Plant Materials
DOE-HDBK-1017/2-93
CLADDING AND REFLECTORS
CLADDING AND REFLECTORS
Nuclear fuels require surface protection to retain fission products and minimize
corrosion. Also, pelletized fuel requires a tubular container to hold the pellets in
the required physical configuration. The requirements for cladding material to
serve these different purposes will vary with the type of reactor; however, some
general characteristics can be noted. This chapter will discuss the general
characteristics associated with cladding and reflectors.
EO 1.5
STATE the four major characteristics necessary in a material used
for fuel cladding.
EO 1.6
IDENTIFY the four materials suitable for use as fuel cladding
material and their applications.
EO 1.7
STATE the purpose of a reflector.
EO 1.8
LIST the five essential requirements for reflector material in a
thermal reactor.
Cladding
Cladding is used to provide surface protection for retaining fission products and minimizing
corrosion. Cladding is also used to contain pelletized fuel to provide the required physical
configuration.
Mechanical properties, such as ductility, impact strength, tensile strength, and creep, must be
adequate for the operating conditions of the reactor core. Ease of fabrication is also important.
It is desirable that ordinary fabrication procedures be applicable in fabricating the desired shape.
The cladding must have a high corrosion resistance to its operating environment. It must have
a high melting temperature to withstand abnormal operating conditions such as high temperature
transients. Thermal conductivity should be high to minimize thermal stresses arising from
temperature differences, and the coefficient of expansion should be low or well-matched with that
of other materials. The cladding material should not be susceptible to radiation damage.
The nuclear properties of fuel cladding material must also be satisfactory. For thermal reactors,
it is important that the material have a reasonably small absorption cross section for neutrons.
Only four elements and their alloys have low thermal-neutron absorption cross sections and
reasonably high melting points: aluminum, beryllium, magnesium, and zirconium. Of these,
aluminum, magnesium, and zirconium are or have been utilized in fuel-element cladding.
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