Nuclear Reactor,how its work?

Nuclear Reactor

 Just as conventional power stations generate electricity by harnessing the thermal energy released from burning fossil fuels, nuclear reactors convert the thermal energy released from nuclear fission.

Fission

When a large fissile atomic nucleus such as uranium-235 or plutonium-239 absorbs a neutron, it may undergo nuclear fission. The heavy nucleus splits into two or more lighter nuclei, releasing kinetic energy, gamma radiation and free neutrons; collectively known as fission products. A portion of these neutrons may later be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on. This is known as a nuclear chain reaction.

The reaction can be controlled by using neutron poisons, which absorb excess neutrons, and neutron moderators, which reduce the velocity of fast neutrons, thereby turning them into thermal neutrons, which are more likely to be absorbed by other nuclei. Increasing or decreasing the rate of fission has a corresponding effect on the energy output of the reactor.

Commonly used moderators include regular (light) water (75% of the world's reactors), solid graphite (20% of reactors) and heavy water (5% of reactors). Beryllium has also been used in some experimental types, and hydrocarbons have been suggested as another possibility.

Heat generation

The reactor core generates heat in a number of ways:

The kinetic energy of fission products is converted to thermal energy when these nuclei collide with nearby atoms.

Some of the gamma rays produced during fission are absorbed by the reactor, their energy being converted to heat.

Heat produced by the radioactive decay of fission products and materials that have been activated by neutron absorption. This decay heat source will remain for some time even after the reactor is shut down.

A kilogram of uranium-235 (U-235) converted via nuclear processes releases approximately three million times more energy than a kilogram of coal burned conventionally (7.2 × 1013 joules per kilogram of uranium-235 versus 2.4 × 107 joules per kilogram of coal).[3][4]

Cooling

A nuclear reactor coolant — usually water but sometimes a gas or a liquid metal or molten salt — is circulated past the reactor core to absorb the heat that it generates. The heat is carried away from the reactor and is then used to generate steam. Most reactor systems employ a cooling system that is physically separated from the water that will be boiled to produce pressurized steam for the turbines, like the pressurized water reactor. But in some reactors the water for the steam turbines is boiled directly by the reactor core, for example the boiling water reactor.

Reactivity control

Main articles: Nuclear reactor control, Passive nuclear safety, Delayed neutron, Iodine pit, SCRAM, and Decay heat. The power output of the reactor is adjusted by controlling how many neutrons are able to create more fissions. Control rods that are made of a neutron poison are used to absorb neutrons. Absorbing more neutrons in a control rod means that there are fewer neutrons available to cause fission, so pushing the control rod deeper into the reactor will reduce its power output, and extracting the control rod will increase it. At the first level of control in all nuclear reactors, a process of delayed neutron emission by a number of neutron-rich fission isotopes is an important physical process. These delayed neutrons account for about 0.65% of the total neutrons produced in fission, with the remainder (termed "prompt neutrons") released immediately upon fission. The fission products which produce delayed neutrons have half lives for their decay by neutron emission that range from milliseconds to as long as several minutes. Keeping the reactor in the zone of chain-reactivity where delayed neutrons are necessary to achieve a critical mass state, allows time for mechanical devices or human operatures to have time to control a chain reaction in "real time"; otherwise the time between achievement of criticality and nuclear meltdown as a result of an exponential power surge from the normal nuclear chain reaction, would be too short to allow for intervention.

In some reactors, the coolant also acts as a neutron moderator. A moderator increases the power of the reactor by causing the fast neutrons that are released from fission to lose energy and become thermal neutrons. Thermal neutrons are more likely than fast neutrons to cause fission, so more neutron moderation means more power output from the reactors. If the coolant is a moderator, then temperature changes can affect the density of the coolant/moderator and therefore change power output. A higher temperature coolant would be less dense, and therefore a less effective moderator.

In other reactors the coolant acts as a poison by absorbing neutrons in the same way that the control rods do. In these reactors power output can be increased by heating the coolant, which makes it a less dense poison.[citation needed] Nuclear reactors generally have automatic and manual systems to Scram the reactor in an emergency shut down. These systems insert large amounts of poison (often boron in the form of boric acid) into the reactor to shut the fission reaction down if unsafe conditions are detected or anticipated.

Most types of reactors are sensitive to a process variously known as xenon poisoning, or the iodine pit. Xenon-135 is normally produced in the fission process, and acts as a neutron absorbing "neutron poison", which acts to shut the reactor down, but can be controlled in turn within the reactor by keeping neutron and power levels high enough to destroy it as fast as it is produced. The normal fission process also produces iodine-135, which in turn decays with a half life of under seven hours, to new xenon-135. Thus, if the reactor is shut down, iodine-135 in the reactor continues to decay to xenon-135, to the point that the new xenon-135 from this source ("xenon poisoning") makes re-starting the reactor more difficult, for a day or two, than when first shut down (this temporary state is the "iodine pit.") If the reactor has sufficient extra capacity, it can still be re-started before the iodine-135 and xenon-135 decay, but as the extra xenon-135 is "burned off" by transmuting it to xenon-136 (not a neutron poison), within a few hours the reactor may become unstable as a result of such a "xenon burnoff (power) transient," and then rapidly become overheated, unless control rods are reinserted in order to replace the neutron absorption of the lost xenon-135. Failure to properly follow such a procedure, was a key step in the Chernobyl disaster.

Reactors used in nuclear marine propulsion (especially nuclear submarines) often cannot be run at continuous power around the clock in the same way that land-based power reactors are normally run, and in addition often need to have a very long core life without refueling. For this reason many designs use highly enriched uranium but incorporate burnable neutron poison directly into the fuel rods. This allows the reactor to be construced with a high excess of fissionable material, which is nevertheless made relatively more safe early in the reactor's fuel burn-cycle by the presense of the neutron-absorbing material which is later replaced by naturally prodused long-lived neutron poisons (far longer-lived than xenon-135) which gradually accumulate over the fuel load's operating life.

Nuclear Energy

Nuclear Explotions

Nuclear potential energy is the potential energy of the particles inside an atomic nucleus. The nuclear particles are bound together by the strong nuclear force. Weak nuclear forces provide the potential energy for certain kinds of radioactive decay, such as beta decay.

Nuclear particles like protons and neutrons are not destroyed in fission and fusion processes, but collections of them have less mass than if they were individually free, and this mass difference is liberated as heat and radiation in nuclear reactions (the heat and radiation have the missing mass, but it often escapes from the system, where it is not measured). The energy from the Sun is an example of this form of energy conversion. In the Sun, the process of hydrogen fusion converts about 4 million tonnes of solar matter per second into electromagnetic energy, which is radiated into space.

n-butyraldehyde

n-butyraldehyde (boiling point: 74.8oC, density: 0.8016) is made by the reaction of propylene (propene-1, CH3CH=CH2), carbon monoxide, and hydrogen (synthesis gas) at 130 to 175oC and 3675 psi (25.3 MPa) over a rhodium carbonyl, cobalt carbonyl, or ruthenium carbonyl catalyst (Fig. 1).

CH3CH=CH2 + CO + H2 → CH3CH2CH2CH=O

The reaction is referred to as the oxo process, and a second product of the reaction is iso-butyraldehyde (boiling point: 64.1oC, density: 0.7891).

CH3CH=CH2 + CO + H2 → CH3CH(CH3)CH=O

The ratio of the normal to the iso product is approximately 4:1. Other catalysts produce different normal-to-iso product ratios under different conditions. For example, a rhodium catalyst can be used at lower temperatures and pressures and gives a normal-to-iso product ratio of approximately 16:1.

Butyraldehyde is used for the production of n-butyl alcohol.

CH3CH2CH2CH=O + H2 → CH3CH2CH2CH2OH

t-Butyl alcohol

t-Butyl alcohol (melting point: 25.8oC, boiling point: 82.4oC, density: 0.7866, flash point: 11.1oC) is a low-melting solid that, after melting,exists as a colorless liquid. t-Butyl alcohol is produced by the hydration of iso-butene. The favored tertiary carbocation intermediate limits the possible alcohols produced to only this one.

(CH3)2C=CH2 → (CH3)3COH

Anion exchanger resin

Ion exchange resins can be used in the separation method or concentration by using redemption equality. Ion exchange resin is an organic high polymer containing ionic functional group, resin, there is generally a polymer granules with various sizes. These pellets are placed in a glass tube long enough to produce the ion exchange column in which ions will happen leveling process.

resin manufacture is a way to enter that in the ionisation cluster into the organic polymer matrix, the most common is polystyrene which acts as adsorbent.


solution through a column called influent, while the solution is out of the column is called effluent. The process is the exchange resin absorption and returns that have been used to shape called regeneration. While spending the ions from the column with the appropriate reagent called elusi. total exchange capacity is the number of cluster-cluster that can be exchanged within the column is expressed in milleknalen, breakthrough capacity is defined as the number of ions that can be taken by the column on the separation conditions.

Elusi analysis has many benefits, for example all the ions are separated leaving the column as factions separate. Elusi process consists of two, the first is the fraction with some eluen and the second is still mengelusi active ions.

anionik resin is a substance that can replace menukaratau anions existing in the surrounding medium. Resin-resin (synthetic) can be derived from solid polymers that bind tightly in a cross with a large molecular weight can come from certain organic substances such as phenol and sterina associated with a particular group can be ionized and alkaline, such as amine or phenol groups or kuartener aluminum is added to the resin polifeniletana stable.

The basic principle is the anion exchange resin can trade for other anion anion hidroksiloleh happened to the ion exchange resin. There are two types of anion exchange resin having strongly basic groups (kuartener ammonium groups) and the resin which has a weak base group (cluster anions).

Surface of a strong base can be used over a pH range of 0 to 12, while the weak base resin exchanger only above a pH range of 0 to 9. Weak base exchanger groups will not let go of a very weak acid, but is preferred for strong acids that may be restrained by a strong base resin like sulfanol.

Ion exchange process is a process of competition between solut ions contained in ion phase with opponent cars are attached to the functional group on the matrix of opposite charge. This means that the solut ion should be able to replace one or more ions are bound by the opponent stationer phase (matrix). When we have exchange positively charged ions or cation exchanger that has bound ions in the phase opposite the car present in the solut ion ion exchange process can act.

Liquid propellants?

All the fuel that can drive called propellant rockets. Propellant is generally classified into 3 types, namely:

1. Solid propellant
2. Liquid propellant
3. Propellant hybrid

Each type of propellant on the advantages and disadvantages of each. However, for the current development, liquid propellant is more commonly used in the field of space.

Examples of liquid propellant please see here


So how rockets can fly into space?

Just like a conventional engine, a rocket of energy use arising from the oxidation reaction of fuel with the oxidant. Only the pressure of fuel in a rocket engine could reach more than 300 psi. Meanwhile, the air pressure outside the engine about 1 atm, sometimes even a vacuum.

Because there is this pressure difference results of the combustion gas velocity changes from slow to very fast. Changes in velocity than occurs because the pressure difference, as well as the results of the combustion gases flowing through the throat of diameter 4 times smaller than the diameter of the engine.

In accordance with the continuity equation, because the flow remains, while the narrower area, then the velocity changes.

Change in velocity per unit of time equal to the acceleration. After the laws of classical physics of Newton, the acceleration will result in the emergence of force (force). The force that drives this arise so that the rocket could be launched.

The Nitration of Benzene

Benzene reacts slowly with hot concentrated nitric acid in an electrophilic aromatic substitution reaction to form nitrobenzene. This reaction is potentially dangerous, however, because nitric acid is a strong oxidizing agent that often explodes in the presence of any material that readily oxidizes. A safer, faster, and more convenient synthesis employs a mixture of concentrated nitric acid and concentrated sulfuric acid. The concentrated sulfuric acid acts as a catalyst allowing nitration to take place more readily at more moderate temperatures.

The nitronium ion (⊕NO2) is the electrophile in the nitration of benzene to form nitrobenzene. Although concentrated nitric acid produces the nitronium ion by itself, the equilibrium is so far to the left that the process is slow. Adding concentrated sulfuric acid to the reaction mixture increases the concentration of the nitronium ion, thereby increasing the rate of the nitration reaction. The nitronium ion forms via a pathway similar to the first step in the dehydration of an alcohol.

After the nitronium ion forms, it reacts with benzene to form the σ complex, the first step of the electrophilic aromatic substitution reaction. This step is slow because the σ complex is not aromatic. Additionally, the σ complex is higher in energy than the benzene and the nitronium ion.

In the next step of the mechanism, the σ complex loses a proton to form nitrobenzene. This step is rapid because the loss of a proton allows the molecule to become aromatic again.

Chemists tested whether the loss of a proton is the fast step or the slow step of an electrophilic aromatic substitution by replacing the hydrogens in benzene with deuterium and then running the reaction. Deuterium (2H abbreviated as D) is an isotope of hydrogen (1H) that contains not only one proton in its nucleus but also one neutron. Thus, deuterium has twice the mass of hydrogen. Because the bond energy between a pair of atoms changes in proportion to the masses of the isotopes involved in that bond, the C—D bond is higher in energy than the C—H bond. This isotope effect is observable in the IR spectrum. The IR absorption of the C—H bond in benzene is approximately 3050 cm–1; whereas the C—D bond of deuteriobenzene is about 2150 cm–1.

Because breaking a C—D bond requires more energy than breaking a C—H bond, a reaction whose rate-determining step involves breaking a C—H bond proceeds more slowly when deuterium is present. Thus, replacing C6H6 with C6D6 results in a reduction of the nitration rate if the breaking of a C—H bond is the rate-determining step. With the electrophilic aromatic substitution reaction, chemists measured no difference in the rate of reaction between C6D6 and C6H6. This shows that the rate-determining step is the formation of the σ complex, not the step that breaks the C—H bond.