RU2271045C1 - Moisture leakage checkup system for nps pipeline - Google Patents

Abstract

FIELD: checking nuclear power station equipment for leak tightness.

SUBSTANCE: proposed system designed for detecting leaks from pipelines carrying water coolant has device for air sampling and transport from air-penetrable heat insulation of pipeline under containment, passage in leak-tight shell of nuclear power station, and device for measuring air humidity incorporating humidity transducer and measuring-computing system; device for air sampling and transport from air-penetrable heat insulation of pipeline under containment is made in the form of pipe connection whose lower end is joined through shell hole with air-penetrable heat insulation of pipeline; air humidity measuring transducer is installed inside pipe connection in a spaced relation to inner side surface of pipe connection and is connected through electric passages by means of electrical communication lines to measuring-computing system.

EFFECT: enhanced speed of system response and reliability, enhanced safety of nuclear power station in operation.

6 cl, 5 dwg

Description

The invention relates to the field of monitoring the tightness of equipment of nuclear power plants (NPPs) and can be used to detect leaks from pipelines with a water coolant and equipment, as well as to control air humidity in other areas, for example, in the power system.

Known humidity control system for leakage of pipelines and equipment of nuclear power plants with PWR, developed by MGP Instruments, France (Nuclear Engineering International October 1993, pp.44-45, DOR No. 1354, IPPE, June 1994, Obninsk). The system consists of air sampling channels from the pressurized shell of nuclear power plants, hydrometer cells measuring the dew point of air samples. The tightness control of the equipment is carried out by the difference in the readings of various hydrometric cells located in the sampling systems, with the data of the cells located in the air of the containment.

The humidity system of MGP Instruments has several disadvantages - low sensitivity to the magnitude of the coolant leak and the determination of the coordinate of the leak, i.e. low sensitivity to the magnitude and location of the leak, and a noticeable dependence of the determination of the magnitude and location of the leak on operational factors, primarily on air pollution and the level of ionizing radiation. The low sensitivity of the MGP Instruments system to leakage is due to the accepted integral method of humidity control, in which it is difficult to predict the behavior of steam in the containment. The dependence of the readings on air pollution is based on the fact that the dew point condensation moisture sensors used are very sensitive to the cleanliness of their surface. The sensitivity of the system to the level of ionizing radiation is explained by the need to place electronic components directly near the pipeline, which is the source of ionizing radiation.

A well-known moisture monitoring system for monitoring the integrity of NPP equipment is included in the monitoring and diagnostics system of ALLY ™ equipment of Westinghouse USA (Integration of monitoring and diagnostics of nuclear power plants, Advertising project of Westinghouse, Copyright Westing-house Electric Company, 2000, p. 8) . This system is close in technical essence to the previously considered humid system from MGP Instruments. The dew point sensors of this humidity system are also installed on various air sampling lines. The dew point temperatures are processed by the data acquisition unit and converted to absolute humidity values.

The disadvantages of the Westinghouse ALLY ™ humidification system include low sensitivity to the magnitude of the detected leak, the dependence of humidity sensors on air purity, and the need to create special sampling lines. These shortcomings are due to the use of condensation humidity sensors and the accepted architecture of the humidity system.

The closest in technical essence and the functions performed to the claimed device is a humid leakage control system FLUES from Siemens. (Siemens brochure. Erkennung und Ortung von Leeks., Verfasser: Reinhard Marko, Sonderdruck aus Techische Ubemachung Heft, 6, 1990). The FLUES system contains a device for the selection and transportation of air (steam, vapor-air mixture) from the air-permeable pipe insulation closed by a casing (thermal insulation under the casing), and a device for measuring air humidity.

The FLUES system air sampling and transportation device consists of an air sampling hose (sensor hose), inlet and outlet hoses, two penetrations in the containment of the nuclear power plant and a compressed air supply module. The air sampling hose (sensor hose) is located along the controlled section of the pipeline under the insulation cover and is a hose in which, after 25 cm, there are porous inserts for diffusion (intake, selection) of steam from the insulation into the hose. At one end, the sensor hose is connected to the inlet hose, which is connected to the compressed air supply module through one of the two penetrations in the containment, from the other end, the sensor hose is connected to the exhaust hose, which is connected to the moisture measuring device through the second penetration (the penetrations allow the inlet hose to be inserted and withdraw the discharge hose through the containment of the nuclear power plant). In addition, the air transportation device contains modules located outside the pressurized shell of the nuclear power plant: a regulatory module that takes into account the mass flow rate of air, its temperature and pressure; valve modules that provide air supply control in measurement cycles; calibration module, which prepares a certain amount of moist air for supplying it to the hose to check the safety of the system characteristics over time; shut-off modules that allow in case of violation of the tightness of the air transport device to cut off the flow of radioactive air from the sealed enclosure to other rooms of the nuclear power plant.

The air humidity measuring device of the FLUES system includes a condensation type absolute humidity sensor and a measuring and computing complex located outside the pressurized shell of nuclear power plants.

The measuring and computing complex is used to convert the signal from the humidity sensor to the value of absolute air humidity, control the operation of the system, analyze air samples, determine the location and magnitude of the leak, and also display and store information.

The well-known humidity system FLUES operates as follows. Before starting the measurement cycle, the hoses are filled with clean, dry air using the compressed air supply module (blower). The moist air resulting from the leakage of the pipe diffuses from the thermal insulation through the porous inserts into the sensor hose. After about half an hour, air from the sensor hose is pumped through the outlet hose through a penetration in the containment to an air humidity measuring device located outside the sealed enclosure of the nuclear power plant. A device for measuring air humidity detects a change in air humidity at the moment of passing a localized bunch (portion) of moist air through the sensor and determines the location of the leak from the measured time interval from the start of air forcing to the portion of moist air to the device for measuring humidity. The leak value is calculated by comparing the system readings with the readings obtained from calibration measurements.

The main disadvantage of the prototype is that the technical characteristics of the FLUES system do not meet the requirements for monitoring the coolant leak within the framework of the “Leak before destruction” concept, which is currently adopted for nuclear power plants. (Guidance on the application of the Leak Before Destruction safety concept to the pipelines of nuclear power plants, R-TPR-01-99, Moscow, Russia, MAE PPI, 1999) Specifically, the system does not provide a determination of the magnitude and location of a leak with a leak value of ~ 3.8 l / min, adopted in this concept as a criterion that determines the possibility of continuing operation of the NPP pipeline. If the leakage exceeds the specified limit, it is necessary to shut down the NPP and carry out repair work on the pipeline.

It should be noted other, also significant, disadvantages of the system:

- the presence of significant "dead" time in the operation of the system, which is due to the cyclical nature of the system, which leads to a delay in information about the state of the monitored pipeline;

- introducing by the system an additional source of increasing the likelihood of depressurization of the pressurized shell of nuclear power plants — penetrations through the pressurized shell of nuclear power plants necessary for the input / output of hoses to the measuring and computing complex, i.e. reduced safety of nuclear power plants in general;

- lack of accuracy in determining the location of the leak, which is a consequence of the remoteness of the sensors of the device for measuring air humidity from the monitoring section of the pipeline;

- the use of a significant number of auxiliary mechanical devices (device for cleaning, drying and supplying compressed air, valve, shut-off devices, regulatory and calibration modules), which reduce the reliability of the system and increase its cost.

The main objective of the invention is to remedy these disadvantages, namely: increasing the upper limit of the recorded leakage, increasing the speed, reliability of the system and the safety of nuclear power plants in general, as well as reducing the cost of the system.

To eliminate the indicated drawbacks in the moisture control system of a NPP pipeline leak, which contains a device for selecting and transporting air from a breathable thermal insulation of a pipeline under a casing, penetrations in a pressurized NPP and a device for measuring air humidity, including a humidity sensor and a measuring and computing complex, it is proposed:

- a device for sampling air from breathable thermal insulation of the pipeline under the casing is made in the form of a pipe, the lower part of which is articulated through an opening in the casing with breathable thermal insulation of the pipeline;

- position the air humidity sensor inside the nozzle with a gap with respect to the inner side surface of the nozzle;

- in a device for measuring air humidity, use a relative air humidity sensor and an air temperature sensor as a humidity sensor;

- replace the penetrations for hoses in the containment of the nuclear power plant with penetrations for the electric communication lines (electrical hermetic penetrations);

- Relative humidity and air temperature sensors should be connected through electrical penetrations using electric communication lines with a measuring and computing complex.

In particular cases of using the system, the following is proposed:

firstly, install at least two pipes with sensors for relative humidity and air temperature in the controlled section of the pipeline;

secondly, to connect the lower end of the pipe with a hole in the insulation casing through a washer, the diameter of the passage section of which is less than the internal diameter of the pipe;

thirdly, additionally install thermal insulation on the outer side surface of the pipe;

fourthly, in the measuring and computing complex to realize the technical ability to determine the magnitude and location of the leak, both by changing the measured values of relative humidity and air temperature, and by changing the calculated value of the absolute humidity.

A comparative analysis of the proposed system with the prototype shows that it has significant differences both in the device for selecting and transporting air from thermal insulation, and in the device for measuring humidity.

Firstly, in the FLUES device, the active principle of transporting air (using a blower) is used, in the claimed one - passive, using the natural temperature difference between the air in the pipe insulation and the air in the containment of the nuclear power plant.

Secondly, in the claimed technical solution, the measurement of air parameters is carried out continuously, and not cyclically, as in FLUES. The lack of cyclicality in the operation of the device for the selection and transportation of air is the basis for the speed of the proposed system, so we can say that the system works almost in real time.

Thirdly, the exclusion from the device for the selection and transportation of air in the inventive system of a number of auxiliary devices increased the reliability of the system as a whole and reduced its cost.

Fourth, the replacement of penetrations in the pressurized shell of nuclear power plants for the inlet and outlet hoses of the FLUES system with electric leakages in the proposed system, due to the higher operational characteristics of the latter, significantly reduced the likelihood of depressurization of the pressurized shell of the NPP due to the fault of the moisture control system for pipeline leaks, which increases the safety of the NPP as a whole .

Fifthly, the replacement of the absolute humidity sensor with relative air humidity sensors and air temperature sensors allowed replacing the FLUES modular air humidity measuring device with a spatially distributed device. (In the proposed system, the relative humidity sensors and air temperature sensors are located directly on the monitored section of the pipeline in the containment of the nuclear power plant, and the rest of the humidity measuring device (measuring and computing complex) is located outside the containment of the nuclear power plant). This made it possible to exclude the inlet and outlet hoses of the FLUES system, which reduced the path of the steam-air front to the sensors and thereby improved the safety of the boundaries of the steam-air front going to the sensors, and, ultimately, made it possible to obtain better accuracy in determining the magnitude and location of the leak.

Sixth, by the totality of the proposed technical solutions, the required measurement range of the coolant leak has been achieved, satisfying the concept of “leak before failure”, which does not allow the technical characteristics of the FLUES system.

The technical results of this invention are:

- increase system performance, i.e. reduction in the value of "dead time";

- a more accurate determination of the location of the leak;

- increase the reliability of the system;

- achieving the required measurement range of the leak;

- reducing the likelihood of depressurization of the containment of nuclear power plants.

The essence of the proposed technical solution is illustrated by drawings, in which Fig. 1 shows a schematic diagram of a humidity control system for a leak of a monitored section of a pipeline of an NPP with three devices for selecting and transporting air with sensors for relative humidity and air temperature in a monitored section of a pipeline, and Fig. 2 is a schematic diagram design options for the nozzle with a washer and additional thermal insulation, figure 3, 4 and 5 show the experimental dependence of the relative moisture NOSTA and temperature and calculated from the measured values of the absolute humidity in the installation locations of sensors in time when leakage coolant flow rate ~ 3.8 L / min.

In figures 1 and 2, the following designations are adopted: 1 - breathable thermal insulation of the pipeline; 2 - sensor of relative humidity; 3 - air temperature sensor; 4 - measuring and computing complex; 5 - casing of thermal insulation of the pipeline; 6 - electric communication lines; 7 - pipe; 8 - electric penetrations; 9 - pipe insulation; 10 - pipeline (pipeline walls); 11 - washer.

The proposed moisture control system for a leak in an NPP pipeline contains a device for selecting and transporting air from breathable thermal insulation of a pipeline, and a device for measuring air humidity.

The device for the selection and transportation of air from breathable thermal insulation 1 of the pipeline 10 consists of a pipe 7, articulated by the lower end with an opening in the casing of the thermal insulation of the pipeline 5. The humidity measuring device contains a relative humidity sensor 2, an air temperature sensor 3, electrical communication lines 6, electrical penetrations 8 and measuring and computing complex 4.

The system operates as follows. The system constantly measures the relative humidity and temperature and calculates the absolute humidity in the places where the sensors are installed (in pipes 7). In the absence of leakage through the wall of the pipeline, the air temperature in the places where the sensors are installed significantly exceeds the air temperature in the sealed shell of the nuclear power plant. As a result, the relative air humidity at the sensor installation sites (in nozzles 7) is low (dry air) and the measured air parameters (relative humidity and temperature) are constant or slowly change in time, and the law of change is the same for all control points. In the presence of a pipeline leak, the generated steam, due to overpressure, propagates from the leak (see FIG. 1) to both sides through breathable thermal insulation of pipeline 1. Some of the steam through the nozzles 7 enters the environment (into the containment of the nuclear power plant). This leads to an increase in humidity and air temperature in the nozzles 7. Changed parameters of the air in the nozzles are recorded by sensors of relative humidity 2 and air temperature 3, the signals from which are sent through the electric communication lines 6 through electric penetrations 8 to the measuring and computing complex 4.

In the measuring and computing complex 4, the absolute humidity is determined from the measured relative humidity and air temperature. The dynamics of changes in air parameters (measured by relative humidity and air temperature and calculated absolute air humidity) determines the fact of a pipeline leak. When installing at least two branch pipes with sensors spaced along the length of the monitored section of the pipeline and knowing the coordinates of the sensors on the monitored section of the pipeline 10, the measuring and computing complex 4 determines the leakage coordinate and its value using the model of vapor distribution along the length of the breathable thermal insulation of pipeline 1.

Figure 2 shows a design diagram of an air transport device, which is characterized by the presence of a washer 11 installed between the hole in the casing of the pipe insulation 5 and the lower end of the pipe 7 and the presence of additional insulation 9 on the outer side surface of the pipe 7.

The main function of the washer 11 is to configure the system to reliably record leaks at levels that meet the requirements of the "leak before failure" concept. The function of thermal insulation 9 on the nozzles 7 is reduced to the creation of temperature conditions in the nozzles, in which moisture condensation is excluded in a given range of leak control.

In support of the system’s operability, FIGS. 3 and 4 show the corresponding experimental dependences of the relative air humidity φ _I , φ _II , φ _III and air temperature T _I , T _II , T _III obtained in a model of the pipeline of the primary circuit of the VVER-1000 reactor in time in places placement of sensors of relative humidity and air temperature during a coolant leak with a flow rate of 3.8 l / min. Figure 5 shows the corresponding dependencies of the absolute air humidity ρ _I , ρ _II , ρ _III in time calculated on the basis of experimental data. From the dependencies shown in FIGS. 3, 4, 5, it can be seen that changes in air parameters at the sensor installation sites during a coolant leak with a flow rate of 3.8 l / min are significant and they occur at different points in time, which depend on the remoteness of the sensors from the leak. The obtained dependences make it possible to reliably fix leaks at levels that satisfy the requirements of the “Leak Before Destruction” concept.

The described technical solution is industrially applicable and can find application in the control of power equipment with a water coolant in nuclear energy and heat power engineering.

Claims (6)

1. A humidity control system for a leak in a nuclear power plant pipeline, comprising a device for sampling and transporting air from a breathable thermal insulation of a pipeline under a casing, penetrations in a pressurized shell of a nuclear power plant, and a device for measuring air humidity, including a humidity sensor and a measuring and computing complex, characterized in that the device for sampling and transporting air from the breathable thermal insulation of the pipeline under the casing is made in the form of a pipe, the lower end of which is articulated through an opening in the casing with an airprot due to thermal insulation of the pipeline, a sensor for measuring air humidity is installed inside the nozzle with a gap with respect to the inner side surface of the nozzle and is connected through electrical penetrations by electric communication lines to the measuring and computing complex. 2. The system according to claim 1, characterized in that at least two nozzles with humidity sensors are installed on the controlled section of the pipeline. 3. The system according to claim 1, characterized in that the relative humidity sensor and the air temperature sensor are used as a humidity sensor. 4. The system according to claim 1, characterized in that the lower end of the pipe is connected to the hole in the casing of the insulation through the washer, and the diameter of the passage of the washer is less than the inner diameter of the pipe. 5. The system according to claim 1, characterized in that on the outer side surface of the pipe additionally installed insulation. 6. The system according to claim 1, characterized in that the measuring and computing complex has the technical ability to determine the magnitude and location of the leak, both by changing the measured values of relative humidity and air temperature, and by changing the calculated absolute humidity.

Images