A pressure transmitter is a device that translates physical force to an electrical signal. The most common type of force transducer uses a diaphragm, piston, bourdon tube, or bellows to sense the physical force, and various strain/force sensing devices to convert the deflection of the physical element to an electrical signal. Traditional strain sensing devices include: capacitive cells, piezoresisitive strain gauges, piezoelectric quartz material, and electromagnetic devices.

Companies such as Rosemount, Cameron/Barton, Foxboro, and Ultra systems have specialized in safety system pressure measurements in the United States (US). These transmitters may still function successfully on some iPWR designs, but many will have to be re-engineered for different mounting configurations, size constraints, and environments. Many iPWR designers, when faced with a modification program, may choose to go with new technologies rather than modifying the old ones. The new technologies may offer advantages in size, redundancy, accuracy, and environmental resilience. Some of these new technologies include micro-electro-mechanical systems (MEMS) sensors, fiber optic sensors, and ultrasonic sensors.

In the optical fiber category, a company called Luna Innovations has developed and successfully tested fiber optic pressure sensors, like the one shown in Figure 6.1, in a research reactor environment. These fiber optic pressure sensors have been shown to operate in radiation environments with flux levels much higher than those compatible with most electronic pressure sensors. With traditional technology it is necessary to protect traditional electronic pressure transmitters from harsh radiation conditions near the core; this requires the use of long pressure sensing lines, which limit the response time to pressure transients and increase the number of wall penetrations. Luna’s fiber optic pressure sensors are designed to operate in harsh environments. When these pressure sensors were combined with Etalon-based fiber optic temperature sensors providing temperature compensation, drift effects were minimized. The attractiveness of this technology for iPWRs is obvious, with the elimination of sensing lines, the minimization of penetrations, the small size of the sensor, the rapid response to pressure fluctuations, and the operability in high radiation fields. With these attributes, this technology bears merit for primary and secondary side pressure measurement.1

Another new technology for pressure sensing is the polymer-derived ceramic MEMS sensor. At the forefront of this technology, a company, Sporian Microsystems

has developed a pressure/temperature sensor made to survive high temperatures (Figure 6.2). This technology offers a solution for pressure sensing in iPWRs due to its hardy environment survivability and its small size. The small size allows for the installation of redundant units and the measurement of pressure at many points, possibly with fewer penetrations than traditional sensors.

These new technologies have attributes like small size, heat survivability, radiation hardness, fast response, and low maintenance. These attributes are highly valued in iPWR designs for obvious reasons.