CN115346698B - Method for determining background noise of power range detector - Google Patents
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Abstract
The invention relates to a method for determining background noise of a power range detector, which comprises the following steps: 1) Acquiring the reactivity change curves of the detector currents I (t) and I (t) after the control rod is lifted; 2) Statistics of detector current I (t) data, determination of minimum value I of detector current min The method comprises the steps of carrying out a first treatment on the surface of the 3) At 0 and I min Between determining background noise assumed value I BKG (i)，0≤I BKG (i)≤I min The method comprises the steps of carrying out a first treatment on the surface of the 4) Based on the reactivity curve of the detector current I (t), the background noise assumed value I is utilized BKG (i) Correcting to obtain a corrected reactivity measurement result rho i (t) curve, selecting a time period when the control rod group is in all the proposed states, and obtaining a change slope k of rho i (t) in the time period i The method comprises the steps of carrying out a first treatment on the surface of the 5) Fitting background noise assumed value I BKG (i) And a change slope k i Obtain I when k=0 BKG The value, i.e., the final determined background noise current value.
Description
Technical Field
The invention relates to the technical field of nuclear reactor reactivity measurement, in particular to a method for determining background noise of a power range detector.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
After the nuclear reactor is built or reloaded, a physical start-up test is required before the nuclear reactor is restarted to perform normal operation so as to verify the consistency of the characteristics of the reactor and the physical design and the rationality of a safety analysis assumption, and a dynamic rod value measurement method is adopted as a physical start-up test technology in the prior art. The method needs to continuously insert the rod group to be measured into the reactor core, introduces a large amount of negative reactivity, reduces the neutron fluence rate level in the reactor core to a very low state, and reduces the current level of the off-reactor detector serving as a reactivity measurement input signal by 1-3 orders of magnitude. In this case, the influence of the detector background noise on the measurement results becomes extremely important, and the accurate determination of the background noise level and the elimination during the test are the key to successfully completing the control rod value measurement by using the dynamic rod value measurement method.
Background noise is also called background noise, and is generally generated by the reaction of gamma rays generated after the core structural material is activated and the sensitive body of the detector, or the electric noise generated by the detector and a cable thereof is a part of the detector signal which does not show neutron dynamics regular change along with the reactor core reactivity change. While the prior art teaches some methods of determining background noise, background noise may vary over time, and may vary considerably over the time period in which different bar set measurements are made, resulting in a greater deviation in the partial bar set measurements after the same background noise compensation settings are employed.
And secondly, in the practice of part of nuclear power plants, the control rod to be detected with great value is inserted into the reactor core and then kept in an inserted state for about half an hour, and the average value of the power range detector signals in the period is used as a background noise signal compensation value. On the one hand, the method still has the problem that the background noise is not changed along with time, and in addition, the key path time of the starting of the nuclear power plant is prolonged, so that the economic effect of the dynamic rod value measuring technology is influenced.
In addition, some methods require trying different background noise hypothesis values by examining the attempted value of the ρ (t) curve at slope K of 0 when the control rod is fully inserted as the background noise current. During the complete insertion of the control rod to be tested, the current level of the detector is low and is influenced by random noise, and the oscillation range of the calculated rho (t) curve at the moment is large, so that the method is theoretically feasible, but the implementation difficulty is high and the failure is easily caused by random influence.
Disclosure of Invention
In order to solve the technical problems in the background technology, the invention provides a method for determining the background noise of a power range detector, which utilizes a current signal during the lifting period of a control rod to perform data processing so as to obtain a background noise current value suitable for the value measurement period of the dynamic rod of each group of control rods. Because the control rod lifting process is an essential link of the dynamic rod value measurement, the method does not need additional specific operation of a unit, so that the critical path time of a physical start test is not increased, and the accurate value of the background noise during the dynamic rod value measurement of each group of control rods can be obtained.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a first aspect of the present invention provides a method for determining background noise of a power range detector, comprising the steps of:
1) Acquiring a detector current I (t) after the control rod is lifted, and obtaining a change curve of the reactivity rho (t) by using the I (t);
2) Statistics of detector current I (t) data, determination of detector current maximumSmall value I min ；
3) At 0 and I min Between determining background noise assumed value I BKG (i)，0≤I BKG (i)≤I min ；
4) Based on the reactivity curve of the detector current I (t), the background noise assumed value I is utilized BKG (i) Correcting to obtain a corrected reactivity measurement result rho i (t) selecting a time period of all the control rod groups in the proposed state to obtain ρ i (t) the slope of change k over the period i ；
5) Fitting background noise assumed value I BKG (i) And a change slope k i Obtain I when k=0 BKG The value, i.e., the final determined background noise current value.
Under the condition of constant positive reactivity rho introduction, the neutron fluence rate level phi (t) in the reactor core is proportional to the detector current I (t) outside the reactor.
Under the condition of introducing constant positive reactivity rho, the data of the neutron fluence rate level phi (t) of the reactor core changing along with time are subjected to logarithmic processing and then change linearly.
Under constant positive reactivity ρ introduction conditions, the time required for increasing phi (t) and I (t) by N times is constant, where the corresponding time when n=2 is the doubling period.
In step 4), the reactor has constant positive reactivity when the control rod group is in the all-extracted state.
Step 1) during a low power physical test, a probe current I (t) is acquired.
In step 4), background noise assumed value I is used BKG (i) Correcting to obtain a corrected reactivity measurement result rho i (t) curve, specifically: by means of (I (t) -I BKG (i) Corrected reactivity measurement result ρ is obtained i (t) curve.
In step 4), the control rod group is in the all-proposed state for a period of time, specifically for a period of time in which the reactor has constant positive reactivity.
The time period during which the reactor has constant positive reactivity satisfies the relation t 1 <t<t 2 I.e. to confirmT-keeping 1 ～t 2 During which no control rod is inserted, where t 1 At a certain point in time, t, after the complete proposal of the previous rod group to be tested 2 At some point before the insertion of the next rod set to be tested is started.
In step 5), a background noise assumed value I is fitted BKG (i) And a change slope k i Specifically, the data of (a) is: couple (I) BKG (i)，k i ) The data series is subjected to polynomial fitting to obtain I when k=0 BKG Values.
Compared with the prior art, the above technical scheme has the following beneficial effects:
1. and (3) carrying out data processing by using the current signals during the lifting period of the control rods to obtain background noise current values suitable for the value measurement period of the dynamic rods of each group of control rods. Because the control rod lifting process is an essential link of the dynamic rod value measurement, the method does not need additional specific operation of a unit, so that the critical path time of a physical start test is not increased, and the accurate value of the background noise during the dynamic rod value measurement of each group of control rods can be obtained.
2. The current signal during the lifting of the control rod is used for processing without carrying out an additional measuring process, so that the economic effect of the application of the dynamic rod value measuring technology is not affected.
3. The time required for the detector current to rise is long enough, and the calculation of the rate of change of ρ (t) is performed using this time period, thereby eliminating the influence of random noise.
4. The accurate value of the background noise signal of the detector can be obtained when different control rod groups are measured, and the method is also applicable to the situation that the background noise signal of the detector is obviously changed during the test.
5. The detector background noise current value is determined by fitting the change slope of the measurement result rho (t) to k=0 in a specified time period, and the detector background noise current value is irrelevant to the specific calculation value of rho (t), namely irrelevant to specific pile type and specific cycle, and has universal applicability.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a schematic illustration of detector current level changes during a critical period of a nuclear power plant in accordance with one or more embodiments of the present invention;
FIG. 2 is a schematic illustration of a change in current level of a detector after a rod is inserted during a dynamic rod etching in a nuclear power plant in accordance with one or more embodiments of the present invention;
FIG. 3 is a flow diagram of a method for determining background noise of a power range detector according to one or more embodiments of the present invention;
FIG. 4 is a schematic illustration of the basic process of a dynamic rod value measurement test provided by one or more embodiments of the present invention;
FIG. 5 is a schematic illustration of the trend of the neutron fluence rate level change in the core under a step positive reactivity introduction condition provided by one or more embodiments of the present invention;
FIG. 6 is a schematic diagram of detector current and reactivity changes during control rod lifting provided by one or more embodiments of the present invention;
FIG. 7 is a schematic diagram of detector current and reactivity variation during lifting of a control rod after background noise compensation provided by one or more embodiments of the present invention.
Detailed Description
The invention will be further described with reference to the drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
The dynamic rod value measurement technology was developed by western house electric company in the united states in the last 90 th century, and in the implementation process of the dynamic rod value measurement technology, the background noise determination method in the prior art has some problems as follows:
1) Part of the method considers background noise to be unchanged with time
The earliest development and application of dynamic rod value measurement technology considered that the background noise of the power range detector during low-power physical test was almost constant, and the background noise determination method was as follows:
i) Measuring the current average value of the power range detector under the condition of partial control rod insertion and deep subcritical condition to be used as a background noise compensation value;
ii) after the control rod is set up, the control rod is set up at a lower sub-critical level (e.g., k eff =0.99), it is confirmed that the compensated signal has no negative value, and if a negative value occurs, the background noise compensation value is newly determined, otherwise, the previously determined background noise compensation value is used.
After the background noise compensation value is determined, it is no longer adjusted during subsequent low power physical experiments (Low Power Physics Test, LPPT).
However, experience in some nuclear power plants has shown that prior to reaching the threshold, the power span detector current signal tends to continue to drop (as shown in FIG. 1) despite the corrective action introduced by boron dilution, control rod extraction, etc. to the core; during the dynamic rod worth measurement test, the power span detector current also programs a trend to drop after the more valuable control rods are inserted into the core (as shown in FIG. 2). This indicates that the power range detector background noise may vary over time and that considerable variation may occur over the time period in which different bar set measurements are made, resulting in a greater variation in the partial bar set measurements with the same background noise compensation settings. Even if the background noise compensation value is redetermined in ii) above, there is still a case of overcompensation during the dynamic rod value measurement test later, i.e. the background noise compensation value is larger than the true background noise value during the dynamic rod value measurement test.
2) Part of the method requires maintaining the control rod inserted state for a long time
In the practice of part of nuclear power plants, a mode of maintaining the insertion state for about half an hour after the control rod to be detected with great value is inserted into the reactor core is adopted, and the average value of the power range detector signals in the period is used as a background noise signal compensation value. On the one hand, the method still has the problem that the background noise is not changed along with time, and in addition, the key path time of the starting of the nuclear power plant is prolonged, so that the economic effect of the dynamic rod value measuring technology is influenced.
3) Part of the method is susceptible to random noise levels
In the partial technology, an arbitrary initial value D (0) is firstly assigned to the correction current, a rho (t) curve of the reactivity of the dynamic rod carving measurement test period changing along with time is calculated, and a change slope K of the reactivity rho of the control rod inserted into the bottom of the reactor core along with time t is solved by utilizing the rho (t) curve after rod inserting; if K is larger than 0, changing the background noise current D (0) into D (0) +d, and then recalculating a rho (t) curve; if K is smaller than 0, the correction current D (0) is changed into D (0) -D, and then the rho (t) curve is recalculated; and finally determining the D (0) value of the rho (t) curve with the slope K of 0 when the control rod is fully inserted as the background noise current through iterative calculation.
This method requires trying different background noise hypothesis values by looking at the try value of the ρ (t) curve when the slope K is 0 when the control rod is fully inserted as background noise current. During the complete insertion of the control rod to be tested, the current level of the detector is low and is influenced by random noise, and the oscillation range of the calculated rho (t) curve at the moment is large, so that the scheme has low feasibility.
Thus, the following example provides a method for determining background noise of a power span detector, which is implemented by collecting current signals of the power span detector during the rise of neutron fluence rate level in a reactor core after the control rod is completely lifted out of the reactor core in a dynamic rod value measurement test, calculating a curve ρ (t) of the change of the reactivity with time, and keeping the control rod at the full lifting positionLinear fitting of the reactivity of (c) to obtain the slope k of the p (t) curve over time by trying different background noise current compensation values I i Obtaining a corresponding series of change slopes k i . For I i ～k i Fitting is performed to determine the I value at k=0 as the final background noise current compensation value. The method solves the defects of the existing method in the aspects of universality, economy and implementation, and improves the use efficiency and economy of users.
Embodiment one:
as shown in fig. 3-7, a method for determining background noise of a power range detector includes the following steps:
1) Acquiring a detector current I (t) and a reactivity change I (t) curve of the control rod after lifting;
2) Statistics of detector current I (t) data, determination of minimum value I of detector current min ；
3) At 0 and I min Between determining background noise assumed value I BKG (i)，0≤I BKG (i)≤I min ；
4) Based on the current I (t) curve of the detector outside the pile, the background noise assumed value I is utilized BKG (i) Correcting to obtain a corrected reactivity measurement result rho i (t) curve, selecting a time period when the control rod group is in all the proposed states, and obtaining a change slope k of rho i (t) in the time period i ；
5) Fitting background noise assumed value I BKG (i) And a change slope k i Obtain I when k=0 BKG The value, i.e., the final determined background noise current value.
Specific:
the basic process of a typical dynamic rod value measurement test, as shown in FIG. 4, is schematically illustrated as follows:
1) Initial working conditions: the control rod groups are all lifted to the top of the reactor, and only 1 control rod group is reserved to be inserted into the reactor core in a small amount (for example, within the range of 30-75 pcm) to control the critical of the reactor core.
2) The group 1 control rods are lifted to the top of the reactor, the reactor core has positive reactivity corresponding to the insertion amount of the control rods in the step 1, and the power range detector current signal starts to continuously rise (mark 1 in fig. 4).
3) When the power range detector current signal increases to a predetermined level (e.g.: 50% of the doppler heat generating spot), beginning to insert group 1 control rods continuously to the bottom of the reactor, during which the probe current first continues to rise (the core still has positive reactivity before the rod is inserted to subcritical), then decreases rapidly as the control rods continue to introduce negative reactivity (label 2 in fig. 4).
4) Analysis was performed using the data during the stick insertion to obtain control stick value measurements for group 1 control sticks.
5) Lifting group 2 control rods to the top of the reactor, the core has a positive response comparable to the control rod insertion of step 1), during which the power span detector current signal begins to rise, but the rate of rise is lower as the power span detector current approaches the background level (labeled 3 in fig. 4).
6) As the power span detector current signal level increases, so does the rate of rise of the power span detector current, approaching a steady doubling period (labeled 4 in fig. 4).
7) When the power range detector current signal increases to a predetermined level (e.g.: 50% of the level of doppler heat generating spot), start to insert the group 2 control rod continuously, and start the measurement of the group 2 control rod (reference 5 in fig. 4). And (3) repeating the steps 3) to 6) to finish the control rod value measurement of all the control rod groups.
As shown in fig. 4, according to the principle of neutron dynamics, under the condition of introducing constant positive reactivity ρ, the neutron fluence level phi (T) (proportional to the detector current I (T) outside the reactor) in the reactor core shows an exponential increase change law (after logarithmic treatment, in linear change) with time, that is, the time required for increasing phi (T) and I (T) by N times is constant, where n=2, this time is called a multiplication period, the length of the multiplication period T is related to the magnitude of the positive reactivity ρ, and the larger ρ is, the shorter the multiplication period T is, and vice versa.
The reactivity measurement is based on a point stack inverse dynamics method, and is analyzed by using a power range detector current signal I (t) which is in direct proportion to the neutron fluence rate level phi (t) of the reactor core as input, so that a continuous measurement result of the reactivity rho (t) is obtained. Similar to the neutron kinetics principle described above, ρ (T) shows an increasing trend when the multiplication period T of phi (T) and I (T) becomes smaller; when the multiplication period T of phi (T) and I (T) becomes large, ρ (T) shows a decreasing trend; when the multiplication periods T of phi (T) and I (T) tend to stabilize, ρ (T) also tends to stabilize at a constant value corresponding to the multiplication period value T.
However, due to the presence of background noise (fixed value in a short time frame under investigation, or very small rate of change, much lower than the exponential change law), the core neutron fluence rate change law will deviate significantly from the exponential change law, and the calculated reactivity will be lower than the true value using the power span detector signal with background noise.
Fig. 6 is an enlarged view of the current levels of the control rod assembly of fig. 4 before and after the complete extraction of the reactor (at which point the core reactivity is about +40 pcm) from the off-stack power range detector, and the reactivity profile measured using the current signal. The data show that when all control rods are out of the stack, although the reactor core has constant positive reactivity (about +40 pcm) equivalent to the insertion amount of the control rods, the current signal level of the power range detector is very low, the main component is background noise current, so that the change rate is remarkably lower than the exponential rising trend, and the measured reactivity is about 0pcm; as the current level of the power range detector rises, the background noise current share is smaller and smaller, the current level rising trend of the power range detector is closer to an exponential rising rule, and the measurement reactivity is approaching to the true value.
According to the principles and phenomena described above, the background noise current is corrected (i.e., the background noise current value I is subtracted) in the off-stack detector current I (t) BKG ) After that, when the reactivity measurement is performed again, the obtained measurement result ρ (t) is a value that tends to be stable, that is, the rate of change over time is zero, and the slope k=0 of the ρ (t) curve.
Based on the principle, a background noise current value I is determined BKG The steps of (a) are as follows:
1) During a low-power physical test, acquiring a detector current I (t) after the control rod is completely lifted, and calculating a reactivity change rho (t) curve by using the I (t);
2) Counting the detector current I (t) data and determining the minimum I min ；
3) At 0 and I min Between which a series of background noise hypotheses I are determined BKG (i)，0≤I BKG (i)≤I min The method comprises the steps of carrying out a first treatment on the surface of the In practice, a plurality of points are generally taken at equal intervals, and the embodiment does not limit the number of the points and whether the points are at equal intervals or not;
4) Based on the current I (t) curve of the detector outside the pile, the background noise assumed value I is utilized BKG (i) Making corrections, i.e. using (I (t) -I) BKG (i) Curve calculation to obtain corrected reactivity measurement result ρ i (t) a curve is selected for a time period (t) during which one control rod group is in the fully extracted state (i.e. the reactor has constant positive reactivity) 1 <t<t 2 I.e. to ensure that no control rods are inserted during t 1-t 2, the reactor has constant positive reactivity during this period of time) ρ is calculated i (t) the slope of change k over the period i Wherein t is 1 At a certain point in time, t, after the complete proposal of the previous rod group to be tested 2 A certain moment before the next rod group to be tested starts to be inserted;
5) Aiming at (I) BKG (i)，k i ) The data series is subjected to polynomial fitting to obtain I when k=0 BKG The value, i.e., the final determined background noise current value (as shown in fig. 7).
The method utilizes the data collected in the basic process of measuring the value of the dynamic rod to analyze, obtains the accurate value of the background noise signal of the detector, and has the following advantages:
1) No additional measurement process is required, so that the economic effect of the application of the dynamic rod value measurement technique is not affected.
2) The time required for the current rise of the detector is long enough, and the influence of random noise can be effectively eliminated by calculating the rate of change of rho (t) in the time period.
3) The accurate value of the background noise signal of the detector can be obtained when different control rod sets are measured, and the method is suitable for the condition that the background noise signal of the detector changes during the test.
4) The detector background noise current value is determined by fitting the slope of the change of ρ (t) to k=0 in a specified time period, and has universal applicability irrespective of the magnitude of the specific calculation value of ρ (t), i.e. irrespective of the specific stack type and specific cycle.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method for determining background noise of a power range detector is characterized by comprising the following steps: the method comprises the following steps:
1) Acquiring a detector current I (t) after the control rod is lifted, and obtaining a change curve of the reactivity rho (t) by using the I (t);
2) Statistics of detector current I (t) data, determination of minimum value I of detector current min ；
3) At 0 and I min Between determining background noise assumed value I BKG (i)，0≤I BKG (i)≤I min ；
4) Based on the reactivity curve of the detector current I (t), the background noise assumed value I is utilized BKG (i) Correcting to obtain a corrected reactivity measurement result rho i (t) selecting a time period of all the control rod groups in the proposed state to obtain ρ i (t) the slope of change k over the period i ；
5) Fitting background noise assumed value I BKG (i) And a change slope k i Obtain I when k=0 BKG The value, i.e., the final determined background noise current value.
2. A method of determining background noise for a power range detector as defined in claim 1, wherein: the step 1) is to acquire the detector current I (t) during a low power physical test.
3. A method of determining background noise for a power range detector as defined in claim 1, wherein: in the step 4), the background noise assumed value I is utilized BKG (i) Correcting to obtain a corrected reactivity measurement result rho i (t) curve, specifically:
by means of (I (t) -I BKG (i) Corrected reactivity measurement result ρ is obtained i (t) curve.
4. A method of determining background noise for a power range detector as defined in claim 1, wherein: in the step 4), the reactor has constant positive reactivity when the control rod group is in the all-out state.
5. The method for determining background noise of a power range detector according to claim 4, wherein: in the step 4), the time period in which the control rod group is in the all-out state is a time period in which the reactor has constant positive reactivity.
6. The method for determining background noise of a power range detector according to claim 5, wherein: the time period for which the reactor has constant positive reactivity satisfies the relation t 1 <t<t 2 I.e. ensure t 1 ～t 2 During which no control rod is inserted, where t 1 At a certain point in time, t, after the complete proposal of the previous rod group to be tested 2 At some point before the insertion of the next rod set to be tested is started.
7. A method of determining background noise for a power range detector as defined in claim 1, wherein: in said step 5), a background noise assumed value I is fitted BKG (i) And a change slope k i Specifically, the data of (a) is: couple (I) BKG (i)，k i ) The data series is subjected to polynomial fitting to obtain I when k=0 BKG Values.
8. A method of determining background noise for a power range detector as defined in claim 1, wherein: under the condition of constant positive reactivity rho introduction, the neutron fluence rate level phi (t) in the reactor core is proportional to the detector current I (t) outside the reactor.
9. The method for determining background noise of a power range detector according to claim 8, wherein: the data of the neutron fluence rate level phi (t) changing along with time in the reactor core is subjected to logarithmic processing and then is changed linearly.
10. The method for determining background noise of a power range detector according to claim 8, wherein: the time required for increases of phi (t) and I (t) by a factor of N is constant, where the corresponding time when n=2 is the doubling period.
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