The Future of Fission

The Future of Fission

by Tamaris Bagrationi, Southron University Astrophysicist in Residence (and at large)

It is broadly assumed that once controlled fusion is mastered, that fissionable materials such as Uranium and Plutonium, and their lesser celebrated cousin Thorium would be relegated to the dustbin of history. A dark toxic waste nightmare we will be more than happy to leave behind us.

Even with controlled fusion, there are still many good uses for fissionable materials.

Fusion weapons are actually fission implosion fusion weapons. A fissionable mass implodes inducing the fusion of the Deuterium/Tritium Mass. There is a physical limit to the efficiency/yield, about 6 million ton TNT equivalent per ton. Compare with 257.75 million tons per ton for idealized antimatter weapons, realistic numbers are closer to about 48 million tons per ton. Nearly 8 times more yield than a fusion weapon, a waste of antimatter if you ask me.

It should be noted that the energy content per unit volume (not per unit mass) of a well made fission weapon is 28 times that of the best fusion weapons. This high energy density per unit volume is why fission implosion is used to trigger fusion bombs.

The energy content per unit volume is also why Anti-Nickel and Anti-Cobalt is so valuable, and ultra-dense Rydberg Condensed Anti-Cobalt Hypermatter even more so. Anti-Nickel and Anti-Cobalt have over 100 times the energy density per unit volume of anti-hydrogen (antiprotium) and 4.6 times the detonation efficiency, and 49 times energy density per unit volume of Anti-Deuterium.

Controlled fusion has a higher efficiency than that used for fusion weapons, but they do not actually make very good explosion weapons. A lot of energy, but the speed of reaction, being CONTROLLED, is not as destructive. Controlled fusion is good for powering beam and particle weapons, shields and propulsion, all great and worthy applications in and of themselves, just not massively destructive explosions.

Explosive damage is not just about the energy content, but the detonation velocity. Fission implosion induced fusion has a higher detonation velocity than controlled fusion. Until you make the jump to antimatter annihilation, 6 million tons per tons is about your maximum explosive weapons yield.

Matter Antimatter annihilation is not as easy as you might think, a lot of it goes into mostly useless (nondestructive) neutrinos and a lot of the antimatter will actually be blown away from the reaction mass. Thousands of 1 gram pellets of antimatter is about the same energy density per unit volume as a well made fission warhead, Making millions of microscopic or billions of nanoscopic pellets of antimatter is a waste of good antimatter. A dilithium bomb is a great shortcut to exceptional efficiency, but is a terrible waste of expensive and rare dilithium. I am certainly not going to waste my expensive and very hard to get Illudium Q-36 Explosive Space Modulator. The efficiency of reaction created by dilithium is what makes it so valuable.

Special Note: If the shields of the ship is more than 21 meters from the hull, fully 30% up to 45% of the energy of the matter-antimatter annihilation in the form of charged pions will have converted into harmless neutrino’s and muons having minimal effects. This is the practical reason for the bubble shields if anyone ever asks you.

Controlled fusion yields vary from 4.25% of C exhaust velocity for Deuterium-Deuterium, to about 8.9% of C exhaust velocity for the rare and expensive Deuterium-Helium3. The efficiency also varies by the method, discussion for another time. Note, there is more to fusion than just the energy content, there is the actual exhaust products. Some fusionable fuels have very low heavy-neutron exhaust and can be safely used within the atmosphere of an inhabited planet. Most have a lot of gamma and neutron byproducts and should only be used in heavily shielded ship and in deep space. Some pricier fusionables actually have proton exhaust products, which are easily managed and convenient for powering weapons and shields. Typical fusionables range between 6.5 to 28.5 times the energy content per unit mass of the fission implosion fusion weapons, but again, good for operating systems, but not sheer destructive power. I am not including in this discussion lesser known but moderately interesting low-yielding fusionables such as Lithium-6 (Tyllium), Nitrogen-15 or Barium-11, which have their own uses.

Fusion reactors do not explode, they fizzle and sputter out quite unspectacularly.

But this is about fissionable. I digress.

Natural Uranium is only about 0.3% of the fissionable Uranium-235, the remaining 99.7% is non-fissionable Uranium-238. Uranium-238, more often referred to as depleted uranium and sometimes as Duranium, is ironically useful as radiation shielding. Its low grade beta radiation can be blocked with wet tissue paper. It is also used as a radiation tamper to reflect back the heavy neutrons and radiation to ensure a higher yield on the fission implosion weapons. Duranium is also used for dense kinetic weapons such as rifle bullets and even railgun ammunition.

Duranium (Depleted Uranium) is also a popular component of ship hulls because it’s high atomic mass makes it remarkably resistant to the Nuclear Destructive Force Effect of Federationalist Zone phaser weapons.

One application of both Duranium and antimatter is the Antimatter Catalyzed Microfusion Engine (ACME). Fission and fusion both don’t scale very well, and as the detonation mass gets smaller, the harder and more complex it is to activate the fission part and the yield drops. The clever folks at ACME, out of Penn State University before they merged with Yoyodyne Propulsion, figured out that you can use a nanoscopic (1 part in a billion) of antimatter to trigger the fission implosion and cause the fusion reaction at almost any scale, but keep the fantastic 6 megatons per ton yield. There is details and nuance, but it is simpler technology that trying to make tactical nukes. Provided you have at least a few micrograms of antimatter per ton of duranium, you are good to go.

Fuel pellets are 2.7 grams of Deuterium/Tritium and 0.3 grams of Duranium (Uranium-238), enclosed within a shell of about 200 grams of lead, and are activated by a pulse of about 100 billion protons, plus another 800 grams of propellant. Each pellet produces about the equivalent of 566 tons of TNT (237 terajoules). One BILLIONTH of a gram of antimatter per 2.6 tons of Deuterium/Tritium/Uranium pellets.

ACME’s value isn’t just its yield and size scalability, but its simplicity and use of materials. The best part about the ACME, is that it does not require some Nobel laureate nuclear physicist to operate and maintain it. Your garden variety fusion-mechanic (space mechanic?) will do adequately. For the most part it is simply a very complex fuel injector system.

Plutonium and Uranium Salt Water Rockets are even simpler. Inject measured amounts of finely powdered plutonium or uranium in water, it heats up and expands as propellant. This is usually only used for deep space, nowhere near inhabited areas. It is remarkably simple, no Nobel laureate or even a fusion mechanic, a space-plumber can operate and maintain it. Its simplicity and reliability is often used for accelerating large masses slowly over long periods of time, like asteroids and comets. Set it, point it, let it go, move on.

Enriching Uranium and Plutonium to be reactor grade or weapons grade is time consuming and costly. Fission Salt Water Rockets can use sub reactor grade fissionables. They’re dirty, but usually used in places where the background radiation is such that it is not going to make an impact on any inhabited systems. The fuel is set at about a 2% solution of only 20% enriched Uranium. That means per ton, 980 kilograms water propellant per 20 kilograms of fissionable fuel, and that 20 kilograms is only 20% fissionable Uranium-235, 4 kilograms net of Uranium-235. The thrust to weight ratio is impressive, about 40 to 1, which is very useful for accelerating a very large mass in deep space when you can have it accelerate a fraction of a G.

Uranium, Plutonium, and their lesser known cousin Thorium, will be useful into the forseeable future, but also Depleted Uranium (Duranium) and even nuclear waste will have a use in deep space operations.