Activists who say federal regulators have not done enough to fix flaws in nuclear power plants exposed by last year’s accident in Japan are arguing that a nuclear safety board should hear their case. The Atomic Safety and Licensing Board met in Boston Thursday to hear from attorneys for Pilgrim Watch, which opposes the Pilgrim Nuclear Power Station in Plymouth. The board was trying to determine if it should hold a broader evidentiary hearing about Pilgrim Watch’s concerns. An attorney for the Nuclear Regulatory Commission argued that under current rules Pilgrim Watch cannot try to overturn fixes that make nuclear plants safer. A Pilgrim Watch attorney said that even if the fixes make plants marginally safer, they still do not adequately protect the public, and that gives Pilgrim Watch standing to try to overturn them.