Engineers at Southern California Edison’s San Onofre nuclear plant have reported that vibration sensors meant to protect bearings in emergency diesel generators could conceivably shut them down during an earthquake.
actual reactor accident conditions would cause emergency systems to
bypass the sensor and keep the diesels running, the plant nonetheless
disabled the electronics in question and reported the discovery to the
Nuclear Regulatory Commission as an unanalyzed condition.
You can download a copy of Southern California Edison’s report to the NRC here.