Patent Description:
The disclosed and claimed concept relates generally to nuclear power equipment and, more particularly, to a detection apparatus usable with a fuel rod and an instrumentation tube of a fuel assembly of a nuclear reactor.

In many state-of-the-art nuclear reactor systems, in-core sensors are employed for directly measuring the radioactivity within the core at a number of axial elevations. Thermocouple sensors are also located at various points around the core at an elevation where the coolant exits the core to provide a direct measure of coolant outlet temperature at various radial locations. These sensors are used to directly measure the radial and axial distribution of power inside the reactor core. This power distribution measurement information is used to determine whether the reactor is operating within nuclear power distribution limits. The typical in-core sensor used to perform this function is a self-powered detector that produces an electric current that is proportional to the amount of fission occurring around it. This type of sensor is generally disposed within an instrument thimble within various fuel assemblies around the core, does not require an outside source of electrical power to produce the current, is commonly referred to as a self-powered detector, and is more fully described in <CIT>, and assigned to the Assignee of this invention.

Another type of sensor capable of measuring various parameters of the core, and which is typically disposed within the instrument thimbles in various fuel assemblies around the core, is described in <CIT>. This type of sensor employs a transmitter device that includes a self-powered neutron detector structured to detect neutron flux, a capacitor electrically connected in parallel with the neutron detector, a gas discharge tube having an input end and an output end, and an antenna electrically connected to the output end in series with a resonant circuit. The input end of the gas discharge tube is electrically connected to the capacitor. The antenna is structured to emit a signal comprising a series of pulses representative of the intensity of the neutron flux monitored by the self-powered detector. Other core parameters can also be monitored by their effects on altering the values of the inductance and capacitance of the resonant circuit.

Still another in-core sensor, one which does not require signal leads to communicate its output out of the reactor, is disclosed in <CIT>, which describes an anomaly diagnosis system for a nuclear reactor core having an anomaly detecting unit incorporated into a fuel assembly of the nuclear reactor core, and a transmitter-receiver provided outside the reactor vessel. The transmitter-receiver transmits a signal wirelessly to the anomaly detecting unit and receives an echo signal generated by the anomaly detecting unit wirelessly. When the anomaly detecting unit detects an anomaly in the nuclear reactor core, such as an anomalous temperature rise in the fuel assembly, the mode of the echo signal deviates from a reference signal. Then the transmitter-receiver detects the deviation of the echo signal from the reference signal and gives an anomaly detection signal to a plant protection system. The sensor actually monitors coolant temperature around the fuel assembly in which it is mounted.

<CIT> discloses a pressure sensitive transducer comprising: means defining a small gas-filled cavity of length less than its transverse dimensions, a diaphragm in said cavity, means for supporting said diaphragm transverse to the cavity and party-way along the length of the cavity, means defining a passageway for gas from one side of the diaphragm to the other, and means for oscillating the diaphragm over a range of frequencies including its resonant frequency.

<CIT> discloses an anomaly diagnosis system for a nuclear reactor, comprising ultrasonic wave reflecting members provided on the fuel assemblies and including a shape memory alloy, and an ultrasonic wave emitter-receiver. The ultrasonic wave emitter-receiver is located exterior of the reactor vessel, and includes means for providing an anomaly detection signal to the plant protection system when the ultrasonic wave reflected by any one of the ultrasonic wave reflecting members is not received by the ultrasonic wave emitter-receiver.

While each of the foregoing sensors directly monitors conditions within the core of a nuclear reactor, such sensor have not been without limitation. Improvements thus would be desirable.

None of the aforementioned sensors directly monitors conditions within a nuclear fuel rod in the core during reactor operation. Before advanced fuel cladding materials can be put into commercial use they have to be rigorously tested to receive regulatory approval. The existing methodology for testing advanced fuel cladding materials requires fuel rods to be tested over several fuel cycles and examined at the end of the irradiation test. This is a lengthy process that takes several years during which time fuel cladding data is not available. In the existing method, critical data is only obtained during the post irradiation examination activities. What is desired is an in-pile sensor that can be placed within a fuel rod, endure the hazardous conditions over several fuel cycles, and does not require penetrations into the cladding of the fuel rod.

Accordingly, an aspect of the disclosed and claimed concept is to provide an improved detection apparatus as claimed in claim <NUM>.

Various embodiments of the detection apparatus are claimed in claims <NUM> to <NUM>.

Another aspect of the disclosed and claimed concept is to provide an improved method of detecting a condition of a fuel rod as claimed in claim <NUM>.

Various embodiments of the method of detecting are claimed in claims <NUM> and <NUM>.

A further understanding of the invention can be gained from the following Description when read in conjunction with the accompanying drawings in which:.

Similar numerals refer to similar parts throughout the specification.

An improved detection apparatus <NUM> in accordance with the disclosed and claimed concept is depicted generally in <FIG>. The detection apparatus <NUM> is usable with a fuel rod <NUM> and an instrument thimble <NUM>, such as are included in a fuel assembly <NUM> (<FIG>) of a nuclear reactor that is depicted schematically in <FIG> at the numeral <NUM>, which signifies a containment of the nuclear reactor <NUM>.

The detection apparatus <NUM> is situated within the containment of the nuclear reactor <NUM>, and the detection apparatus <NUM> is cooperable with an electronic processing apparatus <NUM> that is situated external to the containment of the nuclear reactor <NUM>. The detection apparatus <NUM> is thus intended to be situated within the harsh environment situated within the interior of the containment of the nuclear reactor <NUM> whereas the electronic processing apparatus <NUM> is situated in a mild environment external to the containment of the nuclear reactor <NUM>.

As can be understood from <FIG>, the electronic processing apparatus <NUM> can be seen as including a transceiver <NUM> and a signal processor <NUM>. The transceiver <NUM> is connected with a wired connection with an interrogation apparatus <NUM> that is situated in the instrument thimble <NUM>. The signal processor <NUM> includes a processor and storage <NUM>, with the storage <NUM> having stored therein a number of routines <NUM>, and the storage <NUM> further having stored therein a number of data tables <NUM>. The routines <NUM> are executable on the processor to cause the detection apparatus <NUM> to perform various operations, including receiving signals from the transceiver <NUM> and accessing the data tables <NUM> in order to retrieve values that correspond with aspect of the signals from the transceiver <NUM> that are representative of conditions inside the fuel rod <NUM>.

As can further be understood from <FIG>, the fuel rod <NUM> can be said to include a cladding <NUM> and to have an interior region <NUM> situated within the cladding <NUM> and a number of fuel pellets <NUM> situated within the interior region <NUM>. As employed herein, the expression "a number of" and variations thereof shall refer broadly to any non-zero quantity, including a quantity of one. The fuel rod has a plenum <NUM> in generally a vertically upper end of the fuel rod <NUM>.

The detection apparatus <NUM> can be said to include an electrical circuit apparatus <NUM> that is supported within the plenum <NUM> of the fuel rod <NUM> within the interior region <NUM> thereof. The detection apparatus <NUM> further includes the interrogation apparatus <NUM>, which can be said to be situated within an interior of the instrument thimble <NUM>. As is schematically depicted in <FIG>, the electrical circuit apparatus <NUM> is situated within the interior region <NUM> and communicates with the interrogation apparatus <NUM> without any breaches or other openings being formed in the cladding <NUM>, thereby advantageously keeping the cladding <NUM> intact and advantageously keeping the fuel pellets <NUM> fully contained within the interior region <NUM>.

As can be further understood from <FIG>, and as will be set forth in greater detail below, the electrical circuit apparatus <NUM> and the interrogation apparatus <NUM> communicate wirelessly with one another. Conditions within the interior region <NUM> of the fuel rod <NUM> can be said to include a temperature of the fuel pellets <NUM>, an extent of physical elongation of the fuel pellets <NUM>, and the ambient pressure within the interior of the fuel rod <NUM>, by way of example. These three conditions are directly detectable by the electrical circuit apparatus <NUM> and are communicated through the interrogation apparatus <NUM> to the electronic processing apparatus <NUM>. As will likewise be set forth in greater detail below, various embodiments are disclosed wherein the temperature and elongation of the fuel pellets <NUM> are detected in various ways, and wherein the ambient pressure within the interior region <NUM> of the fuel rod <NUM> is detected in various ways. It is understood that these properties are not intended to be limiting, and it is also understood that other properties potentially can be detectable without departing from the spirit of the instant disclosure.

As can be understood from <FIG>, the electrical circuit apparatus <NUM> can be said to include a resonant electrical circuit <NUM> that operates as a sensor and that includes a plurality of circuit components that include a capacitor <NUM> and an inductor <NUM>. The circuit components have values or properties, such as the capacitance of the capacitor <NUM> and the inductance of the inductor <NUM>, by way of example, which are selected to impart to the resonant electrical circuit <NUM> a unique nominal frequency which, when detected by the interrogation apparatus <NUM>, is usable to identify the particular fuel rod <NUM> within which the electrical circuit apparatus <NUM> is situated.

In this regard, it is understood that a plurality of instances of the electrical circuit apparatus <NUM> can be situated in a plurality of corresponding fuel rod <NUM> of the fuel assembly <NUM>. During operation of the detection apparatus <NUM>, the interrogation apparatus <NUM> interrogates the electrical circuit apparatus <NUM> in order to receive a signal from the electrical circuit apparatus <NUM> that can be interpreted as being indicative of one or more of the properties or conditions within the interior region <NUM> of the fuel rod <NUM>, such as temperature and/or elongation of the fuel pellets <NUM>, ambient pressure within the interior region <NUM> of the fuel rod <NUM>, etc., and by way of example. The fuel assembly <NUM> includes a large number of the fuel rods <NUM>, and a subset of the fuel rods <NUM> of the fuel assembly <NUM> are envisioned to each have a corresponding electrical circuit apparatus <NUM> situated therein. When the interrogation apparatus <NUM> sends out its interrogation signal, the various electrical circuit apparatuses <NUM> will responsively output a signal that is transmitted through the cladding <NUM> or the corresponding fuel rod <NUM> and is received by the interrogation apparatus <NUM>. The various signals from the various electrical circuit apparatuses <NUM> each has a unique nominal frequency that is selected by selecting the various properties of the capacitor <NUM> and the inductor <NUM>, by way of example, of the electrical circuit apparatus <NUM> in order to provide such a signature frequency. The electric processing apparatus <NUM> is thus able to use the frequencies of the various detected signals to determine which signal corresponds with which fuel rod <NUM> of the fuel assembly <NUM>.

As can further be understood from <FIG>, the electrical circuit apparatus <NUM> additionally includes a resonant electrical circuit <NUM> that is usable as a calibration circuit. That is, the resonant electrical circuit <NUM> is usable as a sensor circuit that senses the property or condition within the interior region <NUM> of the fuel rod <NUM>, and the resonant electrical circuit <NUM> is usable as a calibration circuit to compensate the signal from the resonant electrical circuit <NUM> for component degradation, temperature drift, and the like. In this regard, the resonant electrical circuit <NUM> includes a capacitor <NUM> and an inductor <NUM> that are selected to have the same material properties as the capacitor <NUM> and the inductor <NUM> of the resonant electrical circuit <NUM>. However, and as will be set forth in greater detail below, the resonant electrical circuit <NUM> is exposed to the condition that is being measured within the interior region <NUM>, such as the temperature and/or elongation of the fuel pellets <NUM>, and/or the ambient pressure within the interior region <NUM>, by way of example. The resonant electrical circuit <NUM>, being usable as a calibration circuit, is generally not so exposed to the condition being measured. Such calibration is provided by employing a ratiometric analysis such as will be discussed in greater detail elsewhere herein.

As can further be understood from <FIG>, the interrogation apparatus <NUM> can be said to include a transmitter <NUM> and a receiver <NUM>. The transmitter <NUM> is configured to output an excitation pulse <NUM> which is in the form of a magnetic field signal that is capable of being transmitted through the cladding of the instrument thimble <NUM> within which the interrogation apparatus <NUM> is situated and is further capable of being transmitted through the cladding <NUM> of the fuel rod <NUM>. The excitation pulse <NUM> is thus receivable by the inductor <NUM> and the inductor <NUM> of the resonant electrical circuits <NUM> and <NUM>, respectively, to induce a resonant current in the resonant electrical circuits <NUM> and <NUM> in a known fashion. The induced currents in the resonant electrical circuits <NUM> and <NUM> result in the outputting of a response pulse <NUM> from the resonant electrical circuit <NUM> and a response pulse <NUM> from the resonant electrical circuit <NUM>. The responses pulses <NUM> and <NUM> are in the form of magnetic field signals, which are not merely radio frequency signals, and which can be transmitted from the electrical circuit apparatus <NUM> through the cladding <NUM> and through the cladding of the instrument thimble <NUM> and thus be received on the receiver <NUM>.

The excitation pulse <NUM> is of a generally sinusoidal configuration. The response pulses <NUM> and <NUM> are likewise sinusoidal pulses, but they are decaying sinusoidal signals, and it is noted that <FIG> depict a pair of traces that are representative of two different response pulses <NUM>. In this regard, the frequency of the response pulse <NUM> may correlate with one parameters within the fuel rod <NUM>, such as temperature, the peak amplitude of the response pulse <NUM> may correspond with another parameter within the fuel rod <NUM>, such as elongation of the fuel pellets <NUM>, and a decay rate of the response pulse rate <NUM> may correlate with yet another parameter within the fuel rod <NUM>, such as ambient pressure within the interior region <NUM>. As such, the response pulse <NUM> may be correlated with a plurality of parameters or conditions within the interior region <NUM> of the fuel rod <NUM> within which the electrical circuit apparatus <NUM> is situated.

The aforementioned ratiometric analysis of the response pulses <NUM> and <NUM> typically involves taking a ratio of the response pulse <NUM> to the response pulse <NUM> or vice versa, in order to eliminate the effects of component degradation and temperature drift. For instance, the resonant electrical circuits <NUM> and <NUM> may degrade over time thus affecting the signal that is output therefrom. Likewise, the signals that are output from the resonant electrical circuits <NUM> and <NUM> can vary with temperature of the nuclear reactor <NUM>. In order to compensate for these factors, it is assumed that the resonant electrical circuit <NUM> and the resonant electrical circuit <NUM> will degrade at substantially the same rate over time. Furthermore, the resonant electrical circuits <NUM> and <NUM> will be exposed to the same gross, i.e., overall, temperature within the interior of the nuclear reactor <NUM>. By taking the ratio of the response pulses <NUM> and <NUM>, such as the ratio of the frequencies, by way of example, and by using the ratio to look up in the data tables <NUM> a corresponding value for temperature, elongation, and/or pressure, the individual effects of component degradation and temperature drift in the resonant circuit <NUM> are eliminated. This is because the ratiometric signal is independent of component degradation and temperature drift since the resonant electrical circuits <NUM> and <NUM> are assumed to both experience the same component degradation and temperature drift.

As is best shown in <FIG>, the electrical circuit apparatus <NUM> further includes a elongation transmission apparatus <NUM> that is situated within the interior region <NUM> of the fuel rod <NUM>. The elongation transmission apparatus <NUM> includes a support <NUM> that is formed of a ceramic material in the depicted exemplary embodiment and which is abutted against the stack of fuel pellets <NUM>. The support <NUM> has a receptacle <NUM> formed therein, and the elongation transmission apparatus <NUM> further includes an elongated element that is in the form of a ferritic rod <NUM> and that is received in the receptacle <NUM>. The inductor <NUM> includes a coil <NUM> that is situated about and exterior surface of a tube <NUM> that is formed of a ceramic material. The tube <NUM> has an interior <NUM> within which an end of the ferritic rod <NUM> opposite the support <NUM> is receivable.

As the fuel pellets <NUM> increase in temperature, they thermally expand, thus causing the fuel pellets <NUM> to push the support <NUM> and thus the ferritic rod <NUM> in a rightward direction in <FIG>, and thus to be received to a relatively greater extent within the interior <NUM>, which alters the inductance of the inductor <NUM>. Such an alteration of the inductance of the inductor <NUM> adjusts the frequency of the resonant electrical circuit <NUM>, which is detectable when the excitation pulse <NUM> excites an electrical resonance in the resonant electrical circuit <NUM>. The response pulse <NUM> from the resonant electrical circuit <NUM> thus has a frequency that is indicative of the extent of elongation of the fuel pellets <NUM>. The response pulses <NUM> and <NUM> are received by the receiver <NUM>, and the receiver <NUM> responsively sends a number of signals to the electronic processing apparatus <NUM>. The electronic processing apparatus <NUM> uses the ratio of the response pulses <NUM> and <NUM>, or vice versa, to retrieve from the data tables <NUM> an identity of the fuel rod <NUM> within which the electrical circuit apparatus <NUM> is situated, based upon the signature nominal frequency of the response pulses <NUM> and <NUM>, and additionally retrieves from the data tables <NUM> a value that corresponds with the extent of elongation of the fuel pellets <NUM> as exemplified by the response pulse <NUM>. These data can then be sent into a main data monitoring system of the nuclear reactor <NUM>, by way of example, or elsewhere.

In this regard, it is noted that the calibration circuit represented by the resonant electrical circuit <NUM> is not strictly critical for the detection of the properties or conditions such as fuel elongation, center line fuel temperature, and ambient pressure, within the interior of the various fuel rods <NUM>. As such, it is understood that the calibration circuit <NUM> is optional in nature and is usable in order to simplify the data gathering operation and to overcome limitations associated with component degradation and temperature drift, but the calibration circuit <NUM> is not considered to be necessary to the operation of the detection apparatus <NUM>. As such, it is understood the various other types of electrical circuit apparatuses in the various other embodiments that are described elsewhere herein may or may not include a calibration circuit without departing from the spirit of the instant disclosure. In this regard, it is noted that the calibration circuit <NUM> is described only in terms of the electrical circuit apparatus <NUM>, but it is understood that any of the other embodiments of the other electrical circuit apparatuses herein may incorporate such a calibration circuit.

As suggested above, the response pulse <NUM> is a decaying sine wave that has properties such as a peak amplitude, a frequency, and a rate of decay. <FIG> depicts a trace 96A of one such response pulse <NUM>, and <FIG> depicts another trace 96B of another such response pulse <NUM>. It can be understood from <FIG> that the trace of <FIG> has a greater peak amplitude, a higher frequency (as indicated by the shorter period 98A compared with the period 98B in <FIG>), and further has a higher rate of decay than the trace 96B of <FIG>. As such, while any one of temperature, pressure, and elongation can be directly measured from the frequency of either of the traces 96A and 96B, it is understood that a plurality of such parameters can be simultaneously derived from each such trace 96A and 96B depending upon the configuration of the routines <NUM> and the data tables <NUM>, by way of example.

It thus can be said that elongation of the fuel pellets <NUM> can affect the inductance value of the inductor <NUM> by virtue of the relative movement of the ferritic rod <NUM> with respect to the coil <NUM>. This affects the frequency of the response pulse <NUM> that is output by the resonant electrical circuit <NUM>, and which is therefore detectable by the electronic processing apparatus <NUM> through the use of the routines <NUM> and the data table <NUM>.

<FIG> depicts an improved electrical circuit apparatus <NUM> in accordance with a second embodiment of the disclosed and claimed concept. The electrical circuit apparatus <NUM> includes a resonant electrical circuit <NUM> having a capacitor <NUM> and an inductor <NUM>, and is thus similar in that fashion to the electrical circuit apparatus <NUM>. However, the electrical circuit apparatus <NUM> includes a temperature transmission apparatus <NUM> that enables measurement of the center line fuel pellet temperature within the fuel rod <NUM>. Specifically, the temperature transmission apparatus <NUM> includes a modified fuel pellet <NUM> that is modified to have a receptacle <NUM> formed therein. The temperature transmission apparatus <NUM> further includes a tungsten rod <NUM> that is an elongated element and that is received in the receptacle <NUM>. While the elongated element <NUM> is depicted in the exemplary embodiment described herein as being formed of tungsten, it is understood that any of a wide variety of other refractory metals and alloys such as molybdenum and the like can be used in place of tungsten. The temperature transmission apparatus <NUM> further includes a ferritic rod <NUM> that is abutted against the tungsten rod <NUM>, it being understood that the tungsten rod <NUM> is abutted with the modified fuel pellet <NUM>. The inductor <NUM> includes a coil <NUM> that is situated directly on the ferritic rod <NUM>.

During operation, the heat that is generated by the fuel pellets <NUM> and the modified fuel pellet <NUM> is conducted through the tungsten rod <NUM> and thereafter through the ferritic rod <NUM>, thereby causing the temperature of the ferritic rod <NUM> to correspond with the temperature of the fuel pellets <NUM> and the modified fuel pellet <NUM>. The permeability of the ferritic rod <NUM> changes as a function of temperature, and the change in permeability with temperature is depicted in a graph that is shown generally in <FIG>. A portion of the graph of <FIG> is encircled and demonstrates the temperature that is typically seen by the ferritic rod <NUM> after the heat from the modified fuel pellet <NUM> is transferred to the ferritic rod <NUM> by the tungsten rod <NUM> and demonstrates, due to the steepness of the curve at the indicated location in <FIG>, the correlation between temperature of the ferritic rod <NUM> and permeability thereof.

The permeability of the ferritic rod <NUM> which, as noted, varies as a function of temperature, affects the inductance of the inductor <NUM> with the result that the frequency of the response pulse <NUM> that is output by the resonant circuit <NUM> varies directly with the permeability of the ferritic rod <NUM> and thus with the temperature of the fuel pellets <NUM> and the modified fuel pellet <NUM>. As such, the temperature of the fuel pellets <NUM> and the modified fuel pellet <NUM> can be measured by detecting the response pulse <NUM> that is output by the resonant electrical circuit <NUM> through the use of the routines <NUM> and the retrieval from the data tables <NUM> of a temperature that corresponds with the detected frequency of the response pulse <NUM>.

An improved electrical circuit apparatus <NUM> in accordance with a third embodiment of the disclosed and claimed concept is depicted in <FIG> and is usable in a fuel rod in a fashion similar to the electrical circuit apparatus <NUM>. The electrical circuit apparatus <NUM> is receivable in the interior region <NUM> of the fuel rod <NUM> and includes a resonant electrical circuit <NUM> and a temperature transmission apparatus <NUM> that detect the temperature of a set of modified fuel pellets <NUM>. The modified fuel pellets <NUM> each have a receptacle <NUM> formed therein. The temperature transmission apparatus <NUM> includes an amount of liquid metal <NUM> that is liquid during operation of the nuclear reactor <NUM>. The temperature transmission apparatus <NUM> further includes a ferritic rod <NUM> that is engaged with the liquid metal <NUM> and is buoyantly floated thereon and is receivable in the interior of a coil <NUM> of an inductor <NUM> of the resonant electrical circuit <NUM>. The liquid metal <NUM> expands and contracts with temperature increases and decreases, respectively, of the modified fuel pellets <NUM>. The position of the ferritic rod <NUM> with respect to the coil <NUM> is thus directly dependent upon the centerline temperature of the modified fuel pellets <NUM>. Such position of the ferritic rod <NUM> with respect to the coil <NUM> affects the inductance of the inductor <NUM> and therefore correspondingly affects the frequency of the resonant electrical circuit <NUM>. The response pulse <NUM> that is generated by the resonant electrical circuit <NUM> thus is receivable by the receiver <NUM> and is communicated to the electronic processing apparatus <NUM>, and the routines <NUM> and the data tables <NUM> are employed to determine a corresponding temperature of the modified fuel pellets <NUM> and thus of the corresponding fuel rod <NUM>.

<FIG> depicts an improved electrical circuit apparatus <NUM> in accordance with a fourth embodiment of the disclosed and claimed concept. The electrical circuit apparatus <NUM> is usable inside a fuel rod <NUM> and includes a resonant electrical circuit <NUM> and a pressure transmission apparatus <NUM>. The pressure transmission apparatus <NUM> is configured to enable measurement of the ambient pressure within the interior of the fuel rod <NUM> and includes a support <NUM> that abuts the stack of fuel pellets <NUM>. The pressure transmission apparatus <NUM> further includes a ferritic rod <NUM> and a vessel in the form of a bellows <NUM> having a hollow cavity <NUM> and further having a plurality of corrugations <NUM> formed therein. The hollow cavity <NUM> is open and is therefore in fluid communication with the interior region of the fuel rod <NUM>. Moreover, an end of the bellows <NUM> opposite a ferritic rod <NUM> is affixed to the support <NUM>.

The resonant electrical circuit <NUM> includes a capacitor <NUM> and further includes an inductor <NUM> having a coil <NUM> that is formed about the exterior of a hollow tube <NUM> having an interior <NUM> within which a ferritic rod <NUM> is receivable. The bellows <NUM> and the ferritic rod <NUM> are movably received on a support <NUM> and are biased by a spring in a direction generally toward the fuel pellets <NUM>.

As is understood in the relevant art, as the nuclear reactor <NUM> is in operation, fission gases are produced that include one or more noble gases. Such fission gases increase the ambient pressure within the interior region of the fuel rod <NUM>. Since the hollow cavity <NUM> is in fluid communication with the interior region of the fuel rod <NUM>, the increased pressure in the interior region <NUM> bears upon bellows <NUM> within the hollow cavity <NUM> and causes the bellows <NUM> to expand axially, thereby moving the ferritic rod <NUM> with respect to the coil <NUM> and thereby affecting the inductance of the inductor <NUM>. An increase in ambient pressure within the interior region <NUM> of the fuel rod <NUM> thus expands the bellows <NUM>, thereby resulting in an incremental further reception of the ferritic rod <NUM> into the coil <NUM>, which results in a corresponding change in inductance of the inductor <NUM>.

The corresponding change in inductance of the inductor <NUM> affects in a predictable fashion the frequency of the resonant electrical circuit <NUM> and thus likewise affects the frequency of the response pulse <NUM> that is output by the resonant electrical circuit <NUM>. As a result, when the response pulse <NUM> from the resonant electrical circuit <NUM> is received by the receiver <NUM> and is communicated to the electronic processing apparatus <NUM>, the routines <NUM> and the data tables <NUM> are employed to obtain a corresponding value for the ambient pressure within the interior region <NUM> of the fuel rod <NUM>. Such value for the ambient pressure can then be communicated to an enterprise data system of the nuclear reactor <NUM>.

An improved electrical circuit apparatus <NUM> in accordance with a fifth embodiment of the disclosed and claimed concept is depicted generally in <FIG>. The electrical circuit apparatus <NUM> is situated within an interior region <NUM> of a fuel rod <NUM> and includes a resonant electrical circuit <NUM> that includes a capacitor and an inductor <NUM>.

The electrical circuit apparatus <NUM> further includes a pressure transmission apparatus <NUM> that includes a vessel in the form of a Bourdon tube <NUM> which, in the depicted exemplary embodiment, includes a hollow tube that is formed in a helical shape. The hollow tube of the Bourdon tube <NUM> forms a hollow cavity <NUM>, except that an inlet <NUM> is formed in an end of the Bourdon tube <NUM> and thus permits fluid communication with the interior of the Bourdon tube <NUM>. More specifically, the electrical circuit apparatus <NUM> further includes a support <NUM> in the form of a seal that extends between the edges of the Bourdon tube <NUM> adjacent the inlet <NUM> and extends to an interior surface of the interior region <NUM> of the fuel rod <NUM>. The support <NUM> thus divides the interior region <NUM> into a main portion <NUM> within which a number of fuel pellets <NUM> are situated and a sub-region <NUM> within which the Bourdon tube <NUM> and the inductor <NUM> are situated. The Bourdon tube <NUM> is also supported on the support <NUM>. The support <NUM> resists fluid communication between the main portion <NUM> and the sub-region <NUM>, except for the inlet <NUM> which permits fluid communication between the interior of the Bourdon tube <NUM> and the main portion <NUM>.

The pressure transmission apparatus <NUM> further includes a ferritic rod <NUM> that is situated on the Bourdon tube <NUM> at an end thereof opposite the inlet <NUM>. The inductor <NUM> includes a coil <NUM>, and movement of the ferritic rod <NUM> in relation to the coil <NUM> changes the inductance of the inductor <NUM> such that the frequency of the response pulse <NUM> that is generated by the electrical circuit apparatus <NUM> changes corresponding to the ambient pressure within the main portion <NUM> of the interior region <NUM>. More specifically, as fission gases accumulate in the main portion <NUM> of the interior region <NUM>, the ambient pressure within the main portion <NUM> increases, as does the ambient pressure within the hollow cavity <NUM> of the Bourdon tube <NUM>. Since the sub-region <NUM> does not experience the increased ambient pressure that is experienced by the main portion <NUM>, and increase in the ambient pressure within the hollow cavity <NUM> of the Bourdon tube <NUM> results in expansion of the Bourdon tube <NUM> and resultant movement of the ferritic rod <NUM> in the direction of the arrow <NUM> with respect to the coil <NUM>. This results in a corresponding change in the frequency of the response pulse <NUM> that is generated by the electrical circuit apparatus <NUM>.

It thus can be seen that changes in ambient pressure within the main portion <NUM> of the interior region <NUM> result in a change in inductance of the inductor <NUM> and a corresponding change in the nominal frequency of the resonant electrical circuit <NUM> and a resultant change in the frequency of the response pulse <NUM> that is generated by the electrical circuit apparatus <NUM>. When such response pulse <NUM> is received by the receiver <NUM>, a corresponding signal is communicated to the electronic processing equipment <NUM>, and the routines <NUM> and the data tables <NUM> are used to obtain a corresponding value for the ambient pressure within the interior region <NUM> for output as desired.

An improved electrical circuit apparatus <NUM> in accordance with a sixth embodiment of the disclosed and claimed concept is depicted generally in <FIG>. The electrical circuit apparatus <NUM> is similar to the electrical circuit apparatus <NUM> in that a Bourdon tube <NUM> is employed as a vessel having a hollow cavity <NUM>. In the electrical circuit apparatus <NUM>, however, the Bourdon tube <NUM> includes a plug <NUM> at an end thereof opposite a ferritic rod <NUM> such that the hollow cavity <NUM> of the Bourdon tube is not in fluid communication with the interior region <NUM> of the fuel rod <NUM>, and an increase in ambient pressure within the interior region <NUM> causes the Bourdon tube <NUM> to contract. The Bourdon tube <NUM> is supported on a support <NUM> in the vicinity of the plug <NUM>, and a contraction of the Bourdon tube <NUM> due to increased ambient pressure within the interior region <NUM> thus moves the ferritic rod <NUM> in the direction of the arrow <NUM> with respect to the coil <NUM>.

The electrical circuit apparatus <NUM> includes a resonant electrical circuit <NUM> having a capacitor and an inductor <NUM>, and movement of the ferritic rod <NUM> with respect to the coil <NUM> of the inductor <NUM> changes the inductance of the inductor <NUM> and thus changes the nominal frequency of the resonant electrical circuit <NUM>. The electrical circuit apparatus <NUM> thus includes a pressure transmission apparatus <NUM> that is similar to the pressure transmission apparatus <NUM>, except that the pressure transmission apparatus <NUM> includes a Bourdon tube <NUM> whose hollow cavity <NUM> is not in fluid communication with the interior region <NUM> and thus contracts in the presence of an increased ambient pressure within the interior region <NUM>.

An improved electrical circuit apparatus <NUM> in accordance with a seventh embodiment of the disclosed and claimed concept includes a resonant electrical circuit <NUM> having a capacitor <NUM> and an inductor. The capacitor <NUM> includes a pair of plates 652A and 652B that are separated by a dielectric material <NUM>. The electrical circuit apparatus <NUM> is receivable within the interior region <NUM> of a fuel rod <NUM> in order to output a response pulse <NUM> whose frequency is adjusted responsive to a change in ambient pressure within the interior region <NUM> of the fuel rod <NUM>.

More specifically, the dielectric <NUM> is hygroscopic in nature and is configured to absorb at least some of the fission gases that are generated during operation of the nuclear reactor <NUM>. Such absorption of the fission gases by the dielectric <NUM> changes the dielectric constant of the dielectric <NUM>, which adjusts the capacitance of the capacitor <NUM>, with a corresponding effect on the frequency of the response pulse <NUM> that is generated by the resonant electrical circuit <NUM>. As such, a change in the ambient pressure within the interior region <NUM> of the fuel rod <NUM> correspondingly affects the capacitance of the capacitor <NUM> and thus likewise correspondingly affects the frequency of the response pulse <NUM> that is generated by the resonant electrical circuit <NUM>. When the response pulse <NUM> is received by the receiver <NUM>, the receiver <NUM> responsively provides to the electronic processing apparatus <NUM> a signal which is used by the routines <NUM> in conjunction with the data tables <NUM> to obtain and output a value for the ambient pressure within the interior region <NUM> of the fuel rod <NUM> within which the electrical circuit apparatus <NUM> is situated.

An electrical circuit apparatus <NUM> in accordance with an eighth embodiment of the disclosed and claimed concept is depicted generally in <FIG> as being situated within an interior region <NUM> of a fuel rod <NUM>. The electrical circuit apparatus includes a resonant electrical circuit <NUM> that includes a capacitor <NUM> and an inductor <NUM>.

The electrical circuit apparatus <NUM> includes a pressure transmission apparatus <NUM> that includes a support <NUM> upon which the capacitor <NUM> is situated in a stationary fashion and further includes a flexible seal <NUM>. More specifically, the capacitor <NUM> includes a pair of plates 752A and 752B with a dielectric material <NUM> interposed therebetween. The plate 752A is situated on the support <NUM>, and the flexible seal extends between the plate 752B and an interior surface of the fuel rod <NUM> to divide the interior region <NUM> into a main portion <NUM> within which a number of fuel pellets <NUM> are situated and a sub-region <NUM> within which the inductor <NUM>, the plate 752A, the support <NUM>, and the dielectric <NUM> are situated. The support <NUM> is rigid but has a number of openings formed therein such that an increase or decrease in the ambient pressure within the main portion <NUM> will result in movement of the flexible seal <NUM> with respect to the support <NUM>. The flexible seal <NUM> thus resists fluid communication between the main portion <NUM>, which is the location where the fission gases are generated, and the sub-region <NUM>.

When the main portion <NUM> experiences a change in the ambient pressure within the main portion <NUM>, this causes the flexible seal <NUM> and the plate 752B to move with respect to the plate 752A which, being situated on the support <NUM>, remains stationary. The dielectric material <NUM> is configured to be at least partially flexible in response to movement of the plate 752B with respect to the plate 752A. However, such movement of the plate 752B with respect to the plate 752A results in a change in the capacitance of the capacitor <NUM>. This results in a corresponding change in the frequency of the response pulse <NUM> that is generated by the resonant electrical circuit <NUM> as a result of a change in the ambient pressure within the main portion <NUM>. It thus can be understood that a change in ambient pressure within the main portion <NUM> of the interior region <NUM> correspondingly changes the frequency of the response pulse <NUM> that is received by the receiver <NUM> and which resultantly communicates a signal to the electronic processing apparatus <NUM>. The electronic processing apparatus <NUM> then employs its routines <NUM> and its data tables <NUM> to determine a pressure value that corresponds with the frequency of the response pulse <NUM> and which is indicative of the ambient pressure within the main portion <NUM> of the interior region <NUM>.

It thus can be seen that various electrical circuit apparatuses are provided that are able to directly measure parameters such as ambient pressure, centerline fuel pellet temperature, and fuel pellet elongation within the various fuel rods <NUM> of the fuel assembly <NUM>. As noted, any of the electrical circuit apparatuses can include the calibration circuit that is usable to compensate for component degradation and temperature drift. In addition to the direct measurement of the parameters such as centerline fuel pellet temperature, fuel pellet elongation, and ambient pressure within the interior region of the fuel rods <NUM>, it is reiterated that the response pulse <NUM> in certain circumstances can be analyzed in terms of its peak amplitude, frequency, and rate of decay in order to indirectly and simultaneously indicate a plurality the same parameters of the fuel rods <NUM>. Other variations will be apparent.

Claim 1:
A detection apparatus (<NUM>) usable with a fuel rod (<NUM>) from among a plurality of fuel rods of a fuel assembly (<NUM>), the fuel rod (<NUM>) having a cladding (<NUM>) that has an interior region (<NUM>), the fuel rod (<NUM>) being situated within a nuclear reactor (<NUM>), the detection apparatus (<NUM>) being cooperable with an electronic processing apparatus (<NUM>) situated outside of the nuclear reactor (<NUM>), the detection apparatus (<NUM>) characterized by:
a transmitter (<NUM>) positioned outside the cladding (<NUM>) and inside the nuclear reactor (<NUM>) in the vicinity of the fuel rod (<NUM>), the transmitter (<NUM>) being structured to generate an excitation pulse (<NUM>) in the form of a first magnetic field signal and to wirelessly transmit the excitation pulse (<NUM>), the excitation pulse (<NUM>) being structured to travel wirelessly through the cladding (<NUM>) and into the interior region (<NUM>);
an electrical circuit apparatus (<NUM>) having a resonant electrical circuit (<NUM>) supported within the interior region (<NUM>), the resonant electrical circuit (<NUM>) being structured to generate a response pulse (<NUM>) in the form of a second magnetic field signal in response to the excitation pulse (<NUM>) and to wirelessly transmit the response pulse (<NUM>), the response pulse (<NUM>) being structured to travel wirelessly from the interior region (<NUM>) and through the cladding (<NUM>);
the resonant electrical circuit (<NUM>) comprising a plurality of circuit components (<NUM>, <NUM>), at least one circuit component of the plurality of circuit components (<NUM>, <NUM>) having a property which is structured to vary in response to a condition of the fuel rod (<NUM>) and which, responsive to a change in the condition, is structured to cause the property and the response pulse (<NUM>) to vary with the change in the condition and to be indicative of the condition; and
a receiver (<NUM>) supported within the nuclear reactor (<NUM>) outside the cladding (<NUM>) and in the vicinity of the fuel rod (<NUM>), the receiver (<NUM>) being structured to receive the response pulse (<NUM>) and to communicate to the electronic processing apparatus (<NUM>) an output responsive to the received response pulse (<NUM>).