Patent ID: 7894565

Claim:
A method of determining the nearness to criticality of a nuclear reactor having a control rod configuration in a core region of a nuclear reactor vessel and a coolant moderator circulating therethrough, comprising the steps of: Monitoring a first source range detector signal (CMC) during a transient portion of the detector signal to obtain a neutron radiation level of the core when the coolant moderator is at a density corresponding to a first temperature; Raising the temperature of the core to a second temperature; Monitoring a second source range detector signal (CMH) during a transient portion of the detector signal to obtain a neutron radiation level of the core when the coolant moderator is at a density corresponding to the second temperature, the monitored first source range detector signal and the monitored second source range detector signal each having a background non-neutron signal component (N); Determining the background non-neutron signal component based upon the monitored first and second source range detector signals in accordance with the relationship N = { K eff H - K eff C 1 - K eff H + R ⁡ ( T H ) R ⁡ ( T C ) + F H F C - 1 } ⁢ C MC - C MH { K eff H - K eff C 1 - K eff H + R ⁡ ( T H ) R ⁡ ( T C ) + F H F C - 1 } - 1 Removing the background non-neutron signal component from the monitored neutron radiation level obtained at the second temperature to obtain background adjusted neutron radiation level; and Determining the nearness to criticality based upon the background adjusted neutron radiation level.