“The trust that there have been open procedures here is destroyed. Gorleben has a bad mortgage,” BfS President Wolfram König told daily Neue Osnabrücker Zeitung on Thursday.
Documents from 1983 have shown that Helmut Kohl's conservative government tried to suppress unfavourable reports on the Lower Saxony site. Current Environment Minister Sigmar Gabriel from the centre-left Social Democrats has confirmed the existence of the files and called them a scandal.
“[Chancellor] Merkel should clearly distance herself from Kohl and take action,” he said.
Merkel spokesman Klaus Vater said Wednesday that the chancellor would examine the files closely, but criticised the timing of the old documents' release just three weeks ahead of the national election. Merkel was environment minister under Kohl in the 1990s.
BfS runs the facility, and König said the only way to solve the problem is for the organisation to conduct a thorough comparison to other possible storage sites.
After 40 to 50 years of examining the former salt mine, it would be impractical to use a geologically suitable site that wasn't legally defensible, he said.
“It would be a fiasco in the solution for the storage site question,” he told the paper.
Last month the BfS said that Germany needs to look for a new nuclear waste depot because the current Gorleben facility has “many birth defects” and the salt dome formations are not suited to be a permanent storage site.
In May, a leaked internal BfS assessment revealed that Gorleben was developed illegally.
Since work began on the underground facility in the 1980s, only permission for “exploration” has been granted.
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Work at Gorleben has been suspended since 2000, when the government decided to wait until 2010 to resume the controversial project.
The appearance of the documents has confirmed the doubts of nuclear energy opponents, who believed that Gorleben had been earmarked as a permanent storage depot before the safety of the salt dome had been adequately investigated.
Nuclear energy is deeply unpopular in Germany activists often stage protests at Gorleben, which is in the German state of Lower Saxony. The government has approved plans to get rid of its reactors by 2020. But high energy costs and greenhouse gas concerns have some politicians second-guessing the plans.