JPH0348197A - Pyrogenic pin - Google Patents

Abstract

PURPOSE:To prevent a displacement of a wrapping by forming a groove on an outside surface of a cladding tube and by engaging a wrapping wire with the groove. CONSTITUTION:A coil shaped electrical heater 5 is housed in a cladding tube 2 made of a stainless steel or the like, and is insulated by an inorganic insulating material 6 such as a magnesia. On an outer circle of the tube 2, a groove 7 is spirally formed along a contacting line which connects a starting point 1 of a wrapping wire 3 winding to an ending point 11 in order to engage the wire 3 with the groove 7 and to wind the wire 3. At both the starting point 1 of the wire 3 and the ending point 11, both ends of the wire 3 are fixed to the tube 2 by welding or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat generating pin such as a fuel pin used in a nuclear reactor or a simulated fuel pin used in a simulated nuclear reactor.

[Prior Art] A fuel pin is a cladding tube made of a metal tube or the like filled with nuclear fuel material such as fuel pellets, and is an element constituting a fuel assembly. In addition, a mock fuel pin that imitates this,
An electric heater is installed inside the same cladding tube as above, and the same cladding tube is filled with an inorganic insulating material such as magnesia.
The structure is such that the electric heater is insulated.

In order to configure such heating pins as a fuel assembly,
When bundling these, a wrapping wire (spacer wire) is wound helically around the outer periphery of the cladding tube in order to maintain a distance between the heating pins.

[Problems to be Solved by the Invention] The heating pin is used by generating heat from room temperature to a predetermined temperature. When the heating pin generates heat, the longitudinal elongation due to thermal expansion of the wrapping wire creates a spiral pattern around the outer periphery of the cladding tube. Since the amount of expansion along the contact line of the wrapping wire is usually larger than the amount of expansion along the contact line set for the wrapping wire, the wrapping wire often deviates from the predetermined contact line on the outer periphery of the cladding tube.

If the wrapping wire is shifted in this way, the winding pitch of the wrapping wire is disturbed, and there is a problem that when the heating pins are bundled, the interval between the heating pins cannot be maintained normally.

An object of the present invention is to solve the problems with the conventional heat generating pins described above.

[Means for Solving the Problems] That is, in order to solve the above problems, the gist of the means adopted in the present invention is to encapsulate a heat generating means inside the cladding tube 2 and wrap a wrapping wire around the outer periphery of the cladding tube 2. This heating pin is characterized in that a groove 7 is formed on the outer peripheral surface of the cladding tube 2, and the wrapping wire 3 is engaged with the groove 7.

[Function] In the heating pin according to the present invention, since the lapping wire 3 is engaged with the groove 7 formed on the outer periphery of the cladding tube 2, when heat is generated, the lapping wire 3 expands in the longitudinal direction. Even if the elongation is greater than the amount of expansion along the contact line of the wrapping wire set spirally around the outer periphery of the cladding tube, the wrapping wire 3 is held in the groove 7 and prevented from shifting from the predetermined contact line. be done.

According to tests conducted by the present inventor, as will be described later, it is clear that even if the groove 7 that engages the wrapping wire 3 is shallower than expected, it is sufficient to prevent the wrapping wire 3 from slipping. is being used. In other words, the groove 7 prevents stress concentration on the cladding tube 2 and the temperature measuring element 4 on the cladding tube 2.
It has been confirmed that the function of preventing the wrapping wire 3 from slipping is sufficiently exhibited at a depth where there is almost no problem considering the burying of the wrapping wire 3, etc., and the present invention satisfies such confirmation. It was established as a foundation.

[Embodiments] Next, embodiments of the present invention will be specifically described with reference to the drawings.

1 and 2 show a simulated fuel pin as an example of a heat generating pin, a coil-shaped electric heater 5 is housed in a cladding tube 2 such as a stainless steel tube, and this electric heater 5 Inorganic insulation material 6 such as magnesia filled in the tube 2
is insulated by

A spiral groove 7 is formed on the outer periphery of the cladding tube 2 along a contact line connecting the wrapping starting point 1 and the ending point 11 of the wrapping wire 3 to be wrapped, and the groove 7 is formed in a spiral shape along the contact line connecting the wrapping wire 3 to be wound. A wrapping wire 3 is wound around the outer periphery, and the same wire 3 is inserted into the groove 7.
is engaged with.

Both ends of the wrapping wire 3 are the above-mentioned winding starting point l and ending point 1.
1, it is rotated on the cladding tube 2 by means such as welding.

It is desirable to make the groove 7 that engages the wrapping wire 3 sufficiently shallow compared to the wall thickness of the cladding tube 2 in order to avoid stress concentration in the cladding tube 2. However, if it is too shallow, the wrapping wire 3 will be heated to a high temperature. It is not effective in preventing time lag. Specifically, the outer diameter of the cladding tube 2 is 7.5φ, the wall thickness L=0°4 m, the diameter of the wrapping wire 3 is 1.4φ,
If they are all made of the same 5US316 material, and the depth of the groove 7 is 0.1tx, or around 0.04mm, the heating pin wrapped with the wrapping wire 3 can be wrapped around 100mm at room temperature.
It was confirmed that the wrapping wire 3 did not come off the groove 7 at all even when heated to near 0°C.

Figure 3 (a) shows the state in which the wrapping wire 3 is engaged with the groove 7.
), and to describe the relationship between the depth of the groove 7 and the diameter of the wrapping wire 3 that is engaged with it, even when the wrapping wire 3 is engaged with the groove 7 very shallowly, It has been confirmed that displacement of the wrapping wire 3 during heat generation can be prevented to a greater extent than expected.

Specifically, when the groove 7 has an arcuate cross section with a radius of curvature equal to or slightly larger than the radius of the wrapping wire 3, the groove 7 has a depth of about 2 to 3% of the diameter of the wrapping wire 3. If so, it is sufficient to prevent the wrapping wire 3 from shifting.

In FIG. 1, reference numeral 4 indicates a temperature measuring element such as a thermocouple embedded in a groove 8 formed in the longitudinal direction of the cladding tube 2, and the state of the intersection between this temperature measuring element 4 and the wrapping wire 3. is shown in FIG. 3(b) and FIGS. 4(a) and (b). In FIG. 3(b), the depth of the groove 8 is set equal to the sum of the depth of the groove 7 and the diameter of the temperature measurement element 8, or This is the case when it is formed slightly deeper than that. On the other hand, in FIG. 4(a), the depth of the groove 8 is made equal to the diameter of the temperature measuring element 4, and a groove of the same depth as the groove 7 is formed in the portion of the wrapping wire 3 that intersects with the temperature measuring element 4. 9 is formed. Furthermore, Figure 4 (
b) is a case where a through hole 10 is provided in the vertical direction in a deeper part of the cladding tube 2 than the groove 7, at least in the part where the temperature measuring element 4 intersects with the wrapping wire 3, and the temperature measuring element 10 is embedded in this. be.

So far, we have described the case of a simulated fuel pin as an example of a heat generating pin, but in an actual fuel pin, the heat generating means in the cladding tube 2 simply changes from the electric heater 5.5 to nuclear fuel material such as nuclear fuel pellets. , it goes without saying that the present invention can be practiced in the same manner as in the above embodiments in other respects.

[Effects of the Invention] As explained above, according to the present invention, the wrapping wire 3 is stretched to a predetermined extent of the cladding tube 2 due to the difference in elongation due to thermal expansion in corresponding directions of the wrapping wire 3 and the cladding tube 2 during heat generation. It will not deviate from the contact line. As a result, when the heating pins are bundled together, the wrapping wire 3 can perform its function as a spacer in an ideal state.

[Brief explanation of drawings]

Fig. 1 is a side view of a heating pin showing an embodiment of the present invention, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 1, and Fig. 3(a) is an enlarged view of section A in Fig. 2. , FIG. 3(b) is an enlarged view of part B in FIG. 2, and FIGS. 4(a) and (b) are cross-sectional views of the same part as FIG. 3(b) above, showing other embodiments. be. 2... Cladding tube 3... Wrapping wire 5...
Electric heater 7...Groove

Claims (1)

[Claims] A heating pin in which a heating means is sealed inside a cladding tube 2 and a wrapping wire 3 is wound around the outer periphery of the cladding tube 2,
A heating pin characterized in that a groove 7 is formed on the outer circumferential surface of the cladding tube 2, and the wrapping wire 3 is engaged with the groove 7.