JP2013195304A - Neutron detector support structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a neutron detector support structure capable of securing smooth sliding of impurities by preventing the accumulation of the impurities while a furnace water smoothly flows in the gap (narrow part) between components even when impurities are contained in the furnace water.SOLUTION: An in-core detector guide pipe incorporates neutron detection for measuring a level of neutron flux in a reactor core by converting the level of neutron into an electric current. The outer pipe covers an outer peripheral wall of the in-core furnace detector guide pipe with a clearance left on the outer peripheral wall. A coil-like spring body is incorporated into the outer pipe and absorbs thermal expansion by winding on the outer peripheral wall of the in-core furnace detector guide pipe. A plunger is configured such that the lower end portion is located inside the outer pipe and supported by the spring body and an upper end head portion is elastically abutted against to a top guide which is a reactor core internal structure by the spring body. In the fitting portion between the plunger and the outer pipe, an outer pipe inner peripheral wall uses one end portion as a fitting portion fitted to the plunger, and the outer pipe inner peripheral wall except for this fitting portion is used as a furnace water circulation concave portion in which the furnace water circulates between the plunger and the outer pipe inner peripheral wall.

Description

  Embodiments of the present invention relate to a neutron detector support structure including a neutron detector that converts a neutron flux level in a nuclear reactor into a current and measures it.

  A neutron detector (small fission ionization chamber) is provided in the reactor. That is, two electrodes are arranged inside the sealed chamber with a space therebetween, uranium (U235) on the inner surface of the outer electrode absorbs thermal neutrons and causes fission, and the fission fragments ionize argon gas inside the detector. . Ionized ion pairs (positive ions and electrons) are collected on two electrodes to which voltages of different polarities are applied, and measured as current signals. The current signal is a value proportional to the neutron flux.

  For example, [Patent Document 1] discloses an in-reactor neutron instrumentation guide tube. More specifically, as shown in FIG. 6, a detector in-furnace guide tube 1, a plunger 2A, a spring body 3, an outer tube 4, and a spring retainer 5A having a plurality of neutron detectors attached to the lower end portion. Composed. The plunger 2 includes a rod piston guide 6 and a rod piston 7A. A rod piston retainer 9A is connected to the upper end of the outer tube 4, and the outer peripheral wall of the rod piston 7A is fitted into this inner peripheral wall.

JP-A-3-37598

  By the way, the reactor water flows for cooling around the neutron detector support structure, and the reactor water infiltrates through a gap. Over a long period of use, the members constituting the neutron detector tube support structure are dissolved in the reactor water, and impurities (cladding) are generated. Reactor water containing impurities also flows around the neutron detector support structure and enters the interior.

  The neutron detector support structure includes a space between the outer peripheral wall of the rod piston 7A and the inner peripheral wall of the rod piston retainer 9A, and a space between the outer peripheral wall of the upper end of the detector furnace guide tube 1 and the inner peripheral wall of the rod piston 7A. A gap (narrow portion) of about 0.11 to 0.16 mm is formed between the inner peripheral wall of the spring retainer 5A and the outer peripheral wall of the detector furnace guide tube 1, and is slidable with respect to each other.

  However, over a long period of use, impurities accumulate in the gaps and hinder smooth sliding between these parts. Eventually, the members stick to each other (stick), and stress may be locally applied, leading to destruction. Therefore, if there is sticking, it is necessary to cut and remove the neutron detector support structure from the middle part, which is troublesome.

  Under these circumstances, even if impurities are contained in the reactor water, the reactor water flows smoothly through the gaps (narrow parts) between the components, preventing the accumulation of impurities and ensuring a smooth sliding. A support structure was desired.

In this embodiment, the in-core detector guide tube incorporates a neutron detector that converts the neutron flux level in the reactor into a current signal and measures it.
The coiled spring body is built in the outer tube and wound around the outer peripheral wall of the in-furnace detector guide tube to absorb thermal expansion.
The outer tube covers the outer peripheral wall of the spring body and the in-furnace detector guide tube with a gap.
The lower end of the plunger is fitted into the inner wall of the outer tube and is supported by the spring body, and the upper end head is elastically brought into contact with the upper lattice plate, which is a reactor internal structure, by the spring body.
In the fitting portion between the plunger and the outer tube, the inner peripheral wall of the outer tube is used as a fitting portion for fitting one end with the plunger, and the inner peripheral wall of the outer tube excluding this fitting portion receives reactor water between the plunger. A circulation recess for circulating reactor water was used.

The longitudinal cross-sectional view of the neutron detector support structure based on this embodiment. The longitudinal cross-sectional view which expanded the mutually different site | part of the neutron detector support structure based on the embodiment. The figure which compared the dimensional structure of the conventional product and the product of the same embodiment of the rod piston presser which comprises a neutron detector support structure. The figure which compared the dimension structure of the conventional product and the product of the same embodiment of the spring retainer which comprises a neutron detector support structure. The figure which compared the dimension structure of the rod piston which comprises a neutron detector support structure with the conventional product and the product of the same embodiment. The longitudinal cross-sectional view of the conventional neutron detector support structure, and the longitudinal cross-sectional view which expanded the mutually different site | part.

Hereinafter, the present embodiment will be described with reference to the drawings.
FIG. 1 is a partial longitudinal sectional view of the neutron detector support structure S. FIG.
In the figure, reference numeral 1 denotes a detector furnace guide tube, and a plurality of neutron detectors are attached to a lower end portion (not shown) of the detector furnace guide tube 1. A plunger 2 is attached to the upper end of the detector furnace guide tube 1, and between the detector furnace guide tube 1 and the plunger 2, the plunger 2 is wound around the detector furnace guide tube 1. And an outer tube 4 which is a spring cover tube incorporating the spring body 3 is disposed.

  The outer tube 4 covers the detector furnace guide tube 1 from the lower end to the upper end, and the lower end side of the plunger 2 is fitted inside the upper end of the outer tube 4. The lower end of the spring body 3 is supported by a spring retainer 5 fixed in the outer tube 4, and the plunger 2 is pushed up by the spring body 3 and is movable in the axial direction.

  The plunger 2 is a bar piston guide 6 having a solid upper portion, and a hollow piston piston 7 on the lower side. The upper end portion of the rod piston 7 is fitted to the lower end portion of the rod piston guide 6 so as to be integrated. It is connected.

  The upper end portion of the rod piston guide 6 is formed in a head portion 6a having a diameter larger than that of other portions, and a flange portion 6b having a diameter larger than that of other portions is also formed in the lower portion of the rod piston guide 6. A connecting ring 8 having the same diameter as that of the flange portion 6b is fitted into a connecting portion between the rod piston 7 and the rod piston guide 6, and a predetermined gap is formed between the connecting ring 8 and the flange portion 6b.

  Only the lower end portion of the rod piston 7 constituting the lower portion of the plunger 2 is larger in diameter than the other portions, and is integrally formed as an engaging portion 7a that is slidably engaged with the inner peripheral wall of the outer tube 4. The inner peripheral wall of the rod piston retainer 9 that is integrally connected to the upper end portion of the outer tube 4 is slidably fitted into the lower outer peripheral wall of the rod piston 7 excluding the engaging portion 7a.

  That is, with respect to the outer tube 4, the rod piston retainer 9 integrally connected to the upper end of the outer tube 4, and the spring retainer 5 fixed to the lower end of the outer tube 4, the rod piston 7 constituting the plunger 2 The rod piston guide 6 is pushed up by the spring body 3 and is movably fitted, and the detector furnace guide tube 1 is movably fitted in the hollow portion of the rod piston 7.

  The neutron detector support structure S constructed in this way and having an extremely long overall length (about 13M) with respect to the diameter, and a plunger using an in-furnace desorption device for assembly into the reactor Stand upright with 2 on top. A neutron detector (not shown) is located at the bottom.

  The neutron detector support structure S is transported to a predetermined position in the nuclear reactor, and is held by the in-core monitor handling tool from the in-reactor demounting device, and the rod constituting the plunger 2 of the neutron detector support structure S Grasp between the flange of the piston guide 6 and the connecting ring 8 and push down.

  The spring body 3 that elastically supports the plunger 2 is pushed down, and the head 6a of the rod piston guide 6 is forcibly lowered by a predetermined distance. In this state, the in-core monitor handling tool releases the plunger 2 after moving to the recess 10a of the upper lattice plate 10 in the nuclear reactor.

  The elastic force of the spring body 3 acts again, the plunger 2 is pushed up, and the head 6 a of the rod piston guide 6 is elastically engaged with the recess 10 a of the upper lattice plate 10. The neutron detector support structure S is supported by the upper lattice plate 1 in this way.

  Due to radiation exposure and other problems, it is an underwater operation because the reactor water cannot be removed from the reactor. Moreover, the handling of the neutron detector support structure S having a long overall length is required carefully for a thin diameter, and the operator performs a groping state by remote control. Removal of the neutron detector support structure S is the reverse operation procedure.

  In this neutron detector support structure S, a gap (narrow part) is formed between the members described below, and one member is slidable or one member is fixed and the other member is slidable. Yes.

That is,
(1) Between the outer peripheral wall of the rod piston 7 and the inner peripheral wall of the rod piston retainer 9.
(2) Between the upper end outer peripheral wall of the detector furnace guide tube 1 and the inner peripheral wall of the rod piston 7.
(3) Between the inner peripheral wall of the spring retainer 5 and the outer peripheral wall of the detector furnace guide tube 1.

  Originally, since the neutron detector support structure S is immersed in the reactor water, the reactor water also enters the gap described above. However, with long-term use, it is inevitable that some of the constituent members of the neutron detector support structure S melt and impurities are generated in the reactor water. There is a possibility that the impurities stay in the gap and eventually accumulate, eventually filling up the gap and sticking the components to each other.

  Note that there is a gap between the outer peripheral wall of the engaging portion 7 a formed at the lower end of the rod piston 7 and the inner peripheral wall of the outer tube 1. Since a sufficient gap (0.4 to 0.65 mm) is formed so that the rod piston 7 can slide smoothly, no accumulation of impurities is observed.

  Further, the rod piston 7 constituting the plunger 2 has a hollow shape, and the detector furnace guide tube 1 is movably fitted therein. The upper end portion of the rod piston 7 is fitted into the lower end portion of the solid rod piston guide 6 and is in a closed state.

  Even if the reactor water enters from the gap between the outer peripheral wall of the detector furnace guide tube 1 and the inner peripheral wall of the rod piston 7 and accumulates at the upper end of the detector furnace guide tube 1, the upper end of the rod piston 7 Since the portion is closed by the rod piston guide 6, there is no escape route for the air accumulated between them. An air pocket is formed in the rod piston 7 at the upper end of the detector furnace guide tube 1.

(4) On the other hand, when the detector furnace guide tube 1 is pushed up by the spring body 3, the level of the reactor water collected in the hollow portion of the rod piston 7 which is the upper end portion of the detector furnace guide tube 1 Goes up and down. The reactor water level portion of the rod piston 7 repeats a dry and wet state, which causes corrosion over a long period of use.

In the present embodiment, the above-described problems are solved by the configuration shown in FIGS.
(1) About the gap between the outer peripheral wall of the rod piston 7 and the inner peripheral wall of the rod piston retainer 9.

  The inner diameter of the upper end of the rod piston retainer 9 forms the same clearance (0.11 to 0, 16 mm) as the conventional outer peripheral wall of the rod piston 7, but the remaining inner diameter excluding the inner diameter of the upper end is a rod. A gap with respect to the outer peripheral wall of the piston 7 is enlarged to form a recess 99a.

  That is, while the rod piston 7 constitutes the plunger 2 together with the rod piston guide 6, the rod piston retainer 9 is integrally provided at the upper end portion of the outer tube 4, and the rod piston retainer 9 constitutes a part of the outer tube 4. To do.

  Therefore, in the above structure, in the fitting portion between the outer peripheral wall of the blanker 2 and the inner peripheral wall of the outer tube 4, the inner peripheral wall of the outer tube 4 is used as a fitting portion that fits the plunger 2, and this fitting portion is excluded. In other words, the inner peripheral wall of the outer tube is a reactor water circulation recess 99a through which reactor water flows between the outer tube and the plunger 2.

(2) About the gap between the outer peripheral wall of the upper end portion of the detector furnace guide tube 1 and the inner peripheral wall of the rod piston 7.
The inner diameter of the rod piston 7 is expanded without changing the outer diameter of the detector furnace guide tube 1.
(3) Between the inner peripheral wall of the spring retainer 5 and the outer peripheral wall of the detector furnace guide tube 1.
Without changing the outer diameter of the detector furnace guide tube 1, the inner diameter of the spring retainer 5 is enlarged, and a reactor water guide 55a for smoothly guiding the reactor water between the detector furnace guide tube 1 and the detector furnace guide tube 1 is provided. Form.

  With the above configuration, the axial length of the gap (narrow portion) is shortened or the gap is enlarged. Even if the impurities are melted from each member constituting the neutron detector support structure S over a long period of use and flows into the enlarged gap together with the reactor water, the impurities flow out before being deposited. Since no impurities are accumulated in the gap, the members can slide smoothly. The reactor water flows smoothly through each gap to ensure a cooling effect.

(4) Regarding the problem that the detector furnace guide tube 1 is pushed up by the spring body 3 and an air reservoir is formed in the hollow portion of the rod piston 7.
Two small-diameter air vent holes 12, 12 are provided at the upper end of the rod piston 7. Even if the detector furnace guide tube 1 repeats vertical movement and an air reservoir is formed at the upper end, air escapes through the air vent hole 12.

  Alternatively, the reactor water around the plunger 2 flows into the hollow body of the rod piston 7 through the air vent holes 12, 12 and flows out from here. The air vent holes 12 and 12 reduce resistance to vertical movement of the detector furnace guide tube 1 and can move smoothly, and can form a new detector furnace guide tube cooling water channel to improve cooling performance. I can plan.

Next, a specific example of the gap structure with respect to (1) described above will be shown.
FIG. 3A is a manufacturing diagram in which a part of the rod piston retainer 9A having a conventional structure is omitted, and FIG. 3B is a manufacturing diagram in which a part of the rod piston retainer 9 of the present embodiment is omitted.

  As shown in FIG. 3A, the rod piston retainer 9A having a conventional structure has an inner diameter of 13.6 mm over the entire length in the axial direction. Therefore, the same narrow gap exists over the entire length with respect to the rod piston 7 inserted inside.

  As shown in FIG. 3 (B), the inner diameter of the rod piston retainer 9 of the present embodiment is 5 mm from the upper end and remains the same φ13.6 mm as before, but extends from the lower end to the entire length. The inner diameter was φ14.4 mm. A circulation recess 99a for reactor water is formed in which the gap with respect to the outer peripheral wall of the rod piston 7 inserted inside is enlarged.

A specific example of the gap structure for (3) described above is as follows.
FIG. 4A is a manufacturing diagram of the spring presser 5A having a conventional structure, and FIG. 4B is a manufacturing diagram of the spring presser 5 of the present embodiment.
The outer diameter is the same between the prior art and the present embodiment and remains at 23.7 mm, but the inner diameter has been expanded from the conventional 10 mm to 12.7 mm in the present embodiment. As a result, a gap with the outer peripheral wall of the detector furnace guide tube 1 inserted through the inner diameter of the spring retainer 5 is enlarged, a reactor water guide portion 55a is formed, the circulation of the reactor water is facilitated, and impurities are deposited. There is no.

A specific example of the gap structure with respect to (4) described above is as follows.
FIG. 5A is a manufacturing diagram of a rod piston 7A having a conventional structure, and FIG. 5B is a manufacturing diagram of the rod piston 7 of the present embodiment.

  In both the conventional structure and the present embodiment, the outer diameter, the inner diameter, and the length including the engaging portion 7a of the rod pistons 7 and 7A are not changed. However, in the present embodiment, two small holes of φ1.5 mm are provided at a position 8.6 mm from the upper end of the rod piston 7, and these are designated as air vent holes 12 and 12.

  As described above, the upper end portion of the rod piston 7 is fitted to the lower end portion of the rod piston guide 6, and the connector 8 is fitted to the outer peripheral wall. The air vent hole 12 selects the upper limit position that is not blocked by the connector 8. The detector furnace guide tube 1 is at the most moved position and exceeds the air vent hole 12 but is dimensioned so as not to contact the lower end of the rod piston guide 6.

[Table 1] below shows the results of using alumina powder as a substitute for impurities for each type of fitting part.
More specifically, alumina powder (# 800 or # 500) is mixed with water, packed in the gaps (narrow portions) of the components of the neutron detector support structure S described above, and slid with a lateral load of 1K applied. Power was measured and compared with and without countermeasures.

As an experimental result, it was confirmed that the sliding resistance obtained by subtracting the sliding force without alumina powder from the sliding force with alumina powder was statistically significant with or without countermeasures.

  As mentioned above, although this embodiment was described, the above-mentioned embodiment is shown as an example and does not intend limiting the range of embodiment. The novel embodiment can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Detector furnace guide tube, 4 ... Outer tube, 3 ... Spring body, 10 ... Upper lattice board, 2 ... Plunger, 99a ... Recirculation recessed part for reactor water, 7 ... Rod piston, 6 ... Rod piston guide, 12 ... Air vent hole part, 5 ... Spring presser, 55a ... Reactor water guide part.

Claims (3)

An in-core detector guide tube having a built-in neutron detector that converts the neutron flux level in the reactor into a current signal and measures it,
A coiled spring body wound around the outer peripheral wall of the in-furnace detector guide tube and absorbing this thermal expansion;
An outer tube that covers the outer circumferential wall of the spring body and the in-furnace detector guide tube with a gap;
A lower end is fitted to the inner wall of the outer tube and supported by the spring body, and an upper end head includes a plunger that elastically contacts the upper lattice plate, which is a reactor internal structure, by the spring body,
In the fitting portion between the plunger and the outer tube, the outer tube inner peripheral wall has one end as a fitting portion to be fitted with the plunger, and the outer tube inner peripheral wall excluding the fitting portion is a blanker. A neutron detector support structure characterized in that a reactor water circulation recess through which reactor water flows is provided. The plunger is
A rod piston made of a hollow tube, fitted into the inner wall of the outer tube, the furnace detector guide tube is inserted inside, and the spring body elastically contacts the lower end portion;
A solid rod piston guide connected to the upper end of the rod piston and elastically abutting the head with the upper lattice plate by the spring body;
The neutron detector support according to claim 1, wherein the rod piston is provided with an air vent hole for venting air accumulated in the hollow portion of the rod piston as the in-furnace detector guide tube moves. Structure. The lower end of the spring body is supported by a spring retainer in which the outer peripheral wall is fitted and fixed in the outer tube, and the in-furnace detector guide tube is inserted into the inner peripheral wall.
3. The reactor water guide part according to claim 1, wherein an inner peripheral wall of the spring retainer is a reactor water guide portion capable of circulating reactor water between the inner periphery of the detector guide tube and the outer peripheral wall of the reactor. The neutron detector support structure described.

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