Bragg Grating Optical Fiber Arrangement for Nuclear Fuel Rod Mapping
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Solution Overview
Problem
Current methods for measuring temperature and deformation in nuclear fuel rods, such as thermocouples, are limited by their invasive nature, cost, and susceptibility to electromagnetic interference, and fail to provide accurate spatial maps in harsh environments with high temperatures and pressures.
Innovation Solution
A mechanical support system for Bragg grating optical fibers is used, with two fibers: one fixed to measure deformation and the other free to measure temperature, allowing for simultaneous and accurate temperature and expansion measurements without disturbing the thermal flow or being affected by electromagnetic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermocouples are used to measure temperature, then temperature measurement is achieved, but the measurement is limited to point measurements with insufficient spatial resolution
Solution Approach 1:
The patent segments the measurement function by using multiple independent optical fibers along the rod structure, each capable of measuring temperature at its location. This segmentation allows continuous spatial temperature profiling rather than discrete point measurements, resolving the contradiction between measurement accuracy and spatial information completeness.
Solution Approach 2:
The patent transitions from one-dimensional point measurements (single location) to distributed measurements along the longitudinal dimension of the rod. By embedding optical fibers at multiple positions along the length of the rod, the system captures temperature distribution across the spatial dimension, eliminating information loss about the temperature profile.
2Strength
If thermocouples are welded to the wall, then secure mounting is achieved, but the weld creates a cold spot that distorts temperature measurement
Solution Approach 1:
The patent replaces the mechanical welding system with an optical measurement system. Instead of physically welding thermocouples to the rod (which creates thermal disturbances), the invention uses optical fibers that detect temperature remotely through Bragg grating wavelength shifts, eliminating the cold spot effect while maintaining measurement security.
Solution Approach 2:
The patent introduces an intermediary mechanism - the Bragg grating optical fiber - that transfers temperature information from the rod wall to the measurement system without direct thermal coupling. The optical fiber acts as a mediator that senses temperature through thermal expansion and refractive index changes without conducting heat away from the measurement point, thus avoiding distortion.
3Strength
If thermocouples are clamped by a supporting structure, then mounting is achieved, but the supporting structure disrupts cooling fluid flow and distorts temperature measurement
Solution Approach 1:
The patent replaces the mechanical clamping and supporting structure with an optical sensing system. The Bragg grating fibers are embedded within the rod structure itself rather than being externally mounted, eliminating the need for supporting structures that would interfere with cooling fluid flow while maintaining secure measurement capability.
Solution Approach 2:
The patent embeds the optical measurement fibers within the existing rod structure (nesting the measurement system inside the structure being measured). This eliminates the need for external supporting structures that would protrude into the cooling fluid flow, thus avoiding flow disruption while maintaining measurement security through integrated mounting.
4Loss of information
If electrical cables are used to transmit thermocouple signals, then signal transmission is achieved, but electromagnetic noise from high-power devices disrupts the signal
Solution Approach 1:
The patent replaces the electrical signal transmission system with an optical system. Instead of using electrical cables that are susceptible to electromagnetic interference, the invention uses optical fibers that transmit measurement data through light wavelength shifts (Bragg grating changes), which are immune to electromagnetic noise from high-power heating devices.
5Loss of information
If multiple thermocouples are installed to improve spatial resolution, then more measurement points are achieved, but the cost and complexity increase significantly
Solution Approach 1:
The patent employs a universal measurement platform where a single type of Bragg grating optical fiber system performs multiple measurement functions simultaneously - temperature measurement, deformation measurement, and strain measurement - along the entire length of the rod. This multi-functional approach provides comprehensive spatial information without the complexity of multiple specialized measurement systems.
Solution Approach 2:
The patent replaces the complex electrical connection and signal processing system required for multiple thermocouples with a simplified optical system. The optical fibers are passively embedded and read remotely using optical interrogators, eliminating the need for numerous electrical cables, connectors, and shielding complexities associated with multiple electrical thermocouple measurements.
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
This solution provides precise, non-invasive, and cost-effective temperature and deformation mapping along the fuel rod, minimizing hydraulic disturbances and electromagnetic interference, while maintaining accuracy in harsh environments.
Implementation Method 1
The presence within it of sections whose refractive index varies periodically. This periodic variation creates a Bragg grating whose effect is to reflect light within a certain wavelength range, and to transmit it outside of this range. Fiber elongation therefore alters the wavelengths transmitted or reflected by a Bragg grating whose period is changed.
Implementation Method 2
Fiber elongation, regardless of its origin (thermal or mechanical), results in a lengthening of the Bragg grating period within the fiber.
Implementation Method 3
Furthermore, a temperature variation can also cause a change in the fiber's refractive index.
Implementation Method 4
The support is in direct contact with the structure whose deformation is to be measured
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to an optical temperature and expansion measurement device for a structure (1, 2) in a harsh environment, in particular for a nuclear fuel rod wall, comprising: - a support with longitudinal axis X, adapted to be fixed on the structure, so as to be deformed by the expansion of the structure, and comprising at least a first and at least a second recess extending along the X axis; - a first Bragg grating optical fiber (12), intended to allow expansion measurement and temperature measurement, the first Bragg grating optical fiber being housed and fixed at least in part in the first recess of the support;- a second Bragg grating optical fiber (11), intended to allow a temperature measurement, the second Bragg grating optical fiber being housed at least partly in the second recess of the support, one end of the second Bragg grating optical fiber being left free along the X axis.;