CORROSION THEORY
DOE-HDBK-1015/1-93
Corrosion
CH-02
Rev. 0
Page 2
Corrosion of the nuclear fuel cladding may cause the cladding to become brittle and less
ductile. The swelling from the generation of fission gases within the fuel may then cause
the cladding to crack or blister, and highly radioactive fission products may then be
released to the coolant.
Some of the metallic oxide corrosion products released to the coolant may be deposited
on surfaces in the reactor core. The neutron flux in the core produces nuclear reactions
in the corrosion products, and they become highly radioactive. Subsequently, these
activated corrosion products may be released from the core and redeposited on surfaces
outside the core region. The radiation fields resulting from this redeposited material may
then significantly increase radiation levels, thereby complicating maintenance and access
capabilities. The corrosion product oxides may also result in fouling of heat transfer
surfaces and in the accelerated wear of moving parts by corrosion products trapped in
or between them.
Current is the flow of electrons through a medium. An electric current can flow through a metal
conductor, and the metal will not show any obvious chemical changes. This type of conduction
of electricity is called metallic conduction.
Ionization is the process of adding electrons to or removing electrons from atoms or molecules,
creating ions. High temperatures, electrical discharges, and nuclear radiation can cause
ionization. Many metals have a tendency to lose electrons to atoms or ions that have a tendency
to gain electrons. Current can be conducted by the movement of these ions. The compounds
that conduct electric current by ion movement are called electrolytes, and this ionic motion is call
electrolytic conduction. Conductivity is a measure of the ability of a substance to allow electron
flow. In the context of corrosion, conductivity indicates the amount of ions in solution, which
relates directly to the potential of corrosion taking place.
Corrosion is the deterioration of a material due to interaction with its environment. Corrosion
can have many forms, both wet and dry. Electrolysis is the decomposition by electric current
(in the context of corrosion the use of electrical current to bring about chemical change). This
chapter will concentrate on the corrosion of metals in water-based environments (electrolytes).
An electrolyte is defined as an electricity-conducting fluid; that is, it has positive and negative
ions that can move and constitute an electrical current. Pure water has a limited number of
dissociated H and OH ions and is a relatively poor conductor of electricity. Addition of acids,
+
-
bases, or salts that dissociate into ions increases the current-carrying capability of the water
(electrolyte).
