Core monitoring with fixed in-core instruments in PWRs

Fixed in-core instruments (ICIs) allow the core power distribution to be measured on a continuous basis and provide information which is used as input to on-line surveillance and monitoring systems. The use of fixed in-core detectors provides a more accurate assessment of the status of the core power distribution than that which may be inferred by the indirect measurement from ex-core based systems. The higher accuracy translates into a reduction of uncertainties and conservatism which are applied to measured parameters which are monitored to comply with Technical Specifications. Consequently, the higher accuracy results in an effective gain in margin to the licensed thermal limits. The thermal margin gain can be translated into higher allowable power peaks, wider operating spaces or additional flexibility in fuel management