"Russia should not be reprocessing nuclear waste and most certainly should not be importing it," Igor Chestin, director of WWF's Russia branch, told AFP.
"Russia cannot ensure security" of such an installation, he said.
A day earlier, the head of Russia's nuclear energy agency Alexander Rumyantsev said that he did not see any obstacles to constructing the facility.
"Russia has experience in reprocessing combustible waste" as well as appropriate legislation, Rumyantsev told reporters after attending a meeting between Russian President Vladimir Putin and Mohammed ElBaradei, chief of UN's International Atomic Energy Agency (IAEA).
On Monday, ElBaradei said Russia was willing to build a "state of the art" geological depository for spent nuclear fuel and be the first in the world "to accept foreign spent fuel."
But Rumyantsev said the final decision on the facility has not been made and would likely take years.
"Experts at IAEA will be discussing the proposal for several years," Rumyantsev was quoted as saying by Russian news agencies. "And there isn't even agreement that the storage site will be created."
In June 2001, Russia's parliament adopted amendments to environmental legislation that authorized the import of spent nuclear fuel, provoking protests from environmental campaigners.