Discussion

Exercise 7.7

1. What are the advantages and disadvantages of using crude oil as an energy source? Speak about reserves, energy efficiency, environmental effect of extracting, transportation and use of oil and its products.

2. What are the advantages and disadvantages of using natural gas as an energy resource when compared with oil?

3. What are the advantages and disadvantages of using coal as an energy resource?

4. What is your opinion on the current policy of the Russian government to sell our energy resources to other countries?

Unit 8 nuclear energy

The source of energy for nuclear power is nuclear fission, a nuclear change in which nuclei of certain isotopes with large mass number (such as uranium-235) are split apart into lighter nuclei when struck by neutrons; each fission releases two or three more neutrons and energy. Each of these neutrons, in turn, can cause an additional fission.

Multiple fissions within a critical mass form a chain reaction, which releases an enormous amount of energy. The rate at which this happens can be controlled in the nuclear fission rector of a nuclear power plant, and the heat generated can be used to produce high-pressure steam, which spins turbines and thus generates electricity.

Nuclear fission produces radioactive fission fragments containing isotopes that spontaneously shoot out fast-moving particles (alpha and beta particles), gamma rays (a form of high-energy electromagnetic radiation) or both at a fixed rate. The unstable isotopes are called radioactive isotopes. This spontaneous process is called radioactive decay and continues until the original isotope is changed into a new stable isotope that is not radioactive.

Exposure to the alpha, beta, gamma radiation and the high-speed neutrons emitted in nuclear fission can harm cells in two ways. First, harmful mutations of DNA molecules in genes can cause genetic defects in immediate offsprings or several generations later. Second, tissue damage, such as burns, eye cataracts and cancers can occur during the victim’s lifetime.

To evaluate the pros and cons of nuclear power, we must know first how a conventional power plant and its accompanying nuclear power cycle work. Light-water reactors produce about 85% of the world’s nuclear-generated electricity (100% in the United States). It has the following key parts:

• Core containing 35.000  70.000 long, thin fuel rods, each packed with fuel pellets (each about one-third the size of a cigarette). Each pellet contains the energy equivalent of 1 ton of coal.

• Uranium oxide fuel consisting of about 97% nonfissionable uranium-238 and 3% fissionable uranium-235. To create a suitable fuel, the concentration of uranium-235 in the ore is increased (enriched) from 0.7% (its natural concentration in the ore) to 3% by removing some of the uranium-238.

• Control rods, which are moved in and out of the reactor core to absorb neutrons and thus regulate the rate of fission and amount of power the reactor produces.

• Moderator, which slows down the neutrons emitted by the fission process so that the chain reaction can be kept going. This is a material such as 1) liquid water (75% of the world’s reactors, called pressurized water reactors), 2) solid graphite (20% of reactors), or 3) heavy water, (5% of the reactors). Graphite-moderated reactors can also produce fissionable plutonium-239 for nuclear weapons.

• Coolant, usually water, which circulated through the reactor’s core to remove heat (to keep fuel rods and other materials from melting) and produce steam for generating electricity.

In evaluating the safety and economic feasibility of nuclear power, we need to look at the entire cycle, not just the nuclear plant itself. Each part of the nuclear fuel cycle produces solid, liquid, and gaseous radioactive wastes. Wastes classified as low-level radioactive wastes give off small amounts of ionizing radiation and must be stored safely for 100  500 years before decaying to safe levels. From the 1940s to 1970s, most low-level radioactive waste produced in the United States and most other countries was put into steel drums and dumped into the ocean; the United Kingdom and Pakistan still dispose of their wastes in this way. Today, low-level waste materials from commercial nuclear power plants, hospitals, universities, industries and other producers in the United States are put in steel drums and shipped to the two remaining regional landfills run by federal and state governments. Attempts to build new regional dumps for this kind of waste using improved technology have met with fierce public opposition.

High-level radioactive wastes give off large amounts of ionizing radiation for a short time and small amounts for a long time. Such wastes must be stored safely for at least 10.000 years and about 240.000 years if plutonium-239 is not removed by reprocessing. Most of these wastes are spent fuel rods from nuclear power plants now being stored in pools of water at plant sites.

After 50 years of research, scientists still do not agree on whether there is any safe method of storing these wastes. Some scientists believe that the long-term safe storage or disposal of these wastes is technically possible. Others disagree, pointing out that it is impossible to demonstrate that any method will work for the 10.000 – 240.000 of fail-safe storage needed for such wastes. Here are some of the proposed methods:

• Bury it deep underground. This favored strategy is under study by all countries producing nuclear wastes.

• Shoot it into space or into the sun. Costs would be very high, and a launch accident could disperse the wastes over large areas of the earth’s surface. This strategy has been abandoned for now.

• Bury it under the Antarctic ice sheet or the Greenland ice cap. The long-term stability of the ice sheets is not known. They could be destabilized by heat from the wastes, and the retrieving the wastes would be difficult or impossible if the method failed. This strategy is prohibited by international law.

• Dump it into descending subduction zones in the deep ocean. However, 1) wastes eventually might be spewed out somewhere else by volcanic activity, 2) containers might leak and contaminate the ocean, 3) retrieval would be impossible if the method did not work. It is prohibited by international law.

• Change it into harmless, or less harmful, isotopes. Currently there is no way to do this. Even is a method were developed, 1) costs probably would be very high, 2) the resulting toxic materials and low-level (but very long-lived) radioactive wastes would still need to be disposed of safely.

At present, as many as 45.000 sites in the United States may be contaminated with radioactive materials. It will cost taxpayers at least $230 billion over the next 75 years to clean up these facilities (with some analysts estimating that the price will range from $400 to $900 billion). More that 144 highly contaminated sites used to produce nuclear weapons will never be completely cleaned up and will have to be protected and monitored for centuries.

The radioactive contamination situation in the U.S. pales in comparison with the post-Cold War contamination in the republics of the former Soviet Union. Land there is dotted with: (1) areas severely contaminated by nuclear accidents (in 1957 explosion of a nuclear waste storage tank at Mayak, a plutonium production facility in southern Russia, spewed 2.5 times as much radiation into the atmosphere as the Chernobyl accident), (2) 26 operating nuclear power plants with flawed and unsafe design. Nuclear scientists and government officials throughout the world urge the shutdown of these reactors. However, without economic aid from the world’s developed countries, it is unlikely that these potentially dangerous plants will be closed and replaced with safer nuclear or nonnuclear alternatives, (3) nuclear-waste dump sites, (4) radioactive waste-processing plants, (5) contaminated nuclear test sites, (6) coastal waters where nuclear wastes and retired nuclear-powered submarines were dumped.

After approximately 15  40 years of operation, a nuclear reactor becomes dangerously contaminated with radioactive materials, and many of its parts are worn out. Then the plant must be decommissioned or retired by (1) dismantling it and storing its large volume of highly radioactive materials in storage facilities yet to be built, (2) by putting up a physical barrier ant setting up full-time security for 30  100 years before the plant is dismantled, or (3) enclosing the entire plant in a tomb that must last for several thousand years. At least 228 large reactors worldwide are scheduled for retirement between 2002 and 2012; by 2030 all U.S. reactors will have to be retired.

Experience has shown that nuclear power is an extremely expensive way to boil water to produce electricity. The World Bank says that nuclear power is too costly and risky, and The Economist says of nuclear power plants «not one, anywhere in the world, makes commercial sense».