Fusion reaction takes place at high temperature because kinetic energy is high enough to overcome the couloumb repulsion between nuclei.

For nucleus of $$_8{O^{16}}$$
Mass $$ = \left( {16} \right)\left( {1.67 \times {{10}^{ - 27}}} \right)kg$$
Volume $$ = \frac{4}{3}\pi {R^3}$$
$$ = \frac{4}{3}\pi {\left( {3 \times {{10}^{ - 15}}} \right)^3}{m^3} = 36\pi \times {10^{ - 45}}{m^3}$$
Density $$ = \frac{{{\text{mass}}}}{{{\text{volume}}}} = \frac{{16 \times 1.67 \times {{10}^{ - 27}}kg}}{{36\pi \times {{10}^{ - 45}}{m^3}}}$$
$$ = 2.35 \times {10^{17}}kg\,{m^{ - 3}}$$

Electronic configuration of iodine $$\left( {53} \right)$$  is $$= 2, 8, 18, 18, 7$$
∴ Principal quantum number $$n = 5$$
Radius of $$n$$th orbit is given by
$${r_n} = {r_0}\left( {\frac{{{n^2}}}{Z}} \right)\,\,\left( {Z = {\text{atomic number}}} \right)$$
where $${r_0} = 0.53\,\mathop {\text{A}}\limits^ \circ = 0.53 \times {10^{ - 10}}m$$
$$\therefore {r_n} = \left( {0.53 \times {{10}^{ - 10}}} \right) \times \frac{{{5^2}}}{{53}} = 2.5 \times {10^{ - 11}}m$$

Mass defect $$\Delta m = 2 \times 2.014 - 4.0026 = 0.0256\,a.m.u$$
Energy released when two $$_1{H^2}$$  nuclei fuse $$ = 0.0256 \times 931 = 23.8\,MeV$$
Total energy required to be produced by nuclear reaction in 1 year
$$ = 2500 \times {10^6} \times 3.15 \times {10^7} = 7.88 \times {10^{16}}J$$
No. of nuclei of $$_1{H^2}$$  required
$$ = \frac{{7.88 \times {{10}^{16}}J}}{{23.8 \times 1.6 \times {{10}^{ - 13}}}} \times 2 = 4.14 \times {10^{28}}$$
Mass of Deuterium required
$$ = \frac{{4.14 \times {{10}^{28}}}}{{6.02 \times {{10}^{23}}}} \times 2 \times {10^{ - 3}}kg = 138\,kg$$

Power level of reactor, $$P = \frac{E}{{\Delta t}} = \frac{{\Delta m{c^2}}}{{\Delta t}}$$
mass of the fuel consumed per hour in the reactor,
$$\frac{{\Delta m}}{{\Delta t}} = \frac{P}{{{c^2}}} = \frac{{{{10}^9}}}{{{{\left( {3 \times {{10}^8}} \right)}^2}}}kg/\sec = \frac{{3600 \times {{10}^9}}}{{9 \times {{10}^{16}}}} \times {10^3}\frac{{gm}}{{hr}}$$