NUCLEAR POWER PLANTS

• A nuclear power plant (NPP) is a thermal power station in which the heat source is one or more nuclear reactors. As in a conventional thermal power station the heat is used to generate steam which drives a steam turbine connected to a generator which produces electricity.

SYSTEMS IN NUCLEAR POWER PLANT

Nuclear reactorsSteam turbineGenerator Cooling systemSafety valvesFeedwater pumpEmergency power supply

People in a nuclear power plant

• Nuclear engineers• Reactor operators• Health physicists• Emergency response team personnel• Nuclear Regulatory Commission Resident

Inspectors

Plant location• In many countries, plants are often located on the coast, in

order to provide a ready source of cooling water for the essential service water system.

• As a consequence the design needs to take the risk of flooding and tsunamis into account.

• The World Energy Council (WEC) argues disaster risks are changing and increasing the likelihood of disasters such as earthquakes, cyclones, hurricanes, typhoons, flooding.

• Climate change and increased temperatures, lower precipitation levels and an increase in the frequency and severity of droughts may lead to fresh water shortages.

• Seawater is corrosive and so nuclear energy supply is likely to be negatively affected by the fresh water shortage.

• This generic problem may become increasingly significant over time.

nuclear safety systems

• The three primary objectives of nuclear safety systems as defined by the Nuclear Regulatory Commission are to shut down the reactor, maintain it in a shutdown condition, and prevent the release of radioactive material during events and accidents.

• These objectives are accomplished using a variety of equipment, which is part of different systems, of which each performs specific functions

ADVANTAGES OF NUCLEAR POWER PLANTS1. Almost 0 emissions (very low greenhouse gas emissions).

They can be sited almost anywhere unlike oil which is mostly imported.

2. The plants almost never experience problems if not from human error, which almost never happens anyway because the plant only needs like 10 people to operate it. A small amount of matter creates a large amount of energy.

3. A lot of energy is generated from a single power plant.4. Current nuclear waste in the US is over 90% Uranium. If

reprocessing were made legal again in the US we would have enough nuclear material to last hundreds of years.

5. A truckload of Uranium is equivalent in energy to 10,000+ truckloads of coal. (Assuming the Uranium is fully utilized.)

• A nuclear aircraft carrier can circle the globe continuously for 30 years on its original fuel while a diesel fueled carrier has a range of only about 3000 miles before having to refuel.

• Modern reactors have two to ten times more efficiency than the old generation reactors currently in use around the US.

• New reactor types have been designed to make it physically impossible to melt down. As the core gets hotter the reaction gets slower, hence a run-away reaction leading to a melt-down is not possible.

• Theoretical reactors (traveling wave) are proposed to completely eliminate any long-lived nuclear waste created from the process

• Breeder reactors create more usable fuel than they use.

• Theoretical Thorium reactors have many of the benefits of Uranium reactors while removing much of the risk for proliferation as it is impossible to get weapons-grade nuclear materials from Thorium.

DISADVANTAGES OF NUCLEAR POWER PLANT

• Nuclear plants are more expensive to build and maintain. Proliferation concerns - breeder reactors yield products that could potentially be stolen and turned into an atomic weapon.

Waste products are dangerous and need to be carefully stored for long periods of time.

• The spent fuel is highly radioactive and has to be carefully stored for many years or decades after use.

• This adds to the costs. • There is presently no adequate safe long-term storage for

radioactive and chemical waste produced from early reactors, such as those in Hanford, Washington, some of which will need to be safely sealed and stored for thousands of years.

• A lot of waste from early reactors was stored in containers meant for only a few decades, but is well past expiration and, resultingly, leaks are furthering contamination.

• Nuclear power plants can be dangerous to its surroundings and employees. It would cost a lot to clean in case of spillages.

• There exist safety concerns if the plant is not operated correctly or conditions arise that were unforeseen when the plant was developed, as happened at the Fukushima plant in Japan; the core melted down following an earthquake and tsunami the plant was not designed to handle despite the world's strongest earthquake codes.

• Many plants, including in the U.S., were designed with the assumption that "rare" events never actually occur, such as strong earthquakes on the east coast (the New Madrid quakes of the 1800s were much stronger than any east coast earthquake codes for nuclear reactors;

• A repeat of the New Madrid quakes would exceed the designed earthquake resiliency for nuclear reactors over a huge area due to how wide-spread rare but dangerous eastern North American earthquake effects spread), Atlantic tsunami (such as the 1755 Lisbon quake event, which sent significant tsunami that caused damage from Europe to the Caribbean) and strong hurricanes which could affect areas such as New York that are unaccustomed to them (rare, but possibly more likely with global warming)

• Mishaps at nuclear plants can render hundreds of square miles of land uninhabitable and unsuitable for any use for years, decades or longer, and kill off entire river systems

NUCLEAR WASTE MANAGEMENT

• All parts of the nuclear fuel cycle produce some radioactive waste (radwaste).

• The cost of managing and disposing of these wastes is part of the electricity cost, i.e., it is internalized and paid for by the electricity consumer.

• At each stage of the fuel cycle there are proven technologies to dispose of the radioactive wastes safely.

• For low- and intermediate-level wastes these are mostly being implemented. For high-level wastes some countries await the accumulation of enough of it to warrant building geological repositories,

• The radioactivity of all nuclear waste decays with time. Each radionuclide contained in the waste has a half-life - the time taken for half of its atoms to decay and thus for it to lose half of its radioactivity.

• Radionuclides with long half-lives tend to be alpha and beta emitters - making their handling easier - while those with short half-lives tend to emit the more penetrating gamma rays.

• Eventually, all radioactive wastes decay into non-radioactive elements.

• The main objective in managing and disposing of radioactive (or other) waste is to protect people and the environment. This means isolating or diluting the waste so that the rate or concentration of any radionuclides returned to the biosphere is harmless.

• To achieve this, practically all wastes are contained and managed - some need deep and permanent burial - so that harmful pollution is avoided. From nuclear power generation, none is allowed to cause harmful pollution.

Types of radioactive wastes

1. Mine tailings2. Exempt Waste & Very Low Level

Wastes (VLLW)3. Low-level Wastes (LLW)4. Intermediate-level Wastes (ILW)5. High-level Wastes (HLW)

Mine tailings

• Traditional uranium mining generates fine sandy tailings, which contain virtually all the naturally occurring radioactive elements found in uranium ore.

• These are collected in engineered tailings dams and finally covered with a layer of clay and rock to inhibit the leakage of radon gas and ensure long-term stability.

• In the short term, the tailings material is often covered with water. After a few months, the tailings material contains about 75% of the radioactivity of the original ore.

• Strictly speaking these are not classified as radioactive wastes.

Exempt Waste & Very Low Level Wastes (VLLW)• Radioactive waste which contains radioactive materials at a

level which is not considered harmful to people or the surrounding environment.

• It consists mainly of demolished material (such as concrete, plaster, bricks, metal, valves, piping etc) produced during rehabilitation or dismantling operations on nuclear industrial sites.

• Other industries, such as food processing, chemical, steel etc also produce VLLW as a result of the concentration of natural radioactivity present in certain minerals used in their manufacturing processes (see also paper on NORM).

• The waste is therefore disposed of with domestic refuse, although countries such as France are currently developing facilities to store VLLW in specifically designed VLLW disposal facilities.

Low-level Wastes (LLW)

• Generated from hospitals and industry, as well as the nuclear fuel cycle.

• It comprises paper, rags, tools, clothing, filters, etc. that contain small amounts of mostly short-lived radioactivity.

• These wastes do not require shielding during handling and transport and are suitable for shallow land burial.

• To reduce the waste's volume, it is often compacted or incinerated before disposal.

• LLW comprises some 90% of the volume but only 1% of the radioactivity of all radwaste.

Intermediate-level Wastes (ILW)

• contains higher amounts of radioactivity and some requires shielding, usually of lead, concrete or water. It typically comprises resins, chemical sludges, and metal fuel cladding, as well as contaminated materials from reactor decommissioning.

• Smaller items and any non-solids may be solidified in concrete or bitumen for disposal.

• ILW makes up some 7% of the volume and has 4% of the radioactivity of all radwaste.

• The maintenance of a 1000 MWe nuclear reactor produces less than 0.5m3 of long-lived ILW each year. If fuel is reprocessed this is increased to 3m3.

High-level Wastes (HLW)Rise from the "burning" of uranium fuel in nuclear reactors. HLW

contains the fission products and transuranic elements generated in the reactor core. It is highly radioactive and hot, so requires cooling and shielding.

It can be considered as the "ash" from "burning" uranium. These wastes contain the fission products and transuranic elements generated in the reactor core.

It is highly radioactive and hot and thus requires cooling and shielding. HLW accounts for over 95% of the total radioactivity produced in the process of electricity generation. There are two distinct kinds of HLW:

1. used fuel itself in fuel rods, or separated waste from 2.reprocessing the used fuel

Alternative energy Solar energy• Solar energy is generating of electricity from the sun. It is split

up into two types, thermal and electric energy. These two subgroups mean that they heat up homes (and water) and generate electricity respectively.

Wind energy• Wind energy is generating of electricity from the wind. Geothermal energy• Geothermal energy is using hot water or steam from the

Earth’s interior for heating buildings or electricity generation. Biofuel and ethanol• Biofuel and ethanol are plant-derived substitutes of gasoline

for powering vehicles.

Hydrogen• Hydrogen is used as clean fuel for airplanes,

spaceships, and vehicles.

The Future of Nuclear Energy

• Some people think that nuclear energy is here to stay and we must learn to live with it.

• Others say that we should get rid of all nuclear weapons and power plants. Both sides have their cases as there are advantages and disadvantages to nuclear energy.

• Still others have opinions that fall somewhere in between.

• What do you think we should do? After reviewing the pros and cons, it is up to you to formulate your own opinion.

THANK YOU