alpha decay is 24,000 y. The entire sequence is shown in Fig. 12.24. Both neptunium
and plutonium are transuranic elements,none of which are found on the earth because
their half-lives are too short for them to have survived even if they had been present
when the earth came into being 4.5 billion years ago.
The plutonium isotope^239 Pu is fissionable and can be used as a reactor fuel and
for weapons. Plutonium is chemically different from uranium, and its separation from
the remaining^238 U after neutron irradiation is more easily accomplished than the
separation of^235 U from the much more abundant^238 U in natural uranium.
A breeder reactoris one especially designed to produce more plutonium than the(^235) U it consumes. Because the otherwise useless (^238) U is 140 times more abundant than
the fissionable^235 U, the widespread use of breeder reactors would mean that known
Nuclear Transformations 457
Reactor
vessel
Control
rods Pressurizer
Fuel rods
in core
Containment shell
Pump Pump
Steam Condenser
generator
Steam
turbine
Electric
generator
Cooling water
Figure 12.23Basic design of the most common type of nuclear power plant. Water under pressure is
both the moderator and coolant, and transfers heat from the chain reaction in the fuel rods of the
core to a steam generator. The resulting steam then passes out of the containment shell, which serves
as a barrier to protect the outside world from accidents to the reactor, and is directed to a turbine that
drives an electric generator. In a typical plant, the reactor vessel is 13.5 m high and 4.4 m in diameter
and weighs 385 tons. It contains about 90 tons of uranium oxide in the form of 50,952 fuel rods each
3.85 m long and 9.5 mm in diameter. Four steam generators are used, instead of the single one shown
here, as well as a number of turbine generators.
239
94 Pu
24 min
e–
238
92 U
239
92 U
2.3 d
(^239 93) Np e–
n
233
92 U
22 min
e–
232
90 Th
233
90 Th
27 d
(^233 91) Pa e–
n
Figure 12.24^238 U and^232 Th are “fertile” nuclides. Each becomes a fissionable nuclide after absorb-
ing a neutron and undergoing two beta decays. These transformations are the basis of the breeder re-
actor, which produces more fuel in the form of^239 Pu or^233 U than it uses up in the form of^235 U.
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