PROTEC TM TEAR-OFFS: RESULTS OF LONG TERM TESTING

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The Savannah River National Laboratory (SRNL) has completed a series of tests (Phases 1 and 2) to assess the potential use of a Mylar{reg_sign} tear-off system as a primary or secondary protective barrier to minimize acid etching ('frosting'), accidental scratching, and/or radiation damage for shielded cells, glovebox, and/or chemical hood windows. Conceptually, thin, multi-layered sheets of Mylar (referred to throughout this report as the ProTec{trademark} tear-off system) can be directly applied to the shielded cell, glovebox, or hood sash window to serve as a secondary (or primary) barrier. Upon degradation of visual clarity due to accidental scratching, spills/splatters, and/or radiation damage, the outer layer (or sheet) of Mylar could be removed refreshing or restoring the view. Due to the multilayer aspect, the remaining Mylar layers would provide continued protection for the window from potential reoccurrences. Although the concept of using a tear-off system as a protective barrier is conceptually enticing, potential technical issues were identified and addressed as part of this phased study to support implementation of this type of system in the Defense Waste Processing Facility (DWPF). Specific test conditions of interest to the DWPF included the performance of the tear-off system exposed to or under the following conditions: (1) acid(s) (concentrated (28.9 M) HF, concentrated (15.9M) HNO{sub 3}, 6M HCl, and 0.6M H{sub 3}BO{sub 3}); (2) base (based on handling of radioactive sludges with pH of {approx}12-13); (3) gamma radiation (due to radioactive sources or materials being used in the analytical cells); (4) scratch resistance (simulating accidental scratching with the manipulators); and (5) in-situ testing (sample coupons exposed to actual field conditions in DWPF). The results of the Phase 1 study indicated that the ProTec tear-off concept (as a primary or secondary protective barrier) is a potential technical solution to prevent or retard excessive damage that would result from acid etching, base damage (as a result of a sludge spill or splatter), gamma radiation damage, and/or accidental scratching (due to manipulator/tool contact). Although identified as a potential solution, the Phase 1 testing was relatively short-term with exposure times up to 1-2 months for the acid and gamma radiation tests. Phase 2 testing included longer exposure times for the acid resistance (up to 456 days) and gamma radiation exposure (700 days with a cumulative gamma dose of {approx}3.1 x 10{sup 5} rad) assessments. The tear-off system continued to perform well in these longer-term acid resistance testing and gamma exposure conditions. Complete removal of the tear-offs after these long-term exposure times indicate that not only could visual clarity be restored but the mechanical integrity could be retained. The results also provided insight into the ability of the ProTec tear-off system to withstand the chemical and physical abuses expected in off-normal shielded cells operations. The conceptual erasing of scratches or marks by excessive manipulator abuse was demonstrated in the SRNL Shielded Cells mock-up facility through the removal of the outer layer tear-off with manipulators. In addition, the Phase 2 testing included an in-situ assessment of a prototype tear-off system in the DWPF Sampling Cells where the system was exposed to actual field conditions including radioactive sources, acidic and basic environments, dusting, and chemical cleaning solutions over a 5-6 month period. DWPF personnel were extremely satisfied with the performance (including the successful removal of 3 layers with manipulators) of the ProTec tear-off system under actual field conditions. The successful removal of the outer layer tear-offs with the manipulator, using tabs not specifically designed for remote operations, demonstrates that the system is 'manipulator-friendly' and could be implemented in a remote environment. The ability to remove the outer layer tear-off not only regains visual clarity but also reduces waste disposal volumes (i.e., disposal of a thin sheet of Mylar which is 'collapsible' versus the bulk disposal of a rigid Lexan{reg_sign} sheet (alpha shield) or glovebox/sash window) which is more cost effective. The tear-off system could also reduce the number of cell entries needed to replace the Lexan sheet and increase the time interval between glovebox/sash window replacements, which can be costly and time consuming. Although the primary focus of this study addresses the application of the ProTec tear-off system to shielded cells windows, the concept is also potentially applicable to glovebox and hood sash windows. In fact, the tear-off concept is potentially applicable to any system where visual clarity is compromised given the environmental conditions of the test. In addition, the tear-offs could be applied to walls or shelves where a protective barrier would reduce deterioration or discoloration.