Thursday, November 19, 2015

Radiation - Fluctuations and impacts

Radiation - exposure – Fluctuations and impacts

Director, center for environmental studies,
Gitam university, Visakhapatnam.
According to the experts Bushburg of university of California when the radioactive plume passes overhead. Radiation particles fall on you and you will be contaminated outside. But this can be eliminated by a shower bath and change of clothes and it will keep dose to a person below 1 rem or 10 MSV . That is why first EPZ is kept as 10 miles (16km) . If doses are less than 1 rem there are no health effects. Japan reported on 17.3.2011 0.17 MSV per hour at 30K.M. Which is high level were 1- 10 percent and they must persist for 60hours to bring 10 MSV or 1 rem of radiation, not a high dose to bother.
            Sheltering in a distant place is effective form of protection, but it should not be along the plume path.
            Sheltering of people from     20 to 30 KM of Fukushima is ment to minimize ingestion of  radioactivity and to prevent the skin and clothing to get contaminated as the plume below 1 rem or 10 MSV  is treated as healthy dose with no health effects.
             A 1100 MW Nuclear plant has the Nuclear reaction caused by 100 tonnes of uranium oxide fuel in 50,000 packed fuel rods which are tubes of 0.5 diameter of Zirconium  alloy the reactorcore is placed in a thik steam pressure vessel through which 18 tonnes of water is pumped per second to takeaway the heat that is used for making pressure steam which drives a turbine that is linked with a Generator that produces electricity. The fuel rods are kept at 3400 centigrade by circulating cooling water for removes  heat from the rods and if this flow cooling water is blocked the fuel temperature rises to 12000   centi grade and then the Zirconium tubes begin to melt and with this core getting melted , the fuel and the large quantities of radioactivity breaches  all the safety barriers and pushes its way into the open atmosphere. Alternative means are used to flood the the reactor core in emergencies to avoid core melt down and to maintain integrity of the containment building, if the emergency core cooling system fails, a cloud  of radioactivity  will enter the atmosphere  and will be carried by the winds which deposit fissions products of the core in a ribbon pattern downwind for hundreds of miles from the reactor. Health hazardous due to this contamination of Air-water and soil, causes physical, economic and social damages in the Zone of influence. Dosage of radioactivity are estimated and preventive and curative measures , in sheltering the people and giving them medicines and also evacuating people to safe Zones, within  the prescribed time schedules damages to crops, and milk are also estimated to take public health protection  measures.

            A large population can be exposed to a dangerous dose of radioactivity in many ways .Such an event is inevitable result of even the most limited nuclear war. It can happen if an accident to a nuclear reactor caused its containment vessel to burst and allowed material from the core to escape into the atmosphere. The inadvertent release from a reactor of water or gases baring radioactive nuclei would create the danger of an exposure of lesser magnitude still another possibility is an accident during the manufacture, transportation, reprocessing the storage of radioactive material for nuclear reactors or nuclear weapons .
            There are large differences in the amounts of radioactivity that could be released in such events and so each possibility must be considered separately. Who will describe the radioactivity that would probably   each of three events. The first is the detonation of a thermonuclear weapon at a ground level. The second is the melting melting of the core of a nuclear reactor and the bursting of its containment vessel. With a resulting escape of radioactivity. the third is the explosion of a thermo-nuclear warhead on a nuclear reactor.
            We want to emphasize that we shall not include in these comparisons the blast and the heat that constitute the prompt.Exposiveeffect of a thermonuclear weapon. We shall examine and compare only the delayed effects brought on by the release of radioactivity. It emerges none the less that the detonation of a nuclear weapons far more to be reared than any accident of a weapon on a reactor is many times more damaging than the detonation of a weapon on the ground. The nuclear attack turns the reactor into a devastating radiological weapon.
In the course of decay of radioactivity in the course of the decay the   nucleus expels an electron.  Within this context is called a beta ray. Such transformations can again leave the nucleus in an excited state, from which it returns to a lower energy level by emitting electromagnetic radiation.      
The fall out is radioactive in part because some of the newly created nuclei are unstable in general they have an excess of neutrons. The instability is relieved when a neutron is transformed into a proton by the process called bets decay. |IN the course of the decay the nucleus expels an electron which in the context is called a beta ray. Such transformations can again leave the nucleus in an excited statye from which t returns to a lower energy level by emitting electromagnetic radiation, mainly gamma rays. The fallout particles continue to emit bête and gamma rays for many decades after the explosion.
Still it has been  established that if the human body is exposed to more than 500 or 600 rem in an interval not much longer than a day or two, survival is almost impossible.IF THE DOSE IS BETWEEN 200 AND 450 REM.Survival is possible but by no means assured , even if medical care is available. All things considered, it seems reasonable  that a dose of hundred rems in a day implies mortality of 50% or more. Exposal of population  to 100 rems in the same period causes sickness and some deaths. At this dose many people may recover even without medication .
In caliculating land area becoming inhabitable due to radiation we shall take the maximum acceptable dose to 2 rems per year and this is 10 times EPA dose and morethan 20 times background radiation . It is also less than 5 rems per year. The present upper dose for radiation workers. Astandard of 2 rems  per year, may be adopted in the aftermath of a nuclear accident. In nuclear war 2 rems per year is force d on poor people forced to  50 rems that make 50%  fatal and cancer .In some people after some years . In one nuclear accident the total loss of coolent to the fuel rods in the core occurred and the consequent more over heat caused melting which maded contact with water used for cooling and the steam explosion caused the containment vessel was damaged leading to radioactive release into the environment . Another accident is the over heating of the core leading to hydrogen and other flammable gases , which mix with oxygen in the air and then ignite and explode . Again the containment vessel is breached  and radioactivity escapes into atmosphere .
The lower dose rate and the smeller size of the contaminated area due to accident suggest that people might be evacuated before they inhaled much radioactivity dust . This is the principle danger due to reactor accident, and it involves that land as to be decontaminated and afterwards it will be available for reoccupation after atleast one year at distant places(170 to 200km) after one year and 20 years(Upto 80 kilometers) in short distance from the reactor.

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Born in 1932 at Mudinepalli, near Gudivada, Krishna Dist. Andhra Pradesh, received Bachelors degree in Civil Engg., from Viswesaraiah Engineering College, Banglore (1956) and Masters Degree in Environmental Engineering from Rice university, Houston, Texas, (USA) (1962), Ph.D (Hony). Former Head of the Department of Civil Engineering and principal of College of Engineering, Andhra university.Formerly Hony.Professor in Andhra University,Manonmanian Sundarnar University,JNT University. Fellow of the Institution of Engineers,India Recipient of the University Grants Commissions National Award "Swami Pranavananda Award on Ecology and Environmental Sciences" for the year 1991. Recipient of Sivananda Eminent Citizen Award for 2002 by Sanathana Dharma Charitable Trust, Andhra Pradesh state. Presently Working as Director, centre for Environmental Studies, GITAM University,