USA needs nuclear to achieve net zero, says US Energy Secretary Granholm

[NNadir]

57. You have correctly touched on nuclear energy's most important drawback.

Most pressurized water and boiling water reactors, which dominate the world's current nuclear fleet operate at low thermal efficiency, Rankine efficiency, roughly in the neighborhood of 33%. This means that 67% of the primary energy is rejected to the environment for these reactors. This is not a problem generally in winter (when in fact the efficiency is slightly higher because of the Carnot relation), but it is a serious problem in summer, particularly in the era of climate change.

The work that is extracted from a heat engine is called the "exergy." The second law of thermodynamics precludes the exergy from ever reaching 100% of the primary energy expended, but one can increase the exergy by various procedures to much higher percentages than is generally observed in nuclear plants built on 1970's technology. The efficiency is a function of the difference between the heat sink and the heat source.

This problem can be solved - although it may seem counterintuitive - by raising the temperature at which reactors operate - a topic that is the subject of much discussion in nuclear engineering circles.

Most dangerous fossil fuel plants have efficiencies in the same neighborhood of the majority of the existing nuclear fleet. However, in the last century, advances in materials science allowed for the development of "superalloys" and thermal barrier coatings, generally ceramics. These have allowed more efficient dangerous natural gas plants to be built, so called "combined cycle" plants. Some of these operate at thermodynamic efficiencies close to 60%.

My approach to thermodynamically efficient nuclear plants would be this: A Brayton cycle using air as the working fluid, coupled to sulfur iodine thermochemical cycle, coupled to a cycle known at the Allam cycle, although in my thinking one might call it a "reverse Allam cycle" for the capture of carbon dioxide, coupled to a steam (Rankine) cycle, with the cooling coming from the preheat of air for the first (Brayton) cycle. My idea - based on certain chemical considerations - would be for the Brayton cycle to operate at temperatures in the neighborhood of 1500C.

It certainly seems possible to raise the overall thermodynamic efficiency to the realm of 70% or even higher, by such a scheme.

This type of scheme is known as a "heat network," and it is the best idea in energy.

The anti-nuke moron Amory Lovins sold the world a bill of goods saying that the purpose of efficiency is to reduce the use of energy. He made this statement as a result of his poor education and his lack of familiarity with Jevon's paradox.

I, by contrast, embrace Jevon's paradox. For me the purpose of efficiency is not to reduce energy use but rather to extend it to those who lack it, the number of such people being unimaginably and unacceptably large.

Unlike what seems to be the case with the obscene Lovins in his bourgeois aerie in Snowmass, I actually think poor people matter.