IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
experimental analysis of
detection and quantification of
corrosion in mild steel by
gamma ray scattering the
Monte Carlo simulations have
been done by using the Monte
Carlo N- Particle (MCNP) code,
which takes into account the
detailed characteristics of the
source, detector and the
scatterer in calculating the
gamma scattered intensity from
the MS plates. The result of
MCNP PHS simulations and
their comparison with the
experimental ones are shown in
Fig. 6 for the normal MS plate
and in Fig. 7 for the corroded
one. A good agreement in the
shape of the PHS is seen
between the experimental
spectra and MC simulated
ones.
Fig.6 The scattered PHS and its
comparison with MCNP simulated
one for normal MS plate
Fig.7 The scattered PHS and its
comparison with MCNP simulated
one for corroded MS plate
Table1. Density of MS corroded plate (kg/ m3) reconstructed from the
experimental and MCNP simulated gamma scattered intensities and the average
density value obtained by weight and volume measurements
A methodology to reconstruct
the densities of the corroded
regions of the MS plate directly
from the scattered intensities is
developed and implemented. In
this method the density, ρ of the
specimen need not be known
and only the knowledge of the
target material's mass
attenuation coefficients, µ/ ρ
and µ'/ ρ is sufficient to correct
for absorption of incident and
scattered radiation. These mass
attenuation coefficients are
independent of the physical
state of the matter (independent
of density) and the knowledge
of composition of the material
is sufficient for reconstruction.
The experimental and MCNP
reconstructed densities from a
typical voxel of the corroded
MS plate are given in Table 1
along with the average density
value obtained by weighing the
MS plate in a weighing balance
and estimating its volume by
fluid displacement method.
From the Table 1 it can be seen
that a good agreement is seen
between the experimental
values, MCNP calculations and
average density value within
estimated errors.
The measured gamma
scattered photo peak intensity
from corroded MS plate
decreases up to 6.46%
compared to a normal MS plate
and this corresponds to an
average density loss of 0.416 x
10 3 kg/ m 3 (5.24%) due to
corrosion in a MS plate of size
235 x 155 x 10 mm. This
amount of metal loss due to
corrosion has been detected
and quantified in the present
study. The experimental and
MC results show that the
scattering method is highly
sensitive to changes in
electronic and physical
densities of the voxel under
study and the magnitude of
corrosion can be clearly
identified and quantified by
monitoring single scattered
events.
96 FUEL CYCLE