Wide Range Neutron Monitoring (WRNM) System in Boiling Water Reactors (A Short Communication & Memorandum)

The WRNM (wide range neutron monitoring) is a newly developed neutron monitoring channel which was initially conceived as a means to meet Regulatory Guide 1.97 requirements for post-accident neutron monitoring. The scope was expanded to include the startup monitoring function with the aim of replacing both the source and IRMs (intermediate range monitors) in BWRs (boiling water reactors). The WRNMs, consisting of a newly designed fixed incore regenerative sensor and new electronics, which include both counting and MSV (mean square voltage) channels, have been tested in several reactors and its capabilities have been confirmed. The channel will cover the neutron flux range from 10³ nv to 1.5×10³ nv; it has greater than 1 decade overlap between the counting and MSV channels. Because of the regenerative fissile coating the sensor, even though fixed incore, has a life of approximately 6.0 full power years in a 51 kW/L BWR and similar situation has been proposed for newly designed small modular reactor such as BWRX-300 of General Electric Hitachi reactor.