Nuclear

Nuclear is called nuclear as it is about the nucleus of atoms rather than the electrons that orbit it, or the atom as a whole. The topic is generally split in relation to fission in electrical power plants and fusion that powers stars. The processes also occur around black holes and heavier elements also split naturally in the ground. Cascade fission can happen in the ground, but very rarely and generally only in the newest of planets. Both are nuclear processes, but when people talk about it, they are often only really talking about it in regards to power generation or bombs.

The energy for both, comes from releasing the nuclear binding that keeps the nucleus of an atom together, despite the protons being of the same charge and strongly repellent of each other. For comparison, chemical energy, such as the HydrOx reaction is actually due to the movement of electrons (between shells) of shared electrons. For chemical reactions, the nucleus of the atom is unchanged, within which the protons define the element. The nuclear binding force is stronger than the electron sharing force so nuclear power has the potential to release more energy per kg of fuel. Both nuclear and chemical reactions can be exothermic (gives energy) or endothermic (takes energy). Nuclear fission and fusion both have exothermic reactions that can be harvested, but at opposite ends of the periodic table, with the iron element (atomic mass including neutrons of 56) being at the peak energy of both. As Hydrogen (1) fuses to become Helium (2) it gives out energy, and so on up past carbon (12) and oxygen (16). Most of the energy gained however comes from fusing hydrogen (1) with helium (2).

The first nuclear reactions tapped for power used the natural decay of the unstable heavier Uranium isotope (238) into the lighter and stable isotope of Uranium (235). The energy is tapped as heat and so a block of uranium next to a thermoelectric (Seeback) generator, that directly converts heat to electrical energy, can be used to power simple probes for a long time, far out to cold deep space, such as Voyager 1 and Voyager 2 (although they used plutonium 238). Note that Uranium has 92 protons in the nucleus, the relatively unheard of neptunium has 93 protons and plutonium has 94 protons. Incidentally I hope you’ve noticed a planetary theme here. So to be clear, uranium (238) weights the same (near enough) to plutonium (238) but the uranium has two neutrons where plutonium has protons. All elements this size are naturally unstable and so any created naturally above uranium, have by now decayed into uranium if not onemade. Putting together is fusion, pulling apart is fission.

So we have direction. With iron in the middle, small atoms can be fused together heading up in mass, releasing energy, while larger atoms can be broken apart down in mass to release energy. If you really wanted to, you could put energy into breaking helium into two hydrogen atoms but it would be a totally pointless use of energy.

As the heavy stuff is more unstable, fission can leave you with atoms you don’t want, that will still break apart, emitting radiation. This is known as nuclear waste and is dangerous to life. With such a large atom, the process is slow and can take a very long time.

Power

Our electrical power is still mostly generated a process that uses steam. Ok, not steam engines, turbines but they are steam turbines. We still have coal fires heating water to make steam but we can also use nuclear power to make something hot to make steam. As the exothermic nuclear fission or fusion takes place, things get hot. A liquid of some kind called for obvious reasons, a coolant, is used to cool the things that get hot, extracting heat as the coolant gets hot. It gets pumped to a heat exchanger where that heat heats up the metal of the pipe, which then heats the water. As the water heats up the coolant cools, ready to be pumped back to the reactor to get hot by cooling it again. Because of entropy, all things will tend towards the same temporature, which is why this works. The coolant itself locked in a loop and never escapes, so if it becomes radioactive it is contained. The water that is heated is not used until it is superhot steam. Superhot isn’t some media exaggeration of something hot, it is under pressure so its boiling point is raised generating a higher temperature and greater pressure. That steam blows through a very clever fan system known as a turbine, which spins a magnet in a coil that generates electricity. The electricity, in the home can be put in reverse to run a fan heater, also using hot wires.

Nuclear Radiation

α - Alpha. Highly energised helium4 ions (atoms without electrons) made up of two protons and two neutrons. If Alpha radiation gets on or in you it will do the most damage, however, as it is so large it is actually the safest to deal with. When you see people wearing radiation suits, the ‘skin’ of the suit is enough to block the radiation and completely protect the wearer. Note that radiation suits are worn entirely for Alpha radiation; for most other radiation they are useless.
β – Beta. Highly energised electrons that can penetrate through a fair few meters of concrete. Beta is the most deadly radiation due to risk of exposure. Soldiers sent by governments to deal with nuclear meltdown are often given radiation suits as a form of protection. If the radiation is beta however then the protection is slight. The some soldiers received no protection and those sent into Chernobyl by the Soviet government were doomed.
γ - Gamma. Almost unstoppable and made of photons, this actually makes it the safest in regards to exposure risk. It may completely ignore a concrete wall but equally it is likely to ignore you as well. As it is a form of light it behave both like a wave, and as a particle, so it occasionally interacts with an atom.
Light. Not just gamma, x-rays and other light frequencies are possible.
Nuclear Particles. Protons and neutrons are also potential products of nuclear actions.

The thing to remember is that atoms, like everything, follow cause and effect, so the same elements will release the same radiation.

Fission Power

The origin of nuclear power, came with the realisation that heavy atoms were unstable in their nucleus. Uranium, a very common element found in most rock, especially granite, was found to be radioactive. Its isotopes range from 232 to 238, all of which can be found in typical quantities locked in ores, where it is chemically bonded to other elements. The most common ore is uraninite, UO2, which goes by its older name of pitchblende. Scientists realised that the high energy neutrons could trigger the larger unstable isotopes to fiss (I’m going to use this instead of split), which in turn would release three more high energy neutrons. As it’s unstable, uranium will also naturally fiss. What this means is that in order to create a nuclear bomb, all you need to do is get a sufficient quantity of uranium 238 atoms next to each other!

Refine a pure enough sample
Not kill yourself with a spontaneous predetonation once you have a pure enough sample
Trigger a detonation when you want one, i.e. over the enemy and not anywhere else
Not make everything that ever comes near it, including you, toxic to life, especially human life.

Nuclear power stations just use the heat from balanced chain reaction (for every U238 that fisses, only one escaping neutron will hit another U238 (slightly simplified)). The heat is simply used to boil water and the thermal/pressure gradient creates motion that spins a magnet in a coil of wire. The heat power is therefore turned into electrical power. The actual reaction control is brilliantly simple. The uranium is a tube with a hole in the middle and is enriched enough to have a runaway reaction. Control rods that absorb neutrons are hung down the middle. If the reactor is cooling then there isn’t enough reaction so the rods are lifted. If the reactor gets too hot then the rods are lowered. Dropped rods should stop any meltdown, as long as they don’t get stuck. For reasons of safety (and this is just a phenomenal dose of common sense), nuclear reactors never have enough density to have a chain reaction that triggers a nuclear bomb blast. The problem is that meltdowns are still possible where the chain reaction raises the heat to such a level that everything melts, and I do mean everything. As hot things tend to energetically escape a colder place, a nuclear meltdown is where the nuclear core in effect turns into a volcano, except the ash cloud and larva are all radioactive. Atoms generally don’t change and so this lava flow is radioactive with a half-life, on the extreme end, of about the age of the planet, which is about 4.54 billion years. So if a meltdown could be sent back in time to when Earth was formed, the ash would be toxic to the primordial soup, to the dinosaurs and if you walked past it would still be able to give you cancer even now. Note that half-life is the probability of half of it not being uranium and that includes the fast stuff. The half-life curve is one you should look at. Of course most would be fine after a few million years so if one happened now then... it still will be bad.

Fusion Power

Fusion is real but not yet commercially viable. It should be commercially viable in 10 years but it has been 10 years away for the last half century (actually a physics joke in every sense). The fuel it needs is plentiful, found in abundance in sea water, which also makes it cheap. The energy output per unit of fuel is orders of magnitude more that fission, which is also greatly more efficient than burning coal. Also, the radioactive half-life is about 3 years. Additionally it doesn’t need working control rods or cooling to keep it safe as it isn’t dependent on critical mass. If there is something that will change the world, it is fusion energy.

The two proven methods that work are, magnetic confinement, where a doughnut shaped tokamak is used like a magnetic bottle to hold a hot plasma, and the inertial confinement method where heat and pressure are applied in all directions at once via energy beams so containment isn’t an issue.

Inertial confinement requires a way to get energy into a very small space and lasers are the choice method, with hundreds of them all aligned on a small fuel pellet. Fusion has been proven to take place but using the output of energy is the problem for this method. The reaction is not continuous and process is designed to work like a four stroke engine, so I’m calling it four stroke fusion.

Intake (suck)
Compression (squeeze, but with lasers)
Fusion (bang, and for chemical reactions it’s combustion)
Exhaust (blow)

In my opinion, the tokamak is a beautiful thing, and why I chose it to be the base of my Merlin Engine. Fusion this way has been proven and used to generate power where the neutrons are without charge and so fly out of the plasma and heat up the chamber, which ultimately is exchanged in a way that leads to boiling water.

Cold fusion, so called as it can happen in a bottle of water, is currently fiction. The water has to be heavy water, i.e. made up of heavy hydrogen named deuterium (duo neutrons) and tritium (tri neutrons) bonded with oxygen (heavy H₂O). The theory goes that if you apply electrolysis, i.e. pass a current through the water, the electrical energy passing through is enough to cause fusion in a sequence of single atoms as they are very tiny. Experiments have reported excess energy but these are yet unverified and we don’t know where that energy came from. If the reports are true, it might be some form of chemical reaction with the apparatus and not nuclear fusion. It might even be a new way of holding charge, thought to be energy lost earlier in the experiment as heat. I’m please people are experimenting though as science is about finding out, and I really hope cold fusion is real. Evidence is required though.

Early fusion experiments looked to fuse deuterium as a proof of concept as the products, tritium and a proton, can be kept in the plasma to help maintain the temperature. Incidentally, if the proton captures an electron it becomes hydrogen with the isotopic name of protium, electrons act as a shield to the nucleus, which is why we have to heat them up to fly away from the nucleus (which is what plasma is).
D + D -> T with 1.01MeV + p with 3.02MeV
²H + ²H -> ³H with 1.01MeV + p with 3.02MeV
Energy pushes the two nucleuses together so in one location we have two protons and two neutrons. In this process however, some of the mass spontaneously converts to pure energy, a proton flies off with extra energy and we have an extra energised nucleus of one proton and two neutrons held in an electrostatic bond, which is tritium. Remember we humans measure energy as heat.
The net output on these two atoms is 4.03MeV where
1 eV = 1.60217656535*(10^-19) joules, or
1 MeV = 1.60217656535*(10^-13) joules, or
1 joule = 1.60217656535*(10^+13)MeV
It’s a straight ratio as both are a measure of energy. Similarly for mass 1u = 1.66053892173*(10^-27)kg
If you do the math, then this means that a single gram produces 97 Terajoules of energy. This, psychologists will tell you, is an unimaginable amount. In a nutshell, 1 gram generates the same energy as burning a trillion peanuts, which weights a billion kilos. Still unimaginable but I've impressed myself with the ridiculousness of this analogy.

Current fusion research facilities use the even more powerful deuterium tritium fusion generating a massive 17.6MeV per fusion event.
D + T -> ⁴He with 3.5MeV + ¹n
The neutrons are not affected by the magnetic field so it is a method of extracting the extra heat.

My Merlin Engine generates 18.3MeV and uses it, with the aid of fiction, to throw the He4 out into space.
D + ³He -> ⁴He with 3.6MeV + p1 with 14.7MeV
1eV =1.60217656535*(10^-19)J
The Deuterium has a mas of 2u, Helium3 has a mass of 3u, so the total mass used in each reaction is 5u.
1u =1.66053892173*(10^-27)kg

¹n is the mass of a neutron. You normally see n as a charge, as ⁰n
Masses are rounded. A proton has slightly less mass then a neutron. Please note that the energy released here is not from breaking down a neutron or proton into energy. It comes from the mass conversion of either converting a proton to a neutron, or from losing mass in breaking of the atom. You can think of this as glue energy, although no physicist will thank you for it.
E = M C ² is Einstein’s energy to mass ratio and quite handy.

Fission Bomb

The original nuclear bomb was designed in the Manhattan Project, where skipping a very interesting story, it was worked out that critical mass can be kept in two ‘too small’ halves, that an explosive could bring together. Once a lump of a fissile material is likely to trigger more than one fiss for every fiss that takes place, then you have reached its critical mass. At that point you have a runaway chain reaction and the whole mass will get very very hot and pressurised all at once. It will go off like a bomb. You don’t want to be anywhere near any substance that reaches critical mass.

Fusion Bomb

Very scary things, fusion bombs are also known as thermonuclear weapons, hydrogen bomb or h-bomb for short. It is known that fusion of light elements releases far more energy than the fission of heavier elements. The h-bomb is a two stage bomb and the really scary thing is that a fission bomb is used as a firing cap for a fusion bomb. The actual bomb itself is a mix fuel where both parts contribute to an explosion that equates to 10 megatons of tnt. A gram of TNT releases between 4100 and 4602 joules but to have a standard 4184 joules was chosen. TNT (not to be confused with dynamite) has a density of 1.654g per cm³. There is 1,000,000 cubed centermetres in a cubed metre so a cubed meter would weigh 1,654kg or 1.654tons. 10,000,000 tons of tnt would therefore take up 6 million square meters. As a typical stadium is about 1 million square meters in volume then dropping an h-bomb would be like blowing up six stadiums packed with TNT. At a power ratio of 5 to 4, this would at least be under five stadiums if you decided to use the more powerful dynamite. That’s a labour saving tip! TNT was chosen to be a comparative measure as it is a specific chemical explosive. Dynamite mass however varies in both total explosive density and local explosive density. It uses a packing material to hold a very powerful liquid explosive. When comparing power, we scientists don’t like to include sawdust in our explanations; it’s just bad form.

Dirty Bomb

If there is such a thing as honourable war, then it wouldn’t use dirty bombs, as they are dirty in every sense. What makes them dirty is the addition of radioactive material that will permanently ruin the land, people and buildings it explodes onto. So called honourable weapons aim to debilitate the enemy whereas dirty munitions, will harm noncombat civilians and innocent children even more than it will hamper soldiers. For a variety of self-interest reasons, we are fortunate to not have experienced any substantial dirty bombs. In my universe dirty bombs are banned under the EVIL Weapons Act 2088.