Delving through the fog of officially UN-clarified data, the risks are as follows.
The decay heat steam venting is dropping lake levels at potentially ONE MILLION GALLONS PER MINUTE. Lake levels are already dropping and obviously this cooling mechanism cannot continue indefinitely. Note the freshly dropped lake levels in this photo.
To resolve this issue the plant must restart electrical generation post haste. Apparently North Anna Nuclear is aware the need for speed in restarting generation, BUT they claim they are hurrying because they want to lower their customers electrical bills.
"Because the nuclear plants are the lowest-cost source of generation for our customers, we're making all efforts to return the units to service as soon as possible,"
Despite claims to the contrary, it is exceedingly plausible that the earthquake design limits were exceeded. This probability decreases the likelihood that the plant will restart safely and quickly. It also increases the likelihood of a single point failure in the decay heat steam cooling leading to a radiological escape. All of which increase the magnitude of RISK1 above.
A North Anna spokesman has stated on television that the plant was designed for a 6.2 earthquake and that they were "ready for this". To the contrary, because of the shallow nature of the quake, the probability is that ground motion and acceleration exceeded the design limit of the plant (but remained within the ultimate limit).
It is disturbing that a North Anna representative would declare the plant safe based on a general Qualitative measure such as a 5.8 earthquake being less than a 6.2 earthquake, as opposed to a specific Quantitative measures such as ground motion and acceleration of this quake versus the specific engineering limits for those values. Had the seismographs not been removed from the plant because of budget cuts, some of the fog regarding this issue would be clear-able.
Another Emergency has been declared at North Anna as a result of the 8/25/11 after shock; Event Number: 47196. The report states that "There was no radiological release". However, that statement is contradicted by reports that "No release of radioactive material occurred beyond the minor releases associated with normal station operations" One has to ask what exactly are normal releases when the plant is operating in an emergency mode, do they mean no more than expected under this type of emergency?
The fog of Risk3 aside, given that the probability the plant exceeded its design limit from the initial quake, further aftershocks increase the potential of surpassing the ultimate limit of the plant.
A mitigating factor for all of these risks is that the quake did not cause massive infrastructure disruption, hence the logistic response capability appears not to be affected.
Note: Hat tip to ENENEWS for several links