I am writing a series of articles for a training organization called SAM group. I’ve been working with them to develop and offer a course in Nuclear Quality Assurance Auditor Training. We are also working together to provide consulting to businesses interested in getting into the nuclear power industry. The next few blog posts are reprints of those articles.
It occurred to me that while much has been discussed about nuclear power in the news and in many opinion pieces, there has been an assumption that the reader is at least somewhat familiar with the technology. This has created some significant misunderstandings and some unwarranted concerns about commercial nuclear power.
Let me spend a few minutes of your time providing a groundwork about the technology and some of the buzzwords and acronyms that get thrown around by those of us who have lived and worked inside the industry for more years than we care to admit.
Nuclear power plants around the world basically generate heat. That heat is converted to steam and the steam is used to spin a turbine which drives a generator and creates electricity. The concept is the same as coal based electricity generation, just using nuclear fuel to boil water instead of burning coal.
So how is the heat generated? Very simply, when an atom is split, it converts a small about of matter into energy. The energy is in several forms, but all of them can be readily converted to heat. Because Einstein’s famous equation E=MC2 comes into play, very small amounts of matter create very large amounts of energy. This is why small pellets of uranium can create more energy that car loads of coal. It takes about 120,000 tons of coal to equal 1 ton of uranium.
There are several reactor types in operation today. Light Water Reactors (LWR’s) are the most common, by far, of operating reactors around the world today. The concept is a simple one. Regular water (called Light Water) performs two functions within the nuclear core. First, it absorbs the heat being generated and creates steam (directly or indirectly, depending on the specific design). Second, water helps to slow down the neutrons being generated. Slower neutrons do a better job of splitting uranium atoms (specifically a type of uranium called U-235).
In order to make these reactors operate, the amount of U-235 has to be increased above the naturally occurring amount in uranium (about 0.7%). Commercial LWR’s today use uranium enriched to less than 5%. This enrichment level is well below weapons grade. No commercial LWR fuel can be made into a nuclear bomb. Enriching is done via a variety of means. In all cases, one has leftover depleted uranium that contains even less U-235 than natural uranium ore.
For LWR’s the fuel is manufactured into assemblies (also called bundles) of about 100 tubes with stacks of uranium dioxide pellets. Each assembly weighs from 200-400 Kg (440-880 pounds) depending on the specific reactor design. Prior to insertion in a nuclear core, this fuel is quite benign, one can stand next to it and not receive any significant radiation dose. It requires exposure to neutrons to start a chain reaction. A single fuel bundle cannot sustain a nuclear chain reaction even after exposure in the core. Fuel assemblies are generally left in a reactor core for 4-8 years. During this time, each assembly will generate 250,000-500,000 MWh of electricity. That is the equivalent of powering about 3500 homes for that time.
Of course, the natural question. Why call them LWR’s if they use regular water? There is a second technology used today in several countries called a Heavy Water Reactor (HWR). Instead of enriching uranium, these use an enriched form of water. Hydrogen has two naturally occurring isotopes besides the common single proton you might remember from high school physics. The two isotopes add one or two neutrons to the nucleus to increase the mass. Otherwise, these reactors operate similarly.
Spent fuel is stored for at least 10 years under many feet of water. The water again serves two purposes. The first is to provide cooling to the spent fuel assemblies while the hottest isotopes decay away. The second is to provide shielding to those who work at the power plant. By keeping the assemblies underwater, virtually all of the radiation being generated is stopped by the water. After 10 years or so, most of these very high energy isotopes are gone and the fuel is easier to handle.
The rest of a discussion regarding spent fuel is another topic for another day.
Nuclear power is one of the safest and cleanest available sources of power and one of a very few options that can replace coal as our nation’s main source of base load power. The opportunities to support this industry and expand the U.S. based supply for these plants are growing as more utilities and more vendors get into the nuclear industry. SAM group can help you and your team supply parts and services to this industry with training and consulting.