KR800001625B1 - Method and apparatus for mintoring the axial power distribution within the core of anuclear nuclear reactor exterior of the reactor - Google Patents

Abstract

The method that is to monitor externally a nuclear reactor of the flux distribution along a given axis of a nuclear core(18) of the reactor ina manner to representatively reconstruct the relative flux shape along the given axis includes the steps of monitoring the flux exterior of the reactor, converting the value of flux, figuratively dividing the given axis at a plurality of spaced coordinates, and electrically establishing the relative value of flux at each of the spaced coordinates.

Description

Axial Output Distribution Inspection Method of Reactor Core

1 is a plan view of a typical reactor containment arrangement to which the present invention is applied.

2 is a reactor core schematic showing the relative positions of the fuel assembly, the control rods and the outer core detector.

3 is a schematic representation of the relative position and axial cross-section of two embodiments of a core outer detector used in the inspection method of the present invention.

4a, 4b, 4c, 4d, and 4e are graphs showing the distribution of the axes of the axes at various positions of the length control rod and the partial control rod in the core.

5 is a schematic diagram of a buffer circuit used to convert a detector in response to a voltage output.

6 is a schematic diagram of a circuit for processing the voltage output of FIG. 5 to measure the magnitude of the proxy at one core axis coordinate point.

7 is a schematic circuit diagram of the Fxy generator shown in FIG.

FIELD OF THE INVENTION The present invention relates generally to nuclear reactors and relates to an improved method for inspecting the axial power distribution inside the reactor core based on neutron flux measurements obtained from at least three detectors located outside.

Generally, in pressurized water reactors, neutron absorbers are included in the cooling medium when necessary, in amounts adjusted to control the reactivity and heat generated within the core. Moreover, control rods are inserted in the fuel assembly and are movable in the vertical axis direction in the core to control the reactivity of the core, ie the output. Three types of control rods are used for various purposes. That is, the length control rod, the partial control rod and the reactor stop control rod. Partial control rods and on-length control rods are arranged to move in and out of the core to achieve the required degree of control.

Xenon is produced through the beta decay process of radioactive oxo (I) as the product of fission reactions. Xenon has a large neutron absorption cross section and has a great influence on power distribution and reactivity control in the blast furnace core. While other forms of reactivity control are directly related to control, the densification of xenon in the core can cause serious problems in reactor control, resulting in relatively long decay times and at least 20 hours after exchange of power to reach steady state values.

The radial power distribution of the core can be easily driven by the radially, symmetrically arranged control rods throughout the core with a predetermined arrangement of fuel assemblies, but the axial power distribution varies considerably during reactor operation. The axial power distribution of the core caused many problems throughout the reactor operating cycle for various reasons. Normally, the coolant passing through the fuel assembly is directed from the bottom to the top of the core to have a temperature gradient along the axial direction of the core. By varying the rate of fission reaction that depends on temperature, the axial power distribution can be changed. Secondly, the axial change in output distribution changes the axial distribution of xenon, accelerating the change in output distribution along the axial direction of the core. This causes an oscillation of the axial output distribution by the xenon and becomes unstable without correct adjustment of the operator in the core life. Third, inserting the control rods at the top of the core, without proper consideration of the past operating cycle of the reactor, worsens axial output peaking. The change in atomic core output to follow the change in the electrical output of a power plant is called a load follow.

One of the reactor flow control programs recommended by the reactor producer is to use the motion of the length control rod to increase or decrease the output level, and use the partial control rod to control the spatial axial output vibration generated by xenon, To form an output distribution. Changes in reactivity due to changes in xenon concentration are generally compensated for by the relative change in the concentration of neutron absorbers in the core coolant or moderator. In this method of operation, the partial control rod is moved to maintain any desired band, in particular axial offset error of ± 15%. The axial offset is a useful parameter for measuring the axial output distribution and is defined as

Where Pt and Pb are the output rates generated at the upper and lower half of the core, respectively, measured by two detector devices arranged axially outside the core located around the reactor.

Besides keeping the axial offset within the required bands, no effort is made to maintain the core's inherent axial power distribution. The partial control rod is moved to minimize and reduce the axial offset regardless of the preset steady state axial offset. This process causes constant fluctuations in the axial offset while maintaining the loud flow operation, resulting in a number of unexpected operating conditions.

First, axial output pinching, which is axially centered and a large output peak, can occur at values where the axial offset is zero or low. Such output peaks operate at a reduced level of the reactor, resulting in reactor output losses such that such peaks do not exceed the retained feature size.

Retention limits are caused by existing core out-of-core incompatibilities that fail to check the output level at the center of the core. Secondly, a significant change in the axial power distribution of the transient may occur during large loud flow changes due to the insertion of more control rods at reduced output levels.

Third, large xenon transients occur after reduction to the output, resulting in axial output vibration. Fourthly, the use of inadequate partial control rods can result in severe axial output distributions that are not readily discernible by existing core axis detector devices. Fifth, it is necessary to reduce the power output of the reactor so that increased thermal channel factors occur (not hot spots along the cooling channels in the fuel assembly) and in response to severe transients or reverse power distribution. Finally, there is currently protection against severe axial pinching with less axial offset.

Because of the many separate operating conditions experienced during reactor operation during low flow, many current reactor producers are advised to operate the reactor at a constant power without having a low flow capability.

This lack of diversity in plant operations limits the use of nuclear reactors, and petroleum-fired power plants are used to maintain the difference in capacity required for the change in the logs.

In order to effectively establish the loud flow capability, a constant axial power distribution must be maintained during the loud operation. British Patent No. 1,493,735 proposed to maintain a symmetrical xenon axial power distribution in order to solve this problem. However, in order to effectively maintain a constant axial flux distribution, a test that has the ability to actually reshape the axial proxy pattern in the core and to compensate for changes in itself before erroneous dispersion of xenon is affected. A device is required.

The in-core proxy inspection device described in US Pat. No. 3,932,211 can detect the exact shape of the axial proxy distribution, but when used as an in-core detector, such a detector is susceptible to the core's proximal influence and for this purpose. Burns prematurely when used continuously.

Such detectors are generally used to process the core outer detector at the start of the reactor or periodically thereafter, or to know the map of the proxy after the movement of the large control rods in the aforementioned US patent. However, a valid core inspection system requires a continuous core state of axial proxy distribution. It has been used for this purpose in the past as low proxy, dry, low temperature outside the core-outer detector pressure vessels can be expected more at low temperature, relatively low pressure.

As a result, it is a primary object of the present invention to provide an improved method of using the core-outside detector to provide an accurate view of the axial proxy over the entire height of the core.

Briefly, the shortcomings of the prior art are overcome by reconstructing the relative proxy distribution in the core from the reactor proxy signal examined outside of the method and core of the present invention. The reactor proxy signal is checked by three or more detectors that are sensitive to the measured proxy to represent an electrical output. The proximate detectors are located outside of the core, centered on a relatively isolated vertical plane that each divides the core axis into two.

An apparatus is provided for forming a proxy relative value in a number of isolated axis coordinates for reconstruction at a point representing a relative proxy distribution along an axis.

The device for electrically generating the relative value of the proxy at each axial coordinate point uses the sum of the sum of each detector output multiplied by a preset constant. As a result, the proxy distribution at any point in the core can be obtained with the same reliability as related to the detector response of the core outer axis.

In order to understand the present invention in more detail, reference will be made to the accompanying drawings.

FIG. 1 is a schematic representation of a typical pressurized water reactor using the method according to the present invention, including an apparatus for more accurately examining the axial proxy distribution in the core to solve previously encountered operational difficulties. The reactor of FIG. 1 includes vessel 10 and, when sealed by head assembly 12, forms a pressure vessel. The vessel consists of a coolant inlet 16 and a coolant outlet 14 integrally with the cylindrical wall.

As noted above in the art and described in detail in FIG. 2, the vessel 10 includes a core 18 consisting of a plurality of coated fuel elements arranged in an aggregate 20.

In generating heat output in the core, as mentioned above, the important mediators affecting the axial distribution are the insertion level of the length control rod and the partial control rod, the combustion time of the core, the output level of the reactor and the xenon distribution. Examining and ascertaining the past periods of these mediators is absolutely essential to actually forming a flat axial proxy distribution so that the flow flow capability can be achieved without continuously monitoring the axial proxy distribution through the core's axial height. need. These important vehicles include control rod position indicators (such as those described in US Pat. No. 3,858,191 issued Dec. 31, 1974), core-inner thermocouples, resistance temperature detectors with coolant pipes, and core-outer of FIG. It is measured by the information obtained by the neutron detector 32.

The detectors 32 '' and 32 'shown in FIG. 1 are provided with three proxy sensitive sections and four proxy sensitive sections evenly divided according to the core height of the core. Although the axial portion of the core-outer detector arrangement is located symmetrically around the core in a normal operating reactor, the detectors labeled 32 'and 32' 'of the present invention describe two different embodiments to simplify the description. It is to. Although dividing the axis length of the core-outer detector into three, four, or myriads of solutions can solve the problem of proxy indirects between adjacent axis positions, the method and apparatus for processing the signal obtained by the present invention is dependent upon the axis height of the core. It is provided to first form a distribution of laxes. However, the effect of the proxy interference can be minimized by using an improved structure in which each of the detector portions are axially separated from each other, as shown in FIG.

2 is a plan view of a typical pressurized water reactor core 18. Core positions 42 and 44 represent the positions of the on-length control rods and partial control rods used during full output operation, respectively. The remaining core position 20 represents the position and fuel assembly position left for other control purposes. In power operation, the distribution of power in the core is examined based on neutron flux measurements at a number of core out-of-core detector positions 46, 48, 50 and 52 located symmetrically around the vessel. Each detector provides relative proxy information at the upper limit of the core.

Although in this particular embodiment the core is separated into four upper limits by a detector arrangement located at the diagonal position of the core, this upper limit places the detector at 0 °, 90 °, 180 ° and 270 ° positions in the core plane. It is clear that a new upper limit can be defined. Thus, the proxy measurement detected by detector 52 in the illustrated embodiment represents the output occurring at the upper bound bounded by the 0 ° axis and the 270 ° axis that divides the horizontal plane of the top view shown in FIG. It should be separated from the vertical core axis from which the directional proxy distribution is measured. It will be appreciated that the symmetrical placement of the core components results in the output of each upper limit of the core representing the output of another core upper limit. The detector 32 'or 32' 'is therefore located at the outer core detector positions 46, 48, 50 and 52. In order to understand the processing of the detector output, only one of the core-outer detector is considered, and the other part is processed in the same way.

FIG. 3 is a schematic view of the core axially with three separate detector portions 32 '' positioned symmetrically at the top, center and bottom corresponding to the axis length of the core, respectively, denoted by T, M and B. FIG. The four detector sections 32 'include four adjacent detector sections, labeled a, b, c, d, located from the top of the core to the bottom opposite the detector 32' '.

In general, in accordance with the present invention, the value of the proxy at each coordinate point along the axis length of the core is obtained by initial conversion and detailed by a relatively preset constant, which is periodically reconverted during the core lifetime according to fuel consumption. It can be formed from the sum of the electrical outputs that are changed in the course. These constants are highly dependent on the size of the plant and therefore depend on the plant and fuel cycle.

According to the method of the present invention, the axial output form of the core is reformed by a multi-part detector reaction with a Fourier series of sine which is limited by the axial length by the extrapolation of the core. Four terms of the Fourier series are computed in three detector response sections, four terms in four parts, and n terms in n parts. Thus, the axial output distribution is shown below.

Where Z = 0 is the extrapolated boundary at the top of the core and Z = π (180 °) is the extrapolated boundary at the bottom of the core.

Constants C are obtained in the multi-part detector reaction.

The first step is to correlate the detector response and output distribution between the axial portions of the core. In general, the detector current in three parts of the core-outer detector configuration, such as detector part 32 '', is related to the output:

Where P _T is the output at the top 1/3 of the core and P _M is the output at the center 1/3 of the core: P _B is the output at the bottom 1/3 of the core: Aij is a constant at a given detector device. I and j are integers from 1 to n and are equal to the number of detector portions in this embodiment.

Equations (2), (3) and (4) may be represented by a matrix as follows.

The matrix element Aij is obtained by applying the axial output distribution obtained in the core-inner form and the observed detector current, where L _T is the response obtained from detector T and L _M is the response obtained from detector M and L _B from detector B. A similar 4x4 matrix equalizes the output at the axial upper limits of the core obtained from the core-inside proxy test apparatus during conversion of the four detector part signals 32 'and the constant.

The value of P _T P _M P _B is obtained by means of a fixed core-inside inspection device positioned such that the core-inside detector measures the output at the top, middle and bottom of the core or as described in the above-mentioned US patent. It can be obtained by a movable core-inside device such as

In order to accurately calculate the matrix element Aij, the axial output distributions observed for five different proxy distributions, such as the proxy shapes shown in Figures 4a, 4b, 4c, 4d, and 4e, You must match the measured detector flow with. FIG. 4a shows the proxy distribution obtained in a moving core-inside proxy inspection apparatus in which all control rods have been removed from the core.

4b shows the proxy distribution with the partial control rod inserted in the lower part of the core. 4c shows the distribution of the proxy in the state in which the partial control rod is inserted in the upper part of the core. 4d shows the proxy distribution with the partial control rod located in the center of the core. Similarly, FIG. 4E shows the axially pinched proxy distribution obtained with the partial control rod at the bottom of the core and the control rod located at the top of the core.

The proxy distributions obtained in FIGS. 4a-4e are obtained primarily by plant initial measurements. Equation (5) is the general formula for n detectors, and the solution is solved for the axial output at each part of the core with respect to the detector current.

[Aij] ^-1 is a matrix inverse of the core output and detector response.

By solving the following equations, the Fourier constant Cn is found at the 1/3 output of the core.

Here, the above equation is the case where there are three axial detectors, that is, Pn = P ₁₃ = P _B. In the form of a matrix, the solution can be written as

Alternatively, the detector current '' L '' is as follows.

[Cos(jㆍzi)-Cos(jㆍZi+1) (12)이며 Zi는 노심의 국부적 출력 Pi가 계산되는 노심의 위치에 해당하는 노심 영역사이의 경계이다. 행열식[Qij]^-1는 행열식 Q의 역행열식이다. 이러한 방법으로 푸리에 상수는 다중 부분검출기 전류와 고정된 행열식 Q^-1와 A^-1에서 얻어진다. 이러한 역 행열식은 장치의 검사시에만 얻어져야 하며, 양수 또는 음수이다. 4개의 검출기부분에서 얻어진 출력은 4×4행열식을 사용하는 것 이외는 동일한 방법으로 처리된다. Qij의 식은 동일하나, 작동시 검사후 노심내의 축을 따른 어느 점에서 프락스 상대값은 식(1)의 Z를 문제시되는 축좌표를 대치함으로 노심-외축 검출기 반응에서 결정될 수 있다. 실제상 앞으로 설명하는 바와 같이 그 결과는 전자적으로 얻어진다.here

[Cos (j.zi) -Cos (j.Zi + 1) (12) and Zi is the boundary between the core regions corresponding to the core position at which the local output Pi of the core is calculated. Matrix [Qij] ^-1 is the inverse of matrix Q. In this way, the Fourier constants are obtained for the multiple partial detector currents and the fixed matrixes Q- ¹ and A- ¹ . This inverse should be obtained only at the time of inspection of the device, and may be positive or negative. The output from the four detector sections is processed in the same way except using the 4x4 matrix. The equation of Qij is the same, but at some point along the axis in the core after inspection in operation, the proxy relative value can be determined in the core-extraaxial detector response by substituting the axis coordinates in question for Z in equation (1). In practice, as will be explained later, the result is obtained electronically.

In order to simplify the processing of the detector output, a method different from the above-mentioned method may be used according to the present invention. The axial height of the core is graphically divided into a number of apparent coordinate points sufficient to effectively indicate the axial proxy distribution in the core. For example, the core is divided into 25 coordinate points so that the first and last coordinate points are in the core axis of the core.

In the present embodiment, the matrix Ajj can be extended to 100 elements in which four weight detectors are used. The matrix element is a moving core-inside proxy measuring device (described in the above-mentioned US patent) similar to the above mentioned measuring the output at each coordinate point for the five axial proxy shapes shown in FIG. Obtained by the method. The number of proxy shapes required for calibration is the same as the number of detectors used, but five shapes are preferred as shown in FIG. 4 to ensure the accuracy of the calibration.

The matrix elements Aij are obtained from the simultaneous solution of each point for the measured values for each proxy type. The general matrix for obtaining the reconstruction at 25 points in the core axial proxy distribution is:

Where i is an integer from 1-25, j is an integer between 1-n, and n is equal to the number of detector parts. Therefore, the output at each coordinate point is equal to the sum of the product of the constants of the detector outputs.

The latter method of processing such detector output simplifies the circuit components for obtaining the proxy information at each point. Once the dot markings are obtained, the entire axial proxy distribution in the core can be reformed.

In this embodiment, it is important that the Aij matrix element shown in equation (13) is different from the top Aij in equation (11).

Due to the many physical properties of the reactor, the permissible number of kilowatts per cm of fuel rod in the top of the core is severely limited than other axes of the core.

This is because the coolant temperature is far above the top of the core and below the core, and the standard of coolant leakage according to the government's regulations sets the number of kilowatts per centimeter for any control rod on the top of the core to minimize the assumed consequences. Because of that very restrictive fact. In order to form the maximum output rate, it is desirable to observe the distribution of the proxy in more detail at the top of the core than at other parts of the core. As a result, in one embodiment of the present invention, the point coordinates in which the proxy is to be measured in the upper region of the core are closer than the coordinates of the other part of the core.

In the core-external detector arrangement of the three detectors T, M, and B, as in the latter method of signal processing mentioned above, the associated detector reactions LT, LM, LB are shown in FIG. Similarly, they are coupled through the associated isolation amplifiers 34 to produce the corresponding voltages V ₁ , V ₂ and V ₃ , and electrically processed to obtain the necessary numerical transformations for the proxy measurement at each expected coordinate point.

Variable resistor 36 is used to measure each detector output. Furthermore, each detector output is added by a current adder 38 to generate a nuclear signal that is used to standardize the proxy measurement to form an extreme signal compared to a fixed point used primarily for plant operation.

At each coordinate point at which the proxy value is to be formed, the voltage output at each of the detector sections is connected to a gain adjustable amplifier 54 having a gain corresponding to the appropriately measured value of Aij calculated as shown in FIG. have. For each of the 25 point coordinates, it is noteworthy to provide the signal processing circuit shown in FIG. For each coordinate, each detector output voltage is multiplied by the accompanying gain provided by the adjustable gain amplifier 54 and then added by the add amplifier circuit 56 to form an average output value on the X-Y plane at that axis coordinate point. The average power at each coordinate point is then multiplied by the associated peak power ratio Fxy established by the plant manufacturer and an alarm is generated to alert the operator that the limit detector 62 exceeds a value indicating the maximum allowable power at that axis coordinate point. It is emitted. Furthermore the average output Pav is displayed or stored in the appropriate display device or memory 64.

The value of the peak output Fxy depends on the number of control rods at the corresponding axis coordinate point. The appropriate value of Fyx to be supplied to multiplier 60 of FIG. 6 is provided in the circuit of FIG. The decoder receives an input from a rod position signal device that detects whether the partial length control rods and the two control bank groups are at corresponding axis coordinate points. Normally only two control banks are used for 50% full output operation. Such a rod position indicating device for this purpose is described in US Pat. No. 3,858,191, issued December 31, 1974.

Since three independent groups of control rods can be at any given coordinate point, eight possible combinations occur, thus having eight separate proxy peaking coefficients. The decoder 66 decodes the appropriate peak power ratio from the rod position indicating device and connects it to the multiplier 60, and couples the variable function generator 68 supplying the appropriate peak power ratio to the multiplier 60.

It is experimentally confirmed that elements A ₁₃ and A ₃₁ of matrix A can be set to zero in the three-core core-outer detector device for immersing the initial value. This result is obtained because the upper detector core lower third state is unknown and the lower detector does not know the upper third third core.

It has also been experimentally demonstrated that the method and apparatus of the present invention provide a good relationship between the proxy distributions established in the core-inner detector readings of the core-outer detector values.

In this way, a reliable determination of the average power at each coordinate point along the axis length of the core can be determined in the core-outer detector signal.

The fuel rod X-Y average axial linear power density, expressed in kw per cm of fuel rod, can therefore be obtained as a function of axial position. Once this information is obtained, several outputs are performed to control the plant operating parameters. E.g,

a. F8 (X-Y average axial peak power ratio) can be calculated and displayed numerically or with an analog device. The worst-case Fq (nuclear power density peak output ratio) can be displayed by multiplying by the worst-case Fxy and adding up the maximum tolerance.

b. Axial linear power densities can be displayed using CRT or other analog representation at kw per cm. It can also be multiplied by the worst case Fxy and summed the tolerances to indicate linear power density in kilowatts per centimeter for the hot rod.

c. In the above (a) and (or) (b) it is possible to cause the maximum value alarm is generated.

d. Due to the higher cooling temperatures and / or voids, there is a severe limit on the heat transfer relationship to the linear power density towards the top of the core. In the present device, the limit kw per cm can vary depending on the axis position. Thus plant defense signals exceeding this limit may be used. Turbine runback and reactor trip signals occur when kw per cm exceeds a preset limit. In addition, a ΔT defensive penalty may occur when kw per cm exceeds a preset limit. The ΔT penalty is either a digital signal or a value converted into an analog signal or a digital signal to perform directly with an ΔT defense device present in the operating plant. The blast furnace reactor can be operated with significantly increased efficiency and low capacity.

Claims (1)

Arranging at least three proxy detectors each providing a proxy directed electrical output measured at mutual positions in an arrangement perpendicular to the outer position of the reactor core, and wherein the number of said proxy detectors arranged outside the core is said core inner proxy detector; By using at least one intracore proxy detector whose output is equal to or smaller than the number of positions monitored, inspect the output in the core at most locations along a given axis, and at each electrical output at those locations during the actual measurement. Correlate each electrical output with the values obtained at various locations to calculate the multiplied coefficients for each, and run at least three proxy detectors to provide a corresponding electrical output at the initial stage of the actual measurement, Process the output by multiplying it by the calculated rate for multiple locations and directing the output to it. Add the processed electrical output for each of the majority of locations to provide an output signal, and plot the output distribution along a given axis of the reactor core, including comparing the output signal with a reference value indicating the maximum permissible output for each of the majority of locations. How to check.

Images