Abstract
本研究採用實驗與時域分析方法, 進行雙相流系統的穩定性分析與研究, 分析工具是利用一大型、完整且國際間所廣泛使用之電廠熱流分析程式- RETRAN02/MOD5, 建立雙相流穩定性分析之時域模式。為探討完整的雙 定 性問題, 以期對此一問題作深作且完整的瞭解, 本研究分成三大階段來進 行。第一階段為實驗與模式的建立與驗證及相關的文獻探討, 首先進行相 關的文獻探討, 瞭解重要的參數效應對於系統的影響。另外為驗證模式分 析的準確性及觀察雙相流不穩定的現象, 本研究也針對算然循環環路進行 穩定性的實驗, 以實驗裝置模擬分析系統, 找出發生不穩定時,系統所處 的狀態。除了上述實驗之外, 本研究亦收集了國外相關的實驗數據與國內 電廠的測試數據, 進行模式的校驗與比對, 經由此一階段研究,對雙相流 不穩定現象有了更進一步的瞭解, 而且分析模式的準確性與適用性亦獲得 驗證並瞭解程式本身的限制。經由本研究算然對流實驗的觀察與模式分析 結果, 可求出在本實驗狀況下(介於紊流與層流之間), 功率與單相算然循 環流量的 0.4次方成正比。當出口溫度到達飽和時, 系統則迅速進入不穩 定狀態, 其振盪的主要肇因為實驗狀況處於流譜之彈狀流與攪拌流的過渡 區而造成流譜變化的不穩定。變化不同的次冷度實驗中, 可發現在相同的 功率之下, 次冷度愈大, 則出口溫度愈低, 而所要達到振盪的功率則會增 加。RETRAN模式的分析校驗結果顯示, 流量、出口溫度與振盪的肇始功 率, 大致均能符合實驗值, 唯在進入不穩定範圍後, 模式極易因數值的不 收斂而中止計算, 以致無法了解振盪的情形。第二階段為電廠三項穩定性 分析, 對目前BWR 申請運轉執照所需的三項穩定性分析深入地瞭解與探 討, 並且以國內的核一廠與核二廠進行分析研究。分析結果顯示, 國內電 廠在與三項穩定性的分析中, 系統經過擾動而開始振盪後, 均能回復或到 達一平穩的狀態。第三階段則為穩定性判別與電廠暫態與事故之穩定性分 析, 由於三項的穩定性分析, 僅能定性的看出電廠在該狀況之下是否穩 定, 無法進一步地瞭解電廠距不穩定的範圍尚有多廣, 因此本研究模擬分 析核二廠通道流量的加熱狀況, 找出流量振盪的功率肇始以建立系統不穩 定圖譜。類似LaSalle 功率振盪事故的分析結果在不穩定圖譜的流程顯 示, 並未進入不穩定的振盪區, 除非核二廠所使用的阻流板流阻係數很 小, 否則在此類事故暫態下通道流量不易產生振盪。 The study adopts both experimental and time domain analysis methods to conduct the two-phase system stability phenomena. The approach to ivestigate the two-phase flow stability consists of three steps. The first step includes the establishment of the experiment and the analysis mode, the verification of the modeling and related papers review. The experiment uses a low pressure natural circuation loop at the Institute of Nuclear Energy Research (INER) to investigate stability phenomenon under natural circulation condition. The RETRAN model will be established and verifed by experimental data to assess its ability in carrying out natural circulation stability alaysis. In our low pressure natural circulation wxperiments, conter-current or flow patterns transition based flow oscillation begins when the test section outlet condition becomes saturated. RETRAN temperautes, satisfactorily predictions on flow rates, outlet temperautes, and threshold power leves. However, numerical difficulties were encountered during flow oscillations and the calculations could not continue, probably a limitation in the code's capability. The ssecond step is three types of BWR stability analysis. In all cases investigated, the plant operations would be stable under various stability map using RETRAN02/MOD05 code under natural circulation conditions forsheng Nuclear Power Plant (KNPP). Meanwhile, two trandient loci of KNPP recirculation pump trip( RPT) with decresingdwater enthalpy are also drawn on the stability map to assessimilar power oscillaton phenomena as LaSalle-2 event may occur at KNPP. To avoid numerical oscillation of flow stabilitytime domain analysis, several sensitivity studies areout. The results indication that both transient loci have enough stability margins to unstable boundary an reveal that KNPP's operations will bestable under such RPT with decreasing feedwater enthalpy transients.