Nuclear Reactors

In the PWR and BWR types it is a matrix of fuel assemblies stabilised with zircaloy fittings, and with control rods in certain specified channels within this matrix. This is where the nuclear heat is generated, and this heat is carried away by a flow of very pure water circulated by large pumps and at a high pressure.

A nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. A meltdown occurs when the heat generated by a nuclear reactor exceeds the heat removed by the cooling systems to the point which at least one nuclear fuel plate exceeds its melting point.

A meltdown occurs when a severe failure of a nuclear power plant system prevents proper cooling of the reactor core, to the extent that the nuclear fuel assemblies overheat and melt. A meltdown is considered very serious because of the potential that radioactive materials could be released into the environment. A core meltdown will also render the reactor unstable until it is repaired. The scrapping and disposal of the reactor core will incur substantial costs for the operator.

If a nuclear reactor were to "blow up" or experience a core meltdown, it could release radioactive materials into the environment, leading to widespread contamination and health risks for nearby populations. This could result in long-term environmental damage and require costly cleanup efforts. Emergency response measures, such as evacuations and containment strategies, would need to be implemented to minimize the impact.

Pulling the control rods from a nuclear reactor will start it up. Taking them out will cause the reactor to run far too hot and the coolant system will not be able to cool it sufficiently. This may easily result in a meltdown. There are a number of systems that would automatically shut the reactor down if the rods are pulled too far out, by the way.

1.7% of Pakistan electricity is produced by nuclear power stations

Electricity is made at a nuclear power station by creating a controlled nuclear chain reaction, fission, in the reactor core. This fission process generates heat, lots of it, due to the release of binding energy corresponding to the loss of mass in the core. A coolant, usually water, keeps the temperature from reaching excessive levels. In the BWR (Boiling Water Reactor) that coolant flashes to steam. In the PWR (Pressurized Water Reactor) that coolant heats other coolant which flashes to steam. The steam spins a turbine / generator which makes electricity. The steam, which has now been condensed back to water by the turbine and condensor is reheated and fed back to the core (BWR) or steam generators (PWR) to repeat the cycle.

The purpose of a nuclear reactor is to create and sustain a fission chain reaction in order to produce heat to make steam to drive turbines and produce electrical power (extremely simplified explanation).

A fission chain reaction is the interaction of neutrons with fissile materials (elements that can be fissioned, and that go on to produce more neutrons). Some enriched fuel (such as uranium-235) is introduced into the reactor core. It produces neutrons as radiation. If more fissile material is present, that interaction repeats to make more neutrons, and so on. A nuclear reactor is designed to sustain a fission chain reaction and control the rate at which that reaction occurs.

First you have to build the right sort of reactor. You don't use large power reactors like PWR or BWR, because they have very thick pressure vessels operating at high pressure and introducing the sample material would be too difficult. Instead you have a small open pool reactor which is just an assembly of fuel plates in a pool of water, not pressurised, the small amount of heat produced is rejected to atmosphere. There will be built in re-entrant tubes which go into the heart of the reactor and enable material samples to be introduced, left for a while to be irradiated, and withdrawn. So then it's just a matter of choosing the material you want to activate, preparing the sample in the right form, inserting it and removing it into a shielded container.

Thankfully there haven't been many nuclear accidents, however when they do happen they can be severe the worst nuclear accident/disaster was the explosion of reactor No.4 at the Chernobyl Nuclear power plant in 1986 on April the 26th.

The Three Mile Island accident in 1979 was caused by a combination of mechanical failures, design issues, and human errors. A stuck valve prevented coolant from cooling the reactor, leading to a partial meltdown and release of radioactive gas. Confusion and miscommunication among the operators also played a role in the escalation of the incident.

The chain reaction in a nuclear reactor is controlled by inserting control rods made of materials like boron or cadmium into the reactor core. These control rods absorb neutrons and help regulate the rate of the chain reaction by adjusting the number of neutrons available for fission. Moving the control rods in or out of the core allows operators to control the power level and ultimately, the reaction itself.

• the coolant is contaminated with fission products
• if the coolant is water and the fuel pellets are canned in zirconium a chemical reaction may occur that could generate large amounts of hydrogen gas
• if enough core is exposed without coolant, the molten core material could melt through the reaction vessel and eventually the floor of the containment building (this is very unlikely unless there was a severe loss of coolant accident and the emergency coolant system was disabled)

The most common coolant used in nuclear reactors is water, in either liquid or steam form. Water provides effective heat transfer properties and is readily available and cost-effective. Other coolants, such as liquid sodium or gas, are used in specialized reactors but water-cooled reactors are the most prevalent.

Fuel rods in nuclear plants are typically made of zirconium alloy tubes filled with uranium dioxide pellets. The zirconium alloy provides structural support and heat transfer capabilities, while the uranium dioxide serves as the fuel source for the nuclear reaction.

The use of nuclear reactors to generate electricity involves the controlled fission of uranium atoms to produce heat, which is then used to generate steam and turn turbines to produce electricity. This process is highly efficient and produces large amounts of energy without significant greenhouse gas emissions, but it also poses challenges in terms of nuclear waste management and safety concerns.

Water is used as coolant in most reactor plants to keep the reactor cool and prevent over heating. They do not necessarily need to be near a source of water; water just has to be available. However, a lot of nuclear reactors are build by a natural source of water so that the water can be used as an emergency source of coolant to keep the reactor covered with water in case of a rupture.

When B-10 absorbs a neutron, as you say it emits an alpha particle. This contains two protons so the other result is the element with two fewer protons than boron, which is lithium. So the process is starting with B-10 with 5 protons and 5 neutrons, add 1 neutron, then split into alpha which has two protons and two neutrons, and lithium which has three protons and four neutrons. The control rods have to contain enough boron to last the life of the reactor, unless they are to be replaced, which I don't think is needed. In the AGR gas cooled reactors the rods are made of boron steel alloy, in the light water reactors they are boron carbide.

Heat is formed through the transfer of energy between particles within a substance. This energy transfer causes the particles to move faster, resulting in an increase in temperature. Heat can be generated through various processes such as combustion, friction, and nuclear reactions.

Fissile materials are used in conventional nuclear reactors, usually 235U or 239Pu. In either case other materials are prevalent; for example the 235U is often only 4% or 5% of the uranium present, the remainder being 238U.

The fuel in conventional reactors comes in many forms, as metals and metal alloys, or as compounds. The Related Links area below contains a link to a Wikipedia article on Nuclear Fuel.

The power output of a nuclear reactor can vary widely, depending on the design and size of the reactor. Commercial nuclear power reactors typically have power outputs ranging from 500 megawatts (MW) to over 1,500 MW.

For the PWR, the reactor core which is an array of fuel assemblies, inside a very strong pressure vessel made of thick steel. The top of the vessel is removable for fuelling, and also holds the control rods and their mechanisms. The whole thing is enclosed in a secondary containment. Also inside this is the primary circuit which circulates water through the core to carry away the heat produced by the fuel assemblies, and the secondary circuit steam raising units which send steam to the turbine. See link below

1. Dhruva reactor:

http://en.wikipedia.org/wiki/Dhruva_reactor

This reactor is a larger version of CIRUS and can produce up to 25 KG of plutonium per year. No statement has been made about shutting down this reactor, presumably India feels it is not obliged to because unlike CIRUS it was designed and built using Indian resources.

2. CIRUS reactor http://en.wikipedia.org/wiki/CIRUS_reactor. The CIRUS design is based on Canada's Chalk River reactor and was built with Canadian help. India has announced that this reactor will be shutdown in 2010 in accordance with the terms of the recent US-India nuclear deal. CIRUS can produce up to 10 kg of plutonium in a year.

3. KAMINI reactor http://en.wikipedia.org/wiki/KAMINI 4. APSARA reactor http://www.barc.ernet.in/webpages/about/mile.htm

There are two main types of nuclear reactions: fission and fusion. Fission is the process where a heavy nucleus splits into two or more lighter nuclei, releasing a large amount of energy. Fusion is the process where two light nuclei combine to form a heavier nucleus, also releasing large amounts of energy.