Energy and Human Ambitions on a Finite Planet, 2021a

15 Nuclear <strong>Energy</strong> 259
one of the three fissile nuclei, we can convert 43 238 239
U into the fissile Pu
the following way.
238 239
1. A U may absorb a w<strong>and</strong>ering neutron to become U.
239
2. U, whose half life is 23.5 minutes, undergoes β − to become
239Np
in short order.
239
3. Np also undergoes β − with a half life of 2.4 days to become
239
fissile Pu.
Figure 15.17 highlights this process in a simplified region of the Chart
of the Nuclides, while Figure 15.18 shows complete details for the
entire region around the fissile materials—the ones with red isotope
names—which can be used to track the sequence outlined above.
43: . . . called transmutation
Pu239 Pu240 Pu241
24.10 kyr 6.56 kyr 14.4 yr
Np238 Np239
2.117 d 2.355 d
Np240
1.032 h
U237 U238 U239
6.75 d 99.2745 23.47 m
4.47 Gyr
n
Figure 15.17: Breeder route to
239 Pu.
95
94
93
92
91
90
89
Am
Americium
Pu
Plutonium
Np
Neptunium
U
Uranium
238.02891
Pa
Protactinium
231.03588
Th
Thorium
232.0381
Ac
Actinium
Am235 Am236 Am237 Am238 Am239 Am240 Am241 Am242 Am243
15 m 4 m
1.22 h 1.63 h 11.9 h 2.12 d 432.7 yr 141 yr 7.37 kyr
e - capture ? e - capture e - capture e - capture e - capture e - capture
E 2.6 E 3.3
E 1.5
E 2.3 E 0.803 E 1.38 241.056823
243.061373
Pu234 Pu235 Pu236 Pu237 Pu238 Pu239 Pu240 Pu241 Pu242
8.8 h 25.3 m 2.87 yr 45.2 d 87.7 yr 24.10 kyr 6.56 kyr 14.4 yr 375 kyr
e - capture e - capture
e - capture
E 0.39 E 1.14 236.046048 E 0.22 238.049553 239.052157 240.053087 E 0.0208 242.058737
Np233 Np234 Np235 Np236 Np237 Np238 Np239 Np240 Np241
36.2 m 4.4 d 1.085 yr 155 kyr 2.14 Myr 2.117 d 2.355 d 1.032 h 13.9 m
e - capture e - capture e - capture e - capture
E 1.0 E 1.81 E 0.124 E 0.9 237.048167 E 1.292 E 0.722 E 2.20 E 1.3
U232 U233 U234 U235 U236 U237 U238 U239 U240
69.8 yr 159.2 kyr 0.0055 0.7200 23.42 Myr 6.75 d 99.2745 23.47 m 14.1 h
246 kyr
704 Myr
4.47 Gyr
232.037146 233.039628 234.040946 235.043923 236.045562 E 0.519 238.050783 E 1.263 E 0.39
Pa231 Pa232 Pa233 Pa234 Pa235 Pa236 Pa237 Pa238
32.8 kyr 1.31 d 26.967 d 6.69 h 24.4 m 9.1 m 8.1 m 2.3 m
231.035879 E 1.34 E 0.570 E 2.195 E 1.4
E 2.9
E 2.3 E 3.5
Th230 Th231 Th232 Th233 Th234 Th235 Th236 Th237 Th238
75.4 kyr 1.063 d 100 21.83 m 24.10 d 7.2 m 37.5 m 4.8 m ~9.4 m
14.0 Gyr
230.033127 E 0.390 232.038050 E 1.245 E 0.273 E 1.9 E 1.0 E 2.6 E 1.6
Ac229 Ac230 Ac231 Ac232 Ac233 Ac234 146 147 148
1.04 h 2.03 m 7.5 m 2.0 m 2.4 m
40s
E 1.10 E 2.7
E 2.1
E 3.7
E 2.8 E 4.5
Z N 140 141 142 143 144 145
Pu239
24.10 kyr
239.052157
U238
99.2745
4.47 Gyr
238.050783
isotope
half life (radioactive)
primary decay path
mass or decay energy (MeV)
naturally ocurring isotope
% abundance
half life
primary decay path
mass, a.m.u.
Top Half Coloring:
Half Life Guide
< 1 day
1 to 10 days
10 to 100 days
100 days to 10 yr
10 yr to 500 Myr
> 500 Myr or stable
Bottom Half Coloring:
Neutron Absorption (Barns)
< 10
10 to 100
100 to 500
500 to 1000
>1000
1 a.m.u. = 1.66054e-27 kg
1 a.m.u. = 931.49432 MeV/c 2
1 MeV = 1.6022e-13 J
U233, U235, Pu239 are slow-neutron fissile
Figure 15.18: Chart of the Nuclides in the fission region. See also Figure 15.4 for the lower-left corner.
238 239
The result is that sterile U can be turned into fissile Pu that can be
used in fission reactors. This process of transmuting an inert nucleus
into a fissile one is called breeding, <strong>and</strong> is how we get any plutonium
at all. 44
238
A nuclear reactor is a great place to introduce U to neutrons:
both are already in attendance. In fact, breeding happens as a matter of
course in a nuclear reactor: it is estimated that one-third of the fission
44: . . . e.g., for weapons
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.