France starts nuclear reactor on De Grasse Suffren-class attack submarine

France’s fourth Suffren-class nuclear-powered attack submarine, De Grasse (S638), has successfully started its nuclear reactor for the first time, achieving “divergence,” or the controlled initiation of a nuclear chain reaction. This milestone, confirmed by the French Ministry of Defense on December 12, paves the way for the submarine’s upcoming initial sea trials (alpha trials). The De Grasse is part of the Barracuda program, which aims to replace the aging Rubis-class submarines from the 1980s with six advanced Suffren-class vessels. The reactor was developed under the French Atomic Energy Commission with TechnicAtome handling design and maintenance, while Naval Group manufactured the reactor pressure vessels and integrated the propulsion system. The Suffren-class submarines, displacing about 5,100 tons submerged and measuring 99 meters in length, represent a significant upgrade in stealth, endurance, and combat flexibility compared to their predecessors. Powered by a pressurized water reactor generating approximately 150