Energy and Human Ambitions on a Finite Planet, 2021a

15 Nuclear <strong>Energy</strong> 274
41. The sun is a fusion power plant producing 3.8 × 10 26 W of power.
How many kilograms of mass does it lose in a year trough pure
energy conversion? How does this compare to the mass of a
spherical asteroid 50 km in diameter whose density is 2,000 kg/m 3 ?
Hint: the volume of a sphere is 4πR 3 /3.
42. Based on the fractional mass loss associated with turning four
hydrogen atoms into a helium atom, what fraction of the sun’s
mass would it lose over its lifetime by converting all its hydrogen
into helium, under the simplifying assumption that it starts its life
as 100% hydrogen?
43. The three fusion forms in Eq. 15.3 each have different energy
outputs. Looking at Figure 15.10, 90 how would you qualitatively
describe why the three reactions differ in this way?
90: Tritium is not labeled, but visible just
below 3 MeV on the left side.
44. Based on the calculation that 18 TW would require an annual cube
of seawater 300 m on a side to provide enough deuterium, what is
your personal share as one of 8 billion people on earth, in liters?
Could you lift this yourself? One cubic meter is 1,000 L.
45. What are your thoughts about fusion? Are you excited, skeptical,
confused, all of the above? Please offer your thoughtful assessment
of the role you imagine fusion playing in our future—your best
guess.
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.