Comparison of the effects of cadmium-shielded and boron carbide-shielded irradiation channel of the Ghana Research Reactor-1

Abstract

The MCNP model for the Ghana Research Reactor-1 (GHARR-1) was redesigned to incorporate cadmium-shielded irradiation channel as well as boron carbide-shielded channel in one of the outer irradiation channels. Further investigations were made after initial work in the cadmium-shielded channel to consider the boron carbide-shielded channel and both results were compared to determine the best material for the shielded channel. Before arriving at the final design of only one shielded outer irradiation channel extensive investigations were made into several other possible designs; as all the other designs that were considered did not give desirable results of neutronic performance. The concept of redesigning a new MCNP model which has a shielded channel is to equip GHARR-1 with the means of performing efficient epithermal neutron activation analysis. The use of epithermal neutron activation analysis can be very useful in many experiments and projects (e.g. it can be used to determine uranium and thorium in sediment samples). After the simulation, a comparison of the results from the boron carbide-shielded channel model for the GHARR-1 and the epicadmium-shielded channel was made. The inner irradiation channels of the two designs recorded peak values of approximately 1.18 × 10 12 ± 0.0036 n/cm 2 s, 1.32 × 10 12 ± 0.0036 n/cm 2 s and 2.71 × 10 11 ± 0.0071 n/cm 2 s for the thermal, epithermal and fast neutron flux, respectively. Likewise the outer irradiation channels of the two designs recorded peak values of approximately 7.36 × 10 11 ± 0.0042 n/cm 2 s, 2.53 × 10 11 ± 0.0074 n/cm 2 s and 4.73 × 10 10 ± 0.0162 n/cm 2 s for the thermal, epithermal and fast neutron flux, respectively. The epicadmium design recorded a peak thermal flux of 7.08 × 10 11 ± 0.0033 n/cm 2 s and an epithermal flux of 2.09 × 10 11 ± 0.006 n/cm 2 s in the irradiation channel where the shield was installed. Also, the boron carbide design recorded no peak thermal flux but an epithermal flux of 1.18 × 10 11 ± 0.0079 n/cm 2 s in the irradiation channel where the shield was installed. The final multiplication factor ( k eff) of the boron carbide-shielded channel model for the GHARR-1 was recorded as 1.00282 ± 0.0007 while that of the epicadmium designed model was recorded as 1.00332 ± 0.0007. Also, a final prompt neutron lifetime of 1.5237 × 10 −4 ± 0.0008 s was recorded for the cadmium designed model while a value of 1.5245 × 10 −4 ± 0.0008 s was recorded for the boron carbide-shielded design of the GHARR-1.