California has so much solar power it's throwing it away

[NNadir]

8. I will try to respond to this misinformation as gently as is possible.

Last edited Tue Apr 23, 2024, 05:37 PM - Edit history (1)

Let's start here: Almost all current US nuclear reactors, built over a 25 year period in the 20th century, are Rankine cycle (steam) devices of one of two types, a boiling water reactor (BWR) where the steam that turns the turbine is in direct contact with the reactor core, or pressurized water reactors, (PWR) where high pressure liquid water in contact with the core is used to boil lower pressure water not in contact with the core to generate steam to turn the turbine. Basically the plants operate on exactly the same principles as the coal plants they displaced. All thermal reactors including those using gas heat to boil water (as in "flex fuel" power plants that can burn either coal or gas) that rely on steam to turn a turbine are Rankine devices. The thermodynamic efficiency of all such power plants, nuclear, coal, or gas (with the exception I'll describe below) operate at, as a general rule of thumb, at around 33% thermal efficiency. This actual number varies slightly with the weather. If one studies engineering data describing power plants, one will often see discussions of "winter capacity" and "summer capacity," the former being higher because, in a simplified sense, they display Carnot efficiency described by the following formula:





If the temperature of the sink (the ambient weather generally) is low, and the temperature of the device is high, the ratio will be smaller and the efficiency higher.

Because nuclear reactors were built long before antinuke fear and ignorance triumphed, with the result that the planet is now in flames, most power engineers relied, in particular because of the limits of materials science of the time, on Rankine engines, with nuclear power plants being no different.

I don't know where this "5000 degrees" figure comes from, or whether it is in centigrade, kelvin or Fahrenheit, but the melting point of uranium dioxide can be found at the Wikipedia page for the compound for all three temperature scales: 2,865 °C (5,189 °F; 3,138 K)

There is no evidence that under normal conditions nuclear fuel is liquid in a reactor. One can pull pellets out of used nuclear fuel and see that they are swelled (from fission gases) but intact. There are no puddles at the base.

The temperature you gave would suggest that uranium oxide is subject to liquefaction. In general, fuel rods contain uranium or MOX pellets separated from the zircalloy cladding by space. Zircalloy-4 is very common in nuclear reactors. It has a melting point of around 1850°C. There is no evidence that under normal conditions nuclear fuel is liquid in a reactor.

As for the nonsense statement that they must run all the time, they obviously can be shut or run at lower power using control rods. It makes sense to run them at full power however since this provides the cleanest baseload power possible. If they shut them fully restart can take up to 8 hours because of an effect called xenon poisoning.

Any system exposed to a continuous energy flux without removal of heat will melt, but nuclear reactors do have continuously recycling water and the temperature in the fuel is well below the number stated in the post to which I'm responding. To raise thermodynamic efficiency, as in any Rankine plant, be it gas, coal, or nuclear, cooling water is used to lower the temperature of the recycling water.

It is possible to build nuclear reactors that can be air cooled; but only a few reactors of this type, mostly in Great Britain, the AGCR (Advanced gas cooled reactor), which do not use water as a working fluid but rather use carbon dioxide as the working fluid. These devices operate on the Brayton cycle.

Late in the 20th century and early in the 21st, an advance in materials science took place allowing for the use of thermal barrier coatings, using a ceramic layer generally known as YSZ, Yttrium Stabilized Zirconia. This ceramic can be bonded with alumina to a superalloy turbine to allow the turbine to turn from hot gas, including gas flames, creating the opportunity for a Brayton cycle. The exhaust gases can be and often are hot enough to boil water to run a Rankine cycle, which have a thermal efficiency that can exceed 50% slightly.

My son, who is a Ph.D student in nuclear engineering, focusing on nuclear materials is aware of all of the above and more; it should be possible, under the case where antinuke stupidity and ignorance is shown for what it is, stupidity and ignorance, to build combined cycle nuclear plants, and indeed plants can be used to drive chemical reactions, a general term called "process intensification" about which I write frequently in this space. I believe that it should be possible to obtain thermal efficiency for nuclear systems approaching 80%, if one considers the work done in making synthetic fuels, desalinating water, and carrying out material processes. The term for this approach is "exergy recovery."

Now let's turn to the nonsense about batteries. From the above it should be immediately clear that electricity, by its very nature is thermodynamically degraded in all of the systems discussed above. It doesn't matter where it comes from. Most large power plants (except combined cycle plants which can approach and even exceed 50% thermal efficiency) operate at or around the Rankine figure, 33%. This means that 67% of the energy is waste heat. If the heat can be recovered for use, that's wonderful, but current industrial practice is to waste it, something of a shame in my view.

So busbar electricity - electricity at its source - represents only 33% of the original energy used to produce it. Transmission losses are generally 1 to 3%. Modern Lithium batteries charging and discharging operate at between 70% and 80% efficiency. One can feel this losses by noticing that batteries often get hot in use. Some are known to burst into flame. Let's use the figure of 73% overall for transmission, charge and discharge. Thus the efficiency of the systems is now .33 * .73 is now around .24, or 24%. Huge amounts of energy have been wasted in this electrical system.

I don't want to be mean - I'm really trying to be nice - but it is not true that "solar takes heat out of the air, makes electricity." That statement that it does so is absurd. One can easily see this by sticking a solar cell in a dark oven, turning the oven on and seeing if the cell generates electricity. Solar cells absorb light energy - radiation - and convert that light into electricity by exploiting electrons jumping energy levels according to the rules of quantum mechanics. They only capture some of the energy - there's a big hoopla going on when they reach 25% thermodyanmic efficiency in exotic systems like lead based perovskites, but generally the thermodynamic efficiency is lower - the rest of the converted light energy is rejected to the atmosphere as heat. This is why solar cells are black by the way, generally; they absorb light, not heat. They radiate heat as black body radiation, a common term discussed in preliminary college physics courses.

I marvel at how readily critics of nuclear energy are ready to display, often proudly, that they next to nothing about it. This ignorance and mysticism with respect to nuclear energy is part of the reason that the planet is bursting into flames as a consequence of the unrestricted release of dangerous fossil fuel waste, chiefly carbon dioxide, but also including many other noxious materials.

If one is interested in energy production and wishes to understand it, I recommend college level physics and engineering courses, particularly those where thermodynamics are discussed..

Have a wonderful evening.