Controlled chain reactions can be used to generate what kind of energy?

Answer 1

The reactor fuel would overheat, melt, and fall apart.

Answer 2

The chain reaction in a nuclear reactor is controlled by the amount of energy we remove from the primary coolant. That sounds weird or off the wall, but let's look at what's going on in a pressurized water reactor and we'll see how it works. We pull control rods to start the reactor and bring it up to operating temperature. The rods control the chain reactions up to this operating temperature. But once it's hot, we control the reactor in another way. A quick review of fission is in order. In fission, an atomic nucleus absorbs a neutron, becomes unstable, and then fissions. In the fission event, neutrons are released, and they come away with a lot of energy, which you can imagine. Note that neutrons don't cause fission by "slamming into" a nucleus like a cue ball into a rack of billiard balls. Rather, the neutron is absorbed by a nucleus, as stated. But here's the thing: the faster a neutron is moving, that is, the more kinetic energy it has, the lower its chance of being captured and causing another fission. So it's the slower neutrons, the thermal neutrons, that have a higher chance of being captured and continuing the chain. So what slows neutrons down? Glad you asked, 'cause it's the moderator that slows down neutrons. The moderator in a reactor moderates neutrons, or slows the neutrons down. The moderator in a pressurized water reactor is water, and it is the hydrogen in the water that is most effective at slowing down the neutrons. Anyway, the effectiveness of the water at slowing down neutrons depends on the density of the water. The more dense the water, the better it is at slowing down neutrons. And if you guessed that the density of water is dependent on the temperature of the water, you'd be absolutely correct. So what controls the temperature of the water that is the primaty coolant? The amount of energy we take out of it. When we are operating the reactor at normal operating temperature, hot coolant leaves the reactor and goes through a heat exchanger. It then comes back "less hot" and more dense, and this makes it more effective as a moderator. But as long as we take only a minimum amount of energy from the coolant with something like, say, a steam generator, then the chain reaction in the reactor is "limited" by coolant density, which is a function of coolant temperature. Note that the reactor is still critical, but it isn't "making a lot of energy" because we're not taking much out. Let's open the steam stops and draw energy out of the steam generator and see what happens. When we are rolling turbines and causing the steam generators to "take energy" from the primary coolant, the primary coolant goes back into the reactor vessel cooler and more dense. This cooler and more dense coolant goes through the core where the fissions are occuring. The neutrons being created during the fissions are more effectively slowed down, and fewer of them escape and are lost. This means more fissions occur and more heat is generated. See the connection? More energy out of the steam generator, cooler (more dense) moderator back to the reactor, more fissions occur and more heat is produced. The amount of energy we take out of the primary coolant controls the amount of energy generated in the reactor when that reactor is operating at power.

Answer 3

A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating series of these reactions. The specific nuclear reaction may be the fission of heavy isotopes (e.g. 235U) or the fusion of light isotopes (e.g. 2H and 3H). The nuclear chain reaction releases several million times more energy per reaction than any chemical reaction.

Answer 4

The control of the chain reaction in a nuclear reaction is accomplished in a number of ways, and this will depend on the reaction being controlled. In nuclear reactors, the moderator acts to slow down neutrons that are produced in fissions. And in the very common pressurized water reactors, the nuclear chain is controlled by the density of the water, which is a function of the temperature of that water. Let's take a quick look.

A nuclear reactor (a pressurized water one) is idling at a few percent power while we roll the turbines and warm up the secondary plant. The control rods have been pulled to get us up to criticality and set up an average operating temperature in the core. The nuclear chain reaction is happening, and as these reactions release energy (and a few more neutrons), they heat the water. As the water gets hotter, it becomes less dense. The less dense water is less effective as a moderator (it doesn't slow down the neutrons quite as well), and as a result, more neutrons fail to slow down sufficiently. These neutrons, the "less slowed" ones, have a lower chance of causing another fission, and they escape. An equilibrium is established.

As the main steam stops are opened, steam rushes down the headers and the turbines begin to spin. In the steam generator, the primary coolant that has been circulating there to make the steam comes back to the reactor cooler. That's because the feed pumps are pushing more cooler water into the steam generators as steam is being drawn off. That primary coolant returning to the reactor at a lower temperature is more dense, and is a more effective moderator. More neutrons are slowed down, and more fissions occur. More power is generated, and the reactor coolant leaves the reactor hotter and less dense. A new equilibrium is reached where the averagetemperature in the primary coolant is "back to normal" and more fissions are happening. More energy drawn off (taken out of the secondary system) has caused the primary coolant to more effectively moderate the reactor. More moderation means more fissions, and more power out. The temperature differential across the reactor is wider, but the average temperature is essentially the same.

If you have been able to wade through all that, you know that the chain reaction in the reactor is controlled "automatically" by the amount of steam demand in the secondary system. The control rods are pulled to set up the initial conditions, and then the reactor core operates "by itself" to generate power. The chain is controlled by the amount of energy taken out of the secondary system.

Answer 5

Controlled nuclear fission chain reactions produce a steady stream of energy that can be harnessed, usually by the creation of steam that drives turbo-electric generators.

In a stable reaction, what we call KEffective = 1, the number of fission events is constant, which means that the production of neutrons is also constant, which also means that the average number of neutrons initiating fission events is one for one.

In order to maintain this equilibrium, the moderator and/or reactor must respond to changes in energy demand. In the light water moderated reactor, a very common design, the moderator (water) has a negative temperature coefficient, which means that when load goes up, temperature decreases and reactivity increases. Similarly, if load goes down, temperature increases and reactivity decreases. This is a self-regulating process.

Not part of the specific answer to the question, but added for completeness...

In the case of load rejection, such as an unplanned shutdown of the turbine, temperature increases high enough to actually stop the reaction. Of course, other things happen in that case as well, such as automatic insertion of the control rods, enforcing a subcritical state. Last, in the event of a depressurization event, such as a steam line break, the water will flash to steam, and you lose the moderator, causing instant shutdown of the reactor, even before the control rods are fully inserted.

On the other side of the coin, you have nuclear fusion chain reactions. We have not developed the technology to produce a controlled fusion reaction and harness its energy output at this point. Right now, the only known controlled nuclear fusion chain reaction is what is happening in the Sun.

Its a similar situation. As temperature goes up, pressure increases, and density decreases, causing a reduction in the fusion rate, and as temperature goes down, pressure decreases, and density increases, causing an increase in the fusion rate.

Also not part of the specific answer to the question, but added for comparison...

The Sun is a lot larger than any fission plant we have. To put this into perspective, a typical fission plant such as the one I worked at would consume about 6 kg of uranium per day, while producing about 2400 MW of thermal power, or about 850 MW of electrical power, all in steady state conditions.

The Sun, on the other hand, consumes about 620 million metric tons of hydrogen per second. At a helium to mass-equivalent ratio of about 0.7%, that is an equivalent mass-energy conversion rate of 4.26 million metric tons per second, producing about 384.6 yotta watts (3.846 x 1026 W).

Answer 6

It is done inside of Nuclear power reactors. Inside of the reactor's core, the nuclear chain reaction or atomic fission process is controlled by inserting neutron absorbent material rods (for eg.: boron, cobalt, hafnium, dysprosium, gadolinium, samarium, erbium, and europium, or their alloys and compounds, e.g. high-boron steel, silver-indium-cadmium alloy, boron carbide, zirconium diboride, titanium diboride, hafnium diboride, gadolinium titanate, anddysprosium titanate).

When the nuclear fuel (uranium U-235) fission process gets too fast (chain reaction), the fuel gets extremely hot & it must be controlled to avoid the nuclear explosion or nuclear fuel meltdown. This is done by inserting the neutron absorbing material rods inside the reactor's core. Once these rods are inserted, they start absorbing the excess neutrons & helps control the nuclear chain reaction.

Answer 7

Controlled chain reactions can be used to generate a large amount of thermal energy which can be further used to drive turbines in order to produce electricity.

Answer 8

Type your answer here..To control the nuclear chain reaction we use different types of coolants and modulators.