(Reuters) – Two people jumped a security fence at a GE Hitachi research reactor near San Francisco, the U.S. nuclear power regulator said on Thursday, raising concerns over a plant that is one of the few in the country that uses highly enriched uranium, a material that could be used to make an atomic bomb. The intruders jumped a security perimeter fence at the Vallecitos reactor in Alameda County on Wednesday afternoon, a 1,600-acre (647.5-hectare) site about 40 miles (64 km) east of San Francisco,

the U.S. Nuclear Regulatory Commission said on its website in a security threat notice. They escaped security at the plant after being detected, but shortly afterward suspects were detained outside the facility, the NRC said. The Alameda County Sheriff’s Office did not immediately respond to a request for comment. The NRC notice did not mention that the plant is one of the few in the country to use highly enriched uranium or HEU. Such plants have been under pressure from nonproliferation interests to convert to low-enriched uranium, or LEU, a material that cannot be used to make a bomb. READ MORE