JPS5827092A - Reactor control rod - 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 In a fuel assembly of a boiling water nuclear reactor (hereinafter referred to as BWR), voids occur due to evaporation of coolant during operation. The void ratio of these voids is small in the lower and central parts of the core, and larger in the upper part.

The fuel burnup is large at low void ratios and small at high void ratios. However, since the leakage of neutrons is large at the upper and lower ends of the core, the axial distribution of burnup is smaller in the lower part of the core than in the center of the core, and smaller in the upper part of the core than in the lower part. Therefore, Pu produced as a result of combustion of 0.235 is smaller in the lower part of the core than in the middle, and smaller in the upper part of the core than in the lower part. Therefore,
As shown in FIG. 1A, the reactor shutdown margin (subcriticality) is at its minimum at a position X approximately in the center of an area approximately one length of the total length of the core from the upper end of the core.

However, since conventional control rods have almost uniform reactivity over their entire effective length, even if the control rods are fully inserted during reactor shutdown, criticality will be exceeded in the 1F part of the core where the subcritical IW is low. There is a risk that the reactor may not be able to be shut down reliably and safely.

The present invention was made based on the above circumstances, and an object of the present invention is to obtain a control rod for a nuclear reactor that can safely and reliably stop a BWFL.

In the present invention, the above object is achieved by setting high reactivity in the core region K where the burnup is low and the subcriticality is small, and in the portion of the control rods that face each other when fully inserted.

The invention will now be described in detail with reference to the drawings. In FIG. 2, a cruciform control rod 1 has a number of neutron absorption rods 4 loaded in each wing, which is constructed by attaching an elongated U-shaped sheath 3 to each leg of a central structural member 2 having a cruciform cross section. It is well known that

In the present invention, a region 6 having a length t and h from the tip of the control rod has a higher reactivity than other regions.

That is, the portion of the neutron absorbing rod 4 loaded in each wing of the control rod located within the area 6 contains Eu2.
Concentrated O3 pellet or B-10 “6I34”
When the zone 6 is filled with C pellets and the control rod of the present invention having the above configuration is fully inserted into the core, the subcriticality of the core is as shown in Figure 1B.
It becomes as shown in .

This is because the zone 6 with high reactivity in FIG. 2 faces the upper part of the core where the degree of subcriticality is low in FIG. 1A.

This becomes a neutron-absorbing gas in that area, improving the subcriticality of the upper part of the core, that is, the reactor shutdown margin, and making it possible to completely reliably shut down the reactor.

Note that the present invention is not limited to the above embodiments.

For example, E
u203. ``'B4 C pellets are filled in a small-walled Hf tube and placed in the absorption rod cladding tube (2 is also possible. When doing this, the nuclear life of the control rod in the 6th section is extended. Not only can Eu2(J
3. Swelling caused by changes in the properties of concentrated ['''B4 C pellets due to neutron absorption can be sufficiently absorbed by the minute gaps between the ILF tube and the inner peripheral surface of the cladding tube, and the mechanical life can also be improved. In the invention, since Eu2 (J3, ILF, etc.), which are expensive and have a large specific gravity, are only partially used, the cost, weight, etc. of the control rod will not increase significantly.

[Brief explanation of the drawing]

Figure 1A is an axial subcriticality distribution diagram at the time of shutdown of the BWR core, Figure 1B is the ijW R using the control rod of the present invention,
A similar figure, FIG. 2, is a schematic diagram of an embodiment of the present invention. l... Control rod, 2 River central structural member, 3... Sheath, 4... Neutron absorption rod, 6... Area. Application agent Patent attorney Go Kikuchi On sale l Figure A β

Claims (1)

[Claims] (1) A device in which a large number of neutron absorption rods are loaded in a plurality of wings formed by attaching an elongated U-shaped sheath to a central structural member, and the effective length is about -
A control rod for a nuclear reactor whose special purpose is to make the area at the tip of the rod more reactive than the other parts. (2) A portion of each neutron absorption rod facing the area is enriched (3
) Said Eu2o3Hereit tri (i thick) B4
3. The control rod for a nuclear reactor according to claim 2, wherein the control rod for a nuclear reactor is arranged in a neutron absorption rod after inserting the c-Heresotho into a small-walled H5 tube.