Sensitivity of the area method with mono isotopic fission chambers to reactivity changes in subcritical nuclear reactors

Abstract

High-level waste is an important safety issue in the development of nuclear power. A proposed solution is the transmutation of waste in fast reactors. The exclusion of the risk of supercriticality by using subcritical reactors is currently under development. Controlling the subcriticality level in such reactors presents difficulties. A problem is posed by the so-called space effect observed when using in reactors many neutron detectors in different locations of the core and reflector. Reactivity obtained from measurements, for example, by the Sjöstrand method, differs by nonnegligible values. Numerical corrections can partially improve this situation. The use of a monoisotopic fission chamber set, designed for a given reactor, when each chamber is intended for a specific position in the system, can improve the situation. A question arises about the sensitivity of the results to reactivity changes. This issue is analyzed by computer simulation for possible fissionable and fissile nuclides for the total range of control rod insertion, changes in reactor fuel enrichment, and fuel temperature. The tested sensitivity was satisfactory at most levels from several dozen to several hundred pcm. A case study was conducted using the VENUS-F core model.