The effect of heavy reflector on neutronic parameters of core

TL;DR

This study investigates how a heavy steel baffle influences the neutron behavior and criticality of a VVER-1000 reactor core, highlighting the neutron absorption effects of water-filled channels and validating iron cross section data.

Contribution

It provides experimental data on the impact of heavy baffles on reactor criticality and compares different nuclear data libraries for better modeling accuracy.

Findings

Water in cooling channels absorbs neutrons significantly.

ENDF/B-VIII.0 underpredicts criticality compared to experiments.

IAEA's 56Fe evaluation improves calculation accuracy.

Abstract

The reactor baffle is an important component of a nuclear reactor that fixes the location of the fuel assembly in the reactor core. The main types of baffles are called light or heavy. The light baffle has mostly the form of steel plates with outer space filled by water, and the heavy baffle is mostly a forged steel element. Both concepts have advantages as well as disadvantages. In the case of the light baffle, one does not need to solve the issue of void swelling, but the neutron economy is not ideal, while the heavy baffle has a good neutron economy, but void swelling is an issue. This paper deals with the effect of the heavy VVER-1000 baffle on criticality. Criticality was measured using a well-defined core composed of 6 fuel assemblies moved to a simulator of the VVER-1000 internals, which is located at the LR-0 reactor. The experiments confirm the fact that the water filling the cooling channels in the baffle has a strong neutron absorbing effect. The keff calculated using the ENDF/B-VIII.0 library significantly underpredicts the experiment, whereas calculations using a new evaluation of 56Fe by the IAEA (INDEN collaboration) give a better agreement. Generally, the presented results are suitable for validation of iron cross sections.