Former Japanese fishermen plan to seek compensation from the Japanese government for keeping undisclosed for decades records of their radiation exposure linked to a series of U.S. hydrogen bomb tests in the Pacific, sources said Thursday.

About 20 people, including relatives of deceased fishermen, are expected to file a lawsuit with the Kochi District Court possibly next month, each seeking about ¥2 million ($18,000) in compensation, the sources said.

It is the first time that a state compensation lawsuit will be filed in Japan in connection with the hydrogen bomb tests the United States conducted on the Bikini Atoll in the Marshall Islands in 1954 that began with a test explosion code-named Castle Bravo on March 1.