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Description
In the operation of nuclear reactors, the kinetic behaviour of the neutron population is driven by the delayed neutrons. The delayed neutrons fraction is thus one of the key parameters associated to nuclear safety.
The kinetic parameters (delayed neutrons fraction and generation time) of the LR-0 reactor operated by Centrum výzkumu Řež were measured by CEA using a current-mode neutron noise measurement technique. The reactor’s fission rate, which was needed to analyse the data, was calibrated using metallic foils activation (including gold, iron and tantalum). The results obtained show a good agreement with calculations carried out using TRIPOLI-4®, with a calculated value of 787 pcm (JEFF 3.1.1) for a measured value of 782 pcm.
The experimental campaign was also focused on studying the impact of the detector setup. Two fission chambers provided by CV Rez were used in several configurations. One detector was located in the reflector and was moved away from the core. As expected, a degradation of the signal obtained with the peripheral detector was observed, which led to an increasing bias in the results. Standard-point kinetic model were found insufficient to analyse the data obtained in configurations with a peripheral detector far from the core.
With the objective of completing the IRPhE benchmark of LR-0 with a best estimate value of the delayed neutron fraction in the reference configuration (LR(0)-VVER-RESR-003_CRIT-SPEC), a detailed uncertainty analysis was carried out. When integrating dosimetry uncertainty, calculated factors and experimental dispersion, the overall uncertainty is less than 3% (one standard deviation).