Nuclear energy — boon or bane?
Manoj Roorkiwal
IN 1940s Italian born American physicist Enrico Fermi while working on Manhattan project artificially discovered nuclear energy. He designed the first atomic pile on the squash courts of the University of Chicago and produced the first nuclear chain reaction in 1942. From this historical landmark onwards man never looked back and advanced the process of producing electricity to the maximum.

Building tips
Jagvir Goyal
WHILE buying cement, ensure that it is from a freshly manufactured lot. Two-month-old cement loses up to 40 % of its strength as storage is mostly improper and moisture in the air affects it. Look for the manufacturer’s tag on the bags.

UNDERSTANDING THE UNIVERSE
WITH PROF YASH PAL
When travelling by plane from Mumbai to Delhi at about 6 p.m. on January 4 this year I observed from my left window a straight bright line of seven colours running parallel to us. The plane was at a height of about 11 kilometres. Kindly explain this observation at a time when it was quite dark outside.

Nuclear energy — boon or bane?
Manoj Roorkiwal

IN 1940s Italian born American physicist Enrico Fermi while working on Manhattan project artificially discovered nuclear energy. He designed the first atomic pile on the squash courts of the University of Chicago and produced the first nuclear chain reaction in 1942. From this historical landmark onwards man never looked back and advanced the process of producing electricity to the maximum.

Nuclear energy is energy released during a nuclear reaction such as (nuclear breakup) nuclear fission and nuclear fusion. The total mass of products in a nuclear reaction is always less than the total mass of reactants. The total mass is converted into energy in accordance with famous Einstein equation E = MC2 where E is energy, M is mass and C is the velocity of light.

As the value of the velocity of light is very high even small losses of mass are converted into huge amount of energy. Energy obtained from nuclear reactions is millions of times larger compared to the energy obtained from usual chemical reactions like combustion of coal. For example, fission of one kg of Uranium 235u will release energy equal to that obtained by burning three million tonnes of coal. This efficiency of atomic energy has fuelled the race among various countries to build most efficient nuclear reactors.

Otto Hahn and Lise Meitner discovered the phenomenon of nuclear fission and provided a new breakthrough. In nuclear fission atoms break into pieces and the nuclear of the atom splits. Heavy radioactive elements, such as uranium, split into new elements and release large amounts of nuclear energy. Nuclear fission is triggered by the absorption of a neutron by the nucleus of a fissile material. If the fissile material is present in sufficient amount to constitute a critical mass, fission can occur spontaneously.

In nuclear fusion the nuclei of two atoms join or fuse together at very high temperatures. Light elements, such as hydrogen, fuse to make a new element and release nuclear energy. It is nuclear fusion only, which creates intense heat inside the sun, and apart from this all other stars gain their energy from nuclear fusion only. The mass of the product formed in a fusion reaction is always less than the sum of the masses of the reactants. The lost mass is converted into energy. The most common example of nuclear fusion is the fusion of two nuclei of hydrogen isotopes to form a helium nucleus. As both the reacting nuclei are positively charged, normally they repel each other because similar electrical charges repel each other. The repulsion can be overcome if the nuclei are made to collide at very high speeds or the reaction occurs at very high temperatures of the order of 100 million degrees Celsius. Hydrogen bomb is also an example of fusion reaction.

Fusion/fission creates heat in nuclear reactor and boils water to make steam which drives a turbine, which spins the shaft of a generator. Many nuclear power stations are built beside the sea. A reactor is a nuclear-power station containing uranium fuel, a moderator control rod and a coolant. A thick concrete wall surrounds a nuclear reactor, so that radiation is not leaked out. The nuclear energy despite having several plus points also has some fallout. One of them is of nuclear waste, which is highly radioactive and dangerous. Constant contact with this waste can lead to serious bodily deformities, sores and decrease in sperm count. It acts as slow poisoning not only on human beings but to the whole environment and the earth.

In the process of producing more and more electricity we are now generating lot of nuclear waste which is very difficult to dispose off. There is a great need for proper disposal of this nuclear waste that has very long half-life and is never destroyed. The half-life is the amount of time taken for half the atoms in a radioactive substance to decay. The half-life of uranium is 700 million years and polonium is less than a millionth of a second. The half-life of Carbon 14c is 5780 years. It can be assessed now that due to non-destroyable nature of this material the mother earth has to suffer a lot.

It is high time some or the other way was devised to dispose if off safely otherwise we may have to again face the consequences as we did in the case of Chernobyl-nuclear disaster where thousands of people suffered a lot and havoc was created all over the world.

The remains of nuclear fusion obtained from a reactor after the fuel is burnt is known as spent fuel. It contains various radioactive substances like MOX (mixed oxides of radioactive material) Plutonium etc. Plutonium can be used again in nuclear plants by reprocessing it. For the prevention of the contamination of the air released from the reactor, it is normally made to pass through very high efficiency particulate filter, which removes all particulate matter. Thus radiation is prevented from spreading through air. There are three kinds of nuclear wastes normally.

1. Very low active liquid wastes that are disposed off after dilution, into oceans especially for those plants near the oceans. Spent fuel after use is stored under water in spent fuel bays in the plant for an interim period — to cool down — which can take 20 to 25 years.

2. Medium level waste which is solidified into soluble matrix and is kept in reliable containers and buried in totally waterproof concrete tile holes (abandoned mines where walls are made of thick concrete material so that waste disposed in it doesn’t come in contact with ground, water and air).

3. High level waste which is immobilised in glass matrix and doubly encapsulated in corrosion resistant containers (Canisters). It is kept under continuous cooling in water for 20-30 years. Ultimately it is disposed in underground geological formations with additional barriers (gorges in seabed, holes drilled in sea).

In India we have identified two places in Rajasthan and MP to dispose off nuclear waste. Apart from this we have waste immobilisation plant at Tarapur with advanced technologies like complete remote operations maintenance etc. (operated by robots). On the same line two more plants are under construction at Trombay and Kalpakkam for waste disposal.

Generally worldwide the International Atomic Energy Agency (IAEA) looks after and checks the nuclear reactor of the countries who have signed NPT. It also keeps the records of the spent fuel. India is not the signatory to the NPT but it has developed the technology for the reprocessing of the spent fuel with the help of Russia.

The nuclear waste contains Iodine 129, an radioactive isotope which is the major waste product in the nuclear power plants all over the world. Several countries and many scientists all over the world are devising ways of tackling this menace. It has half life of 15.7 million years which makes it dangerous and difficult to dispose off totally.

But the latest issue of"The Journal of Physics" has reported that a team of scientists from Imperial College, Rutherford Appleton Laboratory (RAL), ITU (Karlsruhe), University of Jena and University of Strathclyde has turned radio isotope Iodine-129 into more friendly isotope Iodine 128 by using laboratory lasers. The leader of the team, Prof Ken Ledingham and others irradiated Iodine-129 with a laser beam and turned it into Iodine-128 which has a half life of just 25 minutes thus making the waste safe to be disposed off in an hour only.

This dream team is now trying to develop a laser system large enough to cater to the need of the nuclear power plants the world over and to cope with the volume of Iodine-129 produced by nuclear power industry.

Now it is to be seen how Prof Lendigham and company can succeed in their endeavour and make the dreaded spent fuel easy to dispose. We can only keep our fingers crossed and wait and watch. If they succeed in developing the laser system large enough to cope with the volume of the nuclear waste generated by nuclear plants then the mankind can heave a sigh of relief and can go ahead by building more nuclear reactors and cater to the need of the hour without bothering much about the nuclear waste. It seems happy days are here again.