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article imageSaving nuclear energy — Small modular reactors (Part 1)

By Karen Graham     Aug 8, 2017 in Technology
In today's competitive electricity market, nuclear energy is finding it difficult to compete. One answer to the decline in nuclear power plants may be the small modular nuclear reactor (SMR). They not only cost less but are much smaller and safer.
Even though SMRs are smaller than conventional nuclear reactors, the biggest selling point for SMRs is that they can be manufactured at a plant and brought to a site to be fully constructed. Critics contend that even if SMRs are less costly than conventional nuclear plants, they still can't compete with natural gas and renewable energy sources.
It is hard to believe that we are talking about modular nuclear reactors when it hasn't been that long ago that electricity was first produced using nuclear power. That's right, on December 20, 1951, the Experimental Breeder Reactor I, located near Arco, Idaho became one of the world's first electricity-generating nuclear power plants when it produced sufficient electricity to illuminate four 200-watt light bulbs.
That original reactor had an estimated electrical output of about 45 MW. Today's larger reactors have outputs of over 1,400 MW, so you can see the huge difference in size. However, times are changing and so too is the climate of public opinion surrounding the large, expensive nuclear plants we have today.
The EBR-1 reactor with its National Historic Landmark plaque attached.
The EBR-1 reactor with its National Historic Landmark plaque attached.
Orange Suede Sofa
Most experts today point to the soaring costs of construction of nuclear power plants as one reason for their decline and the increasing use of natural gas and renewables. But as I noted in a story on Monday, it would be wrong to retire nuclear energy as a source of electricity at this time.
Basics of nuclear reactions and technology
To advance our aims on mitigating the impacts of climate change, nuclear energy is needed just as much as efforts to reduce carbon emissions. And with the surge in innovations and technologies in renewables, there has also been the same growth in the field of small modular nuclear reactors.
There are a variety of different types of SMRs. Some are nothing more than simplified versions of our current reactors, while others involve entirely new technologies. In 2002, the International Atomic Energy Agency published a directive relating to countries wanting to keep or expand the use of nuclear energy in generating electricity.
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The agency wrote that any new nuclear-generating capacity should be constructed in the context of use in a deregulated market, and must maintain or exceed current levels of safety and must be economically competitive with alternative ways of generating electricity. This directive opened the door to new research into developing smaller reactors, more efficient technologies, as well as cost-effective pricing.
Regardless of the size of a nuclear reactor, there are certain things that have to happen. Most important is the sustained fission chain necessary to generate nuclear power. To create this sustained fission reaction, certain conditions are required, including the right fuel density so that the neutrons will impact enough other unstable atoms before escaping the reactor.
In order to slow down the speed of the neutrons so a fission reaction will occur, a moderator is needed, with water being the most common source used as a moderator. But keep in mind that as the reaction increases, the temperature of the reactor rises, in turn, increasing the temperature of the water. This actually reduces the rate of nuclear reactions and is called the negative temperature coefficient, making the reactor inherently resistant to "excursion", or a sudden, uncontrolled increase in temperature.
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NuScale Power
Some of the new SMRs are called "fast reactors," meaning they don't use a moderator to slow down the neutrons. And because the atoms have to absorb neutrons traveling at higher speeds, a different type of fuel is required other than Uranium 235. So fast reactors use Plutonium 239 because its atoms are more likely to absorb the speeding neutrons. As far as temperature goes, the negative temperature coefficient also applies here, preventing the reactor from running out of control.
Innovations in design of SMRs
When we are looking at electricity needs in rural or out-of-the-way places, a large nuclear power plant is just not economical. However, this type of situation is ideal for SMRs. They are flexible enough that a choice can be made as to how many modules are needed to supply the electrical demand. SMRs also have a load-following design so that when there is low electrical demand, they will produce less electricity.
As we have already mentioned, advances in new fuels for SMRs has allowed for higher burn-up rates and longer fuel life cycles.This means that with longer refueling cycles, there is a decrease in proliferation risks and a lower chance of radiation escaping into the environment. And with one of the new SMRs located in a remote area, less refueling is advantageous.
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When it comes to safety, again, SMRs have to be designed for use in areas where there is a lack of trained personnel. Most of the world's large nuclear power plants have "active" safety features that require "intelligent input," meaning a human being at the controls. Many of the SMRs being developed today use passive or inherent safety features.Passive features are engineered into the system and do not require human input. Inherent safety features require no engineered moving parts to work. They only depend on physical laws.
There are numerous new reactor designs being generated all over the world. All of the designs are dependent on having a factory to build the modules in the first place. And this one issue is a point many opponents of building any type of nuclear reactors like to tout as a reason for not seeing SMRs come to the marketplace. However, SMRs look to be a sector of the energy market worth watching. We will examine several promising designs and companies in the U.S. Canada and Europe in Part 2.
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