Core Conversion of VVR-K Research Reactors

The conversion of the VVR-K research reactor to low-enrichment uranium fuel includes switching to a compact core with low-enrichment uranium and gradually transitioning from a light-water side reflector to a beryllium reflector with restoration of the working reactivity margin without makeup with fresh fuel. In 2015, the reactor was stopped in order to modernize the main elements of the core, the control and protection system for the channels of the working rods, and the emergency electric power source. First criticality of VVR-K with low-enrichment fuel followed by first start of the reactor occurred in spring 2016. The VVR-KN type FA specially developed for VVR-K make it possible to not only preserve but also improve the neutronphysical characteristics of the core. The design-basis reactivity margin of the working core load ~7%Δk/k is adequate for reactor operation for three 20-day cycles with ~10% average burnup reached in the central FA. The beryllium reflector is built up in stages starting at the fourth cycle. The beryllium reflector will make it possible to preserve the radial dimensions of the core and increase the neutron flux density in the central and peripheral irradiation channels.