Does Malaysia Should Have Its Own NPP? You decide!

Malaysia is already ready to handle with the preparation, safety and handling the Nuclear Power Plant (NPP). A few past decades ago, in the year 1985, Malaysia has sent several engineers to Australia to conduct a training in nuclear science. From the Chairman of the Atomic Energy Licensing Board Malaysia, Prof. Emeritus Datuk Dr. Nooramly Muslim stated that 95% of the nuclear science graduates (Degree, Masters and Ph.D) were currently working in a various sector. Their skills and knowledge gained from the experience will then be hired to support national planning to have NPP. The truth is, we are not delaying to apply nuclear energy as the new resource, but government is deciding to operate NPP in the year 2021. 10 - 15 years needed to train with high level skills before we operate the NPP. As we compared to our neighbor, Bangladesh, is always known as "backward countries" is also looking for NPP as their resource even faster than us! They have a lot of professional workers that working in a developed countries and they will come back to their hometown for their own nuclear industry which is expected to be completed in 2012. At what level is Malaysia now?

Malaysia is not new into this nuclear technology. Knowingly or not, Malaysia already has its own nuclear reactor, known as Reaktor Triga Puspati (RTP), began operations since 1982! For the purpose of research and development that focuses on medical, agricultural and neutron research as conducted by Nuclear Malaysia Agency. They are more than 40 professionals (Ph.D) as the backbone to moves this agency.

Somehow, Malaysian are so scared to have NPP in the country because of WEAK knowledge and exposure about the beauty of nuclear technology. China, the most largest coals producer also already have their own NPP. Did we realized that Japan, the country that was bombed (Hiroshima & Nagasaki) by the nuclear technology itself is also generating their electric resource by using nuclear technology? It was happened for a half century ago! Do we want to still "trauma" about the tragedy? We will let you think, and choose.

Lets have a look with our 2 largest and popular dams in Malaysia; Kenyir Dam and Temenggor Dam, we are still lagging far behind. Why?

Temenggor Dam	Kenyir Dam
4 Turbines	4 Turbines
Installed Capacity : 384 MW	Installed Capacity : 400 MW
Area : 152 km²	Area : 370 km²

NPP at Ikata, Japan.

As compared to the nuclear technology, for an example, lets choose Japan's NPP located in Ikata, Japan. It have 3 reactors, each reactor can operate at minimum electric capacity 566 MW and maximum capacity is 890 MW. Can you imagine how when all of these 3 reactors operates at one time? Maximum electric capacity can be generated is more than 2000 MW in one location only. Is it amazing? Yes, it is brilliantly amazing. Furthermore, this NPP in Ikata just took 18 km² which is only the same size with Bukit Bintang! Compared to our Temenggor and Kenyir Dam, forests as our national treasures have to be explored to build the dams.

Yes, in 2012 we are expected to see Bakun Dam to be operate, located in Sarawak. It have 8 turbines which is can generate 2400 MW electric capacity at one time. But, does we realized how much land it takes to build this "2400 MW"  dam? The answer is 695 km², which is approximately same with Singapore! Can you imagine where does all the greens gone?

Well, nuclear energy is a green technology. Its not like others greenhouse that emit CO2. Nuclear will not release its radioactive to the air as other power plant do by using coals or diesels. Hence, cost to operate this nuclear power will decrease as we not using those coals and fossil fuels. This things will give advantages to all Malaysian, when the electricity tariffs will be more cheaper, and its good to attract inventors into the country.

For the latest news, Malaysian government has stated that they are looking for 8 places to build NPP which is expected to start the construction in 2015 and will announced decisions in 2012. But the question is, where are these 8 places will be? KL? Selangor? Negeri Sembilan? Pahang? Perak? Sabah? Sarawak? We will leave it to you to discuss. (",)

Nuclear Safety

Do you think that it is safe to build NPP in our country? Around your residence area? Are you dare to face this?

Current technologies of NPP using depth in defend concept. It has about six layers to protect from radioactive. As you can see at the right hand side figure, it was designed to put nuclear reactor at high security levels.

As we looking at the Chernobyl disaster, one of the main reason why the accident occurred is because of the design of the reactor itself. It consists only two layers which are control rods and reactor vessel. Current technology is more safer to prevent from terrorists attack. Therefore, there are no points for citizen to worry about or even they live near to the NPP.

Mostly all NPP were built near to sea. The reason is the plant can use the sea water as a coolant. Do you think this NPP design is safe to the sea ecosystem? And to the fisherman? Some of the them claimed that by using this technology will affect their hauls. However, until now there is no proof about the statement. As we look the NPP in Japan, for example, their citizen enjoying their routine life without having any fear, even they are living nearby the NPP. To be remembered, the well known tragedies of Hiroshima and Nagasaki at the WW II, they are still can cope and believe that the past incident just misused of the nuclear technology.

Malaysian should take this kind of mentality. Why we are still thinking of negative feedback about the nuclear? Indeed, this technology doesn't harmful to the environment and lives.

Nuke4iNfernO Crew - Future Nuclear Engineer

Even though each of us are busy with final examinations and FYP thesis but we still able to make some space for our group photo-shoot, and we have fun doing it! (",)

From left : Kepos, Wira, Deli & Hazran

Cheers for Nuclear Technology!

NUCLEAR POWER VS COAL POWER

Hi.What we have learned so far about the nuclear energy in the class,we do not see any cons for nuclear power. Therefore I will tell you the advantage of nuclear power.Nuclear power is the cheapest ways to produce electric power. The generation cost ($/kWh) is definitely  less than the other technologies of electricity generation . We cannot do comparison between nuclear power and  hydraulic power. Everybody can build a nuclear reactor to anywhere they want. However,coal fired plant must be built close to coal mines and a dam can only be built to a very specific place at a river basin.

The cost of generation includes capital cost. The capital cost = interest paid for the load + operaton + maintance cost  + the fuel cost

 Nuclear power plants use small amount of land. The other alternatives need more land than NPP.For example,solar or wind need many times more land to generate similar power.The exhaust gases from fossile fired plants contain CO2. Currently,there is no way to get rid of CO2. This gas is main contributer of temperature increase in our life. Coal consist of sulphur and when burned, SO2 is produced. This gas causes acid rains. The cost of electricity will increase although of the sulphor can be scrubed from the coal while or after the combustion.We must remember,if the burners operate at high temperatures, like in gas turbines and diesel  engines, nitrogen oxides will be generated. This gas is causes of the ozone depletion in the atmosphere.The other info is,the ash from a fossile fired plant accumulates around the power plant as ash mountains.Ash contains toxic elements just like cadmium and radioactive elements (uranium and thorium).

Nuclear power produced very little amount of highly radioactive waste. The toxicidity of this waste dissapear with time.Nuclear enery gives energy independence to a nation.
The nation that do not dependent to foreign energy resouces have  free hand in diplomacy considering the strings attached to gas and petroleum sales in the international markets.

Nuclear Power Plant at Port Dickson ???

Hot issue!!!.MB Negeri Sembilan, Mohamad Hassan wants to build a nuclear power plant in Bukit Kepong Lake near Port Dickson beach resort a lively past, but now almost a dead city.
News about  nuclear power plant in Port Dickson has been reported by a blogger Singalautmetro. Nuclear Agency has issued a number of locations including in Negeri Sembilan and Perak have been considered for the proposed nuclear plant, confirming speculation Tasik Bukit Kepong.Tenaga Nasional Berhad has been given the responsibility to implement the project.Tasik Bukit Kepong unique because its shape is like the crater with a depth of 15 meters from its base. The area is more than 10km able to provide more than 80 hectares of land area needed for a nuclear plant.Tuanku Jaffar power plant near the lake and it has the technical facilities to support a nuclear power plant capacity of 1000MW.DS Najib is expected to announce the location of the first nuclear power plant is estimated to cost between RM6.5 billion to RM9.75 billion in 2012. Nuclear power plant construction scheduled to begin in 2015.

DO YOU ALL AGREE WITH THIS??

Why Nuclear Technology is important for future energy & environment sust...

This is our nuclear video showing a scenario of what happen in the future to Malaysia if we don't take nuclear technology seriously. The video will also explain the environmental effect and how Nuclear Power Plant works.... Hope this video will give you guys a little information about nuclear...

The nuclear power demand.

In this topic, we will debating about the electrical generated by nuclear power plant that supplying the energy daily needed. Although at present the world is fighting the challenge of energy supply, next generations worries will take into account other fundamental aspects as how to run transports and potential lack of water, which are both primary needs. Today, about 85 percent of world energy needs come from exhaustible resources, mainly fossil fuels and as a minor contributor, uranium. The oil supply covers about 34%, by far the largest share, followed by coal (24%), natural gas (21.5%), nuclear (5.5%) and renewables (15%), including traditional biomass. As we know before, one third of these sources is used for electricity production of about 16,000 Terawatt hours per every year. Considering the world energy demand, it must be seriously doubted whether increasing rates of fossil fuel supplies are to be considered sustainable. It is much more likely, that their share will strongly reduce until 2030 in favor of increasing renewable contributions. Moreover nuclear energy today avoids the emission of about 2 billion atm CO₂ annually.

Previously, in 1995, the electric utilities emissions of carbon dioxide world-wide were 32 percent lower than they would have been if nuclear energy had been used instead of fuel fossil. Let we know that the emissions of sulphur dioxide and nitrogen oxide were 35 and 31 percent lower, respectively. Globally, nuclear energy has been the most important factor in preventing carbon dioxide, sulphur dioxide and nitrogen oxide emissions related to electric power generation. As proved, handling with safety, no other industry has invested so much time and money in the safety aspect of their business than has the nuclear industry. Over half the initial capital investment of a nuclear power plant goes into the safety systems, because of these and other relevant aspects, nuclear plant are to be considered among the best solutions to meet great energetic and environmental challenges. 

In addition, hydrogen production by nuclear energy which is electrolitically, and in the future high-temperature reactors, thermo chemically will assumed as a fundamental role. This so much discussed “energy carrier” is widely seen as the main future transport fuel, especially for the world environmental burden. Since ,its combustion produces only water vapor, with no carbon dioxide or carbon monoxide emissions. In addition,lack of potable water must be seriously considered, because it is set to become a constraint on development in many world regions. In fact, at present estimated that one fifth of the world's population does not have access to potable drinking water, and that this portion will increase due to population growth relative to water resources. The worst-affected areas are the arid and semiarid regions of Asia and North Africa. Wars over access to water, not simply energy and mineral resources, are therefore to be considered conceivable.

As a reflection, where water cannot be obtained from streams and aquifers, desalination of seawater or mineralized groundwater is required. Nuclear energy can help also in this direction, through the industrial process of desalination, which it is generally cost competitive with using fossil fuels. Nuclear energy is also an excellent source of process heat for various industrial applications including synthetic and unconventional oil production and from about 2003 various proposals have been made to use nuclear power to produce steam for extraction of oil. Lastly, use of nuclear energy as a heating source is greatly challenged by the economic factor since the nuclear heating reactors have relative small size and often the lower plant load factor. However, use of very simple reactor could be a possible way to supply heat economically.

Uranium in Nature

In Periodic Table of element, Uranium is in transition element. This element is considered to be natural occurring. They can be found in nature and do not need to be created in laboratory. Some natural occurring element has very short half-life and very unstable isotope. Because of Uranium in transition element, they exist in hard rock’s form naturally .It exhibit high boiling point and likely to be hard and brittle. Uranium was discovered by Martin Heinrich Klaproth. Uranium has existed since the born of our earth. It is radioactive element. In rock’s form, Uranium can be found naturally in 3 type of isotope which is U-238(99.29%), U-234(0.005%) and U-235(0.711%).The half-life of U-238 and U-235 is about 4.47 x 10⁹ years and 7.04 x 10⁸ years respectively. Uranium 238 is the most stable isotope because it has half-life about 4.5 billion years. This number is equal to the age of the world!! That is why there is plenty of Uranium in our life today which is about 50% still have plenty time to decay. For fissionable type U-235, it has about 700 millions half-life because it is less stable. Although it is gone about 98.8%, but there is enough U-235 left available in our earth nowadays. We should note that, Uranium is more abundant than silver, zinc and tin.

Canada is the world's biggest producer of uranium with mines in Saskatchewan. This mine produces about 1/3 of the world's uranium. The other producing countries are Namibia, Kazakhstan, Argentina, Australia, Niger, and the US. In Malaysia, we do not produce Uranium, hence we need to import from above countries if we plan in future to use it in nuclear power plant.

Summary of Lecture Series

According to energy consumption map, about 38% energy resources from entire world have been used to generate electricity. This electricity comes from hydro, biomass, geothermal, wind, solar, nuclear, coal and natural gases. The other sources such as petroleum and natural gases go to industrial, commercial, residential, light-duty vehicle, freight and air craft. Nuclear only used for generating electricity which is about 8.13% from total portion of energy resources. The energy consumption in form of transportation, industry, agriculture, domestic and food the day by day is keep increasing according to The British Royal Commission on Environmental Pollution. With the increasing of demand in electricity, the minimum demand (base load) is about 10,258 MW. The latest peak demand is about 15037 MW. How do meet the base load 10,258 MW demand? This base load needs to be supplied by coal, gas and hydro.

All this conventional technologies produce the CO₂ green house gases by process of combustion. This green house gases clearly is not good for our world.  These green gases will make the effect of the earth’s surface warming because it is preventing the infrared radiation from passes through the atmosphere and lost in space. The average concentration of CO₂ today is about 388.15 parts per million (ppm). We must remember that, the breakaway emission of CO₂ is 450 ppm!! With the current population growth, in year 2025, the number of 450 ppm will be achieved. We cannot live anymore when we achieved that number. We are getting closer and closer.

 Increase in carbon concentration is related with the increase in temperature. When the temperature goes up, the temperature at North Atlantic and the Southern Ocean will also goes up. Again, we must remember that this place is the coolest place in our world. This place is the important part of thermahaline circle or The Great Conveyor Belt. What will happen if the heart of this Great Conveyor Belt is affected? We must highlight that, all the phenomenon, the climate change in this world is related with this Great Conveyor Belt. The hot wind is circulated around the world followed this conveyor path and the hot wind is cooled at the North Atlantic and Southern Ocean. We cannot let the heart of Great Conveyor Belt be effected by the rise of temperature. So we have to turn to green energy.

Recovery of uranium for non-conventional Malaysian sources

In this topic, we will learn that the security of uranium fuel supply is an important aspect for countries which that using nuclear power energy. The alternative sources of uranium are identified from the present conventional uranium mines with respect to the present of high demand for nuclear power and uranium. Futhermore, this topic will also describes about the material such as Xenotime(YPO₄) which is a yttrium phosphate mineral is a recovered by product from tin mining industry. Unlike another rare earth mineral called monazite, there is higher content of uranium in Xenotime as to that of thorium. For our knowledge, there are about 1-2% U₃O₈ found in this material and the highest compared to the other tin by product minerals.

The process that we called a “hydrometallurgy” was developed by researcher to produce uranium and yttrium oxide concentrates. This process involved alkaline fusion, acid leaching and frictional precipitation stages. The inclusion fractional precipitation stage in the process enables to separate yttrium from the uranium. Previously, the uranium contaminated organic DEHPA was sent to Malaysian Nuclear Agency for storage and disposal when the Asian Rare Earth plant in Lahat Datu, Perak was closed in year 1996. As we can know that, DEHPA was used as a solvent extraction solvent for separation of light and heavy rare earth elements. There is about 31,500 liters of this waste and EDXRF analysis show that the uranium content is 990 ppm and the total rare earth content is 25,890 ppm present in this waste.

Hence, the distribution coefficient and separation factors for these elements were determined so as to conduct an efficient stripping process. The Malaysian tin by product minerals are also known to be contaminated with radioactive elements. For our general information, the uranium content in Malaysian Zircon mineral ranges from 0.06-0.18% U₃O₈ and Malaysian ilmenite from 0.01-0.07% U₃O₈. As this radioactive elements is found to be contaminated both of the surface  as well as in the crystals, physical and chemical processes were developed to remove them.

The operation and maintenance of electron beam machines from nuclear Malaysia’s experiment.

First of all, we known that the first high energy electron beam machine (EPS3000) was installed in Nuclear Malaysia around 1991. At the beginning, it was a prototype machine that produced by Nissin High Voltage (NHV) with variable energies from 0.5 to 3.0 MeV and maximum power of 90 kWatt. The machine was initially used and operated for research purposes but later the irradiation service was opened for local industries.

Apart from the EPS3000, a smaller and self –shielded Curetron was also installed. It was having energy around 200 keV and maximum power about 0.4 kWatt. By the way, the machine is used only for surface curing or coating related research. The operation of the both machine have carried out by local technician. However, at the earlier stage, the major maintenance works were conducted by designated engineers that provided by the manufacturers.

Over time and experience gained, most of the maintenance are now being carried out by the local engineers and technician. In late 2009, a new 1 MeV, 50 kWatt manufactured by BNP of Russia was installed to complement the current  irradiation service. Lastly we can conclude, this is a different type of EB machine but in term of operational safety and maintenance, the requirements are almost similar.

Why is having a nuclear power plant in your local area is A GREAT IDEA?

Nowadays, the nuclear energy is the greenest energy in the Earth. It is greener as we compared with the other power generating plant in Malaysia. Other construction of power plant is using high amount of concrete to build the structure. As we know, concrete will release high amount of carbon dioxide in the air. For example, now we have under construction Bakun Dam located at Sungai Balui Sarawak. This dam will be the tallest concrete dam in the world and becoming one of the largest dams in Asia. The dam has about 16.71 million cubic meters of filled volume and catchment area about 14,750 km square. The gross storage capacity is 43,800 million cubic meters. Can you imagine how much concrete is required to build this dam? How much carbon dioxide will be released by the concrete? How much environmental creatures need to be sacrificed with that large amount of catchment area? Absolutely, having the nuclear power plant is A GREAT IDEA.

As we can see from TNB itself, but not from political view, TNB actually not completely produce the electricity itself. TNB also depends to the other producer such as IPP (Independent Power Plant). The IPP is owned by individual party such as Tan Sri Al-Bukhary, Vincent Tan and so forth. Because of that, TNB need to buy the electricity from them, then TNB sell to us. We can see that, the price of electricity is indirectly depends from other producer. Then Malaysian life will be affected with the rise of fuel cost and operation cost of IPP. As an alternative, the nuclear energy is more profitable than other energy production. This could help to reduce the electricity cost and the Malaysian should think about it. Absolutely, having the nuclear power plant is A GREAT IDEA

Control Rod

Hi.Today we would like to talk about control rod.As mention before,control rod is one of the main component of nuclear reactor.As we all know,the nuclear power plant can generate the tremendous power,heat and energy through the nuclear fission.However,we need to control it in predictable manner.The failure of controlling control rod will cause the incident like the Chernobyle disaster and Stationary Low-Power Reactor Number One explosion.Control rod can be made using chemical elements which can control the rate of fission of uranium.

Actually,why the nuclear reactor need to control? It is important to make sure the reaction is sustained rather than to start the chain reaction.In case of emergency situations such as a sudden mechanical or structural damage, the reactor needs to be shut down quickly in order to prevent any major disaster like Chernobyl which could be very costly in terms of loss to life and environment.Without having the nuclear reactor in control, the control rod might be melted down. 

The control rod can absorb the amount of neutron to control the nuclear fission reaction.So the material being used in control rod must having high neutron absorbing capacity. Commonly material used are cadmium, boron, iridium and hafnium. For PWR nuclear reactor,the control rod is place on top of reactor but for BWR nuclear reactor,it is place at the bottom. This is because the stim generated inside the BWR reactor will push the control rod if control rod is place on top.

Advantage of having Nuclear Energy in the future.

In the world today, many countries, especially big, heavily industrialized nations rely on nuclear power to satisfy their country’s energy needs. Such nations require huge amounts of energy to run their country. Various

consumers of energy and electricity include industries, residences, commercial establishments, military assets, governmental buildings, agriculture, transport and so on.

 Massive usage of electricity on developed country.

Especially in extremely populated countries, there are in extremely high demand. The bitter truth is, it is just not possible to fill in such a high demand with just conventional sources of energy, countries look toward unconventional sources of energy such as solar, wind and nuclear energy. The yield of solar and wind energy is not that high. Nuclear energy is the answer for sustainable electric source in the future.

The reason why nuclear energy is important for future energy consumption is

1) Nuclear reaction release tremendous amounts of energy. Nuclear energy is so immense that one nuclear plant may provide electricity for a really large area. Thus it is important to have nuclear reactor to sustain future energy demand. This will be a stepping stone for a country such as Malaysia to be recognized as a developed country.

2) Nuclear energy doesn't emit anything into the atmosphere like polluted air, smoke or anything of that sort. France, which has embraced nuclear power has some of the most cleanest air in the world. this is mostly because of the heavy use of nuclear energy and minimum dependence of coal or oil based power plants. Future energy demand will be so demanding that it will be a major concern on the environment if we keep on using fossil fuel as our main source of energy and Malaysia need to take part in preserving the global environment.

Nuclear reactor only emits steam into the air (left) while conventional reactor emits greenhouse gas into the air (right)

to be continue....

references:

1. http://www.buzzle.com/articles/advantages-and-disadvantages-of-nuclear-energy.html 
2.  http://www.planete-energies.com/content/nuclear-energy/future/advantages.html

Nuclear Power Plant

 

What is nuclear power plant (NPP)? Actually, it can be defined as an electrical generating facility using a nuclear reactor as its heat source to provide steam to a turbine generator. In our country Malaysia, there are many type of electricity-generating power station in Malaysia. The make use of hydro-power, gas-fired, coal-fired (combined gas/coal), oil fired, biomass and hybrid power are remain as the main sources to generate electricity. Our country has enough skilled labor to operate power plant. It is simple because we have experience about how to operate hydro-power, gas-fired, coal-fired and etc.The whole system of power plant including steam turbine generator also we are capable of. How about if we replace the others heat sources with nuclear reactor? The concept stills the same, the steam turbine generator still being used. The different is only the heat source. It is sound easy, but the acceptation of Malaysian about nuclear reactor need to be considered. They need to be provided with simple and true information about nuclear power plant. Nuclear reactor is a device in which nuclear fission may be sustained and controlled in self-supporting nuclear reactor. It is heart of a nuclear power plant. A fissionable material of fuel, a moderating material, a reflector to conserve escaping neutrons, provisions of removal heat, measuring and controlling instruments and protective devices are include as parts of nuclear reactor. Figure above shows the general idea how to use nuclear reactor to produce the electricity.

What are the major components of nuclear reactors? There are 5 major components of nuclear reactor as listed as below.

ª      Nuclear fuel

ª      Moderator

ª      Coolant

ª      Reactivity Control Material

ª      Structural Material

 The nuclear fuel is used to undergo nuclear fission by neutrons. It must have high thermal conductivity, irradiation, chemical stability and also excellent nuclear characteristics. The example fuel that can be used is uranium, etc. The moderator is used to reduce neutron energy by scattering without significant capture. It must have desirable characteristics to function efficiently such as large scattering cross section, small absorption cross section, large energy per collision and low atomic number. The example of moderator can be used are Deuterium, graphite and etc. For coolant, it is use to remove the fission heat from the primary heat source such as a reactor core or breeding blanket. The coolant must have excellent heat transfer, chemical stability, small pumping requirement, irradiation stability and abundance (low cost).The most natural coolant is water. The reactivity control material is needed to control the neutron flux in the core by absorbing neutrons. It can be done by using control rod. The structural material is used to maintain geometry. The structural must has high strength, ductility, corrosion resistance, small absorption cross section and high thermal and irradiation resistance. Zircaloy can be used as material.

 Picture above shows the basic components of nuclear power plant. The most common of nuclear reactor  type  that been used nowadays are Pressurize Water Reactor (PWR) and Boiling Water Reactor (BWR). The picture above shows the example of PWR nuclear reactor type.PWR and BWR and the other type of nuclear reactor that commonly used will be discussed in other post.

   
Reference
*Introduction to Nuclear Engineering  MEHB513

Three Miles Island Nuclear Disaster

In 1979 at Three Mile Island nuclear power plant in USA a cooling malfunction caused part of the core to melt in the second reactor. The TMI-2 reactor was destroyed. Some radioactive gas was released a couple of days after the accident, but not enough to cause any dose above background levels to local residents. There were no injuries or adverse health effects from the Three Mile Island accident.

The Three Mile Island power station is near Harrisburg, Pennsylvania in USA. It had two pressurized water reactors. One PWR was of 800 MWe (775 MWe net) and entered service in 1974. It remains one of the best-performing units in USA. Unit 2 was of 906 MWe (880 MWe net) and almost brand new.

**Post under construction . . .

Chernobyl Incident

 

 The Chernobyl accident was occurred in 1986. Two Chernobyl plant workers died immediately and a further 28 people died within a few weeks due to acute radiation poisoning. The peoples around the case area were relocated. The April 1986 disaster at the Chernobyl nuclear power plant in the Ukraine was the product of  a not good design reactor and the also mistake made by  reactor operator in terms of safety culture. The accident destroyed the Chernobyl 4 reactor, killing 30 operators within three months and several further deaths later. Two people were killed immediately at the site. The Chernobyl disaster was the only accident in the history of commercial nuclear power where radiation-related fatalities occurred .However, the design of the reactor is unique and the accident is thus of little relevance to the rest of the nuclear industry outside the then Eastern Bloc.

The Chernobyl incident had experienced positive (+ve) reactivity feedback effect. We need to know first what the reactivity is. Reactivity is a measure of the departure of a reactor from criticality. Actually the criticality is related to the effective multiplication factor, k_eff. Multiplication factor k_eff is the ratio of number of fission in one generation to the number of fission in preceeding generation as shown below.

In diffusion theory when k < 1, the condition of reactor is subcritical. Subcritical mean the neutron population is keep decreasing in each generation. If we have k =1, the condition of reactor is called critical. Critical means the neutron population in the reactor is neither decreasing nor increasing. It is also called self-sustaining for the neutron chain reaction. When we have k > 1, the population neutron is supercritical. We know that the neutron population is increasing to each generation. The k value is important to determine the criticality. Actually the reactivity, ρ is related with k_eff with the equation below:

 

Once we know the amount of reactivity, ρ in reactor core, the population of neutron can be determined. Hence we can predict the reactor power at any given time. We should noted that there are many factor that effect the power level in reactor such as fuel depletion, temperature of reactor, pressure of reactor and poisons. Because there are many parameters to consider, the reactivity coefficient (α_x) is introduced. Actually, the reactivity coefficient (α_x) is the amount of change in reactivity per unit change in parameter and is given by

Where Δρ = reactivity defects and Δx = change in variable parameter that effects reactivity. We can further observe the relationship of each variable in above equation. The Table 1 below shows the relationship of each variable

Δx	Δρ	αx
↑	+ve	+ve
↑	-ve	-ve

Table 1 : Relationship between each variable

 Changes in the physical properties materials in reactor will results in change of reactivity. Hence the reactivity coefficient (α_x) is very crucial in indentifying the reactivity change (Δρ) given the change in physical properties (Δx). In nuclear physics, there are four most important reacticity coefficient α_x listed below 

1)      Moderator temperature coefficient of ρ, α_Tmod                       (moderator/coolant) 
2)      Fuel temperature coefficient of ρ, α_Tfuel                                     (fuel) 
3)      Pressure coefficient of ρ, α_P                                                             (moderator/coolant) 
4)      Void coefficient of ρ, α_void                                                               (moderator/coolant)

Figure 1 : Variation of k_eff and its factors with the fuel-to-moderator ratio

Graph in Figure 1 is applicable to a large core fuelled with low-enriched fuel which is been used in nuclear industry today. We have been introduced with another ratio which is N^m/N^u ratio and also called moderator to fuel ratio. The amount of neutron will increase as we increase the amount of moderator N^m because the high amount moderator will make the leakage of neutron decreases. Then the absorption of neutron will be high and the thermal utilization factor will decrease and also resonance escape probability will increase. All of this trend can be seen in Figure 1. As we decrease the amount of moderator from the right to the left graph, the N^m/N^u ratio will decrease, then increase in slowing down time. This will increase the loss in neutrons by the resonance absorption thus increase the neutron in leakage. In practice, water-moderated reactor is designed with a N^m/N^u so that it can operated under moderated condition as shown in Figure 1. From Figure 1, when the temperature increases, the N^m/N^u decreases and because the water density becomes less, it’s creating the positive reactivity addition. The positive reactivity addition ρ will increase the effective multiplication factor and further increase the power and temperature in a dangerous cycle. This state called over moderated region. However when the same temperature increases would decreases the N^m/N^u and the density of water become decrease, the negative reactivity will be occurred. The effective multiplication factor k_eff will decrease and further decrease the power and the temperature in safe cycle. All of this can be explained in Figure 1. The Chernorbyl reactor power plan used the Boiling Water Reactor (BWR). It is uses water-moderated reactor. The disaster incident happened because there was no negative reactivity feedback effect in this reactor to lower down the reactor power as temperature. We hope that for the future, the engineer must take consideration of N^m/N^u ration in their design and put their design in under moderated region to make sure their reactor becomes more self-regulating.

References : 

1. Lecture Notes (Reactor Theory II) ; by COE, Uniten
2. http://library.thinkquest.org/3426/ 
3. http://en.wikipedia.org/wiki/Chernobyl_disaster