Heat Wave Shuts Down Alabama Reactor

mdsolar writes "In a first for the US, one of three nuclear reactors at the Browns Ferry nuclear plant in Alabama has been shut down because the Tennessee River is too hot to provide adequate cooling for the waste heat produced by the reactor. This is happening as the TVA faces its highest demand for power ever, reports the Houston Chronicle. This effect has been seen in Europe in the past, forcing reduced generation, but the US has until now been immune to the problem. The TVA will buy power elsewhere and impose higher rates, blaming reduced river flow as a result of drought."

Reasons right?

[Anonymous Coward]

I work at a nuclear power plant. We have a limit for the temperature of the river downstream of our returned cooling water for environmental reasons, not reasons related to the power generation process. I suspect the TVA has a similar requirement.

I noted from the nrc website (www.nrc.gov) that their other reactors are operating at reduced load, which is what our reactors must do to limit the heat input into the river.

So this is nothing remarkable.

Not too unusual for power plants

[Anonymous Coward]

This is not that unusual for power plants. Some coal fired units are off as well, for example Dynegy's Wabash River is currently experiencing similar problems. Obviously this hurts everyone (the company loses generation during times when wholesale power prices are high and, if load gets too high, the consumer might experience brown outs or black outs). This problem will likely get worse as well as global warming takes hold.

Re:River too hot?

[Anonymous Coward]

Why not just run the river through a refrigerator to cool it down? After all, you can generate the electricity for the refrigerator in the plant.

Actually, it would be quite possible to do such a thing and you wouldn't even violate the second law of thermodynamics since you are only pumping the heat. One example of such a mechanism is the electrically powered fan on radiators in cars that improve cooling when the car is not moving.

However, it wouldn't change the problem: Where to dump the waste heat. Instead of pumping it in the river, you would be pumping it into the air, which may be better but you only shifted your waste disposal. Lastly, there is this slight technical problem that the waste heat of a nuclear power plant is enormous, usually around 2 GW, which would require a MASSIVE heat pump (i.e. "refrigerator"). That in turn would eat up a large portion of the generated electricity, greatly reducing efficiency.

As it turns out, however, an active heat pump isn't even needed to dump the heat into the atmosphere instead of pumping it into the river, usually that is accomplished with a cooling tower, though in this case there aren't enough available since the plant is not designed to run on towers alone.

Re:Reasons right?

[Wonko the Sane]

Physics: It's not just a good idea, it's the law [wikipedia.org].

Re:Reasons right?

[hankwang]

How efficient is a power generation plant that throws away gigawatts of power as waste heat?

From the heat source to electrical power output is usually in the range 35--50%, depending on the plant design. A fundamental problem is the theoretical limit of the efficiency of a heat engine, a device that converts a temperature difference into mechanical power. It is 1 - Tcold/Thot, where Tcold and Thot are the temperatures of the cold and hot parts, in kelvin. For a steam-operated heat engine, the cold end is around the boiling point of water (373 K), and the hot end might be 1000 K, which limits the efficiency to 63% if there are no other losses. But one can use the waste heat for other purposes in a cogeneration plant [wikipedia.org], for example for residential heating in cold climates or for the industry.

Re:Reasons right?

[Cyberax]

Nope. You can't beat http://en.wikipedia.org/wiki/Carnot_cycle [wikipedia.org] in efficiency. The practical upper limit for nuclear power plants is about 50%. And we're already getting closer to this limit.

We can use some insane things like high temperature (thousands degrees) reactors with gas cooling to get another 10%-15% of efficiency, but it is just not practical.

Learn to spell "its".

[Anonymous Coward]

Spelling matters.

Re:In Soviet Russia

[Belacgod]

Soviet Russia doesn't refer to USSR. It's to distinguish it from Tsarist Russia, or Kievan Russia, or any of the other regimes that ruled Russia. Similar usages in other countries: Napoleonic France, Imperial Rome, Colonial America, Nazi Germany.

Some people sell their "waste" heat

[Colin Smith]

To heat domestic water, space heating and even to power adsorption chillers which can reduce AC requirements. Even coal power stations can hit 88% efficient.

http://www.helsinginenergia.fi/en/tuotanto/benefit s.html [helsinginenergia.fi]

US power stations are still only 40% efficient because ... Well you decide for yourself.

 

Re:Reasons right?

[Dachannien]

Actually, if you really do read the article carefully, nowhere does it state that the water itself is incapable of cooling the reactor. It merely states that the river water is "too hot", which could just as well indicate that adding more warm water - especially in drought conditions where the river level is probably lower than normal - would make the river temperature too hot to safely sustain its ecosystem.

Re:Some people sell their "waste" heat

[Colin Smith]

Unfortunately, only a tiny fraction of the population lives that close.

Not necessarily the case.

In Denmark they have a truly *huge* "district heating" network.

e.g.
http://www.dbdh.dk/ [www.dbdh.dk]

 

Re:What "waste heat"?

[mi]

In practice this is an engineering problem

You misspelled "fundamental limit of thermodynamics"

No, dear, I did not. You are struggling with the Second Law of Thermodynamics [wikipedia.org], which — in the form most applicable to the situation — is spelled as "It is impossible to convert heat completely into work."

My point was, that a better-engineered reactor would convert more energy into work. This increase of the work/heat ratio is a purely engineering problem — the only "fundamental limit of thermodynamics" is that the ratio be below 1...

Re:Waste heat?

[Waffle Iron]

As the difference in temperature between engine input and output gets less, the physical size of the engine you'd need to create a given amount of power goes up exponentially (not exactly, but much faster than linearly anyway). This waste heat mostly comes from the steam condensers for the turbines, so the input temperature available is very low. Due to the laws of physics, a sterling engine that could significantly boost the efficiency of a nuclear plant would be too large and costly to make economic sense.

Of course, you're welcome to study thermodynamic engineering and try to circumvent this issue yourself. If you manage to pull it off, you could make $Billions.

Re:What "waste heat"?

[Wonko the Sane]

the only "fundamental limit of thermodynamics" is that the ratio be below 1...

Assume the reactor produces steam at a temperature of 500 fahrenheit (530 kelvin).

If the temperature of your cooling medium is 50 fahrenheit (280 Kelvin)

Your process can never be more than 47% efficient. No amount of engineering can change this fact.

Now if the temperature of your cooling medium rises to 90 fahrenheit, then you are stuck below 42%.

Thermodynamics not only says that the ratio must be below 1, it also says exactly by how much it must be below 1.

Re:Some people sell their "waste" heat

[Waffle Iron]

That's because so many people in Denmark are close enough to a power plant to run steam tunnels to their locations. The trend in the US over the past decades has been to build huge power plants in the middle of nowhere, so it just wouldn't work here.

Recently, a new trend has been to build smaller cogeneration facilities in populated areas in the US, but due to valid political and environmental concerns, the only viable fuel for these is natural gas. That fuel is already in short supply and dwindling fast, so that's not going to solve the problem by itself.

Re:Reasons right?

[mdsolar]

I agree. I was reading the article saying that the intake was too warm. But, another article gives more detail http://www.decaturdaily.com/decaturdaily/news/0708 17/power.shtml [decaturdaily.com] saying that it is the down stream temperature that is considered important. So, if the intake temperature exceeds the maximum down stream temperature they are hosed.

Re:Air conditioning ruined the South

[Guppy06]

"Before air conditioning, yankees stayed in yankeeland. After air conditioning they moved to places where they weren't welcome."

Actually, refrigeration technology took off in the South before the North. The Yankees you so deride didn't need large plants to manufacture ice for their iceboxes, they had the Great Lakes.

As for electricity generation, you'll note that the New Deal and the Tennessee Valley Authority (TVA in TFA) was interested in improving electricity generation in the South long before consumer air conditioning was available, let alone viable. Southerners were interested in those new-fangled electric lights Northerners were beginning to take for granted.

"We used clothes lines to hang and dry our clothes, not electric driers."

Another technology that caught on in the South more than the North. It's not the North that has to deal with trying to dry clothes in 157% humidity, at least not year-round.

Re:What "waste heat"?

[Wonko the Sane]

A nuclear reaction can produce much higher temperatures than that. Finding a good medium, and a good way to contain/control the reaction is an engineering problem.

Yes, you can engineer reactors to produce steam at higher temperatures.

As the "spent" medium is hotter than fresh (and it always is), its heat could be used again in another cycle. And so on (assuming "endless" supply of fresh medium, which river provides), until the difference in temperatures make another cycle impractical. This is how efficiency can -- in theory -- be brought all the way up to 1 but not quite.

No, you can never beat Carnot efficiency for a given set of source/sink temperatures no matter if you have an infinite supply of river water, or an infinite number of rounds. The efficiency of the series you describe converges to the Carnot efficiency, not to 1.

Re:Renewables question....

[belg4mit]

It's renewable in some sense, but not others. More specfically, big hydro genereally ends up not being sustainable:
fish spawning, methane, changes to the microclimate. On the other hand, we've not done enough with run-of-river.

Re:Renewables question....

[Oktober Sunset]

fish spawning, methane and changes to the micro climate don't effect the dam's ability to generate electricity, so it is still renewable energy.
Renewable != earth loving hippy compatible.

Re:What "waste heat"?

[Wonko the Sane]

A carnot cycle [wikipedia.org] is indeed a closed cycle, but:

Carnot's theorem is a formal statement of this fact: No engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between the same reservoirs.

Your open-cycle system will never be more efficient than a carnot cycle at the same temperatures.

Re:What "waste heat"?

[SEMW]

I'm afraid Wonko's right. The total efficiency converges to Carnot's. If there is any *usable* waste heat left at the end of a cycle to put into another heat engine, then the first cycle wasn't running at full (reversible) Carnot efficiency.

BTW, if a heat engine were ever to be used in a closed system, then its efficiency would quickly converge to 0%, since the hot source would cool down and the cold source would heat up! The Carnot cycle, as I said in my other post, assumes infinite, constant temperature hot and cold sources, i.e. effectively the same as a system where heat is constantly added to the hot source (by a nuclear reactor) and taken away from the cold source (by a running river) to maintain a constant temperature.

Re:Reasons right?

[Wonko the Sane]

You want to cool the water just a little bit below the condensing point, so that your pumps to do not cause the water to boil again (rough on the impellers). Any cooling below the condensing point is waste, so you want to minimize it to a little as practical,

A common error is to forget that the boiling and condensing temperature are highly dependent on pressure. Inside a condenser, the temperature and flow rate of the cooling water will determine the condensing temperature and pressure of the steam.

Meanwhile Back In Alabama

[cluckshot]

A little noted fact of the cold war is that a very large amount of the US total electrical generation capacity is in the TVA region (Tennessee River - Dependent) The loss of this reactor is serious as the whole USA has no reserve capacity at peak load and with the heat wave over the East USA this is a critical loss. If it were the only reactor in danger this might be of no concern. The US TVA operates 5 big reactors and numerous coal fired plants all of which have the Tennessee River at thermal capacity to cool them and the river is dropping daily.

If heavy sustained rain does not fall on the Tennessee River Valley over the next 3 to 4 months an event which is historically unlikely, the loss of something close to 15 times the Browns Ferry reactor in capacity is likely to hit the USA. There is nothing to pick up the load. The loss of this one reactor is nearly equal to all the wind energy the USA generates. This loss threatens the operations of every one of the 48 US States. With the possible loses in Alabama Power pools and their reactors etc as well as Georgia Power, this poses the very real risk of cutting the energy supply of the USA by a very large fraction. As I write the North Alabama region is short 60 inches of rain over the past 18 months. The US TVA has been drawing down storage for 5 years now. There is no reserve and little prospect of one for some years to come.

I had warning of this imminent event when the City of Huntsville requested from TVA more water for its treatment plant and was turned down for supply. I knew then that the supply was gone.

Re:paddle wheels in the heat stream

[QuickFox]

Are you thinking a forest of insulated two-foot steam pipes running all around town? Sounds pretty ugly, noisy, expensive and environmentally disruptive.

Here in Sweden we've had this in the cities forever. It's not ugly, noisy, expensive and environmentally disruptive. Instead it's underground.

Generally they don't transport steam, they transport hot but liquid water.

See, engineers are not idiots.

You must be new here.

Re:TVA net metering policy

[mdsolar]

You'd save money with solar if you had proper net metering. You don't need batteries in that case. Check http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html [blogspot.com] to see how things work in Georgia and Luisiana.

Re:Reasons right?

[Wonko the Sane]

Sorry, there are several types of "water" in these systems...

The steam that drives your turbines is condensed, then is pumped back into your boiler. (secondary water)

The condenser is cooled by the river water.

You don't mix the secondary water and the river water, because the boilers require very pure water with a controlled chemistry.

Excessive cooling of the secondary water is a waste which must be minimized.

Actually...

[danwesnor]

The reactor was shut down because the water exiting the plant's cooling system exceeded an average of 90 degrees F over a 24 hour period. The plants have an agreement with the state to limit the temperature of the water they put into the river. The water in the river is not even remotely 90 degrees F.

Brown's Ferry also just recently started one of its reactors after a long downtime, so this only kicked us back a few months. It's not a big impact to the nation's grid, not even to the local area.

As for why we don't recapture the energy in the heated water to make even more power, well, they just didn't think it was necessary back when we used to build power plants back in the 60's. Investing money in anything nuclear in the US is political suicide.

Re:Meanwhile Back In Alabama

[Ecks]

TFA has the engineering wrong. The problem isn't the river temperature as much as the air temperature. A nuclear power plant needs to be located near a river so it can have a large supply of relatively cool water to use as a working fluid. The river water gets boiled into steam by reactor water in the nuclear reactors primary coolant loop. This is steam is what turns the turbines and generates the electricity. When it exits the turbines it's still steam, it's just cooler and wetter. You can't return it in this state because doing that would dramatically raise the river's temperature. You have to cool it down before you can put it back. To do that you use a passive air to water heat exchanger. But they're having a heatwave down there. Between the starting temperature of the river and the reduced efficiency of the passive heat exchanger using all three reactors in the plant would heat the river to unacceptable levels.

Unacceptable is not boiling it's probably something in low 90F range because if the mean temperature of the river was over 90F for any period of time you raise the risk of algae blooms and fish kills.

Physical conditions are not preventing the plant from running, environmental considerations are. And if the river's temperature is close to or exceeds the contracted discharge temperature without being heated by the plant then reevaluating the environmental decision may be in order.

-- Ecks