熱浸鍍鋅、鋁鋅之核廢料貯存鋼桶材在蘭嶼貯存壕溝中之耐蝕評估

The Evaluation of the Corrosion Resistance of the Hot Dip Zn, Al-Zn Coated Steel for Radiowaste Canister in the Lan-Yu Storage Trench

蘭嶼核廢料貯存壕溝中所用之核廢料貯存鋼桶，經研議採用熱浸鍍鋅技術以增進其耐蝕力。於決定採行熱浸鍍鋅之前曾進行各項研究，以確定材料耐蝕力以及熱浸鍍技術之可行性。本研究延續實驗室之模擬研究，進行蘭嶼壕溝內現場暴露試驗，將歷經七年試驗之試片，以化學分析電子光譜（Electron Spectroscopy for Chemical Analysis, ESCA或稱XPS）之結果進行腐蝕因子分析，並依據金相分析結果以瞭解熱浸鍍鋅、熱浸鍍5%鋁鋅、以及熱浸鍍55%鋁鋅三種鍍層之腐蝕形態以及腐蝕速率。根據分析結果顯示。腐蝕速率以熱浸鍍55%鋁鋅者最低，但熱浸鍍55%鋁鋅有嚴重之孔蝕現象。熱浸鍍鋅與熱浸鍍5%鋁鋅則未見孔蝕，其腐蝕速率分別為2.9微米/年以及1.4微米/年。

A policy has been decided to apply hot dip galvanization for enhancing the corrosion resistance of the radiowaste canisters to be stored in Lan-Yu radiowaste storage trench. A serious of investigations have been conducted for the feasibility of the galvanization technology prior to the decision making. The present study stepped follow the laboratory simulation research on performing the field test of the corrosion resistance of the hot dip Zn, Al-Zn canister steel in the Lan-Yu storage trench. The results of a seven year exposure test are discussed in this present work. ESCA (Electron Spectroscopy for Chemical Analysis) was applied for investigating the corrosion factors. The corrosion behaviors and corrosion rates of the Zn, 5%Al-Zn, and 55%Al-Zn coatings were investigated with the aid of metallography. The experimental results indicate that 55%Al-Zn exhibits the lowest corrosion rate, yet pitting occured for this coating while not for the Zn and 5%Al-Zn coatings. The corrosion rates were estimated to be 2.9 and 1.4 µm/year for the Zn and 5%Al-Zn coatings, respectively.