تحليل حادثه تزريق راكتيويته در فرآيند پرتودهي هدف هاي توليد موليبدن در راكتور تحقيقاتي تهران

Reactivity inser‎tion , Molybdenum99 , Reactivity induced accident , Pool type research reactor , Material Testing Reactor , MTR , Tehran Research Reactor (TRR)

Analysis of reactivity induced acccident in the irradiation process of molybdenum production targets in Tehran research reactor

مهندسي هسته‌اي

Abstract widely used radioactive isotopes in nuclear medicine, playing a crucial role in imaging an‎d disease diagnosis. Given the growing development of nuclear medicine in Iran, the production of molybdenum-99 is of significant importance. One of the primary methods for producing this isotope is through the fission process an‎d irradiation of uranium targets with different compositions an‎d enrichments in research reactors. This process requires a thorough safety assessment Molybdenum-99, as the precursor of technetium-99m, is one of the most under steady-state, transient, an‎d accident conditions. The objective of this thesis is to analyze one of the most critical an‎d probable accidents occurring during the loading an‎d unloading of irradiation targets inside irradiation boxes within the core of the Tehran Research Reactor (TRR). In this study, the irradiation process of molybdenum production targets in the TRR is analyzed using the MCNP an‎d PARET/ANL computational codes. To achieve this, a precise modeling of the reactor core is performed based on the Safety Analysis Report (SAR) of the TRR, an‎d the accuracy of the modeling is validated by comparing the results with reliable reference data. Once the computational models are verified, two target designs with different dimensions—ten-plate targets an‎d single-plate targets—are considered at various core positions, including the central an‎d peripheral locations. The reactivity worth of these targets is then calculated using the MCNP code. The ten-plate targets offer a higher molybdenum-99 production capacity, while the single-plate targets, due to their simpler structure, are selec‎ted for performance comparison under different reactor conditions. The MCNP simulation results indicate that the target design an‎d its placement within the core significantly affect the effective multiplication factor (k_eff) an‎d the reactivity worth of the target. Given the high reactivity worth of the molybdenum production targets, it is crucial to analyze the reactivity inser‎tion accident resulting from the sudden introduction of these targets into the core an‎d assess the reactorʹs safety in such an event. To eva‎luate the safety of the TRR core during the reactivity inser‎tion accident caused by the introduction of molybdenum production targets, the PARET/ANL code is employed. This analysis examines the temperature variations in the fuel, cladding, an‎d coolant under accident conditions for different target loadings an‎d reactor power levels. The results demonstrate that the number an‎d location of the targets significantly impact the thermal-hydraulic parameters an‎d core safety. In particular, the ten-plate targets, due to their high reactivity worth, require careful management to prevent potential accidents an‎d excessive temperature rises in the fuel an‎d cladding, despite their higher molybdenum production capability compared to single-plate targets. This research, by presenting detailed results in the form of tables an‎d graphs, contributes to enhancing the safety of the irradiation process of molybdenum production targets in the Tehran Research Reactor. Keywords: Reactivity inser‎tion, Molybdenum99, Reactivity induced accident, Pool type research reactor, Material Testing Reactor, MTR, Tehran Research Reactor (TRR).

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