JP2003121589A - Detection method for inner pressure creep rupture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the system of inner pressure creep rupture detection, constitute at a low cost and drastically improve reliability of the detection of ruptures. SOLUTION: A cylindrical test piece 44 filled with high pressure gas is contained in a irradiation capsule 30, which is inserted in a reactor using liquid coolant to test inner creep rupture strength. At this time, temperature signal from a temperature sensor (thermocouple 48) installed in the irradiation capsule is detected; when the temperature variation exceeds as upper limit or a lower limit set at the maximum and the minimum of temperature fluctuation amplitude at normal time, this is determined as being an occurrence of creep rupture. Another method is one in which the temperature signal from the sensor is detected at a constant period, the times of exceeding the upper limit or the lower limit set, above and below the prediction line of temperature by considering a temperature fluctuation amplitude are counted, and when the count value exceeds a set times due to the temperature variation within a certain elapsed time, this is determined as being an occurrence of creep rupture.

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 breakage of a test piece during an internal pressure creep rupture strength test in a nuclear reactor using a liquid coolant, and more specifically, an internal pressure sealed type test. When a piece breaks, gas is released into the surrounding liquid to form voids (bubbles), which changes the thermal conductivity and causes a peculiar temperature change, which is used to determine the occurrence of creep rupture. The present invention relates to an internal pressure creep rupture detection method.

[0002]

2. Description of the Related Art In the fast experimental reactor "JOYO", as a part of research and development of materials used in nuclear reactors, creep rupture strength test of materials in liquid coolant under high temperature radiation environment is conducted. . In this test, a cylindrical test piece containing high-pressure gas is housed in an irradiation capsule, and it is inserted into a nuclear reactor to measure the time until the test piece breaks in a liquid under a radiation environment. .

Therefore, in this internal pressure creep rupture strength test, it is important to accurately detect when the test piece breaks. As a conventional technique, there is a method of directly detecting a void generated at the time of breaking (see Japanese Patent Laid-Open No. 9-145891). Here, a void meter sensor is attached directly above the outlet of the coolant outlet tube of the irradiation capsule, and a void detection circuit for detecting the occurrence of a void based on the output signal of this void meter sensor is provided.

[0004]

However, in such a method for directly detecting a void, many devices such as a void meter sensor and a void detection circuit are required to be attached for detecting breakage. There is a problem of becoming expensive.

Further, although this method can detect the void by surely contacting the void meter sensor with the void, it is difficult to reliably contact the void with the void meter sensor, and the size of the void is reduced. The reliability is not always high because it is easily influenced by the principle. For example, the detection accuracy is high in the case of a fracture mode in which the gas inside the test piece is released in a short time and a large amount of voids are generated in a short time. But,
In the case of a rupture mode in which the gas inside the test piece gradually leaks from minute damage holes called pinholes and hair cracks, and the gas is released for several tens of minutes to several hours, voids cannot be detected. , There was a problem that could not be detected.

The object of the present invention is to simplify the system by making effective use of the existing temperature measuring system,
Moreover, it is an object of the present invention to provide an internal pressure creep rupture detection method which can be constructed at low cost. Another object of the present invention is to provide an internal pressure creep rupture detection method capable of significantly improving the reliability of rupture detection regardless of the rupture form.

[0007]

According to the present invention, a cylindrical test piece containing a high-pressure gas is placed in an irradiation capsule, and the irradiation capsule is inserted into a nuclear reactor using a liquid coolant. This is a method for detecting creep rupture when performing a creep rupture strength test. When the internal pressure sealed type test piece breaks,
The enclosed high-pressure gas is released into the liquid coolant in the irradiation capsule and becomes a void. When this void occurs in the irradiation capsule, the thermal conductivity changes to the sum of the thermal conductivity of the liquid coolant and the thermal conductivity of the gas so far, resulting in a change in the irradiation capsule temperature. appear. The present invention utilizes such a phenomenon, and makes a creep rupture determination by measuring temperature fluctuations with a temperature sensor.

Specifically, for example, a temperature signal from a temperature sensor mounted in the irradiation capsule is detected, and the upper limit set value or the lower limit set value provided above and below the normal temperature fluctuation width is exceeded and it is clear. When such a temperature change occurs, it is determined that creep rupture has occurred. Alternatively, the temperature signal from the temperature sensor loaded in the irradiation capsule is detected at a constant cycle, and the number of times the temperature exceeds the upper limit setting value or the lower limit setting value that is set considering the temperature fluctuation width above and below the temperature prediction line. When the count value within a certain elapsed time exceeds the set number of times and the temperature fluctuates, it is determined that the creep rupture has occurred.

A sheath type thermocouple is usually used as the temperature sensor. A thermocouple has previously been loaded in the irradiation capsule to measure its temperature. In the internal pressure creep rupture detection method of the present invention, the thermocouple can be used as it is. Further, in order to increase the detection sensitivity, it is also effective to disperse and load a plurality of thermocouples in the irradiation capsule in addition to the loaded thermocouples.

[0010]

EXAMPLE A cross section of a reactor equipped with an internal pressure creep rupture detection device is schematically shown in A of FIG. 1, and a structure of a sample portion of an irradiation device to be inserted into a reactor is shown in B of FIG. The reactor (here, fast breeder reactor) 10 has a structure in which a reactor core 12 is installed in a reactor vessel 12, and a liquid coolant 16 filled therein is circulated through a pipe. The core 14 is configured by arranging a large number of core constituent elements such as a hexagonal tubular fuel assembly and a control rod assembly. Liquid sodium is used as the liquid coolant, and its liquid surface is covered with a cover gas such as argon gas. A lid 18 is attached to the upper opening of the reactor vessel 12. The lid 18 is composed of a combination of a shield plug 18a and a rotary plug 18b,
An upper core mechanism 20 is mounted on the rotary plug 18b.

A long cylindrical irradiation device body 22 is mounted on the core upper mechanism 20. The irradiation device main body 22 includes a driving unit 24, a holding unit 26, a sample unit 28, and the like, and the sample unit 28 can be inserted into the core 14. Then, the sample unit 28 is loaded with a plurality of irradiation capsules 30 (see B in FIG. 1).

A longitudinal section of the irradiation capsule is shown in FIG. 2A, and a transverse section (xx section) thereof is shown in FIG. 2B. The irradiation capsule 30 has a double-walled cylindrical container including an inner cylinder 32 and an outer cylinder 34, and an upper gas chamber 36 and a lower gas chamber 38 are provided above and below the container. A gas for temperature control can be taken in and out between the double walls of the cylindrical container, and a temperature control gas inlet pipe 40 for putting gas in is attached to the lower side of the lower gas chamber 38. A temperature control gas outlet pipe 42 for discharging gas is attached to the outer cylinder 34 above the heavy wall. When performing the irradiation test by inserting the irradiation capsule 30 into the nuclear reactor, gamma heat of the irradiation capsule or the like by the gamma rays emitted from the core 14 is used. The temperature adjustment of the irradiation capsule 30 is
This is done by adjusting the heat transfer from the irradiation capsule by changing the concentration of the gas in the double-walled structure (eg the mixing ratio of argon gas and helium gas). The upper gas chamber 36 and the lower gas chamber 38 are provided in the irradiation capsule 30.
It suppresses the movement of heat in the up and down direction and reduces the axial temperature difference in the inner cylinder 32.

In the inner cylinder 32, a large number of test pieces 44, a basket 46 for accommodating them, a mandrel for holding the basket 46 at a predetermined position and accommodating a sheath type thermocouple 48 for temperature measurement. 50, a stopper 52 for fixing the basket 46, and the like are provided. Further, in the inner cylinder 32, the same liquid sodium as the coolant in the reactor enters through the sodium inlet pipe 54 and flows out through the upper sodium outlet pipe 56.

Returning to FIG. 1A, a measurement line 58 of the thermocouple 48 attached to the irradiation capsule 30 and a pipe 60 such as a temperature control gas inlet pipe or a temperature control gas outlet pipe.
Is drawn from the sample unit 28 to the outside via the holding unit 26 and the driving unit 24, and the data collecting device 62 and the determination circuit 6
4 and the temperature control gas facility 66.

As shown in FIG. 2C, the test piece 44 has end plugs 72 and 74 attached to both ends of a cylindrical test material 70, and a high pressure gas (for example, several hundreds of atmospheric pressure maximum) is enclosed therein. It was done. Test pieces 44 made of the same material are housed in the same irradiation capsule 30, and each test piece 44 is prepared so as to be sequentially broken at sufficient time intervals exceeding a prediction error of breakage. Then, the irradiation test is performed by inserting it into the reactor.

When the creep rupture of the test piece 44 occurs in the irradiation capsule 30, the high-pressure gas in the test piece 44 is released and becomes a void, which enters the liquid sodium in the inner cylinder 32 and the upper sodium outlet pipe 56. Flows out of the irradiation capsule 30 together with liquid sodium. When the voids enter the liquid sodium in the inner cylinder 32, the heat transfer is deteriorated because the heat transfer of the gas different from the heat transfer up to that time is added. The gamma calorific value of the irradiation capsule itself does not change as long as the reactor output is constant. Therefore, when a void is generated in the inner cylinder 32 and the heat transfer becomes poor, the temperature in the inner cylinder 32 rises and the void is generated. When it is discharged, the phenomenon that the temperature drops because it returns to the heat conduction of liquid sodium only. By utilizing this phenomenon, it is possible to detect the occurrence of voids due to the temperature change.

Therefore, the temperature signal from the thermocouple 48 loaded in the irradiation capsule 30 is detected, and the temperature fluctuation in the state where no void is generated is compared with the temperature fluctuation when the void is generated. Is larger than the former, it is judged that a void has occurred. An example of the determination method is shown in FIG.
An upper limit set value and a lower limit set value are provided above and below the normal temperature fluctuation range, and when the temperature change exceeds the upper limit set value or the lower limit set value, it is determined that creep rupture has occurred. That is, the temperature fluctuation range ≤ setting range (upper limit setting value-
"Lower limit setting value""novoid" Temperature fluctuation range> Setting range (upper limit setting value-lower limit setting value) "void"
Is determined. In FIG. 3, the first half shows the temperature fluctuation in the normal state, and the second half shows the state in which the temperature fluctuation part is determined to be fracture. In this case, fluctuations in reactor output and temperature fluctuations due to temperature control operations are excluded in consideration of such fluctuations. Moreover, in order to prevent erroneous determination due to noise, reliability can be increased by incorporating a filter in the temperature signal.

In the measurement in the fast experimental reactor "JOYO", the fluctuation range of the irradiation capsule temperature in the normal state is about 1 ° C on average. The upper limit setting value and the lower limit setting value are set by creating a prediction line of the temperature at which the current irradiation capsule temperature will change when a certain time elapses, and setting the temperature prediction line above and below. Specifically, for example, when the width of the temperature fluctuation is 1 ° C., there is a method in which the temperature prediction line is set by adding a small amount to the half of the fluctuation width up and down. In experimental reactors such as "JOYO", power adjustment is performed several times a day at fixed intervals, so the output gradually changes from one power adjustment to the next, and the irradiation capsule changes accordingly. Since the internal temperature also changes, a temperature prediction line is created by predicting this temperature change. The prediction line of the created temperature is predicted at any time using the temperature data of the irradiation capsule obtained after that, and the prediction line created previously is corrected.

In such a determination method, "excessive determination" may occur, which is determined to be a break even with noise or a single fluctuation depending on the set value. In such cases,
The determination method shown in FIG. 4 is effective. That is, the temperature signal from the thermocouple 48 loaded in the irradiation capsule 30 is detected at a constant cycle (for example, every 1 minute), and the upper limit set value provided above and below the temperature prediction line in consideration of the temperature fluctuation range. Or, count the number of times the lower limit setting value has been exceeded. Then, when the count value n within the fixed elapsed time T exceeds the specific set number N and the temperature fluctuates, it is determined that a void has occurred (that is, a creep rupture has occurred). In FIG. 4, it is determined that there are no voids in the first half and that voids have occurred in the second half.

FIG. 5A shows an example of time-series data of the irradiation capsule temperature when voids are released due to creep rupture in the internal pressure creep rupture test in the fast experimental reactor "JOYO". It can be seen that the portion where the measured temperature fluctuates greatly over 1 hour near the center of the figure is due to the occurrence of voids and is larger than the temperature fluctuation before that. Incidentally, about 35 cc of gas (converted at 0 ° C.) was enclosed in the broken test piece. In the case of such temperature fluctuation, void detection cannot be performed by the conventional method using a void meter sensor.

In such a case, as shown in FIG. 5B, the temperature prediction line and the set values for judgment above and below the temperature prediction line (here, the temperature prediction line ± 0.5 ° C. is set as the upper limit value and the lower limit value). Value)). By doing so, it is clear that the upper and lower set values for void determination are clearly defined, and that the number of places where the upper and lower limit set values are exceeded is clearly different between the void occurrence part and other places. Furthermore, if the number of the exceeded points is counted at a constant time interval T and if the number n exceeds the set number N, it is determined that the breakage occurs, an erroneous determination is made due to noise or the like at the points other than the void occurrence point Things will disappear.

By the way, in the above embodiment, as shown in FIG. 2, since the thermocouple is located substantially at the center in the length direction of the mandrel, if creep rupture occurs above that, the void is generated. It is also expected that detection will be difficult. In this case, in order to increase the detection sensitivity, a thermocouple other than the existing thermocouple at the center of the mandrel in the longitudinal direction may be installed above the mandrel. Further, as a method of increasing the void detection sensitivity, there is also a method of installing another thermocouple in the liquid sodium between the inner cylinder and the basket.

FIG. 6 shows an example of the installation status of thermocouples in the irradiation capsule. Since the basic structure of the irradiation capsule is the same as that of FIG. 2, the corresponding parts are designated by the same reference numerals and the description thereof will be omitted. FIG. 6A shows a mandrel 50.
The deep inside hole of the thermocouple 48
In addition, the thermocouple 80 is inserted deeply into the upper part. In FIG. 6B, another thermocouple 82 is placed in the liquid sodium in the irradiation capsule.
This is an example in which one or a plurality of test pieces 44 (only one is drawn in FIG. 6B) are arranged at an arbitrary position where the test pieces 44 are arranged between the basket 46 and the basket 46.

[0024]

As described above, the present invention can be applied by using the existing temperature measuring system as it is, so that the system can be simplified and the cost can be reduced. In addition, the internal pressure creep rupture can be reliably detected even in the case of a rupture mode in which the internal sealing gas of the test piece gradually leaks from the minute damage hole and the gas release extends for several hours. Can be greatly improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a sample part of a nuclear reactor and its irradiation device for carrying out the method of the present invention.

FIG. 2 is an explanatory view of an irradiation capsule and a test piece.

FIG. 3 is a graph showing an example of a void detection method.

FIG. 4 is a graph showing another example of the void detection method.

FIG. 5 is a graph showing an actual measurement example of temperature fluctuations when a void occurs and an actual example of a void detection method.

FIG. 6 is an explanatory view showing another example of the irradiation capsule.

[Explanation of symbols]

30 irradiation capsule 32 inner cylinder 34 outer cylinder 36 Upper gas chamber 38 Lower gas chamber 40 Temperature control gas inlet pipe 42 Temperature control gas outlet pipe 44 test pieces 46 baskets 48 thermocouple 50 mandrel 54 Sodium inlet tube 56 Sodium outlet tube

Claims (4)

[Claims] 1. A method for carrying out an internal pressure creep rupture strength test by accommodating a cylindrical test piece containing high-pressure gas in an irradiation capsule, and inserting the irradiation capsule into a nuclear reactor using a liquid coolant. , The temperature signal from the temperature sensor installed in the irradiation capsule is detected, and when the temperature fluctuation exceeds the upper limit setting value or the lower limit setting value provided above and below the temperature fluctuation width during normal operation, the temperature fluctuation is generated. An internal pressure creep rupture detection method characterized by determining that a creep rupture has occurred. 2. A method for carrying out an internal pressure creep rupture strength test by arranging a cylindrical test piece containing high-pressure gas in an irradiation capsule and inserting the irradiation capsule in a nuclear reactor using a liquid coolant. , The temperature signal from the temperature sensor loaded in the irradiation capsule is detected at a constant cycle, and the number of times the upper limit set value or the lower limit set value set above and below the temperature prediction line in consideration of the temperature fluctuation width is exceeded. A method for detecting internal pressure creep rupture, which comprises counting and determining that a creep rupture has occurred when a temperature fluctuation occurs when a count value within a certain elapsed time exceeds a set number of times. 3. The internal pressure creep according to claim 2, wherein a sheath-type thermocouple is used as the temperature sensor, and a plurality of thermocouples are dispersedly loaded in the irradiation capsule to detect temperatures at different positions in the irradiation capsule. Breakage detection method. 4. The internal pressure creep rupture detection method according to claim 3, wherein one or more thermocouples are loaded into the liquid coolant in the irradiation capsule.