Development of Surface Wave Magnetostrictive Sensors for Health Monitoring of Dry Storage Casks, 20-R9721

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Principal Investigators
Charles Duffer
Pavan K. Shukla
Alan Puchot
Todd Mintz

Inclusive Dates:  07/01/07 – 07/01/09

Background -  The U.S. Department of Energy and nuclear reactor utilities use dry storage casks to store spent nuclear fuel assemblies after initial storage in spent fuel pools. The storage casks are licensed for 20 years of service. However, it is expected that they may be used for longer periods because of potential delays in commissioning a high-level waste repository. The storage casks are usually constructed with metallic components that are several meters thick. These metallic components could undergo localized corrosion and stress corrosion cracking under certain environmental conditions, and thereby compromise the integrity of the storage casks. It is proposed that a high-frequency magnetostrictive sensor operating in the frequency range of 250 to 500 kHz could be used to detect corrosion-induced cracks and flaws that could form on the exposed metallic surfaces of storage casks. This proposed sensor would complement the existing magnetostrictive sensors that are used for inspecting the integrity of pipeline systems, plates, and heat exchangers tubes with wall thickness less than one inch. In addition, the proposed sensor could also be used for monitoring the structural integrity of various equipment in the nuclear power industry and pressure vessels in the chemical and petrochemical industries.

Approach - The project includes four research and development activities: assess corrosion induced flaw sizes for dry storage cask system materials using model and published data; design and fabricate the sensor; test the sensor for various metallic plates one-inch thick or more; and develop monitoring plan for one of the commonly used dry storage cask systems. Based on the sensor resolution for detecting crack sizes, range, and surface area coverage, a program plan will be developed that could potentially be used for continuously monitoring dry storage cask systems, thus ensuring their structural integrity.

Accomplishments - Fracture mechanics models and localized corrosion penetration data for stainless and carbon steel have been analyzed to determine the critical flaw sizes on exposed metallic surfaces of dry storage cask systems. The magetostrictive properties of various ferromagnetic materials have been reviewed. Sensor design and fabrication are in progress.

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