Energy and Human Ambitions on a Finite Planet, 2021a

15 Nuclear <strong>Energy</strong> 273
needs. But given realities that only 0.08% of mass is converted to
energy in nuclear reactions, that only 0.72% of natural uranium
235 235
is fissile U, <strong>and</strong> that only half of the U is retrievable 88 <strong>and</strong> 88: . . . given enrichment inefficiency
“burned” in reactors, how many tons of uranium must be mined
per year to support 18 TW via conventional fission, assuming for
the sake of this problem that 5 tons of mass need to convert to
energy via E mc 2 ?
235
33. Based on the abundance of U in the earth’s crust (Table 15.9),
how many kilograms of typical crust would need to be excavated
235
<strong>and</strong> processed per year to provide the ∼ 0.005 kg of U you need
for your personal energy (as in Example 15.4.2)?
i Of course mining does not work this
way, instead seeking concentrations.
34. In crude terms, proven uranium reserves could go another 90
years at the present rate of use. But the world gets only about a
tenth of its electricity from nuclear. What does this imply about
the timescale for the uranium supply if the world got all of its
electricity from conventional (non-breeding) nuclear fission?
35. Replicate the calculation <strong>and</strong> show the work that if we have 2×10 21 J
of proven uranium reserves under conventional fission, we would
exhaust our supply in less than 4 years if using this source to
support the entire 18 TW global energy appetite.
36. Use Figure 15.18 to reconstruct the breeder route from Th to
232
Hint: start by adding a neutron to Th
233U
by describing the associated nuclei <strong>and</strong> decays (<strong>and</strong> half-lives)
involved.
37. For spent nuclear fuel a few decades old, what isotopes are responsible
for most of the radioactivity, according to Figure 15.19?
38. Let’s say that spent fuel rods are pulled out of the holding pool
at the nuclear facility ten years after they came out of the core.
Based on the total radioactive power from waste products (black
line on Figure 15.19), approximately how long will you have to wait
until the radioactivity level is down by another factor of 1,000 from
where it is at the time of extraction?
232
39. Operating approximately 450 nuclear plants over about 60 years
at a total thermal level of 1 TW, we have had two major radioactive
releases into the environment. If we went completely down the
nuclear road <strong>and</strong> get all 18 TW 89 this way, what rate of accidents
might we expect, if the rate just scales with usage levels?
89: . . . also a thermal measure
40. On balance, considering the benefits <strong>and</strong> downsides of conventional
nuclear fission, where do you come down in terms of support
for either terminating, continuing, or exp<strong>and</strong>ing our use of this
technology? Should we pursue breeder reactors at a large scale?
Please justify your conclusion based on the things you consider to
be most important.
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.