Level sensing and indication are a requirement for NSSS control systems. Several NSSS level measurements come from the protection system (safety system) through isolators, such as pressurizer level, steam generator level, and refueling water storage tank level. Other level indications such as boric acid tank level, volume control tank level, and accumulator tank level come directly into the NSSS processing electronics from field sensors and transmitters. It is expected that iPWR NSSS controls will have similar level signal requirements and a similar split between isolated safety signals and direct field signals as large PWRs. Those signals that come direct from the field, and do not go through the safety system, will have the flexibility of using newer technology for level detection, as the qualification of new devices will not be as rigorous or time consuming as a safety sensor qualification. The new technology discussion in Section 6.2.3 also applies to this section.

Another new technology that might be considered for level sensing is vibrating fork technology. This technology uses the principle of a tuning fork to detect level.

With this technology vibrating crystals are submerged in the medium, so when the density of the medium changes, the frequency of the crystals change. Used primarily as a level switch the crystal is placed at the level of actuation in a tank, and when the medium transitions that level, the oscillation changes and instigates a switch for an actuation. The actuation in many cases is an indication or alarm, but in some cases the actuation would be a control valve. The Rosemount 2120 level switch uses this technology. Although this technology is largely for level switches, a string of vibrating forks along the length of the vessel/tank could act as a level indication, not just a switch.

As mentioned in Section 6.2.3, fiber technology offers some efficient solutions for level measurement, and would likely be considered as a solution for certain tanks and vessels.