Patent Description:
Inside nuclear reactors, local power is measured inside the nuclear reactor core with in-core detectors designed to operate and survive in the environment. The in-core detectors include self-powered neutron detectors (SPNDs) or self-powered detectors (SPDs). A short section of detector material, lead-wire and crushable ceramic insulators are assembled inside a long thin metal housing. The metal housing is formed of Inconel or stainless steel tubes and is called a sheath. The sheath outer diameter is reduced multiple times crushing the ceramic insulators around the detector material and lead-wire to insulate it from the sheath producing a continuous length SPND or SPD. The detector material within the sheath is aligned within a specific location of the core when inserted. The lead-wire is connected to the bottom of the short section of detector material and extends along the full length of the sheath to carry the electrical signal from the detector material to a connector so it can be transmitted for plant use.

The detector material within the sheath is aligned within a specific location of the core when inserted. The alignment of the detectors is maintained with a cylindrical oversheath of similar materials and crushed around the individual detectors in a similar manner as the sheath for all of the individual detectors. The lead-wire may be connected to an end of the short section of detector material and extending the full length of the sheath to carry the electrical signal from the detector material to a connector so the electrical signal can be transmitted for plant use. There is also a background signal running parallel to the lead-wire in a background detector, which may be inside the same sheath in a twin lead detector or outside of the sheath as a separate detector.

A self-powered in-core detector arrangement is known from document <CIT>.

When higher than average output signals are needed, a few different techniques are employed conventionally. A first conventional technique for designing in-core detectors involves using a specific detector material that outputs sufficiently high signals for the given application. A second conventional technique is to design the in-core detectors to be sized large enough to provide sufficiently high signal outputs for the given application. A third conventional technique involves using multiple very long elements of different lengths that cover large parts of the reactor core, then subtracting the signals of the elements and using the difference as the measurement for the one location only covered by one of the elements. A fourth conventional technique is to coil the detector, instead of using a straight detector, to generate a stronger signal than a the straight detector can generate.

A detector assembly for measuring flux in a nuclear reactor core includes a plurality of self-powered in-core detector arrangements each for measuring flux at a different one of a plurality of axial locations in the nuclear reactor core, and an assembly connector configured to be connected to a power plant connector. The assembly connector includes a plurality flux signal terminals each connected to one of self-powered in-core detector arrangements. At least one of the self-powered in-core detector arrangements comprises a set of at least two self-powered in-core detectors for measuring flux at a same one of the axial locations in the nuclear reactor core. Each of the at least two self-powered in-core detectors includes a sheath, a detector material section inside the sheath, an insulator between the sheath and the detector material, and a flux signal output line. The flux signal output lines of the at least two self-powered in-core detectors are joined together to provide a combined flux signal.

A method of providing a detector assembly for measuring flux in a nuclear reactor core comprising is also provided. The method includes arranging a plurality of self-powered in-core detector arrangements in the nuclear reactor core each for measuring flux at a different one of a plurality of axial locations in the nuclear reactor core, and connecting an assembly connector to the self-powered in-core detector arrangements. The assembly connector includes a plurality flux signal terminals each connected to one of self-powered in-core detector arrangements. The assembly connector is configured to be connected to a power plant connector. At least one of the self-powered in-core detector arrangements includes a set of at least two self-powered in-core detectors for measuring flux at a same one of the axial locations in the nuclear reactor core. Each of the at least two self-powered in-core detectors includes a sheath, a detector material section inside the sheath, an insulator between the sheath and the detector material, and a flux signal output line. The flux signal output lines of the at least two self-powered in-core detectors are joined together to provide a combined flux signal.

A method of replacing a first detector assembly for measuring flux in a nuclear reactor core with a second detector assembly for measuring flux in a nuclear reactor core is provided. The method includes uninstalling the first detector assembly from the nuclear reactor core. The first detector assembly includes a plurality of first self-powered in-core detector arrangements each for measuring flux at a different one of a plurality of axial locations in the nuclear reactor core, and a first assembly connector configured to be connected to a power plant connector. The first assembly connector includes a plurality of first flux signal terminals each connected to one of first self-powered in-core detector arrangements. At least one of the first self-powered in-core detector arrangements includes a set of at least two first self-powered in-core detectors for measuring flux at a same one of the axial locations in the nuclear reactor core. Each of the at least two first self-powered in-core detectors includes a sheath, a detector material section inside the sheath, an insulator between the sheath and the detector material, and a flux signal output line. The flux signal output lines of the at least two first self-powered in-core detectors being joined together. The uninstalling of the first detector assembly from the nuclear reactor core includes disconnecting the first assembly connector from a power plant electrical connector.

The replacing method also includes installing the second detector assembly in the nuclear reactor core in place of the first detector assembly. The second detector assembly includes a plurality of second self-powered in-core detector arrangements each for measuring flux at a different one of a plurality of axial locations in the nuclear reactor core, and a second assembly connector configured to be connected to a power plant connector. The second assembly connector includes a plurality second flux signal terminals each connected to one of second self-powered in-core detector arrangements.

At least one of the second self-powered in-core detector arrangements includes a set of at least two second self-powered in-core detectors for measuring flux at a same one of the axial locations in the nuclear reactor core. Each of the at least two second self-powered in-core detectors includes a sheath, a detector material section inside the sheath, an insulator between the sheath and the detector material, and a flux signal output line. The flux signal output lines of the at least two second self-powered in-core detectors are joined together to provide a combined flux signal.

The installing of the second detector assembly in the nuclear reactor core includes connecting the second assembly connector to the power plant electrical connector.

The present invention is described below by reference to the following drawings, in which:.

One problem with conventional techniques is that when different detector materials are placed in a specific axial location to be representative of that axial measurement in the core, the different materials will provide higher or lower amount of electrical current output based on each materials radiation induced interactions in the given radiation field. Some of these materials do not always output what is considered a high enough signal for a given application and given detector design. The detector design component dimensions are highly engineered and changing them to increase detector output for a given application is not always possible for a multitude of reasons, for example, limited space in the detector assembly, or cost to re-engineer and analyze detector component designs.

In other words, re-engineering a given detector for every situation just because the signal is not as high as needed or expected can be very costly and is prohibitive in most situations. Most detector materials that provide higher output also have dramatic downsides because for a self-powered detector to provide a higher output there is typically much higher depletion of the material, resulting in the detector becoming a consumable having a very short useful life. Decades of analysis and measurements went into the materials, for example rhodium, platinum and vanadium, used today to get the balance of a high enough output and useful lifetimes. The use of the multiple long pieces that cover large parts of the core are difficult to build, will integrate other undesirable signals into the signals, and have larger uncertainty issues with taking two large signals and subtracting them to make one smaller signal. The coiled design costs more to build and is more difficult to model and analyze, while building an assembly of coils takes up more space, making it too large to fit in some limited spaces.

The present disclosure provides methods for building assemblies that each have multiple detector components in each axial space, with lead wires being tied together and their respective background wires being tied together to create one electrically combined detector with multiples of the single detector signal output for the same axial core location. Such methods are simpler to manufacture when compared to a coiled or multiple long element design. The modeling and analysis is also simplified since you just model normal size and length straight already engineered detector designs. Additionally, the measurement and connector design are simplified as compared to conventional techniques because multiple detectors electrically combined in the assembly will have the same connector with the same number of pins as a single detector per axial space. The uncertainty is expected to decrease by increasing the amount of radiation interaction in the same assembly space, thus increasing the useful signal without needing to do any external subtraction. The assemblies may include as many detectors as fit in the allowed space to increase the output as much as is needed.

<FIG> schematically shows a nuclear reactor pressure vessel <NUM> including a self-powered in-core detector assembly <NUM> provided in a reactor core <NUM> of pressure vessel <NUM> to measure local power in reactor core <NUM>. Pressure vessel <NUM> is centered on a vertically extending center axis CA. Unless otherwise mentioned, the terms axial, radial and circumferential and derivatives thereof are used in reference to center axis CA, with radial direction R and axial direction A being shown in <FIG>. Detector assembly <NUM> includes a plurality of self-powered in-core detector arrangements each comprising a detector set <NUM>, <NUM>, <NUM>, <NUM>. In the embodiment, each of detector sets <NUM>, <NUM>, <NUM>, <NUM> includes two detectors in the form of SPNDs or SPDs, with detector set <NUM> including detectors 16a, 16b, detector set <NUM> including detectors 17a, 17b, detector set <NUM> including detectors 18a, 18b and detector set <NUM> including detectors 19a, 19b. Each detector 16a, 16b, 17a, 17b, 18a, 18b, 19a, 19b includes a first section <NUM> including detector material and a second section <NUM> extending axially from first section <NUM> including at least one lead wire. First section <NUM> has a larger outer diameter than section <NUM> and is a radially thickest portion of the respective detector <NUM>. Second section <NUM> is vertically below first section <NUM> in reactor core <NUM>. Although each detector set <NUM> to <NUM> in the embodiment shown in <FIG> includes only two detectors per set, in other embodiments, each set may include three or more detectors, with the number of detectors per set being based on spaced considerations in the core and how high a signal is needed. In other embodiments, detector assembly <NUM> may be loaded through the reactor head.

As shown in <FIG>, detector sets <NUM> to <NUM> are arranged and configured such that first sections <NUM> of each of the detectors of a respective detector set <NUM> to <NUM> are at a same axial location in core <NUM> and first sections <NUM> of the detectors of each detector set <NUM> to <NUM> are axially offset from the first sections <NUM> of the detectors of the other detector sets <NUM> to <NUM>. In other words, detectors 16a, 16b of detector set <NUM> are at a first axial location in core <NUM>, detectors 17a, 17b of detector set <NUM> are at a second axial location in core <NUM> that is axially offset from the first axial location, detectors 18a, 18b of detector set <NUM> are at a third axial location in core <NUM> that is axially offset from the first and second axial locations, and detectors 19a, 19b of detector set <NUM> are at a fourth axial location in core <NUM> that is axially offset from the first, second and third axial locations. The detectors of each detector set <NUM> of <NUM> are of the same configuration - i.e., same size and shape (within the context of manufacturing tolerances) and materials - as the other detector in the set <NUM> to <NUM>, with detectors 16a, 16b being of the same configuration as each other, detectors 17a, 17b being of the same configuration as each other, detectors 18a, 18b being of the same configuration as each other and detectors 19a, 19b being of the same configuration as each other. All of detectors 16a to 19b have a same sized first section <NUM>, and detectors of each detector set <NUM> of <NUM> have a section <NUM> of the same length and materials as the other detector (or detectors when each detector set includes more than two detectors) of the set <NUM> to <NUM>, but different from the sections <NUM> of all of the other sets. More specifically, detectors 16a, 16b have sections <NUM> of a first length, detectors 17a, 17b have sections <NUM> of a second length that is less than the first length, detectors 18a, 18b have sections <NUM> of a third length that is less than the first and second lengths, and detectors 19a, 19b have sections <NUM> of a fourth length that is less than the first, second and third lengths.

Detectors 16a to 19b are held together by an oversheath <NUM> that is crushed onto detectors 16a to 19b to rigidly hold detectors 16a to 19b together. Oversheath <NUM> may be formed of for example stainless steel or Inconel. Oversheath <NUM> and detectors 16a to 19b extend outside of core <NUM> and pressure vessel <NUM> to join an assembly connector <NUM>. The electrical signals output by detectors of a set <NUM> to <NUM> in response to the flux in the reactor core - hereafter referred to as flux signals - are linked together with other detector(s) of the detector set for outputting a combined flux signal from connector <NUM> of assembly <NUM>. Such a configuration allows connector <NUM> to be inserted into an existing connector <NUM> of the power plant. Power plant connector <NUM> then sends the signals through wires to a power plant computer <NUM> configured for determining the local power in reactor core <NUM> based on the signals from detectors 16a to 19b for display on a graphical user interface and analysis by a user for operating core <NUM>.

Although assembly <NUM> is schematically shown as taking up a large portion of core <NUM>, it should be understood that a typical oversheathed cylindrical assembly <NUM> with up to seven detectors and one thermocouple may for example have an outer diameter < <NUM>, and each sheathed detector 16a to 19b may have a typical outer diameter <<NUM> and the tapered section around half of the detector.

<FIG> shows a cross-sectional view of a detector set <NUM> including detectors 16a, 16b. Detectors of sets <NUM> to <NUM> are configured in the same manner as detectors 16a, 16b, but with sections <NUM> of different lengths that sections <NUM> of detectors 16a, 16b. Detectors 16a, 16b each include a contiguous section of a flux detecting material <NUM> and a lead wire <NUM> extending from a first axial end 30a of detector material section <NUM>. A first axial end 32a of lead wire <NUM> is embedded in first axial end 30a of detector material section <NUM>. Detectors 16a, 16b each also include a background wire <NUM> extending parallel to lead wire <NUM>. A first axial end of background wire <NUM> is spaced axially from detector material section <NUM> such that background wire <NUM> is not directly electrically connected to detector material section <NUM>. Detector material section <NUM> and portions of lead wire <NUM> and background wire <NUM> inside of reactor core <NUM> are embedded in an insulator <NUM> and directly surrounded by insulator <NUM> in the radial direction. A first axial end 33a of background wire <NUM> is axially spaced away from first axial end 30a of detector material section <NUM> by insulator <NUM>. Insulator <NUM> is directly surrounded by a sheath <NUM> in the radial direction and in the axial direction at the second axial end 30b of detector material section <NUM>.

Detector material section <NUM> is a conducting or semiconducting material that emits electrons as a result of neutron and gamma irradiation, and may be formed example rhodium, platinum, vanadium, aluminum, silver, cadmium, gadolinium, cobalt, hafnium or scandium. Detector material section <NUM> is shaped as a cylindrical rod. Insulator <NUM> is electrically insulating and may be formed of ceramic material, for example crushed ceramic material. Wires <NUM>, <NUM> are formed of electrically conductive material, with each lead wire <NUM> conveying the flux signal emitted by the respective detector material section <NUM> and each background wire <NUM> conveying a respective background signal. Sheath <NUM> forms a collector and may be formed of for example stainless steel or Inconel. In response to neutron flux in the reactor core, detector material section <NUM> emits electrons that flow through insulator <NUM> to sheath <NUM>, causing lead wire <NUM> to transmit current that forms a flux signal indicating the flux in the axial location of the reactor core.

Detector material section <NUM> is provided solely in first section <NUM> and a majority of lead wire <NUM> is provided in second section <NUM>. Insulator <NUM> and sheath <NUM> extend through all of sections <NUM>, <NUM>, with sheath <NUM> defining outer circumferential surfaces of sections <NUM>, <NUM>. Accordingly, an outer circumferential surface of sheath <NUM> has larger outer diameter at first section <NUM>, than at second section <NUM>. More specifically, sheath <NUM> includes a first sheath section 36a that is cylindrical and defines the outer circumferential surface of first section <NUM>, a second sheath section 36b that is cylindrical and defines the outer circumferential surface of second section <NUM>. Sheath <NUM> also includes a tapered section 36c extending radially outward while extending axially from second section 36b to first section 36a. Sheath <NUM> further includes an end section 36d axially abutting the portion of insulator <NUM> that contacts second end 30b of detector material section <NUM>. End section 36d defines a closed end of sheath <NUM>. An axial end of second section 36b that is axially furthest from detector material section <NUM> defines an open end of sheath <NUM>. Wires <NUM>, <NUM> of detector 16a extend out through the open end of sheath <NUM> for linking to the wires <NUM>, <NUM>, respectively, of detector 16b, as explained further below with respect to <FIG>.

In other embodiments, as disclosed in <CIT>, the detectors 16a to 19b may include tail sections having tails wires, the detectors 16a to 19b may lack background wires, or the detectors may include tail sections that lack tail wires and include fillers sections such that all of detectors 16a to 19b extend the same length.

<FIG> schematically shows an enlarged view of detector assembly <NUM> shown in <FIG>. As noted with respect to <FIG>, in this exemplary embodiment, detector assembly <NUM> includes four sets <NUM> to <NUM> of detectors, with each set <NUM> to <NUM> including two detectors. It should be understood that other embodiments include different numbers of sets and more than two detectors per set. As discussed with respect to <FIG>, detector sets <NUM> to <NUM> are surrounded by oversheath <NUM>, with the inner circumferential surface of oversheath <NUM> being in contact with outer circumferential surfaces of some or all of detectors 16a to 19b. Connector <NUM> is fixed to an axial end of oversheath <NUM>. The detector material section <NUM> of each of detectors 16a to 19b is a same material and a same size and shape (as understood within the context of manufacturing tolerances).

Outside of sheaths <NUM>, flux signal output lines of the detectors of each set <NUM> to <NUM> are joined together with the flux signal output lines of the other detector (or detectors, where each set includes two or more detectors) in the set to provide a combined flux signal for identifying the flux of the nuclear reactor core at the axial location of the detector material <NUM> of the detector set <NUM> to <NUM>. For example, flux signal output lines 39a, 39b of detectors 16a, 16b, respectively, are joined together to provide a combined flux signal for identifying the flux of the nuclear reactor core at the axial location of the detector material <NUM> of detectors 16a, 16b.

Also, outside of sheaths <NUM>, background signal output lines of the background wire <NUM> of each set <NUM> to <NUM> are joined together with the output lines of the other detector (or detectors, where each set includes two or more detectors) in the set to provide one combined background signal for the respective detector set <NUM> to <NUM>. For example, background signal output lines 41a, 41b of detectors 16a, 16b, respectively, are joined together to provide one combined background signal for background wires <NUM> of detectors 16a, 16b.

More specifically, in the embodiment shown in <FIG>, the second axial end 32b of each lead wire <NUM> forms output line 39a and is joined with the second axial end 32b of the other lead wire <NUM>, which forms output line 39b, in the respective detector set <NUM> to <NUM>, and the second axial end 33b of each background wire <NUM> forms output line 41a and is joined with the second axial end 33b of the other background wire <NUM>, which forms output line 41b, in the respective detector set <NUM> to <NUM>. For example, the second axial end 32b of lead wire <NUM> of detector 16a is joined with the second axial end 32b of lead wire <NUM> in the detector 16b at a junction 40a, and the second axial end 33b of background wire <NUM> of detector 16a is joined with the second axial end 33b of the background wire <NUM> of detector 16b at a junction 40b. Accordingly, the flux signal from lead wires <NUM> are added together at junction 40a to generate a combined flux signal greater than detector material section <NUM> of detectors 16a, 16b generate individually and the background signal from background wires <NUM> are added together at junction 40b to generate a combined background signal greater than background wires <NUM> of detectors 16a, 16b generate individually. A lead wire section 42a downstream of junction 40a transmits the combined flux signal to a first flux signal terminal in the form of a first flux signal pin 44a of connector <NUM> and a lead wire section 42b downstream of junction 40b transmits the combined background signal to a first background signal terminal in the form of a first background signal pin 44b of connector <NUM>.

In other words, detector assembly <NUM> thus includes a plurality of self-powered in-core detector arrangements each for measuring flux at a different one of a plurality of axial locations in the nuclear reactor core <NUM> and assembly connector <NUM> configured to be connected to power plant connector <NUM>. Assembly connector <NUM> includes a plurality flux signal terminals 44a each connected to one of self-powered in-core detector arrangements. At least one of the self-powered in-core detector arrangements a set <NUM> to <NUM> of at least two self-powered in-core detectors 16a to 19b for measuring flux at a same one of the axial locations in the nuclear reactor core <NUM>. Each of the at least two self-powered in-core detectors 16a to 19b includes a sheath <NUM>, a detector material section <NUM> inside the sheath <NUM>, an insulator <NUM> between the sheath <NUM> and the detector material <NUM>, and a flux signal output line 39a or 39b. The flux signal output lines 39a or 39b of the at least two self-powered in-core detectors 16a to 19b are joined together.

In the embodiment shown in <FIG>, the connector <NUM> includes four flux signal pins 44a for eight detector material sections <NUM> and four background signal pins 44b for eight background wires <NUM>. In other words, there is one flux signal pin 44a for each detector set <NUM> to <NUM>, and one background signal pin 44b for each detector set <NUM> to <NUM>. For the embodiment shown in <FIG>, connector <NUM> (<FIG>) includes four flux signal terminals in the form of flux signal receptacles, each for receiving one of pins 44a, and four background signal terminals in the form of background signal receptacles, each for receiving one of pins 44b. Thus, connector <NUM> includes two pins for each detector set and connector <NUM> includes two pin receptacles for mating with the pins for each detector set in the assembly.

<FIG> schematically shows an axial view illustrating how detectors <NUM> to <NUM> may be arranged inside of oversheath <NUM> at A-A in <FIG> in accordance with an embodiment of the present invention. <FIG> schematically shows an axial view illustrating how pins 44a, 44b may be arranged inside of connector <NUM> at B-B in <FIG> in accordance with an embodiment of the present invention.

As shown in <FIG>, oversheath <NUM> may be cylindrical at least in parts and detectors 16a to 19b may be provided in a circular arrangement when viewed axially and the inner circumferential surface of oversheath <NUM> contacts the outer circumferential surfaces of each of sheaths <NUM> of detectors 16a to 19b. A thermocouple <NUM>, which includes two conducting wires 46a, 46b, may also be arranged inside of oversheath <NUM> to measure the temperature within the reactor core.

As shown in <FIG>, connector <NUM> may include four flux signal terminals in the form of pins 44a - one for each detector set <NUM> to <NUM>, four background signal terminals in the form of pins 44b - one background signal pin 44b for each detector set, two thermocouple terminals in the form of thermocouple pins 46c, 46d and one collector signal terminal in form of a collector signal pin 36e, for a total of eleven pins. Electrical lines from all of sheaths <NUM> of detectors 16a to 19b electrically connect sheaths <NUM> to collector signal pin 36e. Such a configuration minimizes the number of pins of the electrical connector for detector assembly <NUM>. For example, if a pin was provided for each of lead wires <NUM> and background wires <NUM> in the present example, the electrical connector would include nineteen pins, which is considerably greater than the electrical connector of the present example. If the number of detectors per each of the four detector sets increased from two to three, the difference in pins would be even greater than with an electrical connector including a pin for each detector, as the electrical connector according to an embodiment of the present invention would still include eleven pins, while an electrical connector including a pin for each detector would include twenty-seven pins. Cabling carrying the signals and the amount of electronics needed to measure all of these signals is much reduced, reducing cost and space outside of the reactor.

The merging of detectors from each detector set allows the same connector <NUM> to be used with different detector assemblies in accordance with embodiments of the present invention. For example, if a first detector assembly configured in the same manner as assembly <NUM>, which is comprised of first detectors 16a to 19b including a first detector material, such as rhodium, has reached the end of its useful life and needs to be replaced, but only detectors including a second detector material, such as vanadium, different from the first detector material are available, second detector sets including a different number of second detectors per set could be used to obtain an acceptably high electrical signal, without changing the number of output terminals on the electrical connector of the second detector assembly in comparison with the first detector assembly. For example, if the each of the first detector sets include only two detectors, but second detector sets each require three detectors because the electrical signals emitted by the second detector material is lower than the electrical signals emitted by the first detector material to obtain an acceptably high signal strength, then the electrical connector <NUM> for the first and second detector assemblies can still be the same and have the same number of pins because the lead wires of detectors of each set are linked to each other and transmitted to a single pin. Accordingly, the electrical connector for each of the first and second detector assemblies is compatible with the power plant electrical connector <NUM>.

In view of this, the present disclosure also provides a method of replacing a first detector assembly for measuring flux in a nuclear reactor core with a second detector assembly for measuring flux in a nuclear reactor core. The method may include uninstalling the first detector assembly from the nuclear reactor core. The first detector assembly may be formed for example in the same manner as the detector assembly <NUM> discussed with respect to <FIG>, and may include a plurality of first self-powered in-core detector arrangements each for measuring flux at a different one of a plurality of axial locations in the nuclear reactor core <NUM>, and a first assembly connector <NUM> configured to be connected to a power plant connector <NUM>. The first assembly connector <NUM> comprising a plurality of first flux signal terminals 44a each connected to one of the first self-powered in-core detector arrangements. At least one of the first self-powered in-core detector arrangements comprising a respective set <NUM> to <NUM> of at least two first self-powered in-core detectors 16a to 19b for measuring flux at a same one of the axial locations in the nuclear reactor core - e.g., a set <NUM> of first in-core detectors 16a, 16b, a set <NUM> of first in-core detectors 17a, 17b, a set <NUM> of first in-core detectors 18a, 18b and/or a set <NUM> of first in-core detectors 19a, 19b. Each of the at least two first self-powered in-core detectors 16a to 19b includes a sheath <NUM>, a detector material section <NUM> inside the sheath <NUM>, an insulator <NUM> between the sheath <NUM> and the detector material <NUM>, and a flux signal output line 39a or 39b. The flux signal output lines 39a or 39b of the at least two first self-powered in-core detectors are joined together. The uninstalling of the first detector assembly <NUM> from the nuclear reactor core <NUM> includes disconnecting the first assembly connector <NUM> from power plant electrical connector <NUM>.

The replacing method may also include installing the second detector assembly in the nuclear reactor core in place of the first detector assembly. The second detector assembly may be configured in a similar manner to detector assembly shown in <FIG> and may include a plurality of second self-powered in-core detector arrangements each for measuring flux at a different one of a plurality of axial locations in the nuclear reactor core <NUM>, and a second assembly connector configured to be connected to a power plant connector <NUM>. The second assembly connector comprising a plurality flux signal terminals 44a each connected to one of second self-powered in-core detector arrangements. At least one of the self-powered in-core detector arrangements comprising a respective set of at least two second self-powered in-core detectors for measuring flux at a same one of the axial locations in the nuclear reactor core. Each of the at least two second self-powered in-core detectors includes a sheath <NUM>, a detector material section <NUM> inside the sheath <NUM>, an insulator <NUM> between the sheath <NUM> and the detector material <NUM>, and a flux signal output line 39a or 39b. The flux signal output lines 39a or 39b of the at least two second self-powered in-core detectors are joined together to provide a combined flux signal. The installing of the second detector assembly from the nuclear reactor core <NUM> includes connecting the second assembly connector to power plant electrical connector <NUM>.

In the replacing method, the detector material sections of the first self-powered in-core detectors may be formed of a first material, such as for example rhodium, and the detector material sections of the second self-powered in-core detectors are formed of a second material, such as for example vanadium, different from the first material. It should be noted that any of the material mentioned above for the detector material section <NUM> may be used. The set(s) of the first self-powered in-core detectors each have a first number of detectors and the set(s) of the second self-powered in-core detectors each have a second number of detectors different from the first number. For example, the first set(s) may include two detectors each and the second set(s) may include three detectors each; or the first set(s) may include four detectors each and the second set(s) may include two detector each. The first assembly connector and the second assembly connector may have a same number of terminals, for example, both sets could include <NUM> terminals as discussed with respect to <FIG>.

In another replacing method, a conventional detector assembly having a single detector per axial level may be replaced with a new detector assembly having at least a detector arrangement with a set of at least two individual detectors coupled for the same axial level. This will allow the replacement of the conventional detector assembly with a single detector with one material such as rhodium by a new detector assembly having a coupled pair of detector of another material (platinum or vanadium) without changing the power plant electrical connector <NUM> because the coupled pair of detectors in the replacement assembly are connected to one pin of connector <NUM>, and without changing the electronic range of the computer input and conversion signal because the signal delivered by the rhodium detector is in the same order than the signal delivered by the coupled pair of detectors.

Claim 1:
A detector assembly (<NUM>) for measuring flux in a nuclear reactor core (<NUM>) comprising
a plurality of self-powered in-core detector arrangements (<NUM>, <NUM>, <NUM>, <NUM>) each for measuring flux at a different one of a plurality of axial locations in the nuclear reactor core; and
an assembly connector (<NUM>) configured to be connected to a power plant connector (<NUM>), the assembly connector comprising a plurality flux signal terminals (44a) each connected to one of self-powered in-core detector arrangements,
at least one of the self-powered in-core detector arrangements comprising a set of at least two self-powered in-core detectors (16a, 16b) for measuring flux at a same one of the axial locations in the nuclear reactor core,
each of the at least two self-powered in-core detectors including a sheath (<NUM>), a detector material section (<NUM>) inside the sheath, an insulator (<NUM>) between the sheath and the detector material, and a flux signal output line (39a, 39b),
characterized in that the flux signal output lines of the at least two self-powered in-core detectors are joined together to provide a combined flux signal.