JPS62147396A - Neutron absorbing 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] [Industrial Application Field] The present invention relates to a neutron absorption rod, and particularly to a neutron absorption rod that prevents leakage of tritium from the neutron absorption material itself sealed within the neutron absorption rod. For example, it can be used as a nuclear fuel element or neutron absorption rod placed in the core of a pressurized water reactor.

[Prior Art] For example, in a pressurized water reactor (PWR), a neutron absorbing material made of a burnable poison such as boron (B) is used to control power peaking and moderator temperature coefficient at the beginning of the operation cycle. A neutron absorption rod, which is enclosed in a rod similar to a fuel rod, is used by incorporating it into a fuel assembly.

Generally, such a neutron absorbing rod has boron-containing alumina pellets (A1.0.-B, C) as a neutron absorbing material in a cladding tube 1 of a Zircaloy ring, as shown in FIG.
2 are stacked and loaded, and sealed.

By the way, when the boron-containing alumina pellet 2 in this neutron absorption rod is irradiated with neutrons, its - part undergoes nuclear transmutation, producing the radioactive isotope tritium (3HX half-life 12.26 years).

If this tritium leaks outside, problems such as environmental pollution will occur.

For this reason, conventionally, leakage of tritium to the outside has been prevented in the following manner.

That is, FIG. 7 is an enlarged view of part A in FIG. 6, and as shown in FIG.
Measures have been taken, such as enclosing a tritium trapping material 5 such as uranium (U) into the neutron absorbing rod 1 (for example, see Japanese Patent Laid-Open No. 59-99392) to trap tritium generated within the neutron absorbing rod 1.

[Problems to be Solved by the Invention]However, in all of these conventional measures, once the tritium generated in the neutron absorbing material comes out from the neutron absorbing material into the neutron absorbing rod l, it cannot be absorbed by neutrons. Tritium is captured using a tritium trapping material that is a separate member from the tritium trapping material.

For this reason, it is difficult to irretrievably capture all the tritium that has entered between the neutron absorption material and the inner wall of the neutron absorption rod L, or between each other's neutron absorption materials. It was difficult to completely eliminate the possibility that tritium would dissolve into the coolant in the event of damage to the coolant.

An object of the present invention is to provide a neutron absorption rod that eliminates the above-mentioned drawbacks.

[Means for Solving the Problems] The present invention includes a tritium trapping material coexisting in the neutron absorbing material itself sealed in a hollow tube.
This prevents tritium from leaking outside the neutron absorbing material.

[Example] FIG. 1 is a partially omitted cutaway view of a neutron absorption rod according to a first example of the present invention.

In FIG. 1, a plurality of boron-containing alumina pellets (A1203-84C) 12 containing a tritium trapping material as a neutron absorbing material are stacked and loaded in a cladding tube 11 made of Zircaloy, and one end thereof, that is, A plenum coil spring Ila is disposed on the upper end side in the figure to press and bias the pellet in the axial direction, and both ends of the cladding tube II are sealed by welding upper and lower end plugs 11b and llc, respectively. ing.

In this case, the tritium trapping material is U.

Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, C
o, Ni, Rh.

Single metals such as Pb and PL or alloys of two or more of these metals may be used alone or in combination.

Moreover, FIG. 2 is a partially omitted cutaway view of a neutron absorption rod according to a second embodiment of the present invention.

In FIG. 2, a borosilicate glass rod 23 containing a tritium trapping material as a neutron absorbing material is loaded into a cladding tube 21 made of Zircaloy, and both ends of the cladding tube 21 are provided with upper and lower end plugs 21b and 21c, respectively. It is sealed by welding.

Examples of the manner in which these tritium trapping materials are combined with the pellets I2 or the borosilicate glass rods 23 include the following.

That is, FIG. 3 is a diagram showing an example in which the tritium trapping material is uniformly dispersed in the neutron absorbing material, and FIG.
Fig. 3 is a partially cutaway perspective view of 5 uniformly dispersed.
B) is a partially cutaway perspective view of a borosilicate glass rod 33 in which powdered or granular tritium absorbing material 36 is uniformly dispersed.

Moreover, FIG. 4 is a diagram showing an example in which a layer of tritium trapping material is included in the neutron absorbing material, and FIG. FIG. 4B is a partially cutaway perspective view of the layer 45 formed thereon, and a thin layer 46 of tritium scavenging material is deposited on the surface of the borosilicate glass rod 43 by vapor deposition or other means.
FIG.

Furthermore, FIG. 5 is a diagram showing an example in which a tritium trapping material formed into a fiber shape is included in a neutron absorbing material, and FIG.
A) is a partially cutaway perspective view of an alumina pellet 52 in which a large number of tritium trapping materials 55 formed into fibers are embedded along the axial direction, and FIG. It is a partially cutaway perspective view of a structure in which a large number of tritium trapping materials 56 formed in a fibrous shape are embedded.

Although not shown, in other embodiments, for example, a layer of tritium scavenging material may be formed in alumina pellets or borosilicate rods concentrically, radially, along the axial direction, along a direction perpendicular to the axial direction, or Tritium trapping materials formed in large numbers along arbitrary directions, tritium trapping materials formed into fibers embedded in various directions or randomly, or tritium trapping materials provided with complex shapes of irregularities to increase the surface area. Various embodiments include incorporating a large number of blocks, or a combination of any two or all of these embodiments.

The above embodiment has the following advantages.

That is, since tritium generated by a nuclear transmutation reaction in the neutron absorbing material is immediately captured by the tritium trapping material coexisting in the neutron absorbing material, it is possible to prevent tritium from escaping from the neutron absorbing material. Therefore, the possibility of contamination with tritium is prevented.

In this case, if powdered or granular tritium trapping material 35 or 36 is uniformly dispersed in the alumina pellets 32 or borosilicate glass rod 33, respectively, as shown in FIG. 3, tritium will be generated. Since the tritium is captured by the tritium capture material 35 or 36 that is present in the immediate vicinity at the same time as it is generated, these pellets 3? Alternatively, if the rod 33 is not filled with tritium and the neutron absorption rod 11 or 21 is damaged, of course the pellet 1
There is no risk of tritium leaking outside even if 2 itself is damaged.

Further, as shown in FIG. 4, when a thin layer 45 or 46 of tritium trapping material is formed on the surface of the alumina pellet 42 or the borosilicate glass rod 43, respectively, the inside of the rod 43 is When the tritium produced in this process is about to escape to the outside, it is captured by the thin layer 45 or 46, and leakage of tritium to the outside can be completely prevented.

Further, as shown in FIG. 5, when a tritium trapping material 55 or 56 formed in a fibrous form is embedded in the pellet 52 or rod 53, the same situation as in case 1 shown in FIG. 3 occurs. In addition to having advantages, the fibrous tritium scavenging material 55 and the pellets 5
2 or serves to increase the strength of the rod 53,
In particular, when a borosilicate glass rod, which is easily damaged, is used as the neutron absorbing material, the risk of the rod being damaged during transportation or handling is reduced.

In addition, if the above-mentioned aspects are combined (t)1, the possibility of tritium leakage can be more completely prevented.

[Effects of the Invention] As detailed above, the present invention allows a tritium trapping material to coexist in the neutron absorbing material itself sealed in a hollow tube, thereby trapping tritium within the neutron absorbing material itself. This eliminates the risk of tritium contamination by capturing the tritium and preventing it from leaking outside.

[Brief explanation of drawings]

FIG. 1 is a partially omitted cutaway view of a neutron absorption rod according to a first embodiment of the present invention, FIG. 2 is a partially omitted cutaway view of a neutron absorption rod according to a second embodiment of the present invention, and FIG. Figure 4 shows an example in which a tritium trapping material is uniformly dispersed in a neutron absorbing material, Figure 4 shows an example in which a layer of tritium trapping material is formed on the surface of a neutron absorbing material, and Figure 5 shows a fibrous material. Figure 6 is a partially omitted vertical cross-sectional view of a conventional neutron absorbing rod, and Figure 7 is a neutron absorbing material containing a tritium trapping material formed in
It is an enlarged view of part A in the figure. +1, 21... Zircaloy cladding tube, 12, 32, 42
．． 52...Polymerized alumina pellets constituting the neutron absorbing material, 23,33,43.53...borosilicate glass rod constituting the neutron absorbing material, 35°36...
・Powdered or granular tritium trapping material, 45°46...
Layer of tritium trapping material, 55.56... Tritium trapping material formed in the form of fibers.

Claims (4)

[Claims] (1) In a neutron absorption rod formed by enclosing a neutron absorption material in a hollow tube, tritium (^3H) is added to the neutron absorption material.
) A neutron absorption rod characterized by the coexistence of a substance that captures neutrons. (2) The neutron absorbing rod according to claim 1, wherein the neutron absorbing material is a material in which a substance that captures tritium is uniformly dispersed. (3) The neutron absorption rod according to claim 1, wherein the neutron absorption material includes a layer formed of a substance that captures tritium. (4) The neutron absorbing rod according to claim 1, wherein the neutron absorbing material includes a tritium trapping substance formed in the form of fibers.