French energy firm EDF on Monday said there was an "increase in the concentration of noble gases" in the cooling system of China's Taishan nuclear plant, after CNN had earlier reported a potential radiation leak. "The presence of certain noble gases (chemically inert elements like argon, helium or neon) is a known phenomenon, studied and provided for in the reactor operating procedures," the power station's part-owner EDF said in a statement, after subsidiary Framatome said it was "supporting resolution of a performance issue" at the plant in southern Guangdong province. jmi/tgb/lth