Earlier quoted context omitted.
There's a nuclear reaction in the sky beaming free energy to us, let's just use that
Hungary is already using that (today we were 90% carbon-free thanks to solar), the problem is what to do when it gets dark.
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Danube's record low levels force shutdown of Hungary's only nuclear plant
141–150 of 252 posts
Re: Danube's record low levels force shutdown of Hungary's only nuclear plant
#142Earlier quoted context omitted.
Wouldn’t a Carnot engine with 33% efficiency produce 2 J of heat per 1 J of mechanical work? With 40% efficiency 1.5 J of heat? Efficiency of the generator should be better than 90 % so I think the 3x estimate is a bit off.
The heat doesn't disappear. Useful work is heat, it's just that some of it is intercepted before final dissipation. If you look at real-world numbers, you're generally going to see 3x the thermal output as electrical output from any thermal energy plant. Two-thirds of that thermal output is wasted, and you'd see your 2x figure there. But the useful electrical output eventually ends up as heat as well, whether in dire…
Well we are still discussing cooling of power plants. The part of the energy that goes into the grid cannot be used to heat the river. It turns into heat somewhere else.
Re: Danube's record low levels force shutdown of Hungary's only nuclear plant
#143> 4,700 cubic metres per second in July, whereas on Wednesday it was down to less than a third of that, at 1,600cm per second.
Did a double take at measuring water flow in cm per second. At least it isn’t in busses or Eiffel or something.
Re: Danube's record low levels force shutdown of Hungary's only nuclear plant
#144Earlier quoted context omitted.
> sometimes fossil fuels are a good fit There is simply NO safe level of fossil fuel use.
I don't know what you mean with "no safe level of fossil fuel use". It doesn't mean anything without contextualizing that statement.
i thought it was pretty clear, personally.
Re: Danube's record low levels force shutdown of Hungary's only nuclear plant
#145Earlier quoted context omitted.
Data centers can afford to spend way more per kWh of heat discharged. Nuclear needs to dump 3+kWh of heat per kWh of electricity generated.
Nitpick here: Nuclear discharges more like 2kWh of heat per kWh of electricity produced. Perhaps slightly more, but its in that ballpark. Seems like a small difference but you are overstating the waste by near 50%. Source: Degree in Nuclear Engineering, previous life was a Reactor Operator. Also, just look up thermal efficiency of currently operating reactors.
That 3+:1 is actually from being pedantic.
2:1 implies 33% thermal efficiency to the grid which is commonly achieved in normal operations.
Unfortunately engineering means you can’t work with such overly simplified models. Many ways of dumping heat run into issues from solar gain prevents dumping significant heat under the employe parking lot etc.
Re: Danube's record low levels force shutdown of Hungary's only nuclear plant
#146Earlier quoted context omitted.
Hungary is already using that (today we were 90% carbon-free thanks to solar), the problem is what to do when it gets dark.
Batteries? Starting this year, in Romania you cannot put new PV capacity online without the storage for it, is mandatory. Possibly for existing ones, but I am not sure.
Yes, absolutely colossal amounts of batteries though - what if it’s quite hot but also cloudy for 5 days in a row?
You either have to significantly oversize the PV (easier said than done, when its energy density is already not that high per m2), or have enough batteries to last for multiple days of full load. If you do the maths that’s a lot of batteries
Re: Danube's record low levels force shutdown of Hungary's only nuclear plant
#147Earlier quoted context omitted.
Nitpick here: Nuclear discharges more like 2kWh of heat per kWh of electricity produced. Perhaps slightly more, but its in that ballpark. Seems like a small difference but you are overstating the waste by near 50%. Source: Degree in Nuclear Engineering, previous life was a Reactor Operator. Also, just look up thermal efficiency of currently operating reactors.
That 3+:1 is actually from being pedantic. 2:1 implies 33% thermal efficiency to the grid which is commonly achieved in normal operations. Unfortunately engineering means you can’t work with such overly simplified models. Many ways of dumping heat run into issues from solar gain prevents dumping significant heat under the employe parking lot etc.
I don't disagree but am having a hard time parsing the second half of your comment.
In my experience we saw some losses when taken as a system that prevented us from hitting 2:1, but they weren't anywhere near 50%. We also ran closer to 40% than 33% thermal efficiency in the power generating loop, so many of the system thermal costs are baked into that 33% efficiency to the grid.
Basically, each reactor install will have it's own minor issues. Overall they should be hitting around 2:1 as an entire system. If they aren't there is something going on that I haven't come into contact with (which is quite a lot, I'm sure).
Re: Danube's record low levels force shutdown of Hungary's only nuclear plant
#148Earlier quoted context omitted.
And it's not cold enough to cool the reactor
The principle cooling mechanism is vapourisation. The heat of vapourisation for water, converting liquid to steam, is 40.66 kJ/mol, or 2257 J/g. It takes a lot of energy to boil off water.[1] That compares with the latent heat of liquid water, the energy required to heat one unit of water by one degree, which is 4.2 J/g*K (where K is the delta temperature in Kelvin). Raising the temperature of input by, say, 10 degre…
Backing this up, these high numbers are for typical cooling towers where they vent to atmosphere.
Once you get into closed loop PWRs the numbers get crazy. Actual figures for Naval Nuclear plants are classified, but as a nice round number example if you pressurize the secondary loop to 250psi you end up with about 1,725 kJ/kilogram to boil it.
Absolutely terrifying stuff.
Re: Danube's record low levels force shutdown of Hungary's only nuclear plant
#149Earlier quoted context omitted.
That 3+:1 is actually from being pedantic. 2:1 implies 33% thermal efficiency to the grid which is commonly achieved in normal operations. Unfortunately engineering means you can’t work with such overly simplified models. Many ways of dumping heat run into issues from solar gain prevents dumping significant heat under the employe parking lot etc.
I don't disagree but am having a hard time parsing the second half of your comment. In my experience we saw some losses when taken as a system that prevented us from hitting 2:1, but they weren't anywhere near 50%. We also ran closer to 40% than 33% thermal efficiency in the power generating loop, so many of the system thermal costs are baked into that 33% efficiency to the grid. Basically, each reactor install will…
> hard time parsing the second half of your comment.
I’ll put it as a spherical cow engineering problem. Let’s suppose the temperature is 30C and you want to dissipate 2GW of heat across a 1kmx1km flat plate, what temperature will it get? That’s a relatively straightforward calculation if you don’t need high precision.
However in the real world it wouldn’t have a single equilibrium temperature. 30C at night the heatsink would be one temperature and in the daytime it would be a different temperature due to sunlight.
Evaporative cooling largely sidesteps this issue, but it’s worth keeping in mind why that’s chosen over other seemingly cheaper options.
Re: Danube's record low levels force shutdown of Hungary's only nuclear plant
#150Where have all the "what do you do when the wind doesn't blow and the sun doesn't shine" commenters gone?