DE102012001509A1 - Device and method for measuring the position of a displaceable control rod - Google Patents

Abstract

The invention relates to a device (0) for measuring the position of a displaceable control rod with a plurality of secondary coils (S'1-S'47) arranged in series along a displacement path, inductively excited by at least one primary coil (1), one or more respective ones Secondary coils (S'1-S'47) are combined to form at least two coil groups such that a position signal (P'1-P'3) generated with the aid of the respective coil group increases or decreases stepwise, when the control rod at the secondary coils (S '1-S'47) is pushed past. Such a device (0) should, on the one hand, require the smallest possible number of measuring lines (M0, M'1-M'3) and, on the other hand, determine the control rod position with high resolution at high operational safety and reliability. For this purpose, the arrangement and interconnection of the secondary coils (S'1-S'47) according to the invention selected such that on the basis of the totality of the position signals (P'1-P'3) of all coil groups a unique determination of the current position of the control rod is possible, and at least one of the coil groups has at least two secondary coils (S'1-S'47) which are interconnected in such a way that the associated position signal (P'1-P'3) drives at least three discrete signal levels (N'0- ') as the control rod advances. N'3). The invention further relates to a corresponding method.

Description

The invention relates to a device for measuring the position of a displaceable control rod with a plurality of successively arranged along a displacement path, inductively excited by at least one primary coil secondary coils, wherein one or more secondary coils are combined to at least two coil groups such that one with help The position signal generated by the respective coil group increases or decreases stepwise as the control rod is pushed past the secondary coils.

The invention also relates to a corresponding method.

In a nuclear reactor, a control rod - also called a control or control rod - serves to control and shutdown a nuclear reactor. The control rod, when in the reactor core, absorbs neutrons released by the nuclear reaction, which are then no longer available for further nuclear fission. In this way the reaction rate is reduced. In addition to other possibilities can thus be regulated by the more or less deep retraction of the control rods in the reactor core of the neutron flux and thus the power. In principle, a deeper retraction of the control rods means a higher neutron absorption and thus a power reduction. The complete retraction of the control rods, the chain reaction can be completely prevented, so that the reactor is switched off.

The exact knowledge about the position of the respective control rods in a reactor core is thus an important information, since it serves on the one hand the power control and on the other hand has a very high safety relevance.

In many nuclear reactors, especially in pressurized water reactors, an inductive measuring system is provided for determining the position of the control rods. This provides for each control rod to be monitored a plurality of successively arranged along its travel secondary coils, which are inductively energized by at least one supplied by AC voltage and thus generating a magnetic alternating current generating primary coil, and the secondary voltage signals can be tapped. The respective control rod and / or its drive rod has a ferromagnetic core, preferably an iron core, which has inductance-influencing properties, in particular the magnetic flux reinforcing properties, so that the voltage signal at the secondary coils changes depending on the control rod position. As a rule, the ferromagnetic core is continuous and often extends over the entire length of the conceivable but is also a ferromagnetic core with a shorter length. As the control rod and / or the drive rod travel along or through a secondary coil, the value of the magnetic coupling of that coil to the primary coil (s) changes. A secondary coil, which is located in the region of action of the respective ferromagnetic core, has a higher magnetic coupling to the primary coils than other coils, which are preferably constructed identically. The tapped off at this secondary coil voltage signal thus has a greater amplitude than that of secondary coils that are not affected by the ferromagnetic core.

By measuring and comparing all position signals generated by the secondary coil voltage signals, a position determination of the control rod is possible. Metrologically, the amplitude of the secondary voltage signal would ideally change stepwise as the control rod traverses a secondary coil. By various effects, however, this is generally not achieved in an ideal manner, so that for the purpose of evaluation usually from the secondary voltage signal, an associated binary signal is generated, which includes the desired step function. This can be done, for example, such that a binary coded signal is generated in an evaluation unit by a comparison of the analog encoded "raw signal", which is tapped at the respective secondary coil, with defined threshold or threshold values.

The accuracy or spatial resolution of the position determination depends essentially on the number and distribution of the secondary coils, sometimes called measuring coils, along the displacement path. The measuring system provides discrete position values of the control rod indicating which secondary coil is the ferromagnetic core or other pulse generator and thus the control rod. The resolution of this measuring system is thus limited by the number of secondary coils. Previous measuring systems, which have a spatial resolution in the range of the secondary coil size, require a large number of secondary coils and a correspondingly high number of measuring lines for high spatial resolution.

A high number of measuring lines is in principle undesirable. So exists in a nuclear power plant to the reactor pressure vessel in which the fuel assemblies are arranged, usually a security container, which is a safety device of nuclear power plants and encloses the reactor pressure vessel. For the control and monitoring of the nuclear reactor is a variety of control, measuring or control lines available, often necessarily be passed through the reactor pressure vessel and the security container. These bushings cause above all because of the required sealing a structural complexity, which is associated with costs. In addition, in case of unwanted leakage scenarios, the bushings are sometimes weak points.

When designing a nuclear reactor, it is therefore desirable to use as few such bushings as possible. Especially in the case of an existing nuclear power plant, it would be desirable to limit the measuring lines necessary for the control rod position determination to a minimum or even to reduce them without incurring information losses. The saved passages would be available for other lines in this case. It would also be conceivable to use the liberated bushings to increase the secondary coil number, which would offer a higher spatial resolution.

A combination of reduction of test leads and simultaneous increase in the number of secondary coils would also be conceivable.

In other applications, it is often necessary to determine the position of a control rod in a similar manner with the least possible number of test leads. For example, clarifiers are also conceivable applications in which a similar desire exists.

The invention is therefore based on the object of specifying a device for measuring the control rod position, on the one hand requires the smallest possible number of measuring lines and determined at high operational safety and reliability on the other hand, the control rod position with a high resolution. Furthermore, a particularly suitable method for measuring the control rod position by means of an inductive measuring principle is to be specified.

With respect to the device, the object is achieved according to the invention by the arrangement and interconnection of the secondary coils are selected such that based on the totality of the position signals of all coil groups a unique determination of the current position of the control rod is possible, and at least one of the coil groups has at least two secondary coils, which are interconnected in such a way that the associated position signal assumes at least three discrete signal levels when the control rod advances.

Advantageous embodiments of the invention are the subject of the dependent claims.

The term "group" is understood to mean that the extreme case of only a single secondary coil is included. In general, however, such a group of secondary coils will usefully have a plurality of secondary coils following the general usage.

The invention is based on the consideration that the positioning of the control rods should be as accurate as possible and that as few measuring lines and thus bushings should be used.

The number of bushings and thus the measuring lines limited namely on the one hand in a device that uses a position signal coming from different secondary coils for position determination using an inductive measuring principle, the number of secondary coils used and thus the accuracy of measurement. On the other hand, but also due to the novel measuring system released lines in an existing nuclear power plant can be used elsewhere. In addition, the desired device should ensure a high level of security, which also ensures already proven measuring systems.

Surprisingly, it was recognized that the position signals of a coil group can consist of more than two discrete signal levels, so that an additional information content in the associated position signal can be activated and used by suitable interconnection of the individual coils of the respective group. By means of a suitable electrical connection of the secondary coils to coil groups and by using more than two discrete signal levels, the number of coil groups and thus also the number of feedthroughs can be achieved compared to using only two discrete signal levels. With the help of all coming from the individual coil groups position signals a code is formed, which clearly indicates the control rod position. Thus, for example, a position signal consisting of three discrete signal levels may be referred to herein as a tertiary signal, the entirety of these tertiary position signals from different coil groups originating from such a code. This code, which has three states in the case of tertiary position signals, requires fewer digits for the same information content than a previously used binary code, that is to say one consisting of two levels or states. In the previously used electrical interconnection and use of only two signal levels for the position detection of the control rod more coil groups are therefore required than in the inventive device. But this is just the transition from a binary system to a system consisting of more than two discrete states for the position signals, with a simultaneous suitable electrical connection of the individual secondary coils to coil groups as advantageous.

For the coding, by means of which the control rod position can be derived unambiguously from the totality of all position signals, various methods are conceivable, advantageously a binary code known gray code, in which adjacent codewords differ only in a single dual digit, or just one analogous generalization of such a Gray code is used on more than two signal levels.

Advantageously, multiple coil groups are used with three discrete signal levels. Often, the number of secondary coils provided for a control rod in existing nuclear power plants ranges from 30 to 50 depending on the core design. When retrofitting an existing nuclear power plant, it may be expedient to leave the secondary coil number unchanged, so that with a suitable electrical interconnection a maximum number of three discrete signal levels may be sufficient to determine the control rod position. If one also uses too high a number of signal levels, it can be difficult to convert the voltage signals into the discrete position signals which are suitable for the evaluation since the size difference of the voltage signal amplitudes corresponding to the signal levels can become too low for good distinctness. Three discrete signal levels therefore offer the advantage, in the sense of a quantitative compromise, on the one hand of converting existing systems without changing the number of secondary coils and, on the other hand, enabling a somewhat simple differentiation of the induced signals.

Advantageously, the secondary coils can be connected in such a way to form coil groups that nevertheless good distinguishable signal levels are fully utilized to ensure the unambiguous determination of the control rod position from a comparison of all position signals. To ensure metrologically safe separation of the individual signal levels, therefore, several discrete signal levels are provided, namely between three and including five.

In addition to the induced alternating voltage signal, other quantities are generally accessible for a measurement. It would be conceivable to measure a current instead of the voltage. Thus, an alternating current in the secondary winding of a transformer causes an alternating current in its primary winding. In terms of metrology, it is usually easier to use the voltage signal. Preferably, therefore, the voltage signal is utilized to generate the associated discrete value taking position signal.

Advantageously, the discrete position signal levels are the same for all coil groups. This allows the use of the same components for the entire measuring system, such as the secondary coils, since the signal levels ideally have the same heights when using the same components of the measuring system described. As a result, a possible setting of false signal levels is also largely avoided since, in this preferred embodiment, there are fewer signal levels overall than in the embodiment with different signal levels for different coil groups.

In order to use the smallest possible number of bushings for the measuring lines of the secondary coils, it is expedient to use as few groups of coils, the discrete signal levels should be well distinguishable from each other. With a secondary coil number in the range of, for example, 40 to 50, it has been found, after combining various electrical interconnections, that ideally three coil groups are provided.

Advantageously, the resolution of the position determination is independent of the position of the control rod. To ensure a constant resolution, inhomogeneities in the magnetic field should be compensated, so that the distance of the secondary coils along the displacement path should always be substantially the same. However, for the most homogeneous possible configuration of the magnetic field, the distance will in most cases not be completely the same.

Advantageously, as many components of the described measuring system are arranged outside the reactor pressure vessel and outside the reactor containment vessel. Among other things, this prevents the contamination of these components. In particular, the electronic components which are necessary for the evaluation of the signals would be exposed to an increased wear in an arrangement within the containment due to the radiation exposure, which may result in a defect or failure. Even in the case of a defect of the reactor pressure vessel, which may have a leak in such a case, these components are relatively safe to access, as they are located outside the reactor containment. In a preferred embodiment, therefore, the secondary coils are connected to an evaluation unit located outside of the reactor safety container via signal lines, so that the discretization of the originally analog measurement signals, but at least the Evaluation and combination of the individual position signals takes place in a possibly protected from radiation environment.

With regard to the method, the stated object is achieved by the arrangement and interconnection of the secondary coils is selected such that based on the totality of the position signals of all coil groups a unique determination of the current position of the control rod is possible, and at least one of the coil groups has at least two secondary coils, the are interconnected such that the associated position signal when advancing the control rod assumes at least three different discrete signal levels. The embodiments and advantages mentioned for the device also apply mutatis mutandis to the method.

The advantages achieved by the invention are, in particular, that a clear statement about the current position of the control rod is possible by the skillful combining of position signals of individual coil groups, wherein - based on the resolution - only a few test leads are necessary because more than two signal levels are used , In particular, the use of more than two signal levels increases in particular the information content of a position signal compared to previously common devices that use two signal levels, so that less measuring lines and thus bushings are necessary in the inventive device than in previously conventional devices.

An embodiment of the invention will be explained with reference to several drawings. Show:

1 In the upper part, a schematic diagram of an inductive measuring arrangement for measuring the control rod position in a nuclear reactor, which illustrates the problem, and in the lower part in an idealized representation, the associated, rectified analog position signals that illustrate the signal coding,

2 a similar measuring arrangement as in 1 , but with inventive design of the interconnection of the secondary coils to coil groups and the signal coding for the position indicator of the control rod, and

3 an actual recorded signal to coil groups of an inductive measuring system as a function of the position of the control rod.

Identical parts are provided with the same reference numerals in all figures.

1 shows a device 0 which, among other things, consists of a primary coil 1 and a plurality of electrically connected secondary coils S1-S40. The device serves to determine the control rod position in a nuclear reactor by means of an inductive measuring system.

The primary coil 1 according to 1 has lines L1 and L2, which supply the primary coil with an AC voltage. The secondary coils S1-S40 are from the primary coil 1 safely electrically separated and along the way one in the 1 Not shown drive rod of the control rod arranged.

The secondary coils S1-S40 are interconnected by electrical series connection to coil groups, each having in addition to the common line M0 separate unilaterally mounted measuring lines M1, M2 and M4-M8. In addition to the said secondary coils S1-S40, there are two further measuring lines M9 and M10, which are connected to two separate secondary coils which serve to indicate the position of the control rod after complete retraction into the reactor core and in the fully extended state. The entire coil assembly is typically located outside of a pressure tube which is flanged to the reactor pressure vessel of a nuclear reactor and receives the control rod or control rod drive rod.

The in a coil group through that of the primary coil 1 generated and partially amplified by the drive rod magnetic field amplified AC signals are first through corresponding signal lines by a shield 2 , which may represent, for example, the reactor pressure and / or the safety container passed. The AC signals are converted into position signals P1, P2 and P4-P8, each consisting of two signal levels N0 and N1, wherein the signal levels may be different for each of the AC signals.

On the basis of the coil group, which is provided with measuring line M1 and consists of the secondary coils S4, S8, S12, S16, S20, S24, S28, S32, S36 and S40, the principle of a binary position signal generation is explained. The primary coil through which an exciter current flows 1 Generate generally an electromagnetic field, which also flows through the secondary coils, This magnetic field induces an AC signal at the individual secondary coils S1-S40. Is the control rod between primary coil 1 and a secondary coil, the magnetic flux density increases in this range and the magnitude of the induced AC signal at this secondary coil increases. With a movement of the control rod in the direction of secondary coil S4 to secondary coil S40, that of the direction of the arrow 3 Accordingly, changes the induced AC signal at secondary coil S4 as soon as the control rod passes this, namely its amplitude increases. This AC voltage signal is converted, for example, by rectification and smoothing in an analog DC voltage signal, the position signal P1, which corresponds to the upper signal level N1 in this case. This position signal is then subjected to a threshold comparison in the assembly to produce a binary output signal.

When passing the secondary coil S8, which is connected in opposite directions compared to the preceding secondary coil S4, the induced AC signal decreases and the rectified and smoothed position signal P1 assumes the value N0. Due to the selected electrical interconnection, in which in each case the adjacent secondary coils of each coil group are interconnected in opposite directions, a step pattern for each one of the position signals P1, P2 and P4-P8, which consists of two values N0 and N1, respectively, arises on passing the control rod , By assigning in this case seven binary position signals to stored position values can be obtained with a suitable coil arrangement and electrical wiring a clear statement about the current position of the control rod, the spatial resolution is essentially characterized by the distance between two secondary coils S1-S40. For the position display, a 7-bit Gray code for coding is available in this wiring diagram.

In the illustrated schematic diagram of 1 Furthermore, a further position signal P3 is generated from the two position signals P1 and P2. At the same signal levels of the position signals P1 and P2, the position signal P3 is assigned a value of N0 for the signal level; at different binary signal values a value of N1. Due to the selected arrangement of the secondary coils and their interconnection, the generated position signal P3 changes when it travels to every second secondary coil S1-S40, so that inter alia a check of the functionality of the measuring system by comparison with otherwise generated position displays is possible.

at 40 Secondary coils S1-S40 are necessary with this device, which primarily uses 7 binary digits for position determination, a total of eight test leads M0, M1, M2, and M4-M8, all of which by a shield 2 be guided. In addition, the two mentioned measuring lines M9 and M10, which are connected to the separate secondary coils.

In 2 the concept of the invention is clarified, which is to use more than two signal levels and the secondary coils so alternately same and vice versa interconnect electrically to coil groups, that from the totality of the position signals a unique determination of the control rod position is possible. In this way, in the illustrated embodiment, as the number of secondary coils increases, S'1-S'47 becomes forty secondary coils, as in FIG 1 shown at forty-seven simultaneous causes a reduction in the measuring lines from eight to four.

In the variant shown, likewise generates a primary coil applied with an AC voltage 1 an alternating magnetic field, which induces an alternating voltage at the secondary coils S'1-S'47 as a function of the position of the control rod. As in the wiring diagram of 1 , are primary coil 1 and secondary coils S'1-S'47 are also electrically isolated from each other. The secondary coils S'1-S'47 are also unilaterally electrically connected to a measuring line M0. Also, the already mentioned two provided for the extreme positions of the control rod in the reactor core secondary coils are connected separately with the measuring lines M9 and M10.

Unlike the out 1 known design, the secondary coils S'1-S'47 are switched to new, namely only three coil groups. In addition to the measuring line M0, these coil groups have a total of three further measuring lines M'1-M'3. The secondary coils S'1-S'47 are interconnected in their respective coil group in such a way that in sections both co-directional and reverse interconnections occur immediately after one another.

The consequence is illustrated by way of example with reference to the coils S'1, S'2, S'3, S'5, S'6 and S'7, which belong to a coil group. When driving along the drive rod at these secondary coils of secondary coil S'1 in the direction of the secondary coil S'7 an AC signal is induced at this coil group, which generates the position signal P'1. First, this has a signal level of N0. When passing through secondary coil S'1, the position signal increases almost stepwise to the value N'1. As a result of the interconnection of the secondary coils S'1, S'2 and S'3 in the same direction, the signal level increases again as the control rod travels past the secondary coils S'2 and S'3 and, starting from the signal level N'1, first to the signal level N. '2 and then N'3. Due to the opposite in comparison to the secondary coils S'1-S'3 interconnection of the secondary coil S'5, the induced AC signal decreases on further passing the control rod and passing through the secondary coil S'5, what this is accompanied by a lowering of the characteristic value of the position signal P'1 to a value of the signal level of N'2. When passing the next two secondary coils S'6 and S'7, the generated position signal again reaches the signal levels N'1 and N'0.

The secondary coils S'1-S'47 are interconnected in such a way that in the exemplary embodiment three coil groups are sufficient to use four signal levels N'0-N'3 for two coil groups which are associated with the position signals P'1 and P'2 and three signal levels N'0-N'2 in a coil group associated with the position signal P'3, to determine the current position of the control rod.

Upon generation of the position signals P'1-P'3 from the induced AC voltages by rectification and smoothing, and subsequent comparison with predetermined thresholds, an output signal with fixed levels can be generated or immediately an evaluation and transmission of a defined position of the control rod can be performed. For this purpose it makes sense to also use similar secondary coils S'1-S'47.

Also, the distances of the secondary coils S'1-S'47 have been selected with care. The distances were chosen so that - taking into account the inhomogeneities of the magnetic field - the level changes occur at the same local distance and thus allow a one-to-one inference to the position of the control rod.

In the illustrated embodiment, the signal levels N'0-N'3 in all position signals P'1-P'3 of the same height, so that in a coding the same states for the different position signals P'1-P'3 can be used , However, the signal levels can also be of different heights (in our case this is the case for the constructive reasons). Under these boundary conditions, however, only the comparison levels in the corresponding evaluation module are to be selected accordingly.

When placing an evaluation unit, not shown outside the reactor containment, the primary and secondary coils are shielded 2 As far as possible shielded from interfering signals. Not shown is a possibly existing further shielding, the primary and secondary coils against further signals, which are caused by any further control rods shields.

In summary, at the in 2 shown, the concept of the invention implementing a reduction of the coil groups achieved, whereby fewer passages through the containment (containment) are necessary

Based on 3 It becomes clear that in reality a restriction of the number of signal levels can make sense.

In 3 For example, measurement signals generated in a measuring system with binary position signals are plotted as a function of the control rod position in a diagram. The abscissa shows some instantaneous positions of the control rod Pos1, Pos2, Pos3, Pos4, Pos5, Pos6 and Pos7. The rms values of the AC signals A1-A5 change depending on the control rod position.

A6 indicates a reference value and is not relevant here. A0 indicates the value of the excitation current of the primary coil, which was kept constant over the position range shown here.

In addition to the two outer coils, a total of five further coil groups are present whose effective value of the alternating voltage signals A1-A5 change as a function of the instantaneous position of the control rod. It can clearly be seen that when the instantaneous position of post is increased to Pos7, that is to say a movement of the control rod in the direction of the arrow 3 , increase various signals, but also degrade. However, the desired step-like behavior is only slightly recognizable. As a result, it may be disadvantageous to introduce too many signal levels. If the size differences of the signal levels are too small, the induced AC signals can lead to incorrect position signals and thus undesired erroneous position indications. Therefore, a limitation to including three to five signal levels inclusive is useful for the individual position signals of the coil groups.

LIST OF REFERENCE NUMBERS

0

contraption

1

primary coil

2

shielding

3

arrow

S1-S40

secondary coils

L1, L2

Cable for the primary coil

M0

Test lead for all secondary coils S1-S40

M1, M2

Test lead for the secondary coils S1-S40 of a coil group

M4-M8

Test lead for the secondary coils S1-S40 of a coil group

M9, M10

Test lead for the beginning and end secondary coils

P1, P2

Position signals of a coil group

P4-P8

Position signals of a coil group

N0, N1

Signal level of the position signals

S'1-S'47

secondary coils

M'1-M'3

Test leads for the secondary coils S'1-S'47 of a coil group

P'1-P'3

Position signals of a coil group

N'0-N'3

Signal levels of the position signals Pos1-Pos7

Pos1-POS7

Momentary adjustment of the control rod

A0

Signal of the exciting current of the primary coil

A1-A5

RMS value of the AC signals

A6

reference value

Claims (11)

Contraption ( 0 ) for measuring the position of a displaceable control rod with a plurality of successively arranged along a displacement path, inductively by at least one primary coil ( 1 ) excited secondary coils (S'1-S'47), wherein in each case one or more secondary coils (S'1-S'47) are combined to form at least two coil groups such that a position signal (P'1-) generated with the aid of the respective coil group P'3) increases or decreases in steps as the control rod is pushed past the secondary coils (S'1-S'47), the arrangement and interconnection of the secondary coils (S'1-S'47) being selected in such a way that the totality of the position signals (P'1-P'3) of all coil groups a unique determination of the current position of the control rod is possible, and at least one of the coil groups at least two secondary coils (S'1-S'47), which are so interconnected in that the associated position signal (P'1-P'3) assumes at least three discrete signal levels (N'0-N'3) as the control rod advances. Contraption ( 0 ) according to claim 1, wherein the displaceable control rod is arranged in a nuclear reactor. Contraption ( 0 ) according to claim 1 or 2, wherein a plurality of coil groups are provided with at least three discrete signal levels (N'0-N'3). Contraption ( 0 ) according to one of claims 1 to 3, wherein between including three and including five signal levels (N'0-N'3) are provided Contraption ( 0 ) according to one of claims 1 to 4, wherein the position signal (P'1-P'3) is generated by an AC electric signal. Contraption ( 0 ) according to any one of claims 1 to 5, wherein discrete signal levels (N'0-N'3) are provided for the position signals (P'1-P'3) of all coil groups Contraption ( 0 ) according to one of claims 1 to 6, wherein three coil groups are provided. Contraption ( 0 ) according to one of claims 1 to 7, wherein the distance of the individual secondary coils (S'1-S'47) to each other is substantially always the same. Nuclear reactor with a device ( 0 ) according to one of claims 2 to 8, wherein the secondary coils (S'1-S'47) are connected via signal lines (M0, M'1-M'3) to an evaluation unit located outside the reactor safety container for control rod position determination. Method for measuring the position of a displaceable control rod by means of an inductive measuring principle, in which a plurality of secondary coils (S'1-S'47) arranged behind one another along a displacement path are separated by at least one primary coil ( 1 ) are inductively energized, wherein in each case one or more secondary coils (S'1-S'47) are combined to form at least two coil groups such that a position signal (P'1-P'3) generated with the aid of the respective coil group increases stepwise or is lowered when the control rod is pushed past the secondary coils (S'1-S'47), wherein the arrangement and interconnection of the secondary coils (S'1-S'47) is selected such that on the basis of the totality of the position signals (P'1 -P'3) of all coil groups a unique determination of the current position of the control rod is possible, and at least one of the coil groups at least two secondary coils (S'1-S'47), which are interconnected such that the associated position signal (P '. 1-P'3) assumes at least three discrete signal levels (N'0-N'3) as the control rod advances. The method of claim 10, wherein the control rod is disposed in a nuclear reactor.

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