RU2100855C1 - Coolant plow monitoring device for nuclear reactor - Google Patents

Abstract

FIELD: nuclear engineering. SUBSTANCE: device has radiation monitoring system automatically thrown in monitoring mode to check for coolant flow in process channels with fuel assemblies in case of failure of standard flowmeters. EFFECT: reduced intensity of failures causing loss of information about coolant flow in process channels, provision for shaping emergency safety signals indicating inadmissible reduction in flowrate in each channel. 1 dwg

Description

 The invention relates to devices for monitoring the technological parameters of nuclear reactors, in particular, for the flow of coolant in the technological channels (TC) with fuel assemblies (FA).

Known devices for controlling the flow rate of the coolant in the fuel cell of nuclear reactors, containing flowmeter systems, each of which is made in the form of a group of channel frequency-pulse flow sensors and the corresponding number of individual converters with an analog output for connection to a common information and computer system of the highest level serving the power unit in general [1]
The main disadvantage of these devices is their low efficiency in ensuring the nuclear safety of reactors, which is due to:
high failure rate, leading to loss of information about the flow rate in the fuel cell with fuel assemblies;
lack of funds for automatic identification of the reasons for the decrease in readings (whether it is a result of a failure or a real change in flow);
lack of tools for diagnosing the resource of the least accessible elements for repair: flow sensors;
the lack of means for generating signals for the automatic switching on of emergency reactor protection means with an unacceptably large decrease in the coolant flow rate in a fuel cell with a fuel assembly.

Closest to the present invention, its prototype is a device made taking into account modern requirements for multichannel control equipment. It contains a system of flow meters, each of which is made in the form of a group of channel flow sensors connected to a measuring unit made in the form of normalizing converters according to the number of channel sensors connected through a switch to a data preprocessing unit and connected through a communication line to a common computing device for all flow meters a complex equipped with access to a high-level information-computing system [2]
The reliability of the prototype device in comparison with analogues is significantly higher, and the availability of means for automatically identifying the reasons for the change in readings makes it more informative. Nevertheless, the failure rate, leading to loss of control over the flow of coolant in the fuel cell with fuel assemblies, including due to the lack of diagnostic tools for the resource of flow sensors, in the prototype device is still too high and does not allow the possibility of using it to form reactor emergency protection flow signals without the participation of a human operator.

 The objective of the invention is to increase the efficiency of the device for channel-by-channel control over the flow of coolant in ensuring nuclear safety of the reactor.

The technical result achieved by using the invention:
a multiple reduction in the failure rate, leading to the loss of information about the flow of coolant in a fuel cell with a fuel assembly, by continuously diagnosing the resource of flow sensors and backups of both each flow meter and the flowmeter system as a whole;
the exclusion of the subjective factor in making decisions on the testimony of the device by automatically generating signals for triggering the reactor emergency protection means according to previously tested algorithms.

 The specified technical result is achieved by the fact that in the prototype device a radiation control system for the coolant is introduced, containing position-controlled gamma sensors made with the possibility of moving along the rows of steam-water communications of the technological channels and connected via control units for the position of the sensors and analog-to-digital converters with a control unit, while galvanic isolation blocks are introduced into each flowmeter, connecting each sensor with the main meter unit and, at least, with two measuring units reserving it, each of which is connected via a corresponding additional communication line to the main and additional computing complexes in terms of the number of redundant measuring units in each flowmeter, equipped with outputs to a common information-computing system and to means generating emergency reactor protection signals by flow rate, each of the communication lines being connected to a computing and control unit and an input storage unit I and data processing to diagnose the resource flow sensors.

 A system of rational control of the coolant of a nuclear reactor containing position-controlled gamma sensors configured to move along the rows of steam-water communications of technological channels and connected via control units for the position of sensors and analog-to-digital converters with a computer-control unit is known [3] However, this system it was involved for additional control over the flow of coolant in cases of doubt in the reliability of the testimony or in case of failure of the flow meters only at the command of a human operator, which led to a delay in receiving information about the results of such control, a subjective assessment of the situation and, ultimately, to increasing the likelihood of making an untimely (belated) decision on the need to launch emergency reactor protection means for consumption, to complication consequences of the accident if it occurred.

The introduction of a coolant radiation monitoring system into the device, which is automatically included in the flow control mode when dangerous failures occur in a permanently operating flowmeter system, removes the above disadvantages and, in addition to backing up the electronic part of the flow meters, many times reduces the flow of failures, which entail a complete loss of information about consumption in a particular fuel cell with fuel assembly. The introduction and use of the data storage and processing unit for diagnosing the resource of flow sensors, the least reliable (due to difficult operating conditions) and the least accessible part of the device for repair, also contributes to this. As a result, taking into account the actual incidence rate of incidents that cause an unacceptably large decrease in the coolant flow rate in at least one fuel cell with fuel assemblies (and there are about one and a half thousand of them in the RBMK type reactor), and also taking into account the real possibilities for early unloading of fuel assemblies from the fuel cell with failed sensors flow rate, but without loss of flow control, the calculated value of the unavailability coefficient of the proposed reactor emergency protection device for flow rate is of the order of 1.0 • 10 ^-5 , which meets the requirements for the control system of reactors according to GOST 2 6843-86 and not less than two orders of magnitude better than the same reliability indicator achieved in current devices of a similar purpose.

The invention will explain the presented on the drawing block diagram of a device for controlling the flow of coolant in the technological channels of a nuclear reactor, where it is indicated:
1 flowmeter system;
2 flow meters;
3 channel flow sensors;
4 blocks of mutual galvanic isolation of electric circuits of flow sensors and measuring units 5 connected to them (for example, isolation transformers);
5 measuring units, each of which converts analog signals from the corresponding group of sensors 3 into a set of code (digital) signals for "system" information processing;
6 blocks for normalizing the signals of flow sensors;
7 analog switches;
8 analog-to-digital converters;
9 data preprocessing units;
10 synchronization and control blocks 7, 8, 9;
11 communication lines of blocks 5 with computing complexes 12 of a flowmeter system, as well as complexes 12 with a system 13, block 18, and an information-computing system of a level not shown in the drawing;
12 computing systems flowmeter systems;
13 system of radiation control of the coolant;
14 gamma sensor;
15 set of blocks for setting coordinates and processing signals of gamma sensors;
16 control units for the position of gamma sensors relative to steam-water communications of technological channels and converting the signals of these sensors from analog to digital form;
17 computing and control unit of the complex 15, which determines the operating mode of the system 13;
18 data storage and processing unit for diagnosing a resource of flow sensors;
19 lines for transmitting command signals from complexes 12 to the means of starting the reactor emergency protection system by flow, not shown in the drawing.

 The system 1 includes flowmeters 2 and three backup complexes 12, connected to each other via lines 11, each flowmeter has a group of sensors 3, the corresponding number of blocks 4, and three measurement blocks 5, which are backing each other, and rationing blocks are part of each measuring block 6 (according to the number of sensors in the flowmeter), switch 7, converter 8 and blocks 9, 10. The system 13 includes several gamma sensors 14, the corresponding number of blocks 16 and the common block 17. The latter is determined t and the mode of operation of system 13 by choosing one or another energy range of gamma quanta used to generate information signals (for example, fission products of nuclear fuel emit gamma quanta with energies of up to 3 MeV, and nitrogen induced in water is -16, used for flow control, above 5 MeV). An important feature of system 13 is that each gamma sensor is designed to service approximately 200 of its “steam” water communications (out of a total of about one and a half thousand), which significantly limits the possibility of choosing the coordinates of simultaneously controlled TCs. Each of the flow sensors is a spinning mechanism integrated in the TC power path, which drives a steel ball that interacts with a magnetic induction converter; the frequency of electrical pulses at the output of the latter is proportional (with known amendments) to the flow rate of the coolant; the number of sensors in the flowmeter is determined by the convenience of the layout of its electronic part and may amount to several tens.

их статистического усреднения за некий принятый временный интервал. В каждом из трех вычислительных комплексов 12 эта информация воспринимается первой группой портов ввода/вывода одновременно от трех разных групп резервирующих друг друга измерительных блоков 5 всех расходомеров, что позволяет осуществлять контроль исправности этих измерительных блоков. Действительно, если три резервирующих друг друга измерительных блока 5 с индексами B, C, D исправны и взаимно идентичны, то, поскольку все они получают входные сигналы синхронно от одних и тех же датчиков расхода, всегда должны выполняться равенства:

Реально, из-за некоторого разброса характеристик блоков 5, эти равенства могут выполняться с некоторым допуском П1 или П2, так что фактически должно проверяться выполнение неравенств:

Для идентификации неисправного блока 5 можно использовать такое решающее правило: блок 5 с тем или иным индексом исправен, если справедливо хотя бы одно из указанных неравенств для переменной с этим индексом, и неисправен, если не выполняются два таких неравенства. Исправность самого вычислительного комплекса 12 может быть установлена путем аналогичного сопоставления результатов расчета, получаемых данным комплексом и двумя другими, его резервирующими (с обменом информацией между комплексами 12 по тем же магистралям 11). Контроль неисправности блоков 15 и комплексов 12 осуществляется и путем из самодиагностики по алгоритмам, здесь не рассматриваемым. Отметим лишь, что средства отображения информации о состоянии системы 1 должны быть выполнены таким образом, чтобы расчетное время обнаружения и замены дефектных модулей не превышало заранее установленного предела (например четверти часа) и вероятность возникновения отказов одновременно в двух измерительных блоках 5 одного расходомера за время эксплуатации реактора от одного планово-предупредительного ремонта реактора до другого ("от ППР до ППР") оказалась не большей, чем вероятность отказа хотя бы одного датчика расхода того же расходомера.The device operates as follows. The voltage pulses from the sensors 3 through blocks 4 galvanic isolation are transmitted to blocks 6 normalization of each of the measuring blocks 5 of the flow meter. Depending on the data processing algorithm specifically adopted in the measuring unit 5, unit 6 can be either just a pulse amplifier or an amplifier with a set of elements for generating voltage equivalents of the current values of the amplitude and period of the pulses. Further, the signals of the flow sensors or equivalent of their parameters are transmitted through the running switch 7 and the analog-to-digital converter 8 to the data preprocessing unit 9, where, with reference to the numbers (coordinates) i of the monitored transformers and the numbers j of the next pulses, they are prepared for transmission to computer complexes 12 in form, for example, instantaneous values of amplitudes A _ij , periods T _ij and results

their statistical averaging over a certain accepted time interval. In each of the three computing complexes 12, this information is perceived by the first group of input / output ports simultaneously from three different groups of measuring units 5, reserving each other, of all flow meters, which allows monitoring the health of these measuring blocks. Indeed, if the three measuring units 5 backing each other with the indices B, C, D are operational and mutually identical, then since they all receive input signals synchronously from the same flow sensors, equalities must always be fulfilled:

Actually, due to some variation in the characteristics of blocks 5, these equalities can be satisfied with some tolerance P1 or P2, so that the inequalities should be verified:

To identify the failed block 5, you can use this crucial rule: block 5 with one or another index is healthy if at least one of the indicated inequalities is true for a variable with this index, and it is faulty if two such inequalities are not fulfilled. The serviceability of the computing complex 12 itself can be established by a similar comparison of the calculation results obtained by this complex and two others that reserve it (with the exchange of information between the complexes 12 along the same highways 11). Failure monitoring of blocks 15 and complexes 12 is also carried out by self-diagnosis using algorithms not considered here. We only note that the means of displaying information about the state of system 1 must be performed in such a way that the estimated time for detecting and replacing defective modules does not exceed a predetermined limit (for example, a quarter of an hour) and the probability of failures in two measuring units 5 of one flow meter simultaneously during operation the reactor from one scheduled preventive repair of the reactor to another ("from PPR to PPR") was no more than the probability of failure of at least one flow sensor of the same flow measure.

 Constantly in the mode of channel-by-channel control over the flow of the coolant is a system of 1 flow meters. Moreover, if a failure in it affects no more than one measuring unit from among each other or one computing complex 12, and all the flow sensors are operational, the rational control system 13 operates in its main mode: identification of fuel assemblies with leaky cladding of fuel elements by the presence in the coolant of fission products of nuclear fuel. In each of the computing complexes 12, signal equivalents of values are generated in the TC, which are transmitted through the above-mentioned input / output ports to each of the highways 11 and further to the higher-level information-computing system; the reliability of the information received there is checked in the same way as it was described for the case of monitoring the health of measuring units 5 and complexes 12.

The failure of at least one flow sensor or at the same time two or more measuring units 5 of one flow meter along signal transmission circuits from the same sensor leads to loss of flow information in the fuel cell, and from this point of view, especially when it comes to fuel cell with fuel assemblies, potentially nuclear hazard. A sudden failure of the flow sensor can be detected, for example, by performing three inequalities for the same value of i:
A $\genfrac{}{}{0ex}{}{\text{B}}{\text{ij}}$ <P3, A $\genfrac{}{}{0ex}{}{\text{C}}{\text{ij}}$ <P3, A $\genfrac{}{}{0ex}{}{\text{B}}{\text{ij}}$ <P3
where P _{3 is the} minimum allowable value of the amplitude of the pulses, at which it is still possible normal operation without failures of the measuring units.

В любом случае, в каждом из вычислительных комплексов 12 формируется сигнал отказа расходомера с указанием координаты i ТК с ТВС, по которому потеряна или идет недостоверная информация о расходе. Этот сигнал передается через первую группу портов ввода/вывода в магистрали 11 и далее в блок 17 системы 13 радиационного контроля теплоносителя. Система 13 переводится в режим контроля за расходом в ТК с заданными координатами: в блоке 17 формируются сигналы на включение соответствующего блока 16 управления положением одного из гамма-датчиков 14 и этот датчик через некоторое время

устанавливается на пароводяную коммуникацию, связанную с заданным ТК; сигнал

гамма-датчика, зависящий от расхода в i_o-ом ТК с ТВС, передается через блоки 16, 17 магистрали 11 и далее в вычислительные комплексы 12 системы расходомеров, где проверяется выполнение неравенства:

где П4 - значение

, при котором расход в ТК с ТВС не ниже допустимого.Failure of two or more measuring units of one flowmeter along signal transmission circuits from the same sensor is recorded if at least two of the three inequalities are not met:

In any case, in each of the computing complexes 12, a flowmeter failure signal is generated indicating the coordinate i of the fuel cell with the fuel assembly, along which false information about the flow is lost or is being transmitted. This signal is transmitted through the first group of input / output ports in the line 11 and then to the block 17 of the coolant radiation monitoring system 13. The system 13 is transferred to the flow control mode in the TC with the given coordinates: in block 17, signals are generated to turn on the corresponding block 16 for controlling the position of one of the gamma sensors 14 and this sensor after some time

installed on steam-water communication associated with a given TC; signal

the gamma sensor, depending on the flow rate in the i _o- th TC with the fuel assembly, is transmitted through blocks 16, 17 of the line 11 and then to the computer complexes 12 of the flowmeter system, where the fulfillment of the inequality is checked:

where P4 is the value

at which the flow rate in the fuel cell with fuel assembly is not lower than the permissible one.

свидетельствует о том, что за время

, в течение которого информация о расходе в i_o-ом ТК с ТВС по показаниям системы 1 отсутствовала или была недостоверной, снижения расхода в этом ТК ниже допустимого не произошло (вероятность появления иного события за это время достаточно мала), но ситуация продолжает оставаться потенциально ядерноопасной, т.к. при отказе и системы 13 контроль за расходом в i_o-ом ТК с ТВС полностью теряется и ситуация переходит в ядерноопасную. Кроме того, если после отказа одного датчика расхода откажет еще и другой, система 13 из-за указанных ранее ограничений может не обеспечить необходимого контроля за расходом в этом новом ТК с отказавшим датчиком расхода даже при отсутствии в ней отказов. Стало быть, включение системы 13 в режим контроля за расходом в i_o-ом ТК с ТВС является практически сигналом к тому, чтобы персоналом АЭС были приняты меры либо по досрочной выгрузке соответствующей ТВС (если отказал датчик расхода), либо по ускорению восстановления работоспособности электронной части расходомера. При этом имеется в виду, что ситуация с потерей непрерывного контроля за расходом в ТК без ТВС не является ядерноопасной.Inequality

indicates that over time

during which information about the flow in the i _o- th fuel tank with fuel assemblies according to the testimony of system 1 was missing or unreliable, there was no decrease in consumption in this fuel tank below the permissible value (the probability of the appearance of another event during this time is rather small), but the situation remains potentially nuclear hazard because in case of failure of system 13, the flow control in the i _o- th fuel cell with fuel assembly is completely lost and the situation becomes nuclear. In addition, if, after the failure of one flow sensor, another fails, the system 13 may not provide the necessary control over the flow in this new TC with a failed flow sensor even if there are no failures due to the above restrictions. Consequently, the inclusion of system 13 in the flow control mode in the i _o- th fuel cell with fuel assemblies is practically a signal for NPP personnel to take measures either to prematurely unload the corresponding fuel assemblies (if the flow sensor failed) or to accelerate the recovery of electronic flowmeter parts. At the same time, it is understood that the situation with the loss of continuous control over the flow in a fuel cell without a fuel assembly is not nuclear hazardous.

сигнал

оказывается не удовлетворяющим неравенству

, что может произойти либо из-за отказа системы 13, любо из-за снижения расхода в i_o-ом ТК ниже допустимого за время

или за время контроля за расходом по показаниям системы 13 до выгрузки ТВС. В любом случае ситуация переходит в ядерноопасную, в каждом вычислительном комплексе 12 формируется и через вторую группу портов ввода/вывода по линиям 19 передается командный сигнал на срабатывание аварийной зашиты реактора по расходу; последняя срабатывает и реактор заглушается, если указанный сигнал воспринимается средствами запуска такой защиты по крайней мере от двух комплексов 12 из трех (логика "2 из 3-х").However, a different outcome of the transition of the system 13 to the mode of flow control in the i _o- th TC with fuel assemblies is possible: through time

signal

is not satisfying the inequality

that can occur either due to a failure of the system 13, due to a decrease in the flow rate in the i _o th TC below the permissible time

or during the monitoring of the flow according to the testimony of the system 13 to the unloading of the fuel assemblies. In any case, the situation turns into a nuclear hazard, in each computer complex 12 it is formed and through the second group of input / output ports along lines 19 a command signal is transmitted to trigger the emergency protection of the reactor by flow rate; the latter is triggered and the reactor is shut off if the indicated signal is perceived by means of triggering such protection against at least two out of three complexes (logic "2 out of 3").

 The signals for the operation of the reactor emergency protection system by flow are generated without loss of time to put the system 13 into the flow control mode, i.e. immediately, if the complexes 12 recorded either a real decrease in the flow rate according to the readings of the flow meters 2 below the maximum permissible value (set point P5), or a failure of two or more redundant blocks 5 or complexes 12 along the signal processing circuits of at least one flow sensor in the fuel cell with fuel assembly.

импульсов при определенном выборе параметров измерительной схемы блоков 5 позволяет оценить степень надежности контактных переходов и цепей магнито-индуктивных преобразователей датчиков расхода. Отметим еще, что окончательное решение по результатам диагностики ресурса датчиков ресурса принимается, как правило, группой специалистов с учетом множества иных факторов, связанных с режимом эксплуатации реактора. Автоматизация накопления и обработка данных для диагностики ресурса существенно облегчает принятие такого рода решений, делает их более обоснованными. Во всяком случае, сигнал, формируемый блоком 18 или комплексами 12 (при обмене информацией с блоком 18) при наступлении события типа
A $\genfrac{}{}{0ex}{}{\text{min}}{\text{ij}}$ /A $\genfrac{}{}{0ex}{}{\text{max}}{\text{ij}}$ < П6 или T $\genfrac{}{}{0ex}{}{\text{min}}{\text{ij}}$ /T $\genfrac{}{}{0ex}{}{\text{max}}{\text{ij}}$ < П7,
может служить человеку-оператору серьезным поводом для принятия решения о досрочной выгрузке ТВС из соответствующего ТК и, тем самым, предотвращении возможности возникновения ядерноопасной ситуации, связанной с потерей контроля за расходом в этом ТК.In each of the computing complexes 12 of the flowmeter system, another important function is realized: the formation and transmission along line 11 to block 18 of the information necessary for diagnosing the resource of flow sensors. Of course, block 18 could be explicitly excluded from the block diagram, and its functions could be transferred to each of the computing complexes 12, which, however, is not of fundamental importance. The important role is played by the diagnostics of the resource of flow sensors in ensuring their reliability during the periods of operation "from PPR to PPR" precisely with the automated accumulation of the necessary data. As for the criteria for assessing the resource, they are related to assessing the degree of wear of the tracks of twisting mechanisms and balls rotating in them, the amplitude of fluctuations caused by this wear in the values of A _ij , T _ij . Operating experience of flow sensors at RBMK-type reactors has shown, for example, that the following decisive rule is valid: the sensor is suitable for further operation during another interval of operation of the reactor at power “from PPR to PPR” if the following inequalities are fulfilled before shutting down the reactor to the next PPR:
1 ≥ (A $\genfrac{}{}{0ex}{}{\text{min}}{\text{ij}}$ / A $\genfrac{}{}{0ex}{}{\text{max}}{\text{ij}}$ ) ≥ A6, 1 ≥ (T $\genfrac{}{}{0ex}{}{\text{min}}{\text{ij}}$ / T $\genfrac{}{}{0ex}{}{\text{max}}{\text{ij}}$ ) ≥ P7
where the indices "min", "max" refer to the minimum and maximum values of the amplitudes and periods of the pulses measured over a certain observation interval (for example, equal to 100 T _ij ) at a constant flow rate in the i-th TC;
P6 ≈0.6; P7 ≈ 0.8 empirically obtained threshold values of the indicated relations;
otherwise, that is, if at least one of the two inequalities is violated, it is better to replace the corresponding sensor during the next SPR. It is possible to effectively use flow rate sensors and other ratios related to the analysis of the time behavior of the standard deviations of the parameters A _ij , T _ij from the average, etc. So, the change in time of average amplitude

pulses at a certain choice of parameters of the measuring circuit of blocks 5 allows you to assess the degree of reliability of contact transitions and circuits of magneto-inductive transducers of flow sensors. We also note that the final decision on the results of diagnostics of the resource of resource sensors is taken, as a rule, by a group of specialists taking into account many other factors related to the operating mode of the reactor. Automation of the accumulation and processing of data for resource diagnostics greatly facilitates the adoption of such decisions, makes them more reasonable. In any case, the signal generated by block 18 or complexes 12 (when exchanging information with block 18) when an event of the type
A $\genfrac{}{}{0ex}{}{\text{min}}{\text{ij}}$ / A $\genfrac{}{}{0ex}{}{\text{max}}{\text{ij}}$ <A6 or T $\genfrac{}{}{0ex}{}{\text{min}}{\text{ij}}$ / T $\genfrac{}{}{0ex}{}{\text{max}}{\text{ij}}$ <P7,
This can serve as a serious reason for a human operator to decide on the early unloading of fuel assemblies from the corresponding fuel cell and, thus, to prevent the possibility of a nuclear hazard situation arising from the loss of control over the consumption in this fuel cell.

Claims (1)

 A device for controlling the flow of coolant in the technological channels of a nuclear reactor, containing a system of flow meters, each of which is made in the form of a group of channel flow sensors connected to a measuring unit made in the form of normalizing converters according to the number of channel sensors connected through a switch to a data preprocessing unit , and is connected via the main communication highway to the main computer complex, equipped with an output to a common information and computer system, distinguishing it consists in the fact that it introduced a radiation control system for the coolant, containing position-controlled gamma sensors made with the possibility of moving along the rows of steam-water communications of technological channels and connected via control units for the position of sensors and analog-to-digital converters with a computing-control unit, galvanic isolation blocks are introduced into each flowmeter, connecting each sensor with the main measuring block and at least two redundant ones and measuring units, each of which is connected via a corresponding additional communication line to the main and additional computer complexes, with the number of redundant measuring units in each flowmeter, equipped with outputs to the general information-computing system and to means for generating emergency reactor protection signals by flow rate, each of which the connection is connected to the computing and control unit and the entered data storage and processing unit for diagnosing the resource of flow sensors Yes.