The department has increased its counter-intelligence personnel, legalized polygraph testing for scientists and improved computer security to prevent leaks, he said.
Richardson also strongly supported the ratification of the Comprehensive Test Ban Treaty (CTBT), which bans the testing or new construction of weapons of mass destruction. The treaty was defeated in the Senate last year.
Richardson said the United States needs to set a good example for other parts of the world, especially in countries that have recently been testing nuclear weapons such as Pakistan and India.
"The failure to ratify tells India and Pakistan that we are not doing what we are telling them to do," he said. "It weakens our national security."
Richardson said open discussion with nations possessing nuclear technology is crucial.
"We must engage in talks with India, Pakistan, and China to get them discussing the issue [of nuclear weapons]," Richardson said. "India is a great nation, and for a long time we have ignored them."