A “peace pilgrimage” to the Lawrence Livermore National Laboratory led to 48 arrests when the protesters attempted to block traffic heading into the lab, authorities reported. About 325 demonstrators gathered at the end of a five-day march from the Concord Naval Weapons Station to the lab, a distance of about 25 miles. Much of the nation’s nuclear arsenal is designed at the Livermore facility, 50 miles east of San Francisco, where research is also conducted in connection with the so-called “Star Wars” defense system. Those arrested included a number of clergymen and a protester named Eldridge Schneider, who was taken into custody for the 100th time at the lab. There were no injuries.