excore

Excore refers to components, instrumentation, or measurements located outside the reactor core, a term widely used in nuclear reactor engineering. It contrasts with in-core instrumentation, which is embedded within the fuel or core region. Excore systems provide a means to monitor reactor conditions from outside the core and are integral to power monitoring, safety, and diagnostic functions.

Excore detectors include neutron detectors such as ionization chambers and fission chambers mounted on the reactor vessel head or surrounding shielding, as well as gamma-ray detectors used to monitor leakage and ambient radiation. Their primary role is to provide reactor power indications, supplement in-core measurements, and support protection systems. They are generally easier to maintain and replace and are less exposed to intense irradiation than in-core sensors, but they sacrifice some spatial resolution and sensitivity to core flux distribution.

Operational use and calibration: ex-core readings are usually calibrated against in-core data or standardized benchmarks to account for shielding and geometry, and they are interpreted with correction factors. Temperature, aging, and shielding changes can affect readings. In practice, ex-core instrumentation is part of a multi-channel, redundant monitoring architecture, providing a reliable external check on core behavior.

See also: in-core detector.