Nuclear Waste Management

              This has been a debut of most people around the world for quite some time now. This is one of the main concerns of people who are anti nuclear around the world and even if Malaysia is about to introduce nuclear power plant in the country, this would be the main issue discussed.
          
              To contain the nuclear waste, the final disposal facility should be located several hundred meters underground. It was found that rocks and sands in the earth's crust would be able to block most of the radiations from coming out of the nuclear waste facility. Scientist have found a natural nuclear reactor that had reactivity and also highly radioactive waste product which stayed put without the elaborate containment we use today on nuclear power plant waste." More than a billion years later, everything is contained within a few meters of its source." (quoted from http://geology.about.com/od/geophysics/a/aaoklo.htm).
            

Fig 1: Underground waste management facility

             The modern waste management facility would look like this. With the disposal canister and all the protection in it, leakage of radiation is impossible but still scientist and engineers have designed the canisters for the worst conditions.The canister itself would look like this. With all the impact absorbers and all the layers of protection it is expected not to leak any radiation.

Fig 2:Disposal Canister

                           For those who are wondering that the radiation is not leaking but it is actually harming the environment by the leakage of the radioactive waste, the solution for it has already been done. It was found that if the radioactive waste is mixed with glass the waste would become immobilized. Which means it would not leak into the environment.

Type Of Reactors And Options

The impotent part of a nuclear power plant is the reactor itself. This is because the fission process takes place in the reactor. There are many different types of reactors which uses many different types of technology's to ensure the fission process is in its optimum performance and it is safe enough to contain the radiation of the fission products. The reactor technology has been improved drastically since the 1950's. These improvement is categorized into few categories according to the year the reactor generation is introduced. From the year 1950 - 1965   were the Generation I reactors (early prototypes), 1965 - 1995 Generation II reactors (commercial reactors used in most of the current nuclear power plant), 1995 -2010 Generation III (Evolutionary reactors), 2010 - 2030 (Evolutionary III+ reactors) and finally 2030 onward there is the Generation IV reactors which can produce hydrogen as the its by product.

In the Nuclear reactors which are available today are categorized in to almost 4 major types of  reactors. Which are; the most comment reactor the Pressurized Water Reactor (PWR). Next is the Advanced Boiling Water Reactor.(ABWR). Other than that there is the Advance Gas Cooled reactor (AGR). Then finally we have the Presurized Heavy Water Reactor or simply the CANDU Reactor.

The table below show the types of Generation III reactors available in the market currently and their details.

Review For Test From SAS (tips)

On the 5th of October we were given some review class for the upcoming test on the 11th. Some tips were also given. I'm listing them down for the reference of students in nuclear class. The tips are as below:


1. Remember the definition of k and ρ and the condition for criticality. ( i.e. k>0, ρ<0)
2. Example from extra handouts 9 is important, example foe case 1 is very important.
3. What is positive reactivity, negative reactivity.
4. Calculation for ξ when A>10 or A<10 .
5. Neutron life cycle calculation.
6. Definition of reactivity.
7. Remember formula for pcm (unit of reactivity)
8. 4 most important coefficients of reactivity.
9. Explanation on the graph for moderator region.
10. Fuel temperature coefficient (from slide number 66)
11.3 purposes of control rod (CR), SCRAM 
12. Sketching of flux graph after insertion of CR
13. Definition of integral CR worth .
14. Burnable, non-burnable , soluble poison.


For question 2:
1. 3 forces acting on nucleus
2. Difference between them
3. Definition of isotopes ( iso=same, topes=proton)
4. Uranium isotopes & their abundance
5. Definition of mass defect & binding energy. (E=mc²)
6. How to derive 1amu = 931.5 Mev
7. 3 modes of radioactive decay.
8. Difference between radioactivity & radiation.
9. Definition of half life.
10. Secular equilibrium
11. Elastic & inelastic equation
12. Function of delay neutron (able to control the power) 

The Role of Control Rods and Neutron Poison in a Reactor

In the previuos post we have talked about control rods and burnable poisons is the reactor an their role in controlling the reactivity in the core, what are actually control rods and neutron poisons and what they do in the reactor to control the reactivity.

The control rod plays a major role in the control of the reactor. The physic behind this kind of control rod unique ability is that these control rods are able to absorb free neutrons. The free neutrons in the reactor will bombard a nucleus and promote the fission activity within the nucleus and this fission produces massive amount of power; so by absorbing the free neutron which bombard the nucleus. Thus, this will automatically reduce the fission occurrence within the reactor. By controlling the control rods position in the reactor we can subsequently control the reactivity of the reactor.

The materials used to manufacture the control rods are usually are silver, indium and cadnium graphite. This is because these materials have a very high capture cross section for neutrons. This will ensure that the neutron which are captured in the control rod will not be able to create another fission process in the reactor.

In most reactor designs, as a safety measure, control rods are attached to the lifting machinery by electromagnets, rather than direct mechanical linkage. This means that automatically in the event of power failure, or if manually invoked due to failure of the lifting machinery, the control rods will fall, under gravity, fully into the pile to stop the reaction. A notable exception to this fail-safe mode of operation is the BWR which requires the hydraulical insertion of control rods in the event of an emergency shut-down, using water from a special tank that is under high nitrogen pressure. Quickly shutting down a reactor in this way is called scramming the reactor. Urban legend has it that the control rods hung above the reactor, suspended by a rope. In an emergency a person assigned to the job would take a fire axe and cut the rope, allowing the rods to fall into the reactor and stop the fission. At some point the title of the person assigned this duty was given as SCRAM, or Safety Control Rod Axe Man (although this may be abackronym). This term continues to be in use today for shutting down a reactor by dropping the control rods.

The burnable poison in the other hand, has large neutron absorption cross-section. Usually this burnable poison or the neutron poison are added into the reactor  to lower the high reactivity of the reactors initial fresh fuel load. When a reactor is initially started with a fresh fuel, the reactivity in the reactor will be very high and moderators alone is not enough to reduce and maintain the reactivity rate in the most preferable and safe stage, so therefore to cope with the high reactivity usually burnable poisons are added into the reactor and mixed with moderator for better neutron absorption. There are 3 type of neutron poison they are burnable poison, non-burnable poison and soluble poison.

 The burnable poison is used to To control large amounts of excess fuel reactivity without control rods, burnable poisons are loaded into the core. Burnable poisons are materials that have a high neutron absorption cross section that are converted into materials of relatively low absorption cross section as the result of neutron absorption. Due to the burn-up of the poison material, the negative reactivity of the burnable poison decreases over core life. Ideally, these poisons should decrease their negative reactivity at the same rate that the fuel's excess positive reactivity is depleted. Fixed burnable poisons are generally used in the form of compounds of boron or gadolinium that are shaped into separate lattice pins or plates, or introduced as additives to the fuel. Since they can usually be distributed more uniformly than control rods, these poisons are less disruptive to the core's power distribution. Fixed burnable poisons may also be discretely loaded in specific locations in the core in order to shape or control flux profiles to prevent excessive flux and power peaking near certain regions of the reactor. Current practice however is to use fixed non-burnable poisons in this service.

 The non-burnable poison on the other hand,Soluble poisons, is one that maintains a constant negative reactivity worth over the life of the core. While no neutron poison is strictly non-burnable, certain materials can be treated as non-burnable poisons under certain conditions. One example is hafnium. The removal (by absorption of neutrons) of one isotop of hafnium leads to the production of another neutron absorber, and continues through a chain of five absorbers. This absorption chain results in a long-lived burnable poison which approximates non-burnable characteristics

Finally the soluble poison is also called chemical shim, produce a spatially uniform neutron absorption when dissolved in the water coolant . The most common soluble poison in commercial pressured water reactor (PWR) is boric acid, which is often referred to as soluble boron, or simply solbor. The boric acid in the coolant decreases the thermal utilization factor, causing a decrease in reactivity. By varying the concentration of boric acid in the coolant, a process referred to as boration and dilution, the reactivity of the core can be easily varied. If the boron concentration is increased, the coolant/moderator absorbs more neutrons, adding negative reactivity. If the boron concentration is reduced (dilution), positive reactivity is added. The changing of boron concentration in a PWR is a slow process and is used primarily to compensate for fuel burnout or poison buildup. The variation in boron concentration allows control rod use to be minimized, which results in a flatter flux profile over the core than can be produced by rod insertion. The flatter flux profile occurs because there are no regions of depressed flux like those that would be produced in the vicinity of inserted control rods. This system is not in widespread use because the chemicals make the moderator temperature reactivity coefficient less negative.

What if by 2021 Malaysia doesn't get nuclear.....

What if we can’t get nuclear by 2021,what are the impacts? 

                   Electricity is an essential need for our daily usage. the use of electricity range from lighting up our bulbs to manufacturing goods. Whereby, the use of electricity in our country increases each and every year and with the amount of electricity that we are producing now, we wont be able to supply enough electricity for the whole country in years to come.


                   Therefore, if nuclear is not introduced by the year 2021, the total amount of energy production wouldn't be enough to cope with the increasing amount of demand for electricity since the fossil fuel in the country is depleting. For the country to be more developed more industries has to be introduced and for the operation of it electricity is needed. Following this, with less electricity the country wouldn't be able to develop. 


                   Besides that, buying over fossil fuel or other means of power generation from foreign countries would result in high tariff for electricity which would reflect directly on the public. Adding to it, if the country that we are getting the fossil fuel supplied from has a political dispute on our country, then the supply of fuel would be cut to none and power production would be put to halt and leaves us in total darkness and this might be the biggest "earth day" celebration in the world.


                   Next, if by 2021 nuclear is not introduced then the amount of coal fired plants would be increased and would result in the emission of more green house gases and leads to a terrible global warming and the north and south poles might melt and raise the sea water level and lead to other disasters. 


                   Therefore, to overcome all this problems and to create a greener and more developed Malaysia nuclear technology has to be adopted into the country. Nuclear reactors raise only one common question, the safety. The latest generation nuclear reactors are designed for safety, actually over designed for safety thus public don't have to worry and should agree for a nuclear reactor to be build here in Malaysia for the betterment of our generation and the future generation.

Nuclear Energy is Green Energy........

               Green energy is the term used to describe sources of energy that are considered to be environmentally friendly and non-polluting, such as geothermal,wind, solar, and hydro.Sometimes nuclear power is also considered a green energy source.Green energy sources are often considered "green" because they are perceived to lower carbon emissions and create less pollution.


               Geothermal, wind and hydro types of power generations are green but the amount of energy produced from these methods are not enough for the amount of energy demand in Malaysia and adding to it these types of energy generations are not suitable for Malaysian environmental conditions. We don't have constant high speed winds in our country to rely on wind turbines. One of our country's main source of energy is hydro but for the production of hydro energy, really big hydro dams has to be built and this requires a big land coverage and in the process of building this dam our mother nature would be harmed.


               One of the best solution for this problems are solar power generation. It has been said that a solar panel could only produce up to 3 kW/h which could be used for a household usage per day. The problem with solar power is also that it is limited whereby it is dependent on the duration of the sun available in the sky which is about 7-8 hours in Malaysia and it is mostly cloudy in Malaysia which would reduce the sun ray intensity and makes it not so suitable for Malaysians use. 


               So the next best thing that is available is the Nuclear Energy. Nuclear energy is a reliable energy source where the reactor wouldn't be turned off unless if there is any safety issues in the reactor. Besides that, the amount of green house emissions are greatly lesser than our conventional methods of power generation. The natural gas accounts to 60% of power generation in our nation , coal accounts for 24 % while hydro and biomass accounts for most of the remaining power generation in Malaysia.The amount of green house gas emission from these power generation method have lead to global warming. For a nuclear reactor, the carbon emission during operation is very much lower compared to our coal power plant. The capital cost for a reactor is twice the amount for the coal fired plant (http://www.upi.com/Science_News/Resource-Wars/2009/07/22/Malaysia-aims-for-nuclear-energy-by-2025/UPI-29381248299408/) .  The cost is said that it could run up to RM 20 billion according to Prof Noramly who is the chairman of Malaysian Atomic Energy Licensing Board (AELB) in  an interview the Malay Mail (http://www.mmail.com.my/content/38629-malaysia-ready-nuclear-energy-says-aelb). From the figures below we could see that the coal plant would produce more green house emission compared to the nuclear reactor. The common misconception in people around the world is that the gas from a nuclear reactor is something radioactive and dangerous to health and nature but it is just merely some steam that is released after the cooling down process in the reactor. From figure 3 we could see that the total amount of carbon emission in nuclear reactor to be very small.

Fig 2: Coal fired plant gas emission

Fig 3: Nuclear power plant emission

              

Fig 3: Carbon emission for a nuclear reactor

Why is a Nuclear Reactor Safe?

After the bombing of Hiroshima and Nagasaki; the word nuclear referred as the weapon of mass destruction; but  if the nuclear power is harvest in a proper way, we could generate mass amount of clean green energy with just small amount of fuel. The question that most of the people ask about  The most commonly asked question about a nuclear power plant is that, is it safe?  As we all know the reason for this question is that the amount of radiation from the nuclear reactor fuel can harm thousands of lives.        

                This concern is not necessary because the nuclear reactor technology is been around for almost half a decade and nuclear scientist and engineers have learned a lot so far on the safety measures of a nuclear power plant. Engineers have equip the nuclear power plants with  lasts technology which ranges from different types of field from radiation containment, reactor temperature control, back-up electricity to plane crash protection.

                If we talk about the radiation containment, the whole nuclear reactor is place inside a ceramic containment building as show in figure 1. This ceramic containment building which is usually called the dome is shield steel and concrete missile shield which could with stand missile attacks and airplane crashes in case of any attacks to nuclear power plant. Furthermore, even thought the core of the reactor melts down the containment building the capability to contain the radiation from the reactor core from spreading out.  

                The next safety features is the moderators and the control rods. Moderators in simple words are the element which slows down the neutron which starts the fission process in the fuel cell. This is important because when neutrons are in thermal (slow), this enables us to control the fission process rate or the reactivity. This way we can ensure that the reaction rate is in the safest level and produce energy in the required amount only. However the control rods in the other hand have the ability to absorb neutron and drastically reduce the reaction rate or the fission rate to minimum level. The control rod are usually used when in emergencies to reduce the fission level when the reaction rate reaches high level and produces high amount of energy. This safety features ensures any kind of reactor melt downs.

                Next is the use of backup generates which help to produce electricity to the power plant in case of any emergency and the plant had to shut down its reactor core. So even thought the plant doesn’t obtain electricity from the reactor, it will have enough electricity to engage active safety features of the power plant. As show in figure 2 the plant has 2 generators instate of one for safety reasons. If the 1^st generator is not working there is always the 2^nd generator to produce enough electricity for the plant.

                Therefore the new generation nuclear power plants are over designed for better safety and to ensure from any nuclear disaster from happening.  We can say that the current and future Nuclear Power Plant are safe and reliable in every way to keep our bulbs glowing with electricity that we need.