| 摘要: | 花崗岩體是理想的核廢料處置母岩之一，但核廢料本身釋放出的熱若有機會加熱地下水，可能造成浸泡在熱水中的花崗岩產生化學及礦物相的變化，使得裂隙增加，放射性核種的外洩機率增大，影響到處置場的安全。金門東部地區的田埔花崗岩是理想的實驗材料，本研究採用此區之花崗岩做為實驗之用。本實驗設計90℃與60℃兩組熱水浸泡實驗。使用溶液的種類採用海水、RO逆滲透水、pH值3、 5、9、11的溶液。為了監測花崗岩岩體在浸泡熱水後初期的礦物及化學轉換，在浸泡後第5、10、20、40、80、120天取出浸泡中的岩體樣本做偏光顯微鏡、螢光顯微鏡觀察以及XRD、SEM等方法對岩體在這段期間所發生的變化做詳細的檢查，而對於浸泡後的溶液一併作ICP-AES實驗。而實驗過程中樣本的重量變化和溶液的pH值變化也進行測量。 實驗結果顯示，浸泡熱水後的20天之內，pH5、RO water、pH9這些初始pH值接近中性的溶液之pH值非常快速的往中性變化。溫度越高溶蝕速率越快，在酸性環境中各種元素溶出的量較大。溶液中的元素可以反映出礦物的溶解情形。Na、Ca、Si反映了斜長石的溶解，Fe、Mg、K、Si反映了黑雲母的溶解，K、Si反映了鉀長石的溶解，Si反映了石英的溶解。花崗岩可流通裂隙的密度在90℃，pH3、pH11、RO逆透水環境中，實驗第10天有大量的增加，但是到了第120天除了pH3實驗組之外，都降低到接近新鮮花崗岩的可流通裂隙密度。顯示酸性環境對於核廢料儲存安全問題較為不利。XRD的實驗結果並沒有偵測到新生礦物。 Granitoid is generally believed to be a good repository for the nuclear waste diposal. However, the heat release from decay of the nuclear waste could combine with the groundwater and cause physical and chemical changes in the mineral phases of the granitic body. These changes may result in occurrence of crack and increase the crack of the granitic body, which could raise the probability of leaking of nuclear species. The Tianpu granite located at East Kimen is an idea experimental material and was used in this study. Samples were soaked in different solutions separately under two temperatures of 60 ℃ and 90 ℃. For practical purposes, the solution with pH value of 3, 5, 9, 11 were used in the experiments. Additionally, the sea water and the RO water were also used. Specimens were removed from the hot water bath each time after 5, 10, 20, 40, 80, 120 days of immersion. The method to monitor the mineralogical and chemical transformation of the granite samples in this study included petrographical and fluorescent microscopy, XRD, SEM and ICP-AES. Beside, the changes of samples weight, pH value of solutions were investigated during the immersion period. The results showed that solutions of pH5, RO water and pH9 were readily neutralized within 20 days after experiment began. Dissolution rate at 90 ℃ condition is higher than at 60 ℃ condition. Likewise, the acidity increase of solutions caused higher dissolution rate. The concentrations of Na, Ca and Si were mainly reflected the dissolution from plagioclase. The Fe, Mg, K and Si were released from biotite. The K and Si were derived from K-feldspar, and minor content of Si were dissolved from quartz. During the immersion test up to 10 days, the density of flowable crack in the granite samples immersed in the solution of pH3, pH11 and seawater were increased. Later, density of flowable crack decreased during immersion up to 120 days in the sea water and the solution of pH11. The results indicated that acid solution adverse to the safety of the nuclear waste repository. In the XRD result, no secondary mineral can be found. |
