福島事件發生後，台電發展出一套稱之為「斷然處置措施(Ultimate Response Guidelines, URG)」的緊急處置方法，以因應電廠遭遇類似福事故等超出設計基準的複合式災害，其發展理念為早期洩壓、注水、透過圍阻體排氣移除衰變熱，確保燃料為水掩蓋，並防止燃料棒護套溫度上升超過1500℉，造成放射性物質自燃料棒釋出。在URG中提出了許多指引與新增設備，增加嚴重事故後電廠救援的能力，本論文的目的是將核二廠URG納入一階安全度評估中，將深入探討核二廠URG對爐心熔損頻率(Core Damage Frequency, CDF)的影響。
本論文使用RELAP5-3D模擬電廠全黑(包含高壓灑水系統柴油發電機不可用)事故發生後，有無早期爐心隔離冷卻系統(RCIC)與釋壓閥開啟後有無成功關回對燃料護套尖峰溫度的影響，以及事件樹成功準則的判定。本研究採用核研所發展之核二廠安全度評估模式，使用WinNUPRA3.0建立相關事件樹與故障樹，將可能影響一階安全度評估的URG策略分別量化，以驗證URG是否能有效影響CDF。
評估結果顯示，URG對類似福島二號機的事故序列，改善效果顯著，能將CDF降低兩個數量級。在所模擬的URG策略中，RCIC延長至24小時對一階安全度評估的改善最大，可將其所影響的事故序列之CDF降低53.4%。

Probabilistic Safety Assessment (PSA) is a powerful tool to assess the safety of nuclear power plants (NPP). The purpose of the study is to evaulate the impact of Ultimate Response Guidelines (URGs) on the Level-1 PSA of Kuosheng NPP of Taiwan Power Company.
After the core damage accidient of Fukushima Daiichi Nuclear Power Plant, Ultimate Response Guidelines (URGs) were developed by Taiwan Power Company to help operators mitigating the consequences of events similar to the Fukushima accident. The purpose of URG is to prevent the peak cladding temperature during the accident from rising above 1500℉, which is the imitation temperature of the release of the gap activity. URG is activated in a seismic event, an event of Station Blackout or an event of losing water injection to core. According to URG, the emergency response staff of the plant is required to implement movable or portable A.C. power and alternate water source within a specific time after the motivation of the accident. If the continuous removal of decay heat can not be assured, operators are directed to depressurize the vessel in order to bring the non-conventional low pressure water keeping the core covered. The decay heat is removed via containment venting. The actions may damage the economic values of the plant due to the injection of dirty or sea water into the core. It can be expected that URG can lower the Core Damage Frequency (CDF) of events similar to Fukushima accident.
In the present study, the impact of URG on the CDF of Kuosheng NPP of Taiwan Power Company is assessed. The plant employs Boiling Water Reactor (BWR6) designed by General Electric. The plant specific PSA model of the plant is adopted on the study. The thermal-hydraulic responses of the system during the assicdent are simulated using RELAP5-3D code. WinNUPRA3.0 code is used in performing PSA analysis.
The results show that in a Station Blackout event, the URG can reduce CDF by 53.4% when the RCIC (Reactor Core Isolation Cooling system) operates 24 hours. For a sequence similar to Fukushima accident, the CDF can be reduced by two orders of magnitude. Nevertheless, the URG has no impact on the sequence with failure of RCIC injection. In such an event, the time to core uncover is too short to implement any extra mitigation actions beyond the design basis.

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