Fessenheim 1 reinforcements complete

Tuesday, 9 July 2013

A project to upgrade the concrete basemat under EDF's Fessenheim 1 has been completed, allowing France's oldest operating reactor to continue producing electricity.

Worker safety was the priority during work to reinforce Fessenheim 1's basemat (Image: EDF)

Measures to increase the resistance of the unit's basemat to the potential effects of molten fuel were mandated by French nuclear regulators following European Union stress tests completed in response to the 2011 Fukushima nuclear accident. Had the work not been completed by the 30 June 2013 deadline set by France's Nuclear Safety Authority (Autorité de Sûreté Nucléaire, ASN) the reactor would have been forced to close for safety reasons.

The project has seen the thickness of the unit's concrete basemat increased by 50 centimetres to enable it to withstand molten corium - a mixture of molten cladding, fuel, and structural steel - in the event of the reactor vessel being breached during a severe accident. Additionally, an extended surface area of some 80 square metres has been provided that would allow corium to spread and to cool.

The work had to be undertaken below and adjacent to the reactor vessel, making extensive use of mechanised techniques with remote-controlled equipment guided by video. The project principally involved civil engineering activities, carried out by Bouygues. ASN inspectors monitored the work, carrying out three unannounced inspections as the project progressed.

Fessenheim's two 880 MWe pressurized water reactors have been in operation since 1977 and 1978 respectively. French reactors are required to undergo an in-depth regulatory review every ten years. In 2011, after Fessenheim 1's third ten-yearly review, the ASN ruled that the unit could continue to operate safely for a further decade provided the prescribed safety improvements were completed. The regulator has also approved a similar program of upgrades to be carried out at Fessenheim 2.

Although the completion of the project ensures that EDF could continue to operate unit 1 for another decade, both Fessenheim units could still face closure in less than four years for political reasons. French president Francois Hollande pledged in 2012 to close France's oldest nuclear plant by 2016, in fulfilment of promises made during election campaigns. A national period of debate over a potential 'energy transition' is ongoing, but its outcome remains to be seen.

Researched and written
by World Nuclear News