energy input vs output of nuclear reactors?


can someone explain how nuclear reactors get their energy? is electricity required to get the fusion/fission to start? and then the heat released from the chemical reaction is used to heat water which then turns turbines, etc.? from what i understand, the amount of energy input into the system is more than what we get out…

so why don’t we just use the energy we put into the system as a source of power rather than putting it into nuclear fusion and getting less energy out of it? in other words, why put in 10 J of energy into something when we know we can only get 3 J back?

You have many misconceptions, nuclear power is very efficient when you look at energy produced per amount of fuel used.
Despite all the cosmic energy that the word &quot:nuclear&quot: invokes, power plants that depend on atomic energy don’t operate that differently from a typical coal-burning power plant. Both heat water into pressurized steam, which drives a turbine generator. The key difference between the two plants is the method of heating the water. While coal plants burn fossil fuels, nuclear plants depend on the heat that occurs during nuclear fission, when one atom splits into two.
There are several components common to most types of reactors:

Fuel. Usually ceramic pellets of uranium oxide (UO2) arranged in Zirconium steel alloy tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core.

Moderator. This is material which slows down the neutrons released from fission so that they cause more fission. It is usually water, but may be heavy water or graphite.

Control rods. These are made with neutron-absorbing material such as silver, cadmium, hafnium or boron, and are inserted or withdrawn from the core to control the rate of reaction, or to halt it. (Secondary shutdown systems involve adding other neutron absorbers, usually boron in the primary cooling system.) This controls the average temperature and allows extra fuel to be added for a extended time between refueling.

Coolant. A liquid or gas circulating through the core so as to transfer the heat from it. In light water reactors the moderator functions also as coolant.

Pressure vessel or pressure tubes. Usually a robust steel vessel containing the reactor core and moderator/coolant, but it may be a series of tubes holding the fuel and conveying the coolant through the moderator.

Steam generator. Part of the cooling system in Pressurized Water Reactors where the heat from the reactor is used to make steam for the turbine. Some reactor designs, called Boiling Water Reactors, do not have S/Gs but instead allow boiling in the reactor core to produce steam for the turbine..

Containment. The structure around the reactor core which is designed to protect it from outside intrusion and to protect those outside from the effects of radiation in case of any major malfunction inside. It is typically a meter (3ft.) thick concrete and steel structure designed to be air/water tight to prevent any leak to the environment in the worst case Loss Of Coolant accident.

Most reactors need to be shut down for refueling, so that the pressure vessel can be opened up. In this case refueling is at intervals of 1-2 years, when a quarter to a third of the fuel assemblies are replaced with fresh ones. The CANDU and RBMK types have pressure tubes (rather than a pressure vessel enclosing the reactor core) and can be refueled while still generating electricity by disconnecting individual pressure tubes.

If graphite or heavy water is used as moderator, it is possible to run a power reactor on natural instead of enriched uranium. Natural uranium has the same elemental composition as when it was mined (0.7% U-235, over 99.2% U-238), enriched uranium has had the proportion of the fissile isotope (U-235) increased by a process called enrichment, commonly to 3.5 – 5.0%. In this case the moderator can be ordinary water, and such reactors are collectively called light water reactors. Because the light water absorbs neutrons as well as slowing them, it is less efficient as a moderator than heavy water or graphite.

Practically all fuel is ceramic uranium oxide (UO2 with a melting point of 2800В°C) and most is enriched. The fuel pellets (usually about 1 cm diameter and 1.5 cm long) are typically arranged in a long zirconium alloy (zircaloy) tube to form a fuel rod, the zirconium being hard, corrosion-resistant and permeable to neutrons. Up to 264 rods form a fuel assembly, which is an open lattice and can be lifted into and out of the reactor core. In the most common reactors these are about 3.5-4.0 meters (3ft.) long.
The uranium 235 in these pellets absorb slowed down (moderated or thermal) neutrons, becoming unstable U-236 which splits, creating: heat, gamma, neutrons, and fission fragments. The heat generated can be calculated from the mass loss in the fission process equal to the famous equation E=MC squared, also known as binding energy. The energy released from a single fuel pellet is equivalent to the energy released burning 1 ton of coal.
The links below have some excellent detailed information and graphics about nuclear power. I hope this helps you to de-mystify nuclear power, it really isn’t that complicated, and is a safe, reliable, environmentally friendly, economical, energy source.

So far, that’s the problem with fusion reactors, nobody has managed to created more energy than it takes to start the reaction. There’s also problems with sustaining the reaction as well. They don’t (yet) exist commercially, because it doesn’t make sense practically or economically. However, there’s a lot of research going into the development of fusion reactors, since they could potentially provide much more energy than any other known source.

Fission reactors on the other hand, produce far more power than they consume. For example, a fission reactor may require something like 50MW to operate, but it will produce 1000MW. So it more than makes up for the energy it consumes. In fact, the only reason energy is required, is to operate all of the control systems to avoid having the reactor overheat and destroy itself.
You don’t actually need to put any energy in to start a fission reaction, you just need room temperature water and enriched uranium. Or otherwise, room temperature heavy water and natural uranium. In fact, there used to be natural fission reactors in Africa (I don’t remember exactly where), back when natural uranium was actually more like modern enriched uranium.

First off … it’s not a chemical reaction that generates the energy. It’s a nuclear one, hence nuclear reactor 🙂
Chemical reactions involve electrons rather than the nucleus.

We get more energy output than input for sure!
Otherwise, we wouldn’t use nuclear power-plants.

Initially, the cost of production on operation will be immensely high. But in the long-run, this is over-weighed by the efficiency of the nuclear energy.

Just look at Einsteins equation: E = mcВІ
A tiny mass will produce a huge amount of energy.
The fuel rods used in reactors are pretty big, so there’s going to be a lot of nuclides in there! Each one yielding the potential to release a decent amount of energy!
Combining all of these energies released, it’s pretty impressive 🙂

Putting 10J of energy into something and getting 3J out is obviously a losing proposition. Fortunately, you are incorrect in your understanding. A fission reactor produces a lot more energy than it consumes. The only energy needed is for the control mechanisms, since fission pretty much works on its own. Fusion, because it is very difficult to control, has not yet reached the break-even point. But it should be possible at some point to turn the corner on that–maybe in the next few years.

There’s no &quot:standard nuclear reactor&quot:, but if we take a 1 GW nuclear plant, it can generate about 8 terawatt-hours/year. A 200 watt solar panel can generate about 1 kilowatt- hour/day, or 365 kwh/year, so that’s about 21 million 200 watt solar panels. However, the power output from the nuclear plant is controllable by the operators, where solar panels only operate at full output for a few hours/day (on clear days – less if there’s cloud). Therefore, to compare the two, you have to factor in some kind of energy storage or backup which will increase the cost of the solar installation (perhaps by a factor of two or more). Despite claims of solar being cheaper than coal now, when one compares apples to apples (i. e. total energy produced, and controllability) solar is still several times more expensive than coal, and about twice as expensive as nuclear even in the U. S. A gram of U-235 can make usable energy equal to three metric tons of coal. Solar energy production has no hazardous by-products, but manufacture of the panels can involve some very hazardous materials like fluorine (for silicon panels) or cadmium (for CdTe panels). This is part of the reason panel manufacture has gone to Asia – they have fewer environmental regulations and it’s easier to dispose of the byproducts of production. DK

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