核電廠大破口冷卻劑流失事故評估方法的演進包含了兩大類方法論，確定論以及風險告知方法論。傳統核電廠設計基準事故中所使用的保守Appendix K確定論評估或BEPU評估方法,傳統確定論方法只量化了因為認知 (epistemic) 和量測計算所造成所造成的不確定性誤差，而這些誤差的來源是由於所使用的計算模型以及所使用電廠狀態參數所造成的。在本文的研究中所採用的風險告知方法論中不僅量化上述傳統方法中所包含的認知 (epistemic) 不確定性誤差，並且透過產生燃料包殼溫度載荷譜 (loading spectrum) 進而量化隨機性 (aleatory) 誤差評估大破口冷卻劑流失事故安全性。
根據法規10 CFR50.46，大破口冷卻劑流失事故被歸類於設計基準事故而此事故的確定論方法必須採用代理序列進行分析從而確定保守性。此代理序列的假設是不考慮序列的發生機率如何只採用單一事故故障原則對代理序列進行假設。然而在未來新法規10 CFR50.46a中所敘述的要求，大破口冷卻劑流失事故將歸類於超越設計基準事故並且分析燃料包殼溫度的安全裕量時必須採用風險告知評估方法論。透過Risk-Informed Safety Margin Characterization (RISMC) 方法論評估台灣馬鞍山核電廠冷卻劑大破口事故，分析量化燃料包殼溫度載荷譜以及定義在此事故下機率發生最主要的14個序列。RISMC評估方法論中，風險告知的PCT裕量可以透過期望值分析評估方法以及序列機率累計評估方法進行分析。與過往傳統的確定論評估方法做比較，採用RISMC評估方法可以提供38.3-42.6 K的PCT安全裕量對比傳統的確定論方法。除此之外，本文的研究結果中發現累計發生機率序列大於99％，此時序列的發生機率為5.07*10-3與傳統的代理序列發生機率5.46*10-5相比發生機率更是相差兩個級距。
最後，在評估大破口冷卻劑流失事故安全度裕量的方法論的演進過程中可以觀察到以下結果，傳統使用Appendix K 方法論中的安全裕量評估可以透過 (i) 鬆綁電廠狀態參數的邊界狀態假設 (DRHM評估方法論) ，(ii) 真實性大破口事故的統計分析，其中分析計算模型的的不確定性以及電廠狀態參數的不確定性 (BEPU評估方法論)以及(iii)風險告知裕量方法論評估燃料包殼溫度安全裕量從而放寬傳統申照序列的保守架設(RISMC) ，對大破口冷卻劑流失事故分析的PCT安全裕量提供更大的空間。

The evaluation of methodology for large break loss of coolant accident (LBLOCA) licensing analysis involves two kinds of methodologies, namely deterministic methodology and risk-informed methodology. In the deterministic methodologies required for design-basis LBLOCA analysis, only epistemic or calculation uncertainty is addressed by either the conservative appendix K approach or the BEPU approach. Calculation uncertainty generally consists of physical model uncertainty and plant status uncertainty. In the risk-informed methodology, not only the epistemic uncertainty but also the aleatory are addressed by conducting a peak cladding temperature (PCT) load spectrum of LBLOCA.
According to the existing 10 CFR50.46, LBLOCA is one of the most essential design-basis accidents (DBA) and a deterministic methodology shall be applied to perform LBLOCA analysis based on a so-called surrogate sequence. Without considering how low this sequence occurrence probability is, this surrogate sequence satisfies all the required licensing assumptions. However, in the to-be-issued 10 CFR 50.46a, the LBLOCA will be categorized as accidents beyond design basis and the peak cladding temperature margin shall be evaluated in a risk-informed manner. According to the risk-informed safety margin characterization methodology (RISMC), a process has been suggested to evaluate the risk-informed PCT margin. Following the RISMC methodology, a load spectrum of peak cladding temperature for LBLOCA has been generated for the Taiwan’s Maanshan Nuclear Power plant and 14 probabilistic significant sequences have been identified. It was observed in the load spectrum that the conditional PCT generally ascends with the descending sequence occurrence probability. With the load spectrum covering both aleatory and epistemic uncertainties, the risk-informed PCT margin can be evaluated by either expecting value estimation method or sequence probability coverage method. It was found that by comparing with the traditional deterministic methodology, the PCT margin evaluated by the RISMC methodology can be enlarged by 38.3-42.6 K. Besides, to have a cumulated occurrence probability over 99% in the load spectrum, the occurrence probability of the sequence referred is about 5.07*10-3, whereas for the traditional surrogate or licensing sequence generally applied in the deterministic methodology, the occurrence probability is only about 5.46*10-5.
Finally, observed from the evolution of LBLOCA methodologies, the safety margin of a LBLOCA can be released from traditional Appendix K methodology by (i) relaxing plant bounding state assumption (DRHM), (ii) performing realistic LOCA analysis with statistical consideration of both model uncertainties and plant status uncertainties (BEPU), and (iii) relaxing licensing sequence assumption and evaluating the peak cladding temperature margin in a proper risk-informed manner (RISMC).

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