CN108877970A - A kind of presurized water reactor primary Ioops boundary leaking monitoring method, system and monitor - Google Patents

Abstract

The invention discloses a method, system and monitor for boundary leakage monitoring of a primary circuit of a pressurized water reactor. The method includes the following steps: at the sampling point, obtain the sampling gas in the containment through a sampling pipeline, and transport the sampling gas In the sampling container; detect the γ-γ coincidence counts of the γ-γ photons emitted by the β ⁺ decay of ¹³ N in the sampling gas of the sampling container by the coincidence detection device, so as to calculate the output γ-γ coincidence counts rate; wherein, the coincidence detection device includes at least two coincidence detectors; according to the γ-γ coincidence count rate in the sampled gas, the leakage rate of the coolant water of the primary circuit pressure boundary of the pressurized water reactor is determined, which can be accurate and efficient The leakage monitoring of the PWR primary circuit is carried out.

Description

A method, system, and monitoring instrument for monitoring boundary leakage of a primary circuit of a pressurized water reactor

technical field

The invention relates to the field of radiation leakage monitoring of nuclear power plants, in particular to a method, system and monitoring instrument for monitoring boundary leakage of a primary circuit of a pressurized water reactor.

Background technique

Nuclear safety is the life of nuclear power. The most important thing to develop my country's independent nuclear power technology is how to improve safety. Although nuclear power is a clean energy source, it still has the possibility of nuclear leakage due to the emission of radioactive substances. In order to ensure the stable development of nuclear power and the situation of going global, the safe operation and monitoring of nuclear power plants is one of the keys related to the stable development and going global of nuclear power. The primary circuit pressure boundary leakage monitoring of nuclear power plants is the core component of nuclear power plant safety monitoring. Because the primary circuit of the pressurized water reactor nuclear power plant contains high-temperature and high-pressure water, this water is used as both a coolant and a neutron moderator. Due to leakage of nuclear fuel element cladding and neutron activation of corrosion products in the primary loop water, the water contains radionuclides. Cracks and cracks occur in the reactor body of the primary circuit of the pressurized water reactor nuclear power plant, welding parts and mechanical interfaces in the pipeline, etc., due to pressure, corrosion and radiation, especially the drive mechanism of the control rod on the top cover of the pressure vessel and the valves. Poor sealing will cause water leakage in the primary circuit. If it is not found in time, the cracks will become bigger and bigger, and the leakage will increase. Once a leak occurs, the radioactive cooling water will leak into the containment atmosphere and pollute the environment, which will not only endanger the health of the staff, but also endanger the normal operation of the reactor and the safety of the nuclear power plant. For these reasons, various countries attach great importance to monitoring the leakage of the reactor primary circuit pressure boundary of the nuclear power plant.

The monitoring of the pressure boundary leakage of the primary circuit of the PWR nuclear power plant is mainly realized by monitoring the radioactive source term of the high temperature and high pressure water in the primary circuit of the PWR nuclear power plant. At present, the monitoring methods used at home and abroad mainly include: measurement of the total β radioactivity of aerosol in the containment, measurement of airborne ¹³¹ I radioactivity in the air in the containment, measurement of the radioactivity of inert gas in the air in the containment, and measurement of the ¹³ N( Nitrogen 13) radioactivity was measured in these four.

The measurement of the total β radioactivity of the aerosol in the containment is mainly to monitor the total β radioactivity of the aerosol in the containment. The aerosol mainly comes from the leakage and gasification of the coolant at the pressure boundary of the primary circuit of the reactor. The fission products and corrosion in the coolant The formation of activation products; the measurement process of the airborne ¹³¹ I radioactivity measurement in the air inside the containment is similar to the measurement of the total β radioactivity of the aerosol in the containment, which is also measured while sampling, but the airborne ¹³¹ I radioactivity measurement in the air inside the containment is The "iodine filter box" made of activated carbon is manually operated to replace the iodine filter box; the radioactivity measurement of the inert gas in the air in the containment vessel is used to monitor the total β radioactivity of the inert gas to monitor the boundary leakage.

The ¹³ N radioactivity in the air inside the containment is measured, and the ¹³ N in the reactor coolant H ₂ O comes from the following nuclear reaction: the fission neutrons in the reactor core elastically scatter with the hydrogen nuclei in the water to produce recoil protons, which are greater than a certain energy (E=5.555MeV) The recoil protons react with ¹⁶ O in water to generate ¹³ N, that is ¹³ N is β ⁺ radionuclide, and the β ⁺ half-life is 9.96min. The positron annihilation effect occurs when the β ⁺ particle interacts with matter, and two photons with energy of 0.511 Mev are emitted, and the two photons move in opposite directions. By measuring the gamma ray count of 0.511 Mev in the sampled gas, the radioactivity of ¹³ N in the sampled air can be obtained, and then converted by the leakage transmission coefficient determined by special calculation, the position of the top cover of the pressure vessel can be calculated (if in where the air is sampled) or the water leakage rate of the primary loop pressurized boundary (if the air is sampled in the containment).

In the process of realizing the present invention, the inventors found that: since the aerosol, ¹³¹ I measurement and inert gas are all nuclear fission products leaked from the nuclear fuel element cladding, their source terms depend on the damage degree of the nuclear fuel cladding and the nuclear reaction of the nuclear fuel To a certain extent, as the zirconium alloy fission product of the fuel cladding is exposed to high temperature and high pressure radioactive water for a long time, a certain degree of corrosion damage, stress damage, etc. will occur, resulting in defects in the nature of trachoma (ie small holes) or fine cracks. Nuclear fuel cladding The damage of the fission product cannot be quantitatively estimated, so the leakage of fission products can only be monitored through the measurement of aerosol, ¹³¹ I and inert gas, but the leakage of fission products cannot be quantitatively calculated, so it can only be measured qualitatively; For ¹³ N radioactivity measurement in the air, since the radioactive source term is the product of neutron activation, the source term can be accurately calculated. Compared with the measurement of aerosol, ¹³¹ I and the measurement of the three fission products of inert gas (ie PIG), it is not only possible to know whether there is Leakage occurs, and the amount of leakage can be accurately calculated according to the source item, which can be used for quantitative measurement. However, using ¹³ N radioactive measurement can give quantitative leakage rate information within the error range of ±20%, but At present, the ¹³ N leakage monitoring that has been developed at home and abroad is measured by the low-background gamma energy spectrum method, which is to put the sampling container into the low-background lead chamber and then use the detector to measure the gamma energy spectrum. However, due to the relatively low concentration of ¹³ N nuclides in the containment, the detection counts of the detectors for ¹³ N are relatively small, and these monitoring equipment will encounter a relatively high detection limit in the actual use process. At present, the level is about 10L/h, but in practical application, the specific user department of the nuclear power plant hopes that the detection lower limit of the instrument can reach the leakage rate of 1L/h, because the current level of leakage in the primary circuit of the pressurized water reactor nuclear power plant is normal. With a leakage of about 40 liters to 120 liters per day, the existing ¹³ N monitor with a lower detection limit of 10 L/h can intelligently detect prominent relatively large leakage accidents, which cannot reflect the situation of the leakage; and use low-cost The bottom gamma energy spectrum method is to measure the 0.511 Mev gamma photons emitted by the β ⁺ decay of ¹³ N by stabilizing the spectrum to realize the leakage monitoring method, which has high requirements on the long-term stability of the instrument. Drift occurs, which will make the measured gamma count rate of 0.511 Mev inaccurate and affect the accuracy of the measurement results.

Contents of the invention

In view of the above problems, the purpose of the present invention is to provide a PWR primary circuit boundary leakage monitoring method, system and monitor, which can accurately and efficiently monitor the PWR primary circuit leakage.

In a first aspect, an embodiment of the present invention provides a method for monitoring boundary leakage of a PWR primary circuit, comprising the following steps:

At the sampling point, the sampling gas in the containment is obtained through the sampling pipeline, and the sampling gas is delivered to the sampling container;

Detecting the gamma-gamma coincidence counts of the gamma-gamma photons emitted by the β ⁺ decay of ¹³ N in the sampling gas in the sampling container by the coincidence detection device, so as to calculate the output gamma-gamma coincidence count rate; wherein, The coincidence detection device includes at least two coincidence detectors;

According to the γ-γ coincidence count rate in the sampled gas, the leakage rate of the coolant water at the pressure boundary of the primary circuit of the PWR is determined.

In a first implementation manner of the first aspect, the coincidence detection device further includes a main detector;

Then described pressurized water reactor primary loop boundary leakage monitoring method also includes:

According to the main detector and the coincidence detector in the coincidence detection device to detect the gamma coincidence background count of the gamma photons emitted by the beta ⁺ decay of ¹³ N in the sampling gas of the sampling container, to calculate the output coincidence background count Rate.

According to the first implementation of the first aspect, in the second implementation of the first aspect,

The sampling container includes an M-S container;

The main detector and the coincidence detector in the coincidence detection device are all NaI(TI) scintillator detectors;

The sampling container has a cylindrical structure, and the material of the sampling container is (1 ± 0.1) mm stainless steel;

The height of the sampling container is (80 ± 0.5) mm;

The sampling container is provided with a first inner cavity and at least two second inner cavities, the first inner cavity is located in the middle of the sampling container, and the first inner cavity, each of the second inner cavities The height of the cavity is (78±0.5)mm;

The main detector in the coincidence detection device is arranged in the first inner cavity, and the coincidence detector is arranged in any one of the second inner cavities.

According to the second implementation manner of the first aspect, in the third implementation manner of the first aspect, in the sampling gas detected by the coincidence detection device in the sampling container, the emission direction of the β ⁺ decay of ¹³ N is opposite The gamma-gamma coincidence counts of the gamma-gamma photons are used to output the gamma-gamma coincidence count rate, specifically:

In the coincidence detection device, the at least two coincidence detectors respectively detect two gamma photons of 0.511 Mev in opposite directions emitted by the beta ⁺ decay of ¹³ N in the sampling gas of the sampling container through the method of card energy;

According to all the gamma photons of 0.511 Mev in opposite directions detected, the gamma-gamma coincidence counting is performed to calculate the output coincidence detection efficiency; wherein, if the coincidence detection efficiency is ε, then In the formula, n is the γ-γ coincidence count, λ is the decay constant, A ₀ is the β ⁺ activity value of ¹³ N measured at t ₀ , t ₁ is the time when the coincidence detection counting starts, and t ₂ is the coincidence detection the moment when counting stops;

Obtain the γ-γ coincidence count rate according to the coincidence detection efficiency and the volume of the sampling container; wherein, assuming the volume of the sampling container is V, and setting the γ-γ coincidence count rate n _n , then n _n =V× ε.

According to the third implementation of the first aspect, in the fourth implementation of the first aspect, the coolant used to determine the pressure boundary of the PWR primary circuit is determined according to the γ-γ coincidence count rate in the sampled gas Water leakage rate, specifically:

Determine the leak rate transfer coefficient according to the coincident detection efficiency; wherein, assuming that the leak rate transfer coefficient is K ₂ , then In the formula, λ is the decay constant of ¹³ N (unit: h ^-1 ), V ₁ is the effective volume of the containment, ε is the detection efficiency, Q is the flow rate of the sampled air, and t ₄ is the flow of water in the containment after the leakage of primary circuit water. internal vaporization dilution time, t ₅ is the transmission time in the sampling pipeline, t ₆ is the measurement time of the detection device in the sampling container;

According to the gamma-gamma coincident count rate in the sampled gas and the leak rate transfer coefficient, determine the leak rate of the coolant water at the primary loop pressure boundary of the PWR; wherein, if the leak rate is V _L , then In the formula, n _n is the γ-γ coincidence count rate, N ₁ is the nuclear density of ¹³ N in the PWR primary circuit water, N ₁ =K ₁ P, P is the reactor power, and K ₁ is the proportionality coefficient.

According to any of the above implementations of the first aspect, in the fifth implementation of the first aspect, the minimum detectable activity and the lower limit of detection are determined according to the detection efficiency of each detector and the local count rate, so as to As the functional evaluation standard of the PWR primary circuit boundary leakage monitoring method; wherein, the detectors include main detectors and each coincidence detectors, assuming that the minimum detectable activity is S ₁ , then In the formula, ε _in is the detection efficiency of the detector, n _b is the counting rate in accordance with the background, and T is the measurement time; if the detection lower limit is L _D , then

In the second aspect, the embodiment of the present invention provides a PWR primary circuit boundary leakage monitoring system, including a sampling unit, a measurement unit, and a measurement processing unit;

The sampling unit is connected with the measuring unit, and is used to obtain the sampling gas in the containment through the sampling pipeline at the sampling point, and transport the sampling gas into the sampling container;

The measurement unit is connected with the measurement processing unit, and is used to detect the γ-γ coincidence of the γ-γ photons emitted by the β ⁺ decay of ¹³ N in the sample gas in the sampling container through the coincidence detection device. counting to calculate the output gamma-gamma coincidence count rate; wherein the coincidence detection means includes at least two coincidence detectors;

The measurement processing unit is used to determine the leakage rate of the coolant water at the pressure boundary of the PWR primary circuit according to the γ-γ coincidence count rate in the sampled gas.

In the first implementation manner of the second aspect, the coincidence detection device further includes a main detector;

The measuring unit is also used to detect the gamma coincidence background count of the gamma photons emitted by the beta ⁺ decay of ¹³ N in the sample gas of the sampling container according to the main detector and the coincidence detector in the coincidence detection device , to calculate the output meets the background count rate.

According to the first implementation of the second aspect, in the second implementation of the second aspect, a display unit and an electrical control unit are also included;

The display unit is connected to the measurement processing unit, and is used for correspondingly displaying the leakage situation according to the leakage rate of the coolant water leaked at the boundary of the PWR primary circuit acquired by the measurement processing unit;

The electrical control unit is used to provide voltage output for the measurement processing unit and the display unit, respectively, with the measurement processing unit and the display unit.

In a third aspect, an embodiment of the present invention provides a monitor, including the PWR primary circuit boundary leakage monitoring system described in any one of the second aspect.

The embodiment of the present invention provides a method, system and monitoring instrument for monitoring the boundary leakage of the primary circuit of the pressurized water reactor, and one embodiment thereof has the following beneficial effects:

At the sampling point, the sampling gas in the containment is obtained through the sampling pipeline, and the sampling gas is transported to the sampling container, and then the coincidence detection device is used to detect the β ⁺ decay of ¹³ N in the sampling gas of the sampling container. gamma-gamma coincidence counting of emitted gamma-gamma photons in opposite directions to calculate the output gamma-gamma coincidence count rate, the coincidence detection device includes at least two coincidence detectors, and finally according to the gamma-gamma in the sampled gas According to the count rate, the leakage rate of the coolant water at the pressure boundary of the primary circuit of the PWR is determined, and the coincidence count rate is calculated by the coincidence method, which improves the detection efficiency of ¹³ N and can effectively reduce the background, which can make the background lower than the conventional method About four orders of magnitude, the detection efficiency is reduced by one order of magnitude, and the lower limit of measurement can be lowered by one order of magnitude, that is, the lower limit of detection can reach a leak rate of 1L/h, which solves the problem of the existing pressurized water reactor nuclear power plant based on the energy spectrum method The lower detection limit of the primary circuit ¹³ N leakage monitoring system can provide more accurate leakage information for the employees of the nuclear power monitoring instrument department, and the stability requirements of the energy spectrum will be greatly reduced in accordance with the law, and the energy spectrum drift will not affect the measurement. Accuracy is affected.

Description of drawings

In order to illustrate the technical solution of the present invention more clearly, the accompanying drawings used in the implementation will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some implementations of the present invention. As far as the skilled person is concerned, other drawings can also be obtained based on these drawings on the premise of not paying creative work.

Fig. 1 is a schematic flowchart of a method for monitoring boundary leakage of a PWR primary circuit provided by the first embodiment of the present invention.

Fig. 2 is a schematic top view of the sampling container, the main detector and each coincidence detector provided by the first embodiment of the present invention.

Fig. 3 is a schematic diagram of the sampling container, the main detector and each coincidence detector provided by the first embodiment of the present invention.

Fig. 4 is a physical schematic diagram of the sampling container provided by the first embodiment of the present invention.

Fig. 5 is a schematic structural diagram of a PWR primary circuit boundary leakage monitoring system provided by the second embodiment of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Please refer to Fig. 1, the embodiment of the present invention provides a kind of PWR primary circuit boundary leakage monitoring method, the PWR primary circuit boundary leakage monitoring method is integrated in the PWR primary circuit boundary leakage monitoring system, and includes The following steps:

S11, at the sampling point, acquire the sampling gas in the containment through the sampling pipeline, and deliver the sampling gas to the sampling container.

In the embodiment of the present invention, the sampling unit first pumps the sampling gas into the sampling container through the sampling pipeline at the sampling point, and the sampling gas in the sampling container is measured by the coincidence detection device in the measuring unit. The sampling container includes but not limited to the M-S container, the sampling container is a cylindrical structure, and the material of the sampling container is (1 ± 0.1) mm stainless steel material, and the height of the sampling container is (80 ± 0.5) mm, the sampling container is provided with a first inner cavity and at least two second inner cavities, the first inner cavity is located in the middle of the sampling container, and the first inner cavity, each of the second inner cavities The heights of the two inner cavities are both (78±0.5) mm. It should be noted that, according to the pressure level classification: pressure vessels can be divided into internal pressure vessels and external pressure vessels; internal pressure vessels can be divided into design pressure (p) There are four pressure levels, specifically divided as follows: (1) low pressure (code L) container 0.1MPa≤p<1.6MPa, (2) medium pressure (code M) container 1.6MPa≤p<10.0MPa, (3) high pressure ( Code H) container 10MPa≤p<100MPa, (4) ultra-high pressure (code U) container p≥100MPa. (1MPa=9.8Kg); classified according to the role of the container in production: (1) reaction pressure vessel (code R): used to complete the physical and chemical reactions of the medium, (2) heat exchange pressure vessel (code E): used To complete the heat exchange of the medium, (3) separation pressure vessel (code S): used to complete the fluid pressure balance buffer and gas purification and separation of the medium, (4) storage pressure vessel (code C, of which the spherical tank code B): use It is used to store and hold gas, liquid, liquefied gas and other media.

S12, detecting the gamma-gamma coincidence counts of the gamma-gamma photons emitted by the β ⁺ decay of ¹³ N in the sampling gas in the sampling container by the coincidence detection device, so as to calculate the output gamma-gamma coincidence count rate; , the coincidence detection device includes at least two coincidence detectors.

In the embodiment of the present invention, it should be noted that the present invention uses the coincidence method to measure the radioactivity of ¹³ N to calculate the leakage rate of the coolant water at the pressure boundary of the primary circuit of the reactor. ¹³ N is a β+ particle emitter, and the half-life For 9.96 minutes, the β+ particle interacts with matter to produce positron annihilation effect, and emits two gamma photons with energy of 0.511MeV, and the two gamma photons move in opposite directions; it conforms to the basic principle of law: in nuclear physics A coincidence event refers to two or more simultaneous events. For example, when an atomic nucleus undergoes a cascade decay and emits beta rays and gamma rays continuously, then the beta and gamma are called a pair of coincidence events. event, if this pair of βγ respectively enters into two detectors, a coincidence pulse can be output when the pulses output by the two detectors are guided to the coincidence circuit, and the output signals of these two detectors are input into the coincidence circuit. The coincidence pulse signal is generated. The coincidence method is a method to select the coincidence event by using the coincidence circuit. After the ¹³ N nuclide undergoes β ⁺ decay and annihilation, two gamma photons with energy of 0.511MeV and opposite directions will be produced. is a coincidence event, and this application utilizes multiple detectors combined into a coincidence detection device to detect these coincidence events.

In the embodiment of the present invention, the coincidence detection device also includes a main detector, and it is determined that the main detector and the coincidence detector in the coincidence detection device are both NaI(TI) scintillators according to the characteristics of gamma rays emitted by positrons The detector, the main detector in the coincidence detection device is arranged in the first inner cavity, and the coincidence detector is arranged in any one of the second inner chambers, preferably, please refer to Fig. 2 and Fig. 3 And Fig. 4, described sampling container has a first inner cavity and 4 second inner cavities, and described coincident detection device comprises a main detector and 4 coincident detectors, and described main detector is positioned at the center of described sampling container In the first inner cavity of the position, the four coincidence detectors are respectively located in the four second inner cavities of the sampling container.

In the embodiment of the present invention, the ¹³ N gas in the sampling container undergoes β ⁺ decay, releasing β ⁺ particles (that is, positrons) with arbitrary directions and energy of 0 to 1.198 MeV, and the β ⁺ particles annihilate with the surrounding substances Afterwards, two gamma photons with opposite directions and energy of 0.511MeV are generated, and the detection process of the NaI (TI) scintillator detector for the gamma photon includes: the gamma photon generated in the sampling container enters the sodium iodide crystal, and The crystal interacts to generate secondary charged particles (electrons), which then cause ionization and excitation of the material. The excited atoms emit light during the de-excitation process, and the photons are emitted from the scintillator and hit the photocathode of the photomultiplier tube. The electrons are shot out on the surface, and the photoelectrons are multiplied by each dynode of the photomultiplier tube, and finally collected by the anode to generate an electrical pulse signal, thereby outputting the electrical pulse signal for recording and analysis; Among them, it should be noted that the interaction between γ photons and matter There are mainly photoelectric effect, Compton scattering and electron pair generation effect. The annihilation of positron in the sampling container produces two gamma photons with energy of 0.511MeV. The gamma photon and sodium iodide crystal have photoelectric effect, Compton effect, The electron pair effect deposits energy in the crystal, so that a signal can be given. When the two detectors have signal output at the same time, it is considered that a positron annihilation has occurred.

In the embodiment of the present invention, the measurement unit detects the gamma coincidence background of the gamma photons emitted by the beta ⁺ decay of ¹³ N in the sample gas of the sampling container according to the main detector and the coincidence detector in the coincidence detection device Counting, to calculate the output compliance with the background counting rate, please refer to Figure 2, Figure 3 and Figure 4, put the detector into the designated position of the sampling container, and measure the boundary leakage monitoring system of the PWR primary circuit under unshielded conditions It can be seen from the placement positions of the 5 detectors that when the coincidence detectors are combined in pairs to output coincidences, it is difficult to form a true coincidence count in the presence of radioactive sources. , does not make much contribution to the improvement of coincidence detection efficiency, so the output signals of 1, 3 coincidence and 2, 4 coincidence are discarded in the background measurement and active measurement, and the measurement system using the coincidence method effectively reduces the coincidence background count, Since the background of the detectors is not a cascading event, the two NaI detectors will output signals at the same time only when there is an accidental coincidence between the backgrounds. It is about four orders of magnitude lower than the background count rate of a single detector, which plays a crucial role in lowering the detection limit of the measurement system.

In the embodiment of the present invention, in the coincidence detection device, the at least two coincidence detectors respectively detect the two emitted by the β ⁺ decay of ¹³ N in the sampling gas of the sampling container through the card energy method. A gamma photon of 0.511 Mev in the opposite direction, the card energy is the energy of the incident particle reflected by the detector when measuring the radiation energy; the detector reflects the information of the incident particle by outputting a pulse signal: the pulse count reflects the number of incident particles 1. The pulse amplitude of a single output signal reflects the particle energy; the detector output pulse amplitude is linearly proportional to the incident particle energy, and the pulse amplitude is converted into the corresponding channel address x through the ADC analog-to-digital converter, which is generally divided into 1024 channels. There is a linear relationship between the number of channels and the energy: E( _xi )=G* _xi +E ₀ ; the energy window for ¹³ N monitoring is (0.465-0.565) MeV, and the corresponding energy can be checked by selecting the corresponding channel site range, and at the same time, due to Use the coincidence method to measure the radioactivity of ¹³ N. Because the energy window of the coincidence channel of this method can be wider, even if the energy window is doubled, it will not affect the counting and background counting of ¹³ N. Therefore, use This method will greatly reduce the stability requirements of the energy spectrum, and the drift of the energy spectrum will not affect the measurement accuracy, and then the measurement unit performs gamma-gamma coincidence counting according to all the detected gamma photons of the two opposite directions of 0.511 Mev , to calculate the output coincidence detection efficiency, let the coincidence detection efficiency be ε, then In the formula, n is the γ-γ coincidence count, λ is the decay constant, A ₀ is the β ⁺ activity value of ¹³ N measured at t ₀ , t ₁ is the time when the coincidence detection counting starts, and t ₂ is the coincidence detection At the moment when the counting stops, it should be noted that in the γ-γ spectrum coincidence method for measuring ¹³ N experiments, the coincidence detection efficiency refers to the ratio of the total measured coincidence counts to the number of decay nuclides within the measurement period, It is an important physical parameter for the calculation of the water leakage rate of the PWR primary circuit. Since the half-life of ¹³ N nuclides is short, only 9.96min, the radioactivity has been changing during the measurement process, so the coincidence efficiency When performing calculations, it is not possible to simply use the initially measured radioactivity values for calculation, but to calculate the number of nuclides that undergo radioactive decay within the measurement period, and then count according to the measured γ-γ coincidence, using These two parameters are used to calculate the coincidence detection efficiency of the sampling detection device; finally, according to the coincidence detection efficiency and the volume of the sampling container, the gamma-gamma coincidence count rate is obtained, the volume of the sampling container is V, and the gamma-gamma The coincidence count rate is n _n , then n _n =V×ε, when the radius of the sampling container is 13 cm, the γ-γ coincidence count rate reaches the maximum.

S13. According to the γ-γ coincidence count rate in the sampled gas, determine the leakage rate of the coolant water at the pressure boundary of the primary circuit of the PWR.

In the embodiment of the present invention, the measurement processing unit determines the leakage rate transmission coefficient according to the coincidence detection efficiency, and the leakage rate transmission coefficient is set to K ₂ , then In the formula, λ is the decay constant of ¹³ N (unit: h ^-1 ), V ₁ is the effective volume of the containment, ε is the detection efficiency, Q is the flow rate of the sampled air, and t ₄ is the flow of water in the containment after the leakage of primary circuit water. Internal vaporization dilution time, _t5 is the transmission time in the sampling pipeline, t6 is the measurement time of the coincidence detection device in the sampling container, and then transmit according to the γ _- γ coincidence count rate and the leakage rate in the sample gas coefficient to determine the leakage rate of the coolant water at the pressure boundary of the primary circuit of the PWR; wherein, assuming that the leakage rate is V _L , then In the formula, n _n is the γ-γ coincident count rate, N ₁ is the nuclear density of ¹³ N in the primary circuit water of the PWR, N ₁ =K ₁ P, P is the reactor power (expressed as a percentage of rated power), K ₁ is the proportional coefficient, and the proportional coefficient K ₁ takes L ¹ (MW) ^-1 as the unit. The nuclear density of ¹³ N in the primary loop water of the reactor is directly proportional to the core power, which can be accurately calculated according to the core structure.

In the embodiment of the present invention, the minimum detectable activity and the detection lower limit are calculated as the function evaluation standard of the PWR primary circuit boundary leakage monitoring method, and the minimum detectable activity and the detection lower limit are determined according to the detection efficiency of each detector and the local counting rate. Detectable activity and detection lower limit, the detector includes the main detector and each coincident detector, assuming that the minimum detectable activity is S _l , then The confidence level of S _l is 95%. In the formula, ε _in is the detection efficiency of the detector, n _b is the counting rate in accordance with the background, T is the measurement time (s); if the lower limit of detection is L _D , then From the minimum detectable activity and the lower detection limit, it can be seen that the detection lower limit of the PWR primary circuit boundary leakage monitoring system is mainly determined by the background count rate and detection efficiency of the PWR primary circuit boundary leakage monitoring system. The present invention reduces the detection lower limit of the PWR primary circuit boundary leakage monitoring system by rationally designing the sampling container and the coincidence detection device and using the coincidence method to measure the radioactivity of ¹³ N, and improves the coincidence detection efficiency and γ-γ, According to the calculation result of the detection lower limit, it can be known that the PWR primary circuit boundary leakage monitoring method of the present application can reduce the measurement lower limit by an order of magnitude through the coincidence measurement method, that is, the detection lower limit can reach the leakage rate of 1L/h, which solves the current problem. There is a problem that the lower detection limit of the ¹³ N leakage monitoring system of the primary circuit of the PWR nuclear power plant based on the energy spectrum method is relatively high.

In summary, the first embodiment of the present invention provides a PWR primary circuit boundary leakage monitoring method. At the sampling point, the sampling gas in the containment is obtained through the sampling pipeline, and the sampling gas is transported to the sampling point. In the container, the γ-γ coincidence count of the γ-γ photons emitted by the β ⁺ decay of ¹³ N in the sample gas of the sampling container is detected by the coincidence detection device, so as to calculate the output γ-γ coincidence count rate , the coincidence detection device includes at least two coincidence detectors, and finally according to the γ-γ coincidence count rate in the sampled gas, the leakage rate of the coolant water at the pressure boundary of the primary circuit of the PWR is determined, and the coincidence is carried out by the coincidence method The calculation of the count rate improves the detection efficiency of ¹³ N, which can effectively reduce the background, which can reduce the background by about four orders of magnitude compared with the conventional method, and the detection efficiency by an order of magnitude. The lower limit can reach the leakage rate of 1L/h, which solves the problem of the high detection lower limit of the existing ¹³ N leakage monitoring system for the primary circuit of the PWR nuclear power plant based on the energy spectrum method. Accurate leakage, and the compliance method will greatly reduce the stability requirements of the energy spectrum, and the drift of the energy spectrum will not affect the measurement accuracy.

Please refer to FIG. 5 , the second embodiment of the present invention provides a PWR primary loop boundary leakage monitoring system, including a sampling unit 11 , a measuring unit 12 and a measurement processing unit 13 .

The sampling unit 11 is connected with the measuring unit 12, and is used for obtaining the sampling gas in the containment through the sampling pipeline at the sampling point, and transporting the sampling gas into the sampling container.

The measurement unit 12 is connected with the measurement processing unit 13, and is used to detect the γ-γ-γ photon emitted by the β ⁺ decay of ¹³ N in the sample gas in the sampling container through a coincidence detection device in the opposite direction. gamma coincidence counting to calculate an output gamma-gamma coincidence counting rate; wherein, the coincidence detection device includes at least two coincidence detectors.

The measurement processing unit 13 is configured to determine the leakage rate of the coolant water at the pressure boundary of the PWR primary circuit according to the γ-γ coincidence count rate in the sampled gas.

In the first implementation of the second embodiment, the coincidence detection device further includes a main detector;

The measurement unit 12 is also used to detect the gamma coincidence background of the gamma photons emitted by the beta ⁺ decay of ¹³ N in the sample gas of the sampling container according to the main detector and the coincidence detector in the coincidence detection device counts to calculate the output versus background count rate.

According to the first implementation of the second embodiment, in the second implementation of the second embodiment, a display unit 14 and an electrical control unit 15 are further included.

The display unit 14 is connected with the measurement processing unit 13, and is used for correspondingly displaying the leakage situation according to the leakage rate of the coolant water leaking from the boundary of the PWR primary circuit obtained by the measurement processing unit 13.

The electrical control unit 15 is used to provide voltage output for the measurement processing unit 13 and the display unit 14 , respectively with the measurement processing unit 13 and the display unit 14 .

According to the second implementation of the second embodiment, in the third implementation of the second embodiment,

The sampling containers include M-S containers.

Both the main detector and the coincidence detector in the coincidence detection device are NaI(TI) scintillator detectors.

The sampling container has a cylindrical structure, and the material of the sampling container is (1±0.1) mm stainless steel.

The height of the sampling container is (80±0.5)mm.

The sampling container is provided with a first inner cavity and at least two second inner cavities, the first inner cavity is located in the middle of the sampling container, and the first inner cavity, each of the second inner cavities The height of the cavity is (78±0.5)mm.

The main detector in the coincidence detection device is arranged in the first inner cavity, and the coincidence detector is arranged in any one of the second inner cavities.

According to the third implementation of the second embodiment, in the fourth implementation of the second embodiment,

The measuring unit 12 is specifically used in the coincidence detection device, the at least two coincidence detectors respectively detect the two emitted by the β ⁺ decay of ¹³ N in the sampling gas of the sampling container through the method of card energy. 0.511 Mev gamma photons in the opposite direction;

According to all the gamma photons of 0.511 Mev in opposite directions detected, the gamma-gamma coincidence counting is performed to calculate the output coincidence detection efficiency; wherein, if the coincidence detection efficiency is ε, then In the formula, n is the γ-γ coincidence count, λ is the decay constant, A ₀ is the β ⁺ activity value of ¹³ N measured at t ₀ , t ₁ is the time when the coincidence detection counting starts, and t ₂ is the coincidence detection the moment the counting stops; and

Obtain the γ-γ coincidence count rate according to the coincidence detection efficiency and the volume of the sampling container; wherein, assuming the volume of the sampling container is V, and setting the γ-γ coincidence count rate n _n , then n _n =V× ε.

The measurement processing unit 13 is specifically configured to determine the leakage rate transmission coefficient according to the coincidence detection efficiency; wherein, assuming that the leakage rate transmission coefficient is K ₂ , then In the formula, λ is the decay constant of ¹³ N (unit: h ^-1 ), V ₁ is the effective volume of the containment, ε is the detection efficiency, Q is the flow rate of the sampled air, and t ₄ is the flow of water in the containment after the leakage of primary circuit water. Internal vaporization dilution time, t ₅ is the transit time in the sampling pipeline, t ₆ is the measurement time of the detection device in the sampling container; and

According to the gamma-gamma coincident count rate in the sampled gas and the leak rate transfer coefficient, determine the leak rate of the coolant water at the primary loop pressure boundary of the PWR; wherein, if the leak rate is V _L , then In the formula, n _n is the γ-γ coincidence count rate, N ₁ is the nuclear density of ¹³ N in the PWR primary circuit water, N ₁ =K ₁ P, P is the reactor power, and K ₁ is the proportionality coefficient.

The third embodiment of the present invention provides a monitor, including the PWR primary circuit boundary leakage monitoring system described in any one of the second embodiments.

In the embodiment of the present invention, the monitor includes the PWR primary circuit boundary leakage monitoring system described in any one of the second embodiment, and the detection lower limit of the monitor can reach a leak rate of 1L/h, solving the problem of The existing detection limit of the ¹³ N leakage monitoring system of the primary circuit of the PWR nuclear power plant based on the energy spectrum method is relatively high. The stability requirements will be greatly reduced, and the energy spectrum drift will not affect the measurement accuracy.

It should be noted that the device embodiments described above are only illustrative, and the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physically separated. A unit can be located in one place, or it can be distributed to multiple network units. Part or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. In addition, in the drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that they have a communication connection, which can be specifically implemented as one or more communication buses or signal lines. It can be understood and implemented by those skilled in the art without creative effort.

The above description is a preferred embodiment of the present invention, and it should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also considered Be the protection scope of the present invention.

Claims (10)

1. a kind of presurized water reactor primary Ioops boundary leaking monitoring method, which is characterized in that include the following steps：

At sample point, the sample gas in containment is obtained by sampling conduit, and the sample gas is transported to sampling In container；

In the sample gas for detecting the sampling container by meeting detection device,¹³The β of N⁺Decay is emitted contrary γ-γ the coincidence counting of γ-γ photon exports γ-γ coincidence counting rate to calculate；Wherein, the detection device that meets includes At least two meet detector；

According to the γ-γ coincidence counting rate in the sample gas, the coolant water of presurized water reactor primary Ioops pressure boundary is determined Slip.

2. presurized water reactor primary Ioops boundary leaking monitoring method according to claim 1, which is characterized in that described to meet detection Device further includes a main detector；

The then presurized water reactor primary Ioops boundary leaking monitoring method further includes：

According to the main detector met in detection device and meets detector and detect in the sample gas of the sampling container ,¹³The β of N⁺The γ of the emitted γ photon of decay meets background count, meets background counting rate to calculate output.

3. presurized water reactor primary Ioops boundary leaking monitoring method according to claim 2, which is characterized in that the sampling container Including M-S container；

The main detector met in detection device, to meet detector be NaI (TI) scintillator detector；

The sampling container is in cylindrical structure, and the material of the sampling container is the stainless steel material of (1 ± 0.1) mm；

The height of the sampling container is (80 ± 0.5) mm；

A first inner chamber and at least two second inner chambers are equipped in the sampling container, the first inner chamber is located at the sampling The middle part of container, and the height of the first inner chamber, each second inner chamber is (78 ± 0.5) mm；

The main detector met in detection device is set in the first inner chamber, and the detector that meets is set on any described In second inner chamber.

4. presurized water reactor primary Ioops boundary leaking monitoring method according to claim 3, which is characterized in that described by meeting Detection device detects in the sample gas of the sampling container,¹³The β of N⁺Decay the contrary γ-γ photon emitted γ-γ coincidence counting, to export γ-γ coincidence counting rate, specially：

In meeting detection device, described at least two meet detector detects the sampling appearance by the method for card energy respectively In the sample gas of device,¹³The β of N⁺The γ photon of the opposite 0.511Mev of the emitted both direction of decay；

γ-γ coincidence counting is carried out according to the γ photon of all described two contrary 0.511Mev of detection, in terms of It calculates output and meets detection efficient；Wherein, if meeting detection efficient is ε, thenIn formula, n For γ-γ coincidence counting, λ is decay coefficient, A₀For t₀What the moment measured¹³The β of N⁺Radioactive activity value, t₁To meet detection At the time of counting beginning, t₂At the time of counting stopping to meet detection；

γ-γ coincidence counting rate is obtained according to the volume for meeting detection efficient and the sampling container；Wherein, if sampling is held The volume of device is V, if the γ-γ coincidence counting rate is n_n, then n_n=V × ε.

5. presurized water reactor primary Ioops boundary leaking monitoring method according to claim 4, which is characterized in that described according to γ-γ coincidence counting rate in sample gas, determines the slip of the coolant water of presurized water reactor primary Ioops pressure boundary, specifically For：

Slip transmission coefficient is determined according to the detection efficient that meets；Wherein, if the slip transmission coefficient is K₂, thenIn formula, λ is¹³Decay coefficient (the unit h of N^-1), V₁For containment Dischargeable capacity, ε is to meet detection efficient, and Q is sampling air mass flow, t₄It is dilute to be vaporized in containment after the leakage of primary Ioops water It releases the time, t₅For the transmission time in sampling conduit, t₆For the time of measuring for meeting detection device in sampling container；

According in the sample gas γ-γ coincidence counting rate and the slip transmission coefficient, determine presurized water reactor primary Ioops The slip of the cold cut agent water of pressure boundary；Wherein, if the slip is V_L, thenIn formula, n_nFor γ-γ coincidence counting rate, N₁For in presurized water reactor primary Ioops water¹³The cuclear density of N, N₁=K₁P, P are reactor capability, K₁For ratio Coefficient.

6. according to claim 1 to presurized water reactor primary Ioops boundary leaking monitoring method described in 5 any one, which is characterized in that According to the detection efficient of each detector and it is described meet local counting rate, determine minimum detectable activity and detection limit, with Functional evaluation standard as the presurized water reactor primary Ioops boundary leaking monitoring method；Wherein, the detector includes main detection Device and it is each meet detector, if the minimum detectable activity be S_l, thenIn formula, ε_inFor detector Detection efficient, n_bTo meet background counting rate, T is time of measuring；If detection limit is L_D, then

7. a kind of presurized water reactor primary Ioops boundary leaking monitors system, which is characterized in that including sampling unit, measuring unit and measurement Processing unit；

The sampling unit is connect with the measuring unit, for being obtained in containment at sample point by sampling conduit Sample gas, and the sample gas is transported in sampling container；

The measuring unit is connect with the measurement processing unit, for detecting the sampling container by meeting detection device Sample gas in,¹³The β of N⁺γ-γ the coincidence counting for the contrary γ-γ photon that decay is emitted, to calculate output γ-γ coincidence counting rate；Wherein, the detection device that meets includes at least two meeting detector；

The measurement processing unit, for determining presurized water reactor primary Ioops according to the γ-γ coincidence counting rate in the sample gas The slip of the coolant water of pressure boundary.

8. presurized water reactor primary Ioops boundary leaking according to claim 7 monitors system, which is characterized in that described to meet detection Device further includes a main detector；

The measuring unit, the main detector for being also used to meet according in detection device and meet detector detection described in take In the sample gas of sample container,¹³The β of N⁺The γ of the emitted γ photon of decay meets background count, meets this to calculate output Bottom counting rate.

9. presurized water reactor primary Ioops boundary leaking according to claim 8 monitors system, which is characterized in that further include that display is single Member and electric control unit；

The display unit is connect with the measurement processing unit, the presurized water reactor for being obtained according to the measurement processing unit The slip of the coolant water of primary Ioops boundary leaking carries out corresponding display leakage situation；

The electric control unit is used to be the measurement processing respectively with the measurement processing unit and the display unit Unit and the display unit provide voltage output.

10. a kind of monitor, which is characterized in that including the presurized water reactor primary Ioops boundary as described in claim 7 to 9 any one Leakage monitoring system.