In-Reactor Laser Ultrasonic Sensor for Fuel Rod Pressure and Fission Gas

Statement of the problem or situation. The development and deployment of many advanced nuclear reactor concepts will require innovative sensors that can reliably operate in the nuclear reactor core. Radiation resistant sensors are needed for multi-point measurement of operational pressure, fission gas products, and cladding wall thickness in a fuel rod. Current sensor technologies in use cannot withstand the high-radiation high-temperature environment, even during reactor downtime. Statement of how this problem is being addressed. Current laser ultrasonic technology has already demonstrated the ability to measure internal pressure in a nuclear fuel rod, as well as changes in wall thickness of the cladding which may indicate corrosion or oxide buildup, and the potential to determine fission gas products from pressure measurement. A small laser ultrasonic probe is already being designed to make noncontact measurements of a fuel rod within a rod array assembly. Further development of this technology is proposed to extend it to the nuclear reactor environment during reactor downtime. Only the probe, which contains no electronics, need withstand this environment, as it is connected via optical fibers to a remote base station. What is to be done in Phase I? In the proposed project, application of laser ultrasonic sensor technology will be extended to in-reactor operation by accomplishing the following: Establish operational and environmental-resistance requirements for an in-reactor laser ultrasonic probe; model and develop probe designs; research probe materials and structures appropriate for use in the high-radiation, high-temperature reactor environment; research materials and structures appropriate for leading optical fibers into a reactor; design and build prototype probes and run thermal resistance tests on them; perform Phase II tests in a more realistic nuclear power plant environment; and develop a preliminary Phase II system design. Commercial Applications and Other Benefits The end users of radiation and high-temperature resistant laser ultrasonic probes developed in this project are the nuclear power utilities, and laboratories with test reactors. Beyond the monitoring of fuel rods, the sensor is expected to also find application in monitoring other reactor components such as the containment vessel and cooling components. The range of applications is extremely broad, and includes both pressurized water reactors and small high-temperature reactors. There is also potential for use in future fusion power reactors. Dual-use commercial markets include conventional (coal-fired or gas-fired) power utilities. This project will contribute to the scientific foundation for life extension of current nuclear power plants and improved instrumentation for more efficient functioning of the next generation of power plant designs. Use of the sensor will benefit the commercial plant operators and the manufacturers of plant components, particularly fuel rods. The public will benefit from reduced power costs and from safer, more reliable, and sustaining power generation.