Determination of the excess of reactivity in a nuclear configuration and its influence on the power level

This work presents experimental results which show that the critical position of a given nuclear configuration changes with the reactor power (expressed by the current measurement). Thus, if the current is 0.6 x 10^-11 A (1 W), then the critical position is, BC1 = 0.0 % while 0.6 x 10^-9 A (100 W), BC1= 46.5 %. The difference is apparent because under a current of 10^-10 A, the reactivity is not significant. Therefore, it is recommended that for reactors like the RP-10 with a lot of neutrons at the 'background' level, the excess reactivity must be measured in current as 0.6 x 10^-9 A (100 W) not less. Finally, the excess of reactivity for the N^o 42 configuration was determined, which was 3032 pcm with uncertainty less than 1 %. (authors).