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Frequently Asked Questions (FAQ's)
What is heavy water?
Heavy Water (D2O) is a compound of an isotope of hydrogen called heavy hydrogen or Deuterium (D) and oxygen. This is also known as Deuterium Oxide. Deuterium has an atomic mass of 2, as against 1 for normal hydrogen (H) due to presence of an extra neutron in the nucleus. Deuterium is present in hydrogen and hydrogen bearing compounds like water, hydrocarbons, etc. and has a small natural occurrence (D/D+H) of about 140 to 160 ppm. So it is necessary to process large quantities of the low concentration feed stock to produce the final product which is enriched to the reactor grade i.e. 99.8 mole %. Heavy Water has great similarity in its physical and chemical properties to ordinary water. But its nuclear properties display a significant variation which makes it an extremely efficient material for use as moderator in a nuclear reactor.
 
What is Moderator?
Moderator is required in a thermal reactor to slow down the neutrons produced in the fission reaction to .025 ev (thermal reaction) so that the chain reaction can be sustained. Different moderators normally in use are Heavy Water, Graphite, Beryllium and Light water. Heavy Water is an excellent moderator. A good moderator should have excellent slowing down power and low absorption cross section for neutrons.
 
What is Coolant?
Heat energy produced in the fission reactor will be removed by coolant. Water is an excellent coolant that can remove the heat from the feed. Heavy Water is used as a primary coolant to transport heat generated by the fission reaction to secondary coolant, light water. In Gas cooled reactors carbon di-oxide gas is used as coolant. Coolant transports heat to secondary coolant, i.e. water for generation of steam at an appropriate pressure for running steam turbines. Steam turbines drive generators to generate Electricity.
 
Is heavy water Radio active?
No, heavy water is not radioactive. It is oxide of deuterium (D2O) which is stable isotope of hydrogen.
 
When & why it is said that there is radio activity in heavy water used in nuclear power stations?
Because some of the deuterium in heavy water gets converted to Tritium by absorbing a neutron a nuclear reactor. Tritium is radio active. Further, some of the ionic impurities that are carried by heavy water as moderator or coolant also get activated in course of irradiation. Hence the radio activity is observed in Heavy Water used in Nuclear reactors.
 
Is heavy water harmful to health?
A small quantity of heavy water is not harmful to human health. In fact, human body contains few grams of heavy water as natural abundance. Small quantities of heavy water have been used in clinical studies and treatment in infants, lactating women and adults without any reported adverse effect. Toxic effects of heavy water begin to appear only when deuterium content of body fluids exceeds 20%, which is most unlikely event. Extremely large intake of heavy water is required for causing any noticeable harmful effect.
 
What is degraded Heavy Water?
Heavy Water which has greater light water content is called degraded heavy water.
 
Why Heavy Water gets degraded?
Heavy Water has greater affinity for light water. It can readily absorb light water present in air. It can also get degraded whenever light water from other processes gets mixed with it.
 
Is there any fixed life for Heavy Water?

There is no fixed life for heavy water if it is blanketed with the dry inert gas (N2, He etc.)

 
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