核能電廠於電廠全黑事故情況下輻射劑量分析

A Study on the Radiation Doses of Station Blackout Accident Scenario for the Nuclear Power Plant

楊健鴻(Jian-Hong Yang)

指導教授 ： 鄧治東

中原大學/工學院/機械工程研究所/碩士(2012年)

https://doi.org/10.6840/cycu201200024

摘要

摘要

美國三哩島（Three Mile Island）事故後，促使核能工業界對核能電廠嚴重事故的研究，美國電力研究所（EPRI）委託FAI公司發展嚴重事故模擬分析程式（MAAP），並廣泛在核能工業界使用，目前MAAP已開發到第五版（MAAP5），除涵蓋原先MAAP4.0.4的所有功能外，也新增劑量（MAAP－DOSE）計算能力，而劑量分析範圍也涵蓋到廠內與廠外人員劑量計算。
2011/03/11日本福島核能事故，主要是因為地震與海嘯造成電廠發生全黑事故（Station Blackout, SBO），電廠又未能及時將冷卻水注入反應爐內，而造成爐心熔融，並使得輻射物質的外釋，透過大氣流與海洋流，核輻射汚染範圍涵蓋全球，核能安全再度成為世人矚目的焦點。
本研究係針對龍門核能電廠模擬電廠發生全黑事故，喪失所有冷却水注水反應爐，引發爐心過熱熔毀，反應爐失效與圍阻體過壓開啟，再計算分裂產物的外釋劑量。另外針對消防水做延遲注水導致RPV失效事件發生作靈敏度分析，取得反應爐失效的時間點，作為電廠在事故救援的判斷與應變手冊製作的依據。
本文模擬劑量分析，於70小時時刻，在距離電廠300公尺之低人口密度區，累積的最高外釋劑量為1.56西弗，對人體所造成影響為噁心、嘔吐。並透過大氣穏定度的分析，得知風向、風速、氣流，對外釋劑量影響的範圍、濃度，有絶對的關聯，而模擬分析結果所得之累積最高劑量為11.08西弗，若全身性一次急性曝露，兩個月內死亡機率將大於90%。
藉模擬嚴重所得物理化學行為顯示之數據得知，其時間線圖可獲得於事故進行過程中得以進行的各項救援措施與對策之有效性，對維持反應爐與圍阻體的完整性與若完整性無法維持時，導致電廠劑量外釋量之多寡，皆得以藉模擬分析其結果。此次福島電廠的嚴重事故，對核能電廠的安全運轉，係危機亦是轉機，可以協助吾輩了解於面對天然災害所造成的嚴重事故，必須加強並改變既有安全措施，期待本文所得結果能對核能的安全運轉具實質貢獻。

關鍵字

全黑事故 ； 核能

並列摘要

Abstract

After Three Mile Island (TMI) accident, nuclear industry started to promote research on severe accidents. MAAP (Modular Accident Analysis Program) code is a severe accident analysis computer program developed by Fauske & Associates (FAI), sponsored by Electric Power Research Institute (EPRI), and is widely used in the nuclear industry. Now, MAAP has been advanced to MAAP5. In addition to including all the functions of MAAP 4.0.4, MAAP5 has a new function of dose calculation (MAAP5-DOSE). It includes on-site and off-site dose calculation.
The Fukushima accident on March 11, 2011 was caused by earthquake and the subsequent tsunami, resulting in a station blackout (SBO) to the plant. The operators couldn’t inject water into core in time and caused core melt. Then, fission products were released into environment. The fission products covered substantial portion of the world by the ensuing air currents and ocean currents. The safety of nuclear power plants becomes the focus again in the world.
The purpose of this study was to simulate the station blackout accident scenario for the Lungmen Nuclear Power Plant (NPP). As a result of loss of all cooling to the core, the core melted, reactor pressure vessel (RPV) melted-through, and containment overpressure protection system (COPS) activated. The release of fission products was then calculated by the MAAP5 code. Sensitivity analyses on RPV melt-through caused by delays of fire water injection were also studied. The results obtained from this study would be useful for the plant operators in evaluating the accident conditions and planning for the response procedures.
With simulated results obtained from dose analysis, the highest dose at low population zone (300 m) was determined to be 1.56 Sv at the end of calculation (70- hr). The direct effect on the human body was nausea. From atmospheric instability analysis, factors such as wind speed, wind direction, and air current were connected with the concentration of radioactive doses and the magnitude of offsite doses. The highest integrated dose was calculated to be 11.08 Sv. If a human body receives such acute exposure (11.08 Sv), the probability of death is above 90%.
The results obtained from severe accident analyses clearly showed that the various mitigation measures would help prevent the melt-through of RPV and the subsequent activation of the containment overpressure protection system, resulting in the offsite doses being released. The Fukushima accident was the turning point to the added concerns regarding the safety of nuclear power plants. It helps us understand natural disaster and its resulting severe nuclear accidents. To enforce current regulation will give a great contribution to the nuclear safety.

並列關鍵字

Station Blackout Accident ； Nuclear

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