A report on the state of Moruroa Atoll in French Polynesia from the French Ministry of Defence has prompted calls for independent scientists and safety measures amid suggestions that it could collapse.
Moruroa and Fangataufa atolls were sites for French nuclear weapon testing from 1966 through to 1996.
The 2011 French Atomic Energy Commission report admits that underground nuclear tests have weakened the atolls.
A collapse would result in a 15-20 metre wave, release radioactive waste and prompt regional tsunami threats.
The president of Moruroa e Tatou, Roland Oldham, says his group only got the report this year, prompting concerns that it is not being kept in the loop.
Mr Oldham says independent researchers would allow preparations for a worst-case scenario.
"We are very worried about the situation because the French government is still keeping the information very secret and we don't get much information about it. To have independent inquiries by independent scientists. We are the people concerned, we live in this area of the pacific ocean and we don't have any information."