地表加速度反應譜譜形對核能電廠風險評估之影響

The Impact of Spectral Shapes of Ground Motions on Seismic Probabilistic Risk Assessment of Nuclear Power Plants

陳宏銘(Hong-Ming Chen)

指導教授 ： 黃尹男

國立臺灣大學/工學院/土木工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.00998

摘要

Huang與Whittaker等人所提出之新一代地震機率式風險評估之流程與方法(Seismic Probabilistic Risk Assessment, SPRA)(Huang et al. 2011a、2011b)，此一套新式SPRA (簡稱HW SPRA)以結構反應參數定義易損性曲線，並利用動力歷時分析求得結構反應，增加核能電廠耐震風險評估之可靠性。目前業界對核能電廠進行耐震風險評估時，所使用的都是以UHS(Uniform Hazard Spectrum)做為目標反應譜之人工地震歷時進行動力分析，其中並無考慮反應譜不同週期之相關性及離散性等影響譜形之因素。
針對以上之現況，本研究利用HW SPRA方法評估一案例核能電廠因地震導致爐心受損之風險，並針對目標加速度反應譜譜形對風險分析結果之影響進行討論。本研究主要重點在於使用不同目標反應譜之地震歷時群進行非線性動力分析以及計算電廠之爐心受損之風險，最後觀察其對於台灣核能電廠地震風險評估之結果的影響程度。本研究中以強度、離散性以及是否考慮反應譜不同週期間之相關性等影響譜形之因素，共建立以下4組地震歷時群：
(a) CS(Conditional Spectrum)群，此群以CMS(Conditional Mean Spectrum)作為目標反應譜，此群地震歷時考慮了反應譜之相關性，且整體的反應譜之中位數值與目標反應譜一致，此外，此群中每一筆地震歷時皆考慮了反應譜之不確定性。
(b) CMS_A群與 (c) CMS_B群，此兩群以CMS作為目標反應譜，皆以數值軟體將其轉換成符合CMS之人工地震歷時，故此兩群皆無考慮反應譜之離散性。然而，此兩群中最大的不同處是垂直方向上之目標反應譜在強度上會有所差異，因為在本研究中所選定之事故序列中有許多設備元件受垂直向反應影響甚鉅。此外，本研究亦建立了計算以上三群之目標反應譜(CMS)所需之適用於台灣本地之加速度反應譜相關係數模型。
(d) UHS群，以UHS作為目標反應譜，並以數值軟體將其轉換成符合UHS之人工地震歷時，故此群並無考慮反應譜之相關性及離散性。
透過本研究分析結果之比較，相較於CMS_A群、UHS群集CMS_B群未考慮反應譜離散性之因素，CS群之地震歷時考慮了反應譜週期間之相關性以及反應譜於條件週期外之反應譜不確定性，此不確定性影響結構反應的離散性與風險計算結果甚鉅，導致等級1~4等較低之地震強度，其爐心受損機率大於其他群之受損機率。最終CS群之爐心受損風險大於譜形較為保守之UHS群之風險，為4群中最高者。

關鍵字

核能電廠 ； 機率式耐震風險評估 ； 非線性動力分析 ； 條件平均反應譜 ； 相關係數

並列摘要

Seismic probabilistic risk assessment (SPRA) has been widely used to compute the core damage frequency of a nuclear power plant (NPP). In this study, seismic risk of a sample NPP is computed using a SPRA methodology proposed by Huang, Whittaker and Luco in 2011. The methodology requires response-history analysis, which often involves the selection and scaling of ground motions for a target spectrum. The use of artificial ground acceleration time series spectrum-matched to a uniform hazard spectrum (UHS) does not consider the correlation in spectral accelerations at different periods and has been criticized to be significantly conservative for some purpose.
In this thesis, the impact of spectral shape of a target response spectrum on the result of SPRA was studied. The seismic risk was defined as the occurrence of a sample accident sequence for the sample NPP. Four sets of ground motions were developed for this purpose:
(a) CS Group. The target spectrum for this group was developed using the Conditional-Spectrum (CS) concept. The distribution of spectral acceleration at a given period for the ground motions in the CS Group fits both the median and dispersion required in the target CS.
(b) CMS_A Group and (c) CMS_B Group. The target spectra for the two groups were developed using the Conditional-Mean-Spectrum (CMS) concept and are the same in the horizontal directions and different in the vertical direction. Each ground motion in the two groups is artificial time series spectrum-matched to the target CMS. A prediction model for correlation coefficients for spectral accelerations at different periods was proposed for ground motions recorded in Taiwan and used to develop the target CMS used in this study.
(d) UHS Group. Each ground motion in this group artificial time series spectrum-matched to a target UHS.
The dispersion in spectral acceleration of ground motions for the CS Group has significant impact on the dispersions in the structural responses and the risk of the sample NPP. The seismic risk of the sample NPP for the CS Group is higher than that for the other groups.

並列關鍵字

Nuclear power plant ； seismic probabilistic risk assessment ； conditional mean spectrum ； nonlinear-history analysis ； correlation coefficient

參考文獻

游青青，「新一代核能電廠耐震機率風險評估與餘熱移除系統耐震行為研究」，碩士論文，國立台灣大學，台北(2014)。

Abrahamson, N. A., and Silva, W. J. (1997). "Empirical response spectral attenuation relations for shallow crustal earthquakes." Seismol. Res. Lett., 68(1), 94-126.

Apsel, R., and Luco, J. (1987). "Impedance functions for foundations embedded in a layered medium: an integral equation approach." Earthquake engineering & structural Dynamics, 15(2), 213-231.

Applied Technology Council (ATC). (2012). "Seismic performance assessment of buildings. Volume 1 – Methodology." FEMA P-58 pre-release version, Federal Emergency Management Agency. Washington, D.C.

Baker, J. W., and Cornell, C. A. (2005). "A vector-valued ground motion intensity measure consisting of spectral acceleration and epsilon." Earthquake engineering & structural Dynamics, 34(10), 1193-1217.