WASHINGTON, Oct 5 (Reuters) - The U.S. nuclear power regulator last month suspended the shipment of radioactive materials and a hydrogen isotope used in reactors to China"s largest state-owned nuclear company, CGN, reflecting Washington"s concerns about the country"s buildup of atomic weapons. The Nuclear Regulatory Commission said in the order, dated Sept. 27, that the White House had determined that the suspension was "necessary to further the national security interests of the United States and to enhance the United States common defense and security consistent with the Atomic Energy Act of 1954." The suspension on the exports covers radioactive materials and deuterium for CGN, or China General Nuclear Power Group (1816.HK), its subsidiaries or related entities. Deuterium is a non-radioactive isotope of the element hydrogen that is used in heavy water fission reactors in nuclear power plants. The suspension further tightens controls set in 2018 by the administration of former President Donald Trump on shipments to China of civilian nuclear technology to prevent it from being used for military or other unauthorized purposes. CGN was placed on a U.S. blacklist in August 2019 for allegedly making efforts to acquire advanced U.S. technology and material for diversion to military uses in China. The Pentagon, in a report to Congress last year, estimated that China could at least double the number of its nuclear warheads over the next decade from the current stockpile "in the low 200s." The head of the U.S. Strategic Command, Navy Admiral Charles Richard, has warned lawmakers thisyear that a new generation of nuclear power plants China is developing could produce large amounts of plutonium that could be used to make nuclear weapons. China has said its nuclear power program is for peaceful purposes.