JPH04310894A - Apparatus and method for cooling coil of control-rod driving mechanism - Google Patents

Abstract

PURPOSE: To cool the coil of a control rod driving mechanism in a nuclear power plant through natural convection. CONSTITUTION: The cooling means comprises air tubes 3 arranged at a position where a control rod mechanism 4 is not located wherein the air tubes 3 are fixed with hoods 21, 22 for introducing the air heated by a coil 20 into the air tubes. Since the high temperature air passing through the air tubes is discharged above a missile shield 10, the ambient air is held in low temperature state. Consequently, natural convection takes place to cool the coil efficiently.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to nuclear power plants. More particularly, the present invention relates to an apparatus and method for passively cooling coils in a control rod drive mechanism (CRDM) in a reactor of a nuclear power plant by natural convection of air.

0002

BACKGROUND OF THE INVENTION In nuclear reactors, CRDMs are used to place movable neutron absorption control rods within the reactor core, thereby controlling core reactivity. The CRDM is located within a pressure housing that extends vertically from the reactor vessel closure. Each CRDM features a latching device located within the lower portion of the pressure housing. The latching device includes a fixed pole piece and a movable pole piece and drives a plurality of gripper latches. The gripper latch is linked to the pole piece so as to be cammed relative to a drive rod passing through the latching device in response to movement of the pole piece. The drive rod assembly also connects the control rod to the latching device. A plurality of circumferential grooves are formed around the drive rod and are spaced apart from each other at regular intervals. The shape of this groove matches the shape of the gripper latch, which can support the drive rod and the control rod attached thereto.

[0003] On the outside of the pressure housing, an actuation coil stack consisting of three independent coils is disposed at the same level as the latching device. When the coil is energized, a magnetic field is generated. The magnetic flux passes through the non-magnetic pressure housing and combines with the steel pole pieces of the latching device to generate a force sufficient to vertically move the control rod.

[0004] During operation of a nuclear reactor, the electromagnetic coil is heated. If no testing is performed, the heat generated can damage electronic circuitry located near the coil. For this purpose, the coil must be cooled during operation. Current cooling mechanisms use electric fans to force air down the coil surface into the exhaust pipe, and then direct the heated air through the manifold to the fan's suction side. The fan exhausts hot air into the containment vessel, where the heat load is handled by a cooling system. There are two major problems with this method. First, to perform maintenance or refueling on the reactor, the exhaust pipe, fan, and manifold must be removed. This disassembly and reassembly of the cooling system is time-consuming and costly, and requires significant man-hours in a radiation environment. Second, because the cooling system is active with electric fans, fan malfunctions or power outages can result in costly downtime.

It would therefore be desirable to provide an apparatus and method for passively cooling CRDM coils without being affected by equipment failures or power outages. Additionally, it would be desirable to provide a cooling system that does not require disassembly and reassembly to access the reactor core.

[0006]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method and apparatus for passively cooling a CRDM within a nuclear reactor by circulating atmospheric air within the containment vessel along the surface of the CRDM.

Another object of the present invention is to induce a layered air flow on the surface of the CRDM by inducing convection in the air surrounding the CRDM.

Still another object of the present invention is to retrofit existing nuclear reactors to incorporate the present cooling system without extensive disassembly and to incorporate the present cooling system into the entire reactor closure assembly. and be removable as a single unit.

The above and other objects are achieved in a nuclear power plant that includes a reactor vessel having a closure lid assembly. A plurality of CRDMs are disposed on and extend above the closure lid. A plurality of air cylinders extending vertically above the closing lid are located within an area where control rods are arranged in a predetermined arrangement (hereinafter referred to as "control rod arrangement"), and control rods within the control rod arrangement are The bars are scattered and placed in unnecessary locations. This air cylinder separates the air flowing into and out of the coils of the CRDM, creating a convection flow of air that causes the atmosphere in the containment vessel surrounding the CRDM to flow downward and into the top of the closure lid. into the inlet of the arranged manifold. The manifold is disposed on top of the manifold and is in airflow communication with a shroud surrounding the coils of the CRDM. Air entering the manifold is directed by the shroud to flow along the CRDM coil, thereby cooling the coil. Air flowing along the surface of the coil and heated by the coil is guided by a baffle assembly and into an inlet formed in the side of the air cylinder. The air rises within an air cylinder that extends through the seismic support platform and missile shield, and is exhausted above the missile shield.

The air cylinder is laterally restrained by a seismic support platform. This is accomplished by attaching a height-adjustable collar to the stack of air cylinders. This collar is combined with a plate element located at the tip of the pressure housing of the CRDM to form an interconnecting structure within the cavity of the seismic support platform.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show a portion of the reactor vessel in the vicinity of the closure assembly. Such reactor vessels are commonly used in nuclear power plants. The closure lid 1 is a generally hemispherical dome formed at the top of the reactor vessel 48. Control rod drive mechanism (CRDM)
) 4 serve to vertically position the control rods within the reactor core. Each CRDM 4 includes a control rod drive shaft 19, a pressure housing 50 surrounding the control rod drive shaft 19 and extending upwardly through the closure lid 1, and a latching device (not shown) disposed within the pressure housing 50. , a coil stack consisting of three electromagnetic coils 20 mounted on the outside of the pressure housing 50. The coil stack is arranged in the middle part of the pressure housing 50, so that a part of the pressure housing 50 is located above the coil stack and another part is located below. C used
The number of RDM4s depends on the particular reactor design. Note that for clarity purposes, only four CRDMs are shown in FIG. 2, but the number of CRDMs is typically greater. C.R.D.
A typical arrangement of M4 is shown in FIG.

The tip of each CRDM's pressure housing 50 is attached to a square plate element 12. This plate element 12 is arranged in a hole or cavity 49 formed in the seismic support platform 2 arranged above the closure lid 1 . A seismic support platform 2 in the form of an annular disk is fixed to the containment wall by tie rods (not shown). Earthquake support platform 2
can laterally restrain the CRDM 4 in the event of seismic activity. The seismic support platform 2 is connected to the closure lid 1 via lift rods 5, so that the closure assembly including the CRDM 4 and the seismic support platform 2 can be attached to the reactor vessel as a single unit during maintenance or refueling. It can be removed from 48.

As previously mentioned, coil 20 must be cooled during operation. According to the present invention, cooling is performed by passively circulating air in the atmosphere inside the containment vessel around the coil 20. This passive cooling is achieved by creating natural convection in the air surrounding the coil 20. Therefore, as shown in FIGS. 2 and 4, a plurality of air cylinders 3 are distributed in a CRDM array. Generally, the control rods are arranged in a vertical and horizontal rectangular array, as shown in FIG. The number of locations in which control rods can be placed in such an arrangement is greater than the number of control rods actually needed to control a nuclear reactor. As a result, empty spaces exist in the control rod arrangement. Since there is considerable flexibility with respect to the number and location of the air cylinders according to the invention, the air cylinders 3 can be placed in existing spaces within the CRDM arrangement. In the arrangement shown in FIG. 4, there are 62 control rods (therefore 62 CRDMs and 62 coils that must be cooled) and 18 air cylinders 3.

As shown in FIGS. 3 and 7, each air cylinder 3 is composed of a main body portion 14 and a stack portion 15 connected to the main body portion 14 by a reducer plate 27. As shown in FIGS. The air cylinder 3 has a square cross section and has an air inlet 2 on each side.
It is characterized by having 5. As shown in Figure 2,
The height position of the air inlet 25 is slightly higher than the position of the coil 20. Each air cylinder 3 has a base plate 40 fixed to a support 41 formed on the closing lid 1 with bolts 47.
It is characterized by In a preferred embodiment, the wall of the body portion 14 of the air cylinder 3 is made up of three layers of sheet metal plates 4.
2, these plates 42 are connected to each other by blocks 46 welded thereto and attached to the base plate 40 by bolts 43. Further, as shown in FIG. 8, the heat insulator 32 is connected to the plate 42
placed in the gap between.

According to an important feature of the invention, baffle assemblies are mounted on the sides and corners of the cylinder body portion 14 directly above the air inlet 25. This baffle assembly is comprised of side hoods 21 attached to each side of the air cylinder 3 and corner hoods 22 attached to each corner. Each side hood 21 is characterized by a mounting plate 26 fixed to the air cylinder body portion 14. Baffle portion 51 of side hood 21 is connected to mounting plate 26 via hinge 23. The corner hood 22 is attached to the corner of the air cylinder 3 via a pivot joint 24. Therefore, both the corner hood 22 and the side hood 21 can be pivoted into the extended position shown in FIG. 3 or into the retracted position overlapping the air cylinder body portion 14. In addition, a semicircular notch is provided in each hood 21.
, 22 is formed at the edge of the air cylinder 3 at a position away from it. The diameter of this notch is such that the hoods 21 and 22 are CRDM4
The diameter of the pressure housing 50 is slightly larger than that of the pressure housing 50 so as to fit around the pressure housing 50.

As shown in FIG. 2, the stack portion 15 of the air cylinder 3 extends through the seismic support platform 2. Support collar 16 is slidably disposed around stack portion 15 and is secured to stack portion 15 by bolts 17 extending through tabs 18 projecting from the sides of stack portion 15 . Bolts 17 are screwed into holes (not shown) in support collar 16. The outer diameter of the support collar 16 is the same as the outer diameter of the plate element 12 attached to the top of the pressure housing 50 of the CRDM 4. According to the above-described method of attaching the support collar 16 to the stack part 15, the height of the collar 16 can be adjusted by turning the bolt 17 and the support collar 16 can be precisely aligned to match the plate element 12. . According to the invention, the support collar 16 and the plate element 12 thus form an interconnected structure within the cavity 49 of the seismic support platform 2. Thereby, the seismic support platform 2 can restrain the air cylinder 3 in the lateral direction similarly to the CRDM 4.

[0017] Connecting tabs 13 are connected to adjacent plate elements 12.
and between the plate element 12 and the support collar 16. Each connecting tab 13 is welded to only one of the two plate elements 12 that it spans, so that the tab 13 restrains relative movement between the plate element 12 and the collar 16 in the vertical direction. However, it is permissible on the plane of the seismic support platform 2.

[0018] In the existing reactor vessel 48, an insert (referred to as a "dummy can") is placed in the space of the plate element arrangement or control rod arrangement (position where no control rods are arranged). . These dummy cans have the same dimensions as the plate elements 12, so that the plate element interconnection structure remains intact. According to the present invention, after removing the dummy can, the air cylinder 3 is slid vertically into the space in the plate element arrangement from which the dummy can has been removed, with the hoods 21 and 22 in the retracted position. The closure lid assembly can be retrofitted into an existing nuclear power plant without disassembling it. This installation process is facilitated for the following reasons. That is, when the side hood 21 and the corner hood 22 are retracted, the maximum cross-sectional dimension of the air cylinder main body portion 14 (i.e., the maximum outer dimension of the air cylinder 3 in a plane perpendicular to the axis of the air cylinder 3) is: This is due to the fact that the dummy can is smaller than the dimensions of the space in the plate element arrangement from which it has been removed (ie the dimensions of the plate element 12 and support collar 16). Once the air cylinder 3 is installed, a clip 44 shown in FIG. 7 is fitted onto the hoods 21, 22 to hold them in the extended position. This clip 44 is attached to the main body portion 14 of the air cylinder 3 using a bolt 45.

As shown in FIG. 2, the missile shield 10
is placed on top of the I-beam 9 which is placed above the seismic support platform 2. Missile shield 10 serves to limit control rod movement in the event of an accident. In the preferred embodiment, the stacked portion 15 of the air cylinder 3 extends through a hole in the missile shield 10 in order to exhaust hot air above the missile shield 10. However, shorter stack sections 15 terminating on the underside of the missile shield 10 to vent hot air around the missile shield 10 can also be used. This modification facilitates retrofitting existing nuclear power plants with thick concrete missile shields according to the invention.

As shown in FIG. 2, a head adapter 11 is attached to the closure lid 1 and serves as a basis for attaching a circular air manifold 7 to the top of the closure lid 1. A plurality of air inlets 8 are formed in the side of the air manifold 7. As shown in FIGS. 2 and 4, a substantially square shroud 6 is attached to the top of the air manifold 6.
is arranged and surrounds the coil 20 of the CRDM 4. During reactor operation, coil 20 transfers heat to the air surrounding it within shroud 6 . The heated air flows upward by convection. The side hood 21 and the corner hood 22 direct the rising air to the inlet 25 of the air cylinder 3.
Furthermore, the air continues to rise inside the air cylinder 3 and is discharged above the missile shield 10 from the outlet of the stack part 15 of the air cylinder 3. Due to the flow of air into the air cylinder 3, the atmosphere surrounding the closure lid assembly is directed downward and into the inlet 8 of the air manifold 7. The manifold 7 guides this atmospheric air to a portion of the pressure housing 50 below the coil 20. Furthermore, this air
The shroud 6 directs the heat onto the coil 20 and cools the coil 20 by convective heat conduction. Insulation 32 in the sidewalls of the air cylinder body portion 14 prevents heat from the rising air from being transferred to the air surrounding the pressure housing 50, particularly the air surrounding the portion above the coil 20. the result,
The rising air that has cooled the coil 20 is maintained at a high temperature, and the descending air supplied to the inlet 8 of the air manifold 7 is maintained at a low temperature. In this way, the air cylinder 3 causes convection by separating the air around the CRDM 4 into descending low-temperature air and ascending high-temperature air.

[0021] Side hood 21 and corner hood 22
In the above-mentioned arrangement configuration, each CRDM 4 has two air cylinders 3
When the air cylinder 3 is disposed between the air cylinders 3 and 3, it functions to sufficiently guide air into the air cylinder 3. That is, as shown in FIG.
All of the air flowing around the coil 20 of M41 flows into the inlets 25 of the air cylinders 31 and 32. Similarly, CRDM
All of the air flowing around the 42 coils 20 is in the air cylinder 3.
3, 34 into the inlet 25. Further, the air flowing along the coil surface of the CRDM 45 adjacent to the CRDM 41 is guided into the air cylinders 31, 32 by the corner hood 22, and the air flowing along the coil surface of the CRDM 43, 47 adjacent to the air cylinders 31, 32 is guided into the air cylinders 31, 32 by the corner hood 22. It is guided by the side hood 21. Air flowing along the coil surface of the CRDM 46 adjacent to the CRDM 42 and the air cylinders 33 and 34
A similar situation occurs for the air flowing along the coil surfaces of the CRDMs 44 and 48 adjacent to the .

However, as mentioned above, the air cylinder 3
The number and location of the control rods is determined by the location in the control rod array where no control rods are needed to control the reactor. Therefore, the above-mentioned air cylinder baffle structure has a surface of the coil 20 of the CRDMs 43 to 48 that are away from the air cylinder 3 (i.e.
The air flowing along the coil surfaces of the CRDMs 43, 44 facing each other, the coil surfaces of the CRDMs 45, 46 facing each other, and the coil surfaces of the CRDMs 47, 48 facing each other) cannot be sufficiently guided. Because the air flowing along the surfaces of these coils cannot be sufficiently guided into the inlet 25 of the air cylinder 3, the air rises in an unseparated state,
It mixes with and heats the descending air entering the manifold inlet 8. According to the present invention, this condition is solved by installing an auxiliary baffle on the CRDM itself, which limits the rise of air in the part of the CRDM remote from the air cylinder and directs the air to the hood.
1, 22 to deflect the air to a position where it can be guided into the inlet 25 of the air cylinder.

That is, as shown in FIGS. 5 and 6, CRD
Restrictor 28 attached to M44, 45, 47
This prevents the upward flow of air along the portions of the CRDMs 43 to 48 that are away from the air cylinder 3. Also, CRDM44,
Deflectors 29 attached to CRDMs 45, 46, and 47 guide the air flowing along the far side surfaces of the coils 20 of the CRDMs 43 to 48 to the corner hood 22 of the air cylinder 3, and from there the air flows to the air cylinder 3. 3 entrance 25. As shown in FIG. 5, a deflector 291 attached to the CRDM 44 guides air to the corner hood 22 of the air cylinder 31, a deflector 292 attached to the CRDM 45 guides air to the corner hood 22 of the air cylinder 33, and The deflector 293 attached to the corner hood 22 of the air cylinder 32 directs air to the corner hood 22 of the air cylinder 32.
The deflector 294 attached to the CRDM 47 guides the air to the corner hood 22 of the air cylinder 34.

The shapes shown in FIGS. 4 and 5 are merely examples, and the quantity and position of the restrictor 28 and deflector 29 in a specific application may vary depending on the specific position of the air cylinder 3 within the control rod arrangement. Please note that Generally speaking, all of the air entering the inlet 8 of the air manifold 7 and the air directed over the coil 20 by the shroud 6 is, as far as possible, connected to the inlet 2 of the air cylinder 3.
5, the restrictor 28 and deflector 29 should be arranged as necessary.

As shown in FIG. 6, the restrictor 28 and deflector 29 are connected to the CRDM 4 by a collar 30 surrounding the CRDM 4 and held in place by a flange 31.
can be attached to. This collar 30 can be attached to the pressure housing 50 directly above the coil 20, as shown in FIG. 6, or alternatively, it can be attached to the body of the upper coil itself, as shown in FIG.

As shown in FIG. 2, all of the structural elements of the CRDM coil cooling system extend radially inside the envelope of the closure lid 1 (ie, extend upward from and have the same diameter as the periphery of the closure flange 52). Note that the cylindrical tube is located radially inside the imaginary cylindrical tube. This feature facilitates reactor maintenance and refueling because the entire closure lid assembly can be removed as a single unit without interfering with CRDM coil cooler components and surrounding structural members in the containment area. to facilitate disassembly.

The present invention may be embodied in other specific forms without departing from its spirit or characteristics, and therefore the foregoing detailed description of the invention may be used as an indication of the scope of the invention. Reference should be made to the claims.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a portion of a closure lid assembly of a nuclear reactor vessel in a nuclear power plant.

FIG. 2 is a longitudinal cross-sectional view of the closure lid assembly shown in FIG. 1;

FIG. 3 is a perspective view of an air cylinder.

FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2;
FIG. 3 is a diagram showing the arrangement of air cylinders within a CRDM arrangement.

5 is an enlarged view showing a portion within a dashed-dotted line V in FIG. 4; FIG.

FIG. 6 is a sectional view taken along line VI-VI in FIG. 5;

7 is a sectional view along the line VII-VII in FIG. 5, showing structural details of the air cylinder; FIG.

8 is an enlarged view showing a portion within the dashed line VIII in FIG. 7; FIG.

[Explanation of symbols]

1 Closing lid 2 Seismic support platform 3 Air cylinder 4 Control rod drive mechanism (CRDM) 7 Air manifold 14 Air cylinder main body part 15 Air cylinder stack part 20 Coil 21 Side hood 22 Corner hood 28 Restrictor 29 Deflector 48 Reactor vessel 50 Pressure housing

Claims (2)

[Claims] 1. A nuclear power plant having a plurality of control rod drive mechanisms extending through a reactor vessel closure and surrounded by an atmosphere, each of the control rod drive mechanisms having at least one coil. and partially surrounded by a housing, wherein a first portion of each housing is disposed above the coil and a second portion is disposed below the coil. a control rod drive mechanism coil cooling system for cooling a control rod drive mechanism coil, the control rod drive mechanism having: (a) a first air flow guide means for directing the ambient air into the second portion of the housing; (c) second air flow guiding means for directing said air directed into two parts to flow along the surface of said coil; means for separating the air flowing through the control rod drive mechanism. 2. A nuclear power plant having a plurality of control rod drive mechanisms extending through a reactor vessel closure lid, each of the control rod drive mechanisms having a coil; A control rod drive mechanism coil cooling method for passively cooling the coil in the nuclear power plant in which the first portion is disposed below the coil, the method comprising: (a) supplying atmospheric air to each of the control rods; (b) causing the guided air to flow along a surface of the coil; (c) separating the air flowing along the coil from the ambient air; (
d) A method for cooling a control rod drive mechanism coil, comprising flowing the separated air upwardly by convection along a vertical flow path away from the closure lid.