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A Closer Look

Three Mile Island and Chernobyl

hree Mile Island (downriver from reducing the excess pressure that was water. The filters had been removed from
T Harrisburg, Pennsylvania, United States) generated because feedwater was not enter- the auxiliary building air vents, allowing
and Cher nobyl (former U.S.S.R., now ing the steam generator to remove heat radioactive gases to escape.
Ukraine) are two nuclear power plants that from the primary loop. The valve should Eleven minutes after the start of the
became famous because of accidents. Here have closed when the excess pressure was accident, an operator restarted the emer-
is a brief accounting of what happened. released, but it did not. It was stuck in gency core-cooling system that had been
an open position. Pressurized water and turned off. With the cooling water flowing
steam were pouring from the primary loop again, the pressure in the reactor stopped
THREE MILE ISLAND into the containment building. As water falling. The fuel rods, some 36,000 in this
It was March 28, 1979, and the 880- was lost from the primary loop, tempera- reactor, had not yet suffered any appreciable
megawatt Three Mile Island Nuclear Plant, tures inside the reactor began to climb. damage. This would be taken care of by the
operated by Metropolitan Edison Company, The loss of pressure resulted in high - next incredible event.
was going full blast. At 4 a.m., the main temperature water flashing into steam. If The next incredible event was that
feedwater pump that pumps water to the an operator had pressed the right button in operators began turning off the emergency
steam generator failed for some unexplained the control room, it would have closed the cooling pumps, perhaps because they were
reason (follow this description in Figure open valve, but this did not happen until vibrating too much. In any case, with the
13.18). Backup feedwater pumps kicked in, 32 minutes later. pumps off, the water level in the reactor
but the valves that should have been open At this point, the reactor could have fell again, this time uncovering the fuel
were closed for maintenance, blocking the recovered from the events. Two minutes rods. Within minutes, the temperature was
backup source of water for the steam after the initial shutdown, the computer high enough to rupture fuel rods, drop-
generator. All of a sudden, there was not a sensors noted the loss of pressure from the ping radioactive oxides into the bottom of
source of water for the steam generator that open valve and kicked in the emergency the reactor vessel. The operators now had a
removes heat from the primary loop. core-cooling system, which pumps more general emergency.
Events began to happen quickly at this water into the reactor vessel. However, for It was 11 hours later that the operators
point. some unknown reason, the control room decided to start the main reactor coolant
The computer sensors registered that operators shut down one pump 4.5 minutes pump. This pump had shut down at the
the steam generator was not receiving water, after the initial event and the second pump beginning of the series of events. Water
and it began to follow a shutdown procedure. 6 minutes later. again covered the fuel rods, and the pres-
First, the turbine was shut down as steam Water continued to move through the sure and temperature stabilized.
was vented from the steam line out through open pressure relief valve into the con- The consequences of this series of
the turbine building. It sounded much like a tainment building. At 7.5 minutes after events were as follows:
large jet plane. Within 6 seconds, the reac- the accident began, the radioactive water 1. Local residences did receive some
tor was “scrammed,” shut down with control on the floor was 2 feet deep and the sump radiation from the release of gases. They
rods dropped between the fuel rods in the pumps started pumping water into tanks received 10 millirems (0.1 millisievert)
reactor vessel. Fissioning began to slow, but in the auxiliary building. This water would in a low-exposure area and up to
the reactor was still hot. become the source of the radioactivity that 25 millirems (0.25 millisievert) in a
Between 3 and 6 seconds, a pressure did escape the plant. It escaped because the high-exposure area.
relief valve opened on the primary loop, pump seals leaked and spilled radioactive

The technology to dispose of fuel rods exists if the decision radioactive decay by the time they could reach the surface.
is made to do so. The longer half-life waste products are mostly Nonetheless, research is continuing on nuclear waste and its
alpha emitters. These metals could be converted to oxides, disposal. In the meantime, the question of whether it is best to
mixed with powdered glass (or a ceramic), melted, and then reprocess fuel rods or place them in permanent storage remains
poured into stainless steel containers. The solidified canisters unanswered.
would then be buried in a stable geologic depository. The glass
technology is used in France for disposal of high-level wastes.
Buried at 610 to 914 m (2,000 to 3,000 ft) depths in solid granite, NUCLEAR FUSION
the only significant means of the radioactive wastes reaching As the graph of nuclear binding energy versus mass numbers
the surface would be through groundwater dissolving the stain- shows (see Figure 13.13), nuclear energy is released when
less steel, glass, and waste products and then transporting them (1) massive nuclei such as uranium-235 undergo fission and
back to the surface. Many experts believe that if such ground- (2) less massive nuclei come together to form more massive nuclei
water dissolving were to take place, it would require thousands through nuclear fusion. Nuclear fusion is responsible for the
of years. The radioactive isotopes would thus undergo natural energy released by the Sun and other stars. At the present halfway

342 CHAPTER 13 Nuclear Reactions 13-20