The Ex-Core Nuclear Instrumentation System (NuNIS) is used to monitor the neutron flux rate of leakage neutrons outside the reactor core. It conditions and amplifies the neutron flux rate signals, converts them into standard signals, and sends them to the PMS for power monitoring and reactor shutdown protection. NuNIS is capable of continuously measuring the ex-core neutron leakage flux rate during and for 4 months after an accident.