VVER REAKTÖRÜNDE TORYUM-URANYUM YAKITLARIN ISIL-HİDROLİK PERFORMANS ANALİZİ
Mercan, Ahmet Kağan
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Today, current nuclear reactors’ future depends on uranium reserves. Researches for materials that can be replaced with uranium or can be used with uranium to obtain similar performances with uranium or better performances than uranium are being done in whole world. Thorium element takes important part in these researches because of creating fissile material. The aim of this thesis is using different concentrated uranium-thorium mixtures in VVER-1000 reactor that is very common in world and calculating thermal performance of these fuels. According to results of these analysis, some accident analysis are examined for the concentration that will give the worst scenario. With this thesis, a basis information is aimed for thorium usage in nuclear reactors. A unit cell is created by using the geometry of VVER-1000 reactor in calculations. Thermal conductivity and heat capacitance were calculated for different concentrated homogenous Th-U mixturesfor fuel that created inside unit cell. Calculated thermal conductivity and heat capacitance parameters were applied to COBRA-TF code and performance of different concentrations was observed. Also performance of fuels were tested with different heat profiles. In addition to this, concentration which showed the worst performance was chosen and 10% decrease of flow, reactivity insertion accidentthat increases and decreases the power by 20% cases were applied. Pump coastdown with reactor shutdown accident at the hottest channel conditionwas also performed. The results show that the highest fuel centerline temperatures are calculated for concentration that includes %40 Th w/o percent, which is 1190 K for average channel conditions and cosine heat skew. Calculated fuel centerline temperature is approximately 103.5 K higher than normal uranium used case. iv When 10% flow decrease case for the sample that includes 40% thorium is observed, about 6 K rise is observed. Positive reactivity insertion to the system leads to increase of the highest fuel centerline temperature by 1367.7 K for thorium and 1184 K for uranium. Negative reactivity insertion case results with approximately 150 K decline of the highest fuel centerline temperature for thorium and about 170 K decline for uranium. In case of pump coastdown with reactor shutdown, the highest fuel centerline temperature increases to 600 K which is 580 for Th included fuel without coastdown for maximum working conditions. According to calculations, if varied concentrated thorium is inserted to the system, system works under limits. System also works under limits when the flow decrease and reactivity insertion accident scenarios exist. In case of pump coastdown at the hottest channel conditions, despite overly decreased flow, system can handle decay heat.