The 1930s were heady times for nuclear physicists. A “hit parade” of discoveries gave us new insights into the properties of the nucleus. The means of unlocking enormous amount of energy stored inside a nucleus seemed at hand. Finally, the discovery of nuclear fission in 1938 ushered in a new era in the history of mankind — the nuclear age. The world has not been the same since then. Our life became inextricably linked forever to the awesome power of the nucleus.
“I am become death, the destroyer of worlds.” These words from the Hindu scripture Bhagavad Gita were chanted by a despondent Robert Oppenheimer after witnessing the mind-boggling destructive power of his creation, the nuclear bomb, at the Trinity Site on July 16, 1945. The energy released by the bomb was compared by him “to the radiance of a thousand Suns.” Oppenheimer reviled at the thought that history will remember him as one who gave mankind the means for its own destruction.
The overwhelming impact of the bomb dropped on August 6, 1945 over Hiroshima radically altered our perception of nuclear energy. Horrified at the human suffering, awed at the technical achievement, Gandhis of the world immediately launched a massive international campaign to beat nuclear swords into plowshares. The “awe” finally won when in 1954 nuclear reactors evolved from embryonic stage into tools for generating electricity. It was a big step toward the peaceful use of nuclear power that most of us hoped for.
Since nuclear reactors are based on nuclear fission, there is a popular misconception that nuclear-fueled power plants are fundamentally different in their mode of power generation than their conventional coal-fired counterparts. They aren’t. The reactor functions primarily as an exotic heat source to turn water into pressurised steam. Only the source of heat energy differs — one uses radioactive nucleus, the other fossil fuel. The rest of the power train is the same. The steam turns the turbine blades, the blades generate mechanical energy, the energy runs the generator, and the generator produces electricity. The major improvement is the elimination of the combustion products of fossil fuels, which have destroyed our environment beyond repair.
Nuclear power plants have very low social acceptability primarily because of safety concerns. What has raised our fear in regard to nuclear power more than anything else is the image of a reactor somehow exploding or melting down and releasing large amounts of deadly radioactive materials into the surrounding atmosphere. In the wake of the accident at Three Mile Island (TMI) in 1979 and the movie The China Syndrome, the fear was heightened by the invisibility of the added lethal component, nuclear radiation.
Because of our deep-rooted horror about and revulsion to nuclear weapons, it is natural to wonder if a nuclear reactor could become a bomb. No, it can’t. A nuclear reactor cannot explode in a way a nuclear bomb explodes because of the many safety features that are in place in a power plant.
The containment of radioactive fission products in a reactor is accomplished by designing into a power plant a series of physical barriers that inhibit or prevent the release of fission products. There is an emergency system to ensure that the heat generated by the reactor, including heat from the radioactive decay of fission products, is cooled if things go south. Besides, there is an outer containment vessel, a large strong steel or steel-and-concrete enclosure, which can be breached only when there is a complete meltdown of the reactor core.
Nuclear power plants have a buffer zone where public access is limited. The zone is divided into three sections. The innermost zone, called the Exclusion Zone, is accessible only to the workers and is directly under the control of the plant. The second zone is an annular ring around the Exclusion Zone. Known as the Sterilized Zone, it is sparsely populated, mostly by essential plant workers. The third or the outermost zone defines the minimum distance beyond which there is no restriction on the population.The accidents at TMI (Pennsylvania) in 1979, at Chernobyl (Ukraine) in 1986, and at Fukushima (Japan) in 2011 alerted us to the dangers inherent in radioactive material used to produce electricity. The TMI accident is the worst commercial reactor accident in US history. The accident, believed to have been caused by malfunction of some safety features, was worsened by operator confusion which turned a minor problem into a major one.
The one at Chernobyl is considered to be the worst in the history of nuclear power. The causes of the accident can be laid partly to design flaws, but mostly to obvious errors made by the operators. The Fukushima-Daiichi accident was caused by a 15-meter high tsunami that followed a monstrous earthquake. It disabled the power supply and the cooling system of three of the reactors, but did not leak radiation into the environment in catastrophic amount.
The severity of accidents in a nuclear power plant is measured according to the International Nuclear and Radiological Event Scale (INES) introduced in 1990. The scale ranges from 1 to 7. It is logarithmic, i.e. a change of 1 corresponds to a change by a factor of 10. An accident rated 7 is considered to be extremely severe. On the INES scale TMI, Chernobyl, and Fukushima were rated 5, 7, and 7, respectively.
These accidents shook our confidence in nuclear power plants and made us view nuclear technology with great suspicion. This natural suspicion is present not only in laymen, but in many scientists as well. We cannot dismiss their suspicion as an emotional manifestation of suppressed fear or of guilt concerning nuclear weapons. They are a sobering demonstration of what we can expect from an accident due to catastrophic reactor failure or human errors.
However, low human deaths and minimal damage to the environment caused by two of the three accidents show the effectiveness of multiple safety systems that were in place for containing nuclear radiation. Nevertheless, these accidents made us aware of some real problems that must be overcome if we are to realise the full potential of nuclear energy. Indeed, the lessons learned from these and other accidents led to the design of reactors that are now many-fold safer.
A 1975 study on reactor safety, called the Rasmussen Report, showed that the probability of a major accident at a nuclear power plant was not more than 1 in 10,000 reactor-years. (A reactor-year is a nuclear reactor operating for one year; e.g. 20 reactors operating for 10 years are 200 reactor-years.) If the estimate is correct, then with 437 nuclear power plants currently operating in 31 countries across the globe, we can expect a major accident every 20 years.
The study was widely criticised by anti-nuclear activists for grossly underestimating the probability of a major accident, as it did not include possibilities of sabotage and human error. The accident at TMI was cited as a proof that nuclear reactors are not safe and that Rasmussen Report is questionable. Criticism of the report still exists but the methodology has survived and is widely used in assessing nuclear risks.
Many nuclear experts believe that an accident resulting from malfunction of a latest reactor is a very small risk even if everything possible goes wrong. They are convinced that a nuclear power plant will not go up in a mushroom shaped cloud releasing dangerous quantity of radiation.
As we reflect 75 years after the “genie” was released from the nucleus, we see that nuclear reactors have matured from the phase of scientific feasibility to today’s status of economic viability. Their safety record, though not impeccable, is nonetheless impressive. In a single day about 120 people die due to car accident in the USA, which is more than the number of deaths due to reactor accidents in the 55-year history of the US nuclear power industry.
In nuclear energy, merchants of death see a sword; advocates of peace see a plowshare. It can end life; it can prolong life. It can cause disease; it can cure disease. It can annihilate us; it can protect us. Where pessimists see a world-wide calamity, optimists see a glowing future. Our romance with nuclear energy is like Prometheus offering the blessings and curses of fire.
The writer is a Professor, Department of Physics and Engineering Physics, Fordham University, New York.