不同硫桿菌菌株對放射性廢棄物桶材腐蝕及腐蝕物遷移之效應

Effects of Different Strains of Thiobacillus spp. on the Corrosion of Radioactive Waste Drum Materials and the Migration of Corroded Materials

本研究目的為探討五株硫桿菌菌株對放射性廢棄物碳鋼桶材腐蝕及腐蝕物遷移作用之差異。採用的受測菌株為硫桿菌（Thiobacillus spp.）五株，受測放射性廢棄物桶材包括冷軋碳鋼（CNS 9278-SPCC-SD）及熱軋碳鋼（CNS 4622-SPHC）二種。各菌株於進行生長條件、移動能力及鞭毛染色等生理測試及型態觀察後，測試其對裝填放射性廢棄物之碳鋼桶材腐蝕及對腐蝕物遷移之效應。本研究的結果發現，將受測碳鋼片置於固化之培養基中，在25℃下連續觀察90天，結果顯示接菌處理之培養基中的碳鋼片較未接菌者的腐蝕為劇烈，光學顯微鏡下檢視可見加速向外遷移之腐蝕物中含有大量的菌體。在測試條件下，影響碳鋼片腐蝕及腐蝕物遷移之模式因菌株而異。其中，以T. thiooxidans對遷移速率之影響最大，測試一星期後已可見明顯的促進腐蝕效應；二株T. ferrooxidans及分離株RWT l次之；以T.thioparus對腐蝕物遷移所造成之影響速率稍緩，但經六星期後T. thioparus所造成之腐蝕及腐蝕物遷移量與未接菌者比較已有明顯差異。感應耦合電漿原子發射光譜分析儀所測得之桶材碳鋼成份向外釋出量與顯微鏡下所觀察腐蝕物遷移現象具一致性。受測之各Thiobacillus spp.菌株均具促進放射性廢棄物碳鋼桶材之腐蝕能力，並具促進腐蝕物遷移之效應，且上述對碳鋼桶材腐蝕及腐蝕物遷移效應具菌株間之差異。

The objective of this research is to investigate the effects of different strains of Thiobacillus spp. on the corrosion behavior of radioactive waste drum materials and on the migration of corrosion products. Five strains of Thiobacillus spp. and two types of radioactive waste drum materials were tested including cold-rolled carbon steels (CNS 9278-SPCC-SD) and hot-rolled carbon steels (CNS 4622-SPHC). Each strain of Thiobacillus spp. underwent physiological tests and morphological observations of growth condition, migration ability and flagellum staining before its effect on the corrosion of carbon steel drums used for disposal of radioactive wastes and the migration of corroded materials were evaluated. A carbon steel sheet was implanted in a solidified biological medium under 25 oC and observed for 90 days consecutively. The results revealed that corrosion of the carbon steel sheets implanted in the bacteria inoculation medium was severer than that of the sheets in the non-inoculated medium. Large amounts of bacteria were observed under an optical microscope in the corrosion products that migrated outward at an accelerated speed. Under the pre-established test condition, the effect of Thiobacillus spp. on the corrosion of carbon steel sheets and the migration pattern of the corrosion products differed between each strain. Of the five strains tested, T. thiooxidans demonstrated the greatest impact on the migration rate in that the corrosion was evident within one week, followed by the effect of the two T. ferrooxidans strains and the isolated strain RWT l. The effect of T. thioparus on the migration of corrosion products was less significant. However there was a significant difference after 6 weeks in corrosion and amount of migration between the carbon steels with and without inoculation treatment. The amount of outward migration of the corrosion products analyzed by the inductively coupled plasma-atomic emission spectrometry was consistent with the migration of the corrosion products observed under an optical microscope. All Thiobacillus spp. strains tested exhibited catalytic effects on both the corrosion of radioactive waste drum materials and the migration of the corrosion products. However the degree of the effect differed among the strains.