Control rod calibration of the Nigeria Research Reactor-1 low-enriched uranium core

Abstract

Calibration of the control rod (CR) is extremely important for startup, monitoring, com
pensating for the loss of reactivity and shutdown of the Nigeria Research Reactor-1 (NIRR
1) low-enriched uranium (LEU) core. The present work calibrated the entire length of the 
NIRR-1 LEU core CR (0–230 mm) experimentally using the period method. The maximum 
differential rod worth  was found to be 0.043 mk when the CR was midway out of the core. 
The integral worth for the entire length of the CR was found to be 6.49 mk. This value is 
0.51 mk (7.0%) less than the 7.0 mk obtained during the on-site zero-power experiment of 
the previous highly enriched uranium core. This implies that for the NIRR-1 to satisfy the 
minimum shutdown margin of 2.5 mk for a typical Miniature Neutron Source Reactor, the 
maximum excess reactivity the NIRR-1 LEU core can have to begin operation is 3.99 mk.