Multivariable measurements of the reactivity equivalent of control rods

The reactivity equivalent of control rods was measured by three-variable measurements. The reactivity of a core was measured upon simultaneous displacement of two control rods from a critical point. The worth of one of the control rods, when the other was not displaced from the critical point, could be obtained by data processing. The results are compared with those from two-variable measurement, in which the reactivity change is determined by the summation of a series of small changes. The results agreed very well between those of the three-variable and the two-variable measurements. The differences were within ±5%. The present experimental procedure is much simpler than required for the currently practiced two-variable measurement.