Fuel rod sensor system having inductive coupling

Abstract

To provide a sensor improved for monitoring fuel central line temperature, the elongation of a fuel pellet laminate and / or fuel rod internal pressure.SOLUTION: A sensor system for a fuel rod including a fuel pellet laminate includes a radio interrogator arranged on the outside of the fuel rod and a passive sensor part arranged in the fuel rod. The passive sensor part includes: a receiver constituted so as to receive a question signal and output an excitation signal in response to receiving the question signal; a reference transmitter constituted so as to output a reference signal to a reference receiver in response to the excitation signal; a sensing transmitter constituted so as to output a sensing signal to a sensing receiver in response to the excitation signal; and a core at least partially arranged in the sensing transmitter and connected so as to move in conjunction with the expansion or contraction of the fuel pellet laminate and move on the basis of pressure change in the fuel rod or change temperature on the basis of temperature change in the fuel rod.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. patent application Ser. No. 16 / 564,150, filed Sep. 9, 2019, and entitled “FUEL ROD SENSOR SYSTEM WITH INDUCTIVE COUPLING,” the contents of which are incorporated herein by reference.

[0002] The disclosed concepts relate generally to nuclear power devices, and more particularly to sensor systems usable with fuel rods in a fuel assembly of a nuclear reactor. Summary of the Invention [Problem to be solved by the invention]

[0003] The reactor system includes a variety of sensors for monitoring various characteristics of the system. One type of sensor is designed to monitor the fuel centerline temperature, the fuel pellet stack elongation, and the fuel rod internal pressure.

[0004] 1 is a schematic diagram of a sensor designed to monitor fuel centerline temperature, fuel pellet stack elongation, and fuel rod internal temperature. The sensor includes a passive sensor portion 10 located within a fuel rod 2 of a nuclear reactor, and a wireless interrogator 20 located within an instrument thimble 4 of the reactor. The passive portion 10 includes an inductor 12 and a capacitor 14, which together form a resonant circuit. The wireless interrogator 20 includes a transmitter 22 and a receiver 24, and is electrically connected to electronics 30 external to the reactor core.

[0005] The sensor operates by passing a current through the transmitter 22, causing the transmitter 22 to generate an interrogation signal that is received by and excites the passive portion 10. In response, the passive portion 10 generates a response signal that is received by the receiver 24. The response signal includes characteristics indicative of the fuel centerline temperature, the fuel pellet stack elongation, and the fuel rod internal temperature. These characteristics change the inductance of the inductor 12 and are reflected in the response signal, for example, by a change in the frequency of the response signal.

[0006] In some methodologies, the inductor 12 is threaded through a ferrite core that is coupled to the stack of fuel pellets, so that the inductance of the inductor 12 changes as the stack of fuel pellets stretches.

[0007] The sensitivity of the sensor in Figure 1 is limited, and therefore there is room for improvement in the sensors within the fuel rods. [Means for solving the problem]

[0008] Embodiments of the disclosed concepts provide improved sensors for monitoring fuel centerline temperature, fuel pellet stack elongation, and / or fuel rod internal pressure.

[0009] In one aspect of the disclosed concept, a sensor system for a fuel rod including a fuel pellet stack includes a wireless interrogator disposed external to the fuel rod and a passive sensor portion disposed within the fuel rod, the wireless interrogator including a transmitter configured to wirelessly output an interrogation signal, a reference receiver, and a sensing receiver, the passive sensor portion including a receiver configured to receive the interrogation signal and output an excitation signal in response to receiving the interrogation signal, a reference transmitter configured to output a reference signal to the reference receiver in response to the excitation signal, a sensing transmitter configured to output a sensing signal to the sensing receiver in response to the excitation signal, and a core disposed at least partially within the sensing transmitter, the core coupled to move in conjunction with expansion or contraction of the fuel pellet stack, to move based on pressure changes within the fuel rod, or to change temperature based on temperature changes within the fuel rod, the receiver, reference transmitter, and sensing transmitter being electrically connected in series.

[0010] In one aspect of the disclosed concept, a sensor system for a fuel rod including a fuel pellet stack includes a wireless interrogator disposed external to the fuel rod and a passive sensor portion disposed within the fuel rod, the wireless interrogator including a primary transmitter configured to wirelessly output an interrogation signal, and a secondary receiver, the passive sensor portion configured to receive the interrogation signal and output an excitation signal in response to receiving the interrogation signal, a linear differential variable transformer (LVDT) including a core coupled to move in conjunction with expansion or contraction of the fuel pellet stack, to move based on pressure changes within the fuel rod, or to change temperature based on temperature changes within the fuel rod, the LVDT configured to receive the excitation signal and output an output signal indicative of a position or temperature of the core, and a secondary transmitter configured to receive the output signal from the LVDT and output a response signal proportional to the output signal to the secondary receiver.

[0011] As another aspect of the disclosed concept, a system includes at least one fuel rod including a fuel pellet stack and at least one sensor system, the at least one sensor system including a wireless interrogator disposed external to the fuel rod and a passive sensor portion disposed within the fuel rod, the wireless interrogator including a primary transmitter configured to wirelessly output an interrogation signal, and a secondary receiver, the passive sensor portion configured to receive the interrogation signal and output an excitation signal in response to receiving the interrogation signal, a linear differential variable transformer (LVDT) including a core coupled to move in conjunction with expansion or contraction of the fuel pellet stack, to move based on pressure changes within the fuel rod, or to change temperature based on temperature changes within the fuel rod, the LVDT configured to receive the excitation signal and output an output signal indicative of a position or temperature of the core, and a secondary transmitter configured to receive the output signal from the LVDT and output a response signal proportional to the output signal to the secondary receiver.

[0012] As another aspect of the disclosed concept, a method of sensing a fuel rod characteristic in a fuel rod including a fuel pellet stack includes the steps of providing a wireless interrogator disposed outside the fuel rod; providing a passive sensor portion disposed within the fuel rod, the passive sensor portion comprising a Linear Differential Variable Transformer (LVDT) including a core coupled to move in conjunction with expansion or contraction of the fuel pellet stack, to move based on pressure changes within the fuel rod, or to change temperature based on temperature changes within the fuel rod, the LVDT configured to receive an excitation signal and to output an output signal indicative of a position or temperature of the core; wirelessly outputting the interrogation signal from the wireless interrogator to the passive sensor portion; providing the excitation signal to the LVDT in response to receiving the wireless interrogation signal; outputting an output signal indicative of a position or temperature of the core from the LVDT; and wirelessly outputting a response signal proportional to the output signal from the passive sensor portion to the wireless interrogator. [Brief description of the drawings]

[0013] The invention will be better understood from reading the following description of the preferred embodiments in conjunction with the accompanying drawings.

[0014] [Figure 1] FIG. 1 is a schematic diagram of a sensor designed to monitor fuel centerline temperature, fuel pellet stack elongation, and fuel rod internal pressure with limited sensitivity.

[0015] [Diagram 2] FIG. 2 is a schematic diagram of a sensor system providing high measurement sensitivity according to an exemplary embodiment of the disclosed concepts.

[0016] [Diagram 3] FIG. 3 is a schematic diagram of a sensor system providing high measurement sensitivity according to another exemplary embodiment of the disclosed concepts.

[0017] [Figure 4] FIG. 4 is a schematic diagram of a sensor system according to an exemplary embodiment of the disclosed concepts.

[0018] [Figure 5A] FIG. 5A is a top view of a linear variable differential transformer according to an exemplary embodiment of the disclosed concepts.

[0019] [Figure 5B] FIG. 5B is a cross-sectional side view of the LVDT of FIG. 4A according to an exemplary embodiment of the disclosed concepts.

[0020] [Figure 6] FIG. 6 is a simplified cross-sectional view of a fuel rod including an LVDT according to an exemplary embodiment of the disclosed concepts.

[0021] [Figure 7] FIG. 7 is a simplified cross-sectional view of a fuel rod including an LVDT in accordance with another exemplary embodiment of the disclosed concepts.

[0022] [Figure 8]FIG. 8 is a schematic diagram of a system including multiple sensors according to an exemplary embodiment of the disclosed concepts.

[0023] [Figure 9] FIG. 9 is a flow chart of a method for sensing a fuel rod characteristic according to an exemplary embodiment of the disclosed concepts.

[0024] [Figure 10] FIG. 10 is a flow chart of a method for sensing a fuel rod characteristic according to an exemplary embodiment of the disclosed concepts. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] 2 is a schematic diagram of a sensor system according to an exemplary embodiment of the disclosed concepts, suitable for monitoring fuel centerline temperature, fuel pellet stack elongation, and / or fuel rod internal pressure in a nuclear reactor system.

[0026] The sensor system includes a passive portion 60 and a wireless interrogator 50. The passive portion 60 is disposed within a fuel rod 2 of a nuclear reactor, and the wireless interrogator 50 is disposed within an instrument thimble of the nuclear reactor. The wireless interrogator 50 is connected to an electronic processing device 200 that is disposed outside the core of the nuclear reactor. The fuel rod 2 is fully enclosed, but the instrument thimble 4 includes a penetration through which electrical conductors pass, such as the conductor between the wireless interrogator 50 and the electronic processing device 200. It will also be understood that the wireless interrogator 50 may be disposed in an area adjacent to the fuel rod 2. For example, the wireless interrogator 50 may be disposed in a different housing than the instrument thimble 4 without departing from the scope of the disclosed concept.

[0027] The wireless interrogator 50 includes a transmitter 52, a reference receiver 54, and a sensing receiver 56. The transmitter 52, the reference receiver 54, and the sensing receiver 56 may be inductors (also called coils). The passive section 60 includes a receiver 62, a reference transmitter 64, and a sensing transmitter 66, electrically connected in series. The receiver 62, the reference transmitter 64, and the sensing transmitter 66 may be inductors (also called coils). The passive section 60 also includes a core 130. The core 130 is at least partially disposed within the sensing transmitter 66.

[0028] The transmitter 52 is configured to generate an interrogation signal. For example, the electronic processing device 200 may generate and provide a signal to the transmitter 52 that energizes the transmitter 52 and causes the transmitter 52 to generate the interrogation signal. The interrogation signal may be a continuous sine wave or a pulsed wave that is received by and excites the receiver 62. For example, the interrogation signal may be a time-varying magnetic field that is generated by the transmitter 52 and induces an electromotive force in the receiver 62, causing a current to flow in the receiver 62, which in turn causes a current to flow in the reference transmitter 64 and the sensing transmitter 66. The current through the reference transmitter 64 and the sensing transmitter 66 causes the reference transmitter 64 and the sensing transmitter 66 to generate a reference signal and a sensing signal, respectively, which are received by the reference receiver 54 and the sensing receiver, respectively. For example, the reference signal and the sense signal may be a time-varying magnetic field generated by the reference transmitter 64 and the sense transmitter 66 in response to current flowing through the reference transmitter 64 and the sense transmitter 66, which in turn induces an electromagnetic force in the reference receiver 54 and the sense receiver 56.

[0029] The core 130 is physically coupled to the fuel pellet stack in the fuel rod 2. In some exemplary embodiments, the core 130 is coupled such that the core 130 moves linearly with the fuel pellet stack. For example, when the fuel pellet stack expands or expands, the core 130 moves upward through the sense transmitter 66 the same distance as the fuel pellet stack stretches. Thus, a physical displacement of the core 130 at the sense transmitter 66 changes the voltage of the sense transmitter 66, which in turn changes the sense signal received by the sense receiver 56 and used to determine the fuel pellet stack stretch. In some exemplary embodiments, the core 130 is coupled such that a temperature change in the fuel pellet stack changes the temperature of the core 130. A temperature change in the core 130 changes the magnetic permeability, which in turn changes the voltage of the sense transmitter 66. This in turn changes the sense signal received by the sense receiver 56 and used to determine the fuel centerline temperature. In some exemplary embodiments, the core 130 is coupled such that a pressure change in the fuel rod causes the core 130 to move with the temperature change. For example, the core 130 may be coupled to a bellows within the fuel rod 2 such that an increase in pressure causes the bellows to expand, further moving the core 130 within the sense transmitter 66. The physical displacement of the core 130 in the sense transmitter 66 changes the voltage of the sense transmitter 66, which in turn changes the sense signal received by the sense receiver 56 and used to determine the pressure within the fuel rod 2. In these exemplary embodiments, the fuel centerline temperature, fuel pellet stack elongation, and fuel pressure are considered sensed parameters, whose values ​​affect the sensed signal. However, these values ​​have little effect on the reference signal output by the reference transmitter 64.

[0030] The sense signal and the reference signal are received by the sense receiver 56 and the reference receiver 54, respectively. The difference between the sense signal and the reference signal may be used to determine the sensed parameter, since the difference between these two signals cancels out any drift due to temperature or other effects common to the reference transmitter 64, the sense transmitter 66, and other elements.

[0031] 3 is a schematic diagram of a sensor according to an exemplary embodiment of the disclosed concepts, suitable for monitoring fuel centerline temperature, fuel pellet stack elongation, and fuel rod internal pressure in a nuclear reactor system.

[0032] The sensor includes a passive part 110 and a wireless interrogator 140. The passive part 110 is located in a fuel rod 2 of the nuclear reactor, and the wireless interrogator 140 is located in an instrument thimble 4 of the nuclear reactor. The wireless interrogator 140 is coupled to an electronic processing unit 200 that is located outside the nuclear reactor core.

[0033] The wireless interrogator 140 includes a primary transmitter 142 and a secondary receiver 144. The passive part 110 includes a primary receiver 112 corresponding to the primary transmitter 142 of the wireless interrogator 140 and a secondary transmitter 114 corresponding to the secondary receiver 144 of the wireless interrogator 140. For example, the primary transmitter 142 is configured to output an interrogation signal and the primary receiver 112 is configured to receive the interrogation signal. Also, the secondary transmitter 114 is configured to output a response signal and the secondary receiver 144 is configured to receive the response signal. It should be understood that the interrogation signal, the response signal, or any other signal exchanged between the wireless interrogator 140 and the passive part 110 is a wireless signal, since the passive part 110 is fully enclosed within the fuel rod 2 and is not wired to any part outside the fuel rod 2.

[0034] The passive portion 110 also includes a linear variable differential transformer (LVDT) 120. The LVDT 120 is configured to sense linear motion of a core 130 contained within the LVDT 120 within the fuel rod. In some exemplary embodiments, the core 130 is coupled to move linearly with the fuel pellet stack to sense the elongation of the fuel pellet stack. In some exemplary embodiments, the core 130 is coupled to move linearly based on the pressure within the fuel rod 2, for example, by sensing the fuel pressure using a bellows as described above. In some exemplary embodiments, the core 130 is coupled to be static and its temperature varies with the fuel centerline temperature. For example, when measuring the fuel centerline temperature, the core 130 may be static in that it does not move and may have a magnetic permeability that varies along its length. Heat is conducted up the core 130 from the fuel pellet stack, so that the bottom of the core 130 is hotter than the top of the core 130. This temperature difference causes a different voltage output from the coil of the LVDT 120, resulting in an output from the LVDT 120 similar to what would occur if the core 130 were moving within the LVDT 120. From this output, the centerline temperature of the fuel can be determined.

[0035] In some exemplary embodiments of the disclosed concepts, the core 130 is constructed from a ferrite material, however, it will be understood that the core 130 may be constructed from other suitable materials without departing from the scope of the disclosed concepts.

[0036] The LVDT 120 is electrically connected to the primary receiver 112 and the secondary transmitter 114. The LVDT 120 is configured to receive an excitation signal from the primary receiver 112. To generate the excitation signal, the electronic processing unit 200 provides a signal to the primary transmitter 142, causing the primary transmitter 142 to output an interrogation signal. The primary receiver 112 receives the interrogation signal, which excites the primary receiver 112, which outputs the excitation signal to the LVDT 120.

[0037] The excitation signal causes the LVDT 120 to generate an output signal that indicates the position of the core 130. For example, at a zero position where the core 130 is centered on the LVDT 120, the output signal of the LVDT 120 is approximately 0V. As the core 130 moves from the zero position, the voltage of the output signal increases linearly. The phase angle of the output signal indicates the direction that the core 130 has moved relative to the zero position. The LVDT 120 is configured to provide the output signal to the secondary transmitter 114.

[0038] Upon receiving the output signal from the LVDT 120, the secondary transmitter 114 outputs a response signal, which is then received by the secondary receiver 144 and provided to the electronic processing device 200. The response signal is proportional to the output signal of the LVDT 120. Thus, any increase or decrease in voltage of the output signal of the LVDT 120 is reflected in the response signal. Similarly, the phase angle of the output signal of the LVDT 120 is also reflected in the response signal. From the response signal, the electronic processing device 200 can determine the position of the core 130 of the LVDT 120.

[0039] The LVDT 120 can more accurately sense the linear motion and position of the core 130. In some exemplary embodiments, the LVDT 120 can monitor the position of the core 130 within ±2 μm.

[0040] Although the exemplary embodiment of FIG. 3 illustrates the wireless interrogator 140 as being within the instrument thimble 4, it will be understood that the wireless interrogator 140 may be located elsewhere outside the fuel rod 2 without departing from the scope of the disclosed concept.

[0041] Figure 4 is a schematic diagram of a sensor according to an exemplary embodiment of the disclosed concepts. The sensor of Figure 4 operates similarly to the sensor of Figure 3. However, Figure 4 shows an exemplary embodiment of the LVDT 120 in more detail.

[0042] For example, in the exemplary embodiment of FIG. 4, the LVDT 120 includes a primary coil 122, a first secondary coil 124, and a second secondary coil 126. The primary coil 122 is disposed between the first secondary coil 124 and the second secondary coil 126. The primary coil 122, the first secondary coil 124, and the second secondary coil 126 are aligned such that the core 130 can pass through all of these coils. In FIG. 3, the core 130 is disposed in a null position where the core 130 is located at the center of the LVDT 120. That is, the center of the core 130 is aligned with the center of the primary coil 122, and the core 130 extends to the first secondary coil 124 and the second secondary coil 126 with equal lengths of extension.

[0043] The first secondary coil 124 and the second secondary coil 126 are equally spaced apart from the primary coil 122. For example, one end of the first secondary coil 124 is spaced from the center of the primary coil 122 by the same distance as one end of the second secondary coil 126. The primary coil 122 is electrically connected to the output of the primary receiver 112 and is configured to receive an excitation signal from the primary receiver 112. In an exemplary embodiment, each of the first and second secondary coils 124, 126 has a first end closest to the primary coil 122 and a second end furthest from the primary coil 122. The first end of the first secondary coil 124 is electrically connected to the output of the LVDT 120, and the second end of the first secondary coil 124 is electrically connected to the first end of the second secondary coil 126. The second end of the second secondary coil 126 is electrically connected to the output of the LVDT 120. However, it will be understood that the positions of the first and second secondary coils 124, 126 may be interchanged without departing from the scope of the disclosed concepts.

[0044] When the primary coil 122 receives an excitation signal, it induces a current in the core 130, which is then sensed by the first and second secondary coils 124, 126. When the core 130 is in the zero position as shown in FIG. 3, the outputs of the first and second secondary coils 124, 126 cancel each other, resulting in an output signal of 0V for the LVDT 120. As the core 130 moves from the zero position, a greater portion of the core 130 is disposed within one of the first and second secondary coils 124, 126 than within the other. A longer length of the core 130 in one of the first and second secondary coils 124, 126 will result in a greater output of one of the first and second secondary coils 124, 126 than the other, as the output of that coil will be greater than the other. Thus, as the core 130 moves further into one of the first and second secondary coils 124, 126, the output of the LVDT 120 rises linearly. Also, as the core 130 moves in one direction from the zero position, the output of the LVDT 120 has a first phase angle, and as the core 130 moves in the opposite direction from the zero position, the output of the LVDT 120 has a second phase angle. Thus, the magnitude of the LVDT 120 output signal indicates the distance the core 130 has moved from the zero position, and the phase angle of the LVDT 120 output signal indicates the direction the core 130 has moved. Taken together, the output signal of the LVDT 120 accurately indicates the position of the core 130.

[0045] 3, the output signal of the LVDT 120 is provided to the secondary transmitter 114. By receiving the output signal of the LVDT 120, the secondary transmitter 114 outputs a response signal proportional to the output signal of the LVDT 120. The response signal is received by the secondary receiver 144 and provided to the electronic processing device 200. The electronic processing device 200 is configured to interpret the response signal to determine the position of the core 130.

[0046] In some exemplary embodiments of the disclosed concepts, the first and second secondary coils 124, 126 are substantially identical. That is, they have substantially the same length and number of turns and are constructed from substantially the same material. If the first and second secondary coils 124, 126 are substantially identical, the outputs of the coils cancel each other when the core 130 is in the zero position, and the output of the LVDT 120 rises linearly as the core 130 moves from the zero position. The primary coil 122 may or may not be substantially the same as the first and second secondary coils 124, 126 without departing from the scope of the disclosed concepts.

[0047] In some exemplary embodiments of the disclosed concepts, the primary transmitter 142, the primary receiver 112, the secondary transmitter 114, and the secondary receiver 144 are coils. However, it will be understood that other elements capable of wirelessly transmitting or receiving signals may be employed without departing from the scope of the disclosed concepts.

[0048] 5A is a top view of an LVDT 120 according to an exemplary embodiment of the disclosed concepts, and FIG. 5B is a side cross-sectional view of the LVDT 120 according to an exemplary embodiment of the disclosed concepts. In some exemplary embodiments of the disclosed concepts, the LVDT 120 may have a cylindrical shape. However, it will be understood that the LVDT 120 may have other shapes without departing from the scope of the disclosed concepts.

[0049] LVDT 120 may include a housing 128, as shown in Figures 5A and 5B. Housing 127 has a hollow center through which core 130 may pass. Housing 128 may include internal compartments that house primary coil 122, first secondary coil 124, and second secondary coil 126, respectively. As previously mentioned, primary coil 122 is disposed between first secondary coil 124 and second secondary coil 126.

[0050] 6 is a simplified cross-sectional view of a fuel rod 2 including an LVDT 120 according to an exemplary embodiment of the disclosed concepts. As shown in FIG. 6, a core 130 passes through the LVDT 120. Fuel pellets 150 of a fuel pellet stack are physically coupled to the core 130 via an elongated member 152, such as a plunger. In this manner, the core 130 moves in conjunction with the expansion or contraction of the fuel pellet stack within the LVDT 120.

[0051] 7 is a simplified cross-sectional view of a fuel rod 2 including an LVDT 120 according to an exemplary embodiment of the disclosed concepts. As shown in FIG. 7, a core 130 passes through the LVDT 120. The core 130 is coupled to a bellows 154, either directly or through an intermediate member 156. The bellows 154 is configured to expand in response to an increase in pressure within the fuel rod 2 and to contract in response to a decrease in pressure within the fuel rod 2. In this manner, the core 130 moves within the LVDT 120 in conjunction with pressure changes within the fuel rod 2.

[0052] It will be appreciated that the configurations shown in Figures 6 and 7 may be used with the sensor system described with respect to Figure 2 without departing from the scope of the disclosed concepts.

[0053] FIG. 8 is a schematic diagram of a system including multiple sensors according to an exemplary embodiment of the disclosed concept. In the example of FIG. 8, multiple sensors are placed in close proximity. For example, multiple wireless interrogators 140 are placed in close proximity to multiple passive units 110. In some exemplary embodiments, the wireless interrogators 140 may output interrogation signals having unique frequencies. That is, one wireless interrogator 140 may output an interrogation signal having a first frequency, and another wireless interrogator 140 may output an interrogation signal having a second frequency. Each of the wireless interrogators 140 may correspond to a respective passive unit 110. Due to the proximity, it is possible that the wireless interrogators 140 receive a response signal from a passive unit 110 that does not correspond. Due to the interrogation signal having a unique frequency, the response signal from the passive unit 110 that corresponds to the wireless interrogator 140 will have the same unique frequency as the interrogation signal. The electronic processing device 200 may have a frequency filtering function and may filter the unique frequency of the interrogation signal. Thus, even if the wireless interrogator 140 receives response signals from non-corresponding passive parts 110, these response signals may be filtered out because they are at different frequencies.

[0054] 9 is a flow chart of a method for sensing fuel rod properties according to an exemplary embodiment of the disclosed concepts. The method of FIG. 9 may be used in conjunction with the embodiments of the disclosed concepts described herein or in other similar applications.

[0055] The method begins at 300 by providing a wireless interrogator disposed external to the fuel rod. The wireless interrogator may be the wireless interrogator 140 described in connection with embodiments of the disclosed concepts. The method continues at 302 by providing a passive sensor portion disposed within the fuel rod. The passive sensor portion includes an LVDT having a core coupled to the fuel pellet stack for movement in conjunction with expansion or contraction of the fuel pellet stack. The passive sensor portion may be the passive sensor portion 110 described in connection with embodiments of the disclosed concepts.

[0056] The method continues with wirelessly outputting 304 an interrogation signal from the wireless interrogator to the passive sensor portion. The interrogation signal may be output, for example, by a primary transmitter of the wireless interrogator and received, for example, by a primary receiver of the passive sensor portion. The method continues with providing 306 an excitation signal to the LVDT in response to receiving the interrogation signal. The excitation signal may be provided, for example, by the primary receiver of the passive sensor portion.

[0057] The method continues with outputting 308 an output signal from the LVDT indicative of the position of the core. Finally, the method continues with outputting 310 a response signal proportional to the output signal from the passive sensor portion to the wireless interrogator. It will be understood that the method may include additional steps, the method steps may be modified, or the method steps may be rearranged without departing from the scope of the disclosed concepts.

[0058] 10 is a flow chart of a method for sensing fuel rod properties according to an exemplary embodiment of the disclosed concepts. The method of FIG. 10 may be used in conjunction with the embodiments of the disclosed concepts described herein or in other similar applications.

[0059] The method begins at 400 by providing a wireless interrogator disposed external to the fuel rod. The wireless interrogator may be the wireless interrogator 50 described in connection with embodiments of the disclosed concepts. The method continues at 402 by providing a passive sensor portion disposed within the fuel rod. The passive sensor portion may be the passive sensor portion 40 described in connection with embodiments of the disclosed concepts and may include a sensing transmitter whose output is affected by a sensed parameter and a reference transmitter whose output is not affected by the sensed parameter.

[0060] The method continues with wirelessly outputting 404 an interrogation signal from the wireless interrogator to the passive sensor portion. The method continues with receiving 406 a reference signal from the passive sensor portion and receiving 408 a sensed signal from the passive sensor portion. The sensed signal is affected by the sensed parameter, while the reference signal is not affected by the sensed parameter. The method then continues with subtracting 410 the reference signal from the sensed signal. The subtraction counteracts temperature drift and other factors that affect all elements in the system. It will be understood that the method may include additional steps, the method steps may be changed, or the method steps may be rearranged without departing from the scope of the disclosed concept.

[0061] Although specific embodiments of the invention have been described in detail, those skilled in the art will recognize that various changes and modifications may be made to these details in light of the overall teachings of the present disclosure, and that one or more selected elements of an exemplary embodiment may be combined with one or more elements of other embodiments without departing from the scope of the disclosed concepts. Accordingly, the specific embodiments disclosed are intended to be illustrative only and not limiting as to the scope of the invention, which is given the full scope of the appended claims, and any and all equivalents thereof.

Claims

1. 1. A sensor system for a fuel rod including a fuel pellet stack, comprising: The sensor system includes: a wireless interrogator disposed external to the fuel rod; A passive sensor portion disposed within the fuel rod; Equipped with The wireless interrogator includes: a transmitter configured to wirelessly transmit an interrogation signal; A reference receiver; A sensing receiver; Equipped with The passive sensor unit includes: a receiver configured to receive the interrogation signal and to output an excitation signal in response to receiving the interrogation signal; a reference transmitter configured to output a reference signal to the reference receiver in response to the excitation signal; a sensing transmitter configured to output a sensing signal to the sensing receiver in response to the excitation signal; a core disposed at least partially within the sensing transmitter, the core being coupled to move in conjunction with expansion or contraction of the fuel pellet stack, to move based on pressure changes within the fuel rod, or to change temperature based on temperature changes within the fuel rod; Equipped with The sensor system, wherein the receiver, the reference transmitter, and the sensing transmitter are electrically connected in series.

2. The sensor system of claim 1 , wherein at least one of the transmitter, the reference receiver, the sensing receiver, the receiver, the reference transmitter, and the sensing transmitter is an inductor.

3. an elongated member disposed between the core and the fuel pellet stack such that the core moves in conjunction with expansion or contraction of the fuel pellet stack; The sensor system of claim 1 , wherein movement of the core causes a change in the sensed signal.

4. a bellows coupled to the core such that the core moves in response to pressure changes within the fuel rod; The sensor system of claim 1 , wherein movement of the core causes a change in the sensed signal.

5. the core is coupled to vary its temperature based on temperature changes within the fuel rod; The sensor system of claim 1 , wherein a change in temperature of the core changes the magnetic permeability of the core, thereby changing the sensed signal.

6. an electronic processing device electrically connected to the wireless interrogator and configured to receive the sensing signal and the reference signal received by the sensing receiver and the reference receiver; The sensor system of claim 1 , wherein the electronic processing unit is configured to determine a difference between the sensed signal and the reference signal.

7. The sensor system of claim 1 , wherein the core is constructed from a ferrite material.

8. The sensor system of claim 1 , wherein the wireless interrogator is disposed within an instrument thimble.

9. 1. A sensor system for a fuel rod including a fuel pellet stack, the sensor system comprising: a wireless interrogator disposed external to the fuel rod; A passive sensor portion disposed within the fuel rod; Equipped with The wireless interrogator includes: a primary transmitter configured to wirelessly output an interrogation signal; A secondary receiver; Equipped with The passive sensor unit includes: a primary receiver configured to receive the interrogation signal and to output an excitation signal in response to receiving the interrogation signal; a linear differential variable transformer (LVDT) including a core coupled to move in conjunction with expansion or contraction of the fuel pellet stack, to move based on pressure changes within the fuel rod, or to change temperature based on temperature changes within the fuel rod, the LVDT configured to receive the excitation signal and to output an output signal indicative of a position or temperature of the core; a secondary transmitter configured to receive the output signal from the LVDT and to output a response signal to the secondary receiver that is proportional to the output signal; Equipped with Sensor system.

10. an elongated member disposed between the core and the fuel pellet stack such that the core moves in conjunction with expansion or contraction of the fuel pellet stack; The sensor system of claim 9 , wherein the output signal of the LVDT is indicative of a position of the core.

11. a bellows coupled to the core such that the core moves in response to pressure changes within the fuel rod; The sensor system of claim 9 , wherein the output signal of the LVDT is indicative of a temperature of the core.

12. the core is coupled to vary its temperature based on temperature changes within the fuel rod; A change in the temperature of the core causes a change in the magnetic permeability of the core, The sensor system of claim 9 , wherein the output signal of the LVDT is indicative of a temperature of the core.

13. the LVDT includes a primary coil, a first secondary coil, and a second secondary coil; The sensor system of claim 9 , wherein the primary coil is electrically connected to the primary receiver and disposed between the first secondary coil and the second secondary coil.

14. The sensor system of claim 13 , wherein the first secondary coil and the second secondary coil are substantially identical.

15. each of the first secondary coil and the second secondary coil having a first end closest to the primary coil and a second end furthest from the primary coil; the first end of the first secondary coil is electrically connected to an output of the LVDT and the second end of the first secondary coil is electrically connected to the first end of the second secondary coil; The sensor system of claim 13 , wherein the second end of the second secondary coil is electrically connected to the output of the LVDT.

16. The sensor system of claim 1 , wherein at least one of the primary transmitter, the primary receiver, the secondary transmitter, and the secondary receiver is an inductor.

17. The sensor system of claim 9 , wherein the core is constructed from a ferrite material.

18. The sensor system of claim 9 , wherein the wireless interrogator is disposed within an instrument thimble.

19. an electronic processing device electrically connected to the wireless interrogator and configured to provide an input signal to the primary transmitter configured to cause the primary transmitter to output the interrogation signal; The sensor system of claim 9 , wherein the electronic processing device is configured to receive the response signal from the wireless interrogator and determine a position or a temperature of the core based on the response signal.

20. the LVDT has a generally cylindrical shape with a hollow center; The sensor system of claim 9 , wherein the core is configured to allow passage through the hollow center.

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