APR: your source for nuclear news and analysis since April 16, 2010

Tuesday, August 23, 2011

More Virginia Earthquake information

At this moment, we do not have any actual operational details from the North Anna Power Station other than that which we have reported. Briefly, those details can be consolidated as the following:

-Both reactors are shut down safely.
-Both reactors shut down when offsite power was lost.
-Offsite power was apparently lost as a result of an on-site switchyard fault.
-North Anna station is presently on diesel power.
-All four site diesels started normally. One stopped later on at some point.

We will likely have some better details from press releases and from reporting to the NRC tomorrow. For the moment, all we can do is speculate. Several further things are fairly clear;

-There will be a report to the NRC of an unusual event; the quake, and LOOP. The stoppage of one diesel may be a further event.
-Although not reported, hinted at, or speculated anywhere else, it should be noted in a prophylactic mode only that there may have been a lifting of either a primary or a secondary relief valve if the plants tripped from at or near full rated power. This is a common occurrence -- and by that we might just go ahead and say that we mean BOTH full reactor scrams and turbine trips from full rated power, and very brief lifting and reseating of relief valves when this happens on pressurized water plants. Many plants each year suffer turbine trips (a full load reject) from 100% power when inclement weather takes out the electrical network; for example, Surry had this exact thing happen this year and so did a number of others.

We report these two things here only because either or both would / will get press coverage and we want our readers to EXPECT them to be reported.

We might also at this point note that we're already aware of the declaration of an Unusual Event at at least six other nuclear plant sites. This is required to be declared as a result of the earthquake; this declaration is an acknowledgement of the earthquake being detected at the site or in the vicinity, and is NOT a declaration that anything unusual or problematic has occurred at the site. With the sole exception of North Anna, all of the plants that today declared UE's as a result of this earthquake have, as we understand it, cleared the conditional declaration. In point of fact none of the plants altered operation one bit, again except for North Anna.

One of the plant sites we understand declared, and then cleared, Unusual Event status is the Three Mile Island (Unit 1.) Do not be surprised when these UE reports hit the press tomorrow after appearing at the NRC site or in owner-operator press releases and then get legs.

Now, getting back to North Anna; I have some preliminary findings here, and some good solid data from the ANS Social Media List, on just what kind of quake the plants at North Anna are designed against and as soon as the USGS puts out some data in some form that people can understand (in other words, accelerations by location and not effects in Modified Mercalli scale, which is practically useless in comparing plant design data that's given in both accelerations in fractions or multiples of "g" or else in the old Richter scale) I will report on the comparison of those data here. For now, I might say it is too early to determine just what the acutal accelerations experienced on site were although it does appear that the plant was within seven to nine miles of the epicenter of a fairly shallow 5.9 Richter / VII Modified Mercalli quake. (Note that the VII region of damage as indicated graphically by the USGS for this quake is quite small, and on the latest USGS "Cities affected" list there is only one city/township in the VII range at all, the rest being less... but which oddly enough is the city North Anna Station is located in.)

Once some hard data comes in from the site's owner-operator we can make some further commentary on plant actions and conditions, but at this moment no news is good news and considering the plant capabilities (Westinghouse PWR) heat removal should be no problem. I will report again with any news, or any NRC posts, or owner-operator releases for the press as soon as I'm aware of them.

10:25 PM Eastern Tuesday August 23, 2011
ATOMIC POWER REVIEW

No comments:

Post a Comment