# Swedes Produce Hot Water, Dump It Into Sea

For historical reasons having nothing to do with engineering or rationality, Swedish nuclear power plants dump a lot of warm cooling water into the sea. In a revealing blog entry, Paddy K offers an estimate of just how much energy that cooling water contains.

It’s one third of the energy produced in the country.

I suddenly don’t feel very motivated to keep my morning showers brief.

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September 4, 2008

A more interesting comparison would be what fraction is that of the nuclear-generated electricity? A nuclear power reactor is a heat engine, as is any thermal generator like a coal plant, gas turbine, or automobile engine. There is an absolute physical limit on the efficiency of the conversion of heat to electricity, equal to the temperature difference between the hot and cold ends, divided by the temperature of the hot end (in absolute degrees, all numbers I use will be in degrees Kelvin, where water freezes at 273 and boils at 373). The cold end is around 300 degrees (assuming it’s rejecting lukewarm water to the environment). So, to get even a 33% efficiency, you need the hot end to be around 450 degrees, well above the boiling point of water at atmospheric pressure. To get a 67% efficiency you need the hot end to be at 900 degrees, more than 600 degrees Celcius.

We accept as normal that a thermal power plant loses more than half of its energy to the environment as waste heat. That’s unavoidable when you convert high-entropy energy like heat into low-entropy energy like electricity.

The part I find wasteful is when electricity is used simply for heating. In an electric stove, or as electric baseboard heaters, you’re using the electricity to send less than half of the heat from the power plant to your home, and throwing out more than half. If you had just run the heat-producing reaction locally, you would have used less than half of the fuel (though a nuclear-powered domestic space heater is probably logistically infeasible, I’m talking about the thermodynamic principles).

2. #2 Lars L
September 4, 2008

According to a bloke I met the nuclear powerplants in Sweden dumps energy worth billions straight into the sea. When the plants were built the energy was cheap, now it´s a bit more expensive…

3. #3 Lassi Hippeläinen
September 4, 2008

The reason for dumping the heat into the sea is that the plants are too far from cities. Therefore the excess heat can’t be used for district heating of houses. And the plants are built so far away because of irrational fears.

Here in Finland someone had the bright idea of growing salmon in the seawater that the plant warms, especially during winter. At least some of the energy was put to good use. People treated those salmons as if they were radioactive. End of experiment.

4. #4 Rien
September 4, 2008

I think I recall reading somewhere that when they built the Forsmark
nuclear power plant, they wanted to funnel the hot water to Uppsala to use for heating. But of course that didn’t fly with the public.

5. #5 Chelonian
September 4, 2008

If I recall correctly at the Center for Nuclear Research (SCK/CEN) in Belgium the cooling waters go into the pond by the executive clubhouse, and some people go swimming there because it gets to a very pleasant temperature. They’re staff from the plant and/or research center so they’re well placed to know it’s harmless. Maybe nuclear power plants should systematically build outdoor pools for their staff, count that as employee benefits.

September 5, 2008

Winter Toad: I realise that of course heat must be removed in the condensate of a steam turbine to make the whole thing work. So how much heat is actually “wasted” depends on how much useful heat you could extract from the cooling water. But there is a LOT of cooling water.

Lassi Hippeläinen: Of course, that is one problem . these facilities are usually far from civilisation. But not always. And the heat could be used for other things than space heating – industrial processes, drying, production of fish and food, and making more electricity using ORC.

And this actual value of 33% came from a lecture at KTH, so I assume the source is a good one.

7. #7 Thomas
September 5, 2008

rien, it is correct that there were discussions about piping the cooling water from Forsmark. There were several reasons this wasn’t done, but mainly it was a matter of economics, it was deemed slightly more expensive than producing the heat locally, especially when it was unclear how long the reactors would be allowed to continue operating. In retrospect a bad decision IMHO.

Incidentally, Sweden’s first commercial reactor in Ågesta was a cogenerating plant producing hot water for southern Stockholm. It operated 1964-1974, at which point security concerns about the design forced it to close down. (It had one very nasty incident that could have turned into a meltdown). The design was partly optimized for a Swedish nuclear weapons program that was cancelled.

8. #8 Gert Franzén
September 8, 2008

Yes, 67% of the energy is “wasted” into the sea. A lot of energy, but it´s not hot at all and cannot be used for domestic heating. To make that possible the plants would have to be totally rebuilt. So, no hot water at all is dumped into sea!