JPH01307694A - Overhead core spray - Google Patents

Abstract

PURPOSE:To suppress damages at the time of welding by providing plural pieces of supporting plates which are distributed in the circumferential direction of a support ring and have large rigidity in the axial direction of a core to the inner peripheral face of the supporting ring and fixing and supporting said ring to the front ends of these supporting plates. CONSTITUTION:The overhead core spray 6 is mounted to the support ring 7 via plural pieces of the support plates 8 disposed radially to the inside peripheral face of the ring 7. The respective support plates 8 are increased in height, i.e., in the size in the axial direction of the reactor pressure vessel, namely, the core thereof to have the large rigidity in said direction. The support plates are, therefore, capable of reacting sufficiently with any of the vertical component and lateral and twist direction components of the vibration force at the time of steam passage. The damages of respective weld zones are thus suppressed as far as possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an overhead core spray installed in a reactor pressure vessel of a boiling water nuclear reactor.

(Prior Art) FIGS. 4 and 5 are a plan view and a vertical sectional view of a conventional overhead core spray. In each of these figures, 1 is a reactor pressure vessel, 2 is a shroud arranged concentrically inside the vessel, 3 is a reactor core arranged inside the shroud 2, 4 is a shroud head that covers the upper surface of the shroud 2, and 5 is a shroud head. The air/water separator provided on the upper surface of the shroud head, 6 indicates an overhead core spray installed suspended on the lower surface of the shroud head 4. In the above configuration, steam generated in the core 3 passes through the shroud head 4 and flows into the steam/water separator 5, where moisture is separated.

If the temperature of the reactor core 3 suddenly rises for some reason, the core components, particularly the fuel cladding tubes, may be melted and damaged due to the rise in temperature, and there is a risk that fission products leaking from the melted portion may mix into the turbine system and the like.

In order to prevent the above-mentioned accident, when the reactor core temperature suddenly rises, the overhead core spray 6 is activated to cool the reactor core urgently and to prevent nuclear fuel cladding from melting.

(Problems to be Solved by the Invention) The conventional overhead core spray described above is provided in the shroud head 4 through which steam generated in the reactor core passes before flowing into the steam separator 5.

Therefore, the steam flowing into the steam separator 5 flows perpendicularly to the piping of the overhead core spray 6, which not only causes turbulence in the flow of steam flowing into the steam water separator 5, but also causes the steam flowing into the overhead core spray 6 may cause vibration.

The above vibration may cause damage such as cracks to the welded portion of the overhead core spray, and may also damage the suspension support structure for the shroud head 4. Depending on the progress of such damage, overhead core spray may fall.

Therefore, it is necessary to periodically inspect overhead core sprays and their suspended support structures, but not only are their locations exposed to high levels of radiation;
Since the inspection target is soil, which is the welded part, the inspection work is quite complicated, and the amount of radiation exposure to the workers increases, which is not preferable. In addition, if the damage to the overhead core spray is severe, it will be updated by replacing it, but the shroud head,
The overhead core spray and steam separator are integrally welded, so even if there is no damage other than the overhead core spray or there is only damage to the extent that it does not interfere with use, the entire It had to be replaced as a whole, which had the disadvantage of unnecessarily increasing the amount of radioactive waste.

The present invention has been made based on the above circumstances, and an object of the present invention is to provide an overhead core spray that makes it difficult to damage welds, facilitates inspection work, and minimizes the amount of radioactive waste generated. The purpose is

[Structure of the Invention] (Means for Solving the Problems) The overhead core spray of the present invention includes a cylindrical shell-shaped support ring sandwiched between a shroud that surrounds the reactor core and a shroud head that closes the upper surface of the shroud. A plurality of support plates having high rigidity in the axial direction of the core are provided on the inner circumferential surface of the support ring and are fixedly supported at the tips of these support plates.

(Function) The overhead core spray of the present invention having the above structure can sufficiently resist the vertical component of the vibration force due to the rigidity of the support plate, and can sufficiently resist the lateral and torsional components due to the mounting structure of the support ring. be able to.

Furthermore, since the overhead core spray of the present invention is a single unit structure independent of the shroud and the shroud head, only the shroud can be replaced in the event of damage.

(Embodiment) FIG. 1, in which the same parts as in FIGS. 4 and 5 are denoted by the same reference numerals, is a cross-sectional view of an embodiment of the present invention, and FIG. 2 is a longitudinal cross-sectional view thereof. In these figures, a cylindrical shell-shaped support ring 7 is engaged with the side wall of the shroud head 4 between the shroud head 4 and the reactor core 3.
A step 4a provided on the upper side wall of the shroud head 4 is in contact with the upper end surface, and a lower end surface of the support ring 7 is in contact with the flange 2a surface at the upper end of the shroud 2. 2 and the upper surface. The overhead core spray 6 is attached to the support ring 7 via a plurality of support plates 8 arranged radially on the inner peripheral surface of the support ring 7.

Each of the support plates 8 is designed to have a large height, that is, a dimension in the reactor pressure vessel, in other words, in the axial direction of the reactor core, and to have large rigidity in that direction.

In the overhead core spray of the present invention having the above configuration, the steam generated in the reactor core 3 is transferred to the overhead core spray 6.
When the steam flows into the steam separator 5 via the steam flow, a force that tries to vibrate the overhead core spray 6 is applied due to the turbulence of the flow of steam, but the vertical component of the force is By setting the height of the support plate 8 (the axial dimension of the reactor pressure vessel) to the necessary size, sufficient resistance can be achieved. This can be adequately countered by a structure in which it is fixed in place.

FIG. 3 is a longitudinal sectional view of another embodiment of the present invention, in which the same parts as those in each case are given the same reference numerals. In this embodiment, the support ring 7 is provided with a flange 7a at its upper end, and this flange is sandwiched and fixed between the flange 2a at the upper end of the shroud 2 and the flange 4b of the shroud head 4. This embodiment also provides the same effects as the embodiments shown in FIGS. 1 and 2. Further, since there is no need to process the step portion 4a for pinching the support ring 7, the number of man-hours for manufacturing the shroud head 4 can be reduced.

[Effects of the Invention] As is clear from the above, the overhead core spray of the present invention is capable of sufficiently resisting all of the vertical, lateral, and torsional components of vibrational force when steam passes. This makes it possible to suppress losses at each welding part as much as possible. In addition, since only the overhead core spray can be removed individually, inspection work during periodic inspections is easy, and it is possible to reduce the radiation exposure of one worker. Furthermore, since the overhead core spray itself is an independent unit structure, it is possible to replace only it when it is damaged, and there is no risk of unnecessarily increasing radioactive waste as in the conventional case.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of one embodiment of the present invention, FIG. 2 is a vertical cross-sectional view thereof, FIG. 3 is a vertical cross-sectional view of another embodiment, FIG. 4 is a cross-sectional view of a conventional example, and FIG. 5 is its cross-sectional view. 1... Reactor pressure vessel 2... Shroud 2a, 4a, 7a... Flange 3...
... Core 4 ... Shroud head 4b
...Stepped section 5...Steam water separator 6...
...Overhead Core Spray 7.

Claims (1)

[Claims] A cylindrical shell-shaped support ring is clamped and fixed between the shroud that surrounds the reactor core and the shroud head that closes the upper surface of the shroud, and the core axial rigidity is distributed on the inner peripheral surface of the support ring in the circumferential direction. An overhead core spray characterized by having a plurality of large support plates fixedly supported at the tips of these support plates.