Seeing a New Future for French Nuclear Site, After the Toxic Dust Has Settled VAUJOURS, France - On a walk through her garden on a recent afternoon, Lisa Leclerc ran a Geiger counter over her mushrooms. "See, normal," she said, looking at a reading showing ordinary background levels of radiation. The reading may have been normal, but the situation perhaps was not. The garden was tidy, the hanging baskets well-tended. But the neat spot where Ms. Leclerc had set up her patio furniture was not a typical garden. It was a corner of a former nuclear weapons testing site. Ms. Leclerc was tending her flowers in a 19th century fort about nine miles from central Paris, where for four decades scientists detonated hundreds of miniature bombs containing combinations of uranium and explosives. Formerly top secret, Fort de Vaujours was a key site for France's nuclear arms program, with core components of the country's first atom bombs developed here in the 1960s. Scientists blew up more than half a ton of uranium in 2,000 explosions at the fort, often outdoors, just 14 miles from the Eiffel Tower. There were no full nuclear detonations at Vaujours, but parts of the fort were coated in radioactive dust. The site was closed in 1997 and, after efforts at decontamination, sealed to the public. These days curtains flap from rows of overgrown buildings; radiation symbols and other graffiti cover the security post, which is filled, weirdly, with women's shoes. The empty housing of a vast supercomputer sits in gloom; vines spill into laboratories. The ruins recall the post-apocalypse landscape of Pripyat, the Ukrainian town evacuated after the 1986 Chernobyl disaster. Yet even as new questions are being raised about its safety, the site has its admirers. Ms. Leclerc and her partner, Bruno Mellier, have converted a former ammunition store there into a homey kitchen and cleared a secret garden. A local mayor allowed the couple to occupy the place in return for keeping vandals away. They do not live on the former nuclear test site, they just spend their days off there. On the recent afternoon, they were drinking black coffee on a patio near the blast chambers. They said they had been entranced by the fort's mystery. "I climbed through a hole in the fence and after that I could never get out," said Ms. Leclerc, a small woman with a bustle of red hair who now devotes herself to repairing the fort. It was fabulous. They are not the only ones with designs on the fort. Placoplatre, a subsidiary of the French conglomerate, Saint-Gobain, wants to demolish it to make way for a quarry for gypsum, a key ingredient in plaster. The company would extend a quarry it already operates next door, which would make it the largest gypsum producer in Europe, worth hundreds of millions of dollars and creating roughly 3,500 jobs. But others are concerned about the safety of the site, and more than 90,000 people have signed a petition to block the project, amid fears that demolition and digging will spread any residual toxic dust. The dispute has drawn in the French government. Government regulators had said the site could be considered sufficiently clean for redevelopment. But in February, independent researchers found contamination in bunkers, embarrassing the regulators who had repeatedly said they could find no evidence of it and reviving a long-running controversy over the site's safety. The environmental advocates who found the contamination have accused the Institute for Radioprotection and Nuclear Safety, a government agency, of either incompetence or a cover-up. "It's very bad," said Bruno Chareyron, head of the Commission for Independent Research and Information on Radioactivity, an independent group campaigning for greater transparency around atomic sites and which found the contamination. In France, he said, the Institute for Radioprotection and Nuclear Safety "is the reference for monitoring radiation." Built in 1881, Vaujours is a huge complex of raised battlements and underground bunkers. Housed inside is the abandoned test center. Vaujours" mission was to develop the core mechanisms of France's bombs, ensuring that a nuclear payload would detonate. The researchers used natural uranium, far more stable than the enriched material found in bombs and unable to accidentally cause a nuclear explosion. Though tests sometimes threw radioactive debris more than a kilometer, there was no risk of turning Paris into Hiroshima. "We never saw a mushroom cloud over the town center," joked Raymond Coenne, a former mayor of a neighboring village, who grew up hearing the explosions. The Atomic Energy Commission, which conducted the explosions, estimates 150 of the 600 kilograms of uranium it used was blown around the fort. Much of this was cleared but, because of how it was scattered, the agency cannot really know where there is residual contamination. In 2011, Christophe Nedelec, a local environmentalist, broke into the fort and, using an amateur Geiger counter, found three spots with elevated levels of radiation. For three years, government regulators, brought in by the site's owners, said they could find nothing to support his findings. But in February, Mr. Chareyron's watchdog group found contamination at the same spots - including a uranium fragment 70 times normal radiation levels - compelling regulators to acknowledge its presence. During the same tests, state technicians from the Institute for Radioprotection and Nuclear Safety again initially missed the contamination; Mr. Chareyron had to help them locate it. The mishaps have thrown the fort's safety into doubt. A government commission is now investigating whether the quarry can proceed. Delphine Ruel, a spokeswoman for the Nuclear Safety Authority, France's overall nuclear safety body which oversaw the tests, acknowledged Mr. Chareyron's findings, but said the agency's inability to find contamination could be attributed to methodological differences. The Institute for Radioprotection and Nuclear Safety has stressed its reports are not full summaries of pollution at Vaujours. The regulators have repeatedly said the contamination is too small to be dangerous. The amounts of uranium found are less than a few grams, and highly localized. They said work could proceed, provided precautions are taken. But a report since issued by the Institute for Radioprotection and Nuclear Safety has warned that Placoplatre's and its own radiation tests could not rule out that there could be "significant contamination" by toxic uranium dust. In February, the regulator had chosen not to check for that type of contamination, and Placoplatre had started its demolition in April. The company has since stopped, and now the regulator recommends the site be re-examined before demolition resumes. Gilles Bouchet, a head of quarry development at Placoplatre, said the company had taken precautions, equipping workers with masks and Geiger counters. He argues that Placoplatre is the best hope of finally decontaminating the fort. "We have a level of contamination considered acceptable for industrial works," said Mr. Bouchet. We have never said we won't find anything. If we do, we will clean it. The activists said the government's turnaround is hardly reassuring. How can we have any trust? Mr. Nedelec, the environmentalist, asked. A biochemist and a beekeeper, he has amassed dozens of documents detailing the extent of the uranium testing. "Either they are incompetent, or they are liars," he said. As he spoke, one of his bees crawled out of his jacket. There are no other explanations. Inside the ruins, Ms. Leclerc and Mr. Mellier, who sells windmills, spend their time clearing undergrowth and replastering. They were brought together, both in middle age, by a shared passion for the fort. Until recently, Ms. Leclerc had led the campaign against the quarry. She said she had started the radiation rumors, hoping to save the fort from demolition. Now, with plans to turn their corner into a museum, she supports the quarry; Placoplatre has offered to finance her project. Ms. Leclerc said she is sure there is contamination at the site, but in amounts too minuscule to cause health problems. She pointed to one of her cats and its amputated tail. "Mimi has lost her tail," she joked, "but it has nothing to do with uranium."