nuclear+versus+coal

Here is a link to [|how nuclear power works].

Most nuclear power plants in operation around the world today are pressurized water reactors(PWRs).


 * Essentially, heat is produced from the reactor vessel, which is used to generate steam.
 * This steam is used to turn a turbine, and in turn a generator, to produce electricity.
 * The steam is then condensed and cooled in the giant cooling towers, and returned to the plant.

Almost all power plants operate in this manner; simply replace the reactor with a coal furnace, for example, and you have a coal power plant.




 * Why nuclear energy?**
 * At one time, it was thought that electricity generated from nuclear power would be so cheap it would almost be free. It takes only a small amount of uranium to generate the same electricity as thousands of times that amount of fossil fuels.
 * Today, nuclear power is a potential alternative to fossil fuels due to the fact that it does not release carbon dioxide.

**__Nuclear Power versus Coal Power__**

 * Facts about coal power plants:**
 * A typical coal power plant uses 10,000 to 50,000 tons of coal per day
 * In Pennsylvania, there are 78 coal power plants that produce about 45-55% of PA's electricity
 * PA's coal power plants consumed [|56 million tons of coal per year in 2006 and 2007]
 * These PA coal-fired plants released [|126 million tons of carbon dioxide] into the atmosphere in 2006 alone
 * in PA, every kilowatt-hour of electricity you use produces 1.268 pounds of carbon dioxide
 * Recently, natural gas has been replacing some coal as a fuel for electricity generation.




 * Facts about nuclear power plants:**
 * A typical nuclear power plant uses 25-30 tons of fuel per year
 * There are 5 nuclear power plants in PA, producing 36% of the state's electricity
 * Nuclear power plants emit no greenhouse gases such as carbon dioxide


 * The US Navy** powers its larger ships and its submarines with nuclear reactors. They have good reasons to do so - a nuclear-powered aircraft carrier, by far the largest ship of the fleet, can go up to 13 years without refueling its nuclear reactor. Four pounds of uranium will produce the same amount of energy as 10 million gallons of fuel oil, drastically reducing the number of trips these vessels would need to make to port for refueling.

Nuclear Waste
Nuclear power plants produce tons of highly radioactive metal and liquid waste annually. Some of this waste is stored in large pools of water until the material cools enough to be sealed in dry casks. The solid material is then stored on the plant's grounds in these dry casks. The waste may remain radioactive for thousands of years.





Long-term nuclear waste storage has been a major issue with nuclear power. One solution was to store it in tunnels under Yucca Mountain, located in the Nevada desert. This plan has not panned out due to uncertainties over the geologic stability of the storage facility.



Coal power plants produce nuclear waste as well. Emissions from a 1000 MW coal power plant include 5.2 tons of uranium per year (74 pounds of U-235). This size plant will also emit 13 tons of thorium per year; one ton of thorium has the potential to produce about 1 GW of electricity, ten times the energy the plant gets from the coal itself. All of the uranium emitted by a single 1000 MW coal power plant would be equal in energy output to 26 billion gallons of fuel oil per year.

**Nuclear Power Plant Accidents**
The use of nuclear energy has been stymied by two major accidents: [|Three Mile Island] and [|Chernobyl]. More recently, the earthquake/tsunami that struck Japan has caused a third disaster at Fukushima.



In 1979, reactor number 2 (TMI-2) at Three Mile Island near Harrisburg, PA [|had an accident] that resulted in a partial meltdown of the reactor core. This in turn led to the release of some radioactive gases (to prevent a steam explosion). It is estimated that the radiation exposure to anyone within ten miles of the plant would have been equal to that of a single chest x-ray.



In 1986, reactor number 4 at the [|Chernobyl nuclear power plant] in Russia (now Ukraine) had a similar meltdown but was followed by a catastrophic steam explosion and resulting core fire. The explosion released up to 30,000 [|Rontgen] (30 billion times the average background radiation), and the plume of radioactive material [|spread for hundreds of miles]. Radiation alarms in a nuclear facility in Sweden were set off from the fallout from Chernobyl.



The core fire was fought for nine days, with firefighters and helicopters dropping 5000 tons of sand and boron onto the exposed core. All of these 'liquidators' were exposed to dangerous levels of radiation. The city of [|Pripyat] (50,000 residents) was evacuated two days later; in all, up to 330,000 people were evacuated from the region. None were permitted to return, and all left behind their personal belongings, as they were told the evacuation ould be temporary.

The exposed core was hastily covered with a large steel and concrete structure called the 'sarcophagus', which today is deteriorating and leaking rain water. There are now plans to build a new shelter (see [|New Safe Confinement]) over the core, for if the current shelter collapses, more radiation may be released by the site.

In December 2011, a devastating earthquake and tsunami struck the east coast of Japan. This severely damaged the Fukushima Daiichi nuclear power plant, which then caused radiation releases.



In summary, let us look at the pros and cons of using nuclear energy.

__Pros:__
 * A nuclear power plant does not generate greenhouse gases.
 * The electricity generated by nuclear power is relatively inexpensive (mass to energy ratio is better than fossil fuels).
 * Fewer power plants are necessary to generate electricity, lowering the cost of maintenance.

__Cons:__
 * An accident could have catastrophic consequences.
 * Long-term radioactive waste storage is a major concern.
 * Uranium and plutonium are fissile materials and could be used in nuclear weapons.
 * Uranium is rare and expensive to mine and process.

__The Future of Nuclear Energy__
Right now, there are two factors bringing the spotlight back to nuclear energy - climate change and limited fossil fuel resources.
 * Nuclear power produces little to no carbon dioxide; its fuel is much more energy-efficient per mass than fossil fuels.
 * Fuels such as uranium are difficult and costly to mine and process, and mining them causes an environmental impact just like the mining of coal.
 * New nuclear fuels are in the pipeline for development. One of these is thorium.

Advantages of Thorium
 * Thorium is many times more abundant than uranium in the Earth's crust.
 * Large quantities of thorium exist in relatively stable regions of the world, such as Australia and Canada.
 * Thorium cannot be used as a weapons-grade material.
 * Thorium can be extracted from coal fly ash.
 * Radioactive waste products from Th reactors are much shorter-lived (still hundreds of years) than those of uranium.

Disadvantages of Thorium
 * To use Th as a fuel, it needs an initiator such as uranium or plutonium. Some have considered using nuclear weapons stockpiles as fuel initiators in thorium reactors.
 * One interesting approach is to 'activate' a dense metal such as lead or depleted uranium using a particle accelerator. This would create enough neutron bombardment to initiate thorium for a nuclear reaction. These are called 'accelerator-driven systems' or ADS reactors.



See this link on particle-accelerator-driven thorium nuclear power.