Fusion is a nuclear reaction in which two or more atomic nuclei collide at a very high speed and join to form a new type of atomic nucleus. It produces a lot more energy than the fission process because in this process when two nuclei collide, not all of the mass is converted to mass of the resultant atom but some of it is converted to photons of energy.
Two important points should always be kept in mind when studying nuclear fusion:
- If the two atoms which have masses lower than iron(Fe) are combined together, then energy is released.
- If the two atoms which have masses greater than iron are combined together, then energy is absorbed.
Fusion occurs in the sun and stars. It is applied to nuclear weapons like the Tsar bomb, Manhattan project. It can only occur at a very high temperature and give an unlimited power if uncontrolled. It increases temperature to millions of degrees and produces radiation.
In a hydrogen bomb the combination of deuterium and tritium form the basis for hydrogen bond and gives out energy. It fuels this process:
2H + 3H à 4He2 + 1n + 17.6MeV
Fusion reaction cannot be controlled, it is though limited by the amount of fuel that it has.
A necessary part of a fusion creation is plasma which is a mixture of atomic nuclei and electron which is required to initiate a self sustaining reaction. It needs a temperature of 40* 106K.
Why so high temperature?
To overcome the proton to proton repulsion in hydrogen, the high heat increases the speed of the hydrogen so that the repulsion is overcome when atoms are close enough because of high speed.
Incidents related to nuclear power and weapon harnessing:-
- · Chernobyl RMBK disaster 1986. It caused a lot of political opposition to the nuclear power.
- · 2011 japan’s nuclear power plant incident.
According to Benjamin Sovacol, 99 incidents have occurred in nuclear areas. 56 of them were in USA like;
- · Three Mile Island( 1979 ).
Nuclear powered submarine mishaps like:-
- · K-19 reactor incident( 1961 ).
- · K-27 reactor accidents( 1968 ).
- · K-431 reactor accidents( 1985 ).
Average binding energy per nucleon
It is binding energy per nucleon of a nucleus.
- The average binding energy per nucleon is 8 MeV.
- The maximum binding energy per nucleon occurs around mass number 50 and corresponds to most stable nuclei.
- Iron is a very stable and it has an average binding energy of 8.8 MeV.
- Nuclei with very low or higher mass number have an unstable or lesser nuclear binding energy.
- Nuclei with a very low mass number can do fusion and become final products with higher binding energy.
- Nuclei with very high mass number can fission to form products. The daughter nuclei has higher and stable energy.
Fusion energy resources:-
In order to start a fusion reaction 200-1000 tons of lithium and 1GW of electricity power is stored on site. Only a small amount of this is used.
Total amount in world is 90000 tons and is an important part of ocean too as 0.17 ppm.
Tritium is produced in nuclear reactor by neutron activation of Lithium 6. It is possible with neutron of any energy and is an exothermic reaction which yields 4.8 MeV of energy.
Li + n à He + T + 4.85MeV.
A lot of neutrons are needed for progressing a fusion reaction. It is because tritium is needed so that it can fuse with deuterium to form helium and neutron and immense energy. A tritium breeding reaction may be lost due to several reasons in a reaction for example it can be absorbed in a reactor. Hence to keep their presence afloat and for their production, Be 9 is needed which produces by;
N + Be-9 à 2n + 2He
It can also be lost in tritium breeding:-
Li + n à He + H + 4.8MeV
An alternate to Be-9 in nuclear reaction multiplicative can be also a fission reactions. It can produce more energy per a fusion reaction. But though it has its disadvantages. Its net safety overall because of radioactive fission products and radiations is decreased.
Fusion Energy Wastes
If the right material is used in a fusion reactor then very little radioactive material is produces as compared to the fission process. The half life of the radioactive wastes produced is very little as compared to the fission process wastes. It can be kept in a radioactive inventory and after 50-100 years its harmful potency is reduced to that of coal ash while fission process materials have a half life of thousands of years.
In a fusion reaction, the design is just limited to choosing the right materials to use to produce lesser radioactive wastes and the reactor materials which can’t get easily radioactive for example, Vanadium which can be used in making a reactor.
Fusion Energy Benefits
- Fusion energy provide much more energy per unit mass as compared to other energy technologies. Its main fuel deuterium exists abundantly in nature like in oceans and can’t easily get scarce like the fossil fuels. It is present in oceans as 1 in 6500 hydrogen atoms. Fusion process can provide power for earth for millions of years.
- Its radioactive waste is very less and the wastes half life is very little.
- Though it is a non-renewable energy source but it can be used in long term and it can not make any green house gases.
- It has a very dense and high power generation and can produce an uninterrupted power irrespective of weather and climate.
- Fusion power can be used in interstellar spaces where solar energy is not accessible.
- Often the prices of energy rises with different locations with different locations where there are resources because of high cost of plant installation, maintenance and etc. While in fusion energy, these costs are not that high because the sites of the plant are not resources.
Fusion type weapons
Fusions weapons are generally referred to as thermonuclear weapons or hydrogen bombs. These weapons usually need a fission weapons to start.
UK, USA, France, China and India have done thermonuclear tests. The thermonuclear weapons are much more difficult to produce than fission processes. The thermonuclear weapons use fission reactions to heat fusion fuel. According to Teller-Ulam design, this is done by keeping both the fission and fusion bomb in a small special container. When the fission bomb detonates and emits radiation which triggers the fusion fuel by creating large quantity of neutrons. This process is carried out in stages:
- Fission( Primary Stage )
- Fusion( Secondary Stage )
Most thermonuclear weapons nowadays use 2-stage designs but multi-stage designs are also possible in which one fusion stage triggers the next stage’s fuel. The example is TSAR bomb of Russia. Its destructive capacity in terms of TNT is 50 million TNT. Whatever radioactive product is produced is because of the fission stage which this bomb has.
Fusion Process Economics
For the fusion process to occur the atoms must be confined in a magnetic field and extremely high temperatures of 100 million kelvin is needed to start this reaction. It needs a lot of electricity and cost. Fusion power is still in early and development stages and billions of dollars have been spent in its research. In Europe, 10 billion euro have been spent till 1990’s and in International Thermonuclear Experimental Reactor( ITER ) 10 billion euro have been spent.
In 2002, a report said that R&D will need 60-70 billion euro for over a period of 50 years to continue and implement this research for power generation.
The temperature of fusion energy is so much, according to an estimate that 750 million euro is given per year for its research while all other energy related projects get only 810 million euro