Wednesday, March 30, 2011

Nuclear Energy and the need for taking up radiation challenges

During last few days I was reading OERs,  other studies and reports on Nuclear energy, and radiation in particular.      So far I am convinced that Nuclear Energy is a reliable source of energy. Most probably we do not have the information about any other sustainable mechanism of energy generation to meet our energy needs. However we cannot help but raise our eyebrows when we think about Chernobyl, Three Mile Island and now Fukushima accidents.

In simple terms radiation is the emission of energy particles or waves from the excited (or high energy developed) nuclei of atoms. It is an effort of the high energy nuclei  to go to a low energy or stable state. It is called radiation because this energy radiates or travels in straight lines to all directions. Light, heat and microwave are radiations in our daily life. Sun and stars send cosmic radiation from times unknown. Our earth is a source of natural terrestrial radiation chiefly through Radon gas and also many other radioactive materials exist in soil and rocks. Even people themselves are a source of radiation as they carry radioactive potassium-40 and carbon-14 inside their bodies from birth. Medical use of radiation is yet another major source, which accounts for 14% of radiation dose on general population. It means every thing in this planet receives radiation doses regularly, of course, in varying degrees. However, high energy radiation is dangerous because it can ionize atoms by knocking out electrons. Such radiation is called Ionizing-radiation. Other type is low charge non-ionizing radiation, the energy level  of which is not enough to ionize atoms..  High amounts of ionizing-radiation is dangerous as it affects living cells, especially the DNA.

The radiation in the context of nuclear energy is ionizing one. A nuclear reactor works through sustainable nuclear chain reaction ( fission) using fissile materials as nuclear fuels. Materials that are capable of providing sustainable nuclear chain reaction such as uranium-235, plutonium-239 etc are called fissile materials.  The technology is like this. When a large fissile atomic nucleus absorbs a neutron, the heavy nucleus (excited nucleus) splits into two or more lighter nuclei, releasing kinetic energy, gamma radiation and free neutrons (to return to a stable state). A portion of these neutrons may later be absorbed by other fissile atoms and trigger further fission, which is called a nuclear chain reaction. The kinetic energy created during the  fission is converted to thermal energy when the free nuclei collide with nearby atoms.This thermal energy created in the reactor is used to produce compressed vapour, which is used to turn turbines to generate electricity. This reaction is controlled using special substances called nuclear poisons that can absorb the excess free neutrons.

Gamma rays that are being emitted during the nuclear fission  are the major radiation from a nuclear reactor. Gama rays are electromagnetic radiation of high frequency. Shielding from gamma rays requires large amounts of mass. They are better absorbed by materials with high atomic numbers and high density. Gamma rays are more penetrating and hence long duration exposure to high radiation may increase the incidence of cancer.

Various scientific literature say, it is not the fission alone that produce radiation in a nuclear power plant. For example, the radioactive substances that are used as fuel in the nuclear plants normally disintegrate or decay by the emission of alpha particles and gamma rays. Another source of radiation is the decay of fission products. Fission products are radioactive substances produced as a result of fission. Some of them would be highly radioactive. Similarly some impurities in the reactor coolant and the reactor coolant itself absorbs some free neutrons and becomes radioactive. This is called activation. But nuclear power plants use effective technologies to prevent all these kinds of radiations from exposure to the environment. However, nuclear fuel transport, fuel change in the plant and removal of waste from the plants etc could turn out to be the occasions of radiation leak outs. Now the challenge before the nuclear technology world is to device perfect systems that can withstand accidents and natural disasters as well as prevent radiation exposures during occasions as discussed above. 

Now we know that everybody, human beings and all other living beings, are exposed to natural radiation from times unknown. Therefore necessarily there should be some effective mechanism in living beings to repair the damages being caused by radiation, because in the absence of such a mechanism living beings would not have originated and sustained with millions of years of history. Now there is no need for guess works on this matter. Science has, without any doubt, proved that human cells are capable of repairing the damages being caused by radiation. It means human beings have inherent radiation adaptation mechanism and the limits of this adaptation may increase as well. Here, the crucial question is how much radiation can a living cell withstand now?

Amidst the fears growing in the world about radiation in connection with Fukushima accident, two days ago I read an interesting ‘View Point’ titled ‘We should stop running away from radiation’ by Wade Allison, University of Oxford on BBC News World website. In this article, while admitting the dangers of high radiations, Wade Alison looks at the present permissible limits of radiation with suspicion because individuals receive more than that level of radiation from normal living environments in different parts of the world without any proven resultant ailments. Citing the confirmed numbers of casualties from the major nuclear-power related accidents, he doubts whether the world is over-reacting.

Different terms are used for measuring radiation on different scenarios like radiation from a radioactive source, the dose of radiation absorbed by an individual, and biological risk (the health effects from exposure to radiation). The amount of radiation emitted by a radioactive substance is measure using the System International (SI) unit becquerel (Bq) or the conventional unit curie (Ci), named for the famous scientist Marie Curie. The dose of radiation absorbed by an individual -that is the amount of energy deposited in human tissue by radiation- is measured using the SI unit of gray (Gy) or the conventional unit of rad (one Gy is equal to 1 joule/kilogram). The biological risk on radiation is measured using the SI unit sievert (Sv) or the conventional unit rem.

Dose of radiation exposure (one day) and effects on human beings:
Dose (SvSymptomsOutcome
0 to 250 milli SvNo effect
250 milli Sv to 1 SvSome people feel nausea and loss of appetiteBone marrow damage, lymph nodes and spleen damaged
1 to 3 SvMild to severe nausea, loss of appetite and infectionSame as above, but more severe. Recovery probable, but not assured
3 to 6 SvSevere nausea, loss of appetite, plus hemorrhaging, infection, diarrhea, skin peels, and sterilityDeath occurs if doses higher than 3.5 Sv are left untreated.
6 to 10 SvAbove symptoms plus impairment of the central nervous systemDeath expected
Above 10 SvDeath

I see nuclear energy as the natural way of generating energy and radiation as the natural way of transmitting it in this Universe. As it being a system used by the Universe itself, it has to be tremendously powerful as well as sustainable. It is really these qualities of the nuclear energy that demands utmost care from us while exploring its possibilities. My intuition is that we have to study further deep into the technologies being used by the Universe to generate, control and transmit nuclear energy. Yes, knowing the universe is the real challenge here as well.

Let us also dream about solutions, because dreaming is an easy (and natural) way to know the universe and arrive at natural remedies.

Some wild thoughts (or dreams?)
  • Do some plants absorb and neutralize radiation? What about growing them around the N power plants?
  • Do some algae filter radiation in water?
  • Do some bacteria filter radiation in the air?
  • As we have terrestrial and cosmic radiations, necessarily there should be some elements in this universe that control and balance it. We know some of them. What about the possibility of finding out more efficient and unknown neutralizers in this universe?

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