RRFM 2009 Transactions - European Nuclear Society

MCNP Simulation of Permanent Cd-lined Irradiation Channel for
Improved Utilization of Commercial MNSR Facilities
S.A. Jonah!, U. Sadiq 2 , S. Hankourou 3 , Y. A. Ahmed 1
1 Reactor Engineering Section, Centre for Energy Research and Training, Ahmadu Bello
University, Zaria, Nigeria
2 Department of Physics, Ahmadu Bello University, Zaria, Nigeria
3 Department of Physics, Gombe State University, Gombe, Nigeria
Abstract:
The Nigeria MNSR (NIRR-1) is one of the commercial MNSR facilities installed outside
China. NIRR-1 was critical in 2004 and has been standardized for routine elemental
analysis via the relative NAA method and the k0-INAA technique. In order to eliminate
exposure to radiation dose from movable shields and perform activation within a
permanently fixed Cd shield, a conceptual permanent Cd lined inside a large outer
irradiation of NIRR-1 was simulated using Monte Carlo transport code, MCNP5 version
1.40. Results of neutronics analysis show that the effect of installation of the Cd- liner in
the outer irradiation channels on core excess reactivity is less than 0.5 mk and the
uniformity of neutron flux in the co-axially arranged irradiation channels is preserved.
Data of simulated neutron energy spectrum in the channel with and without the Cd liner
are presented.
Furthermore, results of calculated data of Cd-ratios together with advantage factors for
the determination of I, Br, C and K in one of the outer irradiation channels of NIRR-1 in
geological samples are presented.
Introduction
Miniature Neutron Source Reactors (MNSRs) are compact low-power nuclear research
reactors designed and manufactured by the China Institute of Atomic Energy (CIAE),
Beijing, China. The seven commercial MNSR and the prototype currently operational in
the world are fueled with highly enriched uranium (HEU). Unlike the commercial
versions, the prototype MNSR is equipped with a permanent Cd-lined irradiation channel
(Hou et al., 1996). The Nigeria MNSR is code-named Nigeria Research Reactor-1
(NIRR-1). NIRR-1 has a tank-in-pool structural configuration and a nominal thermal
power rating of 31 kW. With a built-in clean cold core excess reactivity of 3.77 mk
measured during the on-site zero-power and criticality experiments, the reactor can
operate for a maximum of 4.5 hours at full power (i.e. equivalent to a thermal neutron
flux of 1x10 12 n.cm -2 .s -1 in the inner irradiation channels). NIRR-1 has been standardized
for routine NAA via relative and the k0-standardiation methods (Jonah et al. 2005; 2006;
2009) Like all MNSR facilities, NIRR-1 is specifically designed for use in neutron
activation analysis (NAA) but does not have provision for epithermal neutron activation
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