- 學位論文
核能級石墨於超高溫氣冷反應器爐心環境下之微結構變化及使用壽命評估
Lifetime Evaluation of Nuclear Grade Graphite in Advanced Very High Temperature Gas-cooled Reactor(VHTR) Core Environment Using HRTEM Microstructural Analysis
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摘要
本研究是利用高能量帶電的碳離子(3MeV C2+)在超高真空(<5x10-7torr)高溫條件(>600℃)，用以模擬在新世代核反應器-超高溫氣冷反應器(Very High Temperature Gas-Cooled Reactor: VHTR)爐心內之劑量以及高溫環境下，核能級石墨材料其內部受到粒子轟擊後的顯微結構變化。利用場發穿隧式電子顯微鏡(FEG-TEM)所獲得的低倍率影像以及高解析度影像(HRTEM images)分析離子輻照後核能級石墨內部基面(Basal plane){0002}以及{21 ̅1 ̅0}的晶格常數改變量以及其亂度係數(Disorder coefficient)的分析數據，再結合早期單晶熱解石墨相關文獻，導入結構因子以及孔洞增生因子等系數，修正單晶下之模型，進而評估不同種類之多晶核能級石墨於未來超高溫氣冷反應器內部的使用壽命以及體積變化議題。 藉本研究使用之模型可以觀測到，核能級石墨IG-110在600℃時其最大體積變化率約為-6.02%，其所恢復到原始體積(Lifetime)之劑量約為30.5dpa，而相同輻照環境下之核能級石墨ATR-2E則約為25dpa。而在更高溫之環境下，兩者的使用壽命皆大幅下降，在800℃時IG-110之使用壽命為25.5dpa、ATR-2E則僅為18.5dpa，在950℃時IG-110石墨壽命也降為19dpa，而利用線性外插後所得到之IG-110, 1050℃晶格變化量帶入此模型內，估計其壽命為10.5dpa，若以此壽命估計，在爐心內部承受最高劑量之石墨約每五年就必須更換材料，以確保爐心內部的結構安全性，而利用此模型亦可預測石墨材料於未來更高溫輻照條件下的體積變化及使用壽命評估。 除了使用年限之外，本研究也利用晶格變化來計算高溫時石墨內部受到輻照所儲存的能量，在高溫輻照下，根據本研究所建立之model指出，高溫輻照時之儲存能將不再是一個安全顧慮。
並列摘要
In this work, Nuclear grade graphite were irradiated by 3 MeV C2+ ion under high temperatures(>600℃) and ultrahigh vacuum (<5x10-7torr) environment to simulate the same radiation damage level in High Temperature Gas-Cooled Reactor(HTGR) environment. Graphite {0002} and {21 ̅1 ̅0} plane were investigated by FEG-TEM high resolution images. Fast Fourier transform was applied to calculate the average lattice parameters after irradiation. Microstructural evolution analyzed in this study including change of lattice parameters、disorder coefficients were intergraded with structure factor、pore generation factor to develop a model for lifetime and volume change evaluation inside nuclear grade graphite after different irradiation temperatures and fluences. Our model estimated that IG-110 irradiated at 600℃, its maximum volume change reached -6.02% and its lifetime is about 30.5dpa which is very close to experiment carried by neutron. For ATR-2E graphite, its lifetime reaches 25.5dpa in the same irradiated temperature(600℃). At higher irradiated temperature (800), both the lifetime of two graphite decayed seriously. (lifetime is 25.5dpa for IG-110 and 18.5dpa for ATR-2E). According to calculation, graphite block in the highest irradiation fluence region should be replaced every 5 years to insure the structural integrity under irradiation. Another part of this study showed calculation results of the energy storage inside graphite at high temperature irradiation. At high temperature irradiation condition(>600℃), stored energy is less than 10cal/g. This value is quite small compared to previous study (500cal/g at 150℃). From our results, energy storage in graphite would no longer be a problem in VHTR environment.
參考文獻
公司，2012
【2】 United Nations Environment Programme, Observed concentrations of
CO2 cross 400 parts per million threshold at several Global
Atmosphere Watch stations, world meteorological organization, a
specialized agency of the United Nations