JP2003337191A - Reactor control rod drive equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To speed up scram time of a control rod drive device, reduce the lowering of OLMCPR which is an operational limit condition at a cycle end and design fuel arrangement having fuel economy. <P>SOLUTION: A control rod drive device having a buffer is placed to a control rod drive equipment 2 in place of a control rod drive device without it. On the other hand, a control rod drive hydraulic system equipment is set in as- placed state and a nitrogen gas filling pressure of a nitrogen vessel 24 to be a hydraulic-pressure source placed in a hydraulic control unit 18 is set high by filling within a maximum allowable working pressure of system equipments. In this manner, scram time in emergency of control rod drive device is speeded up. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to control rod drive equipment for a nuclear reactor, and more particularly to a boiling water reactor (BW) as a light water reactor.
The present invention relates to improvements in the operation of the control rod drive mechanism (CRD) used in R) and the control rod drive hydraulic system equipment.

[0002]

2. Description of the Related Art In a boiling water nuclear power plant, a hydraulically driven control rod drive device is used as a control rod drive hydraulic system.
A boiling water nuclear power plant (hereinafter referred to as "BWR plant") that is driven and controlled by a control rod drive hydraulic system system composed of a water pressure control unit group, and an improved type that employs an electrically driven control rod drive device. There is a boiling water nuclear power plant (hereinafter referred to as "ABWR plant").

The output of the nuclear reactor of the BWR plant is controlled by the control rod driving device by inserting or pulling out the control rod into the core. The drive of the control rod drive device is performed by a water pressure control unit provided corresponding to each control rod drive device. If the reactor must be stopped for some reason, a so-called scram operation is performed in which all the control rods are rapidly and simultaneously inserted into the core.

FIG. 7 shows the structure of a conventional general CRD, and FIG. 8 shows a schematic system of control rod drive hydraulic system equipment.

As shown in FIG. 7, the reactor pressure vessel 101
A control rod drive mechanism housing 102 is attached to the lower end plate, and the control rod drive mechanism 2 is inserted and accommodated in the control rod drive mechanism housing 102 from below the housing.

An index tube 4 and a piston tube are housed in a cylinder tube 3 of the control rod drive mechanism 2, a control rod 30 is connected to the upper end of the index tube 4, and a drive piston 4a is attached to the lower end. Are connected.

A collet finger 7 connected to the collet piston 6 is arranged above the cylinder tube 3, and the collet piston 6 and the collet finger 7 are urged downward by a collet spring 7a. . This collet finger 7 engages with a positioning notch 8 normally provided on the outer peripheral surface of the index tube 4 along its length to position the control rod, and the collet finger 7 rises relatively. As a result, the guide cap 9 is brought into contact with the guide cap 9 to open, and the engagement with the notch 8 is released.

Further, the control rod drive mechanism housing 102
An insertion line 10 and a withdrawal line 11 for supplying and discharging water pressure for driving the control rod drive mechanism 2 are provided in the. Further, in the cylinder tube 3, a collet finger releasing passage 12 that connects the drawing line 11 and the lower surface of the collet piston 6 is formed,
In addition, a drive piston pressing flow path 13 that communicates the inside of the piston tube 5 with the space inside the index tube 4 is formed in the upper portion of the piston tube 5.

The insertion line 10 and the withdrawal line 11
Is connected to the control rod drive hydraulic system equipment shown in FIG.

As shown in FIG. 8, the control rod drive hydraulic system equipment includes a pump 15 connected to a water source 30 and the pump 1.
5 is provided with a master control 16 provided on the discharge side, and a water pressure control unit 18 which is connected to the master control 16 by a pipe to switch the drive water flow path and control the drive water.

A flow control valve 16a and a pressure control valve 16b are connected in series to the master control 16,
Further, a stabilizing valve 16c is provided so as to bypass the pressure adjusting valve 16b. The upstream side of the flow rate adjusting valve 16a is connected to the filling water header 20, the upstream side of the pressure adjusting valve 16b is connected to the driving water header 21, and the pressure adjusting valve 16b.
The downstream side of is connected to the cooling water header 22. Further, the downstream side of the pressure adjusting valve 16b is connected to the drain header 23 via the open / close valve 16d.

A plurality of water pressure control units 18 are installed corresponding to the control rod drive mechanism 2 and are connected to the control rod drive mechanism 2 by an insertion line 10 and an extraction line 11. Further, the water pressure control unit 18 includes a nitrogen container 2
4 and an accumulator 25 are incorporated, and a total of four directional control valves 1 for controlling the flow direction of the driving water.
8a, 18b, 18c and 18d are provided. Incidentally, 26a, 26b, 26c and 26d are check valves,
27 is a scrum inlet valve, 28 is a scrum outlet valve, and 29 is a scrum discharge header.

Insertion and withdrawal operations of the control rod drive mechanism 2 as described above will be described. When inserting the control rod 30, the directional control valves 18a and 18d in the water pressure control unit 18 are opened in response to an insertion signal from a central control chamber (not shown), and the drive water pressure adjusting valve 16 in the master control 16 is opened.
The drive water whose pressure is adjusted in b passes through the drive water header 21 into the water pressure control unit 18, and the directional control valve 18
The index tube 4 in the control rod drive mechanism 2 is pushed up from a through the insertion line 10. On the other hand, the water between the index tube 4 and the piston tube 5 is returned from the directional control valve 18c to the master control 16 through the discharge header 23 through the drawing line 11, and the inserting operation is performed.

When the control rod 30 is pulled out, first, the directional control valves 18a and 18d in the water pressure control unit 18 are opened for a short period of time, while the control rod 30 hanging on the collet finger 7 via the notch 8 is removed. The load on the index tube 4 is removed, and then the direction control valves 18b and 18c are opened. Then, the driving water acts on the control rod drive mechanism 2 from the directional control valve 18c through the drawing line 11 and is divided into two directions within the control rod drive mechanism 2, one of which passes through the collet finger releasing flow passage 12 and the collet finger release channel 12. It acts on the piston 6 and pushes the collet fingers 7 apart through the guide cap 9 to release the engagement with the notch 8 of the index tube 4. The other passes through the flow path 13 in the piston tube 5, enters the index tube 4 from the drive piston pressing flow path 13a above it, and works to push down the drive piston 4a of the index tube 4. As a result, the water on the lower surface of the drive piston 4a is
The direction control valve 18b passes through the insertion line 10 and returns to the master control 16 through the drainage header 23, whereby the control rod 30 is pulled out.

Next, the operation at the time of emergency stop (scrum) will be described. Nitrogen container 24 in water pressure control unit 18
The high-pressure nitrogen gas enclosed in the accumulator 25
Of the accumulator 25 and is partitioned by the piston in the accumulator 25. The upper side of the piston of the accumulator 25 is connected to the discharge side of the pump 15 via the check valve 26c, and high-pressure filling water is accumulated in the accumulator 25 with the piston pushed down.

In an emergency, in response to the scrum signal, the scrum inlet valve 27 and the scrum outlet valve 28 are rapidly opened, so that the high pressure water in the accumulator 25 is passed from the insertion line 10 through the scrum inlet valve 27 to the control rod. It flows into the drive mechanism 2 and rapidly pushes up the drive piston 4a. Then, the water between the index tube 4 and the piston tube 5 is pulled out by the drawing line 11 and the scrum outlet valve 2
The scrum operation is performed by discharging the scrum to the scrum discharge header 29 via the switch 8.

Further, during the normal operation without the insertion, withdrawal and scrum operations as described above, the master control 16 is constantly operated to the cooling water header 22 and the water pressure control unit 1.
Cooling water is supplied to the control rod drive mechanism 2 through the insertion line 8 and the insertion line 10.

The filling water header 20 and the driving water header 2
1, each of the cooling water header 22 and the discharge header 23 is connected to a plurality of other water pressure control units (not shown).

By the way, in the BWR plant, the transient change condition is relaxed by increasing the scram speed, and the minimum critical power ratio (Minimum Critical Power Rati
o: A high-speed scrum control rod drive (hereinafter referred to as "high-speed scrum C
RD ". ) Has been developed and applied to a BWR plant (see, for example, "Boiling Water Nuclear Power Plant High Speed Scrum Control Rod Drive Device" (TLR-031 Tokyo Shibaura Electric Co., Ltd., issued in October 1980)).

On the other hand, even in the conventional CRD plant before the adoption of the high speed scrum CRD, it is desired to increase the scrum speed and reduce the decrease in MCPR in response to the adoption of the high burnup fuel or the introduction of the MOX fuel. The needs are increasing.

Therefore, in the conventional CRD plant,
As a method of speeding up the scrum time to reduce the decrease in MCPR and improve the plant operation margin, the control rod drive mechanism and the control rod drive hydraulic system equipment are collectively used in the high-speed scrum C.
It is possible to modify the RD and the control rod drive hydraulic system equipment.

In this case, however, the scope of modification is not only equipment such as control rod drive mechanism, water pressure control unit, pump, etc., but also all the piping of the insertion line and the withdrawal line, and the replacement of other piping is necessary. There is a problem of large scale remodeling work.

[0023]

As described above, the existing control rod drive mechanism (CR) in the conventional CRD plant is used.
D) and control rod drive hydraulic system equipment as a whole should be remodeled into a high-speed scrum CRD and control rod drive hydraulic system equipment by changing control rod drive mechanism, water pressure control unit, equipment such as pump, insertion line and pull-out line. All pipes and other pipes need to be replaced, which causes a problem of large-scale remodeling work.

The present invention has been made in view of the above circumstances, and is suitable in consideration of introduction of high burnup fuel and MOX fuel in a conventional CRD plant without requiring large-scale facility modification. By increasing the scram speed in the range, it is possible to suppress the MCPR drop at the end of the operating cycle, provide a large operating margin, and provide a control rod drive facility for a reactor that enables highly fuel-efficient plant operation. To aim.

[0025]

[Means for Solving the Problems] Operating Limit Minimum Cri of a conventional CRD plant
The tical power ratio (OLMCPR) is determined by considering the deterioration of the scrum reactivity characteristics, and the respective values of the cycle early core and the cycle end core are determined. The load loss event is the decisive event for the end-stage core.

Here, the feedwater heating loss event is a quasi-steady increase in output and scramming, and OLMCPR is determined by the amount of increase in output. There is no.

On the other hand, the load loss event is a transient event accompanied by a pressure increase, and the void is decreased by the pressure increase at that time, so that a positive reactivity is injected,
To alleviate this, a negative reactivity is added by scrum. Therefore, as the scrum speed becomes faster, the effect of alleviating the increase in output becomes greater and the OLMCPR is improved.

The present invention has been made based on such an idea. In the invention according to claim 1, a large number of control rod drive devices for inserting control rods into the core of a nuclear reactor and each of these control rod drives are provided. A control rod drive water pressure system facility having a water pressure control unit for controlling the flow direction of drive water supplied to and discharged from the device and a pump for supplying water from a water source to each water pressure control unit via a master control , Filling the nitrogen gas filling pressure of the nitrogen container serving as a water pressure generating source provided in the water pressure control unit to a high pressure within the range of the maximum operating pressure of the system equipment, and setting the scram time in an emergency of the control rod drive device. Provided is a control rod drive facility for a nuclear reactor, which is characterized by speeding up.

In the invention according to claim 2, a high speed scrum control rod drive device is used as the control rod drive device connected to the control rod drive hydraulic equipment. Provide control rod drive equipment for a nuclear reactor.

According to a third aspect of the present invention, in the high speed scrum control rod drive device, the scrum of the index tube is attached to the tip end portion of the piston tube fixed inside the index tube that moves up and down in the control rod drive mechanism housing. And a buffer piston capable of moving up and down in contact with the drive piston at the lower end of the index tube in the vicinity of the ascending end portion, and a buffer orifice for introducing water on the outer peripheral side of the piston tube into the piston tube by the lifting of the buffer piston. 3. The nuclear reactor according to claim 2, further comprising: a buffer device for increasing the flow path resistance of the drive piston by means of the resistance of water passing through the buffer orifice to decelerate the rising speed of the control rod. Provide control rod drive equipment.

According to a fourth aspect of the present invention, there is provided a control rod drive facility having a control rod drive device having no buffer device according to the third aspect, in contrast to the control rod drive device, a control rod having the buffer device. While installing a drive device, regarding the control rod drive water pressure system equipment, this is set to the existing state, and the nitrogen gas filling pressure of the nitrogen container serving as the water pressure generation source provided in the water pressure control unit is set to the maximum operating pressure of the system equipment. The present invention provides a control rod drive facility for a nuclear reactor, wherein the control rod drive device is filled with high pressure within the range to speed up the scram time in an emergency of the control rod drive device.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the control rod drive equipment according to the present invention will be described below with reference to FIGS.

FIG. 1 shows a schematic structure of a high speed scrum type CRD 2A driven by a control rod driving hydraulic system equipment according to the present embodiment, and FIG. 2 is an enlarged view of a shock absorbing device part in the structure shown in FIG. It is a partial expanded sectional view showing roughly. The same parts as those of the conventional control rod drive mechanism 2 shown in FIG. 6 will be described using the same reference numerals, and overlapping description will be omitted.

As shown in FIGS. 1 and 2, in this high speed scrum control rod drive device 2A, a buffer shaft 31 is fixed to the tip of the piston tube 5. A channel 32 is provided in the center of the buffer shaft 31 in the axial direction, and a buffer orifice 33 composed of a plurality of holes is formed at a predetermined interval from the channel 32 in a direction perpendicular to the axial direction. It is provided and communicates with the flow path at the center of the buffer shaft 31.

A stop piston 34 is fitted on the upper portion of the buffer shaft 31, and a thin cylindrical portion 34a opening downward is formed at the lower end of the stop piston 34. The thin cylindrical portion 34a extends to a position where it covers the buffer orifice 33 formed in the buffer shaft 31, thereby forming a buffer pocket portion 34b.

The outer peripheral surface of the buffer shaft 31 and
A cylindrical buffer piston 35 is provided in contact with the inner peripheral surface of the thin-walled cylindrical portion 34a at the lower end of the stop piston 34, and the buffer piston 35 is fitted to the buffer shaft 31 so as to be slidable in the axial direction. There is. A buffer spring 36 is installed in the buffer pocket portion 34b so as to surround the buffer shaft 31. The cushioning piston 35 is normally pushed down by the cushioning spring 36 to the mechanical lower limit of the cushioning pocket.

In such a structure, when high pressure water acts on the lower surface of the drive piston 4a by the scrum and the index tube 4 fitted integrally with the drive piston 4a is rapidly inserted upward, near the end of the stroke. The upper part of the drive piston 4a is the buffer piston 3 described above.
5 Start contacting the bottom.

After the upper part of the drive piston 4a comes into contact with the lower part of the buffer piston 35, the buffer piston 35 is pushed upward by the drive piston 4a, and the water in the buffer pocket passes through the buffer orifice 33 to the inside of the piston tube 5. It flows in and is finally discharged via the drawing line 11. During this time, when the shock-absorbing piston 35 is pushed up by the drive piston 4a, the shock-absorbing orifice 33 has a structure in which the shock-absorbing orifice 33 is sequentially closed from below as the stroke increases. The resistance increases, and sufficient deceleration is performed until the end of the stroke during scram is reached.

3 and 4 show the high speed scrum CR described above.
The schematic structure of the control rod drive hydraulic system equipment which drives D2A is shown. FIG. 3 is an overall view, and FIG. 4 is an enlarged schematic view of a main part.

As shown in FIGS. 3 and 4, the system configuration is the same as that shown in FIG. 8 except that the control rod drive mechanism to be driven is the high speed scrum CRD 2A. Conventional C
In the RD plant, the piping on the discharge side of the pump 15
The maximum working pressure of the water pressure control unit 18, the insertion line 10 and the drawing line 11 is 12.05 MPa (12
3 kg / cm ² ).

On the other hand, the filling pressure of the nitrogen container 24 in the water pressure control unit 18 is set to 7.45 MPa (76 kg / cm ² ). By increasing the filling pressure of the nitrogen gas in the nitrogen container 24 within the range of the maximum operating pressure allowed in the system equipment and filling the same, the energy for discharging the filling water stored in the accumulator 25 increases. , The scrum insertion speed is increased.

As an example, if the filling pressure of the nitrogen gas in the nitrogen container 24 is 11.17 MPa (114 kg / cm ² ), the scram time to the 90% stroke position of the control rod drive mechanism 2A is 2.6 seconds or less. become.

FIG. 5 is a graph illustrating MCPR in the early and late cycles of a plurality of conventional CRD plants. As shown in FIG. 5, in each plant (A, B, C), the MCPR is higher at the end of the cycle shown by hatching than at the beginning of the cycle shown in white.

FIG. 6 shows, by way of example, 8 shown in B of FIG.
It shows an example of OLMCPR evaluation of a Step III fuel core of a BWR plant of 0,000kWe class.

The scrum time specification value of the conventional CRD plant is the state shown at point A in FIG. 6 because the insertion time up to the 90% stroke position is 3.5 seconds or less. OLMCPR of load loss as scrum speed increases
Is improved along the line AB in FIG.

On the other hand, the OLMC for the water heating loss event
PR is constant independent of the scrum speed, and is shown by a horizontal line CD in FIG.

Since OLMCPR takes the maximum value during the transient event, when the scrum time is changed, it changes on the straight line connecting points AOC in FIG. Even if the scrum time becomes faster than 0.6 seconds, further improvement in OLMCPR cannot be expected. Therefore, even if the scram time of the conventional CRD is shortened, it is not necessary to shorten the insertion time of the high-speed scrum CRD to the core average 75% stroke position to 1.62 seconds or less.

On the other hand, the measured value of the scrum time of the conventional CRD is 2.5 seconds on average, which is 3.0 seconds or less even if 6 times the standard deviation is added to the average value. In order to achieve the scrum time at the point O, the speed may be increased by about 0.4 seconds. The speed of the scrum speed is about this level because the maximum operating pressure of the control rod drive hydraulic system equipment (12.05 MPa)
It has been experimentally confirmed that this can be handled by increasing the filling pressure of the nitrogen container of the water pressure control unit within the range. As an experimental example, when the filling pressure of the nitrogen container of the water pressure control unit is increased from the current 7.45 MPa to 11.17 MPa, the scram time is shortened by about 0.4 seconds.

Further, as the scram speed increases, the shock load acting at the time of braking at the stroke end portion in the control rod drive mechanism main body increases, so the shock absorber is strengthened to withstand the increased shock load. High speed scrum CRD
Replace with.

According to the above embodiment, the water pressure control unit 18, the piping of the insertion line 10 and the withdrawal line 11,
90% stroke by increasing the filling pressure of the nitrogen container of the water pressure control unit and replacing the control rod drive device with a high-speed scrum CRD without the need to replace the control rod drive hydraulic system equipment such as the master control 16. The insertion scrum time can be speeded up. That is, in the conventional CRD plant, by increasing the filling pressure of the nitrogen container 24 of the water pressure control unit within the range of the maximum working pressure thereof, the scram time of the control rod drive device can be increased, and the operation limiting condition at the end of the cycle can be achieved. It becomes possible to reduce the decrease in the OLMCPR, which makes it possible to design the fuel arrangement with fuel economy. As a result, in a BWR power plant of 800,000kWe class, the number of replacement fuel bodies can be reduced by about 10 per cycle, and not only the economic efficiency can be improved but also radioactive waste can be reduced.

By increasing the scrum time, it becomes possible to reduce the OLMCPR improving effect to about 2.6 seconds or less, which is a critical point at which the effect can be expected. Even if the speed is further increased, improvement of OLMCPR cannot be expected.

[0052]

As described above, according to the present invention, in the conventional CRD plant, by increasing the filling pressure of the nitrogen container of the water pressure control unit within the range of the maximum working pressure, the control rod drive device The scram time can be shortened, the decrease in OLMCPR, which is the operation restriction condition at the end of the cycle, can be reduced, the fuel layout can be designed for fuel economy, and radioactive waste can be reduced.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a schematic structure of a high speed scrum control rod drive mechanism according to an embodiment of a control rod drive facility according to the present invention.

FIG. 2 is an enlarged cross-sectional view schematically showing a shock absorber of the high speed scrum control rod drive mechanism in FIG.

FIG. 3 is a schematic system diagram showing a control rod drive hydraulic system facility according to an embodiment of the control rod drive facility according to the present invention.

FIG. 4 is an explanatory view showing a part of the control rod drive hydraulic system equipment shown in FIG. 3 in an enlarged manner.

FIG. 5 is a graph showing a state of an operation limit minimum limit output ratio of a plurality of application target plants in the embodiment.

FIG. 6 is a characteristic diagram showing an example of an evaluation result regarding a relationship between an operation limit and a minimum limit output ratio and a scrum speed of one application target plant in the embodiment.

FIG. 7 is a vertical cross-sectional view showing a schematic structure of a control rod drive mechanism in a conventional control rod drive facility.

FIG. 8 is a schematic system diagram showing an example of conventional control rod drive hydraulic system equipment.

[Explanation of symbols]

101 reactor pressure vessel 102 Control rod drive mechanism housing 2 Control rod drive 2A High Speed Scrum CRD 3 cylinder tube 4 index tube 4a drive piston 5 piston tube 6 collet piston 7 Collet fingers 8 Positioning notch 9 Guide cap 10 Insertion line 11 Drawing line 15 pumps 16 Master control 18 Water pressure control unit 24 nitrogen container 25 Accumulator 29 Scrum discharge header 30 control rod 31 buffer shaft 32 Axial flow path 33 Buffer Orifice 34 stop piston 34a Thin-walled cylindrical portion 34b Buffer pocket 35 buffer piston 36 buffer spring

Claims (4)

[Claims] 1. A large number of control rod drive devices for inserting control rods into a core portion of a nuclear reactor, a water pressure control unit for controlling a flow direction of drive water supplied to and drained from each control rod drive device, and respective water pressures. A control rod drive water pressure system equipment having a pump for supplying water from a water source to the control unit via a master control, and a nitrogen gas filling pressure of a nitrogen container serving as a water pressure generation source provided in the water pressure control unit. To high pressure within the maximum operating pressure range of the system equipment,
Control rod drive equipment for a nuclear reactor, wherein the scram time in an emergency of the control rod drive device is shortened. 2. The control rod drive for a nuclear reactor according to claim 1, wherein a high speed scrum control rod drive is used as a control rod drive connected to the control rod drive hydraulic equipment. Facility. 3. The high-speed scrum control rod drive device comprises: a tip end portion of a piston tube fixed inside an index tube that moves up and down in a control rod drive mechanism housing;
A buffer piston that is capable of moving up and down in contact with the drive piston at the lower end of the index tube near the rising end of the index tube when scramming, and water on the outer peripheral side of the piston tube is moved into the piston tube by the lifting of the buffer piston. 3. A buffer device having a buffer orifice to be introduced, and a buffer device for increasing the flow path resistance of the drive piston by the resistance of water passing through the buffer orifice to decelerate the ascending speed of the control rod. Control rod drive equipment of the described reactor. 4. A control rod drive facility comprising a control rod drive device without a shock absorber according to claim 3, wherein the control rod drive device is replaced with a control rod drive device having said buffer device. Regarding the control rod drive water pressure system equipment, this is an existing state, and the nitrogen gas filling pressure of the nitrogen container serving as the water pressure generation source provided in the water pressure control unit is
Control rod drive equipment for a nuclear reactor, characterized in that the control rod drive equipment is filled with high pressure within the range of the maximum operating pressure of the system equipment to speed up the scram time in an emergency of the control rod drive device.