Energy and Human Ambitions on a Finite Planet, 2021a

17 Comparison of Alternatives 299
D–T Fusion (Sec. 15.5; p. 264): The easier of the two fusion options,
involving deuterium <strong>and</strong> tritium, represents a longst<strong>and</strong>ing goal under
active development since 1950. The well-funded international effort,
ITER, plans to accomplish a 480 second pulse of 500 MW power 25 by
2035. This defines the pinnacle of hard. Fusion brings with it numerous
advantages: enormous power density; only moderate radioactive waste
products; <strong>and</strong> abundant deuterium. 26 Fusion would have no intermittency
issues, can directly produce heat <strong>and</strong> derivative electricity, but like
the others does not directly address transportation. The non-existent
tritium can be knocked out of lithium with neutrons, <strong>and</strong> even though
we are not awash in lithium, we have enough to last many thous<strong>and</strong>s
of years in the absence of dem<strong>and</strong> for batteries. We might expect some
public opposition to D–T fusion due to the necessary neutron flux <strong>and</strong>
associated radioactivity. Fusion is the highest-tech energy we can envision
at present, requiring a team of well-educated scientists/technicians
to run—meaning don’t plan on building one in your backyard, unless
you can afford to have some staff PhDs on h<strong>and</strong>.
D–D Fusion (Sec. 15.5; p. 264): Replacing tritium with deuterium means
abundance of materials is no concern whatsoever for many billions
of years. As a trade, it’s substantially harder than D–T fusion. 27 D–D
fusion requires higher temperatures, making confinement that much
more difficult. It is for this reason that we make a single exception to the
scoring scheme <strong>and</strong> give D–D fusion a −2 score for difficulty.
25: Compare to a real power plant: yearslong
“pulse” at 3,000 MW thermal power.
26: ...though no natural tritium
27: . . . or we would not even consider D–T
17.3 Student Rankings
In Winter 2020, students at UC San Diego did Problem 11 from this
chapter, which asks them to come up with their own weighting for
the ten attributes in the comparison matrix, rather than the simple but
poorly-justified practice of giving each category the same weight. This
section reports the result from that exercise.
On average, the weights did not deviate dramatically from uniform, the
adjustments being within a factor of 1.5 for all cases: ranging from 0.66
to 1.47, when each student’s weighting was re-normalized after the fact
to add to ten points. The attributes getting a clear boost were abundance,
efficiency, <strong>and</strong> transportation capability. Those getting lower weight
were the backyard criterion, acceptance, <strong>and</strong> ability to produce heat. 28
What this says is that students, on the whole, value solutions that can
get the job done efficiently <strong>and</strong> preserve transportation, not caring as
much about individual resilience or acceptance. 29
28: One wonders if students in colder climates
would disregard heating capability.
29: In other words, centralized power less
bound by public opinion is okay.
Table 17.1 summarizes the outcome of this experiment, in which we
see broad agreement with the nominal uniform-weighting scheme,
mostly serving to downgrade the scores of some entries, <strong>and</strong> only
promoting one (thorium breeding). Note that the exercise preserved the
blue/yellow/red color scheme of the figures <strong>and</strong> only changed relative
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.