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
   

The need for better information on Nuclear Energy towards the public.

In general, it seems the people increasingly supportive of nuclear when they feel better informed. Survey in Europe country shows that a quarter feel "completely uninformed" about them and a further half feel  "not very well informed". As seen above, the feeling of being informed is linked to whether or not a country has nuclear power plants....

The mass media are peoples main source of information, with 87% getting their information from television, 44% from radio and 37% from local or regional newspaper. Only a few think that media provide sufficient information to form an opinion on nuclear issues. But then who is trusted to provide information on nuclear safety?, the table below provide some insight towards the issue (From Safety and Energy Technologies polls).....

Although the mass media are the most used sources to gather news, in the case of nuclear safety people tend not to trust journalist as much as more specialized sources of information such as scientist or environmental organisations. National Goverments are trusted by less than 1/3 of the people. lol! =P...

 The public primarily trust scientist and NGOs on nuclear matters. Trust in national governments on these issues is low, presenting a clear problem for how governments can successfully communicate with their public. If Malaysia plan to build Nuclear Power Plant in the future, 60% nationwide must in favor of using nuclear energy.

This will give a rough idea on how to win people support for government plant on building nuclear power plant, that is by providing information on these matter by trusted source.



Lets see what you think about Nuclear energy =)

Who Are We

GROUP PROJECT

INTRODUCTION TO NUCLEAR TECHNOLOGY (MEHB513)

GROUP NAME

“ Nuke4iNfernO ”

GROUP LOGO

GROUP MEMBERS :

Name           : Mohd Saiful Adli B Mohd Sidek

Student ID   : ME078347

Course         : Mechanical  Engineering

Email           : mr_dely@yahoo.com

Birthday      : 31 August 1987

Hometown  : Teluk Intan, Perak

H/P number : 017-5699082

__________________________________________________________

Name           : Mohd Hazran B. Abu Hassan Fikri

Student ID   : EP078741

Course         : Electrical Power Engineering

Email           : hazran_engine2010@yahoo.com

Birthday       : 18 February 1987

Hometown  : Baling, Kedah

H/P number : 017-3995131

_______________________________________________________

Name           : Mohd Fikri B. Nazir

Student ID   : ME078275

Course         : Mechanical  Engineering

Email           : fikri_9786@yahoo.com

Birthday      : 07 September 1986

Hometown  :  Kota Sarang Semut Kedah

H/P number : 017-5555613

_________________________________________________________

Name           : Wira Karya B. Mohd Ariffin

Student ID   : ME078561

Course         : Mechanical  Engineering

Email           : wira_karya87@yahoo.com

Birthday      : 08 February 1987

Hometown  : Petaling Jaya, Selangor

H/P number : 017-2722881

____________________________________________________________