EXECUTIVE SUMMARY The nuclear industry has been slow to incorporate digital sensor technology into nuclear plant designs due to concerns with digital qualification issues. However, the benefits of digital sensor technology for nuclear plant instrumentation are substantial in terms of accuracy, reliability, availability, and maintainability. This report demonstrates these benefits in direct comparisons of digital and analog sensor applications. It also addresses the qualification issues that

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... be addressed in the application of digital sensor technology. Improved accuracy results from the superior operating characteristics of digital sensors. These include improvements in sensor accuracy and drift and other related parameters which reduce total loop uncertainty and thereby increase safety and operating margins. An example instrument loop uncertainty calculation for a pressure sensor application is presented to illustrate these improvements. This is a side-by-side comparison of the instrument loop uncertainty for both an analog and a digital sensor in the same pressure measurement application. Similarly, improved sensor reliability is illustrated with a sample calculation for determining the probability of failure on demand, an industry standard reliability measure. This looks at equivalent analog and digital temperature sensors to draw the comparison. The results confirm substantial reliability improvement with the digital sensor, due in large part to ability to continuously monitor the health of a digital sensor such that problems can be immediately identified and corrected. This greatly reduces the likelihood of a latent failure condition of the sensor at the time of a design basis event. Closely related to the concept of reliability, availability is the probability that the sensor will function on demand. Improvement in instrument loop availability with digital sensors is described again as a function of the continuous on-line monitoring. Advantages for digital sensors in maintainability are also discussed, highlighting improvements that reduce operational and maintenance burdens. Notwithstanding the benefits of digital sensors, there are certain qualification and licensing issues that are inherent with digital technology and these are described in the report. One major qualification impediment for digital sensor implementation is software common cause failure (SCCF). This is being addressed in a related Digital Technology Qualification project by the Oak Ridge National Laboratory. Finally, the transition to more advanced sensor technology is described in terms of the measurement principles used in legacy analog technology, current digital sensor technology, and emerging sensor technology for the measurement of pressure, level, flow, temperature, and neutron flux. The emerging technologies promise even greater design and performance benefits for digital sensors.