Optical Gamma Thermometer Using Fiber Bragg Gratings
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Solution Overview
Problem
Conventional methods for monitoring thermal neutron flux in nuclear reactors, such as traversing in-core probes, are complex, costly, and prone to sensitivity deterioration, while gamma thermometers lack prompt response to power transients and provide a coarser map of reactor conditions due to limited deployment.
Innovation Solution
An optical gamma thermometer system using fiber Bragg gratings within an optical fiber cable is deployed to calibrate local power range monitors, offering a distributed and accurate measurement of gamma flux without the need for extensive cabling or drive mechanisms, allowing for real-time monitoring and calibration of reactor conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traversing in-core probes are used to monitor thermal neutron flux, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical traversing in-core probe system with an optical fiber-based gamma thermometer system. The optical fiber cable with fiber Bragg gratings eliminates the need for complex mechanical drive mechanisms, cables, and valve systems required for inserting and positioning traversing probes. This substitution maintains measurement capability while dramatically reducing system complexity.
Solution Approach 2:
The patent uses optical fibers to transmit gamma ray temperature measurements from the reactor core to external monitoring systems. The optical fiber cable acts as a distributed sensing system that copies the thermal neutron flux information through optical signals, eliminating the need for physical insertion and mechanical positioning of probes.
2Measurement precision
If traversing in-core probes are used for calibration, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The optical fiber-based gamma thermometer system enables continuous monitoring and calibration of thermal neutron flux without interrupting reactor operation. The distributed optical sensing allows real-time measurements at multiple locations simultaneously, eliminating the need to withdraw and reinsert probes for each calibration measurement, thus maintaining continuous useful action throughout the calibration process.
Solution Approach 2:
The optical fiber cable is pre-installed in the reactor core before calibration is needed. The fiber Bragg gratings are pre-positioned at specific locations to measure gamma ray temperature at multiple points simultaneously. This preliminary setup allows immediate begining of calibration measurements without time-consuming insertion and positioning operations.
3Device complexity
If conventional gamma thermometers are deployed, then device complexity is reduced, but measurement precision deteriorates due to limited deployment
Solution Approach 1:
The patent divides the optical fiber cable into multiple segments with fiber Bragg gratings at different locations along the reactor core. Each grating acts as an independent sensing element that measures gamma ray temperature at its specific position. This segmentation allows multiple measurement points to be integrated into a single distributed system, providing detailed spatial resolution of reactor power distribution while maintaining system simplicity.
4Device complexity
If optical fiber cable is used without drive mechanisms, then device complexity is reduced, but ease of operation worsens due to installation difficulty
Solution Approach 1:
The optical fiber cable is designed to be self-positioning within the reactor core through its physical deployment and anchoring at predetermined locations. The fiber Bragg gratings are inherently positioned at specific distances from the reactor wall based on the cable routing, eliminating the need for complex drive mechanisms. The system serves itself by using the reactor core structure as the positioning reference, making installation straightforward while maintaining measurement accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The optical gamma thermometer system provides a more accurate, cost-effective, and space-efficient means of monitoring reactor conditions, enabling real-time calibration and reducing the complexity and cost associated with traditional calibration methods, while offering a finer map of reactor power distribution.
Implementation Method 1
The optical gamma thermometer includes a fiber Bragg grating structure that reflects light at a selected wavelength
Implementation Method 2
The wavelength of the reflected light corresponds to a temperature of the metal mass
Implementation Method 3
A metal mass heats in the presence of gamma flux
Implementation Method 4
The temperature of the metal mass is not measured with a reading thermocouple, but with a fiber optic sensor
Implementation Method 5
An optical fiber cable, rather than with several cables, is used to transport the temperature information
Implementation Method 6
The interrogator includes a light source and a light receiver, and a processor
Data Source
Figure 1
Figure 2~8
Figure 3A~3
AI summary
An optical gamma thermometer (30) includes a metal mass (34) having a temperature proportional to a gamma flux within a core (15) of a nuclear reactor, and an optical fiber cable (32) for measuring the temperature of the heated metal mass. The temperature of the heated mass (34) may be measured by using one or more fiber grating structures (42) and/or by using scattering techniques, such as Raman, Brillouin, and the like. The optical gamma thermometer (30) may be used in conjunction with a conventional reactor heat balance to calibrate the local power range monitors (M) over their useful in-service life. The optical gamma thermometer (30) occupies much less space within the in-core instrument tube (24) and costs much less than the conventional gamma thermometer (T).