Influence of the Thermal Cutoff Energy on the Calculation of Neutronic Parameters for Light Water Reactor Lattices

Two of the methods that can be used for the measurement of the subcriticality of a multiplying system are the inverse kinetic (IK) and the pulsed neutron source (PNS) techniques. These methods depend considerably on correction factors and/or kinetic parameters, which usually need to be calculated using the same neutronic codes as those being validated via the experiments. The use of epithermal detectors to reduce the dependence of area-ratio PNS measurements on calculated correction factors was reported previously. In the current work, for the first time, epithermal detectors have been used for IK measurements. As in the case of the PNS experiments, these were carried out in core/reflector configurations with large spatial effects, systematic comparisons with thermal measurements clearly bringing out the considerably lower sensitivity of the epithermal IK results to calculational corrections. A new two-group pointkinetic model has currently been developed as an extension of the usual theoretical basis (employing a single energy group) for analyzing kinetic experiments. This has been essential for justifying the analysis methodology employed for the epithermal IK measurements.