atw - International Journal for Nuclear Power | 02.2020

atw Vol. 65 (2020) | Issue 2 ı February
| Fig. 3.
Effect of wood as a 2 nd reflector to copper on thermal neutron albedo.
| Fig. 4.
Effect of aluminum as a 2 nd reflector to copper on thermal neutron albedo.
RESEARCH AND INNOVATION 107
| Fig. 5.
Effect of paraffin as a 2 nd reflector to wood on thermal neutron albedo.
| Fig. 6.
Effect of iron as a 2 nd reflector to paraffin on thermal neutron albedo.
the combination of the hardwood is
chosen as 50.2 % carbon, 6.2 %
hydrogen, 43.5 % oxygen, and 0.1 %
nitrogen [9]. The paraffin reflection
coefficient has been measured
0.73 ± 0.01 that is comparable to the
value listed in the literature (0.83)
[10].
The reflection coefficient (albedo)
for wood has been found 4.8 % less
than the paraffin. The albedo for
different reflectors first increased
exponentially then reached to the
saturation value. The maximum
reflection coefficient (albedo) for
monolithic wood has been measured
0.699 ± 0.003, which is comparable
able to analytical simulated value
0.71.
The situation value for neutron
reflection coefficient (albedo) for
copper has been measured 0.12 ±
0.001, which is comparable to value
0.11 reported by Doty, D. R. [11].
Whereas the saturation value of the
reflection coefficient for aluminum
has been measured to 0.27 ± 0.001.
Since the copper has a higher cross
section (Σs = 0.6709 cm-1) compare
to aluminum (Σs = 0.08976 cm-1)
therefore the copper albedo curve
is little steeper as compared to
aluminum. The experimental and
analytical simulated results for
paraffin, wood, aluminum, and
copper are depicted in Figure 2.
In order to see the effect of the 2 nd
layer in neutron reflection coefficient
combinations of different reflectors
has been used. The 2 nd reflector has
been introduced after the saturation
thickness of the first reflector. The
effect of wood as a 2 nd reflector to
copper is depicted in Figure 3. As
predicted the reflection of neutron
increased abruptly as the wood is
added as a 2 nd reflector. The saturation
from copper has been received
at 5 cm of thickness. Addition of
wood as a 2 nd reflector at this point
showed an exponential increase in
reflection coefficient. this is because
of the less scattering correction of
copper and higher scattering crosssection
of wood. Similar behavior
has been seen in analytical simulated
results.
Theoretically, the 2 nd layer with
higher reflection and diffusion
coefficient contributes in increasing
the reflection coefficient. Glasstone
and Edlund [12] derived the
thermal neutron albedo as a function
of 2D/L.
Similarly, aluminum as a 2 nd reflector
plays the same role when added
after cooper saturation thickness. An
increment with a slope of 1.0 × 10 -4
has been observed with aluminum
as a 2 nd reflector. A similar slope has
also been reported by Doty, D. R. [11]
in his experimental study with the
increase in aluminum thickness. The
effect of aluminum as a 2 nd reflector to
copper is depicted in Figure 4. The
experiment results have been found
inconsistent with the analytical
simulated results.
If the 2 nd reflector has nearly the
same reflection coefficient as that for
1 st reflector then no significant effect
has been seen to total reflection coefficient.
This effect has been observed by
introducing the paraffin as the 2 nd
reflector to wood. Since the wood
and paraffin nearly have the same
saturation reflection coefficients and
for both reflectors, the 2D/L value is
almost similar. Therefore, no significant
effect has been observed for
paraffin as the 2 nd reflector to wood.
The effect of paraffin as a 2 nd reflector
to wood is depicted in Figure 5.
Research and Innovation
Experimental Study of Thermal Neutron Reflection Coefficient for two-layered Reflectors ı Khurram Mehboob