He won his first major title at the European championships in 2002, winning the C2 1000m final with Florin Popescu. In 2003 they became world champions at Gainesville, USA. Simioncencu was also a member of Romania's C-4 500 m crew which crossed the line second but was later awarded the gold medal after Russian Sergey Ulegin failed a doping test. A fourth-place finish in the C-4 200 m was also upgraded to bronze for the same reason.