Virginia US Earthquake - Nuclear Plant

[QuantumPion]

Virginia US Earthquake -- Nuclear Plant

The earthquake that just hit the east coast was centered on Mineral, VA, right where http://en.wikipedia.org/wiki/North_Anna_Nuclear_Generating_Station" is.

 

[elektrownik]

The earthquake that just hit the east coast was centered on Mineral, VA, right where http://en.wikipedia.org/wiki/North_Anna_Nuclear_Generating_Station" is.

From reuters:

Traffic lights were knocked out throughout Washington, and units at a nuclear power plant in Virginia went off line by the quake.

 

[~kujala~]

The earthquake that just hit the east coast was centered on Mineral, VA, right where http://en.wikipedia.org/wiki/North_Anna_Nuclear_Generating_Station" is.

It was 5.9:

http://earthquake.usgs.gov/earthquakes/recenteqsus/Quakes/quakes_all.php

Edit: I am 100 % sure it was 5.9 a while ago. Just seconds ago they have updated it:
MAP 5.8 2011/08/23 17:51:04 37.936 -77.933 6.0 8 km ( 5 mi) SSW of Mineral, VA
So it's now 5.8.

Edit 2: And back to 5.9:
MAP 5.9 2011/08/23 17:51:03 37.975 -77.969 1.0 6 km ( 4 mi) SSE of Louisa, VA

The Operating Basis Earthquake for North Anna is 0.06 g (5.4 on
the Richter Scale) and the Design Basis Earthquake for North Anna is 0.12 g (5.9 on the Richter Scale).
(year 2003)

http://pbadupws.nrc.gov/docs/ML0334/ML033440194.pdf
http://www.expertglossary.com/definition/operating-basis-earthquake-obe
http://www.expertglossary.com/water/definition/design-basis-earthquake-dbe

This means there could be some damage but not for components important for safety.
(fingers crossed)
(If they have updated their earthquake parameters since 2003 the situation could be even better.)

 

[QuantumPion]

North Anna has upgraded the event from an unusual event to an alert. They are currently running on diesels.

They upgraded to an alert due loss of offsite power and having to shut down 1 out of 4 diesels. Everything else appears to be working normally.

 

[shadowncs]

from http://www.cnn.com/2011/US/08/23/virginia.quake.nuclear/" about North Anna quote:
"Amanda Reidelbach, an emergency management spokeswoman for Louisa County, said the plant vented steam, but there was no release of radioactive material."

Why are they venting steam? WTH? I hope it's just a misreporting.

 

[QuantumPion]

from http://www.cnn.com/2011/US/08/23/virginia.quake.nuclear/" about North Anna quote:
"Amanda Reidelbach, an emergency management spokeswoman for Louisa County, said the plant vented steam, but there was no release of radioactive material."

Why are they venting steam? WTH? I hope it's just a misreporting.

It's secondary steam, that is a normal occurrence with trips from full power. All the steam that was going to the turbine has to go somewhere! Here's a youtube clip of what it looks like (at Surry, same design as North Anna):

 

[ChernobylMary]

I am curious about the spent fuel pools. They are not required to have back-up power and North Anna has some 1200 tons of spent fuel.

 

[shadowncs]

...

Thanks, makes sense. That video is awesome and without you explaining would have been scary as hell.

 

[QuantumPion]

I am curious about the spent fuel pools. They are not required to have back-up power and North Anna has some 1200 tons of spent fuel.

Don't know where you heard that but it is incorrect. The spent fuel pool coolers run off the same backup power as every other safety-related system.

 

[jim hardy]

""Why are they venting steam? ""

The steam generators are vented to atmosphere through relatively small valves in order to carry away decay heat when the turbine and condenser are unavailable as when you are starting up or shutting down the plant , or when the grid goes away.
They're called " Steam Dump to Atmosphere" valves and they're a normal means of temperature control when plant is in between cold shutdown and power operation - a state often called "hot shutdown".. it's very normal.

Another source of steam is the exhaust pipes from the Terry Turbines that supply the makeup water to the steam generators. Ours were adjacent the Steam Dump to Atmosphere silencers.


The water in the steam generators is ultra purified. It is separated from the reactor coolant water by the steam generator tubes.
You could drink that condensed steam except that ultra pure demineralized water gives you a tummy-ache because it is so mineral free it depletes your electrolytes.

Steam is normal. Do not be alarmed by that. The plant is capable of impressive displays of it, and shouild a steam generator relief valve have opened as a result of grid going down - well - that's quite noisy..
The diesels started, they're dumping steam, sounds like they're doing fine.
But a loss of grid doesn't happen every day - so I'm sure it's a bit hectic there just now. Pray everything goes smooth for them.

When you lose grid the turbine piping has to cool down without help of main condensate pumps and that's sometimes a bit noisy. If you've ever heard an old steam heating radiator creak and clank - imagne one with twenty inch pipes.

oops i see it's been handled... that youtube looks to me more like a relief valve than steam dump to atmosphere.. but i don't know that plant.

old jim

 

[ChernobylMary]

Don't know where you heard that but it is incorrect. The spent fuel pool coolers run off the same backup power as every other safety-related system.

http://pogoblog.typepad.com/pogo/20...-to-withstand-59-61-magnitude-earthquake.html

Is this report incorrect?

 

[ChernobylMary]

To clarify, the link says that the spent fuel ponds are not required to have back up power, which is not the same as saying they don't have back-up power.

 

[Astronuc]

To clarify, the link says that the spent fuel ponds are not required to have back up power, which is not the same as saying they don't have back-up power.

That's not entirely correct. That POGO article is a bit misleading.

The pools were originally designed for less fuel, but they re-racked to increase capacity. Originally, the US government was going to take the spent fuel and reprocess. Well, that didn't happen. Then the US DOE was going to build a final repository, and that hasn't happened. Now, utilities like the one operating North Anna put spent fuel in dry storage pending some government resolution.

The site is required to main coolability of the spent fuel pool. That pretty much guarantees that the pool cooling system has backup power. They aren't required to have an exclusive (independent) back up power system - but that doesn't mean that they don't have back up power.

Also, the steam turbine is part of the secondary system which does not contain radioactive water, unless the steam generator tubes leak. North Anna replaced steam generators, Unit 1 in 1993 and Unit 2 in 1995, in order to remove the original SG tubing, which was prone to IGSCC.

 

[rmattila]

Off-site power appears to have been restored.

http://dom.mediaroom.com/index.php?s=43&item=1015

 

[Astronuc]

FYI

SUBJECT: EMERGENCY DECLARATIONS DUE TO SEISMIC EVENT
At 2:22 p.m. (EDT) on August 23, 2011, NRC entered the Monitoring Mode following the declaration of an ALERT at the North Anna Power Station Units 1 and 2, located in Virginia, at 2:03 p.m. The emergency was declared following a seismic event near the North Anna station. Both North Anna units experienced reactor trips and a loss of all offsite alternating current (AC) power (LOOP) to the emergency buses. The cause of the reactor trips and LOOP are being investigated. The on-site emergency diesel generators (EDGs) initially started and powered the station emergency buses. Subsequently, one of the EDGs was shutdown due to a diesel coolant leak. Another diesel generator was started and all emergency buses continue to be powered.

from - http://pbadupws.nrc.gov/docs/ML1123/ML112360103.pdf

See also - http://www.nrc.gov/reading-rm/doc-collections/event-status/event/en.html#en47181

 

[QuantumPion]

oops i see it's been handled... that youtube looks to me more like a relief valve than steam dump to atmosphere.. but i don't know that plant.

old jim

For a trip where condenser vacuum is lost, full steam flow has to be vented to atmosphere. Condenser vacuum was lost because they lost offsite power.

 

[mheslep]

For a trip where condenser vacuum is lost, full steam flow has to be vented to atmosphere. Condenser vacuum was lost because they lost offsite power.

Sounds like that's another possible accident problem and offsite dependency that could be avoided with a nuclear plant design based on the Brayton cycle? Yes I know the traditional PWR/BWR doesn't generate high enough temperatures, but other designs could.

 

[QuantumPion]

Sounds like that's another possible accident problem and offsite dependency that could be avoided with a nuclear plant design based on the Brayton cycle? Yes I know the traditional PWR/BWR doesn't generate high enough temperatures, but other designs could.

It's not an accident problem, it's simply the design of the system.

A gas cooled reactor using the Brayton cycle would still have to have a way to dump decay heat on a trip, which would involve venting gas or steam to the atmosphere.

I don't understand your comment about LWR's not generating high enough temperatures for a Brayton cycle. You may be confusing with rankine cycle with superheated steam, which is true that most LWR's cannot produce superheated steam.

 

[rmattila]

Sounds like that's another possible accident problem and offsite dependency that could be avoided with a nuclear plant design based on the Brayton cycle? Yes I know the traditional PWR/BWR doesn't generate high enough temperatures, but other designs could.

The reason for having to use the atmosphere as a heat sink is the fact that the ordinary heat sink (=sea / cooling tower) is lost due to stoppage of the condenser cooling pumps. The same goes for any nuclear plant no matter what the cycle used: if you lose the power needed for utilizing the normal heat sink, you need to use an alternative one. In a PWR, the most straightforward alternative heat sink is to blow secondary steam out to the atmosphere and refill the steam generators with fresh water; in a BWR the primary steam is blown to the containment suppression pool and the primary circuit is refilled with fresh weater. An isolation condenser in a BWR makes it possible to use the same decay heat removal method as a PWR.

Needing power for emergency feedwater pumps to replace the lost inventory is not "another" offsite dependency: that's exactly the reason power is needed after the shutdown at all.

 

[mheslep]

It's not an accident problem, it's simply the design of the system.

A gas cooled reactor using the Brayton cycle would still have to have a way to dump decay heat on a trip, which would involve venting gas or steam to the atmosphere.

The issue here, as I think I understand it, is that with the Rankine a condenser is required and that when the condenser stops the system has no way of continuing to transfer heat to the turbine and removing energy (decay heat) from the system. I don't see the need for a condensor in a Brayton. Thus such a system could could continue running turbine at lower power and bleeding off energy after a reactor trip through the normal path.

I don't understand your comment about LWR's not generating high enough temperatures for a Brayton cycle. You may be confusing with rankine cycle with superheated steam, which is true that most LWR's cannot produce superheated steam.

Well IIRC 300K above ambient is typical for an LWR, where as a practical Brayton might run 700K above ambient. And I'm assuming, most likely, He as the gas. Under what trip circumstances He in a Brayton need to be vented?

 

[mheslep]

The reason for having to use the atmosphere as a heat sink is the fact that the ordinary heat sink (=sea / cooling tower) is lost due to stoppage of the condenser cooling pumps. The same goes for any nuclear plant no matter what the cycle used: if you lose the power needed for utilizing the normal heat sink, you need to use an alternative one.

But not necessarily an active one, i.e. active heat removal via pumps. With a molten salt (MS) reactor the idea upon trip is to simply gravity feed the MS to a dump tank, where because of the high temperature (~1000K) it dissipates heat to ambient rapidly and passively. A MSR may have other problems, but a passive, independent shut down is not one of them.

 

[swl]

Thanks for all the great information.

If my understanding is correct, the ground acceleration exceeded the operational basis and this can account for the damage which caused the loss of offsite power.

The area that I know lacks clarity in my mind is the acceleration relative to design basis. It is my understanding that the design basis was only slightly exceeded, and since safety systems are typically over-engineered, there was probably no dangerous structural damage (though I have read of small cracks in the containment building that are not leaking radiation).

furthermore, it is my understanding that this was the strongest quake ever measured in the area, so such an event could not have been predicted by the NRC or the plant designers.

However, now that such a powerful quake is known to be a certainty in the area of the North Anna plant, will it be necessary to either retrofit or decommission the plant?

 

[gmax137]

... the ground acceleration exceeded the operational basis and this can account for the damage which caused the loss of offsite power...

I'm pretty sure that 'ground acceleration' as a single value is not meaningful (in the context of the damage it can cause) without the corresponding frequency. In other words, a high acceleration at a high frequency may be much less damaging than a lesser acceleration at a low frequency. The seismic design is developed from a ground response spectrum, not a single 'g' value. Maybe someone with seismic design expertise could chime in here.

 

[QuantumPion]

I'm pretty sure that 'ground acceleration' as a single value is not meaningful (in the context of the damage it can cause) without the corresponding frequency. In other words, a high acceleration at a high frequency may be much less damaging than a lesser acceleration at a low frequency. The seismic design is developed from a ground response spectrum, not a single 'g' value. Maybe someone with seismic design expertise could chime in here.

Yes, it turns out the plant was designed to withstand earthquakes with a long wavelength which are characteristic of west-coast earthquakes. However this earthquake was a short wavelength one, which is why the concern over design basis limits. Note that it is only the aux building sensors which may have exceeded the design basis earthquake, not the whole plant.

Another interesting tidbit: the dry storage casks moved several inches. Or from what I've been told, the casks remained stationary while the ground underneath them moved!

Here is a video in the Richmond Times Dispatch showing a brief tour inside the plant, if you've ever been curious what it looks like:

http://www2.timesdispatch.com/news/news-video/2011/sep/02/2/a-post-earthquake-tour-of-north-anna-nuc-99830-vi-30316/

 

[mheslep]

I've been water skiing in lake Anna, adjacent North Anna. It is remarkable how un-intrusive a couple GW of nuclear plant is to lake recreation.

 

[Argentum Vulpes]

I've been water skiing in lake Anna, adjacent North Anna. It is remarkable how un-intrusive a couple GW of nuclear plant is to lake recreation.

So how do you like the lake that wouldn't of been if not for the North Anna NNP?

 

[swl]

So how do you like the lake that wouldn't of been if not for the North Anna NNP?

More, or less than the wildlife, valleys and forests submerged by the lake?

 

[zapperzero]

http://www.usatoday.com/tech/scienc...lts-were-double-nuke-plants-design/50304434/1

 

[mheslep]

More, or less than the wildlife, valleys and forests submerged by the lake?

Valleys? The lake is 13K acres, mostly shallow and 80' at its deepest. The area is in the Piedmont of Virginia. A large colony of beavers might have accomplished half as much 500 years ago. Still, the lake should be credited to the total area required by the NA plant.

 

[NUCENG]

http://www.usatoday.com/tech/scienc...lts-were-double-nuke-plants-design/50304434/1

I will be listening in on the public meeting today. Then I will be able to evaluate the article you posted. Sounds pretty sensational to me.