CLADDING AND REFLECTORS
The important information in this chapter is summarized below.
Cladding and Reflectors Summary
Major characteristics required for cladding material:
Mechanical properties such as ductility, impact strength, tensile strength, creep,
and ease of fabrication
Physical properties include high corrosion resistance and high melting
High thermal conductivity
Nuclear properties such as small absorption cross section
Four materials suitable for cladding:
Aluminum is used for low power, water-cooled research, training, and materials
test reactors in which temperatures are below 100C.
Magnesium is used for uranium metal fuel in carbon-dioxide cooled, graphite-
moderated power reactors in United Kingdom.
Zirconium is used for fuel-rod cladding in water-cooled power reactors.
Beryllium is suitable for use as cladding but is not used as such due to its high
cost and poor mechanical properties. It is, however, used as a reflector in some
Reflectors are used to return neutrons leaving the reactor core back to the core.
Essential requirements for reflectors include.
Low macroscopic absorption cross section to minimize loss of neutrons
High macroscopic scattering cross section
High logarithmic energy decrement due to low mass number