In-Pile Thermal Conductivity Sensor for Nuclear Fuel Rods
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Solution Overview
Problem
Current methods for measuring thermal conductivity of nuclear fuels within a reactor are limited, as existing devices are not suitable for extreme environmental conditions and require assumptions that may be invalidated by changes such as fuel swelling and cladding deformation, leading to inaccurate results and the need for costly out-of-pile measurements.
Innovation Solution
A sensor system comprising an insulator, a test material, a conductor, and a gas within an open volume, where an alternating current is used to heat the test material, and voltage is measured over time to calculate thermal conductivity, allowing for in-pile measurements with high accuracy and minimal disruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If steady-state or transient hot-wire methods are used to measure thermal conductivity, then thermal conductivity data can be obtained, but the measurements are inaccurate when fuel swelling and cladding deformation occur because the methods require assumptions about uniform fuel composition and density
Solution Approach 1:
The patent replaces mechanical contact-based measurement methods (hot-wire probes, thermocouples) with an electrical field-based measurement system. The system uses electrical current to heat the fuel rod and measures temperature distribution through electrical resistance changes, eliminating the need for physical contact and associated assumptions about fuel uniformity.
Solution Approach 2:
The patent introduces electrical resistance as an intermediary parameter to measure temperature distribution. Instead of directly measuring temperature with contact sensors, the system uses the fuel rod's electrical resistance, which changes with temperature, as a non-intrusive proxy for temperature measurement throughout the fuel rod.
2Measurement precision
If out-of-pile measurements are performed after irradiation to obtain accurate thermal conductivity data, then measurement accuracy improves, but the process becomes expensive and time-consuming due to repeated sample removal from the reactor
Solution Approach 1:
The patent enables the fuel rod to serve as its own measurement instrument. The fuel rod's electrical resistance properties are used to measure its own temperature distribution and thermal conductivity, eliminating the need for separate measurement equipment and out-of-pile testing.
Solution Approach 2:
The patent enables continuous thermal conductivity measurement during in-pile irradiation operations. The measurement system operates continuously while the fuel rod remains in the reactor, providing ongoing data without interrupting the irradiation process or requiring sample removal.
3Productivity
If in-pile measurement techniques are used to continuously monitor thermal conductivity during irradiation, then measurement efficiency improves and costs are reduced, but existing techniques are unsuitable for extreme reactor conditions and provide inaccurate results
Solution Approach 1:
The patent makes the fuel rod serve multiple functions simultaneously: it continues to generate power through fission while also serving as the measurement sensor for thermal conductivity. The electrical resistance measurement system works universally under various reactor operating conditions without requiring separate dedicated measurement hardware.
Solution Approach 2:
The patent exploits the change in electrical resistance with temperature to enable thermal conductivity measurement. By monitoring how electrical resistance parameters change during irradiation and heating cycles, the system derives thermal conductivity data that accurately reflects the fuel's condition under extreme reactor conditions.
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
Enables accurate, cost-effective, and non-destructive in-situ measurement of thermal conductivity, reducing the need for frequent sample removal and improving the understanding of fuel performance during irradiation, while being robust and inexpensive to manufacture and operate.
Implementation Method 1
An electrical source is configured to provide an alternating current through the conductor to heat the test material
Implementation Method 2
The thermal conductivity can be determined by comparing the temperature of the wire to the logarithm of time
Data Source
AI summary
A sensor for measuring thermal conductivity includes an insulator, a test material over the insulator, a conductor over the test material, and a gas within an open volume adjacent the test material and the conductor. An electrical source is configured to provide an alternating current through the conductor to heat the test material. Leads are connected to the conductor and configured to connect to a voltmeter. A method of measuring thermal conductivity includes disposing the sensor in a reactor core in which a nuclear fuel undergoes irradiation and radioactive decay. An alternating current is provided from the electrical source through the conductor to heat the test material. A voltage is measured as a function of time at the leads connected to the conductor. A thermal conductivity of the test material is calculated based on the voltage measured as a function of time. Methods of forming a sensor are also disclosed.