Welcome to Nuclear Update, the newsletter that makes long nuclear roadmaps feel less like homework and more like an indulgence.

You know the drill by now, while I’m temporarily operating a newborn reactor at home, I have invited long-time Nuclear Update readers to step in.

Alex Kovnat holds an M.S. in Nuclear Engineering from Purdue and wrote his thesis on breeder reactors back in the 1970s. In this guest edition, he makes a serious case: light water reactors are not enough if we want nuclear to power modern civilization long term.

If you care about fast reactors, thorium, or the future of advanced nuclear, this one is for you.

Over to Alex.

But first: this week’s trivia question:

Last week, I asked: 

When is an atom considered stable?

You said: 

⬜️⬜️⬜️⬜️⬜️⬜️ When it has no neutrons. (3%)

🟨🟨🟨🟨🟨🟨 When it has the same amount of electrons as protons. (65%)

⬜️⬜️⬜️⬜️⬜️⬜️ When it has an odd number of valence electrons. (2%)

🟩🟩⬜️⬜️⬜️⬜️ When it has a full outer valence shell. (30%)

Now, let’s dive into the good stuff!💥

⚛️ Why Light Water Isn’t Enough

Hello readers let me introduce myself. 

While Fredrick is taking a breather owing to welcoming a new family member, I was invited to contribute to our weekly nuclear update. 

My name is Alex Kovnat, and I’ve been into nuclear energy since my university days. My undergraduate major was Mechanical and Aerospace Engineering at Illinois Institute of Technology, leading to my Baccalaureate degree in May 1971. During the latter part of my student days I developed an interest in energy and power, and came to believe nuclear energy would be essential to maintain the standard of living we are accustomed to. 

In autumn 1971 I began graduate studies in nuclear power at Purdue University. I wrote my thesis on the problems of breeder reactors, as I believed then and now that light water reactors would not suffice in the long run. In May 1973 I completed my thesis and left Purdue University, carrying with me the parchment certifying my Master of Science degree in Nuclear Engineering.

In September 1973 I was hired in the Mechanical Analytical Division of Sargent & Lundy Engineers in Chicago. Unfortunately the downturn in S & L’s fortunes in 1975 led to my being laid off in April 1976.

After about a year and a half of uncertainty in my life, I was hired by the U.S. Army Tank-Automotive Command in Warren, Michigan in September 1977.

I worked there for almost 40 years, retiring in July 2017. Thanks to the generosity of our government paying the tuition, during 2002-2007 I took courses in automotive engineering at Lawrence Technological University leading to M.S. in Automotive Engineering.

Through all those years I never lost my interest in nuclear power and the broader area of how we can meet our energy needs to sustain our way of life, what with concerns about the world running out of oil and later on, the earth’s atmosphere running out of room for all the fossil fuel carbon dioxide our way of life was generating. 

So much for my life story. I would now like to put forward my views on why we need better nuclear reactors than the light water reactors that are presently most commonly used in the electric power industry. 

Why Coal Runs Hotter

When I was working at Sargent & Lundy, the typical coal-fired electric utility power plant steam generator produced superheated steam at 1000 degrees Fahrenheit and 2400 pounds per square inch absolute pressure (psia) going into a high-pressure turbine driving a huge alternator.

After passing through the HP turbine, the steam – now at lower temperature and pressure – is led back to the steam generator, where it is reheated to 1000 degrees or a little more. Reheated steam then expands through an intermediate pressure turbine and then through a low pressure turbine, whereupon it enters a condenser and is condensed back into liquid water. 

Water coming out of the condenser is preheated by a string of feedwater heaters, which are supplied with steam tapped off the intermediate and low pressure turbines. The feedwater is pumped up to high pressure by a feedwater pump, then fed back to the steam generator to repeat the cycle. 

Coal-fired power plants using the above technology, may attain thermodynamic efficiency of 35% or more at full load. 

Now consider the operating parameters of light water moderated and cooled reactors, in particular pressurized water reactors (PWR’s). In a typical PWR, ordinary water (light water as opposed to heavy water which I’ll explain later) serves as both the moderator and coolant.

So as to maintain said water in liquid state, it is pressurized to approximately 2250 psia. Water enters the reactor at 550 degrees F., and after picking up heat from fission occurring inside the reactor core, exits at 625 degrees.

The heated water progresses to a steam generator, where it transfers heat to a steam turbine power cycle. Steam from the steam generator is typically at 870 psia pressure and no more than approximately 525 degrees F. 

Because main steam temperature and pressure with a PWR power plant are lower than the 1000 degrees and 2400 psia with coal-burning power plants, the overall efficiency in generating electricity of the former will be only about 32-34%. Hence power plants based on light water cooled and moderated reactors (both pressurized and boiling water) produce more waste heat than fossil fuel fired power plants, which must be carefully managed to minimize the problem of “thermal pollution” of rivers and lakes. 

This is the first of two disadvantages of present day light water reactor based nuclear power plants. 

Hotter Reactors, Better Output

There are other nuclear reactor types which operate at higher temperatures, hence can provide steam at higher temperature than LWR’s. Assuming all other aspects stay the same, power plants based on such reactors can provide more electric energy in proportion to the number of fission events in the reactor core, hence more energy in proportion to uranium (or thorium) consumption.

In addition, more thermodynamically efficient power plants (nuclear, or for that matter fossil-fuel fired) produce less waste heat, hence lesser problems with thermal pollution. And with fewer pounds of uranium fissioned in proportion to kilowatt-hours of electric energy, there will also be fewer prounds of fission product waste. 

One promising alternative to water as reactor coolant, is helium. It is inert chemically, hence can be used with graphite-moderated reactors operating at high enough temperatures to provide (allowing for temperature drop in the heat exchanger) 1000 degree steam with which to drive turbine power cycles at efficiencies comparable to fossil-fuel fired power plants. 

Liquid sodium, which is the coolant in most liquid metal cooled fast-neutron breeder reactors built or proposed, is also suitable for operation at temperatures of 1000 degrees. According to World Nuclear News:

The overall thermal efficiency would therefore be 38%, which is better than LWR-based power plants. 

💪Review of the Week

DISCLAIMER: None of this is financial advice. This newsletter is strictly educational and is not investment advice or a solicitation to buy or sell any assets or to make any financial decisions. Please be careful and do your own research