The Science Behind ETERNAL SHADOW #2: Nuclear Reactors in Space
When the world is threatened by a planet-destroying entity, what can we do?
That’s one of the overarching questions which is explored in Eternal Shadow. Given enough time to find an answer - in this case, about ten years - our options aren’t as limited as one would think. A lot of doors can swing open when the difference between decisive action and inaction is total annihilation. Doors swing open, and in the case of the events that play out in my book, one certain technological prejudice is very reluctantly put aside for the sake of our survival.
That prejudice is the opinion the majority have toward nuclear energy.
As the alternate Earth I crafted continued to evolve, solutions to the above question swirled in both my mind and the many characters in Eternal Shadow. It was a very hard question which I admittedly didn’t quite know how I was going to resolve.
Actually, let me clarify: I knew how I wanted the book to end, but for a long time the how just didn’t have an answer. It was a fairly large, game-breaking hole in the plot, for sure. That didn’t stop me from writing nearly half the novel before one of my alpha readers made me realize that I was going about this all wrong. It wasn’t about how humanity could defeat or otherwise have some sort of physical triumph over something several times larger than Earth.
Eternal Shadow is about humanity’s creativity and ability to conjure real-world solutions to truly extraordinary situations. This inventiveness is only intensified when we’re pressed into a corner, needing to fight for our right to exist.
After thinking about the how in this light, the right question was uttered from my mouth.
A week later, I had the solution! Plot hole filled!
When Solar Isn’t Enough
But wait! There were still hurdles to overcome even with this solution. With a book that was to be grounded in the sciences, the solution I discovered would require not only a lot of energy, but a lot of energy in space. After reading about the International Space Station - the largest artificial structure mankind’s built in orbit - and its power requirements, however, I realized that I had to really think outside the box to power what I wanted to have constructed. Solar energy, though improving all the time, just isn’t a truly economical solution if you want many Megawatts (MW) of power generated in space.
I posited a question on Quora to determine what it would take to have, for the sake of the question, a space station which required 100MW of power. In summary, about 37,000 square feet of solar panels (about seven football fields!) would be needed to ensure the array of power storage batteries (totalling 100MW) could be charged in an hour. If you decided to rely only on solar, you’d need a whopping two million square meters (about 350 football fields) of solar panels to keep that power flowing.
Given the timeline humanity was working with, it became abundantly clear that solar simply was not going to work. So… what’s left? What technology do we already have which could generate the power I needed?
The answer came much faster than I expected, but it made so much sense.
I needed to get a nuclear power plant in space.
So where do we begin?
First off, the original, more well-known designs for nuclear power were out. The last thing I wanted was to build something like a pressurized water reactor (PWR) (ex: Three Mile Island, Fukushima). This is the most common design for nuclear reactors today. It’s also the oldest. It also has many disadvantages compared to its modern variants.
How a pressurized water reactor works, in a nutshell:
The primary coolant (water) flows through the reactor core under extremely high water pressure, during which the coolant heats up as a result of exposure to the nuclear fuel (enriched uranium in many cases).
The secondary coolant (also water) flows around the primary coolant (the primary flows through hundreds, if not thousands, of small pipes), evaporating into steam.
The steam is fed to a series of turbines which drives an electrical generator.
I left out a couple of smaller details, but this is the gist of nuclear power generation. If you’d like to learn more, the World Nuclear Association has a ton of information on all the components, fuels, and technologies used as part of nuclear power.
Why is PWR a problem? Three Mile Island and Chernobyl suffered similar fates, though the latter, as we know, fared far worse. In short, the reliance on highly pressurized water over time can (and has) result in coolant failure. This can occur due to the pipes the high-pressure and high-temperature water flows through failing as a power plant ages. If enough primary coolant escapes or evaporates, this can lead to an uncontrolled nuclear chain reaction, ending with an explosion.
And that’s when you’re on Earth. Can you imagine what could happen if a similar incident occurred hundreds of miles over the surface? And this doesn’t take into account just how truly complex a system PWR requires in terms of physical footprint.
So we want something much, much smaller, can still pack a lot of energy into that small space, and ideally cannot suffer from a catastrophic meltdown. Does this sort of nuclear technology exist?
The Future of Nuclear Energy
Enter the fast neutron reactor (FNR). Unlike PWRs, this very modern development does not require a secondary coolant by design, resulting in a significantly smaller power plant size. That is… smaller than a few semis with trailers lined up in a row. Eschewing water, FNRs are cooled with liquid sodium, a liquid which can absorb far higher temperatures than water (a high heat capacity). This heat, unlike PWR, can be radiated away versus cooled by a secondary coolant. And it can be cooled by outside air in the event of a shutdown, thus eliminating any possibility of there being a meltdown.
FNRs require enriched uranium or plutonium as its source of fuel, but due to the fact that FNRs can use the waste it creates into more fuel, such systems can effectively run several decades longer than PWRs without refueling - all while significantly reducing its own nuclear waste footprint.
When I first began exploring this solution, I was first directed to the Toshiba 4S FNR, a design which I modified for use in deep space (with lots of help from Dr. Rorbert August, a nuclear physicist). The documentation was thorough and detailed to the point where everything I needed for a viable spaceborn solution was present.
Designing a nuclear plant in space did have challenges which existed due to the microgravity environment, but they weren’t game-breakers. For example, additional fluid pumps would be needed to continuously move the liquid sodium in a cycle. Another problem was the absence of air for the heat to naturally radiate into and away from the plant. This was solved using large fins made of polyimide, a material used for - among other applications - heat dispersal. Running the heated sodium through these polyimide fins provided a method for effective heat radiation while in space.
There are many obstacles in place today which not only would prevent such innovative use of nuclear technology in space (there would be many benefits if we did, such as allowing the support for significantly larger space stations than the ISS), but even such tech on the ground. The reality of today is that nuclear still has a negative stigma hanging over it. That stigma has resulted in nations like Germany vowing to shut down all their remaining nuclear plants by 2022 and France cancelling the construction of their first fast neutron reactor.
Despite these setbacks, researchers continue plowing forward with innovations in nuclear power generation. One day in the near-future, maybe long after our parents - and maybe even my generation - have gone, our children or grandchildren will embrace the atom once again.
What are your thoughts on nuclear technology? Should it be considered alongside other environmentally-friendly solutions like solar and wind? Comment below!