JPH0325194Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a device for detecting the temperature stratified interface position of a cooling medium in a nuclear reactor, which can continuously and automatically detect the movement of an interface where high and low temperature fluids are stratified. be.

A cooling medium is used in a nuclear reactor to extract the thermal energy associated with nuclear fission. For example, water is used in light water reactors, and liquid sodium is used in fast breeder reactors. By the way, in this case, if the core temperature changes when the reactor is shut down, the temperature of the cooling medium will also change, but since liquid sodium is a metal, it is less effective as a coolant in the core than water, which has a low thermal conductivity. temperature drops rapidly. For this reason, the coolant is not sufficiently mixed inside the reactor vessel like in the case of water, and the liquid sodium, which has rapidly decreased in temperature, sinks downward due to its weight. comes to exist in layers. In this case, as shown in FIG. 3, a boundary surface with an extremely steep temperature gradient is formed at the boundary between the high temperature layer 17 and the low temperature layer 16. Moreover, since the fluid mass in the high temperature layer 17 is drawn into the low temperature layer 16 by the flow of the cold and hot fluid, this boundary surface 15 gradually rises inside the container while shaking with the passage of time. As a result, the high-temperature liquid sodium layer 17 and the low-temperature liquid sodium layer 16 on the reactor vessel wall surface act on the structural material through a steep temperature gradient. The thermal expansion and contraction that occurs at this time gives large stress to the container and internal structures. For example, the boundary surface 15
By rapidly cooling the container wall, which has been kept at a high temperature due to the rise in temperature, by the low temperature layer 16, repeated stress is applied to the container wall. As a result, thermal fatigue is added due to the frequent shutdown of the reactor during its operating life. For this reason, the furnace vessel that uses liquid sodium as a cooling medium is
Compared to those that use water as a cooling medium, they are particularly prone to early deterioration of mechanical strength due to thermal fatigue caused by such repeated stress. Therefore, in order to ensure safety, the above-mentioned boundary surface 15 inside the container must be
In other words, it is necessary to fully understand the flow characteristics of liquid sodium, such as changes in the temperature stratified interface, and to develop countermeasures.

However, in the past, multiple thermometers were placed inside the container or on the wall, and the detection was done by visual reading, which had drawbacks such as inaccurate detection, and was extremely insufficient to meet the requirements. It is. The present invention provides a temperature stratification interface position meter that can accurately grasp the moment-to-moment movement state of the temperature stratification interface in the reactor vessel, and contributes to ensuring the safety of the reactor vessel. be. Next, the details will be explained using the drawings.

When liquid sodium is used as a cooling medium,
The temperature of the upper high-temperature layer forming the temperature-stratified interface remains approximately constant over time despite its upward movement. Moreover, as described above with reference to FIG. 3, a temperature stratification interface is formed between the high temperature layer and the low temperature layer when the furnace operation is stopped, and this temperature stratification interface increases with the passage of time. Based on this, the present invention sets a temperature sensor inside the furnace vessel, and sets the set temperature at a selected temperature within the temperature stratification interface with a temperature gradient, for example, at the third temperature.
As shown in the figure, the servo mechanism is used to raise and lower the temperature between the high temperature layer and the low temperature layer, and by always positioning it at the boundary between the high temperature layer and the low temperature layer, it is possible to accurately and easily control the temperature from the rotation of the servo motor. The idea was that the flow characteristics of liquid sodium could be grasped by continuously and easily detecting fluctuations in the temperature stratification interface using a device.

FIGS. 1 and 2 show a circuit diagram and an example of a thermocouple drive mechanism showing an embodiment of the present invention. In FIG. 1, A indicates a detection section, one of which is a thermocouple and is constructed as shown in FIG. In FIG. 2, 2 is a protection tube, and the thermocouple 1 is housed at the tip thereof. Reference numeral 3 denotes a protective tube holder, which is fixed within the reactor vessel. The thermocouple 1 supports a protective tube 2, which is made to have a length such that it can move from the bottom to the surface of the liquid sodium layer in the reactor vessel, in a vertically movable manner. 4 is a driven spur gear provided on the protection tube 2; 5 is a driving gear coupled to the shaft of a servo motor 12 (to be described later); The protection tube 2 is moved up and down in proportion to the amount. Note that the reference junction portion of the thermocouple 1 is not shown in the figure.

Returning to FIG. 1, reference numeral B designates a control section, of which 6 indicates a DC amplifier, which amplifies the DC output of the thermocouple 1 sent via the signal transmission line 7. 8 is a DC-AC converter, which converts the output of the thermocouple 1 into an AC output. 9 is an AC bridge, and 10 is its AC power source, for example a commercial frequency power source. The AC bridge 9 forms a bridge whose one side is the insulated output of the DC-AC converter 8 (not shown), and the temperature can be set by adjusting the proportional side, and its operation is differential. The same operation as the comparison operation using an amplifier and a DC reference power source is performed in AC. 11 is an AC amplifier; 12 is a servo motor; the motor 12 is driven by the output of the AC bridge 9 amplified by 11;
5. Control the position of the thermocouple 1 via the protection tube 2. Reference numeral 13 denotes a position detection potentiometer, whose rotation shaft is connected to the motor 12, outputs the rotation angle of the motor 12 as a position of a sliding piece or a voltage value, and detects the position of the thermocouple 1; Displays the temperature stratification interface position. Note that 14 is a DC power source such as a DC amplifier 6.

In this way, by setting the detection part such as the thermocouple 1 in the reactor vessel, setting the detected temperature in the AC bridge 9, and operating the device at the same time as the reactor stops, the boundary of the given temperature can be detected. Can measure position.
That is, if the interface 15 shown in FIG. 2 is formed between the low-temperature liquid sodium 16 and the high-temperature liquid sodium 17 as described above due to the stoppage of operation, the thermocouple 1 is Servo motor 1 operated by the output
2, it moves to the boundary surface 15 having the set temperature. When the interface 15 rises as time passes, as shown by the dotted line in FIG. the thermocouple 1 is pulled up from within the cold liquid sodium layer 16 and positioned within the interface 15;
When the detected temperature reaches the set temperature, the servo motor 12
drive is stopped. Then, as the temperature stratified interface 15 rises due to cooling of the furnace, the above operation is repeated, the thermocouple 1 moves following the displacement of the interface 15, and the displacement detecting section connected to the motor 12 moves. The potentiometer 13 delivers a voltage output proportional to the rotation angle of the motor 12. Therefore, if this is recorded on recording paper using the self-recording recorder 18, for example, the displacement of the temperature stratification interface position caused by the high-temperature liquid sodium during the shutdown of the nuclear reactor can be accurately grasped automatically, continuously, and with a simple device. can.

Although the present invention has been described above with reference to an example using an AC servo mechanism, a well-known DC servo mechanism may be used if a decrease in detection stability can be tolerated. Further, although the case where liquid sodium is used as the cooling medium has been described above, the invention can also be applied to cases where other medium (for example, water) is used.

As is clear from the above explanation, according to the present invention, it is possible to continuously and automatically detect the movement of the temperature stratified interface that occurs when the reactor is shut down, especially in liquid sodium, which is the cooling medium of fast breeder reactors. This will greatly contribute to the elucidation of the influence of slope-based stress on the mechanical strength of the reactor vessel.

[Brief explanation of drawings]

1 and 2 are a circuit diagram of an embodiment of the present invention and an explanatory diagram of the mechanism of the detection section, and FIG. 3 is an explanatory diagram of the temperature distribution inside the furnace vessel when the furnace operation is stopped. A...Detection part, 1...Thermoelectric body, 2...Protection tube,
3... Protection tube holder, 4, 5... Gear, 6... DC amplifier, 7... Signal transmission line, 8... DC-AC converter, 9... AC bridge, 10... The alternating current, 11... AC amplifier, 12... Servo motor, 13... Potentiometer for detecting interface position, 1
4... DC power supply such as a DC amplifier, 15... Temperature stratified interface, 16... Low temperature liquid sodium layer, 17... High temperature liquid sodium layer, 18
...Recorder.

Claims (1)

[Scope of utility model registration request] A temperature sensor unit, a vertical mechanism thereof, and a temperature sensor unit that operates based on a difference between an output voltage of the temperature sensor unit and a voltage corresponding to a temperature within a selected temperature stratification interface, which is a set temperature, to control the vertical mechanism; A nuclear reactor comprising: a servo motor that positions the temperature sensor section within a temperature stratification interface; and a detector that detects the position of the temperature sensor section from rotation of the servo motor and sends out an output indicating the position of the temperature stratification interface. A device for detecting the temperature stratified interface position of a cooling medium.