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

To meet NRC regulatory requirements for post-accident power monitoring at a commercial BWR plant, an out-of-core (excore) neutron flux detector to measure reactor power was evaluated and installed. Several multigroup calculations and measurements predicted sufficient flux leakage outside the vessel and are described in detail. Since BWR plants currently use only incore detectors for flux monitoring, the excore 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 may economically utilize excore flux monitors to meet regulatory requirements