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2. Cleaning up the damaged reactor The Chernobyl accident was the result high level and fuel elements ruptured. A
vessel and core required more than of a combination of a poorly engineered steam explosion moved the reactor cap,
10 years to cut it up, pack it into canis- reactor design, poorly trained reactor oper- exposing individual fuel channels and
ters, and ship everything to the Federal ators, and serious mistakes made by the releasing fission products to the environ-
Nuclear Reservation at Idaho Falls. operators on the day of the accident. ment. A second steam explosion knocked a
3. The cost of the cleanup was more than The reactor design was flawed because hole in the roof, exposing more of the reac-
$1 billion. at low power, steam tended to form pockets tor core, and the graphite, which served as a
in the water-filled fuel channels, creating a moderator, burst into flames. The graphite
4. Changes have been made at other
nuclear power plants as a consequence: condition of instability. Instability occurred burned for 9 days, releasing about 324 mil-
18
Pressure relief valves have been because (1) steam is not as efficient at cool- lion Ci (12 × 10 Bq) into the environment.
removed; operators can no longer turn ing as is liquid water and (2) liquid water The fiery release of radioactivity was
off the emergency cooling system; and, acts as a moderator and neutron absorber finally stopped by using a helicopter to drop
operators must now spend about one- while steam does not. Excess steam there- sand, boron, lead, and other materials onto
fourth of their time in training. fore leads to overheating and increased the burning graphite reactor. After the fire
power generation. Increased power can lead was out, the remains of the reactor were
to increased steam generation, which leads covered with a large concrete shelter.
CHERNOBYL to further increases in power. This coupled In addition to destroying the reac-
The Soviet-designed Chernobyl reactor was response is very difficult to control because tor, the accident killed 30 people, with 28
a pressurized water reactor with individual it feeds itself. of these dying from radiation exposure.
fuel channels, which is very different from On April 25, 1986, the operators of Another 134 people were treated for acute
the pressurized water reactors used in the Chernobyl unit 4 started a test to find out radiation poisoning, and all recovered from
United States. The Chernobyl reactor was how long the turbines would spin and sup- the immediate effects.
constructed with each fuel assembly in an ply power following the loss of electrical Cleanup crews over the next year
individual pressure tube with circulating power. The operators disabled the automatic received about 10 rem (100 millisieverts)
pressurized water. This heated water was shutdown mechanisms and then started the to 25 rem (250 millisieverts), and some
circulated to a steam separator, and the steam test early on April 26, 1986. The plan was to received as much as 50 rem (500 mil-
was directed to turbines, which turned a stabilize the reactor at 1,000 MW, but an error lisieverts). In addition to this direct expo-
generator to produce electricity. Graphite was made; the power fell to about 30 MW, sure, large expanses of Belarus, Ukraine,
blocks surrounded the pressure tubes, serving and pockets of steam became a problem. and Russia were contaminated by radio-
as moderators to slow the neutrons involved Operators tried to increase the power by active fallout from the reactor fire. Hundreds
in the chain reaction. The graphite was cooled removing all the control rods. At 1 a.m., they of thousands of people have been resettled
by a mixture of helium and nitrogen. The were able to stabilize the reactor at 200 MW. into less contaminated areas. The World
reactor core was located in a concrete bunker Then instability returned, and the operators Health Organization and other interna-
that acted as a radiation shield. The top part were making continuous adjustments to tional agencies have studied the data to
was a steel cap and shield that supported the maintain a constant power. They reduced understand the impact of radiation-related
fuel assemblies. There were no containment the feedwater to maintain steam pressure, disease. These studies do confirm a rising
buildings around the Soviet reactors as there and this created even more steam voids in incidence of thyroid cancer but no increases
are in the United States. the fuel channels. Power surged to a very in leukemia so far.

point in the Sun’s life—with about 5 billion years to go—the core The fusion process would seem to be a desirable energy
is now 35 percent hydrogen and 65 percent helium. Through source on earth because (1) two isotopes of hydrogen, deuterium
2 3
fusion, the Sun converts about 650 million tons of hydrogen ( H) and tritium ( H), undergo fusion at a relatively low tem-
1 1
to 645 million tons of helium every second. The other roughly perature; (2) the supply of deuterium is practically unlimited,
5 million tons of matter are converted into energy. Even at this with each gallon of seawater containing about a teaspoonful of
rate, the Sun has enough hydrogen to continue the process for heavy water; and (3) enormous amounts of energy are released
an estimated 5 billion years. There are several fusion reactions with no radioactive by-products.
that take place between hydrogen and helium isotopes, includ- The oceans contain enough deuterium to generate electric-
ing the following: ity for the entire world for millions of years, and tritium can be
constantly produced by a fusion device. Researchers know what
1 1 2 0
H + H → H + e needs to be done to tap this tremendous energy source. The
1
1
1
1
2 2 3 0 problem is how to do it in an economical, continuous energy-
H + H → H + n
1
1
1
2
producing fusion reactor. The problem, one of the most difficult
3 3 4 1
He + He → He + 2 H engineering tasks ever attempted, lies in meeting three basic
2
1
2
2
13-21 CHAPTER 13 Nuclear Reactions 343