Functional requirements for PWR instrumentation
Internal reactor instrumentation

Nuclear instrumentation has two objectives that it must fulfill simultaneously:

• the first is to measure the absolute power level, which is equivalent to measuring the overall neutron flux. In general, the unit is the fraction of nominal power or % PN ;

• the second, as we've just seen, is the measurement of the 3D power (or flux) distribution inside the reactor. It is expressed in relative terms, i.e. with a dimensionless number.

Both types of measurement have their own accuracy and response time requirements, depending on how the corresponding signal is used.