Application of statistical correlation techniques for measurement of highly subcritical systems

The paper discusses the techniques developed by us for the measurement of the effective multiplication factor (K) of highly subcritical systems. The central idea in all these techniques is to use a high efficiency (>5%) neutron detection system. The K of the system is obtained by a statistical analysis of the sequence of detected neutron pulses. The results of three earlier techniques, (viz the Shift Register, the Dead Time α (1 st Moment) and the Asymptotic Prompt Variance techniques) tested on the storage tank of the PURNIMA II U-233 uranyl nitrate solution reactor at Trombay have been found to agree well with Monte Carlo calculations. However in all the three techniques knowledge of the source strength (S) is necessary for computing the K from the experimentally measured data. In order to avoid this requirement it is necessary to measure an additional quantity. The authors discuss two new techniques recently developed for this purpose