Nuclear Reactors

No. The sun produces energy by fusion. It is joining hydrogen atoms into larger helium atoms, which releases energy.

Man-made nuclear reactors produce energy by fission. They break large atoms into smaller atoms, which also releases energy.

An artificial nuclear reactor is a device that initiates and controls a sustained nuclear chain reaction. This reaction produces heat, which is used to produce electricity in nuclear power plants. The fission process in these reactors generates energy by splitting atomic nuclei.

Nuclear reactors can be as small as a single room. There are many reactors that are less then 30 MW (a typical reactor is around 1,000 MW), and consider that a normal car engine is about 200 KW (or .2 MW) so some reactors produce the power of only about 100 cars.

The smallest that are standardly used, other then for research, are found on submarines.

The radiation from a properly functioning nuclear power reactor is heavily shielded and cannot be approached close enough to be fatal.

Radiation from damaged or malfunctioning nuclear power plants can be, and has been, fatal. The nuclear reactor incident at Chernobyl is one example. Nuclear reactor failures aboard ships and submarines also prove fatal but are often hidden behind national security; submarine K-19 'the widowmaker' was one such example.

And of course, if one were to get into the reactor room past all of the shielding, any reactor would be fatal.

A nuclear reactor requires the neutrons released from one reaction to trigger the fission of other nuclei. Control rods are required to absorb some of these neutrons so as to prevent a runaway chain reaction.

The control rods absorb the nuetrons which keeps the reaction rate relatively constant (rather than letting it grow exponentially). They create a situation where roughly one neutron per fission goes on to split another atom.

Moderators slow down the neutrons. Fast neutrons are more inclined to bounce/deflect off of the surface of a nucleus so slower neutrons actually lead to a greater number of succesful fissions i.e. moderators don't slow the reaction down, they just help it to take place.

This is going to be a big number! Each fission releases 200 MeV, and 1 MeV = 1.6 X 10-13 Joules, so 1 fission = 3.2 x 10-11 Joules. Now if the thermal power produced by the reactor is 3000 MW (corresponding to an electrical output of 1000 MW) this means 3000 x 106 Joules per second, or 3 x 109 Joules /sec. So the number of fissions/sec in the reactor is 3 x 109 divided by 3.2 x 10-11 , so if we call 3/3.2 = unity, for simplicity, the number of fissions per second is 1020. I said it would be big!

Reactor physicists use a number called the neutron flux to describe the intensity of the nuclear fission process, this is the number of neutrons crossing an area of 1 sq cm per second. This number helps to define the fuel rating and effects on reactor components in the active core. Obviously the total number of fissions occurring in the reactor overall per second depends on this and the size of the reactor.

Hafnium is used in nuclear reactors as a control rod material to regulate the nuclear fission process. It has a high neutron-capture cross-section, meaning it is effective in absorbing neutrons and controlling the rate of the nuclear reaction. The addition of hafnium control rods helps maintain the reactor at a safe and stable operating condition.

The number of control rods in a nuclear reactor can vary depending on the design and size of the reactor. Typically, a nuclear reactor can have anywhere from 50 to 100 control rods. These rods are used to control the rate of the nuclear reaction by absorbing neutrons and regulating the power output of the reactor.

No, the function of the control rods is to absorb surplus neutrons so that the chain reaction proceeds at a steady rate, and to compensate for the reducing reactivity of the reactor as the fuel is burned up over the refuelling cycle. They also have a very important safety function in shutting down the reactor fully when required, by inserting them fully, thus preventing any chain reaction from starting.

We usually find that uranium is used as fuel in nuclear reactors (though some use plutonium).

No, all the uranium on earth was produced in supernova explosions that occurred more than 6 billion years ago, there is no more arriving on earth (except small amounts in meteors and they got their uranium from the same supernovas as did earth). Without building reactors that burn plutonium if we use up all the uranium-235 it will become impossible to build a nuclear fission reactor (nuclear fusion reactors might become possible someday, but not yet).

1. U-235 fissions into Ba-141 and Kr-92, along with three neutrons: U-235 + 0n1 -> Ba-141 + Kr-92 + 3*0n1.

2. U-235 fissions into Xe-144 and Sr-90, along with three neutrons: U-235 + 0n1 -> Xe-144 + Sr-90 + 3*0n1.

3. U-235 fissions into Te-134 and Zr-100, along with four neutrons: U-235 + 0n1 -> Te-134 + Zr-100 + 4*0n1.

Temperature control in a nuclear reactor is crucial to prevent overheating, which can lead to a meltdown and release of radioactive materials. Maintaining the right temperature ensures the reactor operates safely and efficiently. Control systems are in place to regulate temperature by adjusting the rate of fission reactions and cooling mechanisms.

Since the continued chain reaction of a nuclear fission reactor depends upon at least one neutron from each fission being absorbed by another fissionable nucleus, the reaction can be controlled by using control rods of material which absorbs neutrons. Cadmium and boron are strong neutron absorbers and are the most common materials used in control rods. A typical neutron absorption reaction in boron is In the operation of a nuclear reactor, fuel assemblies are put into place and then the control rods are slowly lifted until a chain reaction can just be sustained. As the reaction proceeds, the number of uranium-235 nuclei decreases and fission by- products which absorb neutrons build up. To keep the chain reaction going, the control rods must be withdrawn further. At some point, the chain reaction cannot be maintained and the fuel must be replenished

To slow down the chain reaction in a nuclear reactor, you would insert the control rods. Control rods absorb neutrons and reduce the number available to sustain the chain reaction, thus slowing down the rate of fission reactions occurring in the reactor core.

The first line of shielding is to limit the neutron bombardment of the pressure vessel, to give it a safe life of 40 or more years. Then you need to protect personnel who have to go into areas close to the reactor for maintenance, and also to limit the exposure of equipment which may need maintanance done during the life of the plant

Natural uranium consists of mainly U238 with about 0.7 percent U235, which is the fissile one, so enrichment is to raise the proportion of U235, which can be done by diffusion or by centrifuging, because of the slight difference in density, using uranium hexafluoride which is gaseous.

Boron and/or Cadmium control rods. They are inserted into the core to slow the reaction and withdrawn from the core to speed up the reaction. Both elements have a very high neutron capture crosssection, the more in the core the more excess neutrons they remove from the chain reaction.

Cooling water bathes the control rods and fuel bundles of a nuclear reactor to remove excess heat generated during fission. It helps regulate the temperature within the reactor core, preventing overheating and ensuring safe operation.

Nuclear reactors do not typically use lasers as a primary component in their operation. Lasers are more commonly used in research, industry, and medical applications. Nuclear reactors rely on controlled nuclear fission reactions to generate heat for electricity production.

This depends very much on the type of reactor. PWR's operate at a high pressure in the primary circuit to prevent boiling, and the outlet water temperature is about 315 degC. In BWR's in contrast, boiling is allowed and the outlet temperature is about 285 degC.

Gas cooled reactors can operate at much higher temperatures. In the AGR for example (CO2 cooled, graphite moderated) the gas outlet temperature is designed to be about 540 degC, which allows steam to be produced at conditions the same as in a modern coal fired station, in fact at the last two built the steam turbines were exactly the same as installed in coal fired stations at that time. At these temperatures all steel components in the reactor have to be austenitic, as CO2 oxidises normal steel, and re-entrant gas flow has to be arranged to keep the graphite moderator cool, the gas inlet being at about 300degC.

Designs exist for helium cooled gas reactors which could operate even hotter and drive a gas turbine directly, without a steam circuit. These may or may not be commercially exploited.

Well, scientists have been researching fusion reactors for over 50 years, but nuclear fusion is much more difficult to achieve than nuclear fission, which is what current nuclear power technology is based on. There are many reasons for this, but while there have been tests and advancements in the field, scientists have yet to a) create a sustainable and stable nuclear fusion reaction and b) create a reaction that has a greater output than input.

This is used in the nuclear reactor that is known as Boiling Water Reactor (BWR) in which heat produced by the nuclear fission in the nuclear fuel allows the light water reactor coolant to boil. Then, the nuclear reactor moisture separator is used to increase the dryness of the produced steam before it goes to the reactor steam turbines.