Nuclear energy is the most viable option for the looming energy crisis. It is carbon-free energy since it does not produce carbon dioxide that can cause global warming. However, limitations in the current technology only allow us to use 5% of the uranium rods that are used as nuclear fuel to generate usable energy. That means 95% of the uranium fuel is disposed and placed in permanent storage.
Scientists at the U.S. Department of Energy (DOE) Argonne National Laboratory have developed a new technology to recycle used nuclear fuel. This means we do not need to mine more uranium since we currently have over 60 years of accumulated used nuclear fuel to recycle. An important breakthrough since it is projected that recycling used nuclear fuel could generate sufficient energy to power global needs for the next hundreds of years.
Presently, recycling of used nuclear fuel is not feasible in the U.S. because the prevailing commercial reactor is a type called light-water reactor (LWR). The use of LWR is tested and approved. It is relatively safe to operate, but its main weakness is that it cannot wring the last drop of energy from uranium fuels because it uses ordinary water as coolants.
In order to recycle used uranium fuel, another type of nuclear reactors must be used. These are the so-called fast reactors that use different coolants like sodium and lead.
The main difference between types of reactors is what cools the reactive core where bombarding electrons are accelerated to cause nuclear fission that generates energy. LWR uses water that drastically drops the reactor temperature, effectively stopping all nuclear fission. Fast reactors use sodium or lead. These coolants drop core temperatures by degrees. Hence, bombarding neutrons inside the core are not slowed sufficiently to prevent the fission of a different host of isotopes. The fission of these isotopes can generate more energy and electricity, maximizing the fuel consumption of fast reactors.
Fast reactors can use different types of fuels, including used fuel from LWR. It is projected that fast reactors can recycle 80% of used nuclear fuels in the form of uranium and other actinides. LWR can also burn used fuels, but not as efficiently as fast reactors.
If we switch to fast reactors, we can drastically decrease radioactive waste by as much as 80% by recycling used nuclear fuel. However, before used nuclear fuels are recycled, these must first undergo processing. A processing technique called PUREX is already being applied in other countries for decades. PUREX had its origins in the 1940s when U.S. researchers were finding ways to separate plutonium from used fuel. However, this technique proved to be too risky since it had the ability to extract weapons-grade plutonium. This risk was considered great enough that the incumbent President James Carter banned PUREX in the US in 1978.
Driven by a need to research safer methods of fuel processing, Argonne scientists came up with a new technique they called pyroprocessing. This technique does not isolate pure plutonium. Instead, it uses electric current to separate all the useful elements from spent nuclear fuels.
Used fuel from LWR is composed of 95% uranium, 1% other long-lived radioactive elements and 4% unusable fission products. It is stored as a hard ceramic form in an underground facility within the reactor site. Pyroprocessing breaks down this ceramic form into small pieces and converts it into metal. These are then immersed in a tub of molten salts where an electric discharge separates uranium and other useful elements. The extracted elements are molded into fuel rods.
The unusable fission products left behind are molded into glass discs that will be stable for storage until these revert to the radioactivity of naturally occurring uranium. This process can take hundreds of years. A remarkably vast improvement since untreated fuel generally takes thousands of years to revert to the natural and safe form of radioactivity.
Given all the benefits from recycling used nuclear fuel, the question is why are we not doing this right now? There are two main obstacles.
The first obstacle is lack of monetary support. Uranium is relatively abundant and cheap to mine. Presently, it is more economical to store spent nuclear fuel rather than to develop new and safe methods to recycle it. Light-water reactors are also cheaper to build and the operations of these reactors are tested. Furthermore, the U.S. Regulatory Committee already approves this technology. It would take years to apply and process the approval of new reactor designs.
The second obstacle is the associated risks in processing used nuclear fuels. Processing technology might help terrorist groups get their hands on plutonium and uranium for weaponry. This problem is solved by pyroprocessing because it extracts uranium and plutonium with other radioactive actinides. It would be difficult to create weapons with these processed elements since these do not exist in their pure forms. Another security measure is to build pyroprocessing plants and fast reactors on the secured sites of former LWRs. In this way, there would be no need to transport used and processed fuels from site to site.
Future forecast sees the increased use of nuclear energy as a stable and large-scale source of carbon-free energy. Reactors are already being built throughout Asia as the demand for energy exponentially rises. In China alone, the use of nuclear energy increased by 500% within the last decade.
As of the present, scientists and engineers in Argonne continue to conduct research to make the recycling technology of used nuclear fuels more safe, economical and efficient. They perform engineering-scale test in pyroproccessing using a large glove box. They also use computational modeling to simulate the chemical processes at the molecular level and the industrial level.
Other research projects in Argonne are the design and study of different types of fast reactors and small modular reactors. The ongoing quest is to produce nuclear energy that is economical and safe.