Quantification of system uncertainties in activation experiments at nuclear research reactors

Abstract

Neutron flux measurements in reactor cores are often used for code validation studies, however reported experimental flux uncertainties remain limited in scope. This work presents both a detailed assessment of several flux measurement uncertainties and a guideline for reporting these quantities. The effects of the sample position, the presence of 135Xe, the control rod positions, reactor power, and nuclear data during activation procedures were individually quantified at the McMaster Nuclear Reactor. NiCr flux wires were used to study the 51Cr (n,γ) activation reaction experimentally and through a series of MCNP6 simulations, and the SCALE-6.2.2 252-group library was used to study cross-section data uncertainty for use in translating activation measurements into neutron flux values. The placement of the sample and the reactor power measurements were found to be the most significant contributors to the overall measurement uncertainty. A procedure for reporting the results and uncertainties of an irradiation procedure is provided.