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[Phys-l] Nuclear Power and the Grid



Under the "all-too-predictable blackout" thread, John Denker mentioned that all power plants should have "black-start" capability. He also mentioned that nuclear plants will generally shut down during a cascading blackout, and then be the last to come back online.

I strongly agree that all plants should have black-start capability, and I have been saying that for years.

I also know that nuclear plants tend to SCRAM when there is trouble on the grid, and I wonder if someone can explain that to me. If grid power is lost, and the reactor SCRAMs, and there is no black-start capability, the reactor probably cannot be restarted for a pretty ling time. That means reactor cooling and spent-fuel cooling has to be provided by diesel generators, or something similar... and this might be required for a time longer than there is sufficient fuel to run the backup power.

It's not obvious to me why the reactor has to SCRAM in the first place. Although grid trouble might indicate some sort of nasty thing coming (like an earthquake), why not wait to SCRAM until you know there is something nasty coming. It's difficult to imagine that waiting for a few minutes after a grid anomaly before initiating the shutdown would make much safety difference.

Anyway, if a SCRAM eventually does occur, and if the nuclear plant has black-start capability, once it is ascertained that nothing at the nuclear plant is damaged, the reactor could be restarted, the generators could be brought back up (because black-start is provided) and the nuclear plant can provide its own energy for cooling itself and the spent fuel pools.

So what's the point of a reactor shutdown when the external grid power is lost? Indeed, what in the world would happen in a system where *all* power is provided by nuclear plants, and there is a grid problem? They all shutdown, and you can never get any of them running again if external grid power is a condition of restart. Sounds like you'd have the proverbial "catch-22."


Michael D. Edmiston, PhD.
Professor of Chemistry and Physics
Chair, Division of Natural and Applied Sciences
Bluffton University
Bluffton, OH 45817
Office 419-358-3270
Cell 419-230-9657


-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker
Sent: Friday, September 09, 2011 3:58 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] an all-too-predictable blackout

One more thing:

According to
http://www.sce.com/PowerandEnvironment/PowerGeneration/SanOnofreNuclearGeneratingStation/default.htm?goto=songs

The twin reactor units at ... San Onofre ... are Southern California's
largest and most reliable sources of electricity.

Most reliable? Really?

It is entirely predictable that during a cascading blackout, all nuclear power plants in the area will shut down ... and they will be more-or-less the last to come back up.

As of now, the San Onofre reactors are still shut down:
http://www.songscommunity.com/index.html?from=SONGS

I have long argued that every power plant should have black-start capability.
The lack of such capability makes it harder to recover from a blackout.

In this regard, nuclear power plants are a big step in the wrong direction.
Not only do they require external grid power for startup, they require nice stable external grid conditions while running. In a system containing /only/ nuclear power plants, a blackout would result in deadlock; no recovery would be possible.

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