JP2005172749A - Core monitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a core monitor which can realize the control over a core taking into account histories of the boiling transition in fuel assemblies for a boiling water reactor. <P>SOLUTION: The monitor has a boiling transition determination criterion preparation means 9 for preparing a criterion for determining the presence or absence of boiling transition in advance for at least one fuel assembly specified beforehand in the boiling water reactor, a data collection means 6 for collecting data showing the present operating condition of at least one fuel assembly specified beforehand, a boiling transition determination means 10 for determining the presence or absence of the boiling transition in the specified fuel assembly on the basis of the data collected by the means 6 and the criterion obtained by the means 9 and a boiling transition process recording means 11 for recording the process of the boiling transition obtained by the means 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a boiling water reactor (BWR) core monitoring device, and in particular, when the core is exposed to a transient change, monitors whether or not a boiling transition occurs, and monitors and records the boiling transition progress and history. The present invention relates to a core monitoring device that can perform the above.

  In general, in a boiling water reactor, it is important to accurately evaluate the power distribution and thermal margin of the operating reactor in order to operate the reactor safely and efficiently. For this reason, conventionally, a large number of neutron detectors are arranged in the furnace, and based on the detection signal from the neutron detector, a physical model such as a fitting formula or a three-dimensional nuclear thermal hydraulic model is used. A core monitoring apparatus is provided for obtaining a dimensional power distribution and further obtaining a thermal margin such as a critical power ratio (CPR) and a linear power density.

  An example of a BWR core monitoring device is shown in FIG. A coolant (moderator) 2 and a core 3 are accommodated in the reactor pressure vessel 1. FIG. 4 shows an example of such a BWR core. In the figure, 101 indicates a fuel assembly, 102 indicates a control rod, 103 indicates a horizontal position of the neutron detector assembly, and in this example, about one control rod 102 is provided for every four fuel assemblies 101. The neutron detector assembly 103 is present at a rate of about one for every 16 fuel assemblies 101.

  Now, as shown in FIG. 3, a plurality of neutron detectors 4 are normally installed in the neutron detector assembly 103 in the core 3 so that the neutron flux at each position can be measured. There is also a neutron detector (not shown) that can move in the neutron detector assembly 103, continuously measuring the axial neutron flux distribution, and calibrating the neutron detector 4 whose position is fixed. Can do.

  Around the reactor pressure vessel 1, a reactor current data measuring device 5 is installed. By this reactor current data measuring device 5, the reactor output, the total coolant flow rate, the reactor pressure, the coolant temperature, etc. Core status data is being measured. The signal S5 from the core current data measuring device 5 is input to the data sampler (data collecting means) 6 together with the signals S4 from the neutron detectors 4, and the output is further input to the core performance evaluating means 7. It has come to be.

  Based on the input from the data sampler 6 and information on the core and fuel input in advance, the core performance evaluation means 7 provides thermal margins such as the power distribution in the reactor, the linear power density of the fuel rods, and the CPR. It comes to evaluate. The calculated output distribution and thermal margin are displayed on the display unit of the input / output device 8.

Here, a further description will be given particularly regarding CPR. CPR is
CPR = (output at which fuel assembly reaches boiling transition) / (actual output of fuel assembly)
A boiling transition is expected to occur when this value is below 1. Actually, there are also uncertainties in prediction and operation, and therefore, in operation, even if various uncertainties and transient changes in core monitoring are taken into consideration, the probability of reaching a boiling transition is sufficiently small (that is, CPR). The operation limit value for CPR is defined. Then, the CPR is calculated at appropriate time intervals for all the fuel assemblies in the core, and the operation is continued while confirming that it is equal to or greater than the operation limit value.

  That is, conventionally, the core has been operated in a range in which no boiling transition occurs in the fuel assembly 101 in the core regardless of any transient change. Therefore, if a transient change occurs during operation and the plant is stabilized, if there is no abnormality in the plant, it is possible in principle to continue the operation of the core as it is or to restart it when the core is stopped.

  In such an operation, unless the boiling transition is reached, the fuel cladding is surrounded by the liquid phase of the saturated coolant and is in the nucleate boiling cooling state with good heat transfer efficiency, the change in the surface temperature is small, and the soundness is improved. This is based on the idea that it can be used continuously. This way of thinking about limit conditions is called the boiling transition criterion.

  However, in recent years, the idea of limit values different from the above has been proposed. In the first place, the thermohydraulic limit value such as CPR is set because the surface of the fuel rod cladding tube transitions to the steam cooling state due to boiling transition, and the heat transfer coefficient is greatly reduced. The purpose is to prevent the tube from becoming excessively high and causing significant deformation of the cladding tube and embrittlement damage due to excessive oxidation.

  Therefore, even if a boiling transition occurs, if the temperature of the cladding tube is sufficiently small, or if the fuel rod surface is covered with the liquid phase again in such a short time that such deformation or oxidation reaction does not occur (rewetting) The purpose of ensuring the soundness of the cladding tube is achieved. The limit criterion determined from such a viewpoint is called a time temperature criterion with respect to the boiling transition criterion.

  Since the boiling transition is allowed in the time-temperature standard, of course, the operation restriction is a standard that is looser than the boiling transition standard. By adopting such a standard, the degree of freedom of operation of the BWR is expanded and the economy is improved. be able to.

  FIG. 5 shows an example of criteria for judging the soundness and reuse of the fuel cladding. In FIG. 5, the horizontal axis represents the boiling transition duration, and the vertical axis represents the fuel cladding tube temperature. The time temperature reference is operated in two parts as shown in the figure.

  The first portion 20 is called a soundness criterion. When a transient boiling transition occurs, the failure mechanism of the fuel cladding is brittle failure due to excessive oxidation. Therefore, if the cladding tube temperature and boiling transition duration are within a certain range, the degree of deformation and oxidation of the cladding tube is small, so there is no fuel damage and when handling the fuel assembly after the event has converged. Soundness can be maintained even in Such criteria for fuel integrity are given by the temperature of the fuel cladding and the duration of the boiling transition.

  When the time temperature reference is used, the operation restriction condition during the normal operation is determined so that all the fuels satisfy the soundness determination criteria at the time of an abnormal transient change during the operation to which the reference is applied.

  The second part 22 of the time temperature reference is a criterion for reuse. Many transient events that are likely to occur in reality are quickly reduced in power and rewet, so the temperature rise of the fuel cladding is small and the boiling transition duration is short. In this case, since there are no significant changes in the characteristics relating to the fuel rod performance, not only fuel integrity after the event is ensured, but there is no problem even if the fuel assembly is used again. This criterion for reusability (second part 22) is also given by the fuel cladding temperature and the duration of the boiling transition, but is more extensive than the soundness criterion (first part 20). Becomes smaller.

  Note that the criteria for reuse may not be applicable to fuels that have experienced boiling transitions in the past. In general, the number of times a reuse criterion can be applied to the same fuel is limited, and as a typical example, only one application is allowed.

  Considering the configuration of the time temperature reference described above, the soundness determination standard (first portion 20) can be observed in actual operation by setting an appropriate operation restriction condition in advance. However, the criteria for reuse (second part 22) depend on the nature of the individual transients that have actually occurred, on each fuel in the furnace and on the history of boiling transition experiences in the past of that fuel. It can be seen that the determination of whether or not the standard is satisfied is different. To determine this correctly, it is necessary to analyze the behavior of all fuel in the core after the occurrence of a transient event. Such analysis involves understanding the fuel history and initial core state, and analyzing the events that have occurred. A procedure such as a three-dimensional core simulation is required, and generally a considerable amount of time and labor are required.

  On the other hand, from the point of view of plant economy, the operating rate will be lost unless the operating state is quickly returned to the rated operating state. It was an issue.

  An object of the present invention is to provide a core monitoring apparatus that can realize core management in consideration of the history of boiling transition in a fuel assembly of a boiling water reactor.

  The present invention is directed to the above object, and the invention according to claim 1 is directed to the boiling transition of at least one fuel assembly designated in advance in a boiling water reactor containing a plurality of fuel assemblies. Boiling transition determination criterion creation means for creating a criterion for determining the presence or absence in advance, data collection means for collecting data representing the current operating state of the at least one fuel assembly designated in advance, and collected by the data collection means Boiling transition determination means for determining whether or not there is a boiling transition in the fuel assembly, and the boiling transition obtained from the boiling transition determination means based on the data obtained and the reference obtained by the boiling transition determination criterion creation means. And boil transition progress recording means for recording the progress.

  According to a second aspect of the present invention, in the core monitoring apparatus according to the first aspect, the at least one fuel assembly designated in advance is based on a history of boiling transition recorded by the boiling transition progress recording means. It further has a state judging means for judging reusability and soundness of.

  Further, the invention according to claim 3 is the core transition monitoring apparatus according to claim 1, wherein the boiling transition history recording means records information on the progress of the past boiling transition for the at least one fuel assembly designated in advance. It further has these.

  According to a fourth aspect of the present invention, in the core monitoring apparatus of the third aspect, the predesignated designation is made based on the boiling transition history recorded by the boiling transition progress recording means and the boiling transition history recording means. It further has a state judging means for judging reusability and soundness of at least one fuel assembly.

  Further, according to a fifth aspect of the present invention, in the core monitoring device according to the second or fourth aspect, the state determining means is configured to perform at least the previously specified based on the history of the fuel cladding tube temperature and the boiling transition duration. The reusability and soundness of one fuel assembly are judged, and the reusability requirement is characterized by the soundness requirement as a prerequisite.

  ADVANTAGE OF THE INVENTION According to this invention, the core monitoring apparatus which can implement | achieve the core management which considered the log | history of the boiling transition in the fuel assembly of a boiling water reactor can be provided.

  An embodiment of a core monitoring apparatus according to the present invention will be described with reference to the drawings. Note that parts that are the same or similar to the above-described conventional technology, or parts that are the same or similar to each other, are given the same reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is a diagram showing a first embodiment of a core monitoring apparatus according to the present invention, in which determination and recording means regarding boiling transition are added to the conventional core monitoring apparatus shown in FIG.

  In the present embodiment, the output from the core performance monitoring means 7 is sent to the boiling transition determination criterion creating means 9 separately from the input / output device 8. The function of the boiling transition determination criterion creating means 9 will be described below.

  As described above, if the three-dimensional core simulation analysis is performed, it can be determined whether or not each fuel assembly 101 is in a boiling transition state. However, in general, this analysis requires a considerable amount of calculation time, and is not suitable for the purpose of monitoring the fuel boiling transition in real time during a transient change. Therefore, using the fact that the core performance evaluation is carried out at an appropriate time interval, based on the latest results, the CPR corresponding to the subsequent change in the core state can be obtained in a short time from the core current data. If formulated, it is convenient for monitoring purposes.

Considering the definition of CPR, a boiling transition occurs when CPR = 1. However, considering various uncertainties, if it is determined that a boiling transition occurs when CPR = CPR _BT ,
CPR = F _i (core data)
As
Decision function _i = F _i (core current data) −CPR _BT (1)
Is the output of the boiling transition determination criterion creating means 9. Here, the subscript _i indicates each fuel assembly.

  There are basically as many judgment functions as the number of target fuel assemblies 101. However, several fuel assemblies in the furnace may be collectively represented by one determination function. In addition, when it is not necessary to make a boiling transition determination for each individual fuel assembly 101, it is conceivable that the entire core is represented by a single determination function. This is useful when there is a low possibility of a boiling transition due to a transient event with a high probability of occurrence. This is because the smaller the determination function, the shorter the calculation time in the boiling transition determination means 10 and the higher the monitoring frequency.

  As an example of a specific output of the boiling transition determination criterion creating means 9, an appropriate formula form including several indefinite coefficients is determined in advance for the target fuel assembly, and the value of the indefinite coefficient is output. It is realistic to do.

  Further, as the core current data that is an independent variable of the determination function, a measured value that affects the limit output of the fuel assembly is used. The parameters that greatly influence the limit output include the fuel assembly output, coolant flow rate, pressure, and coolant inlet temperature, and the cores of multiple neutron detector signals and neutron detector signals are measured quantities that have a large correlation with these parameters. Average values (or those subjected to first-order lag processing that simulates fuel rod heat transfer time), reactor pressure, core support plate differential pressure, core coolant pump speed, jet pump drive water flow rate, pump Deck differential pressure, coolant temperature, etc. can be considered. Actually, if not all of them but a parameter having a large influence is selected and used, the calculation time in the boiling transition determination means 10 can be shortened.

  In the above, CPR is always used as a criterion for determining the boiling transition state. However, this is a parameter to be used when determining the transition from the normal state to the boiling transition state, and is an approximate method. When transitioning from the boiling transition state to the normal state, it is most correct to make a determination using the rewet correlation equation. Therefore, the boiling transition determination criterion creating means 9 may output two types of determination functions when shifting to boiling transition and when rewet.

  The boiling transition determination means 10 uses the determination function output from the boiling transition determination reference creation means 9 and the necessary core current data output from the data sampler 6, and the state of the target fuel assembly (or core). Is determined in real time.

For example, if the determination function is the above equation (1),
When the judgment function> 0, the normal state,
When the decision function ≦ 0, the boiling transition state,
The determination result for each fuel assembly is sent to the boiling transition progress recording means 11.

  The boiling transition progress recording means 11 records the time course of the determination result after the monitoring start signal is input. If the time is recorded when the normal state is changed to the boiling transition state or when the boiling transition state is changed to the normal state, the recording amount can be reduced.

  The boiling transition progress signal recorded in the boiling transition progress recording means 11 is sent to the state determination means 12. In the state judging means 12, the number of boiling transitions experienced by each target fuel assembly and the duration of each time are examined, and the presence / absence of boiling transition experience, reusability, soundness, etc. are checked against the time temperature reference. The result is displayed on the display unit of the input / output device 8.

  By adopting the configuration as described above, the operator can always check the soundness and reusability of the fuel to be monitored, and even if a transient event occurs in the plant, the operator must return to operation or stop the plant. It is possible to quickly and accurately determine whether or not it will occur. Actually, since boiling transition does not occur in most transient events, by using this embodiment, almost no time is required for confirmation of reusability, and the plant operating rate can be improved.

[Second Embodiment]
FIG. 2 shows a second embodiment of the core monitoring apparatus according to the present invention. In the present embodiment, a boiling transition history recording means 13 is added to the core monitoring apparatus shown in FIG. The boiling transition history recording means 13 receives the boiling transition history of each fuel assembly before the monitoring start signal is input, and the state determination means 12 monitors the history and the monitoring recorded in the boiling transition progress recording means 11. The presence / absence of boiling transition experience of the target fuel assembly, reusability, soundness, etc. are determined by comparing the boiling transition process after the start signal is input, and the result is displayed on the display unit of the input / output device 8. .

  According to the present embodiment, for example, a correct determination can be made for a fuel assembly that has experienced a boiling transition during a past operation cycle.

The block diagram which shows 1st Embodiment of the core monitoring apparatus which concerns on this invention. The block diagram which shows 2nd Embodiment of the core monitoring apparatus which concerns on this invention. The block diagram which shows the conventional core monitoring apparatus. The typical plane sectional view showing the core arrangement of BWR. The graph which shows the example of two judgment criteria which comprise time temperature reference | standard.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 ... Coolant, 3 ... Core part, 4 ... Neutron detector, 5 ... Reactor present state data measuring device, 6 ... Data sampler (data collection means), 7 ... Core performance evaluation means, 8 DESCRIPTION OF SYMBOLS Input / output device, 9 ... Boiling transition judgment reference preparation means, 10 ... Boiling transition judgment means, 11 ... Boiling transition progress recording means, 12 ... State judgment means, 13 ... Boiling transition history recording means, 20 ... Soundness judgment standard (First part), 22 ... reuse criteria (second part), 101 ... fuel assembly, 102 ... control rod, 103 ... neutron detector assembly, S4 ... signal from each neutron detector 4 , S5: Signal from the core current data measuring device 5.

Claims (5)

A boiling transition determination criterion creating means for creating in advance a criterion for determining the presence or absence of boiling transition for at least one fuel assembly designated in advance in a boiling water reactor containing a plurality of fuel assemblies;
Data collecting means for collecting data representing a current operating state of the at least one fuel assembly designated in advance;
Boiling transition determination means for determining whether or not there is a boiling transition in the fuel assembly, based on the data collected by the data collection means and the criterion obtained by the boiling transition determination criterion creation means;
Boiling transition progress recording means for recording the progress of boiling transition obtained from the boiling transition determination means;
A core monitoring device characterized by comprising:   2. The core monitoring apparatus according to claim 1, wherein reusability and soundness of the at least one fuel assembly designated in advance are determined based on a boiling transition history recorded by the boiling transition progress recording means. A core monitoring apparatus, further comprising a state determining means.   2. The core monitoring apparatus according to claim 1, further comprising a boiling transition history recording means for recording information relating to the progress of a past boiling transition for the at least one fuel assembly designated in advance. apparatus.   4. The reactor core monitoring apparatus according to claim 3, wherein the at least one fuel assembly designated in advance is reusable based on the boiling transition history recorded by the boiling transition progress recording means and the boiling transition history recording means. And a state determining means for determining soundness, further comprising a core monitoring device. 5. The core monitoring device according to claim 2, wherein the state determination unit is configured to reusability of the at least one fuel assembly designated in advance based on a history of fuel cladding tube temperature and boiling transition duration and A core monitoring apparatus for judging soundness, wherein the reusability requirement is a prerequisite for the soundness requirement.

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