Training Program: Nuclear Energy Basics: A Nuclear Physics Primer without Quantum entanglements (gluons, quarks, leptons, fermions, hadrons, bosons and anti-neutrinos).
The only naturally occurring source of nuclear fuel is Uranium. Uranium is found in trace amounts and needs processing to be as pure as possible. The ability to create man-made Isotopes of radioactive elements is partly what is keeping the nuclear industry alive. And although very expensive to build, Nuclear Reactors are still the most efficient electricity producers ever constructed.
Thorium, often mentioned as a nuclear fuel, is technically not a fuel at all. Nuclear fuels are Fissile: capable of sustaining a nuclear chain reaction. Later I’ll explain the Thorium Cycle in which a Furtile material does produce nuclear fuel.
Nuclear Energy is not new – it’s just new to humans. Uranium was officially discovered in 1789 by a Prussian chemist: Martin Klaproth. But the mineral uraninite (or pitchblend) was used in Saxony as far back as 1565. We only started to understand it after Henri Becquerel’s work in 1896. Nuclear Energy has actually been around since the big bang occurred and when the first stars were born 300,000 years later. In fact, have you ever wondered how the center of the earth stays hot and keeps molten lava flowing? It is the presence of thorium, uranium, and other heavy metals changing from one state to another (perpetually releasing energy and heat) that enables the metallic core to remain molten at +4400 °C. Our current fear of radioactivity only began with the Cold War in 1947.
Let’s look at the Chemistry of Nuclear Energy. Transuranic Elements are atomic building blocks which are heavier than Uranium (element 93 on the Periodic Table). Transuranics are less stable than the lighter elements and they exist naturally only as fleeting, individual atoms. Over the Earths history they all decay and convert to other substances – effectively vanishing. These unstable elements, which decay significantly faster, are called “radioactive” (however everything is radioactive to some degree). Transuranic Elements are typically more toxic the quicker their decay rate; which is also called a short half-life.
In spite of occasional discoveries of new deposits, Uranium remains a scarce resource and is expensive to process. The industry has come up with some creative ways to produce fissile Uranium (nuclear fuel), including breeder reactors and the dismantling of nuclear bombs to use as ready-made reactor fuel! Plutonium is very familiar to us by name and is generally man made by using nuclear fission. Because these elements are unstable they will convert to stable or unstable isotopes – meaning they will have an atomic weight more or less near the natural weight plus or minus a few neutrons.
For instance 238U (Uranium isotope 238) is the normal atomic weight of Uranium but they have some 235U and 234U mixed with it. Just trace amounts of these other isotopes can weaken Uranium’s fissile ability so Uranium is usually processed by chemical means either into its useful concentrated 235U or into depleted Uranium-238 which is useless for energy but used in weapons ammunition. So a fissile element is able to convert to a new element and in the process releases energy.
Note: E = mc2, the famous Einstein formula, explains where the energy comes from in a nuclear reaction.
When observing binding forces, in ascending order of atomic weight, atoms actually reverse their ability to bind and these largest atoms are described as too large. The ideal binding elements are, no surprise to chemists, iron and nickel. The study of elemental properties is the key. The instability of Transuranic Elements are caused by their size. It’s actually the opposite of gravitational forces found between large bodies. The larger the atom the greater the density and the instability.
Radium (element 88) was the first synthetically recreated radioactive element back in 1936. Now several isotopes of Uranium and Plutonium are regularly used in Nuclear Power plants. Fission is dependent upon the unstable elements being able to absorb the uncharged unstable neutrons. Actinides (now called Actinoids) are all radioactive and are typically created during fission in nuclear reactions. The atomic number of an element indicates the number of protons within the nucleus. The Actinoid order has atomic weights of 89 through 103. Transuranics are 93-118; so Actinoids also include some of the Transuranics (93-103).
Neutrons are both uncharged and unstable. This unstable state can therefore be harmful – but also very useful. Here’s where the clever idea came from to manipulate the isotopes. If you think of the nucleus as a big ball of protons and neutrons and the forces that bind them together as having a limited range of say… the diameter of an iron or nickel atom… what happens when you have a really big atom like uranium where the protons at the north pole are beyond the attraction range of the protons at the south pole? Now the electromagnetic forces with their long range can start to cancel out some of the overall binding energy since the protons hate each other electromagnetically. Now imagine this ball like a drop of liquid suspended in the micro-gravity of space. Then a neutron comes along and taps the atomic ball – making it wobble… wibble… and at a critical point, the nucleus elongates and you have enough protons outside that short range from each other. The strong nuclear force starts to isolate and rebind these two future twins and the electromagnetic force between these two hemispheres is the only force remaining…. PING… fission!
The smaller pieces added together require a lot less energy to stay together because more of the protons are in range of each other. The leftover energy (heat) is that “PING” that sent them flying away from each other. When a series of these fission pings becomes self-replicating, a nuclear reaction is said to be Critical. This Point of Criticality can be adjusted by a number of ways: vary the size/density of fuel, rearranging the alignment, changing the temperature, or by using a neutron reflector.
The kinetic energy (plus the lesser gamma and neutron energies) of the 2 fission fragments flying away from each other is equal to the “mass defect” between U-235 and FP1 + FP2 (Fission Product 1 + Fission Product 2). As it turns out, all the parts put together in the original uranium atom have a higher mass than the pieces after fission. The mass difference got turned into an energy of approximately 200 MeV (pronounced mega-electron volts). Of this energy, 168 MeV is the kinetic energy of the FP1 and FP2 running away from each other, an average of 2.43 neutrons are emitted with a kinetic energy of ~2 MeV each, and a ~30 MeV gamma.
This curve is one way of expressing how all the stuff of the world behaves according to the size of it’s nucleus (Uranium, at 235, is really proud of it’s nucleus) and compares that nucleus size to how strong each nucleon (neutrons and protons) is glued together. When we fission a heavy nucleus, we are really just taking energy that was stored as mass from when some star went “kablooey” an eon ago and pushed a bunch of basic elements together very tightly: Presto! – all kinds of heavy metals were formed. Since only the short-range nuclear force can hold such a big atom together, all we ever find is Uranium, since it’s pretty stable. Who knows, maybe that Uranium atom was something tremendously big at first but decayed to where it is now. If it wasn’t for the “kablooey” of a stellar nova, we wouldn’t see atoms much bigger than nickel or maybe cobalt.
The Thorium Cycle – Discovered in 1828 by the Norwegian mineralogist Morten Esmark, Thorium was identified and named by the Swedish chemist JJ Berzelius. Thorium has 90 protons and is element 90; so in it’s natural state it has an equal number of protons and electrons. It decays quite slowly with a half-life of 14.05 billion years, so Thorium also makes for an effective radiation shield! The Thorium Cycle is a process where fertile Thorium absorbs a single neutron, converting to Protactinium-233 and then decays after 27 days to become fissile Uranium 233. Best used in a liquid-state, molten salt provides an ideal medium for the Thorium cycle. The salts naturally melt at a higher temperature (+460° C) than highly pressurized water and is safer in reactors because it does not require the high pressures (70+ atmospheres or 1015+ psi) that Light Water Reactors and CANDU reactors need just to keep the water in a liquid state. Fluoride salt has some very stable qualities. Fluoride is the salt of choice for THORIUM LFTR’s …
… to be continued