JPS6233558B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a neutron absorption rod provided as a component of a nuclear reactor control rod, in which B ₄ C powder filled as a neutron absorption material is distributed at a uniform density over the entire length, This invention relates to a neutron absorption rod that enables more accurate control of nuclear reactors.

Generally, in fast breeder reactors (FBRs), sintered _B4C pellets are used as the neutron absorbing material for reactor control rods, while in boiling water reactors (BWRs), pressurized water reactors, In light water reactors such as (PWR), powdered B ₄ C is used as an absorbent. This difference is mainly based on economic reasons, as it is cheaper to use powdered _B4C as absorbent.

By the way, in conventional neutron absorption rods that use powdered B ₄ C as an absorbing material, B ₄ C is directly filled in the powder state, but it is not easy to pack powder into a small diameter tubular neutron absorption rod, and the entire length Since the focal density was not uniform over the period, it had the disadvantage of making accurate control of the reactor difficult. Furthermore, if used for a long time, the B ₄ C powder may shift downward, creating a gap at the top, which may interfere with reactor control. In order to prevent this downward bias, the first step is to
As shown in the figure, several metal balls a, a are inserted together with the B ₄ C powder, and these are arranged at equal intervals by recesses c, c formed from the outside of the absorption rod b. Although attempts have been made to prevent the powder from moving downward, this is not sufficient and also creates new drawbacks that complicate the manufacturing method.

The present invention solves the above-mentioned drawbacks, and the entire length is filled with powder of neutron absorbing material such as B ₄ C at a uniform density, so that there is no upper gap during use, and processing such as recesses is required. The purpose of the present invention is to provide an improved neutron absorbing rod that has a simple structure.

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 is a diagram showing the basic configuration of the present invention, in which a plurality of capsules 2 filled with B ₄ C powder as a neutron absorbing material are coaxially stacked inside a cylindrical bar 3. The rod is inserted, and after replacing the air inside the rod with helium gas 4, it is sealed.

By the way, as shown in FIG. 3, the capsule 2 is composed of a relatively short container 5 and an air permeable end plug member 6 having a communication hole large enough to prevent powder from passing through. After filling the neutron absorbing material with B ₄ C powder, the end plug member 6 is attached and fixed to seal the absorbing material powder. As the end plug member 6, as shown in FIG. 4, a cotton material 8 made of a thin needle-like cotton material may be used, and the cotton material 8 is attached and fixed to the upper opening of the container 5. It is also possible to prevent the absorbent powder inside from flowing out. Thus, the air permeability of the end plug member allows the air within the capsule to be replaced by helium.

When the end plug member 6 is stacked in the cylindrical rod 3, the breathable portion of the end plug member 6 is floated and stacked so as not to be blocked by the lower bottom surface of the upper capsule 2. For example, it is effective to use a spacer or extend a leg portion to the lower end of the capsule.

As described above, the neutron absorbing rod of the present invention has a plurality of air-permeable capsules filled with powder of a neutron absorbing material such as B ₄ C, and the plurality of capsules are coaxially arranged inside a cylindrical rod. Since they are stacked, the packing density of the absorbing powder inside the neutron absorbing rod can be made almost uniform in the axial direction. Moreover, since the neutron absorbing material is completely separated into multiple pieces in the longitudinal direction by multiple capsules, the absorbing material powder is only allowed to move within the filled capsules, and its density is determined by the transport of the neutron absorbing rod. There is little fluctuation in the vertical position even when the absorber is used for a long time or in a nuclear reactor, and there is no worry that the entire absorbent powder will sink downward and create a gap at the top, unlike conventional absorbent absorbent powder. Moreover, in the present invention, a breathable end plug member having a communication path that prevents the powder from passing through is attached and fixed to the container, so even if the absorbent rod is placed horizontally during transportation, the absorbent powder will still be absorbed. It is reliably prevented from flowing out of the capsule, and movement of the powder within the neutron absorption rod can be prevented. Therefore, there is no need to provide a circumferential recess in the absorbing rod as in the conventional method, and the manufacturing method is simplified, resulting in good productivity and cost advantages. Furthermore, the uniform density of the moderator powder can be maintained for a long time, and the nuclear reactor can be controlled accurately.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view of a conventional neutron absorption rod;
The figure is a partially longitudinal front view showing one embodiment of the neutron absorbing rod of the present invention, and FIGS. 3 and 4 are views showing respective embodiments of capsules used in the neutron absorbing rod of the present invention. 1... B ₄ C powder (absorbent powder), 2... Capsule, 3... Neutron absorption rod, 4... Helium, 5...
... Container, 6 ... End plug member, 8 ... Cotton body.

Claims (1)

[Claims] 1 A relatively short container is filled with powder of a neutron absorbing material such as B ₄ C, and a capsule is fitted and fixed with an air-permeable end plug member that has a communication path large enough to prevent the powder from passing through, and the capsule is placed inside a cylindrical rod body. A neutron absorption rod characterized by multiple coaxially stacked, inserted and sealed neutron absorption rods.