The oscillator technique for cross-section measurements in a sub-critical system

Abstract

This paper reviews some aspects of the work undertaken at Idaho State University of the measurement of small worth reactivity samples using open loop oscillator techniques. An earlier study conclusively demonstrated the equivalency of the open and closed loop techniques with regard to uncertainties in reactivity values, i.e., they are limited by reactor noise. Because the open loop technique is much easier to implement we have concentrated all subsequent work using this technique.There has been interest in recent years to construct a large fast neutron sub-critical assembly to provide a platform for conducting measurements of various parameters including cross-sections. This assembly could be driven by a relatively modest neutron generator (e.g., D-T); the impetus is the belief that this could provide valuable data without having to construct an actual fast critical reactor with its substantial costs.However, most (if not all) of the perturbation/oscillation measurements in the past have been performed in a critical system. We are trying to answer the following questions in this program: 1) can meaningful measurements be conducted at sub-critical, 2) if so, down to what level of sub-criticality, and 3) down to what level of source strength? In this paper we will describe our experiments in our AGN-201 reactor at critical and sub-critical (to about k = 0.96, the minimum achievable with all control rods in the least reactive position).