Study Of Core Conversion To A Mixed Core Of HEU And LEU For The Dalat Nuclear Research Reactor

This paper presents the results of design and safety analysis performed in the framework of R-D project of Ministry of Science and Technology for inserting either 36 fresh HEU VVR-M2 (36% enrichment, 3 tubes, U-Al alloy fuel meat 1.40 g U/cm3 and 40.2 g 235U) fuel assemblies currently on-hand at the Dalat Nuclear Research Reactor (DNRR) or 36 LEU VVR-M2 (19.75% enrichment, 3 tubes, UO2-Al fuel meat 2.50 g U/cm3 and 49.7 g 235U) fuel assemblies to be procured when additional reactivity is required for continued operation around April 2006. The design and safety analyses presented in this report provide comparisons of neutronic parameters (fuel-cycle length, power distribution, neutron flux distribution, excess reactivity, shutdown margins, kinetics parameters), thermal-hydraulic safety margins and accident analyses (reactivity insertion transient analyse, maximum positive reactivity insertion, fuel cladding failure) for reloaded cores using 36 additional HEU VVR-M2 or 36 LEU VVR-M2 fuel assemblies in the DNRR. These results of analyses obtained enable to reach the conclusion that it is feasible to replace the current HEU VVR-M2 fuel assemblies with LEU VVR-M2 fuel assemblies that are fully qualified and have been commercially available since 2001 from the Novosibirsk Chemical Concentrates Plant in Russia. (author)