The incore nuclear instrumentation system measures neutron flux distribution and temperatures in the reactor core. The purposes of the incore instrumentation system are to provide detailed information on neutron flux distribution and fuel assembly outlet temperatures at selected core locations. The incore instrumentation system provides data acquisition and usually performs no protective or plant operational control functions.
The incore instrumentation system includes:
- Incore neutron flux monitoring system
- Incore temperature monitoring system
Westinghouse Technology Systems Manual, Section 9.2. Incore Instrumentation System. <available from: https://www.nrc.gov/docs/ML1122/ML11223A264.pdf>.
Incore Temperature Monitoring System
The incore temperature monitoring system consists of incore thermocouples positioned at preselected locations to measure fuel assembly coolant outlet temperature for monitoring the core radial power sharing and coolant enthalpy distribution. It must be noted coolant outlet temperatures are more or less influenced by lateral flow mixing. This system has another purpose for some reactor designs, such as safety function monitoring. This data (coolant outlet temperatures) may be (depending on certain reactor design) used to:
- Provide the operators with indications of inadequate core cooling conditions during emergencies (e.g., core overtemperature)
- Provide information about temperature rise in the fuel assembly. This may indicate a serious core condition (e.g., channel blockage) and should be investigated.
- Provide inputs to the subcooling margin monitors
- Provide inputs to plant computational computer applications which use core-exit temperatures to determine fuel assembly enthalpy rises and limited power distribution information.
Westinghouse Technology Systems Manual, Section 9.2. Incore Instrumentation System. <available from: https://www.nrc.gov/docs/ML1122/ML11223A264.pdf>.