Bugey (France)

Map of Bugey

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A 540 MW GCR station shutdown since 1994.
4 * 900 MW PWR units operating since 1978/79 constructed by Framatome.

Facilities in Bugey

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Two sensors necessary for neutron measurement failed. The reactor had to be shut down. The problem lastet for 5 hours.


Violation of the technical operation specifications:
On the 3rd of Sept. 2008 EDF detected the breakdown of an electronic module, which misdirected the temperature regulation of a primary circuit.
The main primary circuit is a closed circuit, which contains pressurized water. The temperature limits of this circuit guarantee a margin which prevents the risk of boiling water. A malfunction in this area could lead to damage of the fuel would and damage at the pumps of the primary circuit.

source: www.asn.fr


Nuclear safety authority DSIN gave the green light last week, and Electricite de France (EDF) resumed shipping spent fuel this week, with a first convoy leaving the Bugey plant July 6.
Existing rules do not require reporting of deviations from the 4Bq/cm² level.
But the fact that the St. Laurent plant, for example, had no casks contaminated above 4Bq/cm² last year shows that it's possible to keep them clean.


Transformer fire at Bugey. EdF's Bugey-4 PWR will be down three to five weeks following a fire that destroyed its electric transformer October 25. The utility estimates the direct damages at 20-million French francs (about US$ 4-million) and the cost of the downtime at FF 35-million. The fire was caused by a short-circuit of undertermined origin.


Operators allowed RHR pump flow rate and intensity to fluctuate for 8 hours. The incident was caused by improper lowering the primary coolant level in order to drain SG. this can result in loss of RHR when an air-water mixture is sucked into the pumps.


Some electric wires of the RPS were found to be not properly connected.


10th-year RCS hydro tests revealed slight sweating of coolant (<1 liter/hour) from 1 of the 65 penetration sleeves in the reactor vessel head when pessure was increased from operating 155 bar to 207 bar. The penetrations through which control rod drive shafts enter the RPV are made of Inconel 600 an alloy especially susceptible to stress corrosion cracking. Penetration cracking was found also at Bugey-4 and Fessenheim-1. The cracks found are all longitudinal,1 is throughwall. Circumferential cracks would pose a more serious safety problem, because of the threat that penetrations under high stress could snap and be ejected. This would result in an unisolable leak. But even longitudinal cracks are undesirable because of acidic borated coolant can damage the RPV head. Penetration cracking is probably attributed to high vessel head temperatures.


During inspection it was discovered that 3 tubes that were scheduled to have been plugged during the last outage had been left unplugged and 3 healthy tubes had been plugged instead.


Test during refueling outage revealed that a valve on one of the containment spray circuits did not open. The valve is located just after the containment sump and is supposed to open automatically when sump water is placed in recirculation.


During tenth-year inspection corrosion was found at the bottom of steel containment liners (the liners are a metal coating 6 mm thick applied to the inner wall of the 1.2 m concrete containment to ensure leaktightness).Liner corrosion reveald to be a generic problem of EdF's 900 MW PWRs. It is a well known phenomenon that affected reactors elsewhere, notably older BWRs in the USA, whose steel containment plates "stuck" behind concrete and have corroded.


During tenth-year inspection corrosion was found at the bottom of steel containment liners


Coolant temperature rose by some 20 °C, reducing the margin to boiling to about 30 °C. Operating crew did not pay sufficient attention to coolant temperature because they were occupied by equipment testing.


Surface defects in welds of 6 pressure vessel nozzles found during outage. One of them is 500 mm long. Similar defects had already been observed in bimetallic welds in other components (SG, PRZ). Cracks are caused by surface contamination by borated water.


Scram on a high temperature, due to a drop in coolant flow, leading to heterogenous power distribution in the core.


Spurious opening of a valve in the secondary curcuit, led to inflow of large amount of cold water in one of the 3 SGs.-> Scram and safety injection because of a pressure drop in primary circuit.


1 of 2 treatment systems of the reactor carbon dioxide coolant was cut off. With only one of the systems working , the quantity of methane gas introduced into the CO-2 to prevent corrosion of the reactor's graphit moderator dropped below the limit. Condition lasted a few days before the problem was noticed and corrected.