PARIS (Reuters) - How can mankind signal to future generations thousands of years from now that hazardous radioactive waste is buried deep underground in eastern France -- by building a giant pyramid, a museum or a site for art projects or by employing geology?
Patrick Charton, who is in charge of a memory project at France's radioactive waste agency Andra, has been grappling with this philosophical question for the past 16 years.
France, the world's most nuclear-dependent country dotted with 58 reactors, has so far stored the radioactive waste produced in the past three decades in above-ground facilities at a nuclear fuel reprocessing plant in La Hague on the coast of Normandy.
But this site is vulnerable to a potential terror attack or a plane crash, so the agency is studying the possibility of permanently storing its most highly radioactive waste 500 metres below ground near Bure in eastern France.
The Andra already operates an underground laboratory in Bure, and if the storage project goes ahead, operations would start in 2025 and end around 2175.
The highly radioactive waste, enough to fill a football pitch, takes at least 100,000 years to cease being hazardous.
But how does one keep the memory of the burial site alive years after it is permanently shut?
Charton's team is working on that issue and has listed 26 different areas of study to preserve the memory of the site.
"It is not one miracle solution that we need but a cocktail of solutions that will allow us to preserve the memory of the site for a long period of time," Charton told Reuters in an interview.
Proposals for the site include building a museum on radioactive waste, a giant pyramid, or an artist house or betting on long-term digital filing.
Charton's favourite option is what he calls landscape geology to tip off archaeologists, generations from now, that there is something buried below their feet.
Once the tunnels are filled with canned radioactive waste, they will then be packed with earth, but it will have a different density than in the surrounding area, which may lead to a different type of vegetation growing on the surface.
"This could attract the curiosity of a geologist or of a landscape archeologist of the future," he said, adding that one idea was to engrave warning information about the site on copper where gallery holes have been filled.
This leads to another area of research that the Andra is working on: languages and symbols to ensure that future generations can still understand a warning message.
"What can happen once the French language will have disappeared? ... And can the meaning of symbols remain the same over big lapses of time?" asks Charton, who is also the deputy head of the Andra.
All these questions remain open to discussion as Andra researchers still have plenty of time to make a decision, given that the Bure site, if it goes ahead, will not be permanently shut for at least another 250 years.
"I hope that a building will exist for people to monitor the site and dialogue with the public," Charton said.
But the pyramid idea to signal the site is not necessarily the most well thought-out, notably from an aesthetic point of view, he said. "It's a bit outlandish."
(Additional reporting by Benjamin Mallet; Editing by Geert de Clercq and Marie Maitre)
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