A method for monitoring a change in boron concentrations in a reactor coolant system as a result of a reactivity change during a nuclear plant outage comprising the steps of: monitoring an output signal representative of a count rate of a source range neutron detector positioned outside of a reactor vessel within proximity of a core of a reactor, as a function of time, during the nuclear plant outage; monitoring a temperature of a coolant within the reactor coolant system as a function of time; generating a compensation signal which is a function of the monitored temperature, that when combined with the count rate output signal compensates the count rate output signal for substantially any change in the count rate output signal resulting from a change in the temperature of the coolant; applying the compensation signal to the count rate output signal to obtain a compensated count rate output signal; and identifying a preselected increase in the compensated count rate output signal as an indicia of a change in boron concentration in the coolant; characterized in that the compensation signal is defined as a Downcomer Temperature Attenuation Factor, DTAF, given by the expression: DTAF T 1 = e − p T 1 − p T R R; where T 1 is the reactor coolant system temperature, T R is a reference temperature, the value of R is a function of distance between the source range detector and the reactor vessel and the effective macroscopic neutron removal cross section between the source range detector and the fuel assemblies on the core periphery, either empirically from count rate measurements taken at different temperatures while holding the reactivity constant, or analytically using standard neutron transport methods, and p is a density of the water inside the reactor vessel as a function of the reactor coolant system temperature. monitoring an output signal representative of a count rate of a source range neutron detector positioned outside of a reactor vessel within proximity of a core of a reactor, as a function of time, during the nuclear plant outage; monitoring a temperature of a coolant within the reactor coolant system as a function of time; generating a compensation signal which is a function of the monitored temperature, that when combined with the count rate output signal compensates the count rate output signal for substantially any change in the count rate output signal resulting from a change in the temperature of the coolant; applying the compensation signal to the count rate output signal to obtain a compensated count rate output signal; and identifying a preselected increase in the compensated count rate output signal as an indicia of a change in boron concentration in the coolant; characterized in that the compensation signal is defined as a Downcomer Temperature Attenuation Factor, DTAF, given by the expression: DTAF T 1 = e − p T 1 − p T R R; where T 1 is the reactor coolant system temperature, T R is a reference temperature, the value of R is a function of distance between the source range detector and the reactor vessel and the effective macroscopic neutron removal cross section between the source range detector and the fuel assemblies on the core periphery, either empirically from count rate measurements taken at different temperatures while holding the reactivity constant, or analytically using standard neutron transport methods, and p is a density of the water inside the reactor vessel as a function of the reactor coolant system temperature.