Climate Change and the benefits of Nuclear Energy

By Carl Laverghetta, Senior Energy Advisor 

It is “technologically” possible to achieve a zero-carbon electrical grid without nuclear power, but there is a distinct difference between “technologically possible” and “practically feasible” along with the most cost effective means. The elimination of all nuclear power would seriously complicate efforts to decarbonize and, in my view, require “extreme” levels of action in all other areas of our production of electricity and the overall economy to reach zero-carbonization.

If Maryland’s legislature or any legislative body is to be taken seriously about zero-carbonization, then they should read the Intergovernmental Panel on Climate Change’s (IPCC) report on achieving a 1.5 degrees Celsius (C) goal from pre-industrialized levels — nuclear generation is always a part of the solution. In fact, no serious study that I have seen refutes the necessity of nuclear generation. So, in my view, claiming absolute opposition or professing “agnosticism” to nuclear power is avoiding reality. The National Renewable Energy Laboratory has data showing that a doubling of the current amount of nuclear generation in the U.S. is a realistic means to achieve the IPCC’s goal.

“Deep decarbonization” is defined as an 80% – 100% cut in current CO2 emissions. Those who are pushing hard for that level of decarbonization never discuss “affordability.” It is as if cost-to-benefit analysis was some form of alien concept. To go about deep decarbonization in a rational and effective manner, a selected power mix that includes at least one low-carbon resource such as nuclear power or combined cycle natural gas coupled with Carbon Capture and Sequestration is a reasonable and productive approach. 

First and foremost, since nuclear electricity is produced via nuclear fission rather than chemical burning or combustion, the process generates baseload, reliable electricity with no output of carbon, the villainous element of global warming. Second, nuclear power plants operate at much higher capacity factors or the net capacity factor is the unitless ratio of an actual electrical energy output over a given period of time to the maximum possible electrical energy output over that period than renewable energy sources or fossil fuels. Capacity factor is a measure of what percentage of the time a power plant actually produces energy. It is a significant problem for intermittent/variable energy resources. Third, nuclear power releases less radiation into the environment than any other major energy source. This may seem paradoxical to many people, since it is not commonly known that non-nuclear energy sources release any radiation into the environment. Other minerals release radiation but coal is the worst offender because, as a mineral from the earth’s crust, it contains a substantial volume of radioactive elements — uranium and thorium. Combusting coal gasifies its organic materials, concentrating its mineral components into the remaining waste, called fly ash. In fact, so much coal is burned in the world and so much fly ash is produced that coal is actually a major source of radioactive releases into the environment. ¹

What are nuclear power’s downsides? In the public’s perception, there are two issues and both are related to radiation: the risk of an accident and the question of disposal of nuclear waste. There have been three large-scale accidents involving nuclear power reactors since the onset of commercial nuclear power in the mid-1950s: Three-Mile Island, reactor #2 (TMI-2) in 1979, Chernobyl in Ukraine in 1986, then a satellite republic of the old Soviet Union, and Fukushima Daiichi in 2011.

The partial meltdown of TNI-2 in Pennsylvania, while a genuine disaster for the owners of the plant, released only a minimal quantity of radiation to the surrounding population. Regarding TMI-2, the U.S. Nuclear Regulatory Commission commented that, “Approximately 2 million people located around TMI-2 received an average radiation dose of only 1 millirem above the usual background dose. For context, exposure from a chest X-ray is approximately 6 millirem. In spite of serious damage to the actual reactor, the radiation release had negligible effects on the physical health of individuals or the environment. Background radiation is present on Earth at all times.² 

The majority of the background radiation occurs naturally from minerals and a small fraction comes from man-made elements. Naturally occurring radioactive minerals in the ground, soil, and water produce background radiation. The human body even contains some of these naturally occurring radioactive minerals. Cosmic radiation from space also contributes to the background radiation around us. There can be large variances in natural background radiation levels from place to place, as well as changes in the same location over time.³

The Chernobyl meltdown was very likely an accident waiting to happen. The Chernobyl reactor used a RBMK 1000 design, a design that is unique to former Soviet Union and former Eastern Bloc countries. The RBMK, or the channelized large power reactor, was designed to produce both plutonium and electric power. This was a very different design from standard commercial reactors for the production of electricity. The RBMK had a unique combination of a graphite moderator and water coolant. Carbon is used as a neutron moderator, reducing the speed of fast neutrons. The RBMK 1000 is a boiling water reactor. It does not have any pressure vessels; rather, the fuel assemblies are found in pressurized tubes (1000 or more). These fuel channels are separate from one another. The advantage of this is that the channels can function independently of one another and the fuel elements can be removed and replaced online. The fuel that is most commonly used is low enrichment (2%) uranium dioxide. The moderator used is graphite as opposed to light water which is commonly used in Western designs. This explains why the RBMK reactor occupies a much larger land area than most reactors found in Western countries.⁴

One of the most crucial causes of the accident is the large positive void coefficient possessed by the nuclear reactor. One characteristic of the RBMK reactor is that it can have a positive void coefficient. This means that an increase in voids or steam bubbles is associated with a rise in core reactivity. Most other reactor designs have a negative coefficient, which means that the reactor responds to the formation of steam bubbles by decreasing heat output. This is because if the coolant contains lots of steam bubbles, fewer neutrons are slowed down. The faster neutrons are, in turn, less likely to cause fission of the uranium atoms, thus resulting in a lower power output. This is an example of negative feedback that is used to prevent the reactor’s heat output from reaching dangerously high levels. However, the RBMK reactor used had a positive coefficient, which means that the reactor becomes very unstable at low power levels, and vulnerable to dangerous rises in energy production levels. This was one of the reasons for the reactor explosion during the Chernobyl accident.⁵

Another cause was a flaw in the design of control rods. Control rods are meant to control the multiplication factor k of the reactor. Since control rods absorb neutrons, a withdrawal of the rods causes an increase in “k value,” and vice versa. The control rods are inserted from the top of the reactor and are made of graphite. The rods were found to be 1.3 m shorter than stipulated, which is unacceptable. The upper portion of the rods, which acts to absorb neutrons and slow down the nuclear reaction, was filled with boron carbide. When the rods were inserted, the graphite part displaces some of the coolant, thus leading to an increase in fission rate. This is because graphite is a more powerful neutron moderator than light water, i.e., it absorbs less neutrons. This resulted in a dangerous increase in power output.⁶

The Fukushima Daiichi (2011) nuclear disaster was caused by a powerful earthquake that produced a 46′ Tsunami. The systems at the Fukushima facility detected the earthquake and automatically shut down the reactors. The emergency diesel generators turned on to keep the reactor coolant pumping around the cores, which remain incredibly hot even after the reactors shut down. Unfortunately, the water overwhelmed the sea wall, flooding and knocking out the emergency generators. Of course the underlying situation in this tragedy is that the facility should never have been built in a location where there was a significant possibility of earthquakes occurring out at sea. In addition, the Fukushima plant suffered a series of chemical explosions during the event, badly damaging the operations buildings.⁷ 

Opponents of nuclear power regularly complain that it costs too much. Whether or not nuclear power costs too much will ultimately be a matter for markets to decide, but there is no question that a full accounting of the external costs of different energy systems would find nuclear cheaper than coal or natural gas. By external costs I mean, the implicit subsidies where the waste products of energy use are allowed to be dumped into the biosphere are greater than any direct subsidies. 

The largest of these subsidies are given to fossil fuel producers. Nuclear energy has always had to cost in its own waste management and disposal (equivalent to about 5% of generation cost, along with a further similar sum for decommissioning). Renewables give rise to wastes in manufacturing, and while these are sometimes unpleasant or even extremely toxic they are dealt with in the same way as other manufacturing hazards and wastes. Decommissioned wind turbines are often replaced with new ones on the same site, otherwise there may be substantial structural material to remove.

Finally, the issue of nuclear waste disposal. Although a continuing political problem in the U.S. it is no longer a technological problem. Most U.S. spent fuel, actually more than 90% of which could be recycled to extend nuclear power production by hundreds of years, is stored safely in impenetrable concrete-and-steel dry casks on the grounds of operating reactors and its radiation is slowly declining. 

Nuclear power is the second largest source of zero carbon energy after hydropower. The energy needed to mine and refine the uranium that fuels nuclear power and manufacture the concrete and metal to build nuclear power plants is usually supplied by fossil fuels, resulting in CO2 emissions; however, nuclear plants do not emit any CO2or air pollution as they operate. And despite their fossil fuel consumption, their carbon footprints are nearly as low as those of renewable energy. Nature Energy produced a study, “Understanding Future Emissions from Low-Carbon Power Systems by “Integration of Life-Cycle Assessment and Integrated Energy Modelling.” The researchers calculated that a kilowatt hour of nuclear-generated electricity has a carbon footprint of 4 grams of CO2 equivalent, compared to 4 grams for wind and 6 grams for solar energy — versus 109 grams for coal, even with carbon capture and storage.⁸

In the last 50 years, nuclear energy has precluded the creation of 60 gigatons of carbon dioxide, according to the International Energy Agency (IEA). Around the world, 440 nuclear reactors currently provide over 10 percent of global electricity. In the U.S., nuclear power plants have generated almost 20 percent of electricity for the last 20 years. Right now the U.S. has 95 nuclear reactors in operation, but only one new reactor has started up in the last 20 years. Over 100 new nuclear reactors are being planned in other countries, and 300 more are proposed, with China, India, and Russia leading the way.

Today’s modern reactors are safer and more efficient than those three and four decades old designs currently in operation. Unfortunately, the cost of a new nuclear power plant can run $7 billion or more. This elevated cost structure is precisely why “Small Modular Reactors” (SMR) are increasingly relevant as a part of the overall energy mix. 

SMR’s are much less expensive than full-scale reactors and they require far less space. These SMR’s can be as small as 2 MW up to 300 MW. They are generating real interest because:

• Nuclear power offers a carbon-free source of electricity without the intermittency of renewables.
• Modularity allows construction to better match load growth – current nuclear units are built in blocks of 1000 to 2000 MW, which can often take years for load to grow and utilize all the capacity.
• Modularity could allow units to be built more quickly – current nuclear units typically take five or more years to construct after permits are obtained.
• Modularity promises more cost control – units recently under construction have tended to balloon in cost during the construction phase whereas SMRs will be constructed in a factory with control over costs.
• The smaller size may allow units to be used in remote locations without the need to connect to the larger electric grid.
• Some SMRs are designed to be underground for greater security and safety.
• Some SMRs are designed for passive shutdown, meaning if something goes wrong the unit automatically shuts down into a safe mode without human intervention.
• Some SMRs are designed to allow output to be ramped up and down to match variations in load.

Through the Department of Energy’s (DOE) Advanced Reactor Demonstration Program each SMR design will receive $80 million this year and an additional $400 million to $4 billion over the next five to seven years. The DOE also plans to make two to five more awards totaling $30 million for advanced reactor designs by December of 2021.⁹

New modular designs are emerging. Fierce competition should enable a positive design outcome. Companies like TerraPower, GE-Hitachi Nuclear Energy, NuScale, X-Energy, BWRX, and Flibe Energy are all competing for best in class SMR design. The designs include molten sodium metal as a coolant, liquid sodium cooled reactors operating at atmospheric pressure and using depleted uranium, a by-product of the fuel enrichment process that was normally disposed of, and light water reactors with highly simplified design to eliminate pumps and other moving parts. The output of these latter reactors will be under 100 MW and are considered ideal for on-site distributed power applications for sites like military bases, hospital complexes, and airports.

To achieve 80% to 100% decarbonization over the next ten to fifteen years, the use of zero-carbon nuclear reactors is essential. Over the next decade, “developing” countries are still going to utilize coal-fired power generation, China and India among them. Even the more advanced economies of East and Southeast Asia will be utilizing Liquified Natural Gas to power their economies. So, when environmentalists, climate scientists, and legislators talk about energy production, their primary concern is net-zero carbon to combat climate change and meet the IPCC 1.5 degree C temperature goal. This goal is attainable, but nuclear power will have to be an important part of the plan.

Reference points:
¹  Yale University 360: “Why Nuclear Power Must be Part of the Energy Solution.” ResearchGate and Scientific American, Mineral Extraction and Radiation.

² Brokhaven National Laboratory, background radiation studies
³ Ibid.
⁴ International Atomic Energy Agency (IAEA), Design features and reasons for the Chernobyl accident.
⁵ Ibid
⁶  General Atomics for “k value” k= (Neutrons produced in one generation)/ (Neutrons produced in the previous generation). In other words, when the reactor is critical, k=1; when the reactor is subcritical, k <1; and when the reactor is supercritical, k>1. Reactivity is an expression of  the departure from criticality. General Atomics, the manufacturer of the most widely used non-power reactors in the world, TRIGA Nuclear Reactors, teaches the science of reactors. TRIGA stands for “Training, Research, Isotopes, General Atomics.” https://ansn.iaea.org/Common/documents/Training/TRIGA%20Reactors%20(Safety%20
⁷ ResearchGate; Nuclear Safety Research Group of Research Reactor Institute, Kyoto University; Fukushima Daiichi reactor accident.
⁸  Nature Energy: Understanding Future Emissions from Low-Carbon Power Systems by Integration of life-cycle assessment and Integrated Energy Modelling.
⁹  Columbia University, Earth Institute: “The State of Nuclear Energy Today.”