Fessenheim (France)

Map of Fessenheim

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4 * 900 MW PWR units constructed by Framatome

Facilities in Fessenheim

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Cracking of upper tube support plates in older-model French steam generators is now considered a generic problem.
The problem, discovered by an alert inspector last April at Fessenheim-2, potentially affects 18 of EDF´s 34.900-MW PWRs, those with drilled-hole carbon steel tube support plates, according to nuclear safety agency DSIN. In at last one case it is bad enough to warrant replacement of steam generators already this year.
Inspection has shown four different degradation modes, three of which affect the No. 8 tube support plate (TSP) - just below the U-bend area - and the last affecting several plates. Their safety significance varies, but at Fessenheim-2, where large pieces of the No. 8 plate had disappeared - in a phenomenon later traced to improperly conducted chemical cleaning - regulators have called for installation of special cables to prevent vibrations of insufficiently supported tubes.
This year, EDF will install anti-vibration cables (developed after the Mihama-2 steam generator tube rupture event in Japan).
The spreading TSP cracking and wastage phenomenon has given further impetus to a review of steam generator internals which EDF bean early last year in response to an incident at Blayais-3 in June 1994, when two steam generator tube bundle wrappers (or shrouds) were found to have dropped down, one by 20 millimeters and the other by 5 mm. That phenomenon was traced to failure of welds between the wrapper and the steam generator shell.


Pump of the reactor cavity and spent fuel pit cooling was unavailable for RHR, because a liaison valve signaled as opened in the control room, was actually closed.


Corrosion at the bottom of containment liners found throughwall at some places during inspections.


During restart operators raised coolant pressure beyond 7MPa even though the SI system tanks were still isolated from the RCS -> discovered after 2 hours.


Circumferential cracks were found on the outer diameter of several tubes beyond the sludge zone in 1 SG. Inspection turned up a slight irregularity in the form of tubesheet holes.


A metallurgical defect 110 mm long and 30 mm deep was discovered in main steam lines. Defect indications had been found in 1986, but the recent inspections showed it had developed faster than expected.


Periodic monitoring of groundwater under the plant revealed an increase in tritium content in groundwater. 390 Bq/l (normal 40); source unknown.


During refueling 5 m³ of radioactive water were released into the Alsace Canal during emptying of a borated water tank which should be repaired - it had a hole of 50 mm diameter. 3.050 MBq tritium and 215 MBq of other radioctive elements have been released .