NSUF 20-2909: Functional Testing of an Optical Fiber Based Gamma Thermometer in the HFIR Spent Fuel Pool

The objective of this work is to test the functionality of an Optical Fiber Based Gamma Thermometer (OFBGT) in the HFIR spent fuel pool, in one of the spent HFIR cores. The DOE has shown interest in the advancement of new sensors and instrumentation for data generation to improve nuclear power plant control and operations. Sensing technology could be improved, by the development of an OFBGT. An OFBGT is designed to relate temperature measurements made with an optical fiber to an energy deposition rate in a thermal mass, as a consequence of irradiation. An OFBGT could be used to calibrate local power range monitors (LPRMs) in BWRs, and would provide significant advantage over currently employed sensors. The current LPRM calibration method uses traversing in-core probes (TIPs), which must be inserted upon calibration, and removed after calibration, which is a time-consuming, cumbersome and potentially hazardous process. The use of OFBGTs would result in a more rapid calibration procedure, because OFBGTs are not susceptible to sensitivity loss due to burnup, and could be left in-core. Additionally, OFBGTs offer less risk, higher axial spatial resolution, and better scalability for insertion at many locations in the reactor’s transverse plane, due to the small size of OFBGTs in comparison to TIPS and conventional thermocouple–based GTs. As such, the development and use of OFBGTs is consistent with the initiative to include big data in the operation of reactors. This feature of OFBGTs makes them applicable to advanced reactors. Partly for this reason, the proposers were awarded a NEET project to develop OFBGTs and test them in University research reactors. The proposed research is complimentary in that it would expose the OFBGTs to a high gamma-ray flux such as might be encountered in an operating power reactor, without the complications that are introduced by neutrons, such as activation of materials and neutron-induced displacement damage. A prototypical OFBGT has been fabricated already at ORNL, as a part of the NEET project. The OFBGT will be monitored in-situ with an optical backscatter reflectometer (OBR), which will allow for distributed temperature measurements (and therefore distributed dose rate measurements) to be taken by the proposers in the OFBGT. The OFBGT will be placed in 3 spent fuel cores initially, with different ages, for 2 hours each, and then it will be placed in the most recently utilized core for 3 days. It will not require active monitoring by HFIR staff, but will be monitored, with an OBR, continuously by the proposers. The OBR output will allow the us to analyze the functioning of the OFBGT and to compare the OFGBT’s output with the results of computer models. The evolution of the OFBGT output with irradiation time will reveal the functional impact of fiber degradation on the OFBGT; including the effects of radiation induced attenuation and signal drift. The fiber in the OFBGT will be inscribed with fiber Bragg gratings (FBGs). HFIR staff has confirmed that the timeline associated with the project is sufficient for obtaining necessary approvals.

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Abstract	The objective of this work is to test the functionality of an Optical Fiber Based Gamma Thermometer (OFBGT) in the HFIR spent fuel pool, in one of the spent HFIR cores. The DOE has shown interest in the advancement of new sensors and instrumentation for data generation to improve nuclear power plant control and operations. Sensing technology could be improved, by the development of an OFBGT. An OFBGT is designed to relate temperature measurements made with an optical fiber to an energy deposition rate in a thermal mass, as a consequence of irradiation. An OFBGT could be used to calibrate local power range monitors (LPRMs) in BWRs, and would provide significant advantage over currently employed sensors. The current LPRM calibration method uses traversing in-core probes (TIPs), which must be inserted upon calibration, and removed after calibration, which is a time-consuming, cumbersome and potentially hazardous process. The use of OFBGTs would result in a more rapid calibration procedure, because OFBGTs are not susceptible to sensitivity loss due to burnup, and could be left in-core. Additionally, OFBGTs offer less risk, higher axial spatial resolution, and better scalability for insertion at many locations in the reactor’s transverse plane, due to the small size of OFBGTs in comparison to TIPS and conventional thermocouple–based GTs. As such, the development and use of OFBGTs is consistent with the initiative to include big data in the operation of reactors. This feature of OFBGTs makes them applicable to advanced reactors. Partly for this reason, the proposers were awarded a NEET project to develop OFBGTs and test them in University research reactors. The proposed research is complimentary in that it would expose the OFBGTs to a high gamma-ray flux such as might be encountered in an operating power reactor, without the complications that are introduced by neutrons, such as activation of materials and neutron-induced displacement damage. A prototypical OFBGT has been fabricated already at ORNL, as a part of the NEET project. The OFBGT will be monitored in-situ with an optical backscatter reflectometer (OBR), which will allow for distributed temperature measurements (and therefore distributed dose rate measurements) to be taken by the proposers in the OFBGT. The OFBGT will be placed in 3 spent fuel cores initially, with different ages, for 2 hours each, and then it will be placed in the most recently utilized core for 3 days. It will not require active monitoring by HFIR staff, but will be monitored, with an OBR, continuously by the proposers. The OBR output will allow the us to analyze the functioning of the OFBGT and to compare the OFGBT’s output with the results of computer models. The evolution of the OFBGT output with irradiation time will reveal the functional impact of fiber degradation on the OFBGT; including the effects of radiation induced attenuation and signal drift. The fiber in the OFBGT will be inscribed with fiber Bragg gratings (FBGs). HFIR staff has confirmed that the timeline associated with the project is sufficient for obtaining necessary approvals.
Award Announced Date	2020-02-05T14:13:59.903
Awarded Institution	Idaho National Laboratory
Facility	Advanced Test Reactor
Facility Tech Lead	Alina Zackrone, Kory Linton
Irradiation Facility	None
PI	Thomas Blue
PI Email	[email protected]
Project Type	RTE
RTE Number	2909