Criticality safety parametric analyses of spent fuel storage pool for VVER-440
The article is devoted to the parametric analysis of the selected physical quantities that affect the neutron balance in the spent fuel storage facility located at the Mochovce NPP in Slovak Republic, which, due to safety and legislation, has 71 empty positions (without fuel assemblies). The calculation was performed in Serpent 2 code using the nuclear section library ENDF/B-VII. To perform the parametric analyses, a three-dimensional pin-by-pin model of the VVER-440 fuel assembly with a nominal average enrichment of 4.87 wt.% was created. The sensitivity of the multiplication factor to the change of pin pitch, absorption tube pitch, coolant temperature and density, density of fuel and fuel with Gd and weight fraction of boron in absorption steel ATABOR was analyzed. Parametric analysis showed that the multiplication properties of the system are affected by an increase in the pin pitch, an increase in fuel density, a decrease inthe pitch of absorption tubes, a decrease in coolant temperature, and a decrease in the boron content in the absorption tubes. The results obtained are consistent with theory, since most of the parameters considered affect the uranium-water ratio and, therefore, the multiplication coefficient, as expected. The results of parametric analyzes are used as input parameters for the spent nuclear fuel storage pool model for a proposal of an optimization scenario of the spent fuel storage pool by loading absorber parts of the VVER-440 control assemblies after their planned service lifetime in the reactor core. This way, the storage can be fully loaded.
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