 52.

The valve plate 44 is seated on a drive rod 54, which can be actuated in the area of the solenoid 43 with an impact armature 56. The impact anchor 56 sits between two projections 57 and 58 on the rod 54. It is pressed with a spring 59 into the end position facing the valve plate 44. A display bellows 60 is arranged between the projection 58 and a small piston 55, which detects the pressure in the control line on the valve plate 44 and which expands when the valve plate rises (throughput reduction).

On the end of the piston 55 facing away from the valve plate 44 there is an indicator rod 62 which magnetically transmits the bellows movement to the outside via an indicator coil 64.

In the embodiment according to FIG. 5 it can be seen that the central unit 10 can also be attached to the side wall of the reactor pressure vessel 1. It then protrudes with an angled connecting piece 68 through an opening in the reactor pressure vessel, which has a flange 69 for fitting the housing of the central unit 10. After mounting, a tight connection can be made with screws 70.

In the exemplary embodiment according to FIG. 6, in which the drive 17 ′ is arranged above the reactor core 2 and the guide frame 6, the central unit 10 is seated in the middle of the cover 8.

FIG. 7 shows two different embodiments on the right and left of the dash-dotted center line. On the right-hand side, the central unit 10 arranged centrally on the cover 8 feeds the drive 17 via a line 71 which, as part of the line 11, is pluggably joined in the area of the guide frame 6. It can be dismantled to change the fuel element. In contrast, the line 11 shown on the left can be permanently installed between the central unit 10 located on the outside of the reactor pressure vessel 1 and the drive 17 fed from below, because it is located next to the core 2 and the guide frame 6.

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Claims (14)

668 850 1. Nuclear reactor with a reactor core which can be regulated by control rods in a reactor pressure vessel which contains a liquid coolant, and with a device for moving and positioning the control rods which comprises piston-cylinder units which are acted on by the coolant and in which step sections of the piston and cylinder are located with narrower and further gaps, characterized in that several units (17) are each connected to a valve block (23) via a single control line (11), in which control valves (24, 25) for actuating the units (17) are combined and are connected to a common drive pump (22) for the coolant, and that the valve block (23) with all the control lines (11, 28) carrying the coolant is accommodated in a sealed metallic enclosure with the reactor pressure vessel (1). 2. Nuclear reactor according to claim 1, characterized in that the flow of the coolant flowing through the unit (17) in the uppermost control rod position is reduced to a fraction of its value by a support seat effective between the piston and the cylinder. 2nd PATENT CLAIMS 3. Nuclear reactor according to claim 1 or 2, characterized in that a spring or weight-loaded piston (55) or metal bellows (60) is provided in the control valve (24, 51), the movement of which can be electrically detected from the outside. 4. Nuclear reactor according to one of claims 2 or 3, characterized in that the valve block (23) is attached directly to the reactor pressure vessel (1). 5. Nuclear reactor according to claim 4, characterized in that the valve block (23) is surrounded by a hood (20) covering it. 6. Nuclear reactor according to claim 4 or 5, characterized in that the valve block (23) is flange-mounted as a substantially cylindrical steel body directly on the reactor pressure vessel (1) and has parallel, each one unit (17) assigned longitudinal bores, in which radial from the outside mechanical Engage parts of the control valves (24). 7. Nuclear reactor according to one of claims 1 to 6, characterized in that the valve block (23) is assembled with the drive pump (22). 8. Nuclear reactor according to one of claims 6 or 7, characterized in that the drive pump (22) is a directly on the valve block (23) placed canned pump (22) with a central suction channel (27), the pressure chamber (32) in an annular distribution encloses the area of the longitudinal bores leading to the units (17) on the circumference of the valve block (23). 9. Nuclear reactor according to claim 8, characterized in that in the valve block (23) solenoid valves (25) are arranged as large-area connections between the suction and pressure side of the drive pump (22). 10. Nuclear reactor according to one of claims 1 to 9, characterized in that each unit (17) is assigned two valves (24) connected in parallel to act on the coolant. 11. Nuclear reactor according to one of claims 1 to 10, characterized in that the piston-cylinder units (17) consist of a smooth cylinder and a piston grooved in the form of a labyrinth, and in that the associated diameter play stages in the Piston rod and a socket surrounding this at the cylinder end are incorporated. 12. Nuclear reactor according to one of claims 1 to 11, characterized in that the cylinder of the unit (17) as a lifting cylinder forms the central part of a boiling water reactor cross-control rod (4), and that the piston arranged on the upper core edge attaches itself via an approximately fuel element-long tube a lower core support plate, which is part of the control line (11), which is permanently installed in the reactor pressure vessel (1) between the unit (17) and the valve block (23). 13. Nuclear reactor according to one of claims 1 to 12, characterized in that the piston-cylinder unit (17) is arranged at least one core height above the core top edge, and that a releasable coupling is present between the unit and control rod. 14. Nuclear reactor according to claim 13, characterized in that the control line comprises a tube (71) leading from above into the cylinder of the assembly, which is provided with detachable connections for removal when the fuel element is changed.