In the event of an earthquake, a potential rupture of pipes from the water supply systems of the fire protection network (JPP circuit) and raw water filtration (SFI or CFI circuit) would flood the engines of the pumps from the raw water system (SEC), leading to the inoperability of the heat sink.
The SEC draws raw cold water from the river or the sea next to the NPP in order to cool safety systems. The SEC has two totally independent trains, each one being capable of ensuring reactor cooling.
The insufficient seismic resistance of a JPP pipeline was initially detected by EDF at the Belleville-sur-Loire NPP. Thickness measurements requested by the ASN were carried out by EDF in May and June 2017. They revealed thicknesses in several portions of the circuit that were less than the minimal thickness required to ensure the resistance of the JPP system against an earthquake. These degradations are the consequence of the corrosion which could have developed in the absence of an adequate preventive maintenance. ASN had provisionally rated this event at Level 1 of the INES in August 2017.
Following this event, a thickness measurement campaign was carried out on the JPP, SFI and CFI pipes of all NPPs potentially affected. As a result of this measurement campaign and the consequent analysis of earthquake resistance of the concerned piping systems, EDF stated on 10 October 2017 that the risk of a total loss of heat sink also concerns other 900 MWe and 1300 Mwe reactors. 20 reactors are concerned by a risk of a total loss of the heat sink (INES level 2) and 9 other reactors are concerned by a risk of partial loss (INES level 0).
Repairs to the JPP, SFI or CFI piping have been carried out in order to ensure availability of at least one SEC train on all of the reactors concerned. Further repairs will be performed to get back to full availability of SEC in case of an earthquake.
For the list of reactors concerned, see ASN press release.
Event date: Wed, 02-08-2017