A reference neutron field for measurement of spectrum averaged cross sections

Abstract

A new reactor neutron reference field is proposed, which can be used for measurements of spectrum averaged cross sections (SACS). The reference field is identified in the center of a dry irradiation channel surrounded by six 3.3% enriched fuel assemblies assembled in the zero-power LR-0 reactor with negligible burn-up. The neutron field can be defined as a reference one, because of the well-defined neutron spectrum and neutron flux, well-characterized criticality and core power distribution, and reproducibility of results. Extensive experimental validation was undertaken. A new reference field can be used for the measurement of reaction rates and SACS used in nuclear data validation. It is shown that above 6 MeV the spectrum is undistinguishable from the thermal-neutron induced 235U prompt fission neutron spectrum (PFNS). Thus, when a reaction has threshold over this limit, the SACS in the thermal-neutron induced 235U fission neutron field can be derived from reaction rates obtained in this reference neutron field. A comprehensive set of SACS measurements with uncertainties below 5% in the reference field is presented.