Why is heavy water used as a moderator in a nuclear reactor?

Answer 1

Moderator is required in a thermal reactor to slow down the neutrons produced in the fission reaction to .025 ev 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.as it has excellent slowing down power and low absorption cross section for neutrons.

Heavy Water (D2O) is a compound of an isotope of hydrogen called heavy hydrogen or Deuterium (D) and oxygen. 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 150 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.

A good neutron moderator like heavy water is a material full of atoms with light nuclei which do not easily absorb neutrons. The neutrons strike the nuclei and bounce off. In this process, some energy is transferred between the nucleus and the neutron. More energy is transferred per collision if the nucleus is lighter, see elastic collision. After sufficiently many such impacts, the velocity of the neutron will be comparable to the thermal velocities of the nuclei; this neutron is then called a thermal neutron.

Answer 2

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RE:
Why is heavy water used as a moderator in a nuclear reactor?

Answer 3

Actually very few nuclear reactors use heavy water as a moderator. Heavy water has a much lower neutron absorption cross section than regular water. This essentially allows you to go critical with smaller reactor, or it allows you to go critical with a lower enrichment.

Answer 4

Slow the neutrons down so they will hit the uranium 238 and thus produce a fissile material. Thus you can produce a critical reaction without the use of enriched uranium, you just need the natural ratio of 235 and 238 that occurs in uranium you can mine. Fermi figured this out in 1943 beneath the football stadium in Chicago. He also made "Big Bertha" the drum that University of Texas uses today radioactive. Once decontaminated it now graces the football field at UT during halftime.

Answer 5

Heavy water (D2O) has the ability of slowing down neutrons which has the effect of making the reaction more,um, thorough, for lack of a better word!

Answer 6

Because the double proton slows down neutrons without absorbing them. Light water also moderates but it tends to absorb neutrons so quenching the chain reaction.

Ten points please

Answer 7

how about using vegetable oil(non-flammable) instead of heavy water.....

Answer 8

it is used to slow down the process so that uranium could react better

Answer 9

because the protons become unstable due to the staticly enhanced solubility of the molecular structure...

Answer 10

the excess protons will help neutralize..