Nuclear Power Plant Isar, Germany

Spent nuclear fuel pool

Turbine of a nuclear plant



Watt is the international standard power unit in SI.

James Watt (1736-1819), the inventor of the steam engine, accepted it as the unit of power in the SI unit system. It is the unit that measures the energy conversion rate (joules) divided by seconds. The watt symbol is represented by the letter W.

1W = 1 J / s

In mechanics the watt is the power developed by a force of a newton applied to a point that moves one meter for a second. That is, if the point on which a force of a newton is applied is displaced at a speed of 1 m / s, the power is equal to 1 watt:

1W = 1N · 1m / 1s

In electromagnetism, an electric potential difference in volts (V) occurs when a current flow of amperage (A) is one watt, that is:

W = VA


In the nuclear power plant sector, it is common to speak of megawatts to refer to the power of a nuclear power plant.

The megawatt is a unit of power equivalent to one million watts. Many applications can be found in which the transfer, generation or consumption of energy is in this scale, some of the possibilities can be found even in nature, as for example to the electric discharges of the rays, or the dissipation of energy in the large cascades are in megawatt order, an example would be the energy dissipated in the Dettifoss waterfall in Iceland (class 7 according to cascade classifications by volume) where the average potential energy variation of the cascade is in this order.

Examples of machinery that works with powers of this order are for example large electric motors, large ships (such as aircraft carriers and submarines), special machinery and some research and search equipment such as large lasers or supercolisionadors. A large residential or commercial building can consume some megawatts of electrical power and energy for heating.

The productive capacity of electric generators operated by public services can also be measured in MW. In the railway world, modern high-power electric trains can have a maximum power of 5 or 6 MW, although many machines produce much more, the Eurostar, for example, consumes more than 12 MW - while the heavy diesel-electric locomotives they may typically require 3 to 5 MW. In the field of nuclear energy, some plants can have net capacities between 500 and 1300 MW.

The oldest citation of the term "megawatt" appeared, according to the Oxford English Dictionary, the Webster's International Dictionary of English Language. The OED also notes that the term megawatt appeared on November 28, 1947 in an article in the journal Science (506: 2).

Electric Megawatt

The electric megawatt (represented by MWe) is the electrical output of a power plant in megawatts, in our case, in a nuclear power plant. The electrical power of a nuclear power plant is equal to the thermal power generated by nuclear fission reactions in the core of the nuclear reactor multiplied by the efficiency of the power plant.

The efficiency of power plants in light-water nuclear reactors is 33 to 35% compared to up to 40% for modern power plants with coal, oil or gas fossil fuels.

Examples of power

If a person removes a 100-kilogram mass from a 3-meter ladder in 5 seconds, his work is approximately 3,000 (j = Nm).

(Note: g: the gravitational acceleration is approximately 9.8m / s2, so the body weight is 100 kg x 9.8 m / s2 = 1,000 N. Y, work (joules) = force (Newton) x is the trajectory (meter)).

Power deals with how quickly this is done. So, if the power is higher, the same work is done more quickly.

Power = work / time. In our example, 3,000 Nm of work is done in 5 seconds Power (watts) = 3000/5 (Nm / s) = 600 watts available.

A medium volume car engine is 50-100 kW (kilowatts). At half speed, it produces half the power. Larger or higher performance vehicles have more powerful engines.

A normal household light bulb has a power of between 25 and 100 watts. Fluorescent lamps typically consume 5 to 30 watts to produce a similar amount of light, while similar LED lamps use between approximately 0.5 and 6 watts of power.

A normal hydroelectric power plant produces 200-300 MW (megawatts).

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Last review: October 29, 2018