Patent Publication Number: US-11664132-B2

Title: Nuclear reactor system, transmitter device therefor, and associated method of measuring a number of environmental conditions

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional application claiming priority under 35 U.S.C. § 121 to U.S. patent application Ser. No. 15/952,597, entitled NUCLEAR REACTOR SYSTEM TRANSMITTER DEVICE STRUCTURED TO WIRELESSLY EMIT A SIGNAL BASED ON DETECTED NEUTRON FLUX, filed on Apr. 13, 2018, issued on Feb. 1, 2022 as U.S. Pat. No. 11,238,997, the entire disclosure of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     Field 
     The disclosed concept pertains generally to nuclear reactor systems. The disclosed concept also pertains to transmitter devices for nuclear reactor systems. The disclosed concept further pertains to methods of measuring environmental conditions with a transmitter device. 
     Background Information 
     In many state-of-the-art nuclear reactor systems in-core sensors are employed for measuring the radioactivity within the core at a number of axial elevations. These sensors are used to measure the radial and axial distribution of the 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 does not require an outside source of electrical power to produce the current and is commonly referred to as a self-powered detector and is more fully described in U.S. Pat. No. 5,745,538, issued Apr. 28, 1998, and assigned to the Assignee of this invention.  FIG.  1    provides a diagram of the mechanisms that produce the current I(t) in a self-powered detector element  10 . A neutron sensitive material such a vanadium is employed for the emitter element  12  and emits electrons in response to neutron irradiation. Typically, the self-powered detectors are grouped within instrumentation thimble assemblies. A representative in-core instrumentation thimble assembly  16  is shown in  FIG.  2   . The signal level generated by the essentially non-depleting neutron sensitive emitter  12  shown in  FIG.  1    is low, however, a single, full core length neutron sensitive emitter element provides an adequate signal without complex and expensive signal processors. The proportions of the full length signal generated by the single neutron sensitive emitter element attributable to various axial regions of the core are determined from apportioning the signal generated by different lengths of gamma sensitive elements  14  which define the axial regions of the core and are shown in  FIG.  2   . The apportioning signals are ratioed which eliminates much of the effects of the delayed gamma radiation due to fission products. The in-core instrumentation thimble assemblies also include a thermocouple  18  for measuring the temperature of the coolant exiting the fuel assemblies. The electrical signal output from the self-powered detector elements and the thermocouple in each in-core instrumentation thimble assembly in the reactor core are collected at the electrical connector  20  and sent to a location well away from the reactor for final processing and use in producing the measured core power distribution. 
       FIG.  3    shows an example of a core monitoring system presently offered for sale by Westinghouse Electric Company LLC, Cranberry, Pa., with a product name WINCISE™ that employs fixed in-core instrumentation thimble assemblies  16  within the instrument thimbles of the fuel assemblies within the core to measure the core&#39;s power distribution. Cabling  22  extends from the instrument thimble assemblies  16  through the containment seal table  24  to a single processing cabinet  26  where the outputs are conditioned, digitized and multiplexed and transmitted through the containment walls  28  to a computer workstation  30  where they can be further processed and displayed. The thermocouple signals from the in-core instrumentation thimble assemblies are also sent to a reference junction unit  32  which transmits the signals to an inadequate core cooling monitor  34  which communicates with the plant computer  36  which is also connected to the workstation  30 . Because of the hostile environment within the containment walls  28 , the signal processing cabinet  26  has to be located a significant distance away from the core and the signal has to be sent from the detectors  16  to the signal processing cabinet  26  through specially constructed cables that are extremely expensive and the long runs reduce the signal to noise ratio. Unfortunately, these long runs of cable have proved necessary because the electronics for signal processing has to be shielded from the highly radioactive environment surrounding the core region. 
     In previous nuclear plant designs, the in-core detectors entered the reactor vessel from the lower hemispherical end and entered the fuel assemblies&#39; instrument thimble from the bottom fuel assembly nozzle. In at least some of the current generation of nuclear plant designs, such as the AP1000 nuclear plant, the in-core monitoring access is located at the top of the reactor vessel, which means that during refueling all in-core monitoring cabling will need to be removed before accessing the fuel. A wireless in-core monitor that is self-contained within the fuel assemblies and wirelessly transmits the monitored signals to a signal receiver positioned inside the reactor vessel but away from the fuel would allow immediate access to the fuel without the time-consuming and expensive process of disconnecting, withdrawing and storing the in-core monitoring cables before the fuel assemblies could be accessed, and restoring those connections after the refueling process is complete. A wireless alternative would thus save days in the critical path of a refueling outage. A wireless system also allows every fuel assembly to be monitored, which significantly increases the amount of core power distribution information that is available. 
     However, a wireless system requires that electronic components be located at or near the reactor core where gamma and neutron radiation and high temperatures would render semi-conductor electronics inoperable within a very short time. Vacuum tubes are known to be radiation insensitive, but their size and electric current demands have made their use impractical until recently. Recent developments in micro-electromechanical devices have allowed vacuum tubes to shrink to integrated circuit component sizes and significantly reduce power draw demands. Such a system is described in U.S. patent application Ser. No. 12/986,242, entitled “Wireless In-core Neutron Monitor,” filed Jan. 7, 2011. The primary electrical power source for the signal transmitting electrical hardware for the embodiment disclosed in the afore-noted patent application is a rechargeable battery shown as part of an exemplary power supply. The charge on the battery is maintained by the use of the electrical power produced by a dedicated power supply self-powered detector element that is contained within the power supply, so that the nuclear radiation in the reactor is the ultimate power source for the device and will continue so long as the dedicated power supply self-powered detector element is exposed to an intensity of radiation experienced within the core. 
     Accordingly, one object of this disclosed concept is to provide a mechanism to transmit data of environmental conditions within a fuel rod of a fuel assembly to a remote location. 
     SUMMARY 
     These needs and others are met by the disclosed concept, which are directed to an improved nuclear reactor system, transmitter device therefor, and associated method of measuring a number of environmental conditions. 
     As one aspect of the disclosed concept, a transmitter device is provided. The transmitter device includes a neutron detector structured to generate electrical current from neutron flux, an oscillator circuit having an electrostatic switch electrically connected to the neutron detector, and an antenna electrically connected with the electrostatic switch. The oscillator circuit is structured to pulse the antenna. The antenna is structured to emit a signal corresponding to a number of characteristic values of the oscillator circuit. 
     As another aspect of the disclosed concept, a nuclear system is provided. The nuclear reactor system includes a fuel assembly having a fuel rod, and the aforementioned transmitter device. The neutron detector is located in the fuel rod. 
     As another aspect of the disclosed concept, a method of measuring a number of environmental conditions with the aforementioned transmitter device is provided. The method includes the steps of generating an electrical current with a neutron detector, storing energy in a capacitor until a trigger voltage of an electrostatic switch of an oscillator circuit is reached, and emitting a signal with an antenna corresponding to a number of characteristic values of the oscillator circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
         FIG.  1    is a schematic representation of a self-powered radiation detector; 
         FIG.  2 A  is a plan view of an in-core instrument thimble; 
         FIG.  2 B  is a schematic view of the interior of the forward sheath of the in-core instrument thimble assembly of  FIG.  2 A ; 
         FIG.  2 C  is a sectional view of the electrical connector at the rear end of the in-core instrument thimble assembly of  FIG.  2 A ; 
         FIG.  3    is a schematic layout of an in-core monitoring system; 
         FIG.  4    is a simplified schematic of a nuclear reactor system; 
         FIG.  5    is an elevational view, partially in section, of a nuclear reactor vessel and interior components; 
         FIG.  6    is an elevational view, partially in section, of a nuclear fuel assembly that contains an in-core nuclear instrument thimble assembly; 
         FIG.  7    is a schematic, partially cutaway, view of an electrostatic switch, in accordance with one non-limiting embodiment of the disclosed concept; 
         FIG.  8    is an enlarged schematic view of a portion of the electrostatic switch of  FIG.  7   ; 
         FIG.  9    is a schematic circuitry diagram of a transmitter device, including the electrostatic switch of  FIGS.  7  and  8   , in accordance with one non-limiting embodiment of the disclosed concept; 
         FIG.  10    is a graph showing voltage at a location in the transmitter device of  FIG.  9    versus time; 
         FIG.  11    is a graph showing voltage at another location in the transmitter device of  FIG.  9    versus time; 
         FIG.  12    is a schematic circuitry diagram of another transmitter device, in accordance with another non-limiting embodiment of the disclosed concept; 
         FIG.  13    is a schematic circuitry diagram of another transmitter device, in accordance with another non-limiting embodiment of the disclosed concept; and 
         FIG.  14    is a schematic circuitry diagram of another transmitter device, in accordance with another non-limiting embodiment of the disclosed concept. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The primary side of nuclear power generating systems which are cooled with water under pressure comprises a closed circuit which is isolated from and in heat exchange relationship with a secondary side for the production of useful energy. The primary side comprises the reactor vessel enclosing a core internal structure that supports a plurality of fuel assemblies containing fissile material, the primary circuit within heat exchange steam generators, the inner volume of a pressurizer, pumps and pipes for circulating pressurized water; the pipes connecting each of the steam generators and pumps to the reactor vessel independently. Each of the parts of the primary side comprising a steam generator, a pump and a system of pipes which are connected to the reactor vessel form a loop of the primary side. 
     For the purpose of illustration,  FIG.  4    shows a simplified nuclear reactor system, including a generally cylindrical pressure vessel  40 , having a closure head  42  enclosing a nuclear core  44 . A liquid reactor coolant, such as water, is pumped into the vessel  40  by pump  46  through the core  44  where heat energy is absorbed and is discharged to a heat exchanger  48 , typically referred to as a steam generator, in which heat is transferred to a utilization circuit (not shown), such as a steam driven turbine generator. The reactor coolant is then returned to the pump  46  completing the primary loop. Typically, a plurality of the above-described loops are connected to a single reactor vessel  40  by reactor coolant piping  50 . 
     An exemplary reactor design to which this invention can be applied is illustrated in  FIG.  5   . In addition to the core  44  comprised of a plurality of parallel, vertical, co-extending fuel assemblies  80 , for purpose of this description, the other vessel internal structures can be divided into the lower internals  52  and the upper internals  54 . In conventional designs, the lower internals&#39; function is to support, align and guide core components and instrumentation as well direct flow within the vessel. The upper internals  54  restrain or provide a secondary restraint for the fuel assemblies  80  (only two of which are shown for simplicity in this figure), and support and guide instrumentation and components, such as control rods  56 . In the exemplary reactor shown in  FIG.  5   , coolant enters the reactor vessel  40  through one or more inlet nozzles  58 , flows down through an annulus between the reactor vessel  40  and the core barrel  60 , is turned 180° in a lower reactor vessel plenum  61 , passes upwardly through a lower support plate and a lower core plate  64  upon which the fuel assemblies  80  are seated, and through and about the assemblies. In some designs, the lower support plate  62  and the lower core plate  64  are replaced by a single structure, the lower core support plate that has the same elevation as  62 . Coolant exiting the core  44  flows along the underside of the upper core plate  66  and upwardly and through a plurality of perforations  68  in the upper core plate  66 . The coolant then flows upwardly and radially to one or more outlet nozzles  70 . 
     The upper internals  54  can be supported from the vessel or the vessel head  42  and includes an upper support assembly  72 . Loads are transmitted between the upper support assembly  72  and the upper core plate  66  primarily by a plurality of support columns  74 . Each support column is aligned above a selected fuel assembly  80  and perforations  68  in the upper core plate  66 . 
     The rectilinearly movable control rods  56  typically include a drive shaft  76  and a spider assembly  78  of neutron poison rods that are guided through the upper internals  54  and into aligned fuel assemblies  80  by control rod guide tubes  79 . 
       FIG.  6    is an elevational view represented in vertically shortened form, of a fuel assembly being generally designated by reference character  80 . The fuel assembly  80  is the type used in a pressurized water reactor, such as the reactor of  FIG.  5   , and has a structural skeleton which at its lower end includes a bottom nozzle  82 . The bottom nozzle  82  supports the fuel assembly on the lower core support plate  64  in the core region of the nuclear reactor. In addition to the bottom nozzle  82 , the structural skeleton of the fuel assembly  80  also includes a top nozzle  84  at its upper end and a number of guide tubes or thimbles  86  which extend longitudinally between the bottom and top nozzles  82  and  84  and at opposite ends are rigidly attached thereto. 
     The fuel assembly  80  further includes a plurality of transverse grids  88  axially spaced along and mounted to the guide thimbles  86  (also referred to as guide tubes) and an organized array of elongated fuel rods  90  transversely spaced and supported by the grids  88 . Although it cannot be seen in  FIG.  6   , the grids  88  are conventionally formed from orthogonal straps that are interleaved in an egg-crate pattern with the adjacent interface of four straps defining approximately square support cells through which the fuel rods  90  are supported in transversely spaced relationship with each other. In many conventional designs, springs and dimples are stamped into the opposing walls of the straps that form the support cells. The springs and dimples extend radially into the support cells and capture the fuel rods therebetween; inserting pressure on the fuel rod cladding to hold the rods in position. Also, the assembly  80  has an instrumentation tube  92  located in the center thereof that extends between and is mounted to the bottom and top nozzles  82  and  84 . With such an arrangement of parts, the fuel assembly  80  forms an integral unit capable of being conveniently handled without damaging the assembly of parts. 
     As mentioned above, the fuel rods  90  in the array thereof in the assembly  80  are held in spaced relationship with one another by the grids  88  spaced along the fuel assembly length. Each fuel rod  90  includes a plurality of nuclear fuel pellets  94  and is closed at its opposite ends by upper and lower end plugs  96  and  98 . The fuel pellets  94  are maintained in a stack by a plenum spring  100  disposed between the upper end plug  96  in the top of the pellet stack. The fuel pellets  94 , composed of fissile material, are responsible for creating the reactive power of the reactor. The cladding, which surrounds the pellets, functions as a barrier to prevent fission byproducts from entering the coolant and further contaminating the reactor system. 
     To control the fission process, a number of control rods  56  are reciprocally movable in the guide thimbles  86  located at predetermined positions in the fuel assembly  80 . Specifically, a rod cluster control mechanism (also referred to as a spider assembly)  78  positioned above the top nozzle  84  supports the control rods  56 . The rod cluster control mechanism has an internally threaded cylindrical hub member  102  with a plurality of radially extending flukes or arms  104  that with the control rods  56  form the spider assembly  78  that was previously mentioned with respect to  FIG.  5   . Each arm  104  is interconnected to the control rods  56  such that the control mechanism  78  is operable to move the control rods vertically in the guide thimbles to thereby control the fission process in the fuel assembly  80 , under the motor power of control rod drive shafts  76  (shown in  FIG.  5   ) which are coupled to the control rod hubs  102 , all in a well known manner. 
     As mentioned above, it is often desirable to transmit data of a number of environmental conditions within a fuel rod (e.g., one of the fuel rods  90  of the fuel assembly  80 ) to a remote location.  FIGS.  7  and  8    show different schematic views of a component of such a device able to perform such a function. Specifically,  FIGS.  7  and  8    show different schematic views of an electrostatic switch  250  that may be employed in a transmitter device (e.g., without limitation, transmitter device  200 , shown schematically in  FIG.  9   ). The example electrostatic switch  250  includes an A terminal  252 , a B terminal  254 , a first vane  256  electrically connected with the A terminal  252 , and a number of other vanes  258 , 260  electrically connected with the B terminal  254 . In one example embodiment, the vanes  258 , 260  form a unitary component made from a single piece of material. Furthermore, it will be appreciated that the first vane  256  is configured to be located between the second and third vanes  258 , 260 . Referring to  FIG.  8   , the electrostatic switch  250  further includes a first conductor  262  and a second conductor  264 . The first conductor  262  is electrically connected with the A terminal  252  and the first vane  256 . The second conductor  264  is electrically connected with the B terminal  254  and the second and third vanes  258 , 260 . The second and third vanes  258 , 260  may be electrically connected with the B terminal  254  via external wiring (not shown). As will be discussed below, the electrostatic switch  250  is structured to move from an OPEN position to a CLOSED position. As shown in  FIG.  8   , the second conductor  264  includes a generally linear portion  266 , and the electrostatic switch includes a bracket (e.g., without limitation, U-shaped bracket  268 ) extending from the linear portion  266 . When the electrostatic switch  250  is in OPEN position, the first conductor  262  is spaced from the bracket  268 . When the electrostatic switch  250  moves from the OPEN position to the CLOSED position, the first conductor  262  moves into engagement with the bracket  268 . 
     Referring again to  FIG.  7   , the electrostatic switch  250  further includes an external housing  272  and a support fiber  274  (shown schematically). In one example embodiment, the external housing  272  is cylindrical-shaped (see, for example,  FIG.  8   ). In one optional embodiment, the housing  272  and the second and third vanes  258 , 260  form a unitary component made from a single piece of material. Furthermore, it will be appreciated that the second and third vanes  258 , 260  preferably extend from opposite sides of the housing  272  to proximate a middle region of the housing  272 . Continuing to refer to  FIG.  7   , it will be appreciated that the first vane  256  is located internal with respect to the housing  272 . Additionally, the support fiber  274  is coupled to the first vane  256  and the housing  272 , and is configured to provide a torsional preload on the first vane  256 . However, when the electrostatic switch  250  moves from the OPEN position to the CLOSED position, electrostatic attractive forces between the first vane  256  and the second and third vanes  258 , 260  overcome the preload of the support fiber  274  in order to move the electrostatic switch  250  to the CLOSED position. 
     Additionally, the electrostatic switch  250  has a mechanism to be maintained in the CLOSED position. Specifically, as shown in  FIG.  8   , the linear portion  266  of the second conductor  264  is located substantially parallel to the first conductor  262 . As such, when the electrostatic switch is in the CLOSED position, current flows through the first conductor  262  in a first direction (see arrow in first conductor  262 ) and through the linear portion  266  of the second conductor  264  in a second direction (see arrow in linear portion  266 ) generally opposite the first direction. As a result, this creates a repulsive electromagnetic force between the first conductor  262  and the linear portion  266  of the second conductor  264  in order to maintain the electrostatic switch  250  in the CLOSED position. Accordingly, as long as current is flowing (e.g., even at relatively low levels), the electromagnetic repulsive force maintains the electrostatic switch  250  in the CLOSED position. The electrostatic switch  250  will not return to the OPEN position until the repulsive force due to the current drops below the torsional preload of the support fiber  274 . This may occur when the current drops to near zero amperes. Thus, the electrostatic switch  250  is closed by electrostatic forces from an applied voltage, is maintained in the CLOSED position by electromagnetic forces due to the current flowing during closure, and then moves to the OPEN position when the current flow drops and the electromagnetic forces dissipate. 
     Continuing to refer to  FIG.  8   , in one optional embodiment, the electrostatic switch  250  further includes a support post  276 , a container  278 , and an electrically conductive substance (not shown) located internal with respect to the container  278 . The support post  276  is mechanically coupled to the first vane  256  and electrically connected to the A terminal  252 . In this manner, the support post  276  advantageously provides structural support for the first vane  256 . Furthermore, the first conductor  262  extends from the support post  276 . 
     The container  278 , with the electrically conductive substance located therein, electrically connects the support post  276  to the A terminal  252 . The electrically conductive substance is preferably a fusible metal alloy that is solid at room temperature. In this solid state, the fusible metal alloy in the container  278  provides structural support to the vanes  256 , 258 , 260  to minimize and/or prevent damage during fabrication and shipping of the electrostatic switch  250 . However, in operation, once the fuel heats up, the fusible metal alloy melts and the electrostatic switch  250  becomes operational. 
     When the electrostatic switch  250  is in the OPEN position, the first vane  256  does not engage either of the second or third vanes  258 , 260 . In one optional embodiment, when the electrostatic switch  250  is in the OPEN position, the first vane  256  is located substantially parallel to and is spaced from the second and third vanes  258 , 260 . It will be appreciated that in this OPEN position, a torsional preload on the support fiber  274 , and thus on the first vane  256 , maintains the electrostatic switch  250  in the OPEN position. As will further be discussed below, when a voltage is applied to the electrostatic switch  250 , electrostatic forces are developed that attract the first vane  256  toward the second and third vanes  258 , 260 . Once this force exceeds the torsional preload of the support fiber  274 , the first vane  256  will begin to rotate and will cause the electrostatic switch  250  to close. Accordingly, when the electrostatic switch  250  moves from the OPEN position to the CLOSED position, the first vane  256  rotates toward the second and third vanes  258 , 260 . 
     The transmitter device  200 , which includes the electrostatic switch  250 , will now be discussed in greater detail in connection with  FIGS.  9 - 11   . As shown in  FIG.  9   , the transmitter device  200  includes a self-powered neutron detector  210 , an oscillator circuit  220  electrically connected to the neutron detector  210 , and an antenna  240 . The neutron detector  210  is configured to be located in one of the fuel rods  90  ( FIG.  6   ). The example oscillator circuit  220  includes a capacitor  222 , an inductor  224  configured to be electrically connected with the capacitor  222 , and the electrostatic switch  250 . As shown, the capacitor  222  is electrically connected with the neutron detector  210 . The electrostatic switch  250  is also electrically connected to the neutron detector  210  and the antenna  240 . In operation, the oscillator circuit  220  is structured to pulse the antenna  240 , and the antenna  240  is structured to emit a signal corresponding to a number of characteristic values of the oscillator circuit  220 , as will be discussed below. 
     When the transmitter device  200  is located within one of the fuel rods  90  ( FIG.  6   ) of the fuel assembly  80  ( FIGS.  5  and  6   ), the neutron detector  210  is structured to generate an electrical current from neutron flux. Accordingly, the neutron detector  210 , and thus the transmitter device  200 , is advantageously self-powered (i.e., devoid of a separate powering mechanism). That is, the transmitter device  200  has only one single powering mechanism, that powering mechanism being the neutron detector  210 . Additionally, the transmitter device  200  is advantageously devoid of semiconductors. Many known attempts at providing a wireless mechanism to communicate data on environmental conditions typically require more power than is available from a neutron detector, and/or are not able to withstand the relatively harsh radiation environment due to the inclusion of semiconductors. In the example of  FIG.  9   , the capacitor  222  is electrically connected with the A terminal  252  of the electrostatic switch  250 , and the antenna  240  is electrically connected with the B terminal  254  of the electrostatic switch  250 . 
     The operation of the transmitter device  200  will now be discussed in detail. When the transmitter device  200  is located in one of the fuel rods  90  ( FIG.  6   ), the neutron detector  210  functions as a current source that charges the capacitor  222 . The voltage across the capacitor  222  increases as the energy is stored and it continues to climb until a trigger voltage V t  (see, for example,  FIG.  10   ) of the electrostatic switch  250  is reached. See, for example,  FIG.  10   , wherein voltage V 1  is measured at a location of the transmitter device  200  in  FIG.  9   , and the trigger voltage V t  of the electrostatic switch  250  is a predetermined voltage that is reached at this location. As shown, the voltage V 1  increases until the trigger voltage V t  of the electrostatic switch  250  is reached. Once the trigger voltage V t  of the electrostatic switch  250  is reached, the electrostatic switch  250  becomes conductive such that the A and B terminals  252 , 254  electrically connect the capacitor  222  to the antenna  240 . Stated differently, when the trigger voltage V t  of the electrostatic switch  250  is reached, the electrostatic switch  250  moves from the OPEN position to the CLOSED position and connects the capacitor  222  to the inductor  224 , thereby creating the oscillator circuit  220 . This closure by the electrostatic switch causes a relatively strong oscillation of the oscillator circuit  220 , which is inherently unstable, for a short period of time. The damped oscillation continues until the energy is dissipated by electromagnetic emissions from the antenna  240  and other losses (e.g., resistive losses). 
       FIG.  11    shows a graph of voltage V 2  versus time measured in the oscillator circuit  220 . As shown, the voltage V 2  generally begins at zero volts, oscillates for a relatively short period of time, and thereafter returns to zero volts before repeating the cycle. The dampening of the oscillations is due to energy being dissipated by electromagnetic emissions from the antenna  240  and resistive losses. Accordingly, the oscillator circuit  220  pulses the antenna  240 , which emits a wireless signal. 
     It will be appreciated that the period between the pulsed signals emitted by the antenna  240  corresponds inversely to the neutron flux detected by the neutron detector  210 . More specifically, the current generated by the neutron detector  210  is directly proportional to the neutron flux within the corresponding fuel rod  90  ( FIG.  6   ), and the trigger voltage V t  of the electrostatic switch  250  is relatively constant. As such, the period between pulses (see, for example, t 1  in  FIG.  11   ) is also inversely proportional to the neutron flux within the fuel rod  90  ( FIG.  6   ). Therefore, a suitable wireless receiver receiving the signal emitted by the antenna  240  can readily be calibrated to determine the neutron flux within the fuel rod  90  ( FIG.  6   ). Additionally, the energy of the pulsed transmissions of the antenna  240  remains essentially the same even if the reactor core power is very low. The pulses simply occur less often. Furthermore, because the frequency of the transmitter device  200  is independent of pulse operation, a device designer is able to select the frequency of the transmitter device  200 . This advantageously facilitates the use of many different transmitter devices at different locations in the fuel assembly  80  ( FIGS.  5  and  6   ), and in other fuel assemblies in the core. It will be appreciated that the neutron detector  210  and sensors could be located at advantageous locations along the height of the fuel assembly  80  ( FIGS.  5  and  6   ), whereas the transmitter circuit would generally always be in the fuel assembly&#39;s  80  ( FIGS.  5  and  6   ) top plenum (e.g., any fuel rod or assembly). An operator would be able to identify each individual transmitter device by its associated frequency, which is dependent on the values of the capacitance of the capacitor  222  and the inductance of the inductor  224 . Accordingly, environmental conditions such as neutron flux are advantageously able to be monitored wirelessly at many different locations within the fuel assembly  80  ( FIGS.  5  and  6   ). 
       FIG.  12    shows a schematic circuitry diagram of another transmitter device  300 , in accordance with another non-limiting embodiment of the disclosed concept. As shown, the transmitter device  300  is structured similar to the transmitter device  200  ( FIG.  9   ), and like components are labeled with like reference numbers. For ease of illustration and economy of disclosure, only the oscillator circuit  320  and the antenna  340  are indicated with reference numbers. However, as shown, the oscillator circuit  320  of the transmitter device  300  further includes a resistance temperature detector  326  electrically connected in series with the inductor  324  and electrically connected to the capacitor  322 . The resistance temperature detector  326  increases its electrical resistance as the temperature of the environment in which it is located increases. In accordance with one aspect of the disclosed concept, the resistance temperature detector  326  alters the signal emitted by the antenna  340  in a detectable way. More specifically, the amplitude decay rate of the voltage of the oscillator circuit  320  will be altered with the inclusion of the resistance temperature detector  326 . Accordingly, the change in the amplitude decay rate measured by a suitable wireless receiver will allow an operator to readily determine a given temperature at a location within the fuel rod  90  ( FIG.  6   ). It follows that the transmitter device  300  is advantageously able to provide an indication to an operator of neutron flux (i.e., in the same manner as the transmitter device  200  shown in  FIG.  9   ) and also temperature within the fuel rod  90  ( FIG.  6   ). 
       FIGS.  13  and  14    show schematic circuitry diagrams of two other transmitter devices  400 , 500 , respectively, in accordance with other non-limiting embodiments of the disclosed concept. As shown, the transmitter devices  400 , 500  are structured similar to the transmitter devices  200 , 300  ( FIGS.  9  and  12   ), and like components are labeled with like reference numbers. For ease of illustration and economy of disclosure, only the antennas  440 , 540  and the oscillator circuits  420 , 520  are identified with reference numbers. As shown in  FIG.  13   , the oscillator circuit  420  further includes a second inductor (e.g., without limitation, variable inductor  428 ) electrically connected in series with the first inductor  424  and the resistance temperature detector  426 . As shown in  FIG.  14   , the oscillator circuit  520  further includes a variable capacitor  528  electrically connected in parallel with the first capacitor  522 . The variable capacitor  528  is also electrically connected to the inductor  524  and the resistance temperature detector  526 . Advantageously, environmentally induced changes in the electrical values of either the variable inductor  428  or the variable capacitor  528  will produce a detectable shift in the pulse transmission frequency. 
     It will be appreciated that the transmitter devices  400 , 500  are advantageously able to provide an indication to an operator of up to three environmental conditions within the fuel rods  90  ( FIG.  6   ). For example, the transmitter devices  400 , 500  each, via the emitted signals of the respective antennas  440 , 540 , are each able to communicate to a wireless receiver data corresponding to the neutron flux and the temperature within the fuel rod  90  ( FIG.  6   ) in the same manner as the transmitter device  300 , discussed above. Additionally, the variable inductor  428  ( FIG.  13   ) and the variable capacitor  528  ( FIG.  14   ) are each structured to alter the frequency of the emitted signal of the respective antennas  440 , 540  in a detectable way. The altered frequency provides a mechanism by which a third environmental condition (e.g., without limitation, pressure, total neutron dose of a fuel rod over time, water flow rate) can be measured by the transmitter devices  400 , 500  and reported wirelessly to a suitable receiver. For example, the pressure within a fuel rod may create a deformation that causes a movement near a coil of the variable inductor  428  to cause a detectable frequency shift in the emitted signal of the antenna  440 , thus allowing the pressure to be monitored wirelessly. 
     It will be appreciated that a method of measuring a number of environmental conditions with one of the transmitter devices  200 , 300 , 400 , 500  includes the steps of generating an electrical current with the neutron detector  210 , storing energy in the capacitor  222 , 322 , 422 , 522  until a trigger voltage V t  of the electrostatic switch  250  is reached, and emitting a signal with the antenna  240 , 340 , 440 , 540  corresponding to a number of characteristic values of the oscillator circuit  220 , 320 , 420 , 520 . The method may further include altering the signal emitted by the antenna  340 , 440 , 540  with the resistance temperature detector  326 , 426 , 526 . The method may also further include altering the signal emitted by the antenna  440  with the second inductor  428 . 
     While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.