- 學位論文
核一廠與核四廠之預見暫態未急停事故分析
A Study on Anticipated Transient Without Scram Accident Analysis for Chin-Shan and Lung-Men Nuclear Power Stations
摘要
摘要 核子反應爐無論於設計、建造及運轉上對安全上之要求如何周詳與嚴格，但仍不能完全排除核子意外事故發生之可能性。三哩島事故發生之後，核能界開始進行深入之嚴重事故研究，以了解嚴重事故現象，並發展分析程式，以增進嚴重事故之分析能力。而於嚴重事故發生時，則需一套合宜且具整體安全性考慮之指引，來引導運轉員及技術人員以減緩事故之嚴重性甚或將核電廠帶入安全狀態，並檢視其是否得以因應核能電廠嚴重事故，期能增進核能電廠之安全。 本研究係針對金山電廠之沸水式反應爐與龍門電廠之進步型沸水式反應爐，應用已建妥之金山電廠與龍門電廠參數檔，以嚴重核子事故序列分析程式(Modular Accident Analysis Program, MAAP) 4.0.4版本進行穩態(Steady State)模擬，藉以瞭解程式是否能模擬穩態運轉，同時亦可藉由模擬結果獲知參數檔案內各參數是否合宜。 隨後，本研究進行因主蒸汽隔離閥關斷而引發之預見暫態未急停事故 (Anticipated Transient Without Scram, ATWS)之嚴重核子事故分析。研究重點為分析電廠於該事故下爐心、圍阻體及分裂產物等種種之反應。本研究另依核一廠與核四廠之緊急操作程序書(Emergency Operating Procedures, EOPs)，於模擬預見暫態未急停事故中加入運轉員動作之邏輯，隨後，針對事故現象及運轉員所採取之因應措施而導致事故序列變化之差異進行探討，期能了解一旦核子事故發生，緊急操作程序書是否得以應付反應爐及圍阻體內所發生之各類現象。本研究模擬結果顯示，於預見暫態未急停事故中加入運轉員動作邏輯得以使電廠不致持續惡化為嚴重事故且能繼續運轉。由此可見，緊急操作程序書得以能改善甚至避免嚴重事故發生，該項文獻對嚴重事故之預防並萬一發生嚴重事故時得以減緩其嚴重性，此兩項功能具實質貢獻。 此外，於嚴重事故中，爐心功率之移除為另一項安全應變之重點，因此，餘熱移除系統(Residual Heat Removal, RHR)之熱交換器移除爐心功率的能力係屬值得探討之要項。本研究另就依緊急操作程序書而運跑之預見暫態未急停事故，進行餘熱移除系統參數之靈敏度模擬分析，探討餘熱移除系統之熱交換器性能與參數變化之影響。模擬結果顯示，變更Service Water進入之溫度、質量流率及熱交換器之熱傳單位數量等參數設定值，不僅能影響熱交換器完全移除爐心功率之時間，亦可改善抑壓槽及抑壓池之水溫。即餘熱移除系統之熱交換器容量會隨著降低Service Water進入之溫度、增大Service Water之質量流率或增大熱傳單位數量而增加。
並列摘要
Abstract No matter how the nuclear reactors are designed for safety, the accident still occur. After the Three Mile Island accident, the nuclear industry performed a variety of small- and large-scale severe accident research to understand the severe accident phenomena and to develop severe accident analysis code for improving the severe accident sequences prediction capability. Under the severe accident conditions, it is necessary to have realistic emergency operating procedures (EOPs) to pursue an overall evaluation of the conditions for the operators and technical staff to bring the plant to a safe-stable state. Based on the established parameter files of the Chin-Shan and Lung-Men Nuclear Power Stations, the Modular Accident Analysis Program version 4.0.4 (MAAP 4.0.4) was used for steady state evaluation. Performing the steady-state simulations assure the appropriateness of the parameter files used for the MAAP calculations. The purpose of this study is to evaluate the postulated anticipated transient without scram (ATWS) severe accident scenarios for the Chin-Shan and Lung-Men Nuclear Power Stations. In this study, the behaviors of reactor core and containment, and release of fission products were analyzed. Besides, the phenomena associated these scenarios were discussed. Furthermore, the EOPs for the Chin-Shan and Lung-Men Nuclear Power Stations were used. The phenomena associated these scenarios were discussed and the conclusions based on a number of operator actions during the accident were also discussed. In general, EOPs are expected to enhance the safety of reactor during its normal operation and to mitigate the severity of an accident once the accident occurs. The result obtained for the ATWS case with EOPs shows that the operator actions has the potential to bring the plant into a safe-stable state. It is noted that the decay heat is one of the major concerns in the severe accident evaluation. Therefore, the heat exchanger in the residual heat removal (RHR) system plays an important role for the heat removal during ATWS. The base case studied is the ATWS with the EOPs, and sensitivity studies are investigated to understand the performance of heat exchanger using the MAAP code as the evaluation tool. The result shows that the entrance temperature of service water (TWSW), the mass flow rate of service water (WSWHX), and the NTU (number of trandfer unit) of the heat exchanger (NTUHX) have a major impact on the effectiveness of the RHR heat exchanger to remove the heat generated during the ATWS accidents. In other words, the capacity of RHR heat exchanger will increase with a decrease of TWSW, an increase of WSWHX or an increase NTUHX.