Frequently Asked Questions abt Nuclear Power

Frequently Asked Questions abt Nuclear Power Plants:

Why we must look into nuclear technology?

Nuclear power technology is crucial and regarded as one of the alternative energy source to replace the depleting fossil fuel (petroluem and gas) energy sources and a solution to curb global warming. Power generated from nuclear power plant releases very less precentage of global warming gases and it is GREEN. Many have seen the disasterous part of the devastation created and can be created by nuclear weapons. Hence the inertia has grown very high even a significant advantage of nuclear technology has always been an debating issue everywhere in the planet.

As for Malaysia, we depend more on power plant which uses coal, fuel oil and natural gas as they their fuel. This leads one point where soon there will shortage for this fossil fuels. Hence we have to find an alternative energy source to meet our escalating power demand.

Is nuclear power plant costly?

Yes it is. It is double the cost of building a coal powered plant. But the cost to purchase fuel for nuclear power plant is very cheap compared to coal power plant. In a year to generate 1000 megawatt(MW) energy, coal plant needs 2 Million tonnes of coal whereas a nuclear power plant needs 30 tonnes of uranium. This is where a solution to curb global warming is attained!

What happens to the radiation from nuclear power plant?

Nuclear power plants sometimes release radioactive gases and liquids into the environment under controlled, monitored conditions to ensure that they pose no danger to the public or the environment.  These releases dissipate into the atmosphere or a large water source and, therefore, are diluted to the point where it becomes difficult to measure any radioactivity. 

By contrast, most of an operating nuclear power plant's direct radiation is blocked by the plant's steel and concrete structures. The remainder dissipates in an area of controlled, uninhabited space around the plant, ensuring that it does not affect any member of the public.

Do we entitle to any form of radiation naturally?

Yes, we are. Since the beginning of time, all living creatures have been, and are still being, exposed to radiation. Nonetheless, most people are not aware of all the natural and man-made sources of radiation in our environment. Example of natural radiations are cosmic radiation, terrestrial radiation and internal radiation. Cosmic radiation are the stream of radition sent by the sun and planets from the outer space.

Terrestrial radiation are from the mother earth herself, where the presence of radioactive materials (including uranium, thorium, and radium) exist naturally in soil and rock. In addition, water contains small amounts of dissolved uranium and thorium, and all organic matter (both plant and animal) contains radioactive carbon and potassium. Some of these materials are ingested with food and water, while others (such as radon) are inhaled. The dose from terrestrial sources varies in different parts of the world, but locations with higher soil concentrations of uranium and thorium generally have higher doses.

All people have internal radiation, mainly from radioactive potassium-40 and carbon-14 inside their bodies from birth and, therefore, are sources of exposure to others. The variation in dose from one person to another is not as great as that associated with cosmic and terrestrial sources.

How to dispose radioactive wastes from nuclear power plant?

Radioactive wastes are the leftovers from the use of nuclear materials for the production of electricity, diagnosis and treatment of disease, and other purposes.
The materials are either naturally occurring or man-made. Waste products from nuclear power plant can be categorized into two main category which low-level waste  and high-level waste.

Low-level waste includes items that have become contaminated with radioactive material or have become radioactive through exposure to neutron radiation. This waste typically consists of contaminated protective shoe covers and clothing, wiping rags, mops, filters, reactor water treatment residues, equipments and tools, luminous dials, medical tubes, swabs, injection needles, syringes, and laboratory animal carcasses and tissues. The radioactivity can range from just above background levels found in nature to very highly radioactive in certain cases such as parts from inside the reactor vessel in a nuclear power plant. Low-level waste is typically stored on-site by licensees, either until it has decayed away and can be disposed of as ordinary trash, or until amounts are large enough for shipment to a low-level waste disposal site.

While high-level radioactive wastes are the highly radioactive materials produced as a byproduct of the reactions that occur inside nuclear reactors. High-level wastes take one of two forms:

1. 
   
   Spent (used) reactor fuel when it is accepted for disposal
2. 
   
   Waste materials remaining after spent fuel is reprocessed

(1.)Spent nuclear fuel is used fuel from a reactor that is no longer efficient in creating electricity, because its fission process has slowed. However, it is still thermally hot, highly radioactive, and potentially harmful. Until a permanent disposal repository for spent nuclear fuel is built, licensees must safely store this fuel at their reactors.

(2.)Reprocessing extracts isotopes from spent fuel that can be used again as reactor fuel. Because of their highly radioactive fission products, high-level waste and spent fuel must be handled and stored with care. The only way radioactive waste finally becomes harmless is through decaying process, which for high-level wastes can take hundreds of thousands of years, the wastes must be stored and finally disposed of in a way that provides adequate protection of the public for a very long time. It is possible to create such facility as the countries like US, France, Russia, Korea and Japan have created their own high level storage disposing facility. If Malaysia can build a nuclear power plant with the collobaration between country like Russia. Where as part of the deal they offer to dispose the nuclear waste produced by their client at their own disposal facility, and the issue of disposing (dumping) nuclear waste will not be a problem for Malaysia.



High-level Disposal



courtesy of Azrudi Mustapha, TNB NUCLEAR DIVISION

 

Components Inside a Nuclear Reactor

There are several components common to most types of reactors:

Fuel - Usually pellets of uranium oxide (UO₂) arranged in tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core. The core of the reactor contains all of the nuclear fuel and generates all of the heat. It contains low-enriched uranium (<5% U-235), control systems, and structural materials. The core can contain hundreds of thousands of individual fuel pins.

Moderator - This is material in the core 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 cadmium, hafnium or boron, and are inserted or withdrawn from the core to control the rate of reaction, or to halt it. In some reactors, special control rods are used to enable the core to sustain a low level of power efficiently. 

Coolant - The coolant is the material that passes through the core, transferring the heat from the fuel to a turbine. A liquid or gas circulating through the core so as to transfer the heat from it. It could be water, heavy-water, liquid sodium, helium, or something else. In light water reactors the water moderator functions also as primary coolant. Except in BWRs, there is secondary coolant circuit where the steam is made.  (see also later section on primary coolant characteristics)

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 where the primary coolant bringing heat from the reactor is used to make steam for the turbine. (not in BWR)

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 malfunction inside. It is typically a metre-thick concrete and steel structure.

The turbine transfers the heat from the coolant to electricity, just like in a fossil-fuel plant.

The containment is the structure that separates the reactor from the environment. These are usually dome-shaped, made of high-density, steel-reinforced concrete. Chernobyl did not have a containment to speak of.

Cooling towers are needed by some plants to dump the excess heat that cannot be converted to energy due to the laws of thermodynamics. These are the hyperbolic icons of nuclear energy. They emit only clean water vapor.

                     Example of Pressurized Water Reactor (PWR)

                           Example of Boiled Water Reactor (BWR)

(pics taken from NuclearRC USA )

What is a nuclear reactor?

A nuclear reactor is a system that contains and controls sustained nuclear chain reactions. Reactors are used for generating electricity, producing radionuclides (for industry and medicine), conducting research, and military purposes. A nuclear reactor produces and controls the release of energy from splitting the atoms of certain elements. In a nuclear power reactor, the energy released is used as heat to make steam to generate electricity. (In a research reactor the main purpose is to utilise the actual neutrons produced in the core. In most naval reactors, steam drives a turbine directly for propulsion.)

The principles for using nuclear power to produce electricity are the same for most types of reactor. The energy released from continuous fission of the atoms of the fuel is harnessed as heat in either a gas or water, and is used to produce steam. The steam is used to drive the turbines which produce electricity (as in most fossil fuel plants).

Courtesy of NRC USA and Mr.Shamsul Amri, TNB Nuclear Division

The Chernobyl Tragedy

Where? Ukraine
When? Chernobyl Unit 4 reactor at about 1.24 a.m. on 26 April 1986


How??

The accident at the Chernobyl nuclear power station occurred during a low-power engineering test of the Unit 4 reactor. Safety systems had been switched off, and improper, unstable operation of the reactor allowed an uncontrollable power surge to occur, resulting in successive steam explosions that severely damaged the reactor building and completely destroyed the reactor.

Actions taken during this exercise resulted in a significant variation in the temperature and flow rate of the inlet water to the reactor core (beginning at about 1.03 a.m.)

The relatively fast temperature changes resulting from the operators actions weakened the lower transition joints that link the zirconium fuel channels in the core to the steel pipes that carry the inlet cooling water

Other actions resulted in a rapid increase in the power level of the reactor, which caused fuel fragmentation and the rapid transfer of heat from these fuel fragments to the coolant (between 1.23:43 and 1.23:49 a.m.)



This generated a shock wave in the cooling water, which led to the failure of most of the lower transition joints. As a result of the failure of these transition joints, the pressurized cooling water in the primary system was released, and it immediately flashed into steam.


The steam explosion occurred at 1.23am. It is surmised that the reactor core might have been lifted up by the explosion, during which time all water left the reactor core. This resulted in an extremely rapid increase in reactivity, which led to vaporization of part of the fuel at the centre of some fuel assemblies and which was terminated by a large explosion attributable to rapid expansion of the fuel vapour disassembling the core. This explosion, which occurred at about 1.24 a.m., blew the core apart and destroyed most of the building. Fuel, core components, and structural items were blown from the reactor hall onto the roof of adjacent buildings and the ground around the reactor building. A major release of radioactive material into the environment also occurred as a result of this explosion.



The reactor:


The RBMK-1000 is a Soviet-designed and built graphite moderated pressure tube type reactor, using slightly enriched (2% U-235) uranium dioxide fuel. It is a boiling light water reactor, with two loops feeding steam directly to the turbines, without an intervening heat exchanger.

Water pumped to the bottom of the fuel channels boils as it progresses up the pressure tubes, producing steam which feeds two 500 MW turbines. The water acts as a coolant and also provides the steam used to drive the turbines. The vertical pressure tubes contain the zirconium alloy clad uranium dioxide fuel around which the cooling water flows.

The extensions of the fuel channels penetrate the lower plate and the cover plate of the core and are welded to each. A specially designed refuelling machine allows fuel bundles to be changed without shutting down the reactor.

One of the most important characteristics of the RBMK reactor is that it it can possess a 'positive void coefficient', where an increase in steam bubbles ('voids') is accompanied by an increase in core reactivity. As steam production in the fuel channels increases, the neutrons that would have been absorbed by the denser water now produce increased fission in the fuel. There are other components that contribute to the overall power coefficient of reactivity, but the void coefficient is the dominant one in RBMK reactors.

The void coefficient depends on the composition of the core – a new RBMK core will have a negative void coefficient. However, at the time of the accident at Chernobyl 4, the reactor's fuel burn-up, control rod configuration and power level led to a positive void coefficient large enough to overwhelm all other influences on the power coefficient.


Effects:

Chernobyl tragedy dramatically affected people’s life, economy, science and culture of Belarus as it both suffered from the radioactive devastation and lost historic and cultural values of the Belarusian Palesse, a distinctive natural area in the South of the country.

Economic damage of the Chernobyl accident is estimated at $235 billion for 30 years on after the
explosion, making up 32 national budgets as of1985.

Chernobyl disaster vastly damaged the agricultural sector of the Belarusian economy,which is worth over $700 million annually. Due to radioactive fallout, Belarus lost one fifth of all agricultural lands. It also led to contamination of around a quarter of the Belarusian forests, 132 deposits of mineral resources and nearly 350 industrial enterprises.

Human damage of the accident was 2 million people who suffered from its consequences, with over 1.3 million people, including almost half a million of children and adolescents, still living in the contaminated areas.

Rehabilitation of affected areas is still ongoing. Since 1986, Belarus has spent some $18 billion on this purpose. Annually, public spending of Belarus on rehabilitation totals around 5 per cent of the GDP.



Childbirth deformities Deformities among animal due to DNA mutation