JPS5921520B2 - Reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear reactor, and particularly to a nuclear reactor suitable for shortening the time required for core re-flooding in the event of a loss of reactor coolant accident.

In a boiling water reactor, the upper grid plate 1 is located at the upper end of the reactor core as shown in FIG. 1, and its main role is to horizontally position the fuel channels 2.

An upper plenum 3 is formed above the upper lattice plate 1, and a peripheral bypass region 4 and a central bypass region 5 are formed directly below it.

The conventional upper lattice plate has a structure in which the peripheral portion where the fuel channel does not enter is vertically connected, as shown in FIG. 2, or is completely closed, as shown in FIG. 3.

In the case of the upper grid plate shown in Fig. 2, in the event of a loss of reactor coolant accident (hereinafter referred to as LOCA), the upper grid plate portion corresponding to the peripheral bypass area 4 shown in Fig. There is a possibility that water from the emergency core cooling system (hereinafter referred to as ECC8) injected into the upper plenum 3 will be difficult to flow into the peripheral bypass region due to the so-called CCFL phenomenon, which prevents water from flowing down from the upper plenum 3.

This also applies to the central bypass region 5.

Also, in the case of the upper grate shown in FIG. 3, no water enters the peripheral bypass region 4 through the upper plenum 30ECC8 through the periphery of the upper grate.

Therefore, the ECC8 water injected into the upper plenum 3 is
The fuel flows into both bypass regions 4 and 5 through the gap between the upper grid plate portion corresponding to the central bypass region 5 and the fuel channel 2 .

However, even in this gap, ECC cannot be achieved due to the CCFL phenomenon.
8 Water may become difficult to flow in.

In this way, in the upper grid plate of the conventional structure, the LOCA
There are disadvantages such as the long re-flooding time of the reactor core and the inability to ensure the integrity of the reactor core.

The present invention has been made to solve these conventional difficulties, and its purpose is to shorten the time for re-flooding of the reactor core during LOCA, and to create a nuclear reactor that can ensure the integrity of the reactor core. It is on offer.

The present invention provides a steam vent pipe on the periphery of the upper grid plate position, the lower end of which opens into the bypass region, and the upper end of which opens into the space above the water of the emergency core cooling system injected into the upper plenum. This allows the steam to be effectively discharged to the upper plenum side.

The present invention will be explained below based on an embodiment shown in FIGS. 4 and 5.

In FIG. 4, 2 is a fuel channel loaded inside a shroud 7 in a reactor pressure vessel 6, and the upper end of this fuel channel 2 is supported by an upper grid plate 1.

Then, an upper plenum 3 is placed above it through the upper lattice plate 1.
A peripheral bypass region 4 and a central bypass region 5 are formed below the peripheral bypass region 4 and the central bypass region 5, respectively.

A large number of spray nozzles 8 for core spray, which is a type of ECC 8, are arranged on the periphery of the upper plenum 30,
Water 9 of ECC 8 is injected into the upper plenum 3 during LOCA.

The configuration described above is the same as the conventional one, and in this embodiment, the following configuration is further added.

That is, on the peripheral edge of the upper grid plate 10, as shown in FIGS. 4 and 5, there is a water surface 10 of water 9 of the ECC 8 whose lower end opens into the peripheral bypass area 4 and whose upper end is injected into the upper plenum 3. Steam vent pipe 11 that opens upwards
A plurality of lattice plates are provided in the circumferential direction of the upper lattice plate 10.

This steam vent pipe 11 is located between adjacent spray nozzles 8 so as not to obstruct the spray flow.

In addition, when the steam vent pipe 11 is attached to the upper grate plate of the form shown in FIG. 2, it is attached by welding or the like to the grate on the periphery where the fuel channel is not inserted, and it is also attached to the upper grate plate of the form shown in Fig. 3. In this case, a hole is drilled in the peripheral edge indicated by diagonal lines in the figure, and the device is attached to the hole.

Incidentally, the steam vent pipe 11 may be made to protrude to the peripheral bypass area 4 by an appropriate length, but may be made to protrude by a flexible length from the side of the upper plenum 3 so that the water surface 1 of the water injected into the upper plenum 3 is
It is best to avoid falling below 0.

The diameter and number of steam vent pipes 110 will vary depending on the size of the reactor, but about twenty or so pipes with an inner diameter of about 4 cIrL may be provided.

Next, the effect will be explained.

When water 9 of ECC 8 is injected into the upper plenum 3 from the spray nozzle 8 at the time of LOCA, the water 9 stored in the upper plenum 3 is removed as shown in FIG. It flows out through the pipe 11 into the upper space of the upper plenum 3, so that the bypass area 4,
The amount of steam 5 decreases and flows down into the bypass regions 4 and 5 from the gap in the upper grid plate 1 as shown by the arrow 13 without being affected much by the CCFL effect.

As explained above, this embodiment provides the following effects.

(1) The core re-flooding time during LOCA can be shortened, and the integrity of the core can be ensured.

(2) Since the steam vent pipe is located at approximately the same position as the nozzle of the core spray sparger, it does not become a hindrance when replacing a fuel bundle, for example, and does not impair the functionality of a conventional nuclear reactor.

(3) Since the core spray water and the steam vent pipe are located at a position where they do not interfere, the core spray distribution will not be disturbed.

FIG. 6 shows another embodiment of the present invention, in which a steam vent pipe 11 is provided along the inner circumferential surface of the 7-layer tube 7.

That is, on the inner peripheral surface of the shroud at the position of the upper grid plate 1,
As shown in FIG. 6, a steam vent pipe 11 is provided whose lower end opens into the peripheral bypass region 4 and whose upper end opens into the upper space of the upper plenum 3.

The steam in the bypass regions 4 and 5 is then discharged to the upper plenum 3 via this steam vent pipe 11.

With this configuration, there is no need to process the upper lattice plate, so it is particularly effective when the upper lattice plate of the form shown in FIG. 3 is used.

The present invention has been described above based on preferred embodiments. According to the present invention, it is possible to shorten the core re-flooding time during LOCA and ensure the integrity of the core.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing a conventional example, FIGS. 2 and 3 are plan views showing different types of upper lattice plates, and FIG.
The figure is a schematic sectional view showing one embodiment of the present invention, and FIG. 5 is a LO
FIG. 6 is an explanatory view showing the state during CA, and is a schematic cross-sectional view showing another embodiment of the present invention. 1... Upper grid plate, 2... Fuel channel, 3...
Upper plenum, 4... Peripheral bypass area, 5... Center area, 7... Shroud, 8... Spray nozzle, 9... Water, 10... Water surface, 11...
・Steam vent pipe.

Claims (1)

[Claims] 1. In a nuclear reactor equipped with a fuel assembly disposed in a shroud and an upper grid plate located at the upper end of the fuel assembly, the lower end opens into the bypass area and the upper end is located at the periphery of the upper grid plate position. A nuclear reactor characterized by being provided with a steam vent pipe that opens into the space above the water of the emergency core cooling system that is injected into the upper plenum.