JPS63173921A - Apparatus for measuring quality of steam - Google Patents

Abstract

PURPOSE:To accurately measure the presence of ebullition and the quantity of steam at the time of ebullition, by performing the confirmation of the ebullition point of high temp. and high pressure water and the measurement of the quality of steam from the measurement of the signal intensity between a pair of monitor windows. CONSTITUTION:The transmitting sensor 15 connected to a transmitter 14 for sending an optical signal is arranged on the lateral side of one of the monitor windows 13 of a test tank vessel 1, and the receiver 16 receiving the optical signal and a receiving sensor 17 are arranged on the lateral side of the other monitor window 13. The transmitting and receiving data of both sensors and data of temp., pressure or the like are sent to a computer 19 through an interface 18. The quantity of the steam in the two-phase stream of high temp. and high pressure steam can be continuously calculated by the computer 19.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a steam quality measuring device that measures the amount of steam bubbles in a two-phase flow of water and steam bubbles and calculates steam quality.

"Prior Art" In a boiling water reactor (BWR), steam from a steam turbine is preheated by a feed water heater, and this preheated feed water is brought into the reactor via a jet pump. The temperature at the outlet of the feed water heater varies depending on the furnace type, but is approximately 200°C.
It is before and after.

High-temperature, high-pressure water (approximately 70 kg/cm") from the outlet of the feedwater heater is forcedly circulated from the bottom to the top of the reactor core. During this circulation, the UO □
Heat is transferred from pellets (nuclear fuel) etc. through Zircaloy cladding.

High-temperature, high-pressure water brought into the vicinity of the reactor core at a temperature of about 200°C generates bubbles on the surface of the fuel cladding tubes at a distance of approximately 4 m while passing through the reactor core while rising, and begins to boil. The upper part of the reactor core is designed to have a steam quality of 20 to 30%, and this steam quality refers to the proportion (weight ratio) of steam in a two-phase flow of steam and water. This steam passes through a steam-water separator at the top of the reactor pressure vessel and is carried by a steam line to a steam turbine, which rotates the turbine and generates electricity.

In this way, the Zircaloy cladding that covers nuclear fuel is exposed to a variety of environments, including coming into contact with a variety of fluids, from high-temperature, high-pressure water to two-phase fluids where the vapor quality varies depending on the location. has been done.

By the way, in BWR plants, as a source of radioactivity,
In some cases, corrosion products brought in from the water supply system adhere to the surface of the fuel assembly and become activated, and in others, the reactor internal structures in the neutron irradiation field are directly activated.

In this way, the phenomena of adhesion, activation, and re-release of corrosion products occur on the surface of the Zircaloy cladding tube, and these phenomena are closely related to the heat flux, boiling state, and concentration of corrosion products of the fuel. , elucidating these mechanisms is an important academic theme. Furthermore, since the release process of corrosion products is one of the main parameters that determines the radioactivity concentration in the primary system, it has become an issue that cannot be overlooked from the perspective of reducing radioactivity.

Therefore, in recent years, in order to elucidate these mechanisms, a device has been created that can simulate the boiling surface condition of heated water by creating a simulated fuel pin using an electric heater.

"Problems to be Solved by the Invention" However, in these devices, boiling and boiling start point are calculated thermally. For example, with such equipment, the boiling start point varies sensitively due to changes in outside temperature, power supply voltage, etc., and it is difficult to accurately determine the position of the boiling start point. Furthermore, the steam quality on the downstream side where the flow has become a two-phase flow is similarly determined by calculation, and there is a problem in that there is no way to measure whether or not this corresponds to reality.

The present invention has been made in consideration of the above-mentioned facts, and an object of the present invention is to provide an apparatus that can determine whether or not boiling occurs in high-temperature, high-pressure water containing steam, and accurately measure the amount of steam at that time. The purpose is

"Means for Solving the Problem" In order to achieve the above object, the steam quality measuring device according to the present invention includes a monitoring window for monitoring the measurement water, and a certain type of optical signal in the monitoring window. It has a signal generator for transmitting the signal and a signal receiver for receiving the signal passed through the measurement water, and from the signal strength of the signal generator and signal receiver, it is possible to determine whether This is a device that continuously measures the amount of steam flowing into the tank.

"Embodiment" An embodiment of the present invention will be described below based on the drawings. FIG. 1 is a schematic diagram showing a state in which an embodiment of the steam quality measuring device according to the present invention is applied to a device capable of simulating the boiling state on the surface of BWR nuclear fuel.

The test tank vessel 1 has a vertical cylindrical shape and is in a sealed state, and inside the test tank vessel 1, high temperature and high pressure gas is supplied from the supply pipe 2 at the bottom and discharged from the discharge pipe 3 at the top. Water 4 is forcedly circulated. This test tank vessel 1 is equipped with a thermometer 5 that measures the temperature of high-temperature, high-pressure water 4, and an oscillation type pressure gauge 6 that measures the pressure.

At the center of the test tank vessel 1, a simulated fuel pin 7 is arranged vertically. The simulated fuel pin 7 is constituted by an electric heater in which a coil-shaped heating element 11 is embedded in a heat insulating material 9 within a Zircaloy cladding tube 8, as shown in FIG. This simulated fuel pin 7 simulates a fuel pin by replacing the nuclear heating in the BWR with heating by an electric heater.

Horizontal lead-in pipes 12 are formed at appropriate positions on the circumferential surface of the test tank vessel 10 at approximately symmetrical positions, and monitoring windows 13 are provided at the closed portions of the end faces of the lead-in pipes 12, respectively. BWR
Under these temperature and pressure conditions, the monitoring window 13 is made of a light-transmissive material such as a ruby single crystal, and by doing so, the range of choices for the monitoring window 13 can be expanded. For example, quartz has high light transmittance, but BWR,
Although there is a problem of gradual elution under the temperature and pressure conditions of , it becomes possible to use quartz with the above structure.

On one side of the monitoring window 13 of the test tank vessel 1 having such a structure, there is a transmission sensor 15 connected to a transmitter 14 that sends an optical signal, and on the other side of the monitoring window 13 there is an optical signal. A receiver 16 and a reception sensor 17 for receiving signals are respectively arranged.

As an optical signal, white light with various wavelengths, monochromatic light with a short wavelength, laser light, etc. can be used, and this optical signal passes near the circumferential surface of the test chamber vessel 1. ing. -1 Further, all of these transmitted/received data, temperature, pressure, etc. data are sent to the computer 19 via the interface 18. In the vapor quality measuring device having such a structure, an optical signal is sent continuously or in pulses from the transmitting sensor 15, and is received by the receiving sensor 17, and the intensity of the optical signal is measured.

The high-temperature, high-pressure water brought into the test tank vessel 1 by forced circulation receives heat from the simulated fuel pin 7, and when the high-temperature, high-pressure water is heated to a temperature higher than the saturation temperature at the pressure detected by the pressure gauge 6, the simulated Bubbles are generated on the surface of the fuel pin 7 and boiling gradually begins. The amount of steam is the test tank vessel 1.
It increases as you move upwards and has a certain distribution from the boiling point.

Using the steam quality measuring device formed in this manner, first, pure water is forcedly circulated in the test tank vessel 1, and changes in the signal strength of the receiver 16 in response to changes in pressure are measured, as shown in FIG. You will get a result like this. In Figure 3, the vertical axis is (reception strength / (transmission strength 1o) x 100
The reason why this value is not 100 is due to the absorption of light in pure water under atmospheric pressure and the system error of the device. As the pressure of the measurement system increases, the density of water increases, and the proportion of light absorbed between the circulation paths of the high-temperature, high-pressure water 4 increases, reducing the reception intensity of the receiver 16.

For example, the simulated fuel pin 7 is heated while deionized water is forcibly circulated at atmospheric pressure to gradually boil at the position of the monitoring window 13, and the change in reception intensity at this time is shown in FIG. First, the value of the thermometer 5 increases as the output of the simulated fuel pin 7 increases, and at the boiling point, the saturation temperature at atmospheric pressure (
100°C) and there is no temperature change thereafter.

On the other hand, the intensity of the optical signal is constant until the boiling start point, and after that point, gas phase components exist due to bubble generation, and the intensity of the optical signal tends to increase. it is,
This is because the absorption of optical signals in the gas phase is negligible compared to that in the liquid phase, and the amount of the gas phase increases as the amount of bubbles increases. Furthermore, simulated fuel pin 7
When the output of the optical signal is increased, it will eventually become all vapor, and the intensity of the optical signal will again show a constant value.

Next, a method for calculating steam quality will be described.

For example, assume the state at point A of the intensity conversion of the optical signal in FIG. Here, the condition is that the volume ratio of water and steam is 1=1. Since the specific gravity of water and steam at a temperature (100° C.) has been measured, the volume is converted into a weight ratio to obtain the steam quality value.

Similarly, a diagram similar to that in FIG. 4 is obtained under the BWR pressure conditions (70 to 80 atm). However, in this case, the generated bubbles are crushed by the pressure in the atmosphere and become smaller in diameter, so the increase in the intensity of the optical signal after the start of boiling is small compared to atmospheric pressure. However, even with this slight amount of change, by introducing the combinator 19, the water/steam volume ratio can be determined and the steam quality can be calculated accurately.

In this way, by storing the specific gravity of water and steam at the saturation temperature in the target pressure range in the computer 19, performing a series of boiling tests, and dividing the amount of change in the intensity of the optical signal into equal parts, , the steam quality in each can be calculated instantaneously. In addition, when measuring the boiling start point in a high-pressure system, it is difficult to confirm boiling with the naked eye due to the small diameter of the generated bubbles, but with the steam quality measurement device of the present invention, boiling can be easily detected. can.

In the above embodiment, the case where there is one simulated fuel pin 7 for heating has been described, but it is also possible to arrange two simulated fuel pins 7 in parallel and pass an optical signal between them. It is possible.

"Effects of the Invention" As explained above, according to the steam quality measuring device according to the present invention, the boiling point of high-temperature, high-pressure water can be recognized and the steam quality can be measured by measuring the signal strength between a pair of monitoring windows. It can be carried out. Furthermore, the use of this measuring device will greatly contribute to the elucidation of the mechanisms of attachment, activation, and release of corrosion products on the boiling surface of the Zircaloy cladding in BWR fuel rods.

In addition, it is possible to measure the phenomenon that is often seen in general boilers, where scale adhesion to pipes makes heat transfer difficult and the boiling start point changes, and can be used as a guide for the boiler cleaning period. is also possible.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing a state in which an embodiment of the steam quality measuring device according to the present invention is applied to a device capable of simulating the boiling state on the surface of BWR fuel, and Fig. 2 is a longitudinal section showing an example of a simulated fuel pin. The side view, Figure 3 is a correlation diagram between the received strength of the optical signal and the water pressure, and Figure 4 shows the relationship between the temperature change of water under atmospheric pressure and the received strength of the optical signal, and the output of the fuel pin. FIG. 1...Test tank Heracel, 4...High temperature and high pressure water, 5...Thermometer, 6...Oscillating pressure gauge, 7... - Simulated fuel pin, 8...Zircaloy cladding tube, 9...Insulating material, 11...Heating element, 12...Leading pipe, 13... ...Monitoring window, 14...Transmitter, 15...Transmission sensor, 16...Receiver, 17...Reception sensor, 18... ...Interface, 19...Computer, ■...Reception strength, Io...Output strength. Applicant: Japan Atomic Energy Corporation, Agent

Claims (1)

[Claims] A test tank vessel in which a simulated fuel pin for heating is placed in the center and high-temperature, high-pressure water is forcibly circulated, and the high-temperature, high-pressure water inside the test tank vessel is monitored. A pair of monitoring windows are provided on each symmetrical side, a signal generator for sending appropriate optical signals from one of the monitoring windows, and a signal generator that transmits the signal passed through high temperature and high pressure water to the other monitoring window. and a thermometer and a pressure gauge for respectively measuring the temperature and pressure of the high-temperature, high-pressure water, and from the respective signal strengths of the signal generator and the signal receiver, A steam quality measuring device characterized by continuously measuring the amount of steam in a phase flow.