Flow transmitters for NSSS purposes will follow much the same process as the safety system flow devices, only without the safety related qualification program. The devices will have to be accurate and reliable, but will not have the burden of a class 1E safety qualification.

The types of processes that will need measurement in the NSSS iPWR environment are:

• feedwater flow;

• steam flow;

• boric acid flow;

• reactor make-up water flow;

• reactor coolant pump (RCP) seal flow for models with pumps;

• let-down flow;

• charging flow.

In the NSSS controls environment, accuracy will be most important, especially for feedwater flow. Feedwater flow is an important parameter in the calculation of the calorimetric, a calculation from which the reactor power is assessed. The more accurate the instruments, the more megawatts the plant can produce. Also the accuracy afforded by digital control systems will further emphasize the need for accurate measurement devices to mate with the digital processing.

As some of these flow measurements will need to take place close to the reactor vessel, the devices may have to be more radiation, temperature, and pressure hardy than traditional NSSS sensors. This need may drive designers to newer technology, such as the ceramic-based MEMs sensor mentioned in the safety system discussion. Different variations of transit time methods and temperature-based flow methods may find their foothold here with NSSS-based applications. Further discussion on new technologies for flow measurement can be found in Section 6.2.5.