An Optical Fiber-Based Gamma Thermometer with Simple Design and Potential for Adjustable Axial Segmentation

This invention proposes that an Optical Fiber-Based Gamma-Ray Calorimeter (OFBGC) sensor array can be designed, which does not require the distinct metallic thermal masses that are a part of the Optical Fiber-Based Gamma Thermometer (OFBGT).

The Need

As the world continues to grow and industrialize, the need for safe and efficient power is paramount. Currently, in nuclear fission reactors, there are Local Power Range Monitors (LPRM). They are ion chambers that contain fissile material. The electric current between their anode and cathode is monitored to determine the power distribution of the reactor. These LPRMs need to be periodically recalibrated, because it involves moving an ion chamber that is of similar design to the LPRMs, but whcih has not suffered significant burnup (called a Travelling Ion Probe (TIP)), to locations within the core that are near the LPRMs.

The Technology

Researchers at The Ohio State University have created a state-of-the-art gamma thermometer in order to provide accurate power distribution measurements without the complications associated with LPRMs and TIPs. This invention proposes that an Optical Fiber-Based Gamma-Ray Calorimeter (OFBGC) sensor linear array (hereafter called simply an OFBGC) can be designed, which does not require the metallic masses found in other such devices. Within a single OFBGC, an optical fiber is used to measure the axial temperature distribution of an annular cylindrical thermal mass that has a low thermal conductivity, such as silica glass. The thermal mass has the geometrical form of a small diameter circular cylindrical tube, which extends the total axial length of the OFBGC. The hole within the tube has a diameter that is slightly larger than the diameter of an optical fiber. An optical fiber runs the length of the tube and is used to measure the temperature of the thermal mass along its length. The thermal mass is centered within a thin-walled metallic outer sheath. A gas gap fills the volume, between the thermal mass and outer sheath. The temperature of the outer sheath is measured along its length with an optical fiber based temperature sensor that is attached to the outer surface of the sheath. The response of the OFBGC is the temperature difference, which is measured between the two optical fiber based temperature sensors (the one that is within the thermal mass and the one that is attached to the outside of the outer sheath). This response can be measured for any axial position within the OFBGC array; i.e. at any axial height. This design is superior to current state of the art because 1) the number of sensors in the OFBGC sensor array is adjustable and limited only by the spatial resolution of the OFBGC sensors, and 2) the OFBGC sensor design is simpler to build than the other sensor arrays available. Unlike TIPS and LPRMS, it does not suffer sensitivity loss due burnup. Therefore, it can be a permanent installation in nuclear reactors which mitigates the risks associated with recalibrating LPRMs.

Commercial Applications

  • Nuclear Power Plants
  • Manufacturing
  • Control Engineering


  • Efficiency
  • Safety
  • Simplicity

Research Interests

Thomas Blue is currently an Academy Professor, Mechanical & Aerospace Engr. at Ohio State. His research interests include:

  • Space nuclear systems
  • Advanced nuclear reactor instrumentation
  • Semiconductor sensors
  • Static and dynamic characterization of radiation-induced degradation of semiconductor power devices and optical fibers
  • Radiation hardness testing

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