The decrease in the mass of Uranium in a nuclear reactor operating at a power of $12 \text{ MW}$ per day is (Energy released in one ${}_{92}U^{235}$ fission is about $200 \text{ MeV}$):

Slowing down of neutrons: In a nuclear reactor,a neutron of high speed (typically $10^{7} \; m s^{-1}$) must be slowed to $10^{3} \; m s^{-1}$ so that it can have a high probability of interacting with isotope $^{235}_{92}U$ and causing it to fission. Show that a neutron can lose most of its kinetic energy in an elastic collision with a light nucleus like deuterium or carbon,which has a mass of only a few times the neutron mass. The material making up the light nuclei,usually heavy water $(D_{2}O)$ or graphite,is called a moderator.

The binding energy per nucleon for deuteron $(_1^2H)$ and helium $(_2^4He)$ nuclei are $1.1 \, MeV$ and $7 \, MeV$ respectively. Calculate the energy released in $MeV$ when two deuteron nuclei fuse to form a helium nucleus.

In a reactor, $2 \, kg$ of ${ }_{92} U ^{235}$ fuel is fully used up in $30$ days. The energy released per fission is $200 \, MeV$. Given that the Avogadro number, $N_A = 6.023 \times 10^{26} \, \text{per kilo mole}$ and $1 \, eV = 1.6 \times 10^{-19} \, J$. The power output of the reactor is close to $..... \, MW$.

In the Sun,the important source of energy is

In a nuclear fusion process,a certain mass of hydrogen is converted into helium,resulting in a mass defect of $0.02866 \, u$. The energy released per $1 \, u$ of mass formed is ......... $MeV$. (Given $1 \, u = 931 \, MeV$)