RU2584134C1 - Radiation system for monitoring leaks in pipeline of npp with water coolant - Google Patents

Abstract

FIELD: physics; nuclear physics.

SUBSTANCE: invention relates to monitoring nuclear power plant with water heat carrier. System contains a complex of measurement of activity of the analysed medium, including radioactive radiation sensor (6) and device for sampling and transportation of analyzed medium to radiation sensors (6), and information-computing device (10). On each controlled section of pipeline (1) there are additionally installed at least two complexes for measurement of activity of the environment, including radiation sensors (6), which is selectively sensitive to radiation of nitrogen-16. Radiation sensors (6) are located along the whole length of the pipeline (1) at known distances. Device for sampling and transportation of analyzed medium is made in the form of branch pipes (5) passing through the heat insulation (2) of the pipeline (1). Some ends of nozzles (5) are brought in sub-insulation space (4) of the pipeline (1), and the other ends of nozzles (5) are brought to radiation sensors (6). Location and mass flow rate of leak are determined by readings of the involved complexes measuring activity of nitrogen-16.

EFFECT: high accuracy of determining location and mass flow rate of leak.

1 cl, 1 dwg

Description

The invention relates to the technological control of nuclear power plants with a water coolant and can be used to detect, localize and determine the magnitude of a coolant leak from pipelines of the primary circuit.

The known system considered in the article "Development of a radiation monitoring system for coolant leakage from the primary circuit of a WWER-type reactor" (Hydrodynamics and safety of NPPs / Abstracts at the industry conference "Thermophysics-99. - Obninsk, 1999).

The system includes measuring channels, devices for selecting and transporting air from a controlled room to radiation sensors. A diagnostic sign of a leak in the main circulation circuit pipeline with a water coolant is the detection of gaseous products of activation of a coolant in a controlled volume, such as nitrogen-13, nitrogen-16, or fluorine-18. The system with the help of a device for selecting and transporting air from a controlled volume directs it to the detection module. The magnitude of the activity of the gaseous activation products in a controlled volume depends on the magnitude of the coolant leak and the reactor power. Detection of a gaseous product of activation of a coolant in a controlled volume is recognized as a fact of detecting a coolant leak. The leakage value is determined based on the measured volumetric activity of the isotope and knowledge of its concentration in the coolant.

A disadvantage of the known system is that it determines the location of a pipeline leak with an accuracy of up to 10 m for the length of the controlled section of the pipeline. This is due to the fact that some of the controlled isotopes have a relatively short lifetime (nitrogen-16 - 7.11 c) and they disintegrate during transportation through this pipeline to the installation site of the activity measurement complex.

The closest in technical essence to the claimed system is the system considered in the work “Automated system for detecting a coolant leak by volumetric activity of aerosols” (Radiation and technological control systems and equipment. Product catalog of NPP RADIKO LLC, Issue 1, 2011).

The system contains complexes for measuring the volumetric activity of the air environment of rooms, each of which includes a radioactive radiation sensor, a module for processing sensor signals, a device for sampling and transporting air samples from the leak zone to the sensor, and an information and computing device that provides collection, processing, storage, and presentation information.

The operation of the system is as follows. The system takes air samples from the controlled room and transports it through a long pipeline to the installation site of sensors for measuring air volumetric activity. Based on the results of measurements of the surface activity of the filter and the volume of air passing through it, the volumetric activity of the incoming air is determined, and in the case of a statistically significant deviation of this activity from the norm, a conclusion is made about the presence of a coolant leak and its value is estimated.

The disadvantage of the system is the relatively large uncertainties in determining the location and mass flow rate of the leak. The system determines the location of the leak accurate to the size of the room in which the controlled equipment is installed. The error in determining the magnitude of the leak occurs due to the absence of a strict relationship between the magnitude of the leak and the volume activity of aerosols. Aerosol activity depends on the radiation state of the core, the number of fuel rods with defective cladding in the core, and the size of the defects. Since the process of fission products entering the coolant is a random process, this circumstance does not allow us to unambiguously relate the total volumetric activity of the recorded aerosols to the amount of coolant leak.

The objective of the invention is to eliminate this drawback, namely reducing uncertainty in determining the location and mass flow rate of a leak.

The technical result of the invention is improving the accuracy of determining the location and mass flow rate of the leak.

To eliminate this drawback in the radiation control system for a leak of a nuclear power plant pipeline with a water coolant containing a complex for measuring the activity of the analyzed medium, including a radioactive radiation sensor and a device for selecting and transporting the analyzed medium to the sensor, and an information and computing device, it is proposed:

- at each controlled section of the pipeline, additionally install at least two complexes for measuring the activity of the analyzed medium, including radiation sensors that are selectively sensitive to nitrogen-16 radiation;

- arrange radiation sensors along the entire length of the pipeline at known distances;

- devices for the selection and transportation of the analyzed medium to perform in the form of nozzles passing through to the thermal insulation of the pipeline;

- bring some ends of the pipes into the insulating space of the pipeline, and bring other ends of the pipes to the radiation sensors;

- the information-computing device should be equipped with software for determining the location and mass flow rate of the leak according to the combined readings of the involved complexes for measuring nitrogen-16 activity.

The invention is illustrated by the scheme of the radiation monitoring system for a coolant leak and the image of the monitored section of the pipeline, where the following notation: 1 - pipeline; 2 - thermal insulation; 3 - coolant; 4 - insulating space; 5 - pipe; 6 - radiation sensor; 7 - cable communication line; 8 - signal processing module; 9 - information communication line; 10 - information computing device.

The radiation monitoring system for the leakage of a nuclear power plant pipeline with a water coolant contains at least three complexes for measuring the activity of the analyzed medium installed on each controlled section of the pipeline 1, a device for selecting and transporting the analyzed medium to the sensor, and an information-computing device 10.

Each complex for measuring the activity of the analyzed medium includes a radioactive radiation sensor 6, which is selectively sensitive to nitrogen-16 radiation.

The radiation sensors 6 are located along the entire length of the pipeline 1 at known distances.

The devices for the selection and transportation of the analyzed medium are made in the form of nozzles 5 passing through heat insulation 2 of pipeline 1. Some ends of the nozzles 5 are led into the insulating space 4 of the pipeline 1, and the other ends of the nozzles 5 are led to the radiation sensors 6.

Information and computing device 10 is equipped with hardware for software to determine the location and mass flow rate of the leak according to the combined readings of the involved complexes for measuring the activity of nitrogen-16.

In the radiation sensors 6 used the Vavilov-Cherenkov effect. The radiation sensor 6 has a lower threshold for detecting beta radiation in excess of 6.13 MeV.

The signal processing module 8 has a function of receiving signals from a radioactive radiation sensor 6 and issuing a digitized signal proportional to nitrogen-16 activity at the output.

Electrically connect the output of the radiation sensor 6 with the input of the signal processing module 8, located at a distance from the radiation sensor 6.

The radiation sensor 6, the signal processing module 8 and the cable communication line 7 form the measuring channel of the system.

The outputs of the measuring channels are connected by information lines 9 with the information-computing device 10.

The system operates as follows. As an informative physical sign of a leak in pipeline 1, the system uses the fact that a radioactive isotope of nitrogen-16 is detected in the subinsulation space 4 of a controlled section of pipeline 1. The radioactive isotope of nitrogen-16 is formed directly in the coolant 3 when it passes through the reactor core during the interaction of fast neutrons with oxygen-16 nuclei. The beta-decay isotope of nitrogen-16 is converted back to oxygen-16 with a half-life of 7.11 s. A feature of nitrogen-16 radiation is the presence of beta particles with very high energy, reaching 10.4 MeV, which allows the system to use sensors that are selectively sensitive to the radiation of the nitrogen-16 isotope against the background of intense gamma radiation from the pipeline. In the event of a pipeline leak, superheated steam, including radioactive nitrogen-16, from the leak site X _m spreads to both sides of the insulating space 4. When the gas-vapor front reaches the installation sites of the nozzles 5 (X ₁ , X ₂ and X ₃ ), part of the gas mixture under the action of excess pressure will leave the insulating space 4 through the nozzles 5 to the radiation sensors 6. Under these conditions, beta-particles of nitrogen-16 with an energy above 6.13 MeV, falling into the sensitive volumes of the sensors of radioactive radiation 6, will produce signals. Registration of the presence of nitrogen-16 in the insulating space 4 is taken as the fact of leak detection.

определяются по формуламThe location and magnitude of the mass flow rate of the leak is determined from the fact that the radiation radiation sensors 6 are at different and known distances from the leak site X _m and the moments of time for recording nitrogen-16 by three sensors differ and depend on the magnitude of the leak rate. The moments of time t ₁ , t ₂ , t ₃ registration are recorded and used as input to calculate the parameters of the leak - the coordinates of the leak and the magnitude of the leak. Since the characteristic propagation times of the gas-vapor front along the insulating space are comparable with the half-life, T _1/2 = 7.11, with nitrogen-16, the measured time parameters for reaching the settings are corrected by introducing amendments that take into account the decay of nitrogen-16 activity when it propagates from the place leak to the places of installation of radiation sensors 6. Refined time parameters $${\text{t}}_{\text{one}}^{\text{''}}{\text{, t}}_{\text{2}}^{\text{''}}{\text{and t}}_{\text{3}}^{\text{''}}$$

determined by the formulas

where t ₁ <t ₂ <t ₃ .

The coordinate of the leak location X _T and the leak size G _{m are} determined respectively by formulas 4, 5 and 6:

- средняя скорость распространения парогазового фронта вдоль подизоляционного пространства, м/с; $${\text{t}}_{\text{1}}^{\text{'}}{\text{, t}}_{\text{2}}^{\text{'}}{\text{ и t}}_{\text{3}}^{\text{'}}$$

- откорректированные времена достижения соответствующими измерительными каналами показаний, превышающих величину уставки, с; S - площадь сечения подизоляционного пространства, м²; ν - удельный объем пара при температуре подизоляционного пространства и атмосферном давлении, кг/м³.where G is the mass flow rate of the leak, kg / s; $$\overline{\text{W}}$$

- the average velocity of the gas-vapor front along the insulating space, m / s; $${\text{t}}_{\text{one}}^{\text{''}}{\text{, t}}_{\text{2}}^{\text{''}}{\text{and t}}_{\text{3}}^{\text{''}}$$

- corrected times for the corresponding measuring channels to reach readings in excess of the set value, s; S is the cross-sectional area of the insulating space, m ² ; ν - specific volume of steam at a temperature podizolyatsionnogo space and atmospheric pressure, kg / m ^3.

Thus, the use of three nitrogen-16 activity registration systems in the system located on pipeline 1 at known distances allows the use of the time-of-flight method for determining the location and mass flow rate of a leak, which allows meeting modern requirements for leak control systems by the accuracy of determining the mass leak rate equal to ± 50%, and accuracy of determining the location of the leak equal to ± 2 m from the length of the monitored section of the pipeline 1.

The technical feasibility of the proposed system is confirmed by the positive results of the calculations and experiments.

The invention is industrially applicable, it can be used in nuclear power plants with a water coolant to control pipeline leakage.

Claims (1)

A radiation monitoring system for a leak in a nuclear power plant nuclear-water reactor pipeline containing a complex for measuring the activity of the analyzed medium, including a radioactive radiation sensor and a device for selecting and transporting the analyzed medium to the sensor, and an information and computing device, characterized in that it is additionally installed on each controlled section of the pipeline at least two complexes for measuring the activity of the analyzed medium, including radiation sensors that are selective are resistant to nitrogen-16 radiation, radiation sensors are located along the entire length of the pipeline at known distances, the devices for the selection and transportation of the analyzed medium are made in the form of nozzles passing through the pipeline insulation, some ends of the nozzles are led out into the insulating space of the pipeline, and other ends of the nozzles are led out to radiation sensors, the information and computing device is equipped with technical means of software for determining the location and mass Flow rate of total leak indications complexes involved measuring nitrogen-16 activity.

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