Based on the U.S. Nuclear Regulatory Commission Operations Center Event Reports For 08/23/2011 - 08/24/2011, fifteen nuclear plants made emergency notifications related to the 8/23/2011 Virginia earthquake. Out of the 15 different Nuclear plants which made emergency event reports, only the Calvert Cliffs Nuclear Plant nuclear operating plant reported that they DID NOT have any radiological releases [Event Number: 47184].
The most serious of the 15 emergency reports is from the North Anna Power Station in Virginia [Event Number: 47181]. The North Anna station went into complete shutdown as a result the earthquake; it lost all offsite power; it went on emergency backup generators (1 of which failed). The event report states "Decay heat is being removed via the steam dumps to atmosphere".
Based on a quick check of the design of the North Anna unit ( a 3 loop Westinghouse), Radioactive core coolant is being pumped to a heat exchanger were it is cooled by feed water. That non-radioactive feed water is turned to steam and released directly into the environment. Under normal conditions the steam is used to power the generator turbine and is NOT exposed to the environment but is returned in a closed loop system.
In the current situation of direct venting of steam into the atmosphere, the North ANNA plant appears to be operating in a single point of failure mode. Namely, a simple leakage in the heat exchanger (or any seals in the steam generation unit) could result in the escape of radioactive materials directly into the atmosphere via the ongoing decay heat steam venting.
Given that the nuclear reactor has just experienced an earthquake that appears to be at its design limit, it would be wise to be prepared for direct leakage of radioactive material into the atmosphere via the ongoing decay heat steam venting.
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