Study on a new design of Tehran Research Reactor for radionuclide production based on fast neutrons using MCNPX code
Introduction
Most radionuclides are produced by exposing suitable target materials to the neutron flux in a nuclear reactor for an appropriate time. Thermal neutron capture nuclear reactions are currently used for major radionuclide production. Thermal neutrons are those which are in thermal equilibrium with molecules/atoms of the surrounding medium (Manual for reactor produced radioisotopes, 2003). One of the most important factors for radionuclide production is a neutron flux intensity which should be optimized by considering special places within the reactor core or its surrounding (Mele, 1990).
Tehran research reactor (TRR) is commonly used to produce radionuclides via thermal neutrons (Aboudzadeh et al., 2015, Khalafi and Gharib, 2005, Deilami-nezhad et al., 2016). But it is noteworthy to mention that, production of some radionuclides such as 64Cu and 67Cu requires as large fast neutron flux as possible owing to their energy thresholds (Johnsen et al., 2015). In the case of being thermal reactor, it is not easily accessible to produce medical radionuclide via fast neutrons by considering the traditional design of the flux trap which contains only water that normally increases thermal to fast neutron flux ratio. So, some considerations should be taken and some new design should be introduced to produce efficiently.
In this study, some new design was taken to improve fast neutron flux in the central flux trap to produce medical radionuclides as high as possible in the TRR. Accordingly, MCNPX code (MCNPX User'’s manual, 2002) was employed for both benchmarking and simulating the reactor core and then was used to design the proposed different flux trap for reaching to the best results. For this purpose, this paper is organized in 5 sections: In the second section, descriptions of TRR are presented briefly. In the third section, simulation of the reactor core and benchmarking of the obtained results against experimental measurements are carried out. The new proposed designing of the flux trap along with the calculated results, including thermal and fast neutron fluxes have been presented in the section four. Eventually, the fifth section gives the conclusion.
Section snippets
Description of Tehran Research Reactor
Tehran Research Reactor is the only facility for reactor-based production of radionuclides which is needed for the extensive usage in all hospitals and medical centers in the country. This reactor is a 5 MW pool-type light-water moderated, heterogeneous solid fuel reactor in which the water is also used for cooling and shielding (AEOI, 1989, AEOI, 2001). Its core configuration consists of MTR-type fuel elements which are inserted in the specific grid plate assemblies (Khalafi and Gharib, 2005,
Validation and benchmarking
In this section of the study, validation of simulation has been presented. On this basis, the first operating core of TRR was modelled and the results were compared with experimental measurements (Zaker, 2004). Table 1 reflects the comparison between the obtained results and the experimental measurements.
Regarding Table 1, the calculated Relative Percent Errors (RPE) which can be defined as Eq. (1), are below 9% and consequently the validation of the results can be confirmed (Lashkari et al.,
Procedure of new design
In order to design the flux trap and perform the corresponding calculations and simulations, first it is necessary to consider an operational core. On this basis, the core which is shown in Fig. 1 has been considered (Khalafi and Gharib, 1999).
As shown in the Fig. 1, the core configuration includes 22 SFEs and 4 CFEs and one Regulating Rod (RR). The core simulation was also carried out using MCNPX code regarding Table 2 as the required input data.
Prior to applying the new design of the flux
Conclusion
This paper deals with the development and enhancement of the Tehran Research Reactor for production of radionuclides based on the fast neutron flux using MCNPX code. For this purpose, some new designs were proposed both in terms of reducing the fast neutron moderation and increasing the fast neutron production. The first and second designs were comprised of a sealed cube contained air and D2O instead of ordinary water (H2O) to reduce the moderation of fast neutrons. Consequently, the production
Acknowledgements
This project was performed based on the IAEA coordinated research project (contract 21021) and the authors would like to express their gratitude to Nuclear Science and Technology Research Institute which sponsored the project under the scholarship program. The authors also would like to thank the IAEA for suggesting and supporting this research.
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