Four activists participating in a mock “foreclosure” of the Lawrence Livermore national lab in California were arrested without incident Sunday.They were part of a protest commemorating the 67th anniversary of the bombing of Hiroshima, Japan. While the lab was established in 1952, well after the Manhattan Project, it helped develop warheads and nuclear weapons technologies during the Cold War.A rally at a park near the lab included speeches from anti-nuclear-weapons groups and a survivor of the Hiroshima blast. At one point, it was reported that protesters fastened locks and paper chains to the lab's fence, which precipitated the arrests. KTVU news placed the size of the crowd at about 200, while a lab spokeswoman speaking to the Bay Area News Group placed the number at closer to 100. The protest follows the recent security breach at the National Nuclear Security Administration's Y12 facility in Tennessee, where three people made it through multiple fences to paint messages on the side of a secure building. The Livermore, Calif., lab no longer develops weapons, and it now conducts stockpile stewardship efforts, nonproliferation programs and research into advanced computing and other areas.