nuclear power

Nuclear power, or nuclear energy, is the use of exothermic nuclear processes carried out in controlled manner, to generate useful heat and electricity.

Nuclear power works by using the energy from nuclear fission or fusion to generate heat. At the moment, nuclear fusion is still a subject of intense research and not used in production which is a pity. Nuclear fission is basically what is happening in a reactor. Radioactive elements have unstable nuclei and they are constantly going through random fission to shed neutrons and become different elements. It is this breaking of the nucleus that releases the energy that we use. Once the heat is generated, the rest of the nuclear plant works pretty much the same as say the typical coal power plant. The danger with nuclear fission is it’s difficult to control nature and radiation. To understand nuclear fission, one important thing to understand is that you can’t switch it off. Atoms are fissioning in radioactive material all the time. When they collide against other atoms, they trigger fission in them as well. Things that encourage these collisions are called moderators. Moderators block the escape of the atoms in such a way that they rebound back into the material, rapidly increasing the chances of fission. When a lot of atoms are fissioning, the whole thing takes on a life of its own. Triggering it constantly, so to think. This is called a chain reaction and it releases huge amounts of heat. This is what the reactors do, in order to produce the heat. To stop the chain reaction, control rods are inserted between the radioactive materials. These rods slow down the fissions by absorbing neutrons. The nuclear fission energy source never completely stops. It keeps slowing down till finally it reaches its regular random fission patterns. This process takes a long, long time.

Other components of nuclear reactor are:
Core – It’s the focal point of the reactor, where fuel is contained and nuclear fission reactions take place.
Fuel – Generally, fuel is made of small enriched uranium oxide rods, stacked so as to form cylinders, approx. 4 metres long and with a diameter of about one centimetre. These rods are wrapped in metal sheathes (steel or zirconium alloy), which allow heat to pass through while blocking the radioactive elements produced by fission.
Moderator – This is a material placed in the reactor to slow down the neutrons produced by fission, in order to reach the most suitable speed allowing the chain reaction to continue.
Depending on the various reactor models, the moderator may consist of graphite, water or heavy water (water where the hydrogen is present as its heavier isotope, deuterium).
Heat-transfer fluid (or coolant) - This fluid (liquid or gas) cools the core and carries outside the heat that is produced there. The most commonly used fluid is water, but some types of reactors use different fluids (heavy water, molten sodium, carbon dioxide, helium and other fluids).
Control rods – These are rods used in specific materials (silver, indium, cadmium or boron carbide) to control fission inside the core. Since they absorb neutrons, they are capable of controlling the chain reaction which - depending on how deep down the rods are inserted into the core - can be accelerated, slowed down or even stopped, thus changing the capacity of the reactor. Indeed, if necessary, the reactor can be immediately stopped when they are fully inserted.
Vessel – The large steel recipient containing the core, the control rods and the heat-transfer fluid.
All the components of the reactor are container in a solid concrete structure that guarantees further isolation from external environment. This structure is made of concrete that is one-metre thick, covered by steel. The most recent reactors sometimes contain two containment structures and are designed to defy all types of accidental events, even the impact of an aircraft.

The nuclear reactor is the heart of the plant. In its central part, the reactor core 's heat is generated by controlled nuclear fission. With this heat, a coolant is heated as it is pumped through the reactor and thereby removes the energy from the reactor. Heat from nuclear fission is used to raise steam, which runs through turbines, which in turn powers either ship 's propellers or electrical generators.
Since nuclear fission creates radioactivity, the reactor core is surrounded by a protective shield. This containment absorbs radiation and prevents radioactive material from being released into the environment. In addition, many reactors are equipped with a dome of concrete to protect the reactor against both internal casualties and external impacts.

MERITS OF NUCLEAR POWER
1. Nuclear power costs about the same as coal, so it 's not expensive to make
To accurately compare the cost of nuclear against other energy sources, one must include the following costs: I) Fuel costs:
For a nuclear plant, these tend to be lower even though the following steps occur in the production of the fuel assemblies used in the reactor:
i) Mining of the uranium ore, ii) Conversion to U3O8 (uranium oxide - yellowcake form), iii) Conversion to uranium hexafluoride, iv) Enrichment from 0.7% U235 to 2-5% U235,
v) Conversion to uranium dioxide (UO2) pellets, vi) Loading of the pellets into rods, then into fuel assemblies
Transportation costs are high for coal because of the amount of material needed to generate the same energy as the nuclear fuel.

II) Capital costs
For a nuclear plant these may be higher than other energy forms because the buildings used for containment or for safety-related equipment must meet higher standards than the traditional structures. Also, safety-related systems are redundant. Such considerations are not important in other energy forms. On the other hand, coal plants are required to include scrubbers to remove airborne pollutants as sulphur dioxide, nitrous oxides, and particulates.
III) Operation and Maintenance costs This includes the costs of:
1. Labour and overheads (e.g. medical and pension benefits),
2. Expendable materials,
3. NRC (e.g. license changes, on-site and regional inspectors, and headquarters staff) and state (e.g. health department, emergency planning) fees,
4. Local property taxes (varies from state to state).
Labour costs in a nuclear plant include those for operators, maintenance personnel (electrical, mechanical, instrument and controls), health physics technicians, engineering personnel (mechanical, electrical, nuclear, chemical, and radiological, computer).
Materials costs include replacement parts, computer parts, expendable office and other supplies.

IV) Waste-Related Costs
The costs associated with the by-product waste. For a coal plant this is ash. For a nuclear plant, these costs include the surcharge levied by the Department of Energy for ultimate storage of the high level waste. The DOE charge is a flat fee based on energy use.
V) Decommissioning Costs
The costs associated with restoration of the plant site back to "Greenfield" status. Usually restoration would occur over a long period of time, e.g. 20 years. Parts of the plant could be used for energy generation by other sources.
The table below compares nuclear versus coal specific item costs for similar age and size plants on a $ per Megawatt-hour (10 $/Mw-hr = 1 cent/kw-hr):

2. Nuclear power generation emits relatively low amounts of CO2. The contribution of nuclear power to global warming is relatively little.
Nuclear energy makes a significant contribution to the lowering of carbon emissions from the energy sector worldwide. The current use of nuclear energy (accounting for about 15% of the world’s electricity generation) avoids the emission of about 2.1 billion tonnes of CO2eq every year.
Factors Influencing GHG Emission Rates from Nuclear Power
Energy use for fuel extraction, conversion, enrichment and construction / decommissioning (plus materials);
Fuel enrichment by gas diffusion, which is an energy intensive process that can increase GHG releases by an order of magnitude when compared to enrichment by centrifuge;
Emissions from the enrichment step, which are highly country-specific since they depend on the local fuel mix; and
Fuel reprocessing (uranium oxide or mixed oxide), which can account for 10% to 15% of the total nuclear GHG burden.
WNA has carried out a review of over twenty studies assessing the greenhouse gas emission produced by different forms of electricity generation. The results summarised in the chart below show that generating electricity from fossil fuels results in greenhouse gas emissions far higher than when using nuclear or renewable generation.

3. Produces huge amounts of energy from small amounts of fuel.
The amount of energy released in nuclear reactions is astounding. Table shows how long a 100 Watt light bulb could run from using 1 kg of various materials. The natural uranium undergoes nuclear fission and thus attains very high energy density (energy stored in a unit of mass).

4. Produces small amounts of waste
Since nuclear power plants use so little fuel, the volume of nuclear waste is much smaller than the volume of waste from fossil fuel power plants. The amount of waste produced each year would cover only your dining room table! Even though nuclear waste is highly radioactive, its small volume enables safe isolation from society. The waste is stored in fire-, water-, and earthquake-proof capsules to ensure safety.
If all the electricity use of the USA was distributed evenly among its population, and all of it came from nuclear power, then the amount of nuclear waste each person would generate per year would be 39.5 grams. If we got all our electricity from coal and natural gas, expect to have over 10,000 kilograms of CO2/yr attributed to each person, not to mention other poisonous emissions directly to the biosphere (based on EIA emissions data).

Other merits include:
Reliable - Nuclear power plants have very high capacity factors. It can be counted on to produce electricity for many years (average availability over three years is about 80%).
Nuclear power plants only need refuelling once every year to 18 months. The new store of fuel constitutes about 2 metric tons, or 6 truckloads of uranium. Coal power plants require a new trainload of about 100 tons of coal every day.
Reduce dependence on foreign oil/ fuel. Uranium available domestically and in oceans. India announced that the Tumalapalli mine in Andhra Pradesh state of India could provide more than 170,000 tonnes of uranium, making it as the world 's largest uranium mine.
High temperature reactors could produce Hydrogen as well as electricity.
Creates high paying, skilled jobs.

DEMERITS OF NUCLEAR POWER
1. Radioactive Waste
The number one problem of nuclear power is the radioactive waste. The waste from nuclear energy is extremely dangerous and it has to be carefully looked after for several thousand years (10’000 years according to United States Environmental Protection Agency standards). There are not really any solutions to this problem, except for nuclear waste treatment.
These reactive radicals make the sand or the water contaminated. It is known as mixed waste.
The radioactive wastes are usually buried under sand and are known as vitrification. But these wastes can be used to make nuclear weapons.

2. Nuclear Accidents
Nuclear power is reliable, but a lot of money has to be spent on safety - if it does go wrong, a nuclear accident can be a major disaster.
People are increasingly concerned about this - in the 1990 's nuclear power was the fastest-growing source of power in much of the world. In 2005 it was the second slowest-growing.
While so many new technologies have been put in place to make sure that such disaster don’t happen again like the ones Chernobyl or more recently Fukushima but the risk associated with them are relatively high.
Chernobyl disaster: The world 's worst nuclear accident occurred after an explosion and fire at the Chernobyl nuclear power plant. It released radiation over much of Europe. Thirty-one people died in the immediate aftermath of the explosion. Hundreds of thousands of residents were moved from the area and a similar number are believed to have suffered from the effects of radiation exposure. Reactor four suffered a catastrophic power increase, leading to explosions in its core. This dispersed large quantities of radioactive fuel and core materials into the atmosphere and ignited the combustible graphite moderator. The burning graphite moderator increased the emission of radioactive particles, carried by the smoke, as the reactor had not been encased by any kind of hard containment vessel. Fukushima Daiichi nuclear disaster: On 11 March 2011, the Magnitude 9.0 devastating Sendai earthquake and tsunami took place in Japan. As a result, Fukushima Daiichi Nuclear Power Plant consisting of eleven reactors was automatically shut down following the earthquake. At Fukushima Daiichi and Daini tsunami waves went over seawalls and destroyed diesel backup power systems. This loss of power caused severe problems including two large explosions at Fukushima Daiichi and leakage of radiation. Over 200,000 people were evacuated.
3. HIGH COST
Another practical disadvantage of using nuclear energy is that it needs a lot of investment to set up a nuclear power station. It is not always possible by the developing countries to afford such a costly source of alternative energy. Nuclear power plants normally take 5-10 years to construct as there are several legal formalities to be completed and mostly it is opposed by the people who live nearby.
4. National Risk
We have to become more careful and responsible while using nuclear energy to avoid any sort of major accidents. They are hot targets for militants and terrorist organizations. Security is a major concern here. A little lax in security can prove to be lethal and brutal for humans and even for this planet.

5. Fuel Availability
Unlike fossil fuels which are available to most of the countries, uranium is very scarce resource and exists in only few of the countries. Permissions of several international authorities are required before someone can even thought of building a nuclear power plant.
6. Non Renewable
Nuclear energy uses uranium which is a scarce resource and is not found in many countries. Most of the countries rely on other countries for the constant supply of this fuel. It is mined and transported like any other metal. Supply will be available as long as it is there. Once all extracted, nuclear plants will not be of any use. Due to its hazardous effects and limited supply, it cannot be termed as renewable.

CONCLUSION
It is a debatable topic that whether nuclear power is good or bad.
But I think nuclear power is our gateway to a prosperous future.
‘Economic growth will need massive energy. Will we allow an accident in Japan, in a 40-year-old reactor at Fukushima, arising out of extreme natural stresses, to derail our dreams to be an economically developed nation?’ _ A.P.J Abdul Kalam

References used
I) www.world-nuclear.org
II) www.darvill.clara.net
III) www.conserve-energy-future.com
IV) www.wikipedia.org
V) www.cyberphysics.co
VI) www.wordpress.com

References: used I) www.world-nuclear.org II) www.darvill.clara.net III) www.conserve-energy-future.com IV) www.wikipedia.org V) www.cyberphysics.co VI) www.wordpress.com