Preparing a new reference neutron field in the graphite-shaped reference LR-0 reactor core

Abstract

The study described in this paper aimed to modify the neutron spectrum using graphite insertion within the LR-0 reference core, which provides a well-defined neutron source. The modified spectrum is essential for various nuclear research applications. Reactor graphite is an essential material in nuclear physics and is non-negligible in developing new types of, e.g., high-temperature reactors. Experiments were conducted using activation detectors to map the thermal, epithermal, and fast neutron flux within the graphite prism. The reaction rates were determined by measuring the activity of the activation detectors using a high-purity germanium (HPGe) detector. The experimental results showed excellent agreement with MCNP code calculations, particularly for central axial positions, with discrepancies below 4%. The neutron spectrum shape was found to be position-dependent, and the thermal neutron share increased with proximity to the water moderator level. The study provides valuable insights into the neutron flux distribution within the modified graphite cavity and establishes a foundation for further validation experiments and precise mapping. The paper demonstrates the suitability of the LR-0 reactor and the modified graphite cavity for future benchmark experiments and neutron spectrum measurement.