本研究的目的乃在探討各種核燃料退出，例如全爐退出(Full Core Unload)，暫存於用過燃料池(Spent Fuel Pool)內時，用過燃料池對於核燃料所釋放出來的衰變熱(Decay heat)是否有能力移除之。為了分析用過燃料池內部即時的熱流場，本研究引用計算流體力學(Computational fluid dynamics ，簡稱CFD)方法，發展對貯存池本身的熱流分析技術，並建立貯存池之幾何數學模型，且利用多孔性的模擬技巧(Porous medium)的技術來模擬實際眾多數目的燃料束，以達成最佳化的數值模擬工作；用過燃料池液面與空氣間的熱傳與質傳現象，採用等效熱傳係數(Effective heat transfer coefficient)的技巧簡化處理之。由於本研究新建立了雙相流數值方法，因此配合COBRA數值軟體驗證雙相流模式的精準度。在雙相流模式中，雖然CFD尚無燃料加熱模式與壓力效應，但經由鄰近熱牆流體推算與合理的推演，可以發覺與COBRA模擬出來的數據相近。因此證實數值軟體CFD對於本研究有相當的準確度。應用於用過燃料池的模擬中，我們發現基於審查規範中，除了正常大修時的用過燃料池符合法規外。其他事故發生時，若未輔以冷卻系統，則燃料池會產生沸騰現象。若改變燃料的排列方式時，雖然對於燃料池內部均溫性與相變化的程度有一定程度的影響，但效果並不顯著。由此突顯用過燃料池移熱能力再嚴重異常狀況下不足的問題，因此需要搭配強制對流或啟動冷卻系統等方式加以改善。

The objective of this research effort is to study the cool ability of spent fuel pool under various unload scenarios. For example, during full core unload, the fuel rods temporarily stored in the spent fuel pool, it is important to determine whether has proper capability to remove the decay heat. In this research study, we apply CFD (Computational Fluid Dynamics) methodology to develop tool for spent fuel pool thermal hydraulic analysis. The mathematical model, which includes the physical geometry dimension, is established. The large number of fuel rod bundles is approximated with porous media that will impose similar flow resistance to the motion of the fluid. Such treatment enables us to have optimum computational efficiency while maintaining high degree of accuracy of the pool flow behavior. The heat and mass transfer on the air/liquid interface is modeled by using effective heat transfer coefficient. When the power density of the fuel rods exceeds certain criteria, boiling and phase change is possible. A homogeneous two-phase model is implemented. In order to verify the accuracy of the present two-phase model, the result is compared with that computed by COBRA code. It is found that our model has close agreement with the prediction of the COBRA simulations. We conclude that the current model is suitable for the modeling of spent fuel pool thermal hydraulic process. In the case study, we found the current spent fuel pool can meet the requirements of the regulation when it is under the normal operation configurations. However, when the event is beyond the scope of the regulation, it may lead to local boiling if there is no external cooling system included. The temperature distribution and cooling situation could be improved via the layout of the fuel but this effect is limited when abnormals happened. Once those unlikely situations occur in the pool, we may have to start the cooling system for efficient cooling.

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