JP2011153857A - Seal mechanism of fuel cladding tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a seal mechanism which makes seal mechanisms at both ends of a fuel cladding tube have wide gaps so as to be remotely controlled when attaching the fuel cladding tube to a testing machine by remote control, and capable of closing the gaps and allows the slide of the fuel cladding tube on a sealing surface at the time of a high-temperature and a high-pressure test. <P>SOLUTION: The seal mechanism of the fuel cladding tube 11 has end plugs 15 and 21 arranged at both the ends of the fuel cladding tube 11, introduces a pressuring medium into the fuel cladding tube 11 via an inlet hole 13 formed at one end plug 21, and conducts a mechanical characteristic test on the fuel cladding tube 11 where a cross section having a predetermined gap G formed between the fuel cladding tube 11 and itself is composed of a backup ring 16 formed of a bent, hard, and plastic material, and a soft O-ring 14 arranged adjacent to the backup ring 16 before the mechanical characteristic test, and the gap G is closed by the deformation of the backup ring 16 at the time of the mechanical characteristic test. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sealing mechanism for measuring mechanical properties of irradiated fuel cladding used in a nuclear reactor.

  As a technique for measuring the mechanical properties of general tubular materials, in addition to tube tensile testing, one end is welded or mechanically closed, and a stopper with an internal pressure introduction hole is fixed to the other end in the same manner. There are known tests (closed-end internal pressure burst test) for measuring the relationship between the pressure and the amount of expansion of the pipe, the maximum pressure at burst and the plastic deformation at burst, by introducing a pressurized medium consisting of gas or liquid Yes. Well-established techniques such as welding and mechanical fixing can be applied to the seal at that time.

  On the other hand, although the same internal pressure load test method is used for the same purpose, if the end plug structure is slidable rather than fixed at both ends (open end internal pressure burst test), the test piece is shortened or uniaxial There are many technical advantages because data can be obtained under stress loading conditions. In this open-end type internal pressure load test method, at least one end of a pipe is not held at the end by a welded end plug or a mechanical clamping force, but is pulled in the longitudinal direction of the pipe due to the internal pressure. It is necessary to have a structure in which the mutual movement (sliding) between the tube and the pressure sealing end plug mechanism is free so that no force acts. In order to achieve this, a seal mechanism that can slide under high temperature and high pressure has been demanded.

  In order to seal the internal pressure in the prior art, a sealing method according to a clearance value recommended by an O-ring and a JIS standard is generally used as is known, for example, in JIS B2401. As an inherent problem when this sealing method is applied to this technical field, first, a high internal pressure seal of 100 MPa or more is required. As an example of this high-pressure seal, in the prior art, a method of narrowing the fitting size of the O-ring groove, a method of applying a compressive force to the O-ring by an external force, or a bridgeman using an internal / external pressure difference caused by an unsupported region A method of applying a compressive force to the O-ring by the principle of sealing is known (Patent Document 1, Patent Document 2).

However, all of these conventional techniques are based on temperatures near room temperature, and have not been able to cope with a high temperature of about 300 ° C., which is the coolant temperature of the nuclear reactor.
In addition, as a high-pressure sealing technique corresponding to high temperatures, an example in which the cross-sectional shape of a metal or polyimide resin O-ring is improved to a substantially K-shape has been reported (Patent Document 3). Although applicable to seals, small-diameter pipes such as fuel cladding pipes in this technical field have a small amount of elastic deformation due to the small O-ring dimensions, and the seal technology cannot be applied. It was.

  On the other hand, in a strength measurement test of an irradiated fuel cladding tube, a technique is known in which a high-temperature end plug small-diameter portion is sealed by combining an O-ring and a backup ring (Patent Document 4). As the material (nominal operating temperature) of the high-temperature O-ring used there, nitrile rubber (about 90 ° C), silicon rubber (about 180 ° C), fluororubber (about 180 ° C), Teflon (registered trademark) (pure Teflon, about 200 ° C.), Teflon (filler added, about 300 ° C.), polyimide (about 300 ° C.), and perfluoroelastomer (about 300 ° C.) are used.

Japanese Patent Laid-Open No. 8-201124 Japanese Patent No. 2336195 Japanese Patent No. 2630634 JP 2007-256164 A

  The irradiated fuel cladding tube of the reactor targeted by the present invention has the disadvantage that the reaction product is deposited on the inner surface of the reactor and the surface skin becomes rough, and the cross section of the tube is distorted from a perfect circle due to the coolant pressure in the reactor. There was a serious aspect. When using a fuel cladding tube with even stronger radioactivity as a test tube, it is a small device that can be stored in a small chamber called a cell, and the test specimen can be remotely controlled with only a slight clamping force. There was a need to allow assembly. For this reason, in order to assemble the seal mechanism by inserting the O-ring and the backup ring into the pipe together with the end plug, a wider gap than recommended by the JIS standard is required.

  Further, from the viewpoint of the sealing function, the fuel cladding tube due to the internal pressure under a high temperature (about 300 ° C.) equivalent to the coolant temperature and under an internal pressure load condition of about 100 MPa or more at which the irradiated fuel cladding tube bursts. Therefore, it is necessary to maintain the internal pressure while allowing sliding with the end plug due to the shortening of the tube length during expansion. At that time, in the gap adopted in the sealing mechanism of the prior art, even the high temperature O-ring is fluidized and flows out of the gap to lose the sealing function, so that the gap needs to be made narrower. However, it has been technically difficult to assemble a seal mechanism by remotely inserting a hard O-ring having a narrow gap into a small-diameter test tube.

  As for the material of the O-ring, the heat-resistant temperature of the sealing material used in the conventional sealing mechanism shown in Patent Document 4 is a value obtained under conditions of low pressure and sealing the stationary surfaces, As a result of conducting an O-ring selection test with an internal pressure of about 100 MPa at 300 ° C., which is the applicable temperature of the tube, the polyimide material is too hard to close the gap during assembly using elastic deformation. The sealing function did not work. Further, when an O-ring having a narrow gap during manufacture is produced, there is a problem that cracks are likely to occur during assembly at room temperature.

For seals on sliding surfaces, the O-rings of any material cannot avoid large deformation due to internal / external pressure differences under high temperatures and high pressures of 300 ° C and 100 MPa. Under such large plastic deformations, the nominal use described in the catalog Deterioration accelerated at a temperature lower than the temperature, and the sealing performance was lost.
The perfluoroelastomer material has excellent performance in solvent resistance and heat resistance. However, when the pressurizing medium is high-temperature steam, the perfluoroelastomer material is weak and easily melts to deteriorate the sealing performance.

  FIG. 5 shows the behavior of the seal under high temperature and high pressure when the conventional seal structure is adopted. A radial gap of about 25-50 μm is required for the assembly work, but when the soft O-ring softened further at a high temperature of 300 ° C. is subjected to a high pressure of about 100 MPa, it is pushed out to the low pressure side and passes through the gap. Damaged when spilled, losing sealing function.

As described above, the pressure seal on the sliding surface under a high temperature (about 300 ° C.) and high pressure (about 100 MPa) environment requires fluidity in the ring material, and thus requires heat resistance in a largely deformed state. In addition, in order to prevent the O-ring material from flowing out from the gap between the inner surface of the test tube and the seal mechanism, it has been found that the value must be significantly narrower than the gap known in the prior art such as JIS.
On the other hand, in the application field of this technology, since the test tube made of the fuel cladding tube has strong radioactivity, it is necessary to assemble the seal mechanism by remote control in an isolation room called a cell. On the other hand, there is a conflicting requirement such that the gap between the O-ring and the O-ring must be satisfied at the same time.

  The present invention has been made in order to solve the above-described problems. In a mechanical characteristic test in which an internal pressure is applied to a fuel cladding tube in a high temperature environment, when the fuel cladding tube is remotely mounted, the fuel cladding tube The seal mechanism at both ends of the pipe has a wide gap so that it can be remotely operated, and at the time of high-temperature and high-pressure tests, the gap is closed and a seal mechanism that allows the fuel clad pipe to slide on the seal surface is provided. Objective.

  In order to solve the above-mentioned problems, a sealing mechanism for a fuel cladding tube according to the present invention includes end plugs disposed at both ends of the fuel cladding tube, and the inside of the fuel cladding tube via an introduction hole provided in one end plug. In the fuel cladding tube sealing mechanism, a mechanical property test of the fuel cladding tube is performed by introducing a pressurized medium into the fuel cell and measuring an expansion amount and a fracture internal pressure of the fuel cladding tube at a high temperature. Before the mechanical property test, a backup ring made of a hard and plastic material having a bent cross-section with a predetermined gap formed between the fuel cladding tube and a soft 0-ring arranged adjacent to the backup ring; The sealing mechanism is disposed inside the end plugs at both ends so that the backup ring is on the end plug side, and the back-up ring is deformed during the mechanical property test. Characterized in that more the gap is closed.

  According to the present invention, by bending the backup ring of the seal mechanism of the fuel cladding tube, the fuel cladding tube is mounted on the tester by remote control during a mechanical property test in which internal pressure is applied to the fuel cladding tube in a high temperature environment. In this case, the seal mechanism at both ends of the fuel cladding tube has a wide gap so that it can be remotely operated. During high temperature and high pressure tests, the gap is closed and the seal that allows the fuel cladding tube to slide on the seal surface A mechanism can be provided.

The block diagram of the seal mechanism which concerns on embodiment of this invention. The whole block diagram of the seal mechanism concerning the embodiment of the present invention. The block diagram of the backup ring which concerns on embodiment of this invention. The figure which shows the state at the time of the mechanical characteristic test of the seal mechanism which concerns on embodiment of this invention. The block diagram of the conventional sealing mechanism.

The sealing mechanism such as the fuel cladding tube according to the present invention is used as a test tube by appropriately cutting a small-diameter tubular member such as an irradiated nuclear reactor fuel cladding tube as a result of being used in a nuclear reactor, In order to measure the mechanical properties such as the strength of the test tube by applying the internal pressure to the inside of the test tube and measuring the mechanical properties such as the strength of the test tube, both ends of the test tube are connected to the end plugs. The present invention relates to a seal mechanism capable of maintaining a high pressure sufficient to cause a test tube to rupture in a high temperature atmosphere while being slidable with respect to each other.
In the following description, a test tube cut from a long fuel cladding tube to an appropriate length for testing is also referred to as a fuel cladding tube for convenience.

Embodiments of a sealing mechanism for a fuel cladding tube (test tube) according to the present invention will be described below with reference to the drawings.
FIGS. 1 and 2 are layout diagrams of the fuel cladding tube, the end plug, and the seal mechanism when performing the internal pressure burst test of the fuel cladding tube.

  1 and 2, an end plug 15 is fitted to one end of the fuel cladding tube 11 to be tested, and an end provided with an introduction hole 13 for introducing a pressurized medium to the other end. The stopper 21 is fitted. End expansion restraint rings 12 that maintain the fitted state between the fuel cladding tube 11 and the end plugs 15, 21 are disposed on the outer periphery of both ends of the fuel cladding tube 11. Convex portions 15a and 21a are formed on the inner side surfaces of the end plugs 15 and 21, and the convex portions 15a and 21a are bent around the convex portions 15a and 21a in a "<" shape made of a soft O-ring 14 and a high-temperature plastic material. A backup ring 16 is disposed adjacent to the backup ring 16.

  When the internal pressure burst test of the fuel cladding tube 11 is performed, both end plugs 15 and 21 are fixed to the base of the testing machine (not shown), and the internal pressure is applied to the inside of the fuel cladding tube 11 through the introduction hole 13. At this time, force is applied to the both end plugs 11 and 21 by the internal pressure, but the end plugs 11 and 21 are not pulled out of the fuel cladding tube by the reaction forces 22 and 23 from the base.

The operation of the sealing mechanism of this embodiment configured as described above will be described with reference to FIG.
When incorporating the seal mechanism according to this embodiment, the outer diameter of the high-temperature plastic backup ring 16 is processed so as to form a gap G that is sufficiently larger than the inner diameter of the fuel cladding tube 11. Installation can be done easily by remote control.

  When the soft O-ring 14 is pushed out to the side of the high temperature plastic backup ring 16 and the end plugs 15 and 21 by the pressurizing medium 13 when the internal pressure is applied, the backup ring 16 becomes above a predetermined temperature. Plastically deforms into an “I” shape.

  At the time of assembly, the initial gap G between the “<”-shaped backup ring 16 and the fuel cladding tube 11, the length L of the plastic deformation region of the backup ring 16, and the plastic deformation region of the inner surface of the end plug 15 For example, when L is 1.5 mm and θ is 15 °, the gap G is about 0.05 mm (50 μm) by making the inclination angle θ of G = L (1-cos (θ)). Become.

  When the backup ring 16 of this size is made of soft aluminum, the gap G is closed by plastic deformation of the backup ring 16 from a "<" shape to an "I" shape due to internal pressure at a high temperature of 300 [deg.] C. As a result, even if the soft O-ring 14 is fluidized under high temperature and high pressure, the inside of the fuel cladding tube 11 can be kept airtight without flowing out to the outside.

  FIG. 4 is a diagram showing a state in which the backup ring 16 is plastically deformed from a “<” shape to an “I” shape, and the gap G is closed so as to be exactly zero. As a result, the soft O-ring 14 is greatly deformed by high temperature, but does not flow out or break outside.

  In addition, since the initial dimension is determined so that the outer diameter of the backup ring 16 deformed in an “I” shape is substantially equal to the inner diameter of the fuel cladding tube 11, the fuel cladding tube does not mechanically adhere to both metal surfaces. Even if the tube length contracts with the expansion of 11, the end plugs 15 and 21 are slidable.

  In the above-described embodiment, the backup ring has a cross-sectional shape bent in a “<” shape. However, if the gap is closed during the high-temperature and high-pressure test, for example, the cross-section has a curved shape or a wave shape. It may be a bent shape.

  As described above, according to the present embodiment, in the mechanical characteristic test in which the internal pressure is applied to the irradiated fuel cladding tube used in the nuclear reactor under a high temperature environment, the fuel cladding tube is remotely operated by a test machine. When installing the, the seal mechanism at both ends of the fuel cladding tube has a wide gap so that it can be remotely controlled. During high temperature and high pressure tests, the gap is closed and the fuel cladding tube is allowed to slide on the sealing surface. A sealing mechanism can be provided.

  DESCRIPTION OF SYMBOLS 11 ... Fuel cladding tube (test tube), 12 ... End part expansion restraint ring, 13 ... Introduction hole, 14 ... O-ring, 15, 21 ... End plug, 15a, 21a ... Convex part, 16 ... Backup ring, 51 ... Backup ring.

Claims (4)

End plugs are arranged at both ends of the fuel cladding tube, and a pressurized medium is introduced into the fuel cladding tube via an introduction hole provided in one of the end plugs. In the fuel cladding tube sealing mechanism, which performs the mechanical characteristics test of the fuel cladding tube by measuring the internal pressure,
Prior to the mechanical property test, the seal mechanism is disposed adjacent to the backup ring, and a backup ring made of a hard and plastic material having a bent cross section that forms a predetermined gap with the fuel cladding tube. Consisting of a soft O-ring,
The seal mechanism is arranged inside the end plugs at both ends so that the backup ring is on the end plug side, and the gap is closed by deformation of the backup ring during the mechanical characteristic test. Fuel cladding sealing mechanism.   2. The fuel cladding sealing mechanism according to claim 1, wherein the soft O-ring is made of a heat-resistant polymer resin, and the backup ring is made of soft aluminum that undergoes plastic deformation at high temperatures.   3. The fuel cladding tube sealing mechanism according to claim 1, wherein the backup ring has a U-shaped cross section.   The fuel cladding tube sealing mechanism according to any one of claims 1 to 3, wherein the fuel cladding tube is an irradiated fuel cladding tube cut out from a fuel cladding tube of a nuclear reactor.

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