CASE STUDY | Small Modular Reactor Operator Realises Molten-Salt Monitoring with TRND
Non-invasive ultrasonic liquid-level detection for molten-salt (Gen-IV) reactor vessels at surface temperatures up to 600 °C
Key Deliverables
- Demonstrated non-invasive ultrasonic detection of molten-salt liquid level on high-temperature reactor piping — without penetrating the pressure boundary.
- HotSense™ high-temperature transducers paired with TRND monitoring electronics, delivering a simple high/low fill signal to plant control systems.
- Validated long-term survivability where sensors passed a continuous three-month dwell at 600 °C surface temperatures with no significant loss of ultrasonic performance.
- Staged, partnership-led qualification — transducer testing followed by electronics and control software — de-risking a first-of-a-kind Gen-IV reactor application.
Overview
A high-temperature ultrasonic thickness measurement inspection was required on an in-service vessel constructed from SA240 TP321 coarse-grained austenitic stainless steel, operating at temperatures between 270 °C and 360 °C. Initial attempts using a 5 MHz probe provided too much scattering as the wavelength at high-temperatures (lower velocity) presenting a low amplitude backwall response. A technical evaluation determined that a lower frequency 2.5 MHz, larger diameter HotSense™ transducer would be better suited to overcome signal attenuation in coarse-grain structures. The replacement probe was deployed successfully, achieving clear, consistent readings.
The Challenge
- Severe attenuation by scattering from SA240 TP321’s coarse austenitic grain structure caused loss of backwall echo at 5 MHz, producing insufficient signal-to-noise ratio (SNR).
- Elevated temperature conditions (270–360 °C) further increased material damping and reduced wavelength, increasing scattering and attenuation.
- A reliable in-service inspection was required without shutdown, meaning the transducer needed to perform at full operating temperature using high temperature couplants and established procedures.
- Industry compliance was mandatory, requiring work to follow ASME V, Article 4 and ASTM E797.
The Solution
- The site deployed TRND, using HotSense™ high-temperature ultrasonic transducers clamped externally to the pipe with strap deployment — no penetration of the pressure boundary.
- A thermal stand-off keeps the sensing element within its safe operating window while the pipe surface sits at up to 600 °C.
- Each transducer works in pulse-echo mode: when salt rises past the sensor a back-wall reflection appears; bespoke electronics gate this signal and output a simple high/low (level / no-level) switch to the plant.
- A multi-channel ultrasonic system with dynamic gain control drives sensors at low, medium and high fill positions and integrates with site power and control wiring.
The Execution
- Ultra-high-temperature transducers were manufactured, characterised and run under continuous ultrasonic operation at elevated temperature.
- In a three-month continuous dwell at 650 °C, all sensors passed with no significant degradation in amplitude or ultrasonic characteristics, confirming long-term survivability.
- The operator independently achieved (ongoing) testing of the sensors at elevated temperature on their own rig, validating the approach.
- A defined programme continues to harden the sensors against rapid thermal cycling for the most demanding locations — reflecting a transparent, partnership-led path to full qualification.