JPH02310495A - Shroud supporting structure of nuclear reactor - Google Patents

Abstract

PURPOSE:To prevent the oscillation of a control rod guide pipe by the disturbance in the flow of a coolant by lowering the elevation at the bottom end of a shroud supporting ring facing the control rod guide pipe lower than the elevation at the bottom end of the control rod guide pipe. CONSTITUTION:Shroud supporting legs 10 are disposed at equal intervals circumferentially in a nuclear reactor pressure vessel 3. The shroud supporting ring 11 is installed across the supporting legs 10 and form flow passages 12a, 12b, 12c of reactor water from a downcomer part toward the lower part of the reactor core. The control rod guide pipe 9 is installed to face the flow passage 12b formed between adjacent internal pumps 5 and 5 of these flow passages. The elevation at the bottom end of the supporting ring 11 existing in the upper part of the flow passages 12a and 12c is the same as heretofore and the elevation at the bottom end of the supporting ring 11 existing in the upper part of the flow passage 12b is made lower than the elevation of the supporting ring existing in the upper parts of the flow passages 12a and 12c and lower than the elevation at the bottom end of the guide pipe 9. The elevation at the bottom end of the supporting ring 11 is set at about 1/2 to 3/4 the height of the supporting legs 10.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a shroud support structure for a nuclear reactor that supports a shroud, and in particular to a shroud support structure that supports a shroud. The present invention relates to a shroud support structure for a nuclear reactor that makes it possible to prevent vibration of control rod guide tubes.

(Prior Art) A shroud that covers the core of a nuclear reactor is provided at the bottom of a nuclear reactor pressure vessel, that is, below a coolant downcomer.

The shroud support structure that supports the shroud is a core support structure composed of shroud support legs and shroud support rings, and this core support structure supports the shroud, the upper grid plate, the core support plate, and the like.

FIG. 5 and FIG. 6 are a partial vertical cross-sectional view and a partial cross-sectional view of the bottom of the reactor pressure vessel, respectively. A plurality of prismatic shroud support legs 1 are joined to the bottom of the reactor pressure vessel 3 in the circumferential direction. A thin cylindrical shroud support ring 2 is vertically installed above each shroud support leg 1 so as to straddle the shroud support leg 1, and a shroud (not shown) is supported on this shroud support ring 2. Two adjacent shroud support legs 1 and shroud support rings 2 form reactor water flow paths 4a, 4b, and 4C extending from the downcomer portion to the lower part of the core.

A plurality of internal pumps 5 are vertically installed in a downcomer portion between the side wall of the reactor pressure vessel 3 and the shroud as internal reactor recirculation pumps. The internal pump 5 is provided vertically communicating with a boss 3a at the bottom of the reactor pressure vessel 3. A pump impeller 6 is attached to the upper end of the internal pump 5, and a diffuser 7 covers the pump impeller 6. The outside of the diffuser 7 is fixed to the inner wall of the reactor pressure vessel 3 and the shroud support ring 2.

A plurality of control rod drive mechanism housings 8 are provided in a row in the center of the reactor pressure vessel 3 so as to be surrounded by the shroud support ring 2. At the upper end of the control rod drive mechanism housing 8, a larger A control rod guide tube 9 having an outer diameter is attached. The lower end elevation of the control rod guide tube 9 is approximately at the same height as the lower end elevation of the shroud support ring 2 (Japanese Patent Publication No. 62-3
(See Publication No. 8677). This arrangement relationship is schematically shown in FIG. FIG. 7 is a view taken along the line ■-■ in FIG. 5. Fifth
Components similar to those in the figure and FIG. 6 are designated by the same reference numerals, and description thereof will be omitted.

Shroud support leg 1 and internal pump 5
are arranged at equal intervals in the circumferential direction, but the number of shroud support legs 1 is twice the number of internal pumps 5. There are two pumps on both sides of one internal pump 5.
shroud support legs 1 are arranged at equal positions from the internal pump 5.

The pump impeller 6 is rotated by the operation of the internal pump 5, sucks reactor water (coolant) from the downcomer, guides it to the lower part of the reactor core through the diffuser 7, and forces it into the reactor pressure vessel 3. It's being recirculated.

At this time, as shown by the arrows in FIG. 6, the discharge flow of the coolant flows through channels 4a and 4b.

4C and guided into the shroud. There is a control rod drive mechanism housing 8 in front of the flow path 4b, but the flow path 4a
And it is not in front of 4C.

Conventionally, as described above, the lower end elevation of the control rod guide tube 9 is approximately at the same height as the lower end elevation of the shroud support ring 2. Therefore, the coolant guided below the reactor core through the reactor water channels 4a and 4c does not collide with the control rod guide tubes 9 and cause them to vibrate.

However, the coolant guided to the lower part of the reactor core through the reactor water flow path 4b is discharged downward from the pump impellers 6 on both sides of the reactor water flow path 4b, and is then guided to the bottom mirror plate of the reactor pressure vessel 3 and is then guided into the reactor core. guided to the bottom. At this time, the reactor water discharged from the adjacent pump impellers 6 collides with each other at the intermediate portion, and this collision disturbs the flow of the reactor water. This turbulent flow becomes a flow as shown in FIG. Figure 8 shows ■-■ of Figure 6.
FIG. Components similar to those in FIGS. 5 and 6 are designated by the same reference numerals, and their explanations will be omitted.

As can be seen from FIG. 8, a part of the flow becomes an upward flow and collides with the control rod guide tube 9, which has a large outer diameter. In this case, the lower end elevation of the control rod guide tube 9 is connected to the shroud support ring 2.
There is no meaning in aligning it with that of .

One way to deal with this is to make the lower end elevation of the III m rod guide tube 9 higher than that of the shroud support ring 2, but the control rod drive mechanism housing 8 has its functional limitations. It cannot be made any longer than this.

If the control rod guide tube 9 vibrates due to fluid shock, cracks may occur at the joint between the control rod drive mechanism housing 8 and the control rod guide tube 9, and the control rods may vibrate within the reactor core, causing damage to the fuel rods. There is.

(Problems to be Solved by the Invention) As described above, in the conventional shroud support structure, vibration of the control rod guide tube due to turbulent flow could not be completely prevented.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a shroud support structure for a nuclear reactor that prevents control rod guide tubes from vibrating due to disturbances in the flow of coolant.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a plurality of shroud support legs vertically installed at intervals in the circumferential direction at the bottom of a nuclear reactor pressure vessel, and In a nuclear reactor shroud support structure consisting of a shroud support ring installed over the leg and forming a flow path for reactor water, the lower end elevation of the shroud support ring facing the control rod guide tube is connected to the control rod guide tube. To provide a shroud support structure for a nuclear reactor, characterized in that the shroud support structure is lower than the lower end elevation of the reactor.

(Function) In the present invention, in a flow path where there is an IJ11 rod guide tube in front, the lower end of the shroud support ring at the top thereof is made to hang down, so that its elevation is lower than that of the control rod guide tube. do. This limits the amount of turbulence passing through this flow path, and the distance between the upper end of the bracket and the liI control rod guide tube becomes more remote than before, so the coolant flow is
II The possibility of colliding with the l rod guide tube is reduced.

Note that if the lower end elevation of the shroud support ring is lowered on all channels, the pressure loss in the channels will increase and the lift of the internal pump will become insufficient.

In this case, a new high-head internal pump would have to be developed, so the elevation would be lowered only in the upper part of the flow path where the control rod guide tube is in front.

(Example) The present invention will be described in detail below with reference to FIGS. 1 to 4.

FIG. 1 is a partial cross-sectional view of a nuclear reactor pressure vessel illustrating a first embodiment of the present invention, and FIG. 2 is a view taken along the line ■--■ in FIG. In both FIGS. 1 and 2, the same parts as in FIGS. 5 and 7 are designated by the same reference numerals, and the explanation thereof will be omitted.

The configuration in FIG. 1 is basically the same as that in FIG. 5, and the shroud support legs 10 are arranged at equal intervals in the circumferential direction within the reactor pressure vessel 3.

The shroud support ring 11 is installed across the shroud support leg 10, and forms reactor water flow paths 12a, 12b, and 12C extending from the downcomer portion to the lower part of the reactor core. A control rod guide pipe 9 is installed facing a reactor water flow path 12b formed between adjacent internal pumps 5, 5 in this reactor water flow path.

As can be seen from FIG. 2, in this embodiment, the flow path 1
Shroud support ring 1 on top of 2a and 120
1. The lower end elevation is the same as the conventional one. However, the elevation of the lower end of the shroud support ring 11 above the reactor water passage 12b is lower than that above the passages 12a and 12c, and lower than the elevation of the lower end of the control rod guide tube 9. Therefore, the shape of the lower end of the schwaudna boat ring 11 is not a straight line but has an uneven structure.

The elevation of the lower end of the shroud support ring 11 is 1/2 to 3/4 of the height of the shroud support leg 10.
degree is preferred. If the elevation is too high, the effect of the present invention of preventing vibration of the control rod guide tube 9 cannot be obtained,
This is because if the elevation is too low, the pressure loss in the flow path 12b becomes large and the head of the internal pump 5 becomes insufficient.

The flow of coolant outside the shroud is the same as that shown in FIG. 8, and as shown by the arrows in FIG.
2b and 12c to reach the lower part of the core. According to this embodiment, the height of the reactor water flow path 12b is higher than that of the other reactor water flow paths 12a, 1.
2c, even if turbulent flow occurs outside the reactor water flow path 12b, the bellows-shaped protrusion of the shroud support ring 11 restricts this turbulent flow from flowing into the lower core.

In addition, since the distance from the upper end of the reactor water flow path 12b to the lower end of the control rod guide tube 9 is longer than before, the possibility that the turbulent flow passing through the reactor water flow path 12b will collide with the control rod guide tube 9 is extremely reduced. .

FIG. 3 is a partial cross-sectional view of a nuclear reactor pressure vessel illustrating a second embodiment of the present invention, and FIG. 4 is a view taken along the line IV-rV in FIG. 3. In both FIGS. 3 and 4, the same parts as in FIGS. 1 and 2 are designated by the same reference numerals, and explanations thereof will be omitted.

As can be seen from FIG. 3, in this embodiment, the shroud support legs 13 are not arranged at equal intervals in the circumferential direction. The width of the reactor water flow path 14b (the pitch between the shroud support legs 13) is wider than the width of the reactor water flow paths 14a and 14G.

As shown in FIG. 4, the elevation of the lower end of the shroud support ring 15 is lowered at the lower end of the IIJIll rod guide tube 9 rod end inner tube 9 at the upper part of the reactor water flow path 14b, as in the first embodiment. The degree of elevation droop is the first
It is the same as the example.

In this embodiment, since the width of the reactor water flow path 14b is wide, the cross-sectional area of the reactor water flow path 14b is equal to that of the flow path 14a.

It is almost the same as that of 14G. Therefore, reactor water flow path 1
4b without causing any pressure loss of the coolant,
The vibration prevention effect of the &IJill rod guide tube similar to that of the first embodiment can be obtained.

〔Effect of the invention〕

As explained above, according to the shroud support structure for a nuclear reactor of the present invention, among the reactor water flow paths formed by the shroud support legs and the shroud support ring, the upper part of the reactor water flow path facing the control rod guide tube is Make the elevation of the lower end of the shroud support ring lower than the elevation of the lower end of the control rod guide tube. Therefore, the turbulent flow of coolant that occurs outside the reactor water flow path is restricted, and the distance between the upper end of the flow path and the lower end of the control rod guide tube becomes longer. There is very little risk of it colliding with the pipe and causing it to vibrate.

[Brief explanation of drawings]

1 and 3 are partial cross-sectional views of a nuclear reactor pressure vessel according to an embodiment of the present invention, FIG. 2 is a view taken along the line ■-■ in FIG. 1, and FIG. 4 is a view taken along the line IV in FIG. 3. 5 and 6 are respectively a partial longitudinal sectional view and a partial cross sectional view of a conventional reactor pressure vessel, and FIG. 7 is a view taken along the FIG. 8 is a view taken along the line ■-■ in FIG. 6. 10... Shroud support leg, 11... Shoe: Loud support ring, 12a, 12b, 12c...
・Reactor water flow path. Applicant's agent Hisashi Hatano Figure 1 Figure 2 Figure 3 Figure 4 Figure 6 f

Claims (1)

[Claims] A plurality of shroud support legs are installed vertically at the bottom of the reactor pressure vessel at intervals in the circumferential direction, and a shroud support ring is installed over these shroud support legs to form a flow path for reactor water. A shroud support structure for a nuclear reactor comprising: a lower end elevation of a shroud support ring facing a control rod guide tube that is lower than a lower end elevation of the control rod guide tube.