Lesson Learned Statement:Whenever performing a design or design change on any vessel configuration, assure inadvertent pressurization of the vessel is considered in the design.
Discussion:As part of the installation of a permanent pumping system on a hot off gas drain trap at ORNL, a level indicator which utilizes a bubbler was installed for level indication. This bubbler adds a small amount of air (0.6 cubic ft. per hour) to the vessel through a small tube which extends to the bottom of the vessel. Over a long period of time, this addition of air caused the vessel to pressurize, thus preventing the off gas piping system to drain properly into the trap. This caused a low point in the piping to become full of water preventing off gas flow, resulting in a loss of off gas ventilation to the facilities served by this system. A vent equipped with HEPA filtration was added to the trap, thus relieving any pressure and the system operates properly.
Analysis:Included in discussion above.
Recommended Actions:When designing or installing any systems that can possibly add pressure to a closed system assure that the operation of the system cannot be detrimentally affected.
Originator:Bechtel Jacobs Company LLC; Merl Lauterbach; 865-241-5343
Contact:Joanne E. Schutt, (865) 483-0554
Name Of Authorized Derivative Classifier:C. B. Scott
Name Of Reviewing Official:D. D. Holt
Priority Descriptor:Blue / Information
Keywords:pressurization, drain trap
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DOE Function / Work Categories:Construction
Engineering Design and Construction - Non-Nuclear
ISM Category:Develop / Implement Controls
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