Anomaly on safety pumps of 900 MW reactors

An issue has been identified on December 9, 2005, on EDF 900 MW plants likely to involve the unavailability of low pressure safety injection and re-circulation pumps. Real scale tests were performed by EDF to understand the cause of vibrations that were observed on these pumps and confirm the adequacy of the compensatory provisions implemented. When tested at the temperature at which the pumps are supposed to operate, abnormal vibrations of pump engines were observed dues to dilatation and the up shifting of the rotor shaft. The expertise of the pumps has allowed to verify that this phenomenon doesn’t damage the pump. However, given the high level of vibration, the reliability of the pumps cannot be demonstrated, according to EDF, beyond about 30 hours in some accident situations. EDF has proposed to mitigate this anomaly by replacing the engine upper bearings by double stop bearings which will impair the up shifting of the rotor shaft. The French Nuclear Safety Authority (ASN) together with its technical support organisation the IRSN is currently investigating this proposal and will decide if EDF needs to implement complementary provisions. This event is rated at level 2 by the ASN

Location: All NPP - generic
Event date: Fri, 09-12-2005
Nuclear event report
Legenda & explanation