Power Generation - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 208

efficients of reactivity that prevent such runaway accidents. The Chernob-
yl plant would not have been issued a license to operate in the U.S. or
other Western countries.
The Chernobyl accident was in many ways the worse possible sce-
nario having an exposed reactor core and roofless building. Two plant
workers died from the blast and fire, 22 other plant workers and 6 fire-
fighters received huge radiation doses and died within months.
A toxic gas disaster occurred when 2,300 were killed and 200,000
others injured in a few hours when the gas escaped from the Union Car-
bide pesticide plant in Bhopal, India.
RADIOACTIVITY
When uranium undergoes fission, the uranium atoms split and re-
lease neutrons. Some of these neutrons split other uranium atoms, which
produce radioactive waste products. The net result of the fission process
is the generation of intense heat which is used to generate steam for the
generators. A nuclear reactor and a nuclear weapon both release a num-
ber of neutrons during the fission process over a given period of time.
If the number of neutrons are limited for triggering the fission chain-re-
action, the reaction can be controlled for producing energy. If too many
neutrons are released, the chain-reaction will accelerate, resulting in an
explosion. To prevent this from happening, nuclear reactors use control
rods and water circulation to regulate the fission process by absorbing the
extra neutrons. However, some of these neutrons will move into the steel
structures which hold the fuel assemblies and the cooling water which
flows between them. Other neutrons may penetrate the concrete shielding
outside the steel reactor vessel. These neutrons are absorbed by the atoms
of iron, nickel and other elements that they pass through.
When atoms absorb neutrons, they become unstable and release par-
ticles making them radioactive for differing lengths of time. A material
like nickel-59 has a half-life of 80,000 years, it needs to be shielded for
about a million years.
Reactor fuel consists of uranium that has been formed into a usable
metal alloy and provided as small pellets, rods, or plates. The fuel is en-
capsulated with a metal cladding, such as zircaloy, which adds mechani-
cal strength and also prevents radioactive contamination. Nuclear reactor
waste or spent nuclear fuel consists of the fuel pellets that have been used