(Bloomberg) -- Electricite de France SA is investigating an incident during a test at a halted nuclear reactor last week, just as a series of repairs jeopardize the country’s power-supply security for the coming winter.

The utility had to stop a high-pressure hydraulic test of the primary circuit of its Civaux 1 reactor on Nov. 2 when steam was released in a room of the reactor building. The reactor wasn’t loaded with nuclear fuel, no one was hurt nor contaminated, and no radioactivity has been detected outside the building, according to EDF.

The impact of the incident, which is unrelated to so-called stress-corrosion cracks that have undermined the French nuclear giant’s reactor availability, still needs to be assessed, Regis Clement, EDF’s deputy-head for nuclear production, said at a news conference in Paris Tuesday.

The corrosion cracks hobbling EDF reactors this year have put a hole in its finances and made France -- typically an exporter of power to its neighbors -- a net importer. That, combined with Russia’s dwindling gas deliveries, has contributed to a spike in energy prices across Europe and stoked concerns of shortages in case of a windless cold snap this winter.           

The French nuclear giant so far is keeping the Jan. 8 restart date for Civaux 1 unchanged. It aims to have about 42 of its 56 reactors online in December as repairs at a dozen sites affected by cracks progress, up from 30 on Tuesday morning, Clement said. That number is due to rise to 46 in January.

Read more: EDF Strikes Another Blow to EU’s Power With Further Output Cut

At Civaux, where heavy repairs of corrosion cracks have been completed, an inner insulation tube of a pipe used to introduce sensors in the reactor vessel was ejected in a room beneath the reactor during the pressure test, Clement said. That’s because equipment installed specifically for the test phase broke, he said. 

EDF will send a robot in coming days to put the long radioactive tube in a container, he said. Employees will then be able to access the room, close a valve, and assess damage caused by water that’s still flowing into the room and into a special drain, Clement added.

“It’s way too early to say” how that will affect the restart of the reactor, he said.     


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