Extending Transmitter Life and Mitigating Accident Risk Through the Use of Proven Sensor Technology

Pressure, level, and flow transmitters are an integral part of a nuclear power plant’s primary cooling and steam generation system. To function accurately within the plant design specifications, normal operating and event instances of a Gen III or IV plant environment these transmitters will need to possess rugged and long life characteristics. These transmitters need to be high temperature, radiation, and high shock resistant. Lessons learned from legacy plants show the need to be able to both monitor and control cooling processes throughout the lifespan of the plant in addition to operating during and after a Loss of Coolant Accident (LOCA) occurrence. LOCA requirements associated with some new power plant designs stipulate extended performance after exposure to a 425°F (221°C) and 65 psig (4.5 bar) environment. An alternative and proven technology utilizes a bellows and control spring that reacts to the changes in pressure along with a radiation hardened and high temperature resistant Linear Variable Differential Transformer (LVDT) that converts the bellows travel into a VAC output signal. The LVDT VAC output is then converted into a 4 −20mA output using a signal conditioner containing high temperature and radiation hardened components. LOCA testing, performed on pressure and differential pressure transducers of various ranges, has shown that with proper material selection for the bellows, control spring, LVDT, and pressure boundary components, these sensors can successfully withstand environmental profiles of up to 600°F (315°C) at 250 psig (17 bar) for 30 minutes and 230°F (110°C) at 5 psig (0.34 bar), submerged, for 30 days. Application data has shown that these types of sensors possess long term stability and accuracy, require no periodic maintenance, and can have a forty year life. In addition, high impact shock testing per specification MIL-S-901 shows that the bellow/spring/LVDT sensor can withstand greater than 50g’s shock and still continue to function within specification.