JPH0634073B2 - Simulated fuel assembly - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an electric heating type simulated fuel assembly used for an out-of-reactor thermal hydraulic test of a fuel assembly for a nuclear reactor, and in particular, to an improved simulated water rod. The simulated fuel assembly.

[Technical background of the invention and its problems]

In general, a fuel assembly for a nuclear reactor has been subjected to many tests for nuclear, thermal and mechanical reliability in order to confirm safety and performance. Among these tests is the method of inspecting and analyzing the spent nuclear fuel of the actual nuclear reactor.
However, a thermal hydraulic test of a fuel assembly, for example, a pressure loss of each part of the fuel assembly that occurs when the coolant flows in the fuel assembly, or a water flow when the coolant heated by the heat generation of the nuclear fuel flows while boiling- It is technically difficult to measure the volume ratio of steam and the maximum heat output of nuclear fuel in an actual nuclear reactor, and there is a risk of damage to nuclear fuel.

Therefore, such a thermal-hydraulic test usually simulates an actual fuel assembly only in size and shape, and uses a simulated fuel assembly that simulates a heating rod that generates heat due to Joule heat generated when electricity is applied. ing.

FIG. 6 shows an example of an actual fuel assembly A that is actually loaded in the core of a boiling water reactor. This is a plurality of fuel rods 2 and water rods 3 in a rectangular channel box 1. And are bundled by the spacer 4 and housed. The upper ends of the fuel rods 2 and the water rods 3 are supported by the upper tie plate 5, and the lower ends thereof are supported by the lower tie plate 6.

The simulated fuel assembly B simulating the actual fuel assembly A configured as described above is configured, for example, as shown in FIGS. 7A and 7B, and includes a plurality of simulated fuels arranged in a lattice. One or a plurality of, for example, two simulated water rods 3B are arranged in the central portion of the rod 2B, these 2B and 3B are bound into a bundle by the spacer 4 used in the actual machine A, and the upper end portion thereof is placed at the upper part. Upper electrode 5B simulating tie plate 5
Further, the lower ends thereof are supported by lower electrodes 6B simulating the lower tie plate 6, respectively. A DC power supply 7 is connected to the upper and lower electrodes 5B and 6B, and a DC power supply voltage is applied to each simulated fuel rod 2B. The simulated fuel rod 2B and the like configured as described above are housed in a rectangular flow path (not shown) simulating the channel box 1.

The simulated fuel rod 2B is configured as shown in FIG. 8, and the axial intermediate portion of the shaft portion is formed in the heat generating portion 2B ₁ made of a stainless steel pipe having a large electric resistance. Non-heat generating portion 2 consisting of a small resistance steel tube at the top and bottom of the heating portion 2B ₁
B ₂ are integrally or integrally connected to each other, and by applying a DC voltage through both electrodes 5B and 6B,
The heat generating part 2B ₁ is caused to generate heat.

On the other hand, the conventional simulated water rod 3B is configured as shown in FIG. 9 and has the upper electrode 5 via the attachment portion 3B ₂ and the insulator 3B ₃ coupled to the upper end of the non-heat generating hollow tube 3B _1.
It is electrically insulated and fixed to B. Hollow tube 3B ₁
Is the lower end of the introduction hole 3B ₄ for introducing the coolant such as water into the pipe as shown by the arrow in the figure, and the upper end is the horizontal hole 3B ₅ for guiding the coolant flowing in the pipe to the outside of the pipe. It is drilled in each part.

However, in the conventional simulated water rod 3B configured in this way, the outer peripheral surface of the hollow tube 3B ₁ is formed into one electrically conductive path that electrically conducts over substantially the entire length, so that the simulated fuel assembly is formed. An equivalent circuit shown in FIG. 10 is formed between the simulated water rod 3B assembled to the body B and the simulated fuel rod 2B through a coolant such as water flowing through these gaps.

That is, the simulated water rod 3B is electrically connected to the simulated fuel rod 2B electrically connected to the DC power source 7 via the reactor water (W). Moreover, the simulated water rod 3B
As shown in FIG. 11 (A), the outer peripheral surface of is formed as a single conductive path over the entire length from the upper end to the lower end. Therefore, the leakage current i from the simulated fuel rod 2B passes through the coolant W. Flow into the upper portion of the simulated water rod 3B, flow from the upper portion through the conductive paths on the outer peripheral surface to the lower portion in the axial direction,
It is recirculated from the lower part to the lower part of the simulated fuel rod 2B via the coolant W again. Therefore, the simulated water rod 3B
A relatively large potential difference as shown by the parallel horizontal lines in FIG. 11 (B) occurs between and the simulated fuel rod 2B, and electrolysis occurs. That is, according to Faraday's law, electrolysis occurs in which the metal dissolves from the high-potential portion toward the low-potential portion, so that the simulated fuel rod 2B, the simulated water rod 3B, etc. are corroded to reduce the wall thickness.

Further, in the stainless steel portion such as the simulated water rod 3B, the stainless component is combined with other elements such as magnesium (Mg) and aluminum (Al) in the coolant W by the electrolytic action and adheres to the outer peripheral surface. There was a problem.

[Object of the Invention]

The present invention has been made in view of the steam situation, and an object thereof is to provide a simulated fuel assembly with less corrosion.

[Outline of Invention]

In order to achieve the above object, the present invention provides a simulated fuel assembly in which a simulated fuel rod that uses a heating rod that generates heat by energization as a fuel rod and a simulated water rod that uses a non-heating rod as a water rod are bundled together. It is characterized in that an electric insulator is interposed in the simulated water rod in the direction perpendicular to the axis, and the axial conductive path is electrically divided into a plurality of parts.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. In addition, the same reference numerals are given to the portions common to FIGS. 6 to 11.

FIG. 1 shows a vertical cross-section of a simulated water rod 10 incorporated in an embodiment of a simulated fuel assembly according to the present invention with a part thereof cut away. A non-heat-generating mounting portion 12 is provided at the upper end of a hollow outer tube 11. It is joined.

The mounting portion 12 has a horizontal hole 12a formed in the lower hollow portion thereof, while the solid portion of the upper portion is fixed to the upper electrode 5B via an insulator 12b in an electrically insulated state.

The outer pipe 11 of the simulated water rod 10 is configured as a double pipe by coaxially accommodating the inner pipe 13 with a required gap inside, and the inner pipe 13 is a single tubular body with a horizontal hole. 13a are bored at required intervals in the axial direction.

On the other hand, the outer pipe 11 is configured by sequentially connecting a plurality of outer pipe pieces 11a having a required length in the axial direction and connecting a lower outer pipe piece 11b having an inverted conical shape to a lower end. An electrical insulator 14 is interposed between these outer tube pieces 11a.

The electric insulator 14 is formed of an electric insulating material into a substantially hollow cylindrical shape, and an axially intermediate portion of the cylindrical body is integrally formed with a protruding portion that protrudes outward. It is closely fitted. Thereby, the outer pipe 11 and the inner pipe 13 are electrically insulated. In addition, the convex portion of the electric insulator 14 is interposed between the outer pipe pieces 11 _a to form a plurality of outer pipes 11 a.
They are connected to each other in an electrically insulated state, and the outer peripheral surfaces of the connecting portions are formed flush with each other. Therefore, the outer peripheral surface of the simulated water rod 10 is formed into a smooth circumferential surface, and the conductive path of the simulated water rod 10 is formed by the electric insulator 14.
It is electrically divided in the axial direction into a number corresponding to the number of connections of 1a.

Further, in addition electrical insulator 14 is interposed between the lower end of the upper mounting portion 12 of the outer tube piece 11 _a1 disposed at the top, the upper end of the lower outer tube piece 11b disposed at the bottom It is interposed between and, and they are coupled in an electrically insulated state.

The lower outer pipe piece 11b has a small pipe 13b connected to the lower end of the inner pipe 13 fixed thereto via a fixing portion 13c, and a horizontal hole 11c communicating with the lower end opening of the small pipe 13b is bored in the hollow upper portion. , The coolant is introduced into the lower outer pipe piece 11b through the lateral hole 11c, and the inner pipe 13 is passed through the small pipe 13b.
I will guide you inside.

A cylindrical insulating spacer 15 made of an electrically insulating material is tightly fitted around the outer circumference of the inner pipe 13.
3 is fixed to the outer tube 11 in an electrically insulated state.
A plurality of insulating spacers 15 are arranged in the axial direction of the inner tube 13 at a required interval, and are arranged alternately with the electric insulator 14 in the axial direction.

The simulated water rod 10 thus constructed is assembled into a simulated fuel assembly in the same manner as in the conventional example shown in FIG.

Next, the operation of this embodiment will be described.

FIG. 2 shows an equivalent circuit when the simulated water rod 10 is assembled into a simulated fuel assembly. Simulated water rod 1
As shown in FIG. 2, the conductive path 0 is electrically divided into a plurality of, for example, five, electrically conductive paths in the axial direction by the electric insulator 14, so that the coolant W is not connected to the simulated fuel rod 2B (see FIG. 8). Also, a closed circuit is formed through each of the conductive paths, and the potentials of the simulated water rod 10 and the simulated fuel rod 2B are distributed as shown in FIG. That is, the potential 10E of the simulated water rod 10 gradually decreases from the upper end in the axial direction toward the lower end, and the potential difference from the potential 2BE of the simulated fuel rod 2B is significantly reduced over the entire length.

Therefore, the electrolytic action due to the potential difference between the metals is significantly suppressed, the corrosion of the simulated fuel rod 2B and the simulated water rod 10 due to the electrolytic action is suppressed, and the metal member is thinned due to the corrosion and the metal member surface is attached. The amount of attached kimono can be reduced.

Moreover, since the inner pipe 13 that penetrates the outer pipe 11 of the simulated water rod 10 is composed of one piece, the strength of the outer pipe 11 can be reinforced.

Furthermore, the pipe length of one outer pipe piece 11a is further shortened, and the unit conductive path length of the simulated water rod 10 is shortened, so that the simulated water rod 10 and the simulated fuel rod 2B.
It is possible to further reduce the potential difference between and.

The broken line in FIG. 3 indicates the axial distribution of the expected potential 3BE of the conventional simulated water rod 3B shown in FIG.

A second embodiment of the present invention is shown in FIG.

The main difference of the water rod 20 of this embodiment from the water rod 10 shown in FIG. 1 is that a small pipe 13b connected to the lower end of the inner pipe 13 is connected to a lower outer pipe piece at the lowermost stage via a spring 21. This is because the spring 21 absorbs the difference in expansion between the outer tube 11 and the inner tube 13 due to thermal expansion. That is, the spring 21 is coaxially fitted onto the outer circumference of the lower portion of the small tube 13b, the lower end is fixed to the lower outer peripheral wall of the small tube 13b by the fixing portion 13c, and the upper end thereof is connected to the upper end of the lower outer tube piece 11b. Insulator 14b
Stuck to the bottom edge of.

Therefore, according to the water rod 20 of this embodiment,
When a difference in expansion occurs due to thermal expansion between the outer pipe 11 and the inner pipe 13, the difference in expansion can be absorbed by the spring 21, and the soundness of both pipes 11 and 13 can be maintained.

A third embodiment of the present invention is shown in FIG.

The water rod 30 of this embodiment is the inner pipe 13, the insulating spacer 15 and the small pipe 1 of the water rod 10 shown in FIG.
3b etc. are mainly omitted to simplify the configuration, and the central hole 15b of the electric insulator 15a for electrically insulating and connecting the outer pipe pieces 11a to each other is provided with a coolant in a direction of an arrow in the figure. It is formed in the circulation hole for circulation. For this reason, the electric insulator 15a is made of ceramic or hard Teflon having excellent heat resistance and electric insulation. Further, a plurality of lateral holes 11 _a2 are bored in the outer pipe piece 11 _a1 arranged at the uppermost stage of the simulated water rod 30, and the coolant that has flowed through the simulated water rod 30 through these lateral holes 11 _a2. Is to be leaked to the outside.

Therefore, according to the water rod 30 of the present embodiment, the structure of the lower outer pipe piece 11b can be simplified,
The cost can be reduced.

〔The invention's effect〕

As described above, the present invention provides a simulated fuel assembly in which a simulated fuel rod, which uses a heating rod that generates heat when energized as a fuel rod, and a simulated water rod, which uses a non-heating rod as a water rod, are bound into a bundle. An electrical insulator was interposed in the simulated water rod in a direction perpendicular to the axis, and the conductive path in the axial direction was electrically divided into a plurality of parts.

Therefore, according to the present invention, the axial direction of the conductive path of the simulated water rod can be electrically divided into a plurality of parts, so that the potential difference between the simulated water rod and the simulated fuel rod can be reduced and the potential difference can be reduced. It is possible to suppress the electrolytic action caused by the corrosion, and to reduce the corrosion and the wall thickness accompanying the corrosion and the amount of adhered substances.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a simulated water rod of a first embodiment of a simulated fuel assembly according to the present invention with a part cut away,
1 is an equivalent electric circuit diagram of the embodiment shown in FIG. 1, FIG. 3 is an axial potential distribution diagram of the simulated water rod shown in FIG. 1, and FIG. 4 is a simulated water rod of the second embodiment of the present invention. FIG. 5 is a vertical cross-sectional view showing a partial cutaway of a simulated water rod according to a third embodiment of the present invention.
FIG. 6 is a perspective view showing an actual machine of a general fuel assembly partially broken away, and FIG. 7 shows an essential part of a general simulated fuel assembly. (A) shows A in (B). -A line sectional view,
(B) is a sectional view taken along line BB in (A), FIG. 8 is a longitudinal sectional view of a conventional simulated fuel rod, FIG. 9 is a longitudinal sectional view of a conventional simulated water rod, and FIG. 10 is a conventional example. An equivalent electric circuit diagram, FIG. 11 shows a potential difference generated between a simulated fuel rod and a simulated water rod in a conventional simulated fuel assembly and a position where electrolysis is generated. (A) is a schematic diagram, (B) Is a graph. 2B ... Simulated fuel rod, 3B, 10, 20, 30 ... Simulated water rod, 11 ... Outer tube, 13 ... Inner tube, 14 ...
… Electrical insulator, 15 …… Insulating spacer.

Claims (2)

[Claims] Claim: What is claimed is: 1. A simulated fuel assembly in which a simulated fuel rod that uses a heating rod as a fuel rod to generate heat when energized and a simulated water rod that uses a non-heating rod as a water rod are bundled to form a simulated fuel rod. A simulated fuel assembly characterized in that an electrical insulator is interposed in the direction perpendicular to the axis, and the axial conductive path is electrically divided into a plurality of parts. 2. The simulated fuel assembly according to claim 1, wherein a plurality of electrical insulators are arranged in parallel at a required interval in the axial direction of the simulated water rod.