Patent Number: 055815871
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described hereunder with reference to the accompanying drawings. A first embodiment of a control rod driving apparatus according to the present invention will now be described with reference to FIG. 1. Referring to FIG. 1, the same elements as those shown in FIG. 10 are given the same reference numerals and their descriptions are omitted here. A hydraulic motor is accommodated in a motor case 52, the hydraulic motor comprising a hydraulic motor 53 for insertion, a hydraulic motor 54 for withdrawal, bevel gears 55a and 55b serving as transmission mechanisms to convert the direction of rotations of a driving shaft of the hydraulic motor so as to transmit the power to the ball spindle 5 and worm gears 56a and 56b. For the hydraulic motor, one of a gear motor, a vane motor, a piston motor, a turbine motor and so forth may be employed. In this embodiment, the maintenance facility is improved by using a turbine-type hydraulic motor because it has a simple structure composed of small number of sliding elements and therefore its periodical maintenance labor requirements can be decreased. If the normal revolving speed of the turbine-type hydraulic motor is higher than the revolving speed of the ball spindle 5 which is required to drive the control rod 11 in a steady state, the revolving speed is lowered by the worm gears 56a and 56b and the bevel gears 55a and 55b. An embodiment in a case where the operational speed of the transmission mechanism is lowered will now be described. Since the turbine-type hydraulic motor is generally designed in such a manner that its efficiency is improved when it is rotated forwards or reverse, this embodiment comprises a hydraulic motor 53 for insertion and hydraulic motor 54 for withdrawal which are used as the hydraulic motors to respectively insert and withdraw the control rod. When hydraulic pressure is applied to the hydraulic motor 53 for insertion for example, a rotational force is generated in a predetermined direction, the rotational force being transmitted from the bevel gear 55a supported by bearings 62 to the ball spindle 5 through the worm gear 56a disposed coaxially with the bevel gear 55b and the worm gear 56b supported by bearings 63. When the ball spindle 5 is rotated, the ball nut 9 allowed to engage with the ball spindle 5 is moved upwards. Simultaneously, the connection pipe 10 placed on the ball nut 9 is moved upwards. Therefore, the control rod 11 is inserted into the reactor core. Since the turbine-type hydraulic motor has substantially no driven torque in general, another mechanism is required to maintain the positions of the control rod 11 and the connection pipe 10. In this embodiment, the engagement operation of the worm gear 56 maintains the positions of the control rod 11 and the connection pipe 10 even if a vertical force is applied to the same. Therefore, the electromagnetic brake required for the conventional control rod driving apparatus can be omitted from the structure. It is preferable that the number of pipes for supplying hydraulic pressure to the hydraulic motor from the outside of the control rod driving apparatus is minimized in order to simplify the layout of pipes in the lower portion of the pressure vessel for the reactor. In this embodiment, the hydraulic pressure supplied from a hydraulic pipe 57 for driving is changed over by an electromagnetic valve 59 so that the hydraulic pressure is supplied to the hydraulic motor 53 for input and to the hydraulic motor 54 for output through a usual input port 68 and a usual outlet port 64. In this embodiment, discharged water after the hydraulic pressure from the hydraulic motor 53 for input and the hydraulic motor 54 for output has been supplied is discharged into the reactor pressure vessel 2 through a discharge pipe 65. Water may be discharged by another method using a discharge pipe, not shown, communicated with the outside portion of the reactor pressure vessel. If the discharge pipe is provided, maintaining the pressure of the discharged water at a level lower than the pressure in the reactor enables the pressure in the reactor to be used as hydraulic pressure to drive the hydraulic motor. Therefore, the necessity of individually providing a source for driving the hydraulic motor on the outside of the control rod driving apparatus can be eliminated. At the time of the scram, the hydraulic pressure is supplied to a hydraulic pipe 66 for scram operation so that the hydraulic pressure pushes up the connection pipe 10 mounted on the ball nut 9 in the guide tube 8 similarly to the conventional example. As a result, the connection pipe 10 is separated from the ball nut 9 so that scram operation is performed. Although this embodiment has an arrangement such that the water supply at the time of scram operation is performed by means of the hydraulic pipe 66 for scram operation provided individually from the usual driving hydraulic pipe 57, the pipes may be used commonly by employing a structure in which the water passage is changed over by an electromagnetic valve or the like. A second embodiment of the control rod driving apparatus will now be described with reference to FIGS. 2 and 3. Referring to FIG. 2, the same elements as those shown in FIG. 1 are given the same reference numerals and their descriptions are omitted here. The first embodiment has the arrangement in which the pipes for supplying hydraulic pressure for input/output at the time of usual operation of the control rod driving apparatus are formed into a common hydraulic pipe 57 for the usual operation and the electromagnetic valve 59 is used to change over the water passage downstream from the hydraulic pipe 57 for the usual operation. In this second embodiment, the pipes for supplying hydraulic pressure for the insertion operation at the time of the usual operation and those for scram operation are made so that a common introduction port 67 and a change-over valve 60 is disposed to change over the water passage downstream from the introduction port 67. The change-over valve 60 automatically opens/closes the valve in accordance with the flow quantity and the level of the hydraulic pressure so as to change over the water passage for the insertion operation and that for scram operation. FIG. 3 is a schematic view which illustrates the inside portion of the switch valve 60. The change-over valve 60 accommodates valves 68 and 69 which are respectively pressed against valve seats 72 and 73 by springs 70 and 71, respectively. The spring force of the spring 70 is determined so as to be smaller than that of the spring 71. If the hydraulic pressure acting on the introduction port 67 is low, only the valve 68 overcomes the spring force and is separated from the valve seat 72. As a result, the introduction port 67 and the usual insertion port 58 are communicated with each other. The insertion port 58 is communicated with the hydraulic motor 53 for insertion as shown in FIG. 2. Thus, usual insertion is performed similarly to that of the first embodiment. If the hydraulic pressure of the introduction port 67 shown in FIG. 3 is further raised, the valve 68 is pressed against the valve seat 75 by the hydraulic pressure so that communication between the introduction port 67 and the usual insertion port 58 is canceled. Furthermore, the valve 69 overcomes the spring force so as to be separated from the valve seat 73 so that the scram port 80 and the introduction port 67 are communicated with each other. The hydraulic pressure is supplied from the scram port 80 into the guide tube 8 shown in FIG. 2 so that scram is performed. The withdrawal of the control rod 11 shown in FIG. 2 is performed by supplying the hydraulic pressure to a withdrawing pipe 82 to activate the hydraulic motor 54 for withdrawal. In this embodiment, the pipe for supplying the hydraulic pressure for the insertion operation and that for the scram are formed commonly into the introduction port 67. It might be considered feasible to employ a contrary structure in which the pipe for supplying the hydraulic pressure for the withdrawal operation and that for scram are commonly formed. The foregoing case is undesirable because withdrawal operation is performed if the hydraulic pressure of water to be supplied at the time of scram is low. A third embodiment of the control rod driving apparatus according to the present invention will now be described with reference to FIG. 4. Referring to FIG. 4, the same elements as those shown in FIG. 1 are given by the same reference numerals and their descriptions are omitted here. This embodiment employs a turbine-type hydraulic motor 83 which can be rotated both forwards and reversely so that the number of the hydraulic motors is decreased to one. Both insertion and withdrawal of the control rod are performed by the turbine-type hydraulic motor 83. As for the scram, a similar arrangement is made to that according to the first embodiment. A fourth embodiment of the control rod driving apparatus according to the present invention will now be described with reference to FIG. 5. Referring to FIG. 5, the same elements as those shown in FIG. 1 are given the same reference numerals and their descriptions are omitted here. This embodiment has an arrangement that the hydraulic pipes are formed into a multi-pipe structure to decrease the number of the hydraulic pipes so as to simplify the layout of the pipes. The structure shown in FIG. 5 is an example having an arrangement in which a pipe 74 connected to the hydraulic motor 53 for insertion is accommodated in a pipe 85 so that a double-pipe structure is formed. A water flow through a gap between the pipe 85 and the pipe 84 flows through a pipe 86 to be introduced into the hydraulic motor 54 for withdrawal so that the hydraulic motor 54 for withdrawal is operated. Scram operation is performed by supplying hydraulic pressure to the hydraulic pipe 66. The pipe for the scram operation and the pipe for the usual insertion may be formed into a multi-layer pipe to decrease the number of the pipes. A fifth embodiment of the control rod driving apparatus according to the present invention will now be described with reference to FIG. 6. In this embodiment, the change-over valve accommodated in the motor case 52 in the first and third embodiments is disposed on the exterior of the motor case 52. A change-over valve 89 may be disposed at an arbitrary position, such as a position on the inside or outside of the pedestal in the lower portion of the reactor pressure vessel or on the outside of the reactor pressure vessel. The hydraulic pressure supplied through a pipe 90 is, by the change-over valve 89, connected to a usual outlet port 87 or a usual inlet port 88 in accordance with the drive mode so as to operate the hydraulic motor 53 for insertion or the hydraulic motor 54 for withdrawal. In this embodiment, the number of pipes in the pedestal in the lower portion of the pressure vessel for the reactor is increased, resulting in an undesirable pipe layout. However, the ease of maintenance of the change-over valve 89 can be improved. Further, the change-over valve according to the second embodiment may be disposed on the outside of the motor case 52. A sixth embodiment of the control rod driving apparatus according to the present invention will now be described with reference to FIG. 7. The control rod driving apparatus 1 is accommodated in the housing formed integrally with the pressure vessel 2 by welding. A first connection member 93 is attached to the upper portion of a drive shaft 92 which is rotated by a hydraulic motor 91. The drive shaft 92 penetrates a pressure boundary but has no shaft sealing packing. A second connection member 94 is attached to the first connection member 93. A long spindle 95 is connected to the upper portion of the second connection member 94, the spindle 95 having a bearing 96 attached to the top end thereof. The spindle 95 is rotated in synchronization with the drive shaft 92 when the hydraulic motor 91 is rotated. A nut 97 is engaged to the spindle 95, the nut 97 having the top surface with which the lower end of a connection pipe 98 is in contact. Four rollers 99 equally disposed in the circumferential direction are provided for each of the nut 97 and the connection pipe 98, the rollers 99 being in contact with the inner surface of a guide tube 95a. The side surfaces of the rollers 99 are guided by a plate 96b attached to the inner surface of the guide tube 95a to inhibit rotation of the nut 97 and the connection pipe 98. Reference numeral 97b represents a housing. In the control rod drive apparatus 1 constituted as described above, when the spindle 95 is rotated due to the rotations of the hydraulic motor 91, the nut 97 allowed to engage with the spindle 95 is permitted to move only in the axial direction. Therefore, the connection pipe 98 mounted on the nut 97 follows the movement of the nut 97, also causing the control rod 11 connected to the connection pipe 97 to be moved vertically. If the control rod 11 is rapidly inserted, called a scram operation, during an emergency for the reactor, high-pressure water accumulated in an accumulator is supplied through the scram-water injection port 98a to be introduced into the guide tube 95a. As a result, high-pressure water acts on the connection pipe 98 to rapidly pushes the connection pipe 98 in the upward direction. Therefore, the control rod 11 is rapidly inserted into the reactor core. A control rod driving system including a plurality of control rod driving apparatus of the structures described above will be preferably accommodated in a boiling water reactor BWR according to the present invention, which will be described hereunder. FIG. 8 illustrates the structure of a reactor core comprising a plurality of power-adjustment units 150 as designated by diagonal lines. As a control rod driving apparatus for the power-adjustment units 150, any one of the apparatuses according to the first to sixth embodiments is employed. Since the control-rod drive apparatus 1 having the foregoing drive structure causes the control rod 11 to move upwards or downwards in accordance with the rotational angle of the spindle 5 or 95, the control rod 11 can be precisely moved in the core by controlling the rotational angle of the spindle 5 or 95. Therefore, its structure is suitable as a method for driving the control rods for the power adjustment units. The control rod driving apparatus for units except the power adjustment units comprises the control rod driving apparatus having the hydraulic piston drive structure shown in FIG. 11. An example of a system for supplying hydraulic pressure for driving the foregoing control rod driving apparatus will now be described. Among the hydraulic pressure supply systems according to the present invention, the control rod driving apparatus having the hydraulic piston drive structure adapted to units except the power adjustment units 150 comprises the conventional hydraulic pressure supply system shown in FIG. 12. In this case, the conventional structure comprises one stabilizing circuit 105, causing the control rods to be driven one by one. In this embodiment, a plurality of the stabilizing circuits 105 may be provided to enable a plurality of control rods to be driven simultaneously. FIG. 9 illustrates an embodiment of a system for supplying hydraulic pressure to a control rod driving apparatus of a screw-drive type hydraulic drive motor for use in the power adjustment units. It should be noted that a pump 201 of a hydraulic supply portion 200 shown in FIG. 9 may be commonly used with the pump 101 shown in FIG. 12. The hydraulic pressure supply portion 200 has a pipe structure comprising a pump 201, a flow meter 202, a flow-rate adjustment valve 203, a pressure-adjustment valve 204 and a plurality of stabilizing circuits 205. Each stabilizing circuit 205 comprises two systems of electromagnetic valves 206 and 207. One hydraulic-pressure supply portion 200 is provided for one nuclear reactor plant. Pipes represented by pipes 209, 210 and 211 are connected from the hydraulic-pressure supply portion 200 to a hydraulic-pressure control unit 208 which has pipes corresponding to those in the control rod driving apparatus 1. Water flows in the hydraulic-pressure supply portion 200 and in each pipe are designated by arrows. The pipe 209 is a charging pipe for an accumulator 213 which acts when the control rod is inserted to cope with an emergency so that the accumulator 213 is charged with high-pressure water. The accumulator 213 includes a piston 214. The lower portion of the piston 214 is connected to a nitrogen container 216 through a pipe 215. High-pressure nitrogen gas is enclosed in the nitrogen container 216. Reference numeral 217 represents a scram valve which is closed in a usual state so that the accumulator 213 is maintained at a high pressure state. In response to a control-rod emergency insertion signal, the scram valve 217 is opened so that the high-pressure water in the accumulator 213 flows through a scram pipe 219 connected to the lower surface of a connection pipe of the control rod driving apparatus 1 so as to flow in the control rod driving apparatus 1. As a result, a control rod is inserted into the reactor core to cope with emergency. It should be noted that the control rod driving apparatus 1 of the screw-drive structure does not involve scram discharge water. The pipe 210 is a pipe for supplying water for driving the control rod when the output from a reactor is adjusted, the pipe 210 being connected to a direction--control circuit 226 composed of two electromagnetic valves 222 and 223 disposed in the hydraulic-pressure control unit 208. The direction-control circuit 226 acts to change over the rotational direction of the hydraulic drive motor in accordance with the insertion/withdrawal of the control rod. That is, the control rod is inserted by opening the electromagnetic valve 222 so that the driving water flows through the electromagnetic valve 222 and an insertion pipe 220. As a result, the hydraulic drive motor is rotated in a direction which causes the control rod to be inserted. When the control rod is withdrawn, the electromagnetic valve 223 is opened. The driving water flows through the electromagnetic valve 223 and the withdrawing pipe 221 so as to rotate the hydraulic drive motor in a direction which causes the control rod to be withdrawn. In both insertion and withdrawal, drive water rotates the hydraulic drive motor and flows in the pressure vessel 2 through the control-rod drive apparatus 1. The pipe 211 is a purge-water pipe for preventing invasion of foreign materials from the inside portion of the pressure vessel 2 into the control rod driving apparatus 1 so that purge water, the pressure of which has been adjusted to a predetermined level in the purge-water pipe, always flow through the scram pipe 219 to flow in the control rod driving apparatus 1. The electromagnetic valves 206 and 207 of the stabilizing circuit 205 are opened in a usual state so that a quantity required for the insertion of the control rod flows through the electromagnetic valve 206 and a quantity required for the withdrawal of the same flows through the electromagnetic valve 207. As a result, water flows in a purge-water header 227 as a portion of purging water. In the stabilizing circuit 205, the electromagnetic valve 206 is closed when the control rod is inserted to adjust the output so that a quantity of water, which is the same as the quantity of water flowing through the electromagnetic valve 206, flows to the hydraulic drive motor. When the control rod is withdrawn, the electromagnetic valve 207 is closed so that a quantity of water, which is the same as the quantity of water flowing through the electromagnetic valve 207, flows to the hydraulic drive motor. Thus, the stabilizing circuit 205 stabilizes the pressure of drive water similarly to that of the conventional example. Furthermore, a plurality of the stabilizing circuits 205 are provided, thereby simultaneously and stably driving a plurality of control rods. By simultaneously driving control rods of the power adjustment units located at symmetric positions with respect to the central unit in the core for example, the power from the core can be adjusted in such a manner that the symmetry of the distribution of the powers from the core is maintained. By providing a plurality of the stabilizing circuit 205 for the control rod driving apparatus having the hydraulic piston structure as described above, the control rods can be driven similarly in such a manner that the symmetry of the distribution of the powers is maintained. As described above, the control rod driving apparatus according to the present invention comprises a motor which is driven by hydraulic pressure in place of a conventional electric motor so that the necessity of using the shaft sealing packing for the ball spindle can be eliminated and elements which must be periodically changed can be omitted. Therefore, the amount of maintenance required for the control rod driving apparatus can be significantly reduced. As a result, a reduction in the quantity of exposure for operators when a reactor is periodically inspected can be achieved. In addition, it contributes to shorten the time required to complete the latter period of the periodical inspection. Since the shaft sealing portion is omitted from the structure, the drive torque can be reduced and normal operation can be always expected. In addition, the possibility of discharge of the reactor water to the outside of the reactor can be eliminated. As a result, a great contribution can be made to improve the reliability and safety of the reactor. Since the operation of the worm gear maintains the position of the control rod even if external force for vertically moving the control rod acts, the electromagnetic brake, which has been used to prevent the withdrawal of the control rod when a pipe has been broken, can be omitted from the structure. The foregoing boiling water reactor BWR equipped with the control rod driving system according to the present invention enables the control rod to be operated to be adaptable to the function of the core. Therefore, a great contribution can be made to improve controllability of the BWR. By using the motor driven by hydraulic pressure in the control rod driving apparatus of the output adjustment units in place of the conventional electric motor, the necessity of using the shaft sealing packing for the spindle can be eliminated. In addition, the same hydraulic pressure supply system as that for the control rod driving apparatus, except for the power adjustment units, is employed. Therefore, the system can be simplified and a great economical effect can be obtained. Although the present invention has been described hereinbefore in the preferred forms, it is understood that the present disclosure of the preferred forms may be changed or modified in the details of construction, and the combination and arrangement thereof may be resorted to without departing from the spirit and the scope of the appended claims.