- 學位論文
使用MELCOR程式模擬福島一廠三號機事故與放射性物質外釋量之分析
Analysis of Unit 3 Fukushima Nuclear Power Plant Accident Using MELCOR 1.8.5 Code
摘要
日本東北部於2011年3月11日下午2點46分(日本時間)發生芮氏規模9.0的強震，鄰近震央的福島第一、第二核電廠在地震後遭浪高達10公尺以上的海嘯侵襲，使得核電廠的安全面臨了日本史上最嚴峻的考驗。由於福島一廠三號機與我國金山電廠圍阻體同為MARK I的BWR4型核電廠，故本研究中以金山電廠為標的，建立MELCOR輸入檔，模擬福島一廠三號機事故。模擬時，將重要序列包含：高壓注水、洩壓、生水注水、海水注水、圍阻體洩壓等依官方報告中之時間點設定，總模擬時間為300,000秒(共83.3小時)。金山電廠之MELCOR程式輸入數據檔建構完成後，依照福島事故之發展，編寫control function做注水、洩壓等控制設定，完成金山電廠模擬福島一廠事故之MELCOR模型。 模擬結果顯示，程式預測與福島事故發展有所不同，並未觀察到發生於跳機後68.2小時之氫爆，廠房同樣並未毀損。針對氫氣量做探討，MELCOR爐心所產生之氫氣量達529kg，約有67公斤之氫氣在洩漏中被洩漏至廠房內，但由於氫氧濃度未達然爆的條件，並未發生氫氣爆炸；放射源項部分，基本案例中廠房未毀損，放射性物質最終只釋出至廠房內，並未外釋至大氣。延伸案例中使廠房固定於68.2小時(福島事故發生時之廠房崩毀時間點)手動設定其通往外界之通道開啟，模擬結果外釋量最高者為氣態代表核種為Xe，約有1.3% 外洩至環境之中，其於核種均小於1%。與另一嚴重事故模擬程式MAAP5之結果相互比較，可發現MAAP5與MELCOR兩者之間存在許多差異，最明顯者為爐心崩陷 (relocate)時的模擬，MAAP5模擬結果中會在爐渣掉落至壓力槽底部時產生一個極高的壓力尖峰，足以使廠房崩毀，MELCOR中並未發現類似情形；兩者在氫氣產生量上亦有極大差異，MELCOR模擬結果產生之氫氣量為MAAP5之數倍，但兩者洩漏至廠房之氫氣量均因未達然爆所需之濃度，未發生氫爆。
並列摘要
On 2011 March 11, a strong earthquake induced several large waves of tsunami hit the east coast of Japan. The tsunami caused extensive damage to the site of Fukushima Daiich Nuclear Power Plant (NPP). Fukushima Daiichi NPP employed BRW4 reactor with MARK I containment, which is identical to the design of Chinshan NPP of Taiwan Power Company. In the present study, an input deck of MELCOR based on the design of Chinshan NPP is construct to simulate the Fukushima Daiichi Unit 3 accident. In the simulation, the timings of water injection, depressurization, and containment venting are set as specified in the official Japanese government report about the accident. The results of simulation demonstrate that the hydrogen burns observed during the accident are not predicted by the code. The the reactor pressure vessel and the containment are remain intact throughout the accident. As predicted in the MELCOR simulation, there is 67 kilogram of hydrogen leak into the reactor building. Nevertheless, the concentration of hydrogen is still too low to induce hydrogen burn. There is no radionuclide release to environment in the base case simulation due to that the reactor building is kept intact up to the end of the simulation. In a sensitivity study, it is assumed that the reactor building breaches at the time specified in the official government report, The results show that 1.3% of Xe is released to the environment. The releases of other radionuclides are very minor. The results of MELCORE simulation of the accident are compared with the results of MAAP5 simulation. The differences are very significant. The results of MAAP5 simulation indicated that the reactor building breached due to the pressure spike predicted at 68.2 hours after scram, which was caused by the relocation of molten core from core region into vessel lower plenum.
參考文獻
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