JPS62192690A - Fuel aggregate for boiling water type reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a fuel assembly for a boiling water nuclear reactor, and more particularly, to a fuel assembly for a boiling water nuclear reactor that improves the safety of a reactor core in the event of a loss of coolant accident. Regarding fuel assemblies for reactors.

[Technical background of the invention and its problems] Figure 3 shows the structure of a conventional boiling water reactor.

In the figure, a reactor core 2 is housed in a reactor pressure vessel 1, and in the upper part of the reactor pressure vessel 1 there is a main steam that guides the steam generated in the reactor pressure vessel 1 to a steam turbine (not shown). Pipe 3 is installed. Further, a jet pump 5 composing a coolant recirculation system 4 is disposed on the side of the core 2, and the cooling water located at the downcomer bottom 6 is passed through a recirculation pipe 8 by a recirculation pump 7 to the jet pump 5. supplied to the population. Furthermore, a core spray system 9 and a low pressure injection system 10, which are emergency core cooling systems, are installed in the reactor pressure vessel, and pumps 11 and 12 that supply cooling water are installed in these emergency core cooling systems, respectively. It is arranged.

Also, inside the reactor core 2 is a fuel assembly 21 as shown in FIG.
are accommodated in large numbers. This fuel assembly 21 has a large number of fuel rods 23 regularly arranged in a lattice shape in a fuel channel 22, and spacers 26 are arranged at approximately equal intervals in the axial direction to maintain the correct mutual spacing between the fuel rods 23. It is arranged so that it will be installed in

Furthermore, in FIG. 4, the coolant flowing into the fuel assembly 21 from the lower tie plate 25 of the fuel assembly 21 contacts the fuel rods 23 and rises as a gas-liquid two phase due to heat generation within the fuel rods 23. and flows upward from the upper tie plate 24.

By the way, in this boiling water reactor, if the coolant recirculation system 4 connected to the reactor pressure vessel 1 were to break, a situation would occur in which the coolant inside the reactor would be lost, and the so-called coolant It will be a loss accident. When such a loss of coolant accident occurs, the coolant inside the reactor pressure vessel 1 is lost, the coolant flowing inside the reactor core 2 is reduced, the fuel rods 23 are exposed, and the fuel inside the fuel rods 23 and The temperature of the cladding tube covering it will rise.

In reality, in order to prevent such an abnormal temperature rise of the fuel and cladding, emergency core cooling systems such as a core spray 9 and a low-pressure injection system 10 are provided, and in the event of an emergency, these cooling systems are used to remove atoms. Coolant is injected into the reactor to cool the reactor core, and the temperature of the fuel and cladding tubes is set to be below a predetermined temperature. However, even if these emergency core cooling systems operate, there is a possibility that the fuel rods will be exposed as the reactor water level falls, causing a rise in the temperature of the fuel and cladding. In this case, heat removal during the period when the fuel rods are exposed mainly depends on the upward flow of steam generated in the core and lower plenum, but it is also In the central part of the body, heat removal by the above-mentioned upward steam flow may be insufficient.

[Object of the invention] The present invention has been made in view of the above circumstances and necessarily has the following features:
The object of the present invention is to provide a fuel assembly for a boiling water reactor that can enhance the safety of the reactor core against loss of coolant accidents.

[Summary of the Invention] In other words, the present invention provides a boiler comprising a fuel channel, a large number of fuel rods regularly arranged in a lattice pattern within the fuel channel, and a plurality of spacers that maintain the spacing between the large number of fuel rods. In the fuel assembly for a water-type nuclear reactor, the spacing between the plurality of spacers is denser in the center and upper regions of the fuel rods than in the lower region of the fuel rods. Regarding fuel assemblies for boiling water reactors, by installing spacers in this way, the cooling effect of the steam upward flow on the fuel rods in the event of a loss of coolant accident in the reactor is enhanced, and the safety of the reactor is improved. It is designed to improve the

[Embodiments of the invention] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a fuel assembly showing one embodiment of the present invention. In the figure, a fuel assembly 30 has a large number of fuel rods 32 regularly arranged in a lattice shape in a fuel channel 31, similar to the conventional fuel assembly shown in FIG. It is held correctly by a spacer 35. Further, an upper tie plate 33 is installed at the upper part of the fuel assembly, and a lower tie plate 34 is installed at the lower part. However, the spaces between the spacers 35 are not equal as in the conventional case, but are denser in the upper part than in the central part in the axial direction, as shown in the drawing.

As a result of installing spacers at close intervals on the top,
In the unlikely event that a loss of coolant accident occurs in a nuclear reactor, the upward flow of steam generated in the core and lower brenum will become more turbulent in the dense area of this spacer, and this turbulent flow of steam will cause the fuel rods to Cools more effectively than before. Therefore, the cooling effect is enhanced in the central and upper portions of the fuel rods, which are most likely to be overheated due to loss of coolant, and the safety of the reactor is improved.

FIG. 2 is a graph showing the change over time in the maximum temperature of the cladding tube after the occurrence of an accident, where the solid line a shows the case of the present invention and the broken line shows the case of the conventional example. As you can see from this graph,
In the case of the present invention, the cladding tube temperature did not rise as in the conventional case, and the maximum cladding tube temperature began to decrease in a fairly short period of time after the accident.

r Effects of the Invention As explained above, the fuel assembly for boiling water reactors of the present invention can more effectively remove overheated fuel rods than before when a loss of coolant accident occurs in a nuclear reactor. This has the excellent effect of providing cooling access to the reactor, thereby improving the safety of the reactor core.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view of the twist assembly for boiling water reactors of the present invention, and Figure 2 is a comparison of changes in the maximum temperature of the cladding between the fuel assembly of the present invention and a conventional fuel assembly. graph,
FIG. 3 is a longitudinal sectional view of a boiling water reactor, and FIG. 4 is a longitudinal sectional view of a conventional fuel assembly for a boiling water reactor. 30...Fuel assembly, 31...Fuel channel 32...Fuel rod, 33...Upper tie plate 34...Lower tie plate 35...Spacer (8733) Agent Patent Attorney Akira Inomata and 1 other person
Figure 1 Figure 2

Claims (1)

[Claims] (1) Fuel assembly for a boiling water reactor consisting of a fuel channel, a large number of fuel rods regularly arranged in a lattice pattern within the fuel channel, and a plurality of spacers that maintain the spacing between the large number of fuel rods. A fuel for a boiling water nuclear reactor, wherein the plurality of spacers are spaced closer to each other in the central and upper regions of the fuel rods than in the lower region of the fuel rods. Aggregation.