What is the fuel in a nuclear reactor?

The fuel and the fuel composition used in different types of nuclear reactors are different. In thermal reactors, natural uranium is used as the fuel. The fissile isotope present in the natural uranium (U-235 – 0.72%) is utilized during reactor operations. The fission reactions occurring in the fuel generate lot of heat which is taken up by the coolant, and ultimately generates steam for producing electricity.

What is the difference between Research reactor and Power reactor?

Research reactors are generally employ natural or low-enriched uranium metal as fuel to carry out research for nuclear applications. The reactor is used to produce radioisotopes for use in medicine, industry and agriculture. The heat generated in research reactors is not utilized to produce electricity.

Power reactors may use various types of fuels, including natural uranium (but in the oxide form, in PHWR), to generate higher amount of heat. The heat is taken out quickly using pressurized coolant system to generate steam, which runs a turbine to generate electricity.

Why nuclear energy?

Availability of electricity is an essential requirement for industrial development. There exists a large gap between the electricity requirement and the actual generation in India. For sustaining the projected industrial/economic growth, the country needs electricity of all kinds, i.e., thermal (coal, natural gas), hydro, nuclear, wind, solar, etc., etc. However, keeping the pollution and global warming concerns in mind, one has to choose non-fossil fuel-based power plants and work on renewable energy resources. The safety record Indian nuclear power sector is reported to be quite satisfactory.

What is mean by ionizing radiation?

Heat and visible light are the part of electromagnetic radiation that one can feel. There are other kinds of radiation like radio-waves, those human senses cannot detect. The energy content of some kinds of radiation is large enough to penetrate the human body and cause biological damage. Examples are: X-rays and gamma rays, which are parts of electromagnetic radiation, with shorter wavelengths and high energy content. The ionizing radiation while passing through matter can cause some of its atoms to get ionized and the ions generated by such radiation can affect normal biological processes.

In addition to the above, ionizing radiation also comes in different forms such as alpha particles, beta particles and neutrons.

What is half-life?

Radioactivity of a radionuclide diminishes over time at various rates as the atom changes from one to another. Half-life is the time required for the radioactivity to reduce by one-half of the initial amount. The half-lives vary from a small fraction of a second to many millions of years.

How much is the radiation dose received by a person due to natural radiation background?

On an average, a person receives a whole-body dose of 2.4 milliSieverts (mSv) in a year. The dose varies from place to place depending upon the altitude and concentration of naturally occurring radionuclides present in the earth. In Kerala and Orissa coast areas, the dose can be higher due to larger amount of natural radioactivity in the beach sand (called monazite sand). Compared to this, the radiation dose received by the public from man-made radiation sources is negligibly small.

What are the natural radionuclides present in our body?

Carbon-14, Potassium-40, Radium-226, Thorium-232, Thorium-228, radioactive daughter products of uranium and thorium are the radionuclides present in our body in very small amounts.

What is radon?

Radon (Rn-222 and Rn-220) is the gaseous alpha emitting radionuclide produced in the decay chains of naturally occurring U-238 and Th-232 respectively. Radon is ubiquitous, present everywhere. Concentration varies from place to place depending on the amount of uranium and thorium present in the soil and building material.

The internal dose due to inhalation, and deposition of its short-lived particulate daughter products is quite significant.

What is the relationship between radiation dose and harmful effects?

Estimates of risk from exposure to radiation are based on studies of people who were exposed to fairly high doses of radiation and where cancers have been observed. They include the survivors of the atom bombs in Japan, patients exposed to high levels of radiation dose for treatment of cancer, and groups of exposed workers in some industry. Doses of relevance in nuclear industry are low level radiation exposures over time (chronic exposures). In the absence of any concrete proof of radiation risk, and as matter of abundant caution, it is assumed that the stochastic risk is proportional to dose. Smaller the dose, smaller is the health risk of radiation exposure.

What happens if somebody exceeds the dose limits?

The dose limits are prescribed by international agencies like ICRP and the limits are followed worldwide. There is sufficient built-in safety factor in the dose limit values that if by chance some worker exceeds the dose limits no harmful effects are expected to take place. However, such incidences give an opportunity for the management to review their operating procedures so as to maintain the exposures within the dose limits and as low as reasonably achievable (ALARA).

Chernobyl – What do we need to know?

Chernobyl is located in the state of Ukraine of Ex. USSR. A 1000 MWe nuclear power reactor no. 4 of the Chernobyl plant exploded following a succession of technical malfunctions and human errors on April 26, 1986. There was explosion and then fire. Radioactive dust, aerosols and gases were ejected into the atmosphere and got carried away by the winds. Thirty-one fire men called to extinguish the fire died. Over 18 thousand liquidators received radiation doses exceeding 100 mSv. Psychological consequences of the accident, and living in contaminated areas could be seen in the exposed population groups. Thousands and thousands of people were evacuated from the contaminated areas. Radioactive Caesium isotopes deposited in parts of Asia, north America, Europe in states of Ex. USSR, contaminating lakhs of square kilometers of the area. Open water sources, milk, vegetables and fruits got contaminated with the radioactivity releases. The affected reactor is sealed (sarcophagus) to contain the residual radioactivity remaining in the reactor.

Radiation is carcinogenic

There are hundreds of agents present in our environment, which also includes chemical pollutants, and background radiation. Many of the chemical pollutants, particularly, organic chemicals present in the exhausts of the motor vehicles; alcohol, chloroform, asbestos, some heavy metals, etc are known carcinogenic agents. Comparatively, radiation is a week carcinogen.

Exposure of female workers

The radiation dose limit for both male and female workers is same. However, it was observed that the fetus during initial few weeks of pregnancy is more radiosensitive and hence, after declaration of pregnancy, the female worker is treated as a member of the public. However, an equivalent dose limit of 1 mSv to the fetus is applicable for the remaining months of pregnancy.

Exposure of itinerant / contractor’s workers

Radiation protections procedures and standards which are applicable to regular workers are also applicable to itinerant or contractor’s workers. In India, however, the permissible dose limit for itinerant workers is 15 mSv/y, which is lower than the international average annual limit of 20 mSv.

Whether there is any harm in entering X-ray room after the machine is switched off?

X-rays are generated only when the machine is put on. Hence, there is no harm in entering the room after confirming that the machine is put off.

How to measure the radiation exposure received by radiation workers?

All the radiation workers are provided with personal monitoring badges (TLDs), which record the radiation exposure of the person wearing the badge. Excreta of the workers (urine and stool) are also periodically collected and analyzed for detecting any intakes of radioactivity. Thus, external as well as internal exposures of the radiation workers are determined and recorded.

Whether working in nuclear industry is more risky than other industries?

There are many peaceful uses of radiation: in medicine, industry, research, agriculture and to generate electricity. As per the surveys reported, and based on the number of fatalities occurring in different industries, nuclear industry is considered as safe industry. The fatality risk is around one in ten thousand.

On an average how much dose is received by a patient due one X-ray examination?

One X-ray examination of the chest results in a radiation dose of about 2 mSv to the patient. The health risk due to this is negligible. However, multiple X-ray examinations of patients should be decided by the physician based on the risk and benefit analysis.

What is the reliability of dose limits?

The dose limits for the occupational workers and the members of the public are recommended by an international non-governmental organization called International Commission for Radiological Protection (ICRP). Group of experts in various fields go through the available epidemiological data, including that of UNSCEAR periodically, and review the dose limits. The recommendations are generally accepted worldwide.

Radioactive waste is still unresolved problem?

Management of radioactive waste is very well understood and countries like India are well prepared to handle all types of the wastes, including high level wastes safely without disturbing the environment. Disposal sites are selected very carefully keeping the population density, the water table and geological stability in mind. The disposal facilities are well designed considering the type of activity, the half-life and the containment requirement.

What is Dirty Bomb?

Radioactive material is added / incorporated into the conventional explosives, which on explosion spreads radioactive contamination and create panic situation in the public domain.

What are the health concerns of mobile phones?

As the mobile / cellular phone ownership growing, concerns about the possible health risks due to radio frequency emissions from the mobile phone base stations, and due to usage of mobile handsets is also growing. Biological effects that result from heating of tissue by RF are referred to as "thermal effects". Measurable heating of biological tissue can occur from exposure to RF energy at power density levels of 1 - 10 mW/cm2. Frequency of the RF wave is important in the assessment of biological effect.

In general, the quantity used to characterize this energy absorption is called the Specific Absorption Rate (SAR) which is expressed in unit of W/kg. Other health problems commonly attributed to the use of mobile phone handsets are impairment of short-term memory, headaches, brain-tumors, sleep disturbance, depression and tiredness. The mobile phone is designed and manufactured not to exceed the limits for exposure to radio-frequency recommended by international organizations such as National Radiological Protection Board (NRPB), Federal Communication Commission (FCC), and International Commission on Non-Ionizing Radiation Protection (ICNIRP).

National authorities issue country-specific guidelines to be followed. It is assumed that the exposure to RF radiation below the limits set up by NRPB and ICNIRP do not cause adverse effects to the general population. The SAR value is reported for a particular model of mobile phone for the information of the user.

Controlled use of mobile phones and use of hands-free kits are good means of reducing RF exposure to the head and neck region. In the matter of permissions for installation of fresh base stations in heavily populated areas, the sanctioning authorities, as a measure of abundant caution ensure that the antennas and the towers are as far away from residential homes, hospital wards and schools as is reasonably possible.