JP2800931B2 - Method for detecting leak of fuel element for nuclear reactor and fuel element for nuclear reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting leakage of a fuel element for a nuclear reactor and a fuel element for a nuclear reactor, and more particularly, to a method for detecting a pinhole or the like which may occur in a fuel element for a nuclear reactor during operation of the nuclear reactor. Easily and easily check for leaks
Further, the present invention relates to a method for detecting a leak of a fuel element for a nuclear reactor and a fuel element for a nuclear reactor that can be reliably detected.

[0002]

2. Description of the Related Art In general,
Reactor fuel elements are damaged by their use due to various causes such as fretting damage, hydrogenation damage and the like. When such damage causes a leak location in the reactor fuel element, the radioactive gas sealed therein leaks into the cooling water, into which the cooling water enters. Normal,
The leak location occurs during reactor operation, and the temperature of the reactor fuel element is high at this time, so the cooling water that has entered the reactor fuel element is immediately vaporized and diffused as steam. I do. This water vapor contacts fuel pellets in the reactor fuel element and is decomposed into hydrogen and oxygen. This oxygen is consumed in the oxidation reaction of the fuel pellets and the inner surface of the fuel cladding tube in the reactor fuel element, and part of the hydrogen is absorbed by the fuel cladding tube, and the remaining hydrogen remains in the reactor fuel element.

[0003] By the way, the fuel element for a nuclear reactor is, for example,
This is generally treated as a fuel element assembly for a nuclear reactor in which 17 pieces each of which are arranged and held in a square lattice in each of vertical and horizontal directions. When the reactor fuel assembly includes a reactor fuel element having a leak location, the radioactive material leaks from the leak location when the reactor fuel assembly is continuously used. This may lead to radioactive contamination. Therefore, when the fuel element assembly for a nuclear reactor is reused, an operation of detecting whether or not a leak portion has occurred in each fuel element for a nuclear reactor in the fuel element assembly for a nuclear reactor becomes essential.

Conventionally, such detection is carried out by measuring the amount of radioactive gas in the reactor fuel element by measuring the amount of strain of the fuel cladding in the reactor fuel element by inspecting the appearance of the reactor fuel element. It has been performed by such means as evaluating, detecting the water that has entered the reactor fuel element based on the presence or absence of a reflected wave when the reactor fuel element is irradiated with ultrasonic waves.

[0005] However, it is difficult to inspect the entire surface of the fuel element for a nuclear reactor by the above-mentioned appearance inspection. Further, it is very difficult to perform an appearance inspection on the reactor fuel elements arranged and held inside the reactor fuel element assembly. Further, when the leak location is a fine hole such as a pinhole, it is extremely difficult to specify the location. In the evaluation of the amount of radioactive gas in the fuel element for a nuclear reactor, the amount of change in the amount of strain is small, so that the amount of radioactive gas cannot be correctly evaluated. Further, the inspection device becomes large-scale. The detection of water that has entered the fuel element for a nuclear reactor does not necessarily mean that water has entered all the leak locations, and cannot detect a leak location where water has not entered. Therefore, each of the conventional methods for detecting a leak location has a problem.

On the other hand, when detecting a leak location for a plurality of reactor fuel element assemblies, one reactor fuel element assembly includes a plurality of reactor fuel elements. The number is huge. In an actual detection operation, it is necessary to specify which of the enormous number of reactor fuel elements has a leak location in which of the reactor fuel elements. Therefore, regardless of the number of reactor fuel elements to be inspected, a method for detecting a leak of a reactor fuel element and a method for detecting a leak of a reactor fuel element which can easily and easily and surely detect the presence or absence of a leak portion are provided. Fuel elements are desired.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and makes it possible to easily and simply and surely detect the presence or absence of a leak such as a pinhole which may occur in a fuel element for a reactor during operation of the reactor. It is an object of the present invention to provide a method for detecting a leak of a fuel element for a nuclear reactor and a fuel element for a nuclear reactor.

[0008]

According to a first aspect of the present invention, there is provided a foil of a substance which changes in volume by reacting with water vapor or hydrogen derived from water entering from a leak location. By irradiating the foil in the reactor fuel element having ultrasonic waves with ultrasonic waves, measuring the reflected wave thereof, and detecting the presence or absence of a change in the volume of the substance, the leakage point in the reactor fuel element is detected. a leak detection method for a nuclear reactor fuel elements, characterized in that detecting the presence, the invention is a reactor for fuel according to claim 2
In the fuel element where no fuel pellets are loaded
A foil of a substance which reacts with water vapor or hydrogen derived from water invading from a leak point to produce a volume change ,
The foil is a fuel element for a nuclear reactor, characterized in that formed by metallic bond to the fuel elements for the reactor, the billing
The invention according to claim 3, wherein the foil is a nuclear reactor fuel element according to claim 2 which is uranium metal and its alloys.

[0009]

In the method for detecting a leak of a fuel element for a nuclear reactor according to the present invention, a foil of a substance which generates a volume change by reacting with water vapor or hydrogen derived from water intruding from a leak point in the fuel element for a nuclear reactor is provided. Ultrasound is irradiated to the containing site. Then, the ultrasonic wave is reflected by the foil when no leak portion is generated, and is reflected by the foil that has changed in volume when a leak portion is generated. Next, by measuring the reflected wave, the presence / absence of a change in the volume of the foil is detected, and the presence / absence of a leak location in the fuel element for a reactor is detected.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for detecting a leak of a fuel element for a nuclear reactor according to the present invention will be described below together with an embodiment of a fuel element for a nuclear reactor according to the present invention with reference to the drawings. The present invention is not limited to the following embodiments.

FIG. 1 is a schematic sectional view showing an embodiment of a method for detecting a leak of a fuel element for a nuclear reactor according to the present invention.

As shown in FIG. 1, in the method for detecting a leak of a fuel element for a reactor according to the present invention, a fuel element 1 for a reactor and an ultrasonic sensor 7 are used.

The fuel element 1 for a nuclear reactor is used as a normal fuel element for a nuclear reactor, and leaks into a plenum portion 5 which is a gap below the fuel element and is not filled with fuel pellets. It has a uranium metal foil 4 made of uranium metal, which is a substance that reacts with water vapor or hydrogen derived from water invading from a location to produce a volume change.

The uranium metal foil 4 is used to convert uranium metal into Zircaloy-4 in the fuel element 1 for a nuclear reactor.
After being brought into close contact with the inner peripheral surface of the outer tube 2 and co-rolled, unnecessary portions of uranium metal are removed by an acid treatment, so that the Zircaloy-4 is joined and formed on the inner wall of the outer tube 2. I have. At the interface between the uranium metal foil 4 and the zircaloy-4 outer tube 2, there is a zircaloy-uranium alloy part 3, and the uranium metal foil 4 and the zircaloy-uranium alloy part 3 The Zircaloy-uranium alloy part and the Zircaloy-4 outer tube 2 are integrated by metal bonding.

The ultrasonic sensor 7 is disposed on the outer peripheral side surface of the outer tube of the Zircaloy-4 cylinder in the reactor fuel element 1 at a position substantially at the same height as the uranium metal foil 4. The ultrasonic sensor 7 irradiates the uranium metal foil 4 with ultrasonic waves so as to be orthogonal to the central axis of the nuclear reactor fuel element 1 and can measure the peak of the irradiation wave. It has a function of measuring the peak of the reflected wave from the foil 4. Further, the uranium metal foil 4 before the volume change occurs.
And the peak of the reflected wave of the uranium metal foil 4 after the volume change has occurred,
It has the function of detecting the difference between the two peaks and issuing an alarm.
In this embodiment, a known ultrasonic sensor is used.

Next, the measurement principle in the method for detecting a leak of a fuel element for a nuclear reactor according to the present invention will be described.

When the ultrasonic sensor 7 irradiates the uranium metal foil 4 with an ultrasonic wave, a reflected wave from the uranium metal foil 4 reaches the ultrasonic sensor 7 after a predetermined time from the irradiation. The ultrasonic sensor 7 measures a peak of an irradiation wave when the ultrasonic sensor 7 irradiates an ultrasonic wave and a peak of a reflected wave that reaches the ultrasonic sensor 7 after a predetermined time from the irradiation. The measurement result at this time is as shown before the occurrence of a leak in FIG. 2, and the peak of the reflected wave when the uranium metal foil 4 is provided (hereinafter, may be referred to as “inherent peak”) is measured in advance. It appears later by a fixed time a than the peak of the reflected wave when the uranium metal foil 4 is not provided (hereinafter sometimes referred to as a “reference peak”).

When no leak point occurs in the fuel element 1 for a nuclear reactor, a unique peak appearing delayed from the reference peak by a predetermined time a as shown in FIG. 2 is always measured.

If, for example, a leak occurs in the fuel element 1 for a nuclear reactor during use of the nuclear reactor, the radioactive gas sealed inside leaks from the leak and the cooling water enters the inside. At this time, since the reactor fuel element 1 is at a high temperature, the cooling water is immediately vaporized,
It becomes steam and diffuses in the reactor fuel element 1.
In addition, a part of the water vapor contacts the fuel pellets in the reactor fuel element 1 and diffuses in the reactor fuel element 1 while being decomposed into oxygen and hydrogen. Among the water vapor and hydrogen, those that have diffused to the position of the plenum portion 5 and have moved downwardly come into contact with and react with the uranium metal foil 4. Then, the uranium metal foil 4
Undergoes a volume change by the reaction represented by the following reaction formula (1) with the water vapor, and U, which is a fine powdery substance,
Easily changes to ₃ O ₈ . In addition, the reaction with the hydrogen causes a change in volume due to the reaction represented by the following reaction formula (2), and easily changes to UH ₃ which is a fine powdery substance.

[0020] _{3U + 8H 2 O → U 3} O 8 + 8H 2 ··· (1) by _{2U + 3H 2 → 2UH 3 ···} (2) such a reaction, the when uranium metal 4 was finely powdered Joka undergoes volume change Figure 2 shows the measurement results of the characteristic peaks.
And a small unique peak is measured after a fixed time b shorter than the fixed time a from the reference peak.

Therefore, by measuring a small peculiar peak appearing a fixed time b after the reference peak, a volume change of the uranium metal foil 4 indicating that a leak point has occurred in the reactor fuel element 1 is detected, It is possible to detect that a leak has occurred in the fuel element 1 for a nuclear reactor.

According to the method for detecting a leak of a fuel element for a nuclear reactor according to the present invention, it is different from a large intrinsic peak which appears after a predetermined time a from the reference peak, which indicates a state where no leak point has occurred, and a certain time b from the reference peak. Only by measuring a small peculiar peak appearing later, it is possible to easily and simply and surely detect the occurrence of a leak portion such as a pinhole in the fuel element for a nuclear reactor.

In the present invention, a foil made of a uranium metal alloy or the like can be used in place of the uranium metal foil 4. As the uranium, it is preferable to use depleted uranium, natural uranium and the like.

The shape of the uranium metal foil 4 is not particularly limited, and can be appropriately selected, such as a cylindrical shape and a cylindrical piece. The location provided on the reactor fuel element 1 of the uranium metal foil 4, a reactor fuel element
In the gap where no fuel pellets are loaded
Is not particularly limited, for example, Ru can Rukoto like the plenum portion 5.

The arrangement of the ultrasonic sensor 7 can be appropriately selected according to the position of the uranium metal foil 4.

The method for detecting a leak of a fuel element for a nuclear reactor according to the present invention can be carried out, for example, simultaneously for the fuel elements for a nuclear reactor for a pressurized water reactor, which are arranged in a square lattice in 14 rows and 14 rows. . In such a case, the detection operation and the detection result by the ultrasonic sensor arranged for each fuel element for each nuclear reactor are centrally controlled by means of a computer or the like.
It may be configured to manage and display the position, number, etc. of the reactor fuel element in which the leak has occurred, and to issue an alarm. This configuration is very convenient when the number of reactor fuel elements to be measured is large.

(Experimental example) As shown in FIG.
Approximately 30 mm length below the B-type reactor fuel element 1
The uranium metal foil 4 having a notch 6 in a part thereof under the condition that the heating temperature is 500 ° C. and the reaction time is 20 hours on the inner peripheral wall of the zircaloy-4 Was formed. When the cross section of the Zircaloy-4 outer tube 2 in the plenum portion 5 of the PWR-B type reactor fuel element 1 is analyzed, the Zircaloy-4 is formed at the interface between the uranium metal foil 4 and the Zircaloy-4 outer tube 2.
The uranium alloy part 3 is formed, and its thickness is about 10 μm.
m. The thickness of the uranium metal foil 4 was about 0.2 mm, and the thickness of the Zircaloy-4 outer tube 2 was about 0.7 mm. This PWR-B type reactor fuel element was used as a test object.

Next, the portion of the test object not having the uranium metal foil 4 was irradiated with ultrasonic waves and its reflected wave was measured. In addition, a portion of the test object having the uranium metal foil 4 was irradiated with ultrasonic waves, and its reflected wave was measured. The result is as shown in FIG. 2. The peak (intrinsic peak) of the reflected wave in the portion having the uranium metal foil 4 is equal to the peak (reference peak) of the reflected wave in the portion not having the uranium metal foil 4 for a fixed time a Confirmed that only appears late.

Subsequently, the test object was heated at a temperature of 350
Steam treatment was performed for 20 hours under the conditions of 30 ° C. and a pressure of 30 atm. Then, uranium metal foil 4
The surface of the inner peripheral wall in the outer tube of Zircaloy-4 having no, had a glossy black appearance, while the surface of the uranium metal foil 4 had an appearance as if black powder had adhered thereto. Then, a portion of the test object not having the uranium metal foil 4 was irradiated with ultrasonic waves in the same manner as described above, and the reflected waves were measured. In addition, a portion of the test object having the uranium metal foil 4 was irradiated with ultrasonic waves, and its reflected wave was measured. The result is as shown in FIG. 2. The peak (intrinsic peak) of the reflected wave in the case where the uranium metal foil 4 is provided is equal to the peak of the reflected wave in the case where the uranium metal foil 4 is not provided (reference peak). Appeared delayed by a fixed time b. Note that the specific peak at this time was a small peak, and the fixed time b was shorter than the fixed time a.

By measuring a small characteristic peak appearing a fixed time b after the reference peak, it was confirmed that the occurrence of a leak in the fuel element for a nuclear reactor could be detected.

[0031]

According to the present invention, it is possible to easily and simply and surely detect the presence or absence of a leak such as a pinhole which may occur in a fuel element for a reactor during operation of the reactor. An element leak detection method and a reactor fuel element can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic partial cross-sectional view showing one embodiment of a state in which a uranium metal foil in a nuclear reactor fuel element is irradiated with ultrasonic waves to detect a leak point.

FIG. 2 is a schematic explanatory view showing an example of a peak of an ultrasonic wave applied to a reactor fuel element and a peak of a reflected wave from the reactor fuel element before and after a leak occurs.

FIG. 3 is a schematic partial sectional view showing a test object of a fuel element for a reactor having a uranium metal foil partially cut away.

[Description of sign]

 REFERENCE SIGNS LIST 1 Nuclear reactor fuel element 2 Zircaloy-4 outer tube 3 Zircaloy-uranium alloy part 4 Uranium foil 5 Plenum part 6 Notch part 7 Ultrasonic sensor

Claims (3)

(57) [Claims] An ultrasonic wave is applied to the foil of a nuclear reactor fuel element having a foil of a substance which reacts with water vapor or hydrogen derived from water invading from a leak location to produce a volume change and reflects the ultrasonic wave. A method for detecting a leak of a reactor fuel element, comprising detecting a leak location in the reactor fuel element by measuring a wave and detecting a change in the volume of the substance. 2. A fuel pellet in a fuel element for a nuclear reactor.
In a void portion not loaded with a gas, a foil of a substance that reacts with water vapor or hydrogen derived from water invading from a leak location to generate a volume change is provided, and the foil is used for the reactor fuel.
A fuel element for a nuclear reactor characterized by being metal-bonded to a fuel element. 3. The nuclear reactor fuel element according to claim 2, wherein said foil is uranium metal and its alloy.