Abstract:
The biological shield of a nuclear reactor is required
to attenuate both neutrons and gamma rays from the reactor
core. Generally, materials having high densities are used as
bio 1ogica1 shie1d materia1s in a nuc lear reactor. Concrete
has been widely used as shielding materials due to its
satisfactory material strength and good shielding
properties. The density of conventional ordinary concrete is
not adequate for.a biologiGal shield in a nU,clear reaGtor.
Types of concrete possessing high density, should be
developed in order to attenuate both neutron and gamma
radiation emitted from the nuclear reactor. The heavy
aggregates such as barite, magnetite, ilmenite, limonite
etc. have been widely used for preparing a high dens~ty
concrete for-biological shield in a nuclear reactor. While
fabricating the high density concretes, due consideration
should be given to the local availability of the aggregates.
Since the magnetite and ilmenite aggregates are available as
-by products in the beach sand processing pilot plant at
Cox's Bazar of the Bangladesh Atomic Energy Commission, this
work was undertaken to design and fabricate high density
concrete shields indigenously with the objective of avoiding
costly imports and also to develop -local know how.
In this study, high density concrete with and without
boron additives using ilmenite and magnetite sand have been
studied. For comparison, ordinary concrete with and without
boron additives have also been studied. In addition, mixed
conc~ete used in the biologic~l shield of 3 MW TRIGA Mark-II
research reactor of the Bangladesh Atomic Energy Commission
has been studied with and without bo~on additives for
comparison with the other three types of concretes with and
wihtout boron additives. The density, compressive strength,
modulus of elasticity and splitting strength were measured
for these concretes. The densities of ilmenite and magnetite
concretes are found considerably higher than that of
ordinary concrete.
The nuclear parameters such as attenuation coefficient,
removal cross section, half value thickness, and relaxation
length, which are of interest for reactor shielding have
been evaluated for these concretes with a spontaneous
fission source (252Cf). The investigation concerning the
attenuation properties reveals that the shielding properties
of boron loaded heavy concretes are better than those of
ordinary concretes and slightly better than those of heavy
concretes without boron additives.
