Nuclear reactions involve nucleons and nuclei and deal with much greater amounts of energy than chemical reactions, which involve whole atoms.
The typical nuclear reaction process involves a projectile particle colliding with a target nucleus, forming a compound nucleus which instantly decays to a residual nucleus and an emitted particle. This reaction is represented symbolically by:
A + a –> C* –> b + B
where A is the target nucleus, a is the incident particle, C* is the compound nucleus, b is the emitted particle, and B is the residual nucleus.
The shorthand notation for this reaction is A(a,b)B or just A(a,b).
For the entire reaction, charge, nucleons, and mass and energy are conserved (even though some mass may be converted to energy or some energy converted to mass).
Here are some examples of nuclear reactions:
7-N-14 + 2-alpha-4 –> 1-H-1 + 8-O-17
(the first artificial nuclear reaction)
5-B-10 + 0-n-1 –> 4-alpha-2 + 3-Li-7
Typical projectiles are gamma rays, neutrons (n), protons (p), deuterons (H-2 nuclei), tritons (H-3 nuclei), and alpha particles (He-4 nuclei).
Since E=mc^2, it can be seen that Q-value is the difference in mass (or energy) of the products and reactants in the reaction. Thus, if Q>0, the reaction is exoergic (gives off energy). Therefore, regardless of the kinetic energy of a (the projectile particle), the reaction can energetically occur.
However, if Q<0, the reaction is endoergic (energy is required to make the reaction occur). Thus, Ka must be sufficiently greater than -Q to account for the increase in mass, plus enough energy to conserve linear momentum. This total minimum energy is called threshold energy.
This section covers the fundamentals of how an atom looks, what it is composed of, and examines the electron shell structure.
ATOM: the most basic form in which an element can exist – i.e., a single atom of oxygen, O.
An atom consists of a nucleus, consisting of protons and neutrons, and an orbital cloud of electrons. Protons and neutrons together are known as “nucleons,” as they are found in the nucleus. The electrical neutrality of the atom is maintained by having the same number of electrons in orbit about the nucleus as there are protons in the nucleus. The reason for this will soon become clear.
The NUCLEUS is the core of the atom, and has a diameter of around 10e-15m. The following equation gives the rough estimate for the nucleus of a specific element:
R=1.3(A)^(1/3) x 10e-13 cm
where A is the atomic mass number (the SUM of the numbers of neutrons and protons in that nucleus).
Atomic size is larger than that of the nucleus, due to the fact that the electrons orbit at far distances from the nucleus. The size of an atom is around 10e-10m.
The mass of an atom is usually around 10e-27 kg. It is awkward to deal with such a small mass in kilograms, thus we use ATOMIC MASS UNITS. By definition, 1 AMU = 1/12th. the mass of the C-12 atom. Thus, 1 AMU = 1.6605 x 10e-27 kg. Also, due to Einstein’s famous E=mc^2, mass can be expressed as an energy equivalence, which is 1 AMU = 1.49239 x 10e-3 g cm^2s^-2 = 1.49239 x 10e-3 erg = 931.467 MeV. In calculations, it is typical to use the value of 1 AMU = 931.5 MeV for simplification.
The symbol Z is used to refer to atomic number (the number of protons) and A is used to refer to mass number (the sum of the number of protons and neutrons. This leads to a shorthand notation for elements telling us how many protons, neutrons, and which element it is we’re talking about:
Atoms have another characteristic: ATOM DENSITY. This is the number of atoms per some unit volume. Atom density N is given by:
N = N[o](density)/AW
where N[o] is Avogadro’s number, 6.0225 x 10e23 atoms/mole, [density] is the density, and AW is the atomic weight, in grams per mole.
This calculation also works for molecules, but you replace atomic weight with molecular weight to find molecular density.
Visible light is a form of elctromagnetic (EM) radiation, as are X-rays, gamma rays, and radio waves. At the beginning of the 20th. century, it was observed that in some experiments, light acted like a wave (it could be diffracted), and in others it acted like a particle (it could be scattered with a decrease in energy). This was called “wave-particle duality.” The following equation sums this up:
E = hu = hc/[lambda] and h/[lambda] = p
where h = Plank’s constant (6.6252 x 10e-27 ergs-s); u = frequency (oscillations per second) of the photon, c = speed of light in a vaccuum (2.998 x 10e8 m/s, [lambda] = wavelength of the photon, and p = the momentum of the photon.
People often tend to use the words “atomic” and “nuclear” interchangeably. In actuality, the terms mean different things. “ATOMIC” refers to processes involving the orbital electrons of the atom, such as chemical bonding. “NUCLEAR” means things that involve the nucleus, such as nuclear fission and fusion.
It wasn’t until almost the turn of the century before we started probing into the structure of the atom. In 1897, J.J. Thompson experimentally discovered the electron, but atomic structure was still uncertain. In 1913, Bohr proposed that electrons orbit the nucleus at fixed distances from the nucleus in “quantized energy levels.” This opposed the idea of classical physics that said that the electrons would simply spiral down into the nucleus.
Bohr also suggested that electrons could only move from one energy level to another by gaining or losing energy, This was accomplished through the absorption or emission of a photon of the right energy. Some of the photons given off when an electron drops an energy level are called X-rays. X-rays are also produced whenever a substance is bombarded by high speed electrons.
In the figure above, energy input to a K-shell electron causes the K-electron to transfer to the L-shell. However, since all lower electron shells must be filled, the empty K-shell position is rapidly filled by an outer electron, releasing energy in the form of a photon of X-ray energy.
The nucleus was discovered in 1911 by Thomas Rutherford while shooting alpha particles at gold foil. He noticed that occasionally the alphas would rebound straight back to where they came from. Rutherford said, “…it was about as credible as if you had fired a 15 inch shell at a piece of tissue paper and it came back and hit you.” Based on these experiments, Rutherford developed his “planetary” model of the atom.
Each element has a nucleus consisting of A nucleons and Z protons. Each element is defined by the number of protons it contains, but an element may have several different forms which contain different numbers of neutrons. Each of these forms of an element is called an isotope. Hydrogen, for example, has 1 proton in its nucleus. However, hydrogen has three forms, namely, H-1, H-2, and H-3. H-1 has one nucleon (the single proton), H-2 has two nucleons (one proton, one neutron), and H-3 has three nucleons (one proton, two neutrons). These configurations are pictured below.
Within the nucleus, nuclear forces hold the nucleons together. These forces are very powerfull, but of very short range. There is actually a net energy benefit for holding the whole nucleus together, thus, due to Einstein’s mass-energy equivalence, the mass of the atom is actually less than the sum of the constituent particles. This difference is called the binding energy (B.E.).
The binding energy is the energy released when a nucleus is formed from particles. This is the source of the energy in fission and fusion reactions. Also, the binding energy is the energy required to split the atom into a total of Z seperate protons, Z seperate electrons, and A-Z neutrons.
The planet is facing several issues that must be dealt with very soon. Concern over the environmental impact of energy production and the replenishing of energy reserves are the primary concerns. We live in a world of ever increasing energy demands, and ever increasing awareness of the damage that we, humans, can do to the environment.
Worldwide energy demand will nearly triple by the year 2060, and within that, electrical power demand will more than quadruple within that same timespan. Oil and gas currently provide greater than 70% if US energy, and known world energy reserves only provide a sufficient supply for the next 20 years’ worth of worldwide demand. Coal provides about 20% of US energy, and known reserves can provide US electricity needs for another 200 years, but at a cost of 250 new mines, 160,000 new miners, and $20 billion in capital in order to increase coal supply to 40% of US power.
Solar power, hydroelectric, wind, and biomass power are all insufficient in magnitude to make a significant contribution to electrical power generation. The energy required to build a solar generation station would equal the output of that station in a 30 or 40 year span. Wind power could conceivably produce 5% of US electrical demand, but only if we used 500 foot turbines, space 500 feet apart, stretching from the Canada border to the Mexico border, with a constant 20 mile per hour wind. In other words, absolutely impractical.
Current uranium reserves could very well provide all US electrical power for 60 years with current reactor technology, or greater thatn 1000 years with the use of breeder reactors. The energy output from ONE 1000 MWe nuclear power plant equals all the energy output for all autos, trucks, buses, trains, ships, and planes for a city the size of greater Portland, OR (1+ million people).
In fact, the US currently has 300,000 tons of mined, refined, and stored Uranium-238, which could provide all US power for 150 years, without turning another shovel. This is three times the world oil reserves. And all this uranium is sitting in storage as we speak.
The environmental impact of fossil fuel use is staggering. Man releases 7 billion tons per year of carbon into the air, and the release of SO2 and NO causes air pollution and acid rain. The burning of fossil fuels scatters heavy metal and radioactive particulate matter into the air. A 1000 MWe coal plant burn 100 train cars of coal per day, generating 33 train cars per day of ash that must be disposed of.
Granted, modern nuclear reactors have their downside, too. There is the volume of radioactive waste and the increase in amount of heat discharged to cooling channels, such as rivers and streams. However, with the use of fuel reprocessing and breeder reactor technology, the waste generated from nuclear reactors with have a radioactivity LESS than when the uranium was initially dug out of the ground after a 600 year decay span. Also, all the waste generated from a 1000 MWe plant in one year could easily squeeze into the space under your dining room table.
Many people are similarly uninformed about radiation hazards. The average American receives a natural background dose of 300 to 350 millirem of radiation per year. Everything around you is potentially radioactive. Bricks, stones, dirt, food, even the air you breathe has some amount of radioactive elements in it.
At the Piqua Ohio nuclear/coal plant, a power plant with both nuclear reactors and coal fired sides on the same plant, when the coal plant is fired up, the nuclear side’s radiation monitors have to be turned off due to the high level of radioactive material released by the coal burning. Also, under current federal regulations governing radiation exposure within a plant, the Capital Building in Washington, D.C. would be unlicensable by the NRC, as the stone construction of the building puts out a higher level of radiation than the federally allowed level. And, on average, whiskey has approximately 120 times the radioactivity per liter of nuclear plant discharge water. In other words, you receive a much higher internal radiation dose from a shot of whiskey than you would if you swigged a shot of nuclear power plant effluence.
It is also interesting to note the safety record of the nuclear industry. The accidents at all US nuclear power plants have shortened the lifespan of the average American by the same factor as smoking one cigarette every 20 years or gaining 1 ounce in body weight.
Meeting the energy demands of the future will require forthright planning and great technical ferocity. Environmental concerns are paramount, and future generations of humans must still have a planet to call home. Nuclear power must be part of the solution for a safer, happier future for planet Earth.
The 1970 edition of the “Radiological Health Handbook” published by United States Public Health Service (US Department of Health, Education, and Welfare) is one of the most coveted and difficult to obtain publications in the world of rad health. It has been a staple of the industry as a reference work for 40 years in the world of radiation protection. Radiological Control Technicians (RCT – the DOE term for the profession) and Health Physics Technicians (the commercial nuclear power term for the field) use it to this day as a reference for dose calculations, determining shielding requirements, and more.
I was incredibly lucky to obtain a copy of the book via another RPT back in the day when I needed it. It’s been sitting on my shelf for several years now, but I’m trying to clean out material possessions. A search of the Internet revealed that nobody had yet taken apart their copy, scanned it, and made it available online, at least that I could find.
The very meaty middle of the Rad Health Handbook consists of the periodic table, chart of the nuclides, and table of isotopes as it existed in January 1970. These three pieces are both copyrighted (the government was given special permission by the copyright holders to reprint at the time) and are INCREDIBLY out of date. Otherwise, everything else in the book appears to be public domain, as it was published by the US Government at taxpayer expense. Therefore, I have removed those three particular sections and created the best quality scan that I could — this is the result of 6 attempts.
For an updated version of the Chart of the Nuclides, which every RCT should own anyway, the current version is always published by whomever is running the Knolls Atomic Power Laboratory (operated by the Navy’s Naval Reactors Program). The current contractor is Bechtel Marine Propulsion Corporation. To order a copy, NuclidesChart.com, or call 865-220-2327. Get the book, it’s more convenient than the wall chart for day to day use. I have the last Lockheed version, the 16th edition, from 2002, and it’s about 90 pages, so pretty compact.
Even with the nuclide chart and other stuff omitted, the PDF is 15 MB and almost 300 pages. Also bear in mind that while this is a great reference piece, you should obviously rely on your Navy, DOE, or utility guidance first and foremost when it comes to procedures for radiation protection.
Regardless of your personal feelings about nuclear power, it is a dominant means of electrical power generation in the industrialized world. With the growing public and political pressure against the burning of fossil fuels, and with alternative energy sources such as wind and solar only being capable of generating power during daylight or when the wind blows, nuclear energy is experiencing a resurgence as an alternative to fossil fuel plants as a means of producing more of our baseline energy needs.
As such, I think it’s important for people to understand some basic science and engineering principles behind nuclear power, as knowledge is the most powerful thing in the world. It’s been a long time since I’ve written much about nuclear power, but the time has definitely come to revisit the topic.
Let’s start with the most basic question: Big picture, how does a nuclear power plant generate electricity?
The tongue-in-cheek answer that is thrown around by people in the industry is this: “Hot rock make steam make turbine go roundy-roundy.”
Let’s break that down into a little bit more detail.
You’re probably aware that friction between two things creates heat, like when your brakes get hot because two surfaces are rubbing together. For the brakes on your car, there is an energy conversion process going on. The energy of the motion of your car (kinetic energy) is being turned into heat energy via friction. So, your car stops, but your brakes get hot (and wear away part of your brake pads every time you stop).
Something similar happens inside a nuclear reactor. Every atom in a reactor core that fissions breaks up into chunks, and each of these chunks is sent flying for a very short distance by the little fission blast. These chunks are slowed down by interaction with other matter in the reactor, and that interaction converts the motion energy of the chunk into heat. Since there are a LOT of these tiny interactions going on, it creates a lot of heat overall. Therefore, we have our hot rock.
What happens when you throw water onto a hot rock, like in a sauna? Most of it flashes to steam. If you contain that steam within an enclosed container, it will build pressure. Something similar happens in a nuclear power plant: Our hot rock is cooled by passing another substance over it (usually water, but other things work, too, but that’s beyond the scope of this post). When that water heats up inside it’s container, it builds pressure. Actually, a LOT of pressure.
If you’ve ever seen a windmill operate, then this next part will make obvious sense. Just as a windmill’s blades turn when wind runs through it, the blades of a turbine are constructed so that when high pressure steam is passed over them, it forces the turbine to turn. Since we’re talking about really high steam pressure, we’re also talking about spinning our turbine really fast.
The other end of that turbine shaft is what’s connected to the electric generator. The speed of the generator has to be regulated in order to maintain the proper output voltage and frequency for transmission to your home, which is done via steam regulators and controlling the rate of the nuclear reaction to produce no more steam than is really necessary.
It should be noted that many of the components of a nuclear power plant are almost identical to any other power plant. Almost all power plants rely on a steam cycle system (often referred to as the “secondary system”), and the steam system components could literally be moved from one plant to another, hooked up, and be up in running. What makes each plant unique is what makes the steam. You can boil water with many heat sources: burning coal, burning natural gas, burning oil, burning methane from biofuels, etc. A nuclear reactor is just another means of creating heat to boil water, but with no greenhouse emissions (yes, there are obviously other issues — we’ll get into those in future posts).
I hope this was useful to somebody out there on the Interwebs. I’ll add to this series over time, delving into different aspects of the primary plant, including everybody’s favorite issue, that of radioactive waste. For the really geeky, I’ll get into reactor physics, stuff like neutron capture cross sections, the neutron lifecycle, fission fragment ratios, reactor poisons, and one of my favorite subjects – reactor startup delays due to decay product buildup (I always thought it kind of funny that operating our reactors created something that prevented us from starting our reactors once we shut them down…yeah, I’m a nerd).
Until my next post, be great, be happy!