Characterization of irradiated fuel at triga puspati research reactor

Abstract

The TRIGA PUSPATI reactor is a custom model research reactor that allows storage of the irradiated fuel in the reactor tank, at the out-core. The fuel storage rack is positioned 1 m from the core, in the same vicinity of the reactor tank. In order to create a fuel-specific blueprint that validates the fuel type for safeguards and fuel characterization purposes, this study was undertaken to assess two fuel elements which were stored at the fuel storage rack. To achieve this objective, the study was divided into three main parts. The first part was focused on the assessment of neutron flux in the core using MCNP code. Profiles of fast neutrons and thermal neutrons were plotted and it was observed that thermal neutrons were fully thermalized at 158 cm with maximum flux of 1 × 1012 n.cm?2.s?1. As for the fast neutrons, the maximum flux occurred at the central thimble with the value of 5 × 1013 n.cm?2.s?1 and travelled 70 cm before became fully thermalized at the distance of 158 cm from the core. The second part, ORIGEN calculation code was used and data pertaining to radionuclide composition, energy of each radionuclide and burn up were obtained. The result of the calculation was series of photon energy emission rate in 18 energy groups as a function of irradiation or decay time and a summary table listing the principal nuclide contributors to each of the 18 energy groups. The data base produced was the fission products that were produced from spontaneous fission, and bremsstrahlung. The third part, the underwater autoradiography technique had been used in these experiments. The autoradiography analysis required a new and special-designed underwater gamma scanner rig to be developed. The underwater gamma scanner consisted of four main units; the arm block, the collimator, the stand and the main structure while the control system comprised electro-pneumatic system and control lifting system. The design of the scanner took into account conditions in the reactor pool and safety matters to avoid any incident or accident during the operation. The main results of this experiment were radiographic film images that had different brightness according to the type of wt% 235U of irradiated fuel. The 3D pixel view showed the presence of AgBr in the control sample while the pixel of the film exposed to uranium 8.5 wt% fuel indicated that most of the AgBr reduced to silver build up in the film. Changes in 3D pixel view profiles analyzed for 12 wt% 235U fuel exposure showed serious effects on photon impact on film. The effect of the blockade caused the pixel value to decrease by almost 29.3 % compared to the pixel value of the control sample and this made the resulting film darker than all analyzed samples. The film's gray value for exposure to 8.5 wt% 235U was 128 compared to 78 for 12 wt% of fuel. Overall, when a specific fuel image was mapped with neutron-character data, then a blueprint that outlines the type and the characterization of irradiated fuel was established.