Many misconceptions have entered the nuclear folklore in recent decades. Major fables propagated by opponents of nuclear power are summarized here, and countered with facts. These facts are based on studies and data published by professional societies, representing some 250,000 diploma-ed engineers from around the world. Factual statements are backed up by data in later chapters.
Fable (1): "Nuclear reactors are like nuclear bombs".
Fact: This half-truth is frequently suggested by newspaper journalists who have little or no background in science and engineering. It is as erroneous and flawed as assuming that nitro-glycerin medicine used by heart-patients is as dangerous as nitroglycerin used in explosives, or that dihydrogen-oxide (water) is a dangerous chemical that drowns many people and should be banned. The uranium in a reactor is dispersed through a collection of fuel elements through which a coolant passes that absorbs heat and drives turbogenerators when the uranium undergoes fission. Nuclear reactors are designed so fissioning rates due to neutron multiplications are balanced and controlled by neutron-absorbing "control rods", yielding steady heat production. In today's reactors, if the core gets too hot, thermal expansion of moderator/coolant reduces neutron multiplication ("negative reactivity"), and the reactor shuts itself down automatically. This happens even if control rods are accidentally stuck and not instantly inserted in the core as would normally occur if a pre-set temperature is exceeded. In other words, the reactor always shuts down if it gets too hot.
The design of a nuclear fission weapon is entirely different. It comprises two halves or four quarters of highly enriched nearly critical fissionable uranium or plutonium which when slammed together (e.g. by springs), cause supercritical neutron multiplication and sudden production of an enormous amount of fission heat. This heat instantly evaporates all bomb material. If detonated in the atmosphere, it induces a shockwave that overturns and destroys any object in its path within a radius of a few kilometers. The physical arrangement that can cause a nuclear weapon to explode is totally absent in a power reactor. It is physically impossible for a reactor to explode like a bomb, just as much as it is impossible for a nitroglycerin-carrying heart-patient to be ignited and explode.
Fable (2): "We don't need more nuclear power; there is plenty of natural gas, oil, and coal."
Fact: In the 1990's, demand versus supply curves of natural gas and oil (petrol) crossed over, as predicted by Hubbert [Ref. 2]. Increases in demand now exceed discoveries of new oil deposits, and with these trends, oil and gas will be in serious short supply by 2030. Coal, if substituted for oil and uranium to provide all global energy needs might last 160 years. If more breeder reactors are put into service, uranium and thorium can supply the world with electricity and synfuels for at least 1,500 years in place of oil, gas, and coal. Like petrol, coal-burning power plants produce enormous amounts of air pollution and emit globe-warming carbon dioxide gas. Once oil is depleted, coal is more valuable as raw material for making organic chemicals, and should not be burnt. Non-air-polluting nuclear plants presently produce 21% of all US electric power. To avoid global warming, they should replace coal-burning power plants. The latest NEI (Nuclear Energy Institute) cost figures in 0/kWh for electricity are: 1.71 (0.45) for nuclear, 1.85 (1.36) for coal, 4.06 (3.44) for natural gas, 4.41 (3.74) for oil, where parentheses give fueling costs [Ref. 37].
Fable (3): "Nuclear power is not needed. "Free" renewable solar, wind, hydro, and geothermal power will do. The utilities and government should invest more in them."
Fact: A1200 MW(e) nuclear plant (e = electric) at 85% capacity factor produces 8,800 million kilowatt-hours of electricity per year, compared to about 50 million kilowatt-hours per year from a large SOLAR-2 station generating 15 MW(e) when the sun shines, with a 38% duty cycle. Thus it takes one hundred seventy-six SOLAR-2 stations occupying 25,000 acres (100 km2) of land and an investment of 10 billion dollars, to replace one nuclear plant occupying forty acres of land, costing 1.8 billion dollars. Solar energy is not free. Energy production has three cost components: fuel, maintenance, and capital write-off. It takes large maintenance crews and vehicles to keep solar panels free from dust, rain stains, and bird droppings, and to replace panels eroded or damaged by sand from dust storms. Also many square kilometers of collection surfaces are needed, so capital investment and write-off costs for solar stations dwarf the fuel costs for equivalent nuclear electricity. With ten-year solar-cell replacement cycles, one finds hazardous chemical wastes in manufacturing silicon, gallium-arsenide, or copper-indium-diselenide solar cells (requiring toxic silanes, arsenic, etc. as raw materials), far exceed uranium fuel wastes, when one compares 176 SOLAR-2 stations with 1 nuclear plant, each producing a year-averaged 1000 MW(e).
Regarding wind power, one comes to similar conclusions. Five-hundred 2 MW(e) windturbines costing 1.0 billion dollars, put on 30,000 acres (120 km2), could yield 1000 MW(e) of electric power at full capacity. However the wind is not always blowing, and typical capacity factors for windfarms are 20%. To provide 1000 Mw(e) steadily for a whole year, electric storage batteries are needed (adding costs) and five times as many wind-turbines must be in place. In short, one needs 2,500 wind turbines of 2 MW(e) at a cost of $ 5 billion + $ 2 billion for interim storage, or a total of $ 7 billion to provide 1000 MW(e) year around. The typical capacity factor of a nuclear plant is 85%, so a 1200 MW(e) reactor costing $ 1.8 billion can provide an average of 1000 MW(e) during a year. Besides the high cost of maintaining 2,500 windmills, wind-farms have the problem of killing hundreds of birds and spoiling nature's scenery.
In summary, while the sun and wind may provide free fuel, it is not steady and highly diluted compared to enormously concentrated, reliable nuclear fission energy. To deliver large quantities of solar and wind-generated electricity, great expanses of collection equipment are required which vastly increase maintenance and capital costs relative to nuclear power plants. Solar and wind farms are very useful in providing electricity for small communities in remote locations (e.g. Alaska) or for low-power applications. However they could not economically replace nuclear or coal-fired power plants to feed an industrialized city with sufficient energy for manufacturing steel, bridges, buildings, or to produce massive quantities of portable synfuels for our transportation fleets of cars, trucks, ships, aircraft.
As a final example, let us compare in round numbers what it takes to generate a total of one million equivalent electrical megawatts presently consumed in the US, using either wind, solar, or nuclear power. With solar power, one finds that one must build 176,000 advanced SOLAR-2 plants (each producing a year-averaged 5.7 MW(e)), costing $ 10 trillion to deliver an average of one million MW(e) year around. This is more than the US gross domestic product (GDP) of $ 9 trillion. By the numbers shown above, providing one million MW(e) of windpower constantly during a year, requires 2,500,000 wind-turbines of 2 MW(e) peak power at a cost of $ 7 trillion. Compared with 1,000 nuclear plants of 1200 MW(e) each, that feed 1 million MW(e) to the entire USA with 85% capacity factor at a cost of $ 1.8 trillion, it is obvious what capital investors will decide when choosing between $ 1.8, $ 7, or $ 10 trillion. Note there are 438 nuclear power plants worldwide and 103 in the USA. The latter provide 21% of all electric grid power in the US.
Hydroelectric and geothermal power generation are maxed out in the USA. Most suitable rivers have already been dammed to feed hydroelectric turbogenerators; in fact environmentalists want to dismantle some hydroelectric dams. In Cobb, California, a geothermal power plant generating 55 MWe in the 1960's, experienced large drops in steam pressure and after six years was shut down. Recent geothermal projects are more promising but only useful in a few locations for a few decades.
Fable (4): "We only have 30 years of uranium ore to sustain a world fueled by fission power. Coal reserves would last at least 120 years, so we should concentrate on coal power."
Fact: The oft-quoted 30-year limit on uranium availability is based on "burning" the fissionable 235 isotope of uranium (U-235) only. Breeder reactors have been developed at slightly higher capital cost than U-235 burners, that consume U-238 as well as U-235 via in-core conversion of non-fissionable U-238 to fissionable plutonium-239, after U-238 absorbs a neutron (Section 5.1.2). Since uranium ore contains 140 times more U238 than U-235, consumption of U-238 (^ Pu-239) gives the world uranium-based electricity for 140 x 30 = 4,200 years, or about 1,260 years with 30% utilization. Thorium after neutron absorption yields fissionable U-233, giving 300 more years of nuclear energy.
Coal is an alternative raw-material source for making industrial hydrocarbons such as plastics. Presently, oil provides the raw chemicals for manufacturing plastics, in addition to supplying petrol for the world's transportation fleets. Since oil reserves will be gone in forty years, it would be foolish to burn coal to deliver electricity, when non-polluting uranium fission power is available to generate all needed electricity. Besides, coal burning emits globe-warming carbon dioxide and other air-pollutants. It should not be burned.
Fable (5): "We should wait for development of nuclear fusion which produces no radioactivity."
Fact: Fusion reactors do generate radioactive isotopes in containment materials due to neutron activation. They burn deuterium and tritium making helium and neutrons. Removable neutron-absorbing inner linings have been proposed for fusion reactor chambers and these will become highly radioactive. Making fusion viable for nuclear power generation is a much more formidable task than generating electric power from fission. The minimum plant size to extract energy from a controlled fusion reaction (a miniature sun) is a hundred times that of a uranium fission reactor. It is estimated it will take at least another fifty years of research and development before the first fusion power plant might be built. We have waited fifty years already for a net-electric-energy-producing fusion pilot plant, and the no-oil period is approaching fast. Clearly we must proceed now with the expansion of proven uranium fission breeder technology.
Fable (6): "Hydrogen-consuming fuel-cell engines and electric energy storage batteries can replace petrol-burning automobile engines in the future; nuclear is not needed."
Fact: To be able to replace all present petrol-burning auto engines with fuel-cell engines, will depend on nuclear electricity or heat to produce the massive quantities of gaseous hydrogen (H2) fuel needed for these new engines. Fuel-cell enthusiasts neglect to mention that H2 gas is not a primary earth resource like oil, and must be manufactured. One needs electricity or heat from power plants to make lots of hydrogen. In effect this means that non-portable nuclear energy is transformed into portable hydrogen energy. Worldwide replacement of petrol-burning engines with fuel-cell engines is thus dependent on large-scale H2 production obtainable only via nuclear- or coal-based power or heat.
There are at least five practical propulsion systems that could replace present automobile engines when oil is depleted. These are: (a) Combustion engines burning synthetically made fuels (synfuels) instead of petrol; (b) Hydrogen-consuming fuel-cell engines; (c) High-energy flywheels; (d) Electric battery packs, (e) Steam engines. Solar- and wind-driven cars are fun but cannot transport large numbers of people and goods. Future cars, trucks, ships, trains, and airplanes will most likely be propelled by synfuel-burning internal combustion engines (ICEs) or hydrogen-consuming fuel-cell engines (FCEs).
Large-scale hydrogen fuel production to replace all petrol presently used in transportation fleets, can be achieved by electrolysis or chemical reduction of water (H2O) yielding hydrogen (H2) and oxygen (O2). The electricity or heat needed for this can be provided by nuclear power plants for more than fifteen hundred years or by coal-fired plants for over a hundred years. H2 gas might be piped through gas pipelines to people's garages where it can be compressed in high-pressure cylinders to be carried on-board automobiles, or stored in a H2-adsorbing "bladder", possibly the vehicle fuel-tank of the future. Alternatively, utility tap water might be electrolyzed to hydrogen and oxygen with available electric grid power in people's garages during the night. A porous fuel bladder can suck up hydrogen gas by adsorption on its inner surfaces and release it when slightly heated. ICEs or FCEs using oxygen from the air and H2 fuel to move pistons or make electricity, exhaust only water. Thus water for making H2 fuel (using electricity) is returned to water in a fuel-cell's exhaust. This is an eco-friendly cycle compared to globe-warming carbon-dioxide exhausts from petrol-burning ICEs.
If H2 pipeline delivery or production in garages proves to be too expensive or unsafe, H2 can be picked up at public fueling stations instead, either to refill hydrogen-adsorbing bladders or to replace liquid or compressed-gas cylinders filled with H2. Proposals to bio-engineer H2-producing organisms may be useful for low-quantity applications, but could never provide enough H2 for all the transportation fleets in the world, as is generally the case for all biomass energy conversion concepts.
At present the main obstacles to the large-scale introduction of clean H2-fuel-cell-powered cars is the H2 storage problem and fuel-cell electrode fouling. Electric car engines have been developed, but replacement of the space presently occupied by an automobile fuel tank with the best H2 adsorbing bladder or compressed-gas tank, results in a vehicle that can be driven for only one hour or 100 km (60 miles). Present techniques for H2 bladder storage or compression need therefore a five-fold density increase to make H2-fuel-cell-powered cars competitive with present-day petrol-fueled autos. Progressive fouling of fuel-cell electrodes may require their periodic replacement, like worn spark-plug replacements in today's combustion engines. This may be acceptable if the costs are reasonable.
Should the development of fuel-cell engines for automobile propulsion prove difficult, use of today's ICEs might be continued for a while after oil and gas reserves are gone, by fueling them with manufactured portable "synfuels" instead of petrol. With assistance of electric power, coal and water can be converted to syn-petrol (synthetic petrol) as is presently done in South-Africa's SASOL plant. Other synfuels producible with the assistance of electricity are hydrazine and ammonia synthesized from air and water, and ethanol obtained from sun-grown corn. To be efficient, the energy packed into a portable synfuel should not greatly exceed the amount of electric energy needed for its manufacture, although some energy conversion losses are justified. A nuclear plant does not fit in a car of course. To make abundant uranium-generated energy available for automotive uses, some losses are acceptable when this energy is converted and locked up in a portable synfuel or hydrogen. In making ethanol from sunshine and corn, electricity is used to manufacture fertilizers and farm machinery, and for husk removal, fermentation, and distillation operations. The combustion energy of ethanol (alcohol) is close to the electric energy required to make it. In a corn-alcohol-only economy this is unacceptable, but aided by nuclear electricity it is sustainable.
Use of methane (CH4) or ethanol (C2H5OH) in a combustion engine still produces undesirable carbon dioxide (CO2) emissions, while hydrazine (N2H4) or ammonia (NH3) synfuels (e.g. for aviation) may generate unhealthy NOx gases. Even if pure H2 is used as synfuel in a combustion engine, high temperatures cause formation and exhausts of NOx from reactions of oxygen (O2) with nitrogen (N2) in the air intake. Already developed catalytic NOx converters or scrubbers might remedy the NOx problem, but non-NOx-producing fuel-cells operating at lower temperatures are preferred if practical.
Electric storage batteries and flywheels are other possible means of providing automotive power. However the most advanced flywheel systems and lightest battery packs developed to date are only able to provide enough energy to drive a small car for one hour. Flywheel or electric storage systems face the problem of diminishing returns: more energy storage to achieve a longer driving range means more battery or flywheel mass, which means more batteries and flywheels, etc. Unless a major breakthrough occurs that increases the kilowatt-hours/kilogram capacity of batteries and flywheels five-fold, it appears at present that fuel-cells and synfuels are the most promising for empowering the next generation of engines for mobile vehicles.
Fable (7): "Coal-fired power plants seem more bio-friendly than nuclear power plants."
Fact: Coal power requires coal transports using hundreds of railroad cars and release of tons of carbon-dioxide and natural radioactive elements into the atmosphere.
A 1000-MWe coal-fired power plant which consumes 4 million tons of coal per year, releases annually 900 pounds of coal-entrained uranium, in addition to 530 pounds of mercury, 120 million pounds of SOx, 59 million pounds of NOx, and 22 billion pounds (= 11 million tons) of CO2 gas into the atmosphere.
Instead of dispersion through the atmosphere, nuclear-plant-produced radioactive waste is solid and contained. It is ultimately placed in some underground repository. A nuclear power plant is refueled once every 1.5 to 3 years with uranium encapsuled in solid fuel elements which are shipped in a few trucks. During refueling, the burnt-out "spent" fuel elements containing internal fission product wastes are removed and replaced with fresh fuel. After a brief cool-down period in a pond, the spent fuel elements are placed in a few collision-proof "caskets" for transport to a permanent nuclear waste site like the Yucca Mountain facility in Nevada under construction by the US Department of Energy. Here, after removing non-radioactive and short-lived radioactive species, long-life radio-isotopes are concentrated and stored in special nickel alloy containers, placed in underground caverns.
When uranium fissions, its energy is conducted through solid material to heat adjacent water (or gas) that runs the steam (or gas) turbines. In this heat transfer, radioactive fission products stay in the solid fuel elements, in contrast to coal burning, where species embedded in coal are sent into the atmosphere when coal is burning with oxygen in the air. Fissioned uranium products cannot undergo further fission or explode. They produce only low-level heat from radioactive decay. Even if a spent-fuel element were exposed to air during its transport in a collision-proof casket (e.g. if a terrorist fired a bullet into the casket), the solid form of radioactive products in fuel elements prevents their entry into the air. The heavy steel caskets are designed to tolerate external bomb blasts. It would take a casket-piercing missile with high explosives to vaporize a fuel element into radio-active aerosols.
Comparing safety in mining of coal versus uranium shows that many more accidents with loss of life occur in coal mines. Also daily railroad transportation of kilotons of coal are more accident-prone than monthly uranium transports of kilograms of uranium yellow-cake with a few trucks.
Fable (8): "Nuclear reactor operations are unsafe."
Fact: Two "maximum credible" nuclear power plant accidents involving core meltdowns occurred in the last fifty years, one at Three Mile Island (TMI) and the other at Chernobyl. They proved the soundness and safety of US and Western-Europe designed reactors, while they high-lighted the poor regard for safety and accident prevention under the former USSR regime. The Chernobyl power reactor had no heavy steel and concrete containment vessel as required in nearly all other countries, and was housed in a hangar. It also used graphite (very pure carbon) as moderator, which has a positive temperature coefficient of reactivity. In layman's terms this means that when the Chernobyl reactor core accidentally heated up beyond the control level, it promoted increased uranium fissioning that can cause a run-away power surge followed by a meltdown, unless halted by insertion of neutron-absorbing control rods. In contrast, in the USA and Western Europe, civilian reactors use water as moderator and coolant which has a negative coefficient of reactivity. When such a reactor gets too hot, the chain reaction terminates and the reactor shuts itself down.
The TMI accident happened because operators mistakenly forced it to overheat (thinking they were lowering the power level), causing the core to partially melt. However the safety features designed in the water-moderated TMI reactor fulfilled their function. The containment vessel held all radioactive core material in place. Except for minor escapes of tritium gas, no nuclear fall-out occurred. In the Chernobyl accident, maintenance technicians pulled out control rods in error, inducing runaway fissioning in the reactor core. The graphite moderator (a form of coal) got very hot and started burning with oxygen from the air as in a coal fire, because there was no containment vessel and unrestricted inflow of air. Firemen who had never been briefed about nuclear reactors tried to put out the fire but unknowingly exposed themselves to lethal levels of radiation. The 3 maintenance technicians instrumental in starting the Chernobyl accident were instantly killed by flying debris, while 28 firemen and rescue-workers died from radiation overdoses within months [Ref. 34]. Heart attacks killed 3 more, while 11 succumbed from medical complications years later. Another 30 rescue-workers exposed at the Chernobyl site suffered permanent disabilities.
The fear of nuclear power plant accidents seems irrational when compared to air and car accidents. Air and car crashes kill thousands of people each year, yet few people want to abolish cars and airplanes. In the past fifty years, less than a hundred people worldwide died in nuclear accidents, even though nuclear power provides 21% of all electricity in the US and 85% in France. To produce clean non-air-polluting electricity in the US, it is imperative that more nuclear power plants be built to replace coal- and gas-fired units. The latter will be inoperable when gas reserves are depleted.
Fable (9): "We don't know what to do with "dangerous" radioactive waste from nuclear reactors."
Fact: We do know what to do. The annual fission product waste from all 103 nuclear power plants in the USA, which produce nearly one trillion (1012) kilowatt-hours of electricity per year, can be extracted, concentrated, and compacted as ceramic marbles in a few hundred drums, to be stored underground in the national nuclear waste repository at Yucca Mountain, built in the Nevada desert. Because of antinuclear politicking, completion of the Yucca facility which was supposed to have been ready by 2000, has suffered delays. Even though collision-proof caskets will be used which have been crash-tested extensively, transportation of nuclear wastes over US highways and railroads is still opposed by anti-nuclear activists.
This has forced nuclear plant operators to temporarily store used fuel elements in water-shielding swimming pools until Yucca is operational. If properly prepared, temporary swimming-pool storage of spent fuel elements is safe. But it is still better to store the waste in one place rather than on a hundred different sites. Aside from civilian nuclear power plants, the US Nuclear Navy has similar spent-fuel loads to dispose of each year. There appears to be a misconception among nuclear-power opponents that "dangerous" radioactive waste can somehow explode like uranium through nuclear fission. Radioactive waste cannot explode and is absolutely non-fissionable. It only suffers from slow nuclear decay, which entails emissions of betas (= fast electrons) and gammas (= high-energy photons similar to x-rays).
Fable (10): "The longer the lifetime of a radioactive element, the more dangerous it is for man."
Fact: Just the opposite is true. The intensity of radiation from a gram of radioactive material is lower the longer its decay lifetime. Conversely it is higher, the shorter its life is. We are surrounded by natural long-lifetime radioactive materials on our planet. In fact, each human is internally radioactive because of the potassium (K) present in every human cell. Natural potassium has 0.12% radioactive potassium-40 (K-40) isotope in it. K-40 emits beta and gamma radiation and decays with a half-life of a billion years compared to a four billion year half-life for uranium-238 decay. A recent uproar in Europe over depleted uranium-238 used in military projectiles, shows the technical ignorance of "green" politicians who are easily brain-washed by anti-nuclear propaganda. Mildly radioactive "yellow-cake", a uranium oxide produced after uranium mining and pre-processing, is not a "nuclear explosive" as some mistakenly believe. It is as harmless as a potassium-carrying mineral or thorium-oxide mantle in a Coleman lantern. Besides unremitting exposure to internal K-40 radiation, man is bathed in natural radiation coming from cosmic sources and from the earth. He has evolved just fine with all this radiation. Recent studies show mild radiations may even be beneficial [Ref. 35].
Fable (11): "Thousands of people can die after a nuclear plant meltdown."
Fact: There have been two major nuclear reactor meltdown accidents since the beginning of the nuclear power era, one in the USA and one in Russia. The actual fatalities are 0 deaths in the USA from the Three Mile Island (TMI) accident, and 45 in the former USSR at Chernobyl in the Ukraine [see Section 6.6 and Reference 34]. I personally visited Chernobyl and the regional hospital near Pripyat, and talked to local residents and operators of the three Chernobyl reactors (only one had a meltdown). Shortly after the Chernobyl accident, scare-mongers predicted thousands would die later from fall-out radiation. This is total nonsense. Actual nuclear fall-out victims in the Chernobyl region were children who drank contaminated milk from cows that had eaten contaminated grass (avoidable if authorities had warned farmers). These children accumulated radioactive iodine in their thyroids. By administration of iodine-displacement therapy and waiting till the radioactivity subsided (Iodine-131 has an 8-day half-life), the affliction disappeared for most of them after a few months. Of an estimated 3000 people exposed to fall-out, 9 people were recently reported to have died, allegedly from exposure to Chernobyl's nuclear fall-out.
Claims of thousands of future cancers due to Chernobyl fall-out made by antinuclear groups are based on distorted probability calculations not acceptable to statisticians. Under-reported pre-Chernobyl cancers, and cancer cases due to modern chemicals which cannot be distinguished from nuclear-fallout-generated cancers, produce flawed statistics. As all mortals do, most of the 140,000 evacuated inhabitants in the direct fall-out path of Chernobyl's radioactive plume will die between ages 60 and 100. Based on world-wide cancer-death statistics, at least 14,000 (~ 10%) of them are expected to die from cancer due to non-nuclear causes. Antinuclear propaganda claims all these deaths will be due to Chernobyl, a totally untenable charge. It is akin to claiming that coffee kills 20% of all people, based on the fact that 20% of all people drink coffee and all will ultimately die.
Fable (12): "Exposure to "radiation" causes long-term after-effects in one's body."
Fact: The word "radiation" is repeatedly misused by lay people and substituted for radioactive particles (see below). In physics, gamma radiation from radioactive processes falls in the same class as visible light radiation, infrared heat radiation, and radio waves. All are made up of massless electromagnetic waves or evanescent photons which can be absorbed or reflected once, but do not "stick" as some people mistakenly believe. Like heat which emits infrared photons, a little bit of radiation is harmless and even beneficial (e.g. a heating pad), but too much can kill you (heat in an industrial furnace incinerates you). Nuclear reactor cores emanate alpha and beta particles, neutrons, and gammas. Emanations with mass such as the beta particles (which are fast electrons) and alphas (Helium ions) are stopped by less than a millimeter of metal or concrete, while neutrons are absorbed or reflected back into the reactor core. Only gamma radiation emitted by decaying fission products requires thicker stopping materials. Massless gamma radiation is like massless solar ultraviolet light, except the frequency and thus photon energy is higher. Reactors have enough shielding around them to absorb most massless gammas, allowing only an insignificant harmless number to get through.
A person's exposure to a beam of gamma photons emitted by a radioactive compound can cause breakage of a few biochemical bonds in body tissue. However the body does not differentiate between broken biomolecular bonds from a scratch, a knife-cut, cosmic radiation, or from gamma photons. A scratch may be more detrimental than gamma damage since broken bonds are closer together in a scratch, while molecular breakages due to gammas are spread out. People don't know what it means when told they have been exposed to "100 millirems of radiation". This number can be put in perspective, knowing body damage from a 2 cm long, 0.1 cm deep scratch on one's skin causes biomolecular bond breakages equivalent to 100 millirems. The human body repairs broken bonds rapidly and has done so during a million years of evolution in a radiation-rich environment.
A more important nuclear safety concern is inhalation or ingestion of radioactive particles or dust present in the "fall-out" plume of atomic bombs or in the debris cloud from the meltdown of a reactor without a containment vessel such as Chernobyl. Some body organs (e.g. thyroid gland) and bones have an affinity for certain uranium fission products, mainly radioactive iodine, cesium, and strontium. The body can extract these elements from inhaled or ingested radioactive dust, and concentrate them unless they are eliminated ("anti-radiation" pills are available today that can force the body to expel such undesirable elements). When lodged in the body they can constantly emit betas and gammas in surrounding tissue and irritate or destroy it (this is exploited in nuclear medicine to kill cancer cells, but here cancerous tissue is pre-selected).
In the unlikely event one is in the path of the debris cloud from an atomic bomb or Chernobyl-like explosion, the best protection against fall-out is to enter a shelter with closed windows. If outside, one should filter the air one breathes using a wet handkerchief or gas mask, and wash off all dust by taking a swim or shower after the cloud has passed. If available, one should take anti-radiation pills. Of course the best protection is to run or drive away from such a usually slow-moving cloud.
To avoid possible radioactive fallout entirely in nuclear melt-downs, today all power reactors in the world must have a steel and concrete containment vessel surrounding them. This vessel must keep all nuclear reactor debris contained under the worst imaginable ("maximum credible") accident such as a core meltdown, an M-8 earthquake, airplane crash, (non-nuclear) bomb attack, sabotage, etc. The (almost incredible) Three-Mile-Island (TMI) accident proved its effectiveness in limiting damage.
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.