RU2437176C1 - Method and channel of detection of heat carrier boiling in reactor core of wwpr - Google Patents

Abstract

FIELD: power industry. ^ SUBSTANCE: method and channel of detection of heat carrier boiling in reactor core of WWPR (water-to-water power reactor) includes evaluation of fluctuation of neutron current, processing and extraction of signals of detectors with the specified parameters. At that, fluctuations of neutron current, processing and extraction of signals of detectors with the specified parameters are evaluated as to height of controlled fuel assembly (FA) considering the corresponding compensations calculated as per readings of all assemblies with neutron sensors (NS) in relation to fluctuations of neutron current at the inlet of this FA. In addition, fluctuations of neutron current are recorded with FA assembled in certain order as to height and uniformly distributed in reactor core by means of sensors constituting a measuring channel. At that, false signals are compensated and signals related to industrial inductions are suppressed; the specified parameters of processed signals are set in frequency range of 0.1 Hz to 8 Hz. ^ EFFECT: timely detection of heat carrier boiling in reactor core and specification of heat removal conditions in certain reactor core of water-to-water power reactor type. ^ 2 cl, 2 dwg

Description

The invention relates to nuclear energy and allows you to control the boiling and density of the coolant in different states of the reactor.

Known technical solution:

RU 2032235, IPC 6 G21C 17/038. A method for controlling sodium boiling in the core of a nuclear reactor.

The inventive pulse acoustic signals are measured at three points located on the periphery of the active zone above the heads of the fuel assemblies symmetrically relative to its center. Discriminate the measured pulses in amplitude from the background acoustic noise. By the presence of pulses from the monitoring points for a period of time t = l / V, where l is the maximum distance between the sensors; V is the speed of the acoustic signal in sodium; sodium boiling is judged. Comparison of the measured time intervals between pulses with tabular values for each fuel assembly and determine the place of boiling sodium.

The indicated solution is designed to detect boiling of sodium as a coolant, does not take into account the features of detecting boiling of coolant - water in VVER reactors, and does not allow, accordingly, to clarify the real conditions of heat removal in a specific active zone, more accurately determine the design limits of more intense active zones for reactors of the type VVER.

The solution is also known:

RU (11) 2063653, IPC 6 G21C 17/00. Detector of coolant boiling on the surface of a fuel element in the core of a nuclear reactor.

The boiling detector is a direct charge detector, in which the fuel rod core is used as an emitter of electrons, and isolated sections located around the fuel rod are used as an electron collector. One of the sections of the electron collector is directly adjacent to the cladding of the fuel rod, and there is a gap between the other sections and the cladding, inside which there is a coolant layer, the fact of which boiling or its density is established.

However, the known solution also does not allow its application in VVER reactors, for which it is not allowed to place foreign elements on the fuel rod walls or introduce elements into the inter-fuel space due to deterioration of heat removal, which, accordingly, does not allow timely detection of coolant boiling in the reactor core and quickly to prevent the deterioration of heat transfer, to clarify the real conditions of heat removal in a particular core, to more accurately determine the design limits of more stressed core zones. Closest to the claimed one is the solution: SU 865024 A1, IPC 5 G21C 17/038.

A device for diagnosing coolant boiling in the core of a nuclear reactor, comprising a neutron detector, a bandpass filter, a comparison unit, boiling diagnostic tools, a nonlinear conversion unit, a differentiation unit, the first and second signal dispersion determination units, and a division unit.

In this solution, only a channel with signal processing elements is proposed, but no method for detecting coolant boiling in the reactor core is not specified. The channel proposed in the application differs from the proposed one in that only the declared permission to register changes in the neutron flux up to 0.001% at the rated power of the reactor in a given frequency band is required. In this case, any known method of processing the variable part of the neutron detector signal can be applied. Also, the proposed channel is characterized in that it measures the constant component of the signal proportional to the neutron flux, the value of which requires the proposed method.

With prolonged boiling of the coolant in the core of a nuclear reactor, deposits form, which leads to a significant deterioration in heat transfer. In addition, during boiling, active impurities (lithium, chlorine, fluorine) accumulate in the pores of the TVEL cladding, which enhance the corrosion rate of the zirconium alloy with 1% niobium. Monitoring the moment of occurrence of the coolant boiling will make it possible to clarify the real conditions of heat removal in a particular active zone and more accurately determine the design limits of more stressed active zones.

That is, in the known solution, the timely detection of the coolant boiling in the reactor core, the prevention of heat transfer deterioration, the accumulation of active impurities (lithium, chlorine, fluorine) that enhance the corrosion rate of the zirconium alloy with 1% niobium, clarification of the actual heat removal conditions in a concrete core, more accurate definition of design limits of more stressed core areas.

Thus, the technical task of the proposed solution is the timely detection of coolant boiling in the reactor core, prevention of heat transfer deterioration, accumulation of active impurities (lithium, chlorine, fluorine) that enhance the corrosion rate of a zirconium alloy with 1% niobium, clarification of real heat removal conditions in a specific core , a more accurate determination of the design limits of more stressed active zones for VVER-type reactors.

The solution of this technical problem provides the use of the proposed combination of essential features.

A method for detecting coolant boiling in the VVER reactor core, including estimating neutron flux fluctuations, processing and isolating detector signals with predetermined parameters, and neutron flux fluctuations, processing and isolating detector signals with preset parameters, are estimated by the height of the controlled fuel assembly (FA) taking into account the corresponding compensation calculated according to the testimony of all the assemblies of the DN with respect to fluctuations of the neutron flux at the entrance to this fuel assembly, fluctuations of the neutron flux they are recorded reliably, sensors collected in a certain order along the fuel assembly height and uniformly distributed in the reactor core constituting the measuring channel, moreover, when detecting neutron flux fluctuations, they provide a resolution of not more than 0.001% at the rated power of the reactor, and to isolate the signal at the sensitive location parts of the detector compensate for spurious signals and suppress signals associated with industrial interference, the specified parameters of the processed signals are set to often a wide range from 0.1 Hz to 8 Hz and the processed signals are transmitted to a computer complex for their further processing, which ensures the detection of the presence of boiling coolant.

A channel for detecting coolant boiling in the VVER reactor core, including neutron detectors, a bandpass filter to isolate the frequency range characteristic of boiling diagnostics, signal processing units, and neutron detectors are made in the form of direct charging sensors with a rhodium sensitive element, uniformly distributed over the height controlled fuel assembly (FA) and at the entrance to this FA, moreover, the parameters of the processed signals are set in the frequency range from 0.1 Hz to 8 Hz, signal processing units equipped with means for recording the constant component of the detector signal proportional to the neutron flux and means for recording the variable component proportional to the change in the neutron flux, having a resolution of not more than 0.001% at the rated power of the reactor, means for compensating spurious signals to isolate the signal at the location of the sensitive part of the detector, signal suppression means, associated with industrial interference, means of converting an analog signal into a digital code for transferring giving a signal to a computer complex for analysis.

The proposed technical solution is based on an assessment of the change in the relative sensitivity of the fluctuations of the neutron flux over the height of the controlled fuel assembly (FA) to fluctuations in the parameters of the coolant, taking into account the corresponding compensations calculated according to the readings of all the assemblies of the beam. Fluctuations of the neutron flux along the height of the controlled fuel assemblies are estimated with respect to fluctuations of the neutron flux at the entrance to this fuel assembly. With the occurrence of coolant boiling, the relative sensitivity of the fluctuations of the neutron flux in the region of vaporization to fluctuations in the parameters of the coolant changes significantly. Exceeding the relative value of the fluctuation of the neutron flux of a given limit determines the vaporization in a controlled fuel assembly. Fluctuations in the neutron flux are detected by neutron sensors (NDs), capable of detecting fluctuations in the neutron flux in the frequency range up to about 8 Hz. The sensors must be located in a certain order according to the height of the fuel assemblies in the sensor assembly. Sensor assemblies should be as evenly distributed as possible in the reactor core. The regular arrangement of neutron sensors in the VVER core is suitable for this method of detecting coolant boiling.

Due to various factors such as:

- rotation of the blades of the main circulation pumps (MCP);

- different temperatures of the coolant loops of the cold thread of the 1st circuit;

- heterogeneous mixing of the coolant in the lower mixing chamber;

- acoustic waves, etc.,

in the coolant there are always fluctuations in the properties of the coolant. These fluctuations lead to fluctuations in the density of the coolant in the core and, due to this, to fluctuations of the neutron flux in the fuel assembly. Fluctuations of the neutron flux depend on fluctuations in the density of the coolant due to a change in the moderating properties of the coolant.

The magnitude of the fluctuation of the neutron flux depends on:

- the magnitude of the neutron flux;

- burnout fuel assemblies;

- sensitivity and burnout of the neutron sensor; the ratio of fluctuations and amplitude values of different parameters of the coolant (flow rate, temperature, pressure), etc. The amplitude of the fluctuation of the neutron flux is proportional to the average value of the neutron flux. Fluctuations of the neutron flux are determined by the variable component of the DN current, and the average value of the neutron flux is determined by the main component of the DN current. As an estimated parameter of the coolant fluctuation, the value of the standard deviation of the alternating component of the DN current, reduced to the average current of the DN, was selected. All values are determined on the analysis interval.

The amplitude of fluctuations of the neutron flux, without boiling of the coolant, varies along the height of the fuel assembly. This change depends on the ratio of amplitudes, phases of temperature fluctuations, pressure and coolant flow. These relationships do not have significant differences at the input to all FAs in the core in the analyzed frequency range. Since the relative sensitivity of the neutron flux by the height of the fuel assembly to the lower part of the fuel assembly is estimated, the corresponding compensation calculated according to the readings of all the assemblies of the beam is constantly introduced.

When vaporization occurs, the relative sensitivity of the neutron flux along the height of the fuel assembly to the lower part of the fuel assembly changes significantly. Fluctuations in the parameters of the coolant and the resulting deformations of the axial profile of energy release lead to a height drift of the boundaries of the beginning and end of vaporization, which leads to an increase in the nonlinearity of the change in the density of the coolant with the onset of boiling. The amplitude of fluctuations in the density of the coolant caused by fluctuations in its parameters increases significantly during vaporization, as a result of which the sensitivity of the neutron flux detected by the sensor to fluctuations in the parameters of the coolant increases.

Thus, a local increase in the relative sensitivity of the neutron flux noise to fluctuations in the parameters of the coolant serves as a signal of the presence of boiling coolant.

To implement the indicated method for detecting coolant boiling, a measuring channel including neutron detectors, measuring equipment, and signal pre-processing means is suitable.

In the proposed measuring channel, direct charge sensors with a rhodium sensitive element (RPS) used in standard core core monitoring systems can be used as detectors.

The channel should provide registration of the constant component of the detector signal proportional to the neutron flux, and registration of the variable component proportional to the change in the neutron flux to 0.001% at the rated power of the reactor. The measuring channel should provide compensation for spurious signals to isolate the signal at the location of the sensitive part of the detector. In the measuring channel, signals associated with industrial interference must be suppressed. To highlight the frequency range characteristic of boiling diagnostics, the measuring channel should contain a band-pass filter. To transmit a signal to a computer complex for analysis, the channel must provide the conversion of the analog signal into a digital code.

It should be noted that the structure of the measuring channel, shown as an example in FIG. 1, explains the specific solution, but, while providing the necessary characteristics, it may have a structure different from the given graph.

The proposed solution is illustrated graphically.

Figure 1 presents a diagram of the measuring channel (channel detecting the boiling of the coolant in the core of the WWER reactor).

Figure 2 presents an illustration of a diagnostic method for boiling a coolant.

In the drawings (Fig. 1, Fig. 2), the positions indicated:

1 - neutron detectors;

2 - differential amplifier;

3 - analog-to-digital Converter constant components of the signal;

4 - high-pass filter;

5 - signal amplifier;

6 - notch filter;

7 - signal amplifier;

8 - band-pass filter;

9 - signal amplifier;

10 - analog-to-digital Converter variable signal components;

11 - signal processing units;

12 - values of dynamic limits calculated for each processed detector signal at the time of analysis of the state of the active zone;

13 - the moment of exceeding the dynamic limits;

14 - the values of the analyzed quantities obtained by processing the variable and constant components of the signals of the detectors (for TV S-2 two sets of values);

15 - values of the curve of approximation of the analyzed values at the locations of the DPS;

16 - the values of the analyzed values at the entrance to the fuel assembly, relative to which the relative sensitivity is estimated;

17 - allowable limits of the analyzed values at the entrance to the fuel assembly, calculated at the time of analysis of the state of the active zone.

Figure 2 also shows:

TVS-1, TVS-2 - symbols of various graphs.

In accordance with the proposed solution

neutron detectors 1 are made in the form of direct charging sensors with a sensitive element of rhodium and are uniformly distributed over the height of the controlled fuel assembly,

differential amplifier 2 of the detector signal provides compensation for spurious signals and signal amplification,

analog-to-digital Converter 3 provides processing of the constant component of the detector signal, which is proportional to the neutron flux, the high-pass filter 4 serves to remove the constant component of the detector signal,

suppression of signals associated with industrial interference, provides a notch filter 6,

the band-pass filter 8 is designed to highlight the frequency range characteristic of the diagnosis of boiling and additional suppression of industrial interference,

additional analog-to-digital Converter 10 provides the processing of the variable component of the detector signal,

signal processing units 11 form a computing complex inside the reactor noise diagnostics - VKVRShD, receiving data from the reactor installation, digitized values of the constant and variable components of the detector signals for analysis and diagnostics of boiling.

Moreover, as mentioned earlier, the channel for processing the variable component of the signal, proportional to the change in the neutron flux, has a resolution of not more than 0.001%, at the rated power of the reactor.

Claims (2)

1. A method for detecting coolant boiling in the VVER reactor core, including estimating neutron flux fluctuations, processing and isolating detector signals with predetermined parameters, characterized in that neutron flux fluctuations, processing and isolating detector signals with predetermined parameters are estimated by the height of the controlled fuel assembly ( FA) taking into account the corresponding compensations calculated from the readings of all assemblies by neutron sensors (ND) with respect to the fluctuations of the neutron flux at the entrance to this TV C, neutron flux fluctuations are additionally recorded by sensors assembled in a certain order along the fuel assembly height and uniformly distributed in the reactor core constituting the measuring channel, and when registering neutron flux fluctuations, they provide a resolution of not more than 0.001% at the rated power of the reactor, in order to isolate the signal in place the location of the sensitive part of the detector compensates for spurious signals and suppresses signals associated with industrial interference, the specified processing parameters proxy signals set in the frequency range from 0.1 Hz to 8 Hz, and transmitting the processed signals to a computer system for further processing, which provides detecting the presence of coolant boiling. 2. A channel for detecting coolant boiling in the VVER reactor core, including neutron detectors, a bandpass filter for isolating the frequency range characteristic of boiling diagnostics, signal processing units, characterized in that the neutron detectors are made in the form of direct charge sensors with a rhodium sensitive element, evenly distributed over the height of the controlled fuel assembly (FA) and at the entrance to this fuel assembly, and the parameters of the processed signals are set in the frequency range from 0.1 Hz to 8 Hz, blocks about signal processing is equipped with means for detecting the constant component of the detector signal proportional to the neutron flux, and means for detecting the variable component proportional to the change in the neutron flux, having a resolution of not more than 0.001% at the rated power of the reactor, means for compensating spurious signals to isolate the signal at the location of the sensitive part of the detector, means for suppressing signals associated with industrial interference, means for converting an analog signal to digital oic code for transmitting a computer system for analysis.

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