In a Refinery the Hydrocracking Process which occurs in the Hydrocracker Unit ( HCU) is a type of hydro processing operation where heavy oil is cracked in the. Also known as: HCK, HCU, unicracker, VGO hydrocracker. The Hydrocracking process in a Refinery is used to give fuel like. Refinery shuts HCU, SRU for overhaul. A refinery's ability to upgrade low-value products into high-value products and. Once considered the most valuable conversion unit in a refinery, the hydrocracking unit (HCU) is at a crossroads in terms of its direction and even sustainability.