The traditional instrumentation in a nuclear power plant consists of temperature, level, flow, pressure, and power. Almost all actuation and monitoring signals are derived from these five measurements. Recently, however, diagnostic measurements have become increasingly more important. With the advent of new unobtrusive ways to determine the health of plant equipment, the diagnostic measurement field is becoming the fastest growing instrumentation field in nuclear plants. The capability to catch a problem before it leads to a failure is a powerful capability in a nuclear plant. It is expected that iPWRs will take advantage of the latest in diagnostic technology, especially in the field of prognostics.

Diagnostic signals are not likely to become safety related measurements, but they will become more prevalent in future large — and small-scale reactor designs. For large reactors they are important for license extension justification; for iPWRs they are important for containment entrapped systems, as the access to containment (at power) during an operating cycle is not possible in several iPWR designs.

Diagnostic technology has provided a significant advantage for nuclear plants over the past few years. Many decisions about current and future system health have been determined on diagnostic evidence. Currently, one of the most common of diagnostic measurements is temperature, especially with rotating equipment. Thermography ‘guns’ have provided additional insight for electrical components that may be malfunctioning. Oil samples are another precursor to failure in rotating equipment.

Vibration measurements on rotating, oscillating, or even stationary equipment can provide valuable insight on the equipment’s health. While all these measurements are valuable to a large traditional PWR, most of them require a maintenance technician to go out to the equipment and take measurements or samples. The key diagnostic measurement in an iPWR is going to be embedded or in-place sensors with automatic processing and indication, as design and operating constraints will prevent the human interface during power operations.

A manufacturing technique called shape deposition manufacturing (SDM) is a technique for embedding thin film sensors or fiber optic sensors for the continuous measurement of temperature and strain in a metal vessel or casing. Reactor vessels or other critical structures may have these sensors embedded during manufacturing for detection of increased strain or precursors to cracking.13 Another technology which will be considered for some equipment is the use of fiber sensors for strain measurement.14

The field of diagnostic measurement and testing is developing quickly. The advantages for iPWRs are obvious. With the iPWR paradigm for less staff and the fact that between cycle maintenance and testing may not be possible, diagnostic and prognostic tools are necessary. Embedded sensors and the automation of these sensors are important for iPWRs.

Good resources for prognostic information can be found in IEEE publications and IAEA publications. Grant work funded by the DOE has produced several approaches which have value.15