高溫水環路不銹鋼材質之電化學電位測定

Electrochemical Potential Measurement of Stainless Steel in High Temperature Dynamic Water Loop

高溫電化學電位的測試，有靜態及動態環路兩種測定方法，作為核電廠中水質環境之研判標準之一。靜態實驗中使用高壓釜容器及外載雙接合式高溫參考電極，改變氯化鉀的濃度，對316不銹鋼於水溶液中進行升溫及降溫實驗，所產生的電化學電位變化趨勢，與Macdonald的實驗結果一致。SS 304在特定溫度（280℃）及壓力（1050 psi）純水中連續測定14天，而SS 304L則維持二個月測定，顯示參考電極之穩定性良好。ECP是高溫高壓環境中，不銹鋼材質與水溶液中的化學添加物達到平衡所顯現的電化學電位值。動態環路系統中（在280℃溫度及1050 psi壓力，流速80 ml/min, pH=6.0，溶氣300 ppb，導電度1.5 us/cm純水）分別測定SS 304及SS 316 14天，ECP（SS 304）為－170 mv, ECP（SS 316）為－160 mv，穩定性良好。SS 316 ECP測定於冷卻水中加入硼酸及氫氧化鋰時，其電化學電位值，往正方向移動，移動之大小，視硼鋰的濃度而定，顯現ECP值與改變含硼或鋰水溶液濃度下之導電度呈現線性關係。

There are two kinds of ECP test methods-one is static and the other is in the dynamic state by using the test loop. Cortest double junction external reference electrode is used in our laboratory. The ECP of SS 316 in pure water at different KCl concentrations is dependent upon temperature varation. Working electrode is designed and constructed in our laboratory. Long term ECP measurement at specific temperature (280 ℃) and pressure (1050 psi) for working electrode has been tested over two months. The stable ECP is obtained in the controlling water conditions. The water chemistry conditions under dynamic water loop are as follows: temperature=280℃, pressure= 1050 pis, flow rate=80 ml/min, pH=6.0, dissolved oxygen=300 ppb, conductivity=1.5 us/cm, Working electrode measures continuously for 14 days under dynamic water loop. The ECP of SS 316 migrates to positive direction after the addition of boric acid and lithium hydroxide to the coolant. The magnitude of migration of ECP depends upon the concentration of boron and lithium concentration. The relationship seems to be linear between ECP and B/Li variation.