Walter McKenzie's assignment toward the end of the Cold War was to mop up after mishaps at a nuclear weapons factory. With a crew of other laborers from rural Georgia, he swabbed away leaks and spills inside the secret buildings, until one day his body became so contaminated with radiation that alarms at the factory went off as he passed.

"They couldn't scrub the radiation off my skin -- even after four showers," McKenzie, 52, recalled of his most terrifying day at the Savannah River nuclear weapons plant near Aiken, S.C. "They took my clothes, my watch and even my ring, and sent me home in rubber slippers and a jumpsuit."

Later, when doctors discovered the first of 19 malignant tumors on his bladder, McKenzie followed the same torturous path as thousands of nuclear weapons workers with cancer: He filed a claim for federal compensation. It was denied.

Unable to access secret government files, or even some of his own personnel records, McKenzie could not sufficiently prove that he was exposed to something that may have made him sick. Nor can most of the 104,000 other workers, retirees and family members who have sought help from a federal program intended to atone for decades of hazardous working conditions at scores of nuclear weapons facilities around the country.