It is so often the simple things that bring down complicated mechanisms.
In a May 24 report, Entergy Nuclear Vermont Yankee discovered a missing conduit seal, which opened below-grade electrical switch rooms to flooding via an exterior manhole chamber.
It is likely that the missing seal was discovered during an examination of VY flooding vulnerabilities, recently ordered by the Nuclear Regulatory Commission in response to lessons from Fukushima. Otherwise, the missing seal might not have been discovered until flood-induced failure of the safety related components listed in the report.
There is some indication from news reports of the Fukushima site accident response that flooding of electrical components in below-grade structures contributed to power loss to vital safety systems.
The NRC has issued numerous warnings to its licensees that flooding of electrical equipment (cables, switches, relays, etc.) not designed for submerged duty can lead to, in the worst case, station blackout and loss of accident mitigation systems.
However, on the day before the Fukushima disaster, March 10, 2011, the NRC turned down New England Coalition's (NEC) final contention regarding Entergy Nuclear Vermont Yankee's license renewal application.
The NEC contended that Entergy had inadequate aging-management plans for non-qualified electrical components vulnerable to submersion.
Two weeks later, despite the pleas of the Vermont congressional team to sort out the Fukushima accident before doing so, the NRC went ahead and issued a renewed VY license.
The NEC recently objected that NRC's 2011 Annual Assessment Letter for VY should not, based on the scope of its annual inspections, claim that the overall plant was operated in a manner to protect the public health and safety.
The NRC typically inspects only 5 to 10 percent of licensee activities, systems, structures, and components (even on paper). In this case, the seal was among the 90 to 95 percent. It was uninspected post-Fukushima and, as likely as not, for many years before.
Just so we can stop laughing about tsunamis on the Connecticut River, the concern here is simple flooding, not monster waves.
In May 2010, the NRC reported that Entergy had found several electrical cable vaults (manholes) flooded at VY, exposing non-qualified electrical cables to submergence. The NRC permitted the issue to be buried in Entergy's Corrective Action Program, the activities of which are not reflected in public documents - and darkness once again fell on the Vernon shores of the Connecticut.