looks like a third party mod has removed kovarex enrichment process or renamed it. "bobingabout-enrichment-process" is impossible to research.
temporary fix 'commented out' line 88 of technology-nuclear.lua fixed. But not sure what mod has removed or renamed kovarex-enrichment-process.
permanent fix: check in data-final-updates if technology "kovarex-enrichment-process" exists, if not, remove prerequisite. this should solve, regardless of specific mod causing the deleted tech.
