JPS62137590A - Water-level monitor device for nuclear reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a core monitoring device for a nuclear reactor, and more particularly to a water level detection device suitable for monitoring the core water level in the event of an accident in which coolant is lost.

[Conventional technology]

As a means of detecting the water level in the reactor core tube during a nuclear reactor accident, as described in JP-A-59-112290, a thermocouple is mounted inside a long cylindrical body such as reactor neutron detection piping. There is a method of installing multiple thermocouples in different directions and determining the water level based on the output difference between the thermocouples. This device detects the water level in the reactor core shroud using the principle that if the output difference between the thermocouples is approximately O, the reactor water level is higher than the upper thermocouple.

[Problem that the invention seeks to solve] The above-mentioned conventional technology has a relatively simple mechanism.

If the temperature of the coolant is not uniform, there is a risk of incorrect determination. Monitoring the water level in the core shroud becomes important in the event of an accident such as loss of coolant, in which case the emergency core cooling system is activated.

Cooling water with a large degree of unsaturation is supplied to the inside of the reactor core 7, particularly to the core bypass section, and a salinity distribution is likely to occur in the cooling water. In this case, it becomes difficult to judge the water level, and in reality, 2
Even though the water level is above two thermocouples, it may be determined that the water level is between the two thermocouples, or vice versa. Therefore, this device has the problem of misjudging the water level when an accident occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a device that can monitor the water level without making erroneous judgments even if the temperature of the cooling water becomes uneven during a coolant loss accident.

[Means for solving problems]

The above object is achieved by utilizing the magnitude relationship between the temperature indicated by one temperature measuring section installed in the furnace and the saturation temperature corresponding to the pressure inside the furnace.

In the present invention, a temperature measuring section is attached to the reactor internals (and a device for measuring the pressure inside the pressure vessel and an arithmetic device for calculating the saturation temperature corresponding to the pressure from the pressure,
A device is provided to compare the thermocouple temperature and the saturation temperature, and the position of the liquid level is determined from the magnitude relationship.

[Effect]

In the present invention, a thermocouple attached to the reactor internals indicates the temperature of the coolant it is in contact with when it is below the liquid level. However, if the thermocouple is exposed to steam,
The temperature of the thermocouple is usually higher than the saturation temperature. This is because it receives heat radiation due to radiation and is affected by the temperature of the structure due to heat conduction. Compare the saturation temperature obtained from the pressure with the thermocouple temperature, and if the thermocouple temperature is higher than the saturation temperature, it is determined that the liquid level is below the thermocouple position, and conversely, if it is equal to or lower than the saturation temperature, determines that the liquid level is above the thermocouple position.

Figure 4 shows an example of temperature measurements from a thermocouple installed in the reactor core bypass in an experiment simulating a loss of coolant accident in a nuclear reactor. The present invention will be explained in detail with reference to this figure. Five thermocouples were installed in the height direction. As the coolant flows out, the pressure decreases and the saturation temperature also decreases. The core bypass temperature was unsaturated in steady state, but became saturated in about 10 seconds as the saturation temperature decreased. 1 in about 60 seconds
The temperature of the specific thermocouple ■ installed at the top exceeds the saturation temperature, and the
At 0 seconds, the temperature of the third thermocouple ■ also exceeds the saturation temperature. In this experiment, a differential pressure gauge was used to measure the water level in the core bypass section for comparison, but the water level determined by the core bypass water level measurement value by the differential pressure gauge and the temperature measured by the thermocouple exceeding the saturation temperature. is compatible. Also after 150 seconds.

Since unsaturated emergency core cooling water is being injected, the temperature at the measurement points will vary, but all parts immersed in the liquid will be below the saturation temperature. Even when the temperature of the coolant is not uniform, by comparing the saturation temperature and the measured value,
It can be determined whether the measurement point is above or below the liquid.

Furthermore, in an actual nuclear reactor, a thermocouple exposed in steam receives heat radiation from radiation, and thus exhibits a temperature higher than the saturated steam temperature, that is, the saturated temperature.

Therefore, even when the pressure increases and the saturation temperature increases,
By comparing the temperature of the thermocouple and the saturation temperature, /1!
It can be determined whether it is above the surface or not.

According to the present invention, the saturation temperature is determined only by pressure and is not affected by water temperature, so if the thermocouple temperature can be measured accurately, there is no problem of misjudging the water level even if there is a temperature distribution in the coolant. .

〔Example〕

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A water level monitoring device for a nuclear reactor according to the present invention will be explained below with reference to an embodiment shown in FIG. FIG. 1 is a longitudinal sectional view when the present invention is applied to a jet pump type boiling water reactor. In the figure, 1 is a pressure vessel, 3 is a core shroud wall, 4 is an upper core support plate, and 5 is a lower core support plate. It consists of a portion surrounded by a lower core support plate 5 and a core shroud wall 3, a fuel assembly 2 constituting the core, and a core bypass 15. Since the fuel assembly 2 constitutes a plurality of independent flow paths, the liquid level may take a different value depending on each assembly, or the liquid level 12i-
t takes a substantially constant value in the radial direction. In the present invention, a plurality of thermocouples 20 are installed on the surface of the temperature instrumentation tube 16. A compensation conductor 21 is connected to the thermocouple 20, and a temperature compensation circuit 22 is connected to the thermocouple 20.
to calculate the temperature at the measurement point.

On the other hand, the pressure in the steam dome 1O is measured by the pressure gauge 24, and the calculation device 25 calculates the saturation temperature corresponding to the pressure.

This saturation temperature and the temperature at the measurement point are compared by the calculation device 7, and if the 1jllj constant value is smaller than the saturation temperature or the flow rate is the same, it is determined that the liquid level is above the temperature measurement point, and conversely, the measurement point is If the point is higher, it is determined that the liquid level is below the temperature measurement point. By installing a plurality of measurement points in the height direction, it is possible to track changes in the liquid level 12 of the core bypass 15 over time.

FIG. 2 shows a cross-sectional view of a thermocouple added to the temperature instrumentation tube. A sheath type thermocouple is used as the thermocouple. 7-su31
has a cylindrical shape, and a pair of thermocouple wires is placed inside it. As the thermocouple wire, for example, chromel 32 and alumel 33 can be used.

A thermal junction 34 is formed near the tip of the chromel 32 and alumel 33 sheath 31, and the temperature is measured at this thermal junction. The sheath 31 and the thermocouple wire are insulated with an insulating material 35.

The thermocouple protrudes from the wall of the temperature instrumentation tube 16 so that the outer core bypass temperature can be measured. In addition, a cover 37 is provided to prevent direct contact with emergency core cooling water injected from above the thermocouple.

FIG. 3 shows another embodiment in which the present invention is applied to a boiling water reactor using an internal pump.

In this embodiment, a plurality of thermocouples were installed inside the core shroud wall 3 in the height direction. The pressure in the steam dome is measured, the saturation temperature for the pressure is calculated, and the comparator 26 compares it with the temperature at the temperature measurement point. The results are as shown in Figure 4, the shape of the graph of Kff 1 degree and the needle hanging above the liquid level.
It is displayed on the display device 27 in the form of 1st cost, etc.

In the present invention, since the thermocouple is constantly exposed to radiation, deterioration such as a shift in measured values occurs. However, since the saturation temperature based on the pressure group constant does not change, by correcting the thermocouple temperature during normal operation with respect to this temperature, it is possible to operate accurately in the event of an accident.

The present invention is also applicable to pressurized water reactors.

〔Effect of the invention〕

As described above, one of the water level measuring devices of the present invention is as follows.

The water level inside the reactor at the time of an accident can be accurately measured with a simple structure. As a result, even in the event of a nuclear reactor accident, information regarding the water level in the reactor core shroud can be provided to operators, thereby preventing erroneous judgments and erroneous operation of the emergency core cooling system (ECC5). As a result, the safety of the nuclear reactor is improved.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a nuclear reactor showing an example of a water level monitoring device;
FIG. 2 is used in the present invention. @The installation of the electric couple is shown in the figure, and Figure 3 is an explanation of another embodiment of the nuclear reactor according to the present invention, a clear diagram, and the fourth factor f'! , is a diagram showing the relationship between temperature and time. 1... Pressure vessel, 2... Fuel assembly that constitutes the reactor core, 3... Reactor IL? Shroud wall, 4... Upper core support plate, 5... Lower core support plate, 6... Jet pump, 7... Recirculation system piping, 8... Recirculation pump, 9
...Lower plenum, 10...Steam dome, 11...
・Separator, 12... Water surface, 13... Downcomer, 14... Internal pump, 15... Core bypass, 16... Neutron detection piping, 20... Thermocouple, 21... Compensation conductor, 22...temperature compensation circuit, 24
...Pressure gauge, 25...Saturation temperature calculation device, 26...
・Ratio 1! ! 2 device, 27... display device, 31... sheath, 32... chromel, 33... alumel, 3
4...Thermal junction, 35...Insulating material, 36...Temperature measurement tube, 37 Agent: Patent attorney Okikata Ogawa, -Niso No. 1
Figure 16-1 Temperature instrumentation tube 20-- S'Ahma We static 24-11 Pressure pipe

Claims (1)

[Scope of Claims] 1. One or more temperature measurement units installed on the inner wall of the reactor vessel or a structure within the reactor vessel, a device that receives a signal from the temperature measurement unit and calculates the temperature, and a pressure vessel. It is equipped with a device that measures the pressure inside the liquid and a calculation device that calculates the saturation temperature corresponding to the pressure from the pressure.If the temperature of the temperature measurement part is higher than the saturation temperature, the temperature measurement part is A water level monitoring device for a nuclear reactor, characterized in that it determines whether the water level is 2. The water level monitoring device for a nuclear reactor as set forth in claim 1, wherein the temperature measuring section is composed of a thermocouple.