CN111489842B - Method for measuring power distribution of pressurized water reactor core when xenon poison is not balanced yet - Google Patents
Method for measuring power distribution of pressurized water reactor core when xenon poison is not balanced yet Download PDFInfo
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- Y02E30/00—Energy generation of nuclear origin
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Abstract
The invention discloses a method for measuring the power distribution of a pressurized water reactor core when xenon poison is not balanced, which utilizes core nuclear design software to calculate and generate a core theoretical database when the core power distribution measurement is implemented; measuring the power distribution of the reactor core and processing the power distribution based on a theoretical database to generate three-dimensional power distribution of the reactor core, wherein the obtained radial power distribution of the reactor core is considered to be the distribution when xenon is balanced, and the axial power distribution is obtained through the subsequent steps; based on the change of the out-of-core neutron detector signals in a period of time before the core power distribution measurement is implemented, the law that the in-core axial power distribution changes along with the time is extracted, the axial power distribution during the xenon-toxicity balance is deduced, and the obtained radial power distribution is combined to obtain a complete core power distribution result. The method can measure without waiting for xenon poison balance, greatly shortens the time required by the nuclear power plant to run when the nuclear power plant is increased to full power, and can obviously improve the running efficiency of the nuclear power plant.
Description
Technical Field
The invention belongs to the technical field of nuclear power, and particularly relates to a method for implementing a reactor core power distribution measurement test on each liter of power platform in a pressurized water reactor nuclear power plant.
Background
Nuclear reactors are the heart components of nuclear power plants, the locations where nuclear energy is continuously converted into heat energy, and the locations where radioactivity is most concentrated in nuclear power plants. In order to ensure the safety of the nuclear reactor, nuclear power operators need to ensure that the position (hot spot) of the volume heat release rate peak value in the reactor is always effectively cooled, so as to ensure that the nuclear fuel element does not fail. However, since nuclear fuel is always sealed in a thick and heavy steel pressure vessel when the reactor is operated, detailed information of core power distribution cannot be obtained only by means of a nuclear probe disposed outside the reactor. In order to accurately grasp the operating state of the reactor, the relevant specifications of the pressurized water reactor nuclear power plant in China clearly specify the individual power platforms (e.g. 30% P) which are required for the start-up operation of the reactor N 、50％P N 、75％P N 、87％P N Etc.) and full power (100% N ) At different burn-up stages after operation, core neutron flux density/power distribution measurement tests are performed to determine key safety parameters (such as nuclear hotspot factor F) associated with the core power distribution q N Nuclear enthalpy rise factor
Quadrant power ramp ratio QPTR, etc.) is confirmed and supervised within operating limits, while also verifying the correctness of the core design and core nuclear fuel loading of the core.
Currently, the measurement of the reactor core neutron flux density/power distribution of most pressurized water reactor nuclear power units in service in China is realized by a mobile reactor core neutron flux measurement system. The system consists of a hardware system for performing in-stack measurements and a software system for measurement data processing.
As shown in fig. 1, when core power distribution measurement is performed, an operator sends a command through a main control cabinet of a measurement system in a main control room, a driving device between core instruments sends a mobile neutron detector 1 (a miniature fission chamber) into a fuel assembly selected by the control system from the bottom of a pressure vessel 2 along a preset finger sleeve 3, the mobile neutron detector moves to the top of the fuel assembly at a high speed, then the mobile neutron detector is drawn back at a low speed, detector current signals at different heights are recorded in the drawing back process to perform measurement, and the mobile neutron detector is drawn back to a mechanical origin at a high speed after the detector completes measurement of one fuel assembly.
In view of the fact that a large commercial pressurized water reactor often has hundreds of groups of fuel assemblies, in order to improve the measurement efficiency, a mobile reactor core neutron flux measurement system is often provided with a plurality of detectors to simultaneously measure different fuel assemblies in the reactor (the number of the detectors is different from 3 to 5 according to the difference between the reactor power and the number of the reactor core fuel assemblies in engineering), and the movable detectors simultaneously complete the measurement process, namely completing one measurement process.
When the movable neutron detector is used for carrying out in-reactor measurement, all fuel assemblies in the reactor are not covered, because the nuclear fuel loading scheme of a large commercial pressurized water reactor core often has certain symmetry, in the reactor design stage, a design party can select a part of fuel assemblies (usually the number is between 1/4 and 1/3 of the total number of the nuclear fuel assemblies in the reactor) to preset thimble tubes on the basis of considering the symmetry, and only the selected fuel assemblies have the condition for carrying out in-reactor neutron flux density/power measurement. FIG. 2 shows the distribution of measuring channels in a certain pressurized water reactor in China. In engineering, a single in-pile measurement process that passes through a plurality of measurement ranges and passes through all measurement channels in a pile is generally and visually called as drawing a full flux map or a single full flux map measurement, and a single in-pile measurement process that is only carried out on partial measurement channels is called as drawing a partial flux map or a single partial flux map measurement.
After the measurement signals are obtained by the hardware system, the specific software matched with the neutron flux measurement system in the movable reactor core is required to process the detailed information of the three-dimensional space distribution of the power (heat release rate) of the fuel assemblies in the reactor core. The special processing software applied in the current engineering generally comprises two parts, wherein the first part is mainly used for preprocessing the measurement data, such as converting the measured current signal of the detector into the reaction rate of nuclear reaction between a sensitive nuclide and neutrons in a reactor (the reaction rate is in direct proportion to the neutron flux density level of the position where the probe passes), aligning the reaction rate values given by different measuring ranges and different detectors in the same measuring range, and performing proper smoothing processing on the reaction rate data finely distributed along the height direction. The second part of software generally corrects various factors of data given by the previous software processing, such as correcting the background signal of a detector and the influence of the total power level fluctuation of the reactor between different measuring ranges, correcting the influence of different detector sensitivities and the like, and then finally gives a measured value of the detailed three-dimensional power distribution of the whole reactor core by combining a theoretical calculated value of the reaction rate of sensitive nuclides at a measuring channel given by the reactor core design software and a corresponding theoretical calculated result (generally called as a theoretical database or a theoretical library) of the neutron flux density/power distribution in the whole reactor core.
The method for obtaining the reactor core three-dimensional power distribution measurement value through the measurement of the part of the measurement channel in the reactor and the combination of the theoretical calculation result of the whole reactor core is the common practice of the pressurized water reactor nuclear power engineering at present. One obvious disadvantage of the practice is that after the reactor power is increased to the level required by the core power distribution measurement test, the unit is required to be operated for a period of time after the platform is stably operated. As required by the specifications of some types of pressurized water reactors at 30% N 、75％P N 、87％P N (if necessary) the measurement can only be carried out after the power plateau has stabilized for 24 hours, at 100% N The measurement can be carried out after the power platform is stabilized for 48 hoursAmount, and the like. Obviously, such a requirement would extend the time for the unit to reach full power to generate electricity after each shutdown and refueling, thereby compromising the economics of the unit.
The requirement of the existing method for the stability time of the unit before the test is mainly due to the limitation of the theoretical library for test data processing in the aspect of applicability. Since the theoretical library is prepared in the prior art before the actual measurement is started, the specific core conditions, especially the concentration level and spatial distribution of xenon (neutron "toxin" xenon-135, which is a fission product having the greatest influence on the operation of a pressurized water reactor) lagging behind the core power variation, cannot be known in advance when the theoretical library is generated, but the core is assumed to be in a xenon equilibrium state at the corresponding power level. After the actual reactor is raised to a new power level, the xenon poison level and the spatial distribution in the actual reactor can reach or basically reach an equilibrium state after a period of slow evolution, namely the application condition of a prefabricated theoretical library is reached. This is the most fundamental reason that current methods prescribe the settling time of the unit before each power-liter platform performs the in-stack measurement.
It should be further noted that the final measurement of the given core power distribution, in particular the nuclear fuel assembly power and F, is carried out as required by the current PWR core power distribution measurement test procedures q N and F Δ N h And comparing the key safety parameters with corresponding values given by the nuclear design software to determine whether the safety parameters are within the operation limit range, and verifying the correctness of the core design. Similarly, because the core design is completed earlier than the reactor is started, the relevant parameters given by the core design are all values when the xenon poison in the reactor is already in equilibrium.
Disclosure of Invention
The invention provides a method for measuring the power distribution of the reactor core of a pressurized water reactor nuclear power plant under the condition that xenon poison is not balanced aiming at the defect that the conventional reactor core power distribution measuring method of the pressurized water reactor nuclear power plant can carry out measurement after each liter of power platform needs to wait for the xenon poison to be balanced, so that the time required by the nuclear power plant to run when the power is increased to full power is obviously shortened. The method does not need any hardware modification on the conventional movable reactor core neutron flux measurement system of the nuclear power plant, and can be realized only by changing the test flow and the measurement data processing method.
Therefore, the technical scheme of the invention is as follows: a method of pressurizing a water reactor core power distribution measurement while xenon poison is not yet balanced, comprising the steps of:
1) Calculating and generating a reactor core theoretical database when the reactor core power distribution measurement is implemented by utilizing reactor core nuclear design software;
2) Measuring the power distribution of the reactor core and processing the power distribution based on a theoretical database to generate three-dimensional power distribution of the reactor core, wherein the obtained radial power distribution of the reactor core is considered to be the distribution when xenon is balanced, and the axial power distribution is obtained through the subsequent steps;
3) Extracting the law of the change of the in-core axial power distribution along with the time based on the change of the out-of-core neutron detector signal in the previous period of time for measuring the core power distribution, deducing the axial power distribution when obtaining the xenon balance, and combining the radial power distribution obtained in the step 2) to obtain a complete core power distribution result.
The theoretical basis of the invention is as follows: because the radial dimension of the commercial pressurized water reactor is often smaller than the axial dimension, the inherent design characteristic is that the power rise process of a nuclear power plant, the disturbance source causing the change of the reactor core power distribution shape mainly comes from the movement of an axial control rod, and after the power is changed, the xenon poison distribution in the reactor is different in the radial and axial evolution rules. Equilibrium distribution is achieved more quickly in the radial direction (large commercial stacks are generally substantially in equilibrium for 6 hours); while in the axial direction the equilibrium is reached over a much longer time evolution. In practice, however, the evolution of the reactor axial power distribution can be monitored in real time by just the out-of-reactor neutron detector. The method lays a foundation for carrying out the core power distribution measurement under the condition of unbalanced xenon poison by radial and axial separation.
More specifically, the present invention may employ the following steps:
(1) Generating a theoretical database implementing in-heap measurement conditions:
existing nuclear design software is used to generate a theoretical database for in-core measurements (xenon toxicity is not balanced).
Similar to the current method, the invention also requires a theoretical database to be combined with the in-core measurement data to obtain detailed three-dimensional power distribution information of the whole reactor core. However, unlike current theoretical libraries, which are all generated for xenon poison balanced cores, the theoretical database of the present invention is generated for xenon poison unbalanced cores. Specifically, the theoretical library used in the present invention is generated for the core state at which the in-core measurements are taken several hours (e.g., 6 hours) after the reactor reaches the power-up platform. The theoretical library can be prepared according to the determined power-up rate, specific control rod operation rules of various types of reactors and other information before in-reactor measurement, or can be generated afterwards according to specific reactor operation history after in-reactor measurement. The software tools used to generate the theoretical library, as well as the data content and data format contained in the theoretical library, are the same as those used in the current practice, and may be generated, for example, using the pressurized water reactor core design software system SCIENCE, or using the ORIENT system developed by the inventor.
(2) Recording the out-of-stack power range detector signal:
unlike current core power distribution measurements that use only in-core measurement signals, the implementation of the present invention also requires the use of an out-of-core power range detector signal. For this purpose, the overboard power range detector signal is recorded completely after the reactor reaches the power level corresponding to the test and before the core power distribution measurement is actually performed (for example, 6 hours). It should be noted that these signals are provided by the existing external nuclear measurement system of the pressurized water reactor, and the present invention is only to use these signals for the present invention.
(3) Full-flux map measurements were performed:
the existing mobile reactor core neutron flux measurement system of a pressurized water reactor power plant is utilized to carry out primary total flux map measurement. The implementation method is completely consistent with the current practice. It should be noted that the current practice requires waiting 24 hours at the power-up platform to perform the in-heap measurement, while the method of the present invention only needs waiting 6 hours to perform the in-heap measurement.
(4) Obtaining three-dimensional core power distribution under measurement conditions
After a theoretical library is generated in the step (1) and the in-core flux measurement result is obtained in the step (3), the measured three-dimensional reactor core power distribution is processed and generated by using the existing in-core flux measurement data processing software (such as CEDRIC/CARIN/ETALONG) according to the existing processing method. The power distribution is typically made up of an axial multi-level (e.g., 57 levels) two-dimensional power distribution and a corresponding core-averaged axial power distribution (existing software may also give axial power distributions for more levels (e.g., 230 levels)). It should be noted that, in the present invention, since step (1) and step (3) are both performed on the xenon unbalanced core, the three-dimensional core power distribution obtained in this step is also under the xenon unbalanced condition, and a subsequent data processing step is also performed to obtain a core power distribution result similar to that obtained in the existing method and capable of being used for verifying the nuclear design.
(5) Scale coefficient for generating out-of-pile power range by using' one-point method
According to the reactor core three-dimensional power distribution result generated in the step (4) and the out-of-core power range detector signal corresponding to the measurement state, the scale coefficient of each out-of-core detector channel under the corresponding power platform, namely K, is generated by applying the method invented by the applicant (patent number: ZL 2017 1 0897802.0) for completing the scale of the out-of-core detector by utilizing single in-core flux measurement U 、K L And alpha. The method comprises the following specific steps:
(1) obtaining the sensitivity of each out-of-pile detector by using a primary in-pile flux measurement result;
(2) generating different reactor core axial power deviation states and theoretical calculation values of the current of each out-of-core detector corresponding to each state through numerical simulation;
(3) correcting the off-stack detector current value generated by the numerical simulation in the second step by using the detector sensitivity derived from the first step;
(4) according to a traditional test data processing method, scale coefficients of the out-of-pile detector are generated, and the implementation method is as follows:
i) And (4) merging and generating the upper and lower currents of each detector channel outside the pile based on the result of the step (3):
ii) against datasets
And &>
K =1,2 …, K is respectively subjected to least square linear fitting, and for each out-of-pile detector channel i, the following two linear relations are obtained:
I U ＝a U ×AO+b U
I L ＝a L ×AO+b L
iii) Generating an axial deviation gain coefficient alpha and upper and lower detector current conversion coefficients K of each out-of-pile detector channel according to the fitting result of the previous step U And K L
Wherein the axial deviation gain coefficient alpha is calculated by the following formula
α＝1/(50×a U /b U -50×a L /b L )
And the current conversion coefficient K of the upper and lower detectors U And K L Then after the current is normalized, the current is calculated according to the following formula:
K U ＝50/(b U ×K norm )
K L ＝50/(b L ×K norm )
in the formula (I), the compound is shown in the specification,K norm normalizing the analog calculation current of the detector to the factor of the actually measured current;
wherein: the order of step (1) and step (2) may be interchanged.
(6) Backtracking the fluctuation of the deviation of the reactor power and the axial power before the flux measurement in the reactor is carried out under the current power platform, and selecting and determining a time period for analysis according to the fluctuation:
based on the current signal of the out-of-reactor ionization chamber recorded in the step (2) and the scale coefficient obtained in the step (5), the change of the reactor power P and the axial power deviation delta I along with the time t in the period of 6 hours before the in-reactor flux measurement is carried out under the current power platform is obtained by the following formula:
P(t)＝K U ×I U (t)+K L ×I L (t)
ΔI(t)＝α[K U ×I U (t)-K L ×I L (t)]
and selecting and determining a starting time t for subsequent data analysis depending on whether the reactor power is stable and whether the Δ I has exhibited a relatively stable time-varying law 0
The meaning of each symbol here is expressed as follows:
I U : the current signal of the out-of-core power range detector positioned at the upper half part of the reactor core;
I L : the current signal of the out-of-core power range detector is positioned at the lower half part of the reactor core;
K U : the conversion coefficient between the current of the upper half power range detector and the power of the upper half reactor core;
K L : the conversion coefficient between the current of the lower half power range detector and the power of the lower half reactor core;
α: core axial deviation gain factor.
(7) The change of the axial power distribution in the reactor along with the time is constructed based on the out-of-reactor power range detector signal:
selecting the position t in the out-of-pile detector signal obtained in the step (2) 0 To t M Data of time periods, where t, to construct a fine axial power distribution in the reactor over time M The moment at which the in-stack flux measurement is performed for step (3). The specific construction method is as follows:
here, the
For a column vector formed by the measurement signals of N detectors in one channel of the out-of-stack detector at time t, and
is the normalized power of N axial layers in the reactor deduced according to the measuring signal. Intermediate for conversion [ C]、[T]And [ S ]]The specific meanings of these three matrices, which are well known in the art, can be found in the literature: xue Bin, fan Zhiguo, jing, et al, neutron transmission matrix research, nuclear power engineering, vol 30, no. 6 (supplement), pages 88-91, month 12 in 2009; zhang Hong, power distribution measurement and processing in nuclear power plant core in Bay of great Asia, nuclear science and engineering, vol.17, no. 1, pages 1-11, 3 months 1997.
It should be noted that, in the present invention, both the correction matrix [ C ] and the transmission matrix [ T ] are considered to be known, which results in a method that is well established in the industry. And the sensitivity matrix [ S ] can be regenerated in the present invention based on the results of the three-dimensional power distribution of the core generated in step (4) using the method reported in the aforementioned document.
(8) Obtaining the law of the reactor core power distribution changing along with time, and deriving the distribution under the xenon poison balance condition according to the law:
this step needs to be completed in several sub-steps:
a) Based on the result of step (7), calculating
b) Order to
Each element of (1) Δ P n N =1,2, …, the time-varying law of N satisfies
And based on t 0 To t M Period deltaP n A is determined by a least square fitting method n And λ n 。
c) Calculating the deviation between the axial power distribution of the core obtained by measurement in the non-equilibrium state of xenon according to the result of the sub-step b) and the equilibrium state of xenon, i.e.
Here, the
Is the coefficient a determined by sub-step b) n N =1,2, …, N. />
d) Expanding the deviation information determined in sub-step c) to a finer scale (e.g. 57 or 230)
The specific meaning of the geometric matrix [ G ] is also found in the documents [1-2], which are also considered to be known in the present invention, which leads to methods well established in the art.
e) Obtaining fine axial power distribution in a xenon-poison equilibrium reactor
Here, the
Fine axial power distribution in the reactor obtained by the step (4) processing.
f) Combining the fine axial power distribution in the reactor obtained in the sub-step e) and the two-dimensional power distribution of each axial layer obtained by processing in the step (4), the three-dimensional power distribution of the reactor core which can be finally compared with the result given by the software for designing the reactor core nuclear under the invention is obtained. Key safety parameters related to the core power distribution may also be generated further from the distribution.
By adopting the method, the measurement can be carried out without waiting for xenon-toxicity balance, the time required by the nuclear power plant to run at full power is greatly shortened, and the running efficiency of the nuclear power plant can be obviously improved.
Drawings
The following detailed description is made with reference to the accompanying drawings and embodiments of the present invention
FIG. 1 is a schematic diagram of a neutron flux measurement system for a movable reactor core;
FIG. 2 is a distribution diagram of the in-stack measurement channel (D).
Labeled in the figure as: the device comprises a detector 1, a pressure container 2, a finger sleeve 3, a driving cable 4, a guide pipe 5, a separation wall 6, an isolation valve 7 and a sealing section 8.
Detailed Description
The embodiment creatively provides a method for measuring the power distribution of the reactor core of a pressurized water reactor nuclear power plant under the condition that xenon poison is not balanced aiming at the defect that the measurement can be implemented only when each liter of power platform needs to wait for the balance of the xenon poison, and the method comprises the following steps:
1) Calculating and generating a reactor core theoretical database when measuring the power distribution of the reactor core by using reactor core nuclear design software;
2) Measuring the power distribution of the reactor core and processing the power distribution based on a theoretical database to generate three-dimensional power distribution of the reactor core, wherein the obtained radial power distribution of the reactor core is considered as the distribution of xenon-toxicity balance, and the axial power distribution is obtained through subsequent steps;
3) Extracting the law of the change of the in-core axial power distribution along with the time based on the change of the out-of-core neutron detector signal in the previous period of time for measuring the core power distribution, deducing the axial power distribution when obtaining the xenon balance, and combining the radial power distribution obtained in the step 2) to obtain a complete core power distribution result.
The present embodiment can adopt the following detailed steps:
(1) Generating a theoretical database implementing in-heap measurement conditions:
existing nuclear design software is used to generate a theoretical database when in-core measurements are performed (xenon toxicity is not yet balanced).
Similar to the current method, the invention also requires a theoretical database to be combined with the in-core measurement data to obtain detailed three-dimensional power distribution information of the whole reactor core. However, unlike current theoretical libraries, which are all generated for xenon poison balanced cores, the theoretical database of the present invention is generated for xenon poison unbalanced cores. Specifically, the theoretical library used in this embodiment is generated for the core state at which the in-core measurements are performed several hours (e.g., 6 hours) after the reactor reaches the boost platform. The theoretical library can be prepared according to the determined power-up rate, specific control rod operation rules of various types of reactors and other information before in-reactor measurement, or can be generated afterwards according to specific reactor operation history after in-reactor measurement. The software tools used to generate the theoretical library, as well as the data content and data format contained in the theoretical library, are the same as those used in the current practice, and may be generated, for example, using the pressurized water reactor core design software system SCIENCE, or using the ORIENT system developed by the inventor.
(2) Recording out-of-stack power range detector signals:
unlike the current core power distribution measurement method that only uses the in-core measurement signal, the present embodiment also needs to use the out-of-core power range detector signal. For this purpose, the overboard power range detector signal is recorded completely after the reactor reaches the power level corresponding to the test and before the core power distribution measurement is actually performed (for example, 6 hours). It should be noted that these signals are provided by the existing pwr uncore system, and the present embodiment is only to use these signals in the present embodiment.
(3) Full-flux map measurements were performed:
the existing mobile reactor core neutron flux measurement system of a pressurized water reactor power plant is utilized to carry out primary total flux map measurement. The implementation method is completely consistent with the current practice. It should be noted that the current practice needs to wait 24 hours at the power-up stage to perform the in-stack measurement, while the embodiment only needs to wait 6 hours to perform the in-stack measurement.
(4) Obtaining three-dimensional core power distribution under measurement conditions
After a theoretical library is generated in the step (1) and the in-core flux measurement result is obtained in the step (3), the measured three-dimensional reactor core power distribution is processed and generated by using the existing in-core flux measurement data processing software (such as CEDRIC/CARIN/ETALONG) according to the existing processing method. The power distribution is typically made up of an axial multi-level (e.g., 57 levels) two-dimensional power distribution and a corresponding core-averaged axial power distribution (existing software may also give axial power distributions for more levels (e.g., 230 levels)). It should be noted that, since step (1) and step (3) are both performed on the xenon poison unbalanced core, the three-dimensional core power distribution obtained in this step is also under the xenon poison unbalanced condition, and a subsequent data processing step is also performed to obtain a core power distribution result similar to that obtained in the existing method and used for verifying the nuclear design.
(5) Scale coefficient for generating out-of-pile power range by using' one-point method
According to the reactor core three-dimensional power distribution result generated in the step (4) and the out-of-core power range detector signal corresponding to the measurement state, the scaling coefficient, namely K, of each out-of-core detector channel under the corresponding power platform is generated by applying a method for completing out-of-core detector scaling by utilizing single in-core flux measurement (patent number: ZL 2017 0897802.0) invented by the applicant U 、K L And alpha. The method comprises the following specific steps:
(1) obtaining the sensitivity of each out-of-pile detector by using a primary in-pile flux measurement result;
(2) generating different reactor core axial power deviation states and theoretical calculation values of the current of each out-of-reactor detector corresponding to each state through numerical simulation;
(3) correcting the off-stack detector current value generated by the numerical simulation of the step two by using the detector sensitivity derived from the step one;
(4) according to a traditional test data processing method, scale coefficients of the out-of-pile detector are generated, and the implementation method is as follows:
i) And (4) merging and generating upper and lower currents of each detector channel outside the pile based on the result of the step (3):
ii) against datasets
And &>
K =1,2 …, K performs least square linear fitting respectively, and obtains the following two linear relations for each out-of-stack detector channel i:
I U ＝a U ×AO+b U
I L ＝a L ×AO+b L
iii) Generating an axial deviation gain coefficient alpha and upper and lower detector current conversion coefficients K of each out-of-pile detector channel according to the fitting result of the previous step U And K L
Wherein the axial deviation gain coefficient alpha is calculated by the following formula
α＝1/(50×a U /b U -50×a L /b L )
And the current conversion coefficient K of the upper and lower detectors U And K L Then after the current is normalized, the current is calculated according to the following formula:
K U ＝50/(b U ×K norm )
K L ＝50/(b L ×K norm )
in the formula, K norm Normalizing the analog calculation current of the detector to the factor of the actually measured current;
wherein: the order of step (1) and step (2) may be interchanged.
(6) Backtracking the fluctuation of the deviation of the reactor power and the axial power before the flux measurement in the reactor is carried out under the current power platform, and selecting and determining a time period for analysis according to the fluctuation:
based on the current signal of the out-of-reactor ionization chamber recorded in the step (2) and the scale coefficient obtained in the step (5), the change of the reactor power P and the axial power deviation delta I along with the time t in the period of 6 hours before the in-reactor flux measurement is carried out under the current power platform is obtained by the following formula:
P(t)＝K U ×I U (t)+K L ×I L (t)
ΔI(t)＝α[K U ×I U (t)-K L ×I L (t)]
and selecting and determining a starting time t for subsequent data analysis depending on whether the reactor power is stable and whether the Δ I has exhibited a relatively stable time-varying law 0
The meaning of each symbol here is expressed as follows:
I U : the current signal of the out-of-core power range detector positioned at the upper half part of the reactor core;
I L : the current signal of the out-of-core power range detector is positioned at the lower half part of the reactor core;
K U : the conversion coefficient between the current of the upper half power range detector and the power of the upper half reactor core;
K L : the conversion coefficient between the current of the lower half power range detector and the power of the lower half reactor core;
α: core axial deviation gain factor.
(7) The change of the axial power distribution in the reactor along with the time is constructed based on the out-of-reactor power range detector signal:
selecting the position t in the out-of-pile detector signal obtained in the step (2) 0 To t M Data of time periods, where t, to construct a fine axial power distribution in the reactor over time M The moment at which the in-stack flux measurement is performed for step (3). The specific construction method is as follows:
here, the
For a column vector formed by the measurement signals of N detectors in one channel of the off-stack detector at time t, and
is the normalized power of the N axial layers in the reactor deduced from the measured signal.
The three matrices [ C ], [ T ] and [ S ] used for the conversion in between, the specific meanings of which are well known in the art, can be found in the literature: xue Bin, fan Zhiguo, jing li, et al, neutron transmission matrix research, nuclear power engineering, volume 30, no. 6 (supplement), pages 88-91, 12 months 2009; zhang Hong, power distribution measurement and processing in nuclear power plant core in Bay of great Asia, nuclear science and engineering, vol.17, no. 1, pages 1-11, 3 months 1997.
It should be noted that, in the present embodiment, the correction matrix [ C ] and the transmission matrix [ T ] are considered to be known, which results in a method that is well-established in the industry. And the sensitivity matrix [ S ] can be regenerated in this embodiment based on the results of the three-dimensional power distribution of the core generated in step (4) using the method reported in the aforementioned document.
(8) Obtaining the law of the reactor core power distribution changing along with time, and deriving the distribution under the xenon poison balance condition according to the law:
this step needs to be completed in several sub-steps:
g) Based on the result of step (7), calculating
h) Order to
Each element of (1) Δ P n N =1,2, …, the time-varying law of N satisfies
And based on t 0 To t M Duration Δ P n A is determined by a least square fitting method n And λ n 。
i) Calculating the deviation between the axial power distribution of the reactor core obtained by measuring the xenon gas in the nonequilibrium state and the xenon gas in the equilibrium state according to the result of the substep b), namely
Here, the
Is the coefficient a determined by sub-step b) n N =1,2, …, N.
j) Expanding the deviation information determined in sub-step c) to a finer scale (e.g. 57 or 230)
The specific meaning of the geometric matrix G is also found in the above-mentioned documents, which are also considered to be known in the present embodiment, which results in a method well established in the industry.
k) Obtaining fine axial power distribution in a reactor in a xenon poison equilibrium state
Here, the
Fine axial power distribution in the reactor obtained by the step (4) processing.
Combining the fine axial power distribution in the reactor obtained in the sub-step e) and the two-dimensional power distribution of the axial layers obtained by the processing in the step (4), the three-dimensional power distribution of the core which can be finally compared with the result given by the core nuclear design software in the embodiment is obtained. Key safety parameters related to the core power distribution may also be generated further from the distribution.
Claims (1)
1. A method for measuring the power distribution of a pressurized water reactor core when xenon poison is not balanced is characterized in that: comprises the following steps:
1) Calculating and generating a reactor core theoretical database when measuring the power distribution of the reactor core by using reactor core nuclear design software;
2) Measuring the power distribution of the reactor core and processing the power distribution based on a theoretical database to generate three-dimensional power distribution of the reactor core, wherein the obtained radial power distribution of the reactor core is considered to be the distribution when xenon is balanced, and the axial power distribution is obtained through the subsequent steps;
3) Extracting the law that the in-core axial power distribution changes along with time based on the change of the out-of-core neutron detector signal in a period before the reactor core power distribution measurement is carried out, deducing the axial power distribution when the xenon is balanced, and combining the radial power distribution obtained in the second step to obtain a complete reactor core power distribution result;
more specifically, the above method comprises the steps of:
(1) Generating a theoretical database under the condition of implementing in-pile measurement;
(2) Recording the out-of-pile power range detector signal;
(3) Performing a full-flux map measurement;
(4) Obtaining three-dimensional reactor core power distribution under the measurement condition;
(5) Generating out-of-pile power range scale coefficients by using a 'one-point method';
(6) Backtracking the fluctuation of the deviation of the reactor power and the axial power before the flux measurement in the reactor is carried out under the current power platform, and selecting and determining a time period for analysis according to the fluctuation:
based on the current signal of the out-of-reactor ionization chamber recorded in the step (2) and the scale coefficient obtained in the step (5), the change of the reactor power P and the axial power deviation delta I along with the time t in the period of 6 hours before the in-reactor flux measurement is carried out under the current power platform is obtained by the following formula:
P(t)＝K U ×I U (t)+K L ×I L (t)
ΔI(t)＝α[K U ×I U (t)-K L ×I L (t)]
and selecting and determining a starting time t for subsequent data analysis depending on whether the reactor power is stable and whether the Δ I has exhibited a relatively stable time-varying law 0 ；
The meaning of each symbol here is expressed as follows:
I U : the current signal of the out-of-core power range detector positioned at the upper half part of the reactor core;
I L : the current signal of the out-of-core power range detector is positioned at the lower half part of the reactor core;
K U : the conversion coefficient between the current of the upper half power range detector and the power of the upper half reactor core;
K L : the conversion coefficient between the current of the lower half power range detector and the power of the lower half reactor core;
α: core axial deviation gain coefficient;
(7) The change of the axial power distribution in the reactor along with the time is constructed based on the signals of the out-of-reactor power range detector:
selecting the position t in the out-of-pile detector signal obtained in the step (2) 0 To t M Data of time periods, where t, to construct a fine axial power distribution in the reactor over time M The moment when the in-stack flux measurement is performed for step (3); the specific construction method is as follows:
here, the
For a column vector formed by the measurement signals of N detectors in one channel of the out-of-stack detector at time t, and->
The normalized power of N axial layers in the reactor is deduced according to the measurement signal; [ C ]]To correct the matrix, [ T ]]For the transmission matrix, [ S ]]Is a sensitivity matrix;
(8) Obtaining the rule of the reactor core power distribution changing along with time, and deriving the distribution under the xenon-toxicity balance condition according to the rule;
the method is completed by the following substeps:
a) Based on the result of step (7), calculating
b) Order to
Each element of (1) Δ P n N =1,2, …, the time-varying law of N satisfies
And based on t 0 To t M Period deltaP n A is determined by a least square fitting method n And λ n ；
c) Calculating the deviation between the axial power distribution of the core obtained by measurement in the non-equilibrium state of xenon according to the result of the sub-step b) and the equilibrium state of xenon, i.e.
Here, the
Is the coefficient a determined by sub-step b) n N =1,2, …, N;
d) Expanding the deviation information determined in substep c) to a finer scale;
in the above formula, [ G ] is a geometric matrix;
e) Obtaining fine axial power distribution in a reactor in a xenon poison equilibrium state
Here, the
Fine axial power distribution in the reactor obtained by the step (4);
f) Combining the refined axial power distribution in the reactor obtained in sub-step e) and the two-dimensional power distribution of the axial layers obtained by the processing in step (4), a three-dimensional power distribution of the core is obtained which can be finally compared with the results given by the core nuclear design software.
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