THE NUCLEAR OPTION (click figures to enlarge)
IF there must be alternative sources of energy, nuclear power should be foremost. Detractors cite major nuclear power plant disasters but those occurred in plants designed in the 1960’s. Current designs are much safer, better addressing the most serious danger: loss of cooling of the reactor. See the figure 1 below: a.) the reactor generates high temperature heat, b.) the reactor coolant (most commonly water) removes heat from the reactor and in the steam generator (via heat exchanger) steam is produced from the cooling water to c.) drive a turbine whose shaft is connected to the d.) electric generator. e.) Spent steam is liquified back to water in the condenser (another heat exchanger) by thermal contact with condenser water, which itself is cooled f.) by a cooling tower. Both the steam generation and cooling water regeneration relies on the pumps for circulation. If either pump fails, unless the reactor is shut down, intense heat and very high pressure steam will develop in the reactor having a catastrophic result.
Figure 1
It is important to know that most existing fossil fuel fired power plants generate steam in boilers fired by natural gas, petroleum products or coal; I.e., the nuclear reactor in Figure 1 above is replaced by a fossil fuel fired boiler.
NUCLEAR ELECTRIC POWER GENERATION
Nuclear reactions generate heat, subatomic particles, lighter weight and usually radioactive byproducts, and very dangerous gamma radiation. There are two types of nuclear reaction: fission and fusion.
About one-tenth of all electric power worldwide comes from nuclear power plants. France is electric power is 78% nuclear. The navies of many countries include nuclear-powered warships; almost half of U.S. combat warships are nuclear-powered. Most commercial nuclear reactors are thermal reactors. Two types of light-water reactors in use throughout the world are the boiling-water reactor and the pressurized-water reactor. In the liquid-metal fast-breeder reactor, fuel is utilized 60 times more effectively than in light-water reactors.
Fission
Today all nuclear electric power is from fission. Fission is the splitting of very heavy (high atomic weight) atoms with low energy neutrons. The fissionable atom of uranium is uranium 235 (U235), which is a small component of natural uranium, therefore an extensive refinement process is required to obtain fissionable U235. See Figure 2. When natural uranium (mostly U238) is bombarded with low energy neutrons plutonium 239 (P239) is produced which itself is fissionable by low energy neutrons. See Figure 3.
Figure 2 Fission of U235 Figure 3 Creation and Fission of Pu239
Fusion
Fusion is the combination of very two light atoms to form a heavier light atom. This is usually the fusion of two hydrogen isotopes to form a helium isotope. This type of reaction energizes the sun and is the reaction of the hydrogen bomb. The isotopes of hydrogen are most common one (1H), having only a proton and an electron. Deuterium (2H or “D”) is hydrogen with one neutron and tritium (3H or “T”) is hydrogen with two neutrons. Tritium is not found in nature and must be synthesized by bombarding lithium with fast neutrons, yielding tritium and 4He. NOTE: The numeric superscript represents the sum of the number of protons and neutrons of the isotope, the atomic number represents only the number of protons, and is one for the three isotopes of hydrogen.
There are two ways to fuse hydrogen into helium: a.) fusing 2H and 1H to form helium3 (3He) see Figure 3 and b.) fusing tritium (3H) and deuterium (2H) to form helium4 (4He) see Figure 4. Helium has two protons, hence its atomic number is 2. In process a.) a total of two protons and one neutron make a product of 3 nuclear particles, hence no by products are produced, only energy in the form of gamma rays which turn to heat. For process four protons and three neutrons make a product of 4 nuclear particles, two protons and two neutrons. The fifth neutron is a high energy byproduct neutron, along with the gamma rays.
Figure 4 Fusion of Hydrogen and Deuterium Figure 5 Fusion of Deuterium and Tritium
It is seen that the fusion process for creating electric power is preferable to fission because a.) the reactants are much easier available and b.) there is no nuclear waste. However the technology of hydrogen fusion with a net positive energy input is only at the brink of success. Until recently, in the laboratory, fusion has been achieved only by using more energy than that created. The sun’s fusion is successful because its huge mass (mostly hydrogen) causes the very high temperatures and pressures necessary for the process. The hydrogen bomb works because a small fission (uranium) bomb is used to ignite fusion.
The Status of Fusion Power
Once the fusion process in the laboratory is proven reliable, it must be brought to the level of economic large reactor systems. This process is decades away. The objective is first, in the laboratory, to create a fusion reactor that can sustain a net positive generation of energy (energy out is greater than the energy in). At the National Ignition Facility of the Lawrence Livermore Laboratory at U.C. Berkley in August of 2021 conducted an experiment that required 1.9 megajoules of energy in the form of ultraviolet lasers to instigate a fusion reaction in a small, frozen pellet of hydrogen isotopes, — an inertial confinement fusion reaction design — and released 1.3 megajoules of energy, or about 70% of the energy put into the experiment. The output, in other words, was more than a quadrillion watts of power, even if released for only a small fraction of a second. Once this technology is advanced to sustaining the reaction, it must be upgraded to large scale and cost efficient commercial reactors.
European laboratories are also advancing the technology quite well.
NUCLEAR POWER COSTS vs OTHER POWER SOURCES
In the Figure 6 below , the Levelized Cost of Electricity (LCOE), refers to the estimated revenue required to build and operate a generator over a specified cost recovery period. CAPEX represents the capital expenditure required to build the plant. The figure represents costs per MWh of power in 2010 Euros. It shows LCOE for 1,000 4,000 and 8,000 hours per year operation. Nuclear power is competitive at 8,000 hours per year. This allows 760 hours or 32 days per year for maintenance, requiring nuclear to provide the base load to which it most suited.
Figure 6 LCOE of Various Types of Power Generation (Zoom out after opening)
“EPR” = 3rd Generation Pressurized Water Reactor Design
“SupCr” = Supercritical (very high temperature) steam
“GasCC = Natural Gas Combined Cycle, where natural gas is used to energize a turbine, the exhaust of which goes to a steam boiler which drives a steam turbine to produce more work (to generate electricity).
A typical nuclear power plant has a generating capacity of approximately one gigawatt (GW; one billion watts) of electricity. At this capacity, a power plant that operates about 90 percent of the time (the U.S. industry average) will generate about eight terawatt-hours (tera = trillion) of electricity per year. The predominant types of power reactors are pressurized water reactors (PWRs) and boiling water reactors (BWRs), both of which are categorized as light water reactors (LWRs) because they use ordinary (light) water as a moderator. and coolant. LWRs make up more than 80 percent of the world’s nuclear reactors, and more than three-quarters of the LWRs are PWRs.
NOTE: light water H2O is composed of natural hydrogen, the atoms of which have no neutrons. Heavy water is composed of water with deuterium atoms (D2O) each of which is hydrogen containing one neutron and is not radioactive. A hydrogen atom containing two neutrons, tritium, is radioactive (beta rays) and does not occur in nature. The hydrogen fusion process uses combinations of hydrogen-deuterium or deuterium-tritium
PROBLEMS WITH NUCLEAR POWER
The benefits of applying nuclear power to supplant a good portion of fossil fueled power are substantial, but they are tempered by a number of issues that need to be considered, including the safety of nuclear reactors, their cost, the disposal of radioactive waste, and a potential for the nuclear fuel cycle to be diverted to the development of nuclear weapons. All of these concerns are discussed below.
The four reactors involved in the Fukushima accident were first-generation BWRs designed in the 1960s. Newer Generation III designs, on the other hand, incorporate improved safety systems and rely more on so-called passive safety designs (i.e., directing cooling water by gravity rather than moving it by pumps) in order to keep the plants safe in the event of a severe accident or station blackout. For instance, in the Westinghouse AP1000 design, residual heat would be removed from the reactor by water circulating under the influence of gravity from reservoirs located inside the reactor’s containment structure. Active and passive safety systems are incorporated into the European Pressurized Water Reactor (EPR) as well.
Traditionally, enhanced safety systems have resulted in higher construction costs, but passive safety designs, by requiring the installation of far fewer pumps, valves, and associated piping, may actually yield a cost saving.
The Three Major Nuclear Disasters
| LOCATION | YEAR OCCURRED | YEAR DESIGNED | CAUSE | EFFECTS |
| Three Mile Island, Pennsylvania | 1979 | 1960’s | Equipment Failure & Human Errors | Very Minor, No Fatalities. INES Level 5 |
| Chernobyl, Ukraine | 1986 | 1964-66 | Equipment Design & Human Errors | Severe, 59 Fatalities, INES Level 7 |
| Fukujima, Japan | 2011 | 1960 | Earthquake & Tsunami | Very Bad, but no direct fatalities, INES Level 7 |
The Nuclear Waste Problem Spent nuclear reactor fuel and the waste stream generated by fuel reprocessing contain radioactive materials and must be conditioned for permanent disposal. The amount of waste coming out of the nuclear fuel cycle is very small compared with the amount of waste generated by fossil fuel plants. However, nuclear waste is highly radioactive (hence its designation as high-level waste, or HLW), which makes it very dangerous to the public and the environment. Extreme care must be taken to ensure that it is stored safely and securely, preferably deep underground in permanent geologic repositories.
Nuclear waste is commonly stored in radiation containing barrels.
Figure 6 These barrels are stored at the power plant or are transported to remote storage sites.
Despite years of research into the science and technology of geologic disposal, no permanent disposal site is in use anywhere in the world. In the last decades of the 20th century, the United States made preparations for constructing a repository for commercial High Level Waste (HLW) beneath Yucca Mountain, Nevada, but by the turn of the 21st century, this facility had been delayed by legal challenges and political decisions. Pending construction of a long-term repository, U.S. utilities have been storing HLW in so-called dry casks aboveground. Some other countries using nuclear power, such as Finland, Sweden, and France, have made more progress and expect to have HLW repositories operational in the period 2020–25.
When Hydrogen Fusion becomes commercially available, the waste problem will be minimized because waste from the fusion process is very little to none.