Optical fiber-based gamma calorimeter (OFBGC)
Inventors
Blue, Thomas E. • Birri, Anthony • Petrie, Christian M.
Assignees
UT Battelle LLC • Ohio State Innovation Foundation
Publication Number
US-12247937-B2
Publication Date
2025-03-11
Expiration Date
2041-03-26
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Abstract
An optical fiber-based gamma-ray calorimeter (OFBGC) sensor array which uses a thermal mass with a low thermal conductivity is provided. Advantages of the OFBGC sensor array include: 1) the number of sensors in the OFBGC sensor array is adjustable and limited only by the spatial resolution of the OFBGC sensors, within the OFBGC sensor array, and 2) the OFBGC sensor design is simpler to build than a conventional optical fiber-based gamma thermometer (OFBGT) sensor array. One purpose of the OFBGC is to determine the power distribution in nuclear reactors.
Core Innovation
The invention provides an optical fiber-based gamma-ray calorimeter (OFBGC) sensor array which incorporates a thermal mass with low thermal conductivity. This sensor array utilizes distributed optical fiber sensors running through an insulating tube placed within the thermal mass, allowing temperature monitoring along the length of the sensor. The OFBGC further comprises an outer sheath surrounding the thermal mass, with a gas gap backfilled with an inert gas such as argon between the mass and sheath. The core operation is based on measuring the temperature difference between the thermal mass and the outer sheath using optical fibers, enabling the determination of gamma-ray dose rates and reactor power distribution.
The problem addressed arises from the limitations of existing local power range monitors (LPRMs) in boiling water reactors, which require recalibration due to material burnup and present challenges related to complex calibration processes and the risk of radioactive material release. Conventional gamma thermometers (or gamma-ray calorimeters) employ fixed, distinct metallic masses and intricate construction, limiting their scalability and flexibility. The optical fiber-based gamma thermometer described in prior art provides limited adjustability and involves complex assembly, making widespread deployment or high spatial resolution difficult.
The OFBGC sensor array solves these issues by allowing the number of sensors to be adjustable and limited only by the spatial resolution of the sensors, rather than being fixed by the discrete placement of thermal masses. Its design, using low thermal conductivity materials in a continuous annular cylindrical form, is simpler to construct than arrays reliant on individually fabricated metallic masses. The design's simplicity, combined with the capability for fine spatial resolution by distributed optical fiber sensing, enables efficient, permanent deployment for power distribution measurement and LPRM calibration in nuclear reactors, and provides improved axial resolution compared to conventional thermocouple-based approaches.
Claims Coverage
There are two independent claims in this patent, each outlining a set of inventive features related to the structure and calibration of an optical fiber-based gamma calorimeter (OFBGC) and its sensor array.
Optical fiber-based gamma calorimeter with calibratable thermal mass and heating wire
The OFBGC comprises: - A thermal mass with an insulating tube disposed centrally. - A plurality of optical fiber sensors running through respective holes in the insulating tube, configured to monitor the temperature of the thermal mass. - An outer sheath enclosing the thermal mass, with a gas backfilling between the thermal mass and the outer sheath. - A heating wire running through two holes in the insulating tube, having a predetermined length and linear heating rate, used to derive a relationship with an axially dependent temperature difference between the optical fiber sensors to calibrate the OFBGC.
Sensor array utilizing optical fiber measurement of annular low thermal conductivity mass
The OFBGC sensor array includes: - An optical fiber for measuring the temperature of an annular cylindrical thermal mass with low thermal conductivity. - A heating wire with a predetermined length and linear heating rate, utilized to derive a calibration relationship with an axially dependent temperature difference between the optical fiber and a second optical fiber-based temperature sensor.
The inventive features focus on the combination of a low thermal conductivity annular thermal mass, distributed optical fiber temperature measurement, gas-filled gap, and an integrated heating wire for calibration, enabling adjustable segmentation and improved structural simplicity in gamma-ray calorimetry applications.
Stated Advantages
The number of sensors in the OFBGC sensor array is adjustable and limited only by the spatial resolution of the OFBGC sensors.
The OFBGC sensor design is simpler to build than a conventional optical fiber-based gamma thermometer sensor array.
The OFBGC enables improved axial resolution of reactor power profiles as compared to conventional thermocouple-based gamma thermometers.
The small footprint of the OFBGC allows it to be retrofitted into existing reactor guide tubes without disturbing facility conditions.
OFBGC sensors can provide a long term, permanent, and safe solution for monitoring the spatial power distribution within nuclear reactor cores.
Documented Applications
Calibrating local power range monitors (LPRMs) in boiling water reactors.
Determining the power distribution in nuclear reactors.
Providing improved axial resolution of reactor power profiles compared to conventional thermocouple-based gamma thermometers.
Use in conjunction with or as a replacement for conventional thermocouple-based gamma thermometers in nuclear reactors.
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