Out-of-core detector for power monitoring at commercial BWR plant

To meet NRC (US Nuclear Regulatory Commission) regulatory requirements for post-accident power monitoring at a commercial BWR (boiling-water reactor) plant, an out-of-core (ex-core) neutron-flux detector to measure reactor power was evaluated and installed. Several multigroup calculations and measurements, which predicted sufficient flux leakage outside the vessel, are described in detail. Since BWR plants currently use only in-core detectors for flux monitoring, the ex-core detector installation required backfit inside the reactor shield wall. The modification of removable shield blocks was readily accomplished during a scheduled outage. It is concluded that some BWR plants can economically utilize excore flux monitors to meet regulatory requirements.< >