本研究係針對核四廠所採用之進步型沸水式反應器,應用MAAP 4.04程式進行電廠全黑(SBO)及失水事故(LOCA)之模擬分析。並將兩事故依據緊急運轉程序書(EOP)進行探討。研究重點係針對依據EOP控制程序而模擬之兩事故,以MAAP 4.0.4程式計算所得之事故序列變化,並分析兩者間所得之事故序列中,各現象之差異性。 電廠全黑事故的模擬共分為兩個個案,個案一為一般之電廠全黑,即假設所有廠區(On-Site)及廠外(Off-Site)的交流電皆無法供電,除爐心隔離冷卻系統(RCIC)外,其他所有注水系統均喪失注水功能,而於RCIC失效後,反應爐水位即迅速下降,爐心裸露、過熱、熔毀、重置,最終圍阻體因壓力達其過壓保護系統(COPS)之設定點而排氣;個案二則另加入EOP之設定,並依EOP於RCIC失效後,操作員由廠外藉手動方式注入消防水至反應爐中以維持爐心水位,故反應爐得以持續保持於完整狀態而未失效,但圍阻體最終仍因抑壓池上部氣室壓力超過COPS之設定點而遂行排氣。 失水事故的模擬,破口位置係設定於飼水管路,破口面積則係假設為兩頭截斷破口之情形(破口面積設定為 0.24平方公尺)。本模擬亦分為兩個個案,個案一為一般之失水事故,所有的緊急爐心冷卻系統,均依照系統設定點自動開啟與關閉。系統自動啟動高壓及低壓灌水系統以維持爐心之水位,故爐心於模擬過程中從未有裸露之情形。但圍阻體仍因抑壓池上部氣室壓力過高,超過COPS之設定點而進行排氣,因過程中爐心從未裸露亦未過熱,且並未有任何分裂產物釋出,因而無任何分裂產物因COPS啟動而逸至圍阻體外之狀況;而個案二則另外加入了EOP之設定,並根據EOP由操作員藉手動方式開啟高低壓注水系統以維持爐心水位,且開啟兩串餘熱移除系統(RHR)以降低抑壓池之水溫至308 K以下。 由本研究所探討之核四廠電廠全黑及失水事故兩類個案結果顯示,運轉員採用EOP以進行事故序列模擬均較一般事故之序列結果來得和緩,並將決定反應爐爐心是否得以維持其完整而免於導致爐心熔毀;且在電廠全黑個案中,雖廠區及廠外皆未能供電,至多只能啟動RCIC及COPS;由此可知,EOP對於此兩類嚴重事故之處理,係屬合宜。
The purpose of this study is to evaluate the postulated severe accidents, including LOCA and SBO, of Lungmen Nuclear Power Plant (LNPP). The methodology used is the MAAP 4.0.4 computer code, developed by Electric Power Research Institute (EPRI). In addition, simulations of severe accidents follow the plant-specific Emergency Operator Procedures (EOPs) for the LNPP. Subsequently, comparisons of the results between the cases with and without EOP are discussed in the conclusion. The station blackout (SBO) scenario is divided into two cases. Case I assumed that the plant lost all its on-site and off-site power, leading to loss of all motor-driven coolant injection capabilities. However, the reactor core isolation cooling (RCIC) system, driven by steam provided by the reactor, was the only coolant injection system available under such SBO condition. Case II is the same as Case I before RCIC trips. According to the EOPs, the fire water (AC-Independent Water Addition, ACWIA) becomes available once RCIC is lost. The loss-of-coolant accident (LOCA) scenario is also divided into two cases. Case I assumed that the accident was initiated by a Double-Ended Break at the feedwater pipe, with ensuing loss of coolant in the primary system. The case II is the same with case I, except that according to the EOP, the operator was assumed to make the high pressure core flooder HPCF and low pressure core flooder LPFL available manually to maintain the water level of core. In addition, two trains of the residual heat removal (RHR) systems were also made available to remove the decay heat of the reactor system. Results obtained from this study indicated that implementation of the EOPs is useful to mitigate the postulated severe accidents for the LNPP.