JPH02140696A - Hydraulic control unit of control rod driving mechanism - Google Patents

Abstract

PURPOSE:To insert a control rod at the same inserting speed as that of a scram time at the time of rated operation even at the time of nuclear reactor scram in the case of low hydraulic pressure in a pressure vessel by providing a flow rate control unit between a scram valve and a housing of a control rod driving mechanism. CONSTITUTION:A piping 28 is divided into two in an installation position of a flow rate control unit 40, a tube end of a piping 28a of a housing 6 side of divided control rod driving mechanisms becomes a cylindrical shape expanded and opened gradually toward a piping 28b, and a housing 40a of the unit 40 is formed. In this state, when a nuclear reactor scram state is generated at the time of rated operation in which pressure of a reactor pressure vessel 1 is high, high pressure water from an accumulator 31 flows into the housing 6 of the control rod driving mechanism 4 at a set flow velocity, and the whole insertion of the control rod is executed in a set time. Also, when pressure of the pressure vessel is low, since a cross sectional area of a passage is decreased, comparing with that of the piping 28, the inflow of high pressure water of a high speed and a large quantum caused by differential pressure of hydraulic pressure in the accumulator 31 and pressure in the pressure vessel 1 does not occur, and the whole insertion of the control rod is executed in a roughly set time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a hydraulic control unit for a control rod drive mechanism in a boiling water nuclear reactor.

(Prior Art) FIG. 2 is a vertical cross-sectional view conceptually showing the schematic configuration of a boiling water nuclear reactor. In this figure, a reactor core 2 is housed in a reactor pressure vessel 1, and control rods 3 for adjusting the core output are inserted into and removed from the reactor core 2 from the lower part of the pressure vessel 1. control rod 3
is driven by a control rod drive mechanism 4 located below, and guided by a guide tube 5 to move up and down. In addition, 6 in the figure
is a housing that houses the control rod drive mechanism 5, and is fixed to the bottom of the pressure vessel 1 by welding.

FIG. 3 shows a longitudinal section of an example of the control rod drive mechanism 4 of the electric motor drive type. In this figure, the rotation of the electric motor 11 is caused by the shaft 1
2 is rotated, and this rotation is transmitted to the connecting member 13 via the key at the tip of the shaft 12, and the rotation of the connecting member 13 is transmitted to the connecting member 14 through the spline connection. Connection member 1
4, the lower end of a long screw shaft 15 is fixed to the center of the upper surface. A bearing 16 is provided at the upper end of this screw shaft, and its lower end is brought into contact with the upper surface of a nut 17 screwed into the lower part of the screw shaft 15, and inside a hollow piston 18 that operates in conjunction with a water pressure control unit not shown in this figure. It is designed so that it can be slid. On the surfaces of the nut 17 and the piston 18, four rollers 19 are provided, which are in contact with the inner circumferential surface of a tube 20, which will be described later, and are equally spaced in the circumferential direction, concentrically surrounding the nut 17 and the piston 18. Inside the tube 20, the nut 17. An axial plate 21 in the form of a circular arc strip, which has a fan-shaped cross section with a length corresponding to the movement stroke of the piston 18, that is, two concentric large and small arcs connecting both ends of the arcs with the diameters of those arcs, is attached. ing. This plate 21 prevents the nut 17 and piston 18 from rotating about their respective axes.

In this figure, 22 indicates a head, and a spring 24 is interposed between this head and a sleeve 23 that is slidably engaged with the piston 18. Further, 28 indicates a control piping for actuation during emergency insertion, and 29 indicates a ball check valve provided in this piping.

In the control rod drive mechanism having the above configuration, the nut 17. Since rotation of the piston 18 about these axes is suppressed, the screw shaft 15 is rotated by the electric motor 11.
When rotated, the nut 17 and the piston 18 in contact with its upper surface are allowed to move only in the axial direction,
The control rod connected to the piston 18 will be moved up and down.

During normal operation of the nuclear reactor, the control rod drive mechanism 4 shown in FIG. 2 adjusts the reactor output through the control rod operations described above.

Therefore, the control rod emergency insertion is schematically shown in Fig. 4, in which the same parts as in Figs. 2 and 3 are given the same reference numerals, as those that operate when emergency control rod insertion is required. A mechanism is provided. That is, a piping shown at 28 in FIG. 3 that opens into the housing 6 and is provided with a ball check valve 29 near the opening to the housing 6 is connected to the water pressure control unit 30. The water pressure control unit 30 includes an accumulator 31 and a pressurizing container 32, which are communicated through a pipe 33. Note that the pressurizing container 32 is filled with high-pressure nitrogen gas. Further, the piping 28 is connected to the accumulator 31 via a scram valve 34,
A pipe 35 from a discharge port of a pump 36 is connected between the scram valve 34 and the accumulator 31. Note that 31a in the figure indicates a floating piston within the accumulator 31.

5 Normally, the scram valve 34 is in a closed state, and the high-pressure water applied to the accumulator 31 from the pump 36 via the piping 35 depresses the floating piston 31a and releases nitrogen gas in the pressurizing container 32. Maintains pressure and equilibrium.

In the control rod emergency insertion mechanism configured as described above, when a scram signal is issued due to an abnormality in the reactor, the scram valve 34 is opened and high pressure water from the accumulator 31 flows into the pipe 28. As a result, the balance between the pressure of high-pressure nitrogen gas in the pressurizing container 32 and the pressure of high-pressure water in the accumulator 31 is disrupted, and the floating piston 31a is pushed up at once by the gas pressure, causing a large amount of high-pressure water in the accumulator 31 to be pushed up. housing 6 through piping 28 all at once.
flow inside. The ball check valve 29 is opened and the high pressure water flows into the housing 6, causing the piston 1 shown in FIG.
8 rapidly. In the control rod drive mechanism 4,
As shown in FIG. 3, a spring 24 that decelerates the piston 18 at the end of its upward stroke moves integrally with the piston 18 near the end of the stroke, working together with the piston 18 to compress the spring 24. Since the sleeve 23 and the head 22 that resist the spring force are provided, emergency insertion of the control rod into the reactor core 2 is performed by the rapid movement of the piston 18.6 In the control rod emergency insertion mechanism having the above configuration, The relationship between the control rod insertion position and the nitrogen pressure in the pressurizing container 32 during the emergency insertion is schematically shown in FIG. This figure shows that under initial conditions, the nitrogen pressure in the pressurizing vessel 32 is sufficient to overcome the water pressure in the reactor pressure vessel at rated operation, approximately 10 kg/d, and raise the piston 18 (approximately 130 kg/cd). ), and the nitrogen pressure is shown to gradually decrease as the control rod is inserted. Then, the control rod is fully inserted,
Even when the nitrogen pressure reaches its lowest value, it is set to maintain a pressure higher than the pressure inside the reactor pressure vessel.

(Problem to be Solved by the Invention) However, the state in which a reactor scram occurs is not limited to only during its rated operation, but also when the water pressure inside the reactor pressure vessel is reduced (for example, to about atmospheric pressure). You must also consider what to do if the situation occurs.

Figure 6 shows that, as mentioned above, the water pressure inside the reactor pressure vessel is approximately 7.
In a water pressure control unit designed to operate safely at 0 kg/ad, this diagram schematically shows changes in the time required to fully insert the control rods when the pressure inside the reactor pressure vessel changes. In this figure, ts is the reference value for insertion time, and the control rods must be fully inserted within 1 hour.The pressure inside the reactor pressure vessel during rated operation is 70 kg/c.
The total insertion time at point j is t2, and the setting of the water pressure control unit 30 is such that this time t2 is less than or equal to time ts, allowing for some margin.

In the water pressure control unit 3° set as described above, the total insertion time of the control rods when the water pressure in the reactor pressure vessel has decreased to about atmospheric pressure, for example.

As shown in FIG. 6, the time t4 is much smaller than t. This is because the energy of the hydraulic control unit 30 becomes excessive, as shown by hatching in FIG. 5, and the control rod insertion speed increases.

As mentioned above, at the control rod fully inserted position, that is, near the end of the stroke of the piston 18, the control rods are decelerated and stopped when fully inserted, but the water pressure inside the reactor pressure vessel is low and the control rod insertion speed is high. In this case, the deceleration (in other words, the acceleration) described above will have a large adverse effect on the control rod drive mechanism and others.

The present invention has been made based on the above circumstances, and even during reactor scram when the water pressure inside the reactor pressure vessel is low, the insertion speed is controlled at almost the same speed as during reactor scram during rated reactor operation. It is an object of the present invention to provide a hydraulic control unit for a control rod drive mechanism that allows insertion of rods.

[Structure of the Invention] (Means for Solving the Problems) The hydraulic control unit of the control rod drive mechanism of the present invention includes an accumulator having a floating piston and applying high gas pressure to the lower surface of the floating piston of this accumulator. a pressurizing vessel for pressurization, a pipe connecting the space above the floating piston of the accumulator and the housing of the control rod drive mechanism, a scram valve provided in this pipe and opened when a reactor scram state occurs, and and a pump that communicates a discharge port between the accumulator and the scram valve and applies high-pressure water to the accumulator, the reactor pressure When the pressure inside the vessel is at the pressure at the reactor's rated operation, the cross-sectional area of the piping is maintained at its original size, and when it is lower than that at the rated operation, the cross-sectional area of the piping is restricted. The present invention is characterized by being equipped with a flow rate control unit.

(Function) In the water pressure control unit of the control rod drive mechanism of the present invention having the above configuration, if a reactor scram condition occurs during rated operation when the pressure inside the reactor pressure vessel is high, the high pressure water from the accumulator is controlled at the set flow rate. flows into the housing of the rod drive mechanism and performs full insertion of the control rod at a set time;
When the pressure inside the reactor pressure vessel is low, the cross-sectional area of the flow path is smaller than that of the piping, so a high-speed, large amount of high-pressure water flows in due to the differential pressure between the water pressure inside the accumulator and the reactor pressure vessel. Full insertion of the control rod can be accomplished within a set time.

(Example) FIG. 1A is a longitudinal cross-sectional view of an embodiment of the present invention during rated operation of the reactor, FIG. FIG. 1 is a cross-sectional view taken along line C-C in FIG. 1 of the embodiment. The flow rate control unit of the present invention has the piping 28
is installed between the scram valve 34 and the housing 6 of the control rod drive mechanism. In FIGS. 1A and 1B, A indicates the scram valve side, and B indicates the housing side of the control rod drive mechanism, respectively. The pipe 28 is divided into two at the installation position of the flow control unit 40, and the pipe end of the pipe 28a on the housing 6 side of the divided control rod drive mechanism has a conical shape that gradually expands toward the pipe 28b on the scram valve 34 side. and forms a housing 40a of the flow rate control unit 40. The housing and the pipe 28b are connected by flanges, and the peripheral edge of the disc spring 41 is airtightly sandwiched between these flanges. On the upper surface of the disc spring 41, that is, on the surface on the side of the housing 6 of the control rod drive mechanism, a ring 42, which is attached to the upper end of the housing of the flow control unit 40, is concentrically attached.

The disc spring 41 is provided with a through hole 41a that communicates with the hollow portion 42b of the ring and has a diameter larger than that of the hollow portion. The outer diameter of the straight portion of the ring 42 is sufficiently smaller than the inner diameter of the straight portion of the housing 40a of the flow control unit 40, and the inner diameter of the hollow portion 42b is
Let it be smaller than that of . Further, between the ring 42 of the disc spring 41 and the housing 40a of the flow control unit 40, there are a plurality of cylinders, for example, four through holes 41 equally distributed in the circumferential direction.
b, and the sum of the total opening area of these through holes and the opening area of the hollow part 42b of the ring 42 is the piping 28 (28a,
The opening area is made equal to the opening area of 28b). The flow rate control unit 40 having the above configuration operates as follows.

First, when the reactor is in the rated operating state and the water pressure in the reactor pressure vessel is at the specified value, the disc spring 41 is in the state shown in FIG.
As shown in FIG. 2, the high pressure within the reactor pressure vessel acts on the top surface of the disc spring 41, and the top surface is held substantially flat. Even if a reactor scram occurs in this state and the scram valve 34 is opened and high-pressure water enters the pipe 28a from the accumulator 32, it must flow through the pipe against the water pressure in the pressure vessel. The flow velocity is low and the force toward the B side due to the pressure loss acting on the ring 42 is balanced with the elasticity of the disc spring 41, and the disc spring 41 is held in a flat state, and the ring 42 has its tapered part 42a attached to the housing 40a. It is maintained in a state separated from the inner surface of the tapered portion. Since the sum of the opening area of the hollow portion 42b of the ring 42 and the opening area of the through hole 41b is equal to the opening area of the pipe 28, the high-pressure water flow path opening area is 28a, 28b), the piston 18 of the control rod drive mechanism will rise at a preset speed and full insertion of the control rod will occur at time t7 shown in FIG.

On the other hand, if a reactor scram occurs when the water pressure inside the reactor pressure vessel is, for example, about atmospheric pressure, the high pressure water that has entered into the piping 28a due to the opening of the scram valve 34 will be transferred to the piping because the pressure inside the reactor pressure vessel is low. The internal flow velocity is high and the resulting pressure loss pushes the ring 42 up against the disc spring 41, pushing it upward (
The tapered portion 42a at the upper end of the ring 42 is pressed into contact with the housing 40a. This results in
The opening area for high-pressure water to flow into the pipe 28a is limited to the opening area of the hollow portion 42b, and the increased pressure drop prevents the flow from increasing as in the conventional case, reducing the time it takes to fully insert the control rod. can be limited to about L2.

As described above, according to the water pressure control unit of the present invention, control rods can be completely inserted at a substantially constant speed and time when a scram occurs, regardless of the level of water pressure in the reactor pressure vessel.

In the above embodiment, the sealing portion between the upper end of the ring 42 and the housing 40a is conical, which facilitates positioning and sealing during assembly.Since the flow velocity between the conical portions is high, the difference between the upper and lower ends of the ring is reduced. The pressure is large and the ring can be sensitive to flow velocity.

Furthermore, the present invention is not limited to the above embodiments. For example, the present invention can also be applied to a hydraulic drive type control rod drive mechanism in the same manner as described above.

[Effects of the Invention] As is clear from the above, the hydraulic control unit of the control rod drive mechanism of the present invention allows the control rods to be fully inserted at a substantially constant speed regardless of the pressure level in the reactor pressure vessel. As a result, the impact acceleration when the control rods stop during a reactor scram at low reactor pressure is greatly reduced, and the load acting on the pistons or control rods is also reduced, significantly improving their structural and strength reliability. Improved.

[Brief explanation of the drawing]

FIG. 1A is a vertical cross-sectional view of an embodiment of the present invention during rated operation of the nuclear reactor, FIG. 1B is a vertical cross-sectional view of the reactor in a scram generation state at low reactor pressure, and FIG. 1C is the C of FIG. 1B. -A cross-sectional view taken along line C, Figure 2 is a conceptual diagram of a boiling water reactor, Figure 3 is a longitudinal sectional view of an electric motor-driven control rod drive mechanism, and Figure 4 is a conceptual diagram of an emergency control rod insertion mechanism. , FIG. 5 is a graph showing the relationship between the pressure inside the pressurizing vessel of the control rod emergency insertion mechanism and the control rod insertion position, and FIG. 6 is a graph showing the relationship between the pressure inside the reactor pressure vessel and the time required to fully insert the control rods. It is a graph showing a relationship. 1...Reactor pressure vessel 2...Reactor core
3... Control rod 4... Control rod drive mechanism 5... Guide tube 6.40a... Housing 17... Nut 18... ...Piston 28.28a, 28b, 33.35...
Piping 29...Ball check valve 3o...
・Water pressure control unit 31・Old...Accumulator 3
1a... Floating piston 32... Pressurizing container 34... Scram valve 36...
Old...Pump 4゜...Flow control unit 4
1... disc spring 41a, 41b... through hole 42... old... ring 42a... eye... taper part
42b...Hollow part

Claims (1)

[Claims] an accumulator equipped with a floating piston, a pressurizing container that applies high gas pressure to the lower surface of the floating piston of the accumulator, and piping that connects a space above the floating piston of the accumulator and a housing of a control rod drive mechanism. and a scram valve that is provided in the piping and is opened when a reactor scram state occurs, and a pump that communicates a discharge port between the accumulator of the piping and the scram valve and applies high-pressure water to the accumulator. , between the front scram valve of the piping and the housing of the control rod drive mechanism, when the pressure inside the reactor pressure vessel is the pressure at the reactor rated operation, the cross-sectional area of the piping is increased to its original size. A hydraulic control unit for a control rod drive mechanism, characterized in that a flow rate control unit is provided to maintain the flow rate at a constant flow rate and to limit a flow passage cross-sectional area of the piping when the flow rate is lower than that during rated operation.