在沸水式反應器中，冷卻水會在反應器中發生沸騰的現象，其流動的不穩定性會與反應器的功率經由空泡耦合在一起形成一種複雜的不穩定現象，主要分為同相位和異相位不穩定。在本論文中我們使用頻域分析工具LAPUR5.2對於核一廠cycle22 reload design的運轉邊界做平行驗證，在邊界上選擇一個功率流量點探討參數對於異相位不穩定的分析，根據分析結果我們可以知道異相位不穩定容易發生在燃料週期開始、許多控制棒插入、爐心設計大、軸向功率底部尖峰（bottom peak）的情況下。由參數靈敏度分析我們可以知道除了再循環迴路增益與時間常數之外，其它參數對於同相位和異相位不穩定有相同的影響性，同時也知道對於異相位不穩定而言只有功率和流量的變化有較大的影響，其他參數的變化對於異相位不穩定而言幾乎沒有任何影響性。

In BWR, the cooling water takes place of boiling phenomenon in the core. The flow instability can become a complicated instability phenomenon by coupling the reactor power via the void reactivity. The instability can mainly be divided in-phase and out-of-phase instability. In this research, we use frequency domain tool LAPUR5.2 to do stability analysis on the ChinShan NPP unit 2 cycle reload design stability boundary and compare the results with the vendor’s results. And then we choose a operation point on the stability boundary and discuss the parameter effects on regional mode instability . According the result, it can conclude that out-of-phase instability happen easily in begin of fuel cycle, many control rods inserted, large core size, axial power bottom-peak. According to parameter sensitivity study, we can find that except the parameters of recirculation loop gain and time constant, other parameters have the same influence between in-phase and out-of-phase instabilities. At the same time, we know the parameters of core power and flow have significant effect on out-of-phase instability, others influence can be ignored.

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