Nuclear Physics and Energy

Dhruva reactor is India's largest nuclear research reactor, which is located in the Mumbai (Bombay) suburb of Trombay at the Bhabha Atomic Research Centre (BARC). It is India's primary generator of weapons-grade plutonium-bearing spent fuel for its nuclear weapons program. Originally named the R-5, this pool-type reactor first went critical on 8 August 1985 after 10 years of construction.

The sievert (Sv) is the International System of Units (SI) of equivalent radiation dose, effective dose and committed dose. Quantities that are measured in sieverts are designed to represent the stochastic biological effects of ionising radiation. This SI unit is named after Rolf Maximilian Sievert.

Commonly used moderators include regular (light) water (roughly 75% of the world's reactors), solid graphite (20% of reactors) and heavy water (5% of reactors). Beryllium has also been used in some experimental types, and hydrocarbons have been suggested as another possibility.

In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235.

Accidents involving nuclear power plants are disastrous and have very grave consequences.

Nuclear fission reaction involves the splitting of a big atom into smaller atoms with a tremendous release of energy.

Today, the term 'heavy water' is somewhat colloquial and pure heavy water for research and commercial use is generally commercially offered, and referred to, as deuterium oxide. It is not radioactive. It is about 11% denser than water, but otherwise physically and chemically it is similar. Heavy water has a higher specific heat capacity than normal water. The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. A coolant in a nuclear reactor is used to remove heat from the nuclear reactor core and transfer it to electrical generators and the environment should have a high specific heat capacity. Thus, heavy water is ideal as a coolant in a nuclear reactor.

Correct Answer: controlled chain reaction

In a nuclear fission reaction, heavier nucleus breaks up into lighter nuclei and releases energy.

Following are the major drawbacks of a nuclear power plant: (i)   It contaminates environment with hazardous radiations. (ii)  It is very costly to set up. (iii) It uses uranium, which is scarcely available and not in abundance. Since all these are the drawbacks of a nuclear power plant, then option (4) is correct.

The principle underlying a microwave is similar to that used in thermal radiation. A microwave oven does emit thermal radiation to heat up food, which is also called infrared radiation. Microwave radiation is thermal radiation.

Nuclear fission releases energy primarily as heat due to the conversion of mass into energy (E=mc²). The kinetic energy of fission products manifests as thermal energy, which is then used to generate electricity in nuclear power plants. While some light may be produced (Cherenkov radiation), heat is the primary useful output.

In nuclear power reactors,

1. uranium-235 is used as the fission material
2. graphite is used as a moderator
3. rods of cadium are used to control the rate of nuclear reaction 

Heavy water (D2O - deuterium oxide) is used as a moderator in nuclear reactors. It slows down neutrons effectively to sustain the nuclear chain reaction while absorbing fewer neutrons than light water. Heavy water's neutron moderation properties make it essential for certain types of nuclear reactors, particularly those using natural uranium.

Hydrogen bombs (thermonuclear weapons) are based on nuclear fusion - combining light atomic nuclei (like isotopes of hydrogen) to form heavier ones, releasing massive energy. Nuclear fission is used in atomic bombs. The bomb requires fission to trigger fusion initially, but the main destructive yield comes from fusion, not fission alone.