What are the benefits of gamma thermometers in nuclear reactors?
Precise, durable, efficient reactor power measurement
Gamma thermometers (GT) are proven sensors that use differential thermocouples to measure local gamma flux up to reactor full power. Although these gamma thermometers have generally been used in local power range monitors (LPRMs), they can be a fundamental component for new plant designs.
Because gamma thermometers require no drive mechanism and remain in place during normal reactor operation, they provide a durable, efficient alternative to gamma traversing incore probe (TIP) and neutron TIP detectors for LPRM calibration. Unlike neutron TIP detectors, gamma thermometers can provide independent LPRM power readings throughout reactor power operation without sensitivity depletion.
Product configuration and operation
Gamma thermometers are stainless steel rods with short sections that are thermally insulated from the reactor coolant by chambers of Argon gas. Interactions between the gamma flux and stainless steel sensor generate heat in the gamma thermometer. A thermally isolated thermocouple junction and a reactor water-cooled thermocouple junction create a measurable temperature differential that is proportional to the gamma flux. At steady-state reactor power condition, the gamma flux is then used to calibrate fission chamber sensitivity and measure reactor power.
Each gamma thermometer includes an integrated heater wire providing GT calibration against a known heat source independent of the gamma flux. Gamma thermometer calibration provides a repeatable response curve of thermocouple output from a known given heat input which is used to correlate sensor response with gamma flux.
Benefits
• Fixed in-core assembly
• Compact size, no drive equipment required
• Continuous measurement for in-situ power monitoring
and fission chamber calibration
• No fissile material
• Low cobalt construction to minimize neutron activation
lowering radiation exposure and reducing disposal costs
• More accurate representation of reactor power
FACT:
Reuter-Stokes has several decades of experience manufacturing gamma thermometers which have been used for calibrating LPRM fission chamber detectors in boiling water reactor (BWR) plant designs.
Reuter-Stokes gamma thermometers have been tested in four operating reactors in the U.S., Japan, and Mexico, including multiyear testing for up to ten years.
Gamma Thermometer Applications
Gamma thermometers are typically integrated in LPRMs and installed as a single GT LPRM device for nuclear power instrumentation (non-safety) applications.
The U.S. Nuclear Regulatory Commission has outlined a gamma thermometer methodology for calibrating in-core instrumentation in reactor monitoring. Some ASME Code assemblies have included Reuter-Stokes gamma thermometers.
As the nuclear industry is growing, gamma thermometers can be an integral piece of your control philosophy and risk mitigation strategy.
Customizable Solutions
Reuter-Stokes can customize gamma thermometers for a variety of lengths with various chamber lengths and positions, up to a maximum of 9 chamber locations within a GT detector assembly. We can incorporate the GT into a combined assembly with other types of detectors.
